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Aerobic reaction between the pyridine-2-carboxamide-2-aminophenol N3O ligand (H3L1) and Zn(ClO4)2·6H2O in CH3CN affords an N3 phenoxazinylate coordinated Zn(II) complex; its diradical electronic structure [ZnII{(L1*)˙−}2] has been elucidated from redox, spectroscopic (UV-VIS and EPR), and magnetic measurements and DFT calculations. Isolation and characterization of the metal-assisted redox-driven modified N3 ligand as a radical cation (H2L1*)˙+ and its Ni(II)-diradical complex [NiII{(L1*)˙−}2] have also been achieved. [ABSTRACT FROM AUTHOR]

A novel family of cobalt(II) compounds with tridentate pyridine-2,6-diiminephenyl type ligands featuring electron-withdrawing substituents of general formula [Co(n-XPhPDI)2](ClO4)2·S [n-XPhPDI = 2,6-bis(N-n-halophenylformimidoyl)pyridine with n = 4 (1–3) and 3 (4); X = I (1), Br (2 and 4) and Cl (3); S = MeCN (1 and 2) and EtOAc (3)] has been synthesised and characterised by single-crystal X-ray diffraction, electron paramagnetic resonance, and static (dc) and dynamic (ac) magnetic measurements combined with theoretical calculations. The structures of 1–4 consist of mononuclear bis(chelating) cobalt(II) complex cations, [CoII(n-XPhPDI)2]2+, perchlorate anions, and acetonitrile (1 and 2) or ethyl acetate (3) molecules of crystallisation. This unique series of mononuclear six-coordinate octahedral cobalt(II) complexes displays both thermally-induced low-spin (LS)/high-spin (HS) transition and field-induced slow magnetic relaxation in both LS and HS states. A complete LS ↔ HS transition occurs for 1 and 2, while it is incomplete for 4, one-third of the complexes being HS at low temperatures. In contrast, 3 remains HS in all the temperature range. 1 and 2 show dual spin relaxation dynamics under the presence of an applied dc magnetic field (Hdc), with the occurrence of faster- (FR) and slower-relaxing (SR) processes at lower (Hdc = 1.0 kOe) and higher fields (Hdc = 2.5 kOe), respectively. On the contrary, 3 and 4 exhibit only SR and FR relaxations, regardless of Hdc. Overall, the distinct field-dependence of the single-molecule magnet (SMM) behaviour along with this family of spin-crossover (SCO) cobalt(II)-n-XPhPDI complexes is dominated by Raman mechanisms and, occasionally, with additional temperature-independent Intra-Kramer [LS or HS (D > 0)] or Quantum Tunneling of Magnetisation mechanisms [HS (D < 0)] also contributing. [ABSTRACT FROM AUTHOR]

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)0.5(2,5-pzdc)0.5]n (1) [H4bttb = 1,2,4,5-tetrakis(4′-carboxyphenyl)benzene and H2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb4− tetraanion in 1 adopts the bridging and chelating–bridging pseudo-oxo coordination modes while the 2,5-pzdc2− dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (5D4 → 7F5) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (Sm) of 0.76% K−1 at 295 K (δT = 0.05 K), constituting a TbIII ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0–300 K show the expected behavior for the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0–10.0 K, either in the absence or presence of a static dc magnetic field. [ABSTRACT FROM AUTHOR]

A reaction between CoCl2 and L3-(CO2−)2 (2 : 1 stoichiometry) in CH3OH affords a discrete complex [Co II4- {L3-(CO2−)2}2(μ3-OCH3)2(CH3OH)2(H2O)2Cl2] (1) [L3-(CO2−)2 = 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear CoII{L3-(CO2−)2}Cl units connected by a dimeric Co II2 (μ3-OCH3)2(CH3OH)2(H2O) unit present in the centre through two methoxo (μ3-OCH3)- and two carboxylate (μ-1,1-OCO-) bridges affording a tetranuclear coordination cluster of Co(II) with a defective dicubane topology. In 1, Co1 (terminal) has distorted octahedral CoIIN2O3Cl and the central Co2 has CoIIO6 coordination. Such coordination arrangements afford the observed topology. Variable-temperature magnetic studies reveal anti-ferromagnetic coupling in 1. Three magnetic exchange interactions (one anti-ferromagnetic and two ferromagnetic: J1 = +3.3 cm−1 (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ3-OCH3 bridges), J2 = −2.5 cm−1 (Co⋯Co 3.228 Å; μ-1-OCO- and μ3-OCH3 bridges) and J3 = +10.6 cm−1 (Co⋯Co 3.084 Å; two μ3-OCH3 bridges)) have been identified, with the inclusion of the orbital reduction parameter (α = Aκ = 1.38), spin–orbit coupling (λ = −158 cm−1) and axial distortion (energy gap Δ = −975 cm−1 between singlet and doublet levels), rationalized by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Two new tetradentate N4 ligands (LN4), LN4 = Me2,Me2PyzTACN (1-(2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl)-4,7-dimethyl-1,4,7-triazacyclononane) and Me2,MeImTACN (1-((1-methyl-1H-imidazol-1-yl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane) have been synthesized and their corresponding Fe(II) complexes [FeII(Me2,Me2PyzTACN)(CF3SO3)2], 1Pz, and [FeII(Me2,MeImTACN)(CF3SO3)2], 1Im, have been prepared and characterized. Complexes 1Pz and 1Im catalyse the hydroxylation of C–H bonds of alkanes with excellent efficiencies, using hydrogen peroxide as oxidant. The high H/D kinetic isotope effect values for C–H hydroxylation, large normalized tertiary/secondary C–H (C3/C2) bond selectivities in adamantane oxidation, and high degrees of stereoretention in the oxidation of cis-1,2-dimethylcyclohexane are indicative of metal-based oxidation processes. The complexes also catalyse the oxidation of cyclooctene to form its corresponding epoxide and syn-diol. For 1Pz the epoxide is the main product, while for the analogous complex 1Im the syn-diol predominates. The active oxidant is proposed to be an [(LN4)FeV(O)(OH)]2+ species (2Pz, LN4 = Me2,Me2PyzTACN and 2Im, LN4 = Me2,MeImTACN) which may exist in two tautomeric forms related by a proton shift between the oxo and hydroxo ligands. Isotope labelling experiments show that the oxygen atom in the hydroxylated products originates from both water and hydrogen peroxide, and labelling experiments involving oxygen atom transfer to sterically bulky substrates provide indirect information on the steric influence exerted by the two ligands in the relative reactivities of the two hypervalent iron tautomers. Based on these labelling studies, the steric influence exerted by each of the ligands towards the relative reactivity of the oxo ligands of the corresponding pair of Fe(V)(O)(OH) tautomers can be derived. Furthermore, this steric influence can be gauged relative to related complexes/ligands. [ABSTRACT FROM AUTHOR]

Five cobalt(II) complexes of formula [CoCl2(Ln)2] [1 with L1 = 1-benzyl-2-phenyl-1H-benzimidazole, 2 with L2 = 2-(furan-2-yl)-1-(furan-2-ylmethyl)-1H-benzimidazole, 3 with L3 = 1-(4-chlorobenzyl)-2-(4-chlorophenyl)-1H-benzimidazole, 4 with L4 = 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole and 5 with L5 = 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzimidazole] have been synthesised, spectroscopically characterised and cryomagnetically investigated. The crystal structures of 1, 3, 4 and 5 have been determined by X-ray diffraction on single crystals. Each cobalt(II) ion is four-coordinate in a distorted tetrahedral environment built by two chloride anions and two benzimidazole ligands. The neutral molecules are well separated from each other, shortest intermolecular cobalt⋯cobalt distances being greater than 9.0 Å. Static (dc) magnetic susceptibility measurements in the temperature range 2.0–300 K of 1–5 reveal the occurrence of a Curie law behaviour of magnetically non-interacting spin quadruplets in the high-temperature domain with a downturn at low temperatures due to magnetic anisotropy. The values of the D and E/D parameters for these compounds vary in the ranges −8.75 to +8.96 cm−1 and 0.00140 to 0.23, respectively. Dynamic (ac) magnetic susceptibility measurements of 1–5 show slow magnetic relaxation in the lack (1) or under the presence (1–5) of applied dc magnetic fields, a feature which is typical of single-molecule magnet behaviour (SMM). The analysis of the ac data shows that a thermally activated Orbach relaxation mechanism dominates this behaviour. Complexes 1–5 also act as efficient and highly selective eco-friendly catalysts in the coupling reaction between CO2 and epoxides to produce cyclic carbonates under solvent-free conditions. Under optimized reaction conditions, different epoxides were converted to the respective cyclic carbonate, with excellent conversions, using catalyst 4. [ABSTRACT FROM AUTHOR]

Three square planar nickel(II) complexes of a new asymmetric tetradentate redox-active ligand H3L2 in its deprotonated form, at three redox levels, open-shell semiquinonate(1−) π radical, quinone(0) and closed-shell dianion of its 2-aminophenolate part, have been synthesized. The coordinated ligand provides N (pyridine) and N′ and N′′ (carboxamide and 1,2-phenylenediamide, respectively) and O (phenolate) donor sites. Cyclic voltammetry on the parent complex [Ni(L2)] 1 in CH2Cl2 established a three-membered electron-transfer series (oxidative response at E1/2 = 0.57 V and reductive response at −0.32 V vs. SCE) consisting of neutral, monocationic and monoanionic [Ni(L2)]z (z = 0, 1+ and 1−). Oxidation of 1 with AgSbF6 affords [Ni(L2)](SbF6) (2) and reduction of 1 with cobaltocene yields [Co(η5-C5H5)2][Ni(L2)] (3). The molecular structures of 1·CH3CN, 2·0.5CH2Cl2 and 3·C6H6 have been determined by X-ray crystallography at 100 K. Characterization by 1H NMR, X-band EPR (gav = 2.006 (solid); 2.008 (CH2Cl2–C6H5CH3 glass); 80 K) and UV-VIS-NIR spectral properties established that 1, 2 and 3 have [NiII{(L2)˙2−}], [NiII{(L2)−}]+/1+ and [NiII{(L2)3−}]−/1− electronic states, respectively. Thus, the redox processes are ligand-centred. While 1 possesses paramagnetic St (total spin) = 1/2, 2 and 3 possess diamagnetic ground-state St = 0. Interestingly, the variable-temperature (2–300 K) magnetic measurement reveals that 1 with the St = 1/2 ground state attains the antiferromagnetic St = 0 state at a very low temperature, due to weak noncovalent interactions via π–π stacking. Density functional theory (DFT) electronic structural calculations at the B3LYP level of theory rationalized the experimental results. In the UV-VIS-NIR spectra, broad absorptions are recorded for 1 and 2 in the range of 800–1600 nm; however, such an absorption is absent for 3. Time-dependent (TD)-DFT calculations provide a very good fit with the experimental spectra and allow us to identify the observed electronic transitions. [ABSTRACT FROM AUTHOR]

A unique π-conjugated benzothiadiazole-ortho-vanillin ligand (HL), characterized by single crystal X-ray diffraction and DFT calculations, has been prepared by condensation between 4-amino-benzothiadiazole (BTD) and ortho-vanillin. Its reaction with cobalt(II) acetate afforded the complex of formula [CoL2]·CH2Cl2 (1), for which the coordination environment of the cobalt centre is a distorted octahedron and the ligand acts as a monoanionic tridentate NNO chelate in its phenolate form. Intermolecular π–π stacking interactions between the π-conjugated BTD units provide an antiferromagnetic coupling pathway, as indicated by the analysis of the dc magnetic measurements of a crystalline sample of the complex and supported by DFT type calculations. The static magnetic behaviour of 1 is analysed according to spin–orbit coupling and zero-field splitting models. Remarkably, the complex exhibits slow relaxation of the magnetization under dc applied magnetic fields being thus a new example of field-induced mononuclear single-molecule magnet (SMM). [ABSTRACT FROM AUTHOR]

A new series of cyanido-bridged {FeIIILnIII}2 neutral molecular squares of general formula [Fe{HB(pz)3}(CN)(μ-CN)2Ln(NO3)2(pyim)(Ph3PO)]2·2CH3CN [Ln = Ce (1), Pr (2), Nd (3), Gd (4), Tb (5), Dy (6) and Er (7); {HB(pz)3}− = hydrotris(pyrazolyl)borate, pyim = 2-(1H-imidazol-2-yl)pyridine and Ph3PO = triphenylphosphine oxide] were obtained by reacting the low-spin [Fe{HB(pz)3}(CN)3]− species with the preformed [LnIII(pyim)(NO3)2(pyim)(Ph3PO)]+ complex anions (generated in situ by mixing the nitrate salt of each Ln(III) ion with pyim and Ph3PO molecules). Single-crystal X-ray diffraction studies show that 1–7 are isostructural compounds that crystallize in the triclinic P1¯ space group. Their crystal structures consist of centrosymmetric cyanido-bridged {FeIIILnIII}2 molecular squares where two [Fe{HB(pz)3}(CN)3]− units adopt bis-monodentate coordination modes towards two [LnIII(pyim)(NO3)2(pyim)(Ph3PO)]+ moieties. The cis-oriented convergent sites from both low-spin FeIII and LnIII fragments form a quasi square-shaped molecule in which the 3d and 4f ions alternatively occupy the corners of the square. Both FeIII ions show a distorted octahedral surrounding (C3v symmetry), whereas the LnIII ions exhibit a distorted muffin-like geometry (Cs symmetry) in 1–7. The intramolecular FeIII⋯LnIII distances across the two cyanido-bridges range from ca. 5.48/5.46 up to ca. 5.58/5.61 Å. The molecular squares in 1–7 are interlinked through hydrogen bonds, weak π⋯π stacking and very weak C–H⋯π type interactions into three-dimensional supramolecular networks. The analysis of the solid-state direct-current (dc) magnetic susceptibility data of 1–7 in the temperature range 1.9–300 K reveals the occurrence of weak intra- and intermolecular antiferromagnetic interactions. The small intramolecular antiferromagnetic couplings in 4 compare well with those previously reported for parent systems. Although the coexistence of the spin–orbit coupling (SOC) of the low-spin iron(III) and lanthanide(III) ions in the remaining compounds together with the ligand field effects mask the visualization and make difficult the evaluation of the possible magnetic interactions in them, we were able to do it through a SOC model applied on exact or effective Hamiltonians. Frequency-dependent alternating current magnetic susceptibility signals in the temperature range 2.0–9.0 K under zero and non-zero static fields were observed for 5–7 which indicate slow magnetic relaxation (SMM) behavior. The usual absence of χ′′M maxima moved us to estimate their energy barriers through ln(χ′′M/ χ′M) vs. 1/T plots, obtaining values from 25 to 40 cm−1. [ABSTRACT FROM AUTHOR]

In this work, we present the synthetic pathway, a refined structural description, complete solid-state characterization and the magnetic properties of four new cobalt(II) compounds of formulas [Co(H2O)6][Co2(H2mpba)3]·2H2O·0.5dmso (1), [Co(H2O)6][Co2(H2mpba)3]·3H2O·0.5dpss (2), [Co2(H2mpba)2(H2O)4]n·4nH2O (3), and [Co2(H2mpba)2(CH3OH)2(H2O)2]n·0.5nH2O·2ndpss (4) [dpss = 2,2′-dipyridyldisulfide and H4mpba = 1,3-phenylenebis(oxamic) acid], where 2 and 4 were obtained from [Co(dpss)Cl2] (Pre-I) as the source of cobalt(II). All four compounds are air-stable and were prepared under ambient conditions. 1 and 2 were obtained from a slow diffusion method [cobalt(II) : H2mpba2− molar ratio used 1 : 1] and their structures are made up of [Co2(H2mpba)3]2− anionic helicate units and [Co(H2O)6]2+ cations, exhibiting supramolecular three-dimensional structures. Interestingly, a supramolecular honeycomb network between the helicate units interacting with each other through R22(10) type hydrogen bonds occurs in 2 hosting one co-crystallized dpss molecule. On the other hand, for the first time, linear (3) and zigzag (4) cobalt(II) chains were isolated by slow evaporation of stirred solutions of mixed solvents with cobalt(II) : H2mpba2− in 1 : 2 molar ratio at room temperature. Magnetic measurements of Pre-I revealed a quasi magnetically isolated S = 3/2 spin state with a significant second-order spin–orbit contribution as expected for tetrahedrally coordinated cobalt(II) ions. The analysis of the variable temperature static (dc) magnetic susceptibility data through first- (1 and 3) and second-order spin–orbit coupling models (2 and 4) reveals the presence of magnetically non-interacting high-spin cobalt(II) ions with easy-axis (1 and 4)/easy-plane magnetic anisotropies (2 and 4) with low rhombic distortions. Dynamic (ac) magnetic measurements for Pre-I and 1–4 below 8.0 K show that they are examples of field-induced Single-Ion Magnets (SIMs). [ABSTRACT FROM AUTHOR]

The coexistence of field-induced slow magnetic relaxation and moderately large magnetocaloric efficiency in the supra-Kelvin temperature region occurs in the 2D compound [Gd III2 (ox)3(H2O)6]n·4nH2O (1), a feature that can be exploited in the proof-of-concept design of a new class of slow-relaxing magnetic materials for cryogenic magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The synthesis of phosphinic amides containing one 4-amino-TEMPO substituent at the ortho position has been achieved through copper(I) catalyzed cross-coupling reactions of ortho-iodophosphinic amides with 4-amino-TEMPO. The method has been extended to the preparation of the first example of a P-stereogenic ortho-(4-amino-tempo)phosphinic amide radical 10. The reaction of 10 with Cu(hfac)2 afforded the P-stereogenic CuII complex 19. The crystal structure of both chiral compounds is reported. The molecular structure of 10 consists of a supramolecular zig-zag chain formed by intermolecular hydrogen bonds between the NH group of the phosphinic amide moiety and the nitroxide oxygen atom. In complex 19, the ligand acts as a bridge between two CuII ions coordinated to the oxygen atoms of the P＝O and N–O· groups leading to the formation of a polymeric helicate chain in which the metal ions exist in a distorted octahedral geometry. The magnetic behavior of ligand 10 is characterized by very weak intermolecular antiferromagnetic interactions, whereas ferro- and anti-ferromagnetic interactions are present in complex 19. [ABSTRACT FROM AUTHOR]

Two one-dimensional dysprosium(III) complexes based on α-glycine (gly) and β-alanine (β-ala) amino acids, with the formula {[Dy2(gly)6(H2O)4](ClO4)6·5H2O}n (1) and {[Dy2(β-ala)6(H2O)4](ClO4)6·H2O}n (2), have been synthesised and characterised structurally and magnetically. Both compounds crystallise in the triclinic system with the space group P1¯. In 1, two DyIII ions are eight-coordinate and bound to six oxygen atoms from six gly ligands and two oxygen atoms from two water molecules, showing different geometries (bicapped trigonal prism and square antiprism). In 2, two DyIII ions are nine-coordinate and bound to seven oxygen atoms from six β-ala ligands and two oxygen atoms from two water molecules in the same geometry (capped square antiprism). In the crystal packing of both compounds, cationic {[Dy2(L)6(H2O)4]6+}n [L = α-glycine (1) and β-alanine (2)] chains, ClO4− anions, and water molecules generate a network connected through H-bonding interactions. The study of the magnetic properties of 1 and 2 through dc magnetic susceptibility measurements reveals different magnetic behaviour 1 and 2. In addition, ac magnetic susceptibility measurements show a field-induced slow relaxation of magnetisation for both compounds, pointing out that the single-molecule magnet (SMM) phenomenon occurs in both 1 and 2. [ABSTRACT FROM AUTHOR]

Three mononuclear complexes [M(hfac)x(ATEMPO)y], where M = Cu (11) and Co (12), x = y = 2; M = Nd (13), x = 4, y = 1, and two polynuclear complexes [{Cu(hfac)2(ATEMPO)}n], where n = 2 (14) and 4 (15), were obtained by the reaction of M(hfac)x (M = CuII, CoII, NdIII; x = 2, 3) with 4-amino-TEMPO (4-amino-2,2,6,6-tetramethylpiperidin-N-oxyl) in good yields and their structural, electrochemical and magnetic properties were examined. In all cases, the radical is coordinated to the metal through the amino group, except 15, and the metal ions have an octahedral geometry, except 13. Different coordination architectures of the copper complexes were obtained as a function of the stoichiometry and solvents used. In complexes 11 and 12 the radicals show an equatorial–equatorial and axial–equatorial arrangement, respectively, giving rise to two distinct 2D supramolecular systems through intermolecular interactions. Compound 13 is the first example of a lanthanide complex of the ATEMPO radical. The NdIII ion adopts a rare nine-coordination via binding to four hfac ligands and the radical. The dinuclear complex 14 shows a (Cu–O)2 core in which the CuII ions are bridged by the oxygen atoms from the hfac ligands. In compound 15 the ATEMPO radical acts as a bidentate ligand through the amino and nitroxyl groups leading to an unprecedented tetranuclear square-shaped framework. Cyclic voltammetry showed redox processes associated with the copper and TEMPO moieties. Electrochemical impedance spectroscopy revealed the temperature dependence of the conductivity for compound 15 with a maximum of 2.09 × 10−5 S cm−1 at 408 K. The magnetic behavior of complexes 11–15 is determined by metal–radical interactions. Ferromagnetic interaction has been observed for complex 11 due to the existence of two different exchange pathways arising from the conformational arrangement of the radicals around the metal center, whereas the single conformation of the radical in complex 14 resulted in a weak antiferromagnetic coupling. In complex 15 both O–Cu and N–Cu contacts are present giving rise to ferromagnetic and antiferromagnetic interactions, respectively. [ABSTRACT FROM AUTHOR]

Substituted pyrazines were successfully used to prepare two new coordination polymers of formulas {[Co(dca)2(NH2pyz)2]·H2O}n (1) and [Co3(dca)6(HOpyz)5(H2O)2]n (2) [dca = dicyanamide, NH2pyz = 2-aminopyrazine and HOpyz = 2-hydroxypyrazine] whose structures were determined by single-crystal X-ray crystallography. The structure of 1 consists of a two-dimensional rhombus grid of cobalt(II) ions where the dca ligand adopts the μ1,5 bridging mode with trans-positioned monodentate NH2pyz molecules completing the six-coordination around each metal ion. Compound 2 exhibits a stair-like two-dimensional structure where the intralayer connections are performed by the dca and HOpyz groups exhibiting μ1,5 and bis-monodentate coordination modes, respectively. The values of the cobalt–cobalt separation through the dca bridges are 8.2107(3) (1) and 8.4746(4) and 8.5249(4) Å (2) whereas the value through the hydroxypyrazine is 7.2052(6) Å (2). Solid-state direct-current magnetic susceptibility analyses in the temperature range of 1.9–300 K for 1 and 2 reveal the occurrence of magnetically isolated high-spin cobalt(II) ions with a significant contribution to the magnetic moment (1 and 2), D = +95.4 (1) and +76.5 cm−1 (2) and the antiferromagnetically coupled pairs of cobalt(II) centres through the bis-monodentate 2-hydroxypyrazine, J = −0.3 cm−1 (2). Both compounds exhibit frequency dependence of the out-of-phase alternating current (ac) magnetic susceptibility (χ′′M) under non-zero applied dc fields, a feature which is characteristic of single-ion magnet behaviour (SIM). Q-band EPR studies on the polycrystalline samples of 1 and 2 at low temperatures confirm the positive sign of D and reveal the occurrence of a strong asymmetry in the g-tensors. Theoretical calculations by CASSCF/NEVPT2 support these results. An analysis of the dynamic behaviour of 1 and 2 suggests that the relaxation of the magnetization occurs in the ground state under applied fields through two Orbach processes possibly bound to low-lying vibrational modes in the high temperature range, and to the slowing down of the fast interconversion between the two contributions of the ground Kramers doublet at lower temperatures induced by the applied dc field. [ABSTRACT FROM AUTHOR]

The successful utilization of the “direct synthesis” approach yielded the unprecedented hexanuclear complex of formula [Co2MnII2MnIV2(L1)4Cl2(μ3-O)2(dmf)4]·2dmf (1) (H3L is the Schiff base derived from the condensation of salicylaldehyde and 3-aminopropane-1,2-diol). Single crystal X-ray analysis revealed that 1 crystallizes in the monoclinic system P21/c and it contains a rare mixed-valence {CoIII2MnII2MnIV2(μ2-O)8(μ3-O)2} core where all metal ions are linked through the phenolato and alkoxo groups of the L3− ligand. Besides the charge balance resulting from the X-ray structure, the oxidation state of the metal ions has been confirmed by XPS spectroscopy. Cryomagnetic studies indicate the coexistence of ferro- (MnIV–MnII, J2 = +1.10(3) cm−1, J3 = +2.19(3) cm−1; MnII–MnII, j = +0.283(3) cm−1) and antiferromagnetic interactions (MnIV–MnIV, J1 = −17.31(4) cm−1), with the six-coordinate CoIII ions being diamagnetic. DFT type calculations were carried out to substantiate these values. The energy diagram for the different spin states using the best-fit parameters shows the occurrence of six low-lying spin states (S = 0–5) which are close in energy but clearly separated from the remaining ones, with the ground spin state being S = 5. Complex 1 is found to be the first example where weak ferromagnetic exchange between MnII ions through the long –O–MnIV–O– pathway takes place. [ABSTRACT FROM AUTHOR]

We herein present the synthesis, spectroscopic analysis, description of the crystal structures and magnetic properties of four new complexes of the formula [{Cu(opba)(H2O)1.2}{Cu(dmphen)(SCN)}2]·dmf (1), [{Cu(opba)}2{Cu(dmphen)Cl}4]·1.5dmf·2.5dmso (2), [{Cu(opba)}2{Cu(dmphen)Br}4]·dmf·2.3dmso (3) and [{Cu(opba)}{Cu(dmphen)(dca)}2]n (4) [H4opba = N,N′-1,2-phenylenebis(oxamic acid), dmphen = 2,9-dimethyl-1,10-phenanthroline and dca = dicyanamide anion]. 1 is a neutral tricopper(ii) complex where an inner [Cu(opba)]2− fragment adopts a bis-bidentate coordination mode towards two outer [Cu(dmphen)(NCS)]+ units. 2 and 3 are bis-trinuclear species where two oxamato-bridged [Cu(opba){Cu(dmphen)X}2] [X = Cl− (2) and Br− (3)] tricopper(ii) entities are connected by two single X ions involving the central and one of the peripheral copper(ii) ions. 4 is a neutral chain made up of oxamato-bridged [Cu(opba){Cu(dmphen)(dca)}2] fragments linked through a single end-to-end dicyanamide ligand that connects the central copper(ii) ion with one of the peripheral copper(ii) ions. Magnetic susceptibility measurements on polycrystalline samples of 1–4 in the temperature range 1.9–300 K show the occurrence of strong antiferromagnetic interactions between the copper(ii) ions through the oxamate bridge [J = −328(2) (1), −288(2) (2), −431(2) (3) and −370(1) cm−1 (4), the Hamiltonian being defined as H = −J(S1·S2 + S1·S3)] and a weak ferromagnetic coupling across the equatorial-axial exchange pathway provided by the single halide bridge [j = +3.08(3) (2) and +2.34(1) cm−1 (3)]. These values are analyzed by simple orbital symmetry considerations and compared with those reported in the literature for polynuclear copper(ii) complexes with these bridging ligands. [ABSTRACT FROM AUTHOR]

Two new examples of cyanido-bridged {FeIIILnIII}2 molecular squares, with pyim and PPh3O as capping ligands at the LnIII sites, exhibit weak antiferromagnetic interactions [Ln = Eu (1), Sm (2), pyim = 2-(1H-imidazol-2-yl)pyridine, PPh3PO = triphenylphosphine oxide]. [ABSTRACT FROM AUTHOR]

Using a potentially tridentate o-aminophenol-based redox-active ligand H2L1 (2-[2-(benzylthio)phenylamino]-4,6-di-tert-butylphenol) in its deprotonated form, [Cu(L1)2] has been synthesized and crystallized as [CuII(L1)2]·CH2Cl2 (1·CH2Cl2). A cyclic voltammetry experiment (in CH2Cl2; V vs. SCE (saturated calomel electrode)) on 1·CH2Cl2 exhibits two oxidative (E11/2 = 0.20 V (peak-to-peak separation, ΔEp = 100 mV) and E21/2 = 0.90 V (ΔEp = 140 mV)) and two reductive (E11/2 = −0.52 V (ΔEp = 110 mV) and E21/2 = −0.92 V (ΔEp = 120 mV)) responses. Upon oxidation using a stoichiometric amount of [FeIII(η5-C5H5)2](PF6), 1·CH2Cl2 yielded [Cu(L1)2](PF6) (2). Structural analysis (100 K) reveals that 1·CH2Cl2 is a four-coordinate bis(iminosemiquinonato)copper(ii) complex (CuN2O2 coordination), and that the thioethers remain uncoordinated. The twisted geometry of 1 (distorted tetrahedral) results in considerable changes in the electronic structure, compared to well-known square-planar analogues. Crystallographic analysis of 2 both at 100 K and at 293 K reveals that it is effectively a four-coordinate complex with a CuN2OS coordination; however, a substantial interaction with the other phenolate O is observed. The metal–ligand bond distances and metric parameters associated with the o-aminophenolate rings indicate a valence-tautomeric (VT) equilibrium involving monocationic (iminosemiquinonato)(iminoquinone)copper(ii) and bis(iminoquinone)copper(i). Complex 1·CH2Cl2 is a three-spin system and a magnetic study (4–300 K) established that it has a S = 1/2 ground-state, owing to the strong antiferromagnetic coupling between the unpaired spin of the copper(ii) and the iminosemiquinonate(1−) π-radical anion. Electron paramagnetic resonance (EPR) spectral studies corroborate this result. Complex 2 is diamagnetic and the existence of VT in 2 was probed using variable-temperature (248–328 K) 1H NMR and EPR (100–298 K) spectral measurements and X-ray photoelectron spectroscopic studies at 298 K. Remarkably, modification of the well-studied 2-anilino-4,6-di-tert-butylphenol by incorporation of a benzylthioether arm leads to the occurrence of VT in 2. The electronic structure of 1·CH2Cl2 and 2 has been assigned using density functional theory (DFT) calculations at the B3LYP-D3 level of theory. Time-dependent (TD)-DFT calculations have been performed to elucidate the origin of the observed UV-VIS-NIR absorptions. [ABSTRACT FROM AUTHOR]

The preparation, X-ray crystal structure, spectroscopic and variable-temperature dc and ac magnetic properties of two six-coordinate cobalt(ii) complexes of formula [Co(bim)4(tcm)2] (1) and [Co(bmim)4(tcm)2] (2) (bim = 1-benzylimidazole, bmim = 1-benzyl-2-methylbenzimidazole and tcm− = tricyanomethanide ion) are reported. 1 and 2 crystallize in the monoclinic P21/n and C2/c space groups with the asymmetric units composed of one tcm− ion and half the [Co(bim)4]2+ and [Co(bmim)4]2+ complex cations, respectively. Their cobalt atoms are in compressed (1)/rhombic (2) CoN6 octahedral environments, the axial positions being occupied by monodentate tricyanomethanide anions. The neutral molecules in 1 are linked through weak C–H…N type interactions into supramolecular chains, which are further interconnected into supramolecular 2D motifs by C–H…π stacking. No short intermolecular interactions occur in 2. The values of the shortest intermolecular cobalt–cobalt separation are 10.901(1) (1) and 10.577(3) Å (2). Detailed ac and dc magnetic studies indicate that 1 and 2 are field-induced single-ion magnets (SIMs) with D = +46.1 (1)/+80.1 cm−1 (2) thus presenting new examples of SIMs with transversal magnetic anisotropy. Theoretical calculations by CASSCF/NEVPT2 support these results and suggest that the relaxation of the magnetization occurs in the ground state under applied fields through two Orbach processes possibly bound to low-lying vibrational modes. Q-band EPR study for polycrystalline samples 1 and 2 at low temperatures confirms the positive sign of D, allows the rough estimation of the E/D ratio [0.144 (1) and 0.180 (2)] and reveals the occurrence of a strong asymmetry in the g-tensors. The values found for the spin-reversal barrier, Ea≈ 28 and 11 cm−1 (1) and 20 and 9 cm−1 (2), are within the range of those found in other cobalt(ii) field-induced SIMs with a pseudooctahedral trans-CoN4N′2 chromophore. [ABSTRACT FROM AUTHOR]

Aerobic reaction of the ligand H2L1, 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol, CoCl2·6H2O and Et3N in MeOH under refluxing conditions produces, after work-up and recrystallization, black crystals of [Co(L1)2] (1). When examined by cyclic voltammetry, 1 displays in CH2Cl2 three one-electron redox responses: two oxidative, E11/2 = 0.30 V (peak-to-peak separation, ΔEp = 100 mV) and E21/2 = 1.04 V (ΔEp = 120 mV), and one reductive E1/2 = −0.27 V (ΔEp = 120 mV) vs. SCE. Consequently, 1 is chemically oxidized by 1 equiv. of [FeIII(η5-C5H5)2][PF6], affording the isolation of deep purple crystals of [Co(L1)2][PF6]·2CH2Cl2 (2), and one-electron reduction with [CoII(η5-C5H5)2] yielded bluish-black crystals of [CoIII(η5-C5H5)2][Co(L1)2]·MeCN (3). A solid sample of 1 exhibits temperature-independent (50–300 K) magnetism, revealing the presence of a free radical (S = 1/2), which exhibits an isotropic EPR signal (g = 2.003) at 298 K and at 77 K an eight-line feature characteristic of hyperfine-interaction of the radical with the Co (I = 7/2) nucleus. Based on X-ray structural parameters of 1–3 at 100 K, magnetic and EPR spectral behaviour of 1, and variable-temperature (233–313 K) 1H NMR spectral features of 1–3 and 13C NMR spectra at 298 K of 2 and 3 in CDCl3 point to the electronic structure of the complexes as either [CoIII{(LAP)2−}{(LISQ)}Ṗ−] or [CoIII{(L1)2}Ṗ3−] (delocalized nature favours the latter description) (1), [CoIII{(LISQ)Ṗ−}2][PF6]·2CH2Cl2 (2) and [CoIII(η5-C5H5)2][CoIII{(LAP)2−}2]·MeCN (3) [(LAP)2− and (LISQ)Ṗ− represent the redox-level of coordinated ligands o-amidophenolate(2−) ion and o-iminobenzosemiquinonate(1−) π-radical ion, respectively]. Notably, all the observed redox processes are ligand-centred. To the best of our knowledge, this is the first time that six-coordinate complexes of a common tridentate o-aminophenolate-based ligand have been structurally characterized for the parent 1, its monocation 2 and the monoanion 3 counterparts. Temperature-dependent 1H NMR spectra reveal the existence of valence-tautomeric equilibria in 1–3. Density Functional Theory (DFT) calculations at the B3LYP-level of theory corroborate the electronic structural assignment of 1–3 from experimental data. The origins of the observed UV–VIS–NIR absorptions for 1–3 have been assigned, based on time-dependent (TD)-DFT calculations. [ABSTRACT FROM AUTHOR]

Three heterobimetallic complexes of formula [Ca2Cu3(mpyba)2(2-apyma)(H2O)7]·8.3H2O (1), [Sr2Cu3(mpyba)2(2-apyma)(H2O)8]·11.6H2O (2) and [Sr4.5Cu4(mpyba)4(ox)(H2O)20]·8.5H2O (3) [H4mpyba = N,N′-2,6-pyridinebis(oxamic acid), 2-apyma = 2-(6-aminopyridinyl)oxamate and ox = oxalate] have been synthesized and structurally characterized. Complexes 1 and 2 are isostructural compounds, with tricopper(ii) units having mpyba and its hydrolytic product (2-apyma) as ligands. They are interlinked through strontium(ii) (1) and calcium(ii) (2) ions to afford neutral two-dimensional networks. Two of the copper(ii) ions are five-coordinate in distorted square pyramidal (Cu3) and trigonal bipyramidal (Cu1) surroundings, whereas the other (Cu2) is six-coordinate in an elongated octahedral environment. The main difference between their structures, apart from the number of water molecules, resides in the nature of the alkaline earth cation coordinated to the oxamate fragments, Sr2+ (1)/Ca2+ (2), which exhibit eight and seven coordination, respectively. The π–π interactions and an extensive network of hydrogen bonds in 1 and 2 lead to supramolecular 3D structures. The relatively small size of their cavities, in the micropore domain, hinders the inclusion of N2 but allows CO2 adsorption (0.45 and 0.52 mmol g−1 for 1 and 2, respectively). The structure of 3 is made up of [3,3] metallacyclophane-type motifs, having the formula [Cu2(mpyba)2(H2O)2]4−. These act as tetrakis(bidentate) ligands towards the strontium(ii) ions (Sr1, Sr2 and Sr3), leading to a sheet-like polymer growing in the bc plane, which extends further along the crystallographic a axis by a bis(chelating) oxalate between the Sr1 atoms. The investigation of the magnetic properties of 1–3 in the temperature range 1.9–300 K shows the occurrence of an overall antiferromagnetic behaviour for 1 and 2 [J12 = J23 = −9.71(2) (1) and −10.81(5) cm−1 (2), with the Hamiltonian being defined as H = −J12S1·S2−J23S2·S3 + gβH[S1 + S2 + S3], and a ferromagnetic coupling within the dicopper(ii) metallacylophane unit of 3 [J = +1.86(1) cm−1 through the Hamiltonian H = −JS1·S2 + gβH(S1 + S2)]. Simple orbital symmetry considerations (1–3) and the spin polarization mechanism (3) account for the observed magnetic properties. [ABSTRACT FROM AUTHOR]

A new series of {FeIII2LnIII2} heterobimetallic squares of general formula [FeIII{HB(pz)3}(CN)(μ-CN)2Ln(pyim)x(NO3)2(H2O)y]2·zH2O [Ln = La (1), Gd (2), Tb (3) and Dy (4); {HB(pz)3}− = hydrotris(pyrazolyl)borate and pyim = 2-(1H-imidazol-2-yl)pyridine; x = 2, y = 0 (1), x = y = 1 (2–4) and z = 10 (1), 6 (2), 2.76 (3), 4 (4)] were synthesized by reacting the low-spin [FeIII{HB(pz)3}(CN)3]− complex anion with the preformed [LnIII(pyim)x(NO3)2(H2O)y]+ complex cation [formed in situ by mixing the lanthanide(iii) salt and the pyim ligand]. Single-crystal X-ray diffraction shows that 1–4 crystallize in the P1̅ triclinic space group, 2–4 being isomorphous. In all cases, the structure comprises neutral cyanido-bridged {FeIII2LnIII2} molecular squares in which two [FeIII{HB(pz)3}(CN)3]− units act as bis-monodentate ligands towards two [LnIII(pyim)x(NO3)2(H2O)y]+ moieties through two of the three cyanide groups. The iron(iii) and lanthanide(iii) cations regularly alternate in the corners of the square and the edges are defined by the cyanide bridges. Each iron(iii) ion in 1–4 is six-coordinate in a distorted octahedral surrounding with a tridentate tris(pyrazolyl)borate ligand and three cyanide groups in an approximately C3v symmetry. The lanthanum(iii) ion in 1 is ten-coordinate in a rare distorted sphenocorona environment, while the lanthanide(iii) ions in 2–4 are all nine-coordinate with a muffin-like geometry. The values of the FeIII…LnIII distances across the cyanide bridges are 5.579(1) and 5.687(1) Å (1), 5.4695(20) and 5.4781(29) Å (2), 5.4550(12) and 5.4464(14) Å (3), 5.4463(10) and 5.4478(12) Å (4). The tetranuclear units in 1–4 are further interconnected through hydrogen bonds, π–π stacking and very weak C–H…π type interactions leading to supramolecular three-dimensional networks with different topologies. Solid-state direct-current magnetic susceptibility analyses in the temperature range 1.9–300 K reveal the occurrence of weak intra- and intermolecular antiferromagnetic interactions in 1 [JFeFe′ = −2.32(3) cm−1, gFe = 2.198(4), ϑ = −0.650(7) K and χTIP = 266(5) × 10−6 cm3 mol−1, the Hamiltonian being defined as H = −JFeFe′SFeSFe′ + gβH(SFe + SFe′)] and 2 [JFeFe′ = −2.06(3) cm−1, JFeGd = −0.210(4) cm−1, gFe = 2.23(1), gGd = 2.0 (fixed), ϑ = −0.450(5) K and χTIP = 280(5) × 10−6 cm3 mol−1]. The coexistence of the spin–orbit coupling of the low-spin iron(iii) and lanthanide(iii) ions [TbIII (3) and DyIII (4)], together with the ligand field effects, masked the visualization of the possible magnetic interactions in 3 and 4. The small antiferromagnetic couplings in 1 and 2 are in line with previously reported weak antiferromagnetic interactions for these couples of ions through single cyanide bridges. [ABSTRACT FROM AUTHOR]

Three, mononuclear complexes of the formula [Co(bmim)2(SCN)2] (1), [Co(bmim)2(NCO)2] (2) and [Co(bmim)2(N3)2] (3) [bmim = 1-benzyl-2-methylimidazole] were prepared and structurally analyzed by single-crystal X-ray crystallography. The cobalt(ii) ions in 1–3 are tetrahedrally coordinated with two bmim molecules and two pseudohalide anions. The angular distortion parameter δ was calculated and the SHAPE program (based on the CShM concept) was used for 1–3 to estimate the angular distortion from an ideal tetrahedron. The molecules of 1–3 are effectively separated, and the values of the shortest distance of cobalt–cobalt are 8.442(6) and 6.774(8) Å for 1, 10.349(8) and 10.716(8) Å for 2 and 6.778(1) and 9.232(1) Å for 3. Direct current (dc) magnetic susceptibility measurements on the crushed crystals of 1–3 were carried out in the temperature range 1.9–295 K. The variable-temperature magnetic data of 1–3 mainly obey the zero-field splitting effect (D) of the 4A2 ground term of the tetrahedral cobalt(ii) complexes (2D being the energy gap between the ☋±1/2〉 and ☋±3/2〉 levels of the spin). The analysis of their magnetic data through the Hamiltonian H = D[S2z− S(S + 1)/3] + E(Sx2−Sy2) + gβHS led to the following best-fit parameters: g = 2.29, D = −7.5 cm−1 and E/D = 0.106 (1), g = 2.28, D = + 6.3 cm−1 and E/D = 0.007 (2) and g = 2.36, D = + 6.7 cm−1 and E/D = 0.090 (3). The signs of D for 1–3 were confirmed by Q-band EPR spectra on powdered samples in the temperature range 4.0–20 K. Field-induced SIM behaviour was observed for 1–3 below 4.0 K, and the frequency-dependent maxima of χ′′M were observed for 1 and only incipient signals of χ′′M occurred for 2 and 3. The values of the exponential factor (τ0) and activation energy (Ea) for 1–3 which were obtained from the Arrhenius plot suggest a single relaxation process characteristic of an Orbach mechanism. [ABSTRACT FROM AUTHOR]

A one-pot synthesis of a 3d–3d′–3d′′ heterotrimetallic coordination polymer with double diphenoxido, single cyanido and bis-bidentate oxalate as alternating bridges which exhibits an overall antiferromagnetic behaviour has been developed. [ABSTRACT FROM AUTHOR]

A μ-phenoxo-bis(μ2-1,3-acetato)-bridged dicopper(ii) complex [CuII2(L1)(μ-O2CMe)2][NO3] (1) has been synthesized from the perspective of modeling phosphodiesterase activity. Structural characterization was done initially with 1·3Et2O (vapour diffusion of Et2O into MeOH solution of 1; poor crystal quality) and finally with its perchlorate salt [CuII2(L1)(μ-O2CMe)2][ClO4]·1.375MeCN·0.25H2O, crystallized from vapour diffusion of n-pentane into a MeCN–MeOH mixture (comparatively better crystal quality). An asymmetric unit of such a crystal contains two independent molecules of compositions [CuII2(L1)(μ-O2CMe)2][ClO4] and [CuII2(L1)(μ-O2CMe)2(MeCN)][ClO4] (coordinated MeCN with 0.75 occupancy), and two molecules of MeCN and H2O (each H2O molecule with 0.25 occupancy) as the solvent of crystallization. These two cations, each having five-coordinate (μ-phenoxo)bis(μ-acetato)-bridged CuII ions, differ by only the coordination environment of only one CuII ion, which has a weakly coordinated acetonitrile molecule in its sixth position. Temperature-dependent magnetic studies on 1 reveal that the copper(ii) centres are antiferromagnetically coupled with the exchange-coupling constant J = −124(1) cm−1. Theoretically calculated J = −126.51 cm−1, employing a broken-symmetry DFT approach, is in excellent agreement with the experimental value. The dicopper(ii) complex has been found to be catalytically efficient in the hydrolysis of 2-hydroxypropyl-p-nitrophenylphosphate (HPNP). Detailed kinetic experiments and solution studies (potentiometry, species distribution and ESI-MS) were performed to elucidate the reaction mechanism. DFT calculations were performed to discriminate between different possible mechanistic pathways. The free-energy barrier for HPNP hydrolysis catalyzed by 1 is comparable to that obtained from the experimentally-determined value. The involvement of non-covalent (hydrogen-bonding) interaction has also been probed by DFT calculations. The activity of 1 is found to be the highest, compared to the structurally-characterized MnII2, CoII2, NiII2 and ZnII2 complexes of L1(−) reported earlier, under identical experimental conditions, in which each metal centre is six-coordinate. [ABSTRACT FROM AUTHOR]

The assembly reaction between the low-spin [CoII(dmphen)(CN)3]− metalloligand and the [MnIII(salen)(H2O)]+ complex cation yielded the one-dimensional compound {[MnIII(salen)(μ-NC)2CoII(dmphen)(CN)]·2H2O}n (1), which behaves as a ferrimagnetic chain, the intrachain magnetic coupling being J = −1.71(1) cm−1. [ABSTRACT FROM AUTHOR]

Theoretical calculations on a series of molecular models based on amino derivatives of linear and cycled acenes acting as organic linkers between two copper(ii) ions have shown a wire-like magnetic behaviour, so that the intermetallic magnetic communication does not vanish when the linker becomes larger due to its polyradical nature. Hence, these models can be considered as molecular magnetic wires, which can be used as active components for molecular spintronics, where the information transport is based on spin carriers instead of the more conventional charge transport. The nature of the spin ground state along these two series of models is governed by the topology of the organic linker, in agreement with the spin polarization mechanism, allowing a wide diversity in the design of molecular spintronic circuits. Different approaches to search for the more stable spin configuration have been tested, the most efficient being the one that allows generating a guess function that agrees with the spin polarization mechanism. [ABSTRACT FROM AUTHOR]

Using a dicarboxylate ligand appended with (2-pyridyl)ethylamine unit, a new cluster [NiII8(L4)6(DMF)2(CH3OH)2(H2O)6][ClO4]4·2CH3OH·2CH3CO2C2H5 (1) [L4(2−): 3-[N-{2-(pyridin-2-yl)ethyl}amino]-bis(propionate)] has been synthesized, through ‘coordination-driven self-assembly’. The crystal structure of 1 reveals a centrosymmetric octanuclear carboxylate-bridged nickel(ii) tetracation, with a distorted cubane topology. The four crystallographically independent nickel(ii) centres differ markedly in their coordination environment. Magnetic studies (2–300 K) reveal that in 1 the net magnetic-exchange is antiferromagnetic. Based on geometric parameters associated with two interacting nickel(ii) centres, six magnetic-exchange coupling constants (J values) were considered for magnetic data analysis. Notably, 1 provides the first example of a NiII8 cluster (i) bridged solely by carboxylates in three bridging modes (monatomic, syn–anti and anti–anti), (ii) exhibiting four ferromagnetic and two antiferromagnetic magnetic-interactions and (iii) demonstrating a good agreement between six J values (obtained from experimental data analysis) and those obtained from DFT calculations, at the B3LYP-level of theory. [ABSTRACT FROM AUTHOR]

Three cobalt(ii) complexes of formulae [Co(dca)2(bim)4] (1), [Co(dca)2(bim)2]n (2) and [Co(dca)2(bmim)2]n (3) [dca = dicyanamide, bim = 1-benzylimidazole and bmim = 1-benzyl-2-methylimidazole] were prepared and structurally analyzed by single-crystal X-ray crystallography. Compound 1 is a mononuclear species where the cobalt(ii) ion is six-coordinate with four bim molecules in the equatorial positions [Co–Nbim = 2.1546(15) and 2.1489(15) Å] and two trans-positioned dca ligands [Co–Ndca = 2.1575(18) Å] in the axial sites of a somewhat distorted octahedral surrounding. The structures of 2 and 3 consist of two-dimensional grids of cobalt(ii) ions where each metal atom is linked to the other four metal centres by single dca bridges exhibiting the μ1,5-dca coordination mode [Co–Ndca = 2.190(3)–2.220(3) (2) and 2.127(3)–2.153(3) Å (3)]. Two trans-coordinated bim (2)/bmim (3) molecules achieve the six-coordination around each cobalt(ii) ion [Co–Nbim = 2.128(3)–2.134(4) Å (2) and Co–Nbmim = 2.156(3)–2.163(39) Å (3)]. The values of the cobalt–cobalt separation through the single dca bridges are 8.927(2) and 8.968(2) Å in 2 and 8.7110(5) and 8.7158(5) Å in 3. Magnetic susceptibility measurements for 1–3 in the temperature range of 2.0–300 K reveal that these compounds behave as magnetically isolated high-spin cobalt(ii) ions with a significant orbital contribution to the magnetic moment. Alternating current (ac) magnetic susceptibility measurements for 1–3 show a frequency dependence of out-of-phase susceptibility under static applied fields in the range of 500–2500 G, a feature which is characteristic of the single-ion magnet behaviour (SIM) of the Co(ii) ion in them. The values of the energy barrier for the magnetic relaxation (Ea) are 5.45–7.74 (1), 4.53–9.24 (2) and 11.48–15.44 cm−1 (3). They compare well with those previously reported for the analogous dca-bridged 2D compound [Co(dca)2(atz)2]n (4) (Ea = 5.1 cm−1 under an applied static field of 1000 G), which was the subject of a previous report. [ABSTRACT FROM AUTHOR]

Two novel families of coordination polymers, [Ln(bzlida)(Hbzlida)]·H2O (Ln = La, Nd) and [Ln2(bzlida)3]·3H2O (Ln = Nd, Sm, Eu, Gd) were prepared by hydrothermal reaction of Ln2O3 with benzyliminodiacetic acid (H2bzlida). The conditions of synthesis, in particular the pH value, were selected on the basis of previous speciation studies reported in this work. The first type of complex consists of 1D chains built by a fully deprotonated ligand bridging two lanthanide ions and protonated Hbzlida− ligands connecting three cations. The second type is formed by [Ln2(bzlida)3] bimetallic units in which the ligand has a tridentate NOO coordination mode. This is expanded to a 2D network through carboxylate linkers. Under similar synthetic conditions but including copper acetate in the reaction mixture, a new compound was also obtained and characterized: [Cu(bzlida)2{Er(AcO)(H2O)5}2][Cu(bzlida)2]·6H2O (AcO = acetate). This salt is made up of the [Cu(bzlida)2{Er(AcO)(H2O)5}2]2+ heterotrimetallic complex cation containing an acetato bridge, and the [Cu(bzlida)2]2− anion. The same reaction produces the monomeric [Cu(Hbzlida)2]·4H2O whose structure was also elucidated. Magnetic properties of the Gd(iii) derivative were studied and analyzed experimentally and theoretically. The results are compared and discussed with respect to those reported in the literature and a magnetostructural correlation is suggested. [ABSTRACT FROM AUTHOR]

A novel series of copper(ii) coordination polymers [Cu2(O2CC8H9)4(pyz)]n (1), [Cu2(O2CC8H9)4(dps)]n (2), {[Cu(O2CC8H9)2(dps)(H2O)]·H2O}n (3), {[NaCu(O2CC8H9)2(bpm)(NO3)]·H2O}n (4), and [Cu4(O2CC8H9)6(OH)2(bpp)2]n (5) [O2CC8H9− = 3-phenylpropionate anion, pyz = pyrazine, dps = di(4-pyridyl)sulfide, bpm = 2,2′-bipyrimidine, and bpp = 1,3-bis(4-pyridyl)propane] have been synthesized and magneto-structurally investigated. Compounds 1 and 2 belong to a large group of copper(ii) carboxylates where bis-monodentate pyz (1) and dps (2) ligands connect the paddle-wheel [CuII2(μ-O2CC8H9)4] units leading to alternating copper(ii) chains. The structure of 3 consists of uniform chains of trans-[CuII(O2CC8H9)2] units linked by the bis-monodentate dps ligand. Compound 4 consists of heterobimetallic chains where [NaI2CuII2(μ-O2CC8H9)4(NO3)2] units are doubly bridged by bis-bidentate bpm ligands. Compound 5 is also a chain compound whose structure is made up by tetranuclear [CuII4(μ3-OH)2(μ-O2CC8H9)4(O2CC8H9)2] units which are doubly bridged by bis-monodentate bpp ligands. The magnetic properties were investigated in the temperature range 1.8–300 K. Strong antiferromagnetic interactions across the quadruple syn–syn carboxylate are observed in 1 and 2 [J = −378 (1) and −348 cm−1 (2)] whereas a weak ferromagnetic coupling through the double out-of-plane oxo(carboxylate) bridge occurs in 4 [J = +2.66 cm−1], the spin Hamiltonian being defined as H = −JS1·S2 with S1 = S2 = SCu = 1/2. A quasi Curie law is observed for 3 (ϑ = −0.36 cm−1), the bis-monodentate dps ligand being a very poor mediator of magnetic interactions. The analysis of the magnetic properties of 5 is quite complex because of the presence of two crystallographically independent tetracopper(ii) units with single-μ-hydroxo, di-μ-hydroxo, μ3-hydroxo and single-μ-hydroxo plus double syn,syn carboxylate bridges in each one. The nature and values of the magnetic couplings for 5 obtained by fitting (intermediate, strong and weak antiferromagnetic interactions for the three former exchange pathways respectively, and intermediate ferromagnetic interactions for the latter one) were substantiated by DFT type calculations. [ABSTRACT FROM AUTHOR]

Two new Re(iv) compounds of formulae H2tppz[ReCl6] (1) and [Cu(bpzm)2(μ-Cl)ReCl3(μ-ox)Cu(bpzm)2(μ-ox)ReCl3(μ-Cl)]n (2) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and bpzm = bis(pyrazolyl-1-yl)methane] have been prepared and their crystal structures determined by X-ray diffraction on single crystals. Compound 1 is a mononuclear species whose structure consists of octahedral hexachlororhenate(iv) anions and diprotonated H2tppz2+ cations which are arranged in the unit cell as alternating anionic and cationic layers, held together by electrostatic forces. The structure of 2 is made up of alternating [Cu(1)(bpzm)2]2+ and [(ox)ReCl3(μ-Cl)Cu(2)(bpzm)2(μ-Cl)ReCl3(ox)]2− entities interlinked by oxalate bridges to afford a neutral heterobimetallic chain. The oxalate group adopts the didentate (at Re)/monodentate (at Cu) bridging mode. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.9–295 K. 1 is a magnetically diluted Re(iv) complex, the relatively large value of the zero-field splitting of the ground level [D = −15.8(2) cm−1] accounting for the variation of χMT in the low temperature range. Weak intrachain ferromagnetic interactions between Re(iv) and Cu(ii) through oxalate (J1 = +0.15 cm−1) and single chloro (J2 = +4.9 cm−1) bridges occur in 2 which are obscured by the large zero-field splitting of the Re(iv) ion (DRe = 42 cm−1). In addition, interchain antiferromagnetic interactions are also involved in 2 which are responsible for the metamagnetic behavior observed, the value of the critical dc magnetic field (Hc) being 20 kOe. [ABSTRACT FROM AUTHOR]

The novel Re(ii) complex NBu4[Re(NO)Br4(Hnic)] (1) and the heterodinuclear compounds [Re(NO)Br4(μ-nic)Ni(dmphen)2]·½CH3CN (2), [Re(NO)Br4(μ-nic)Co(dmphen)2]·½MeOH (3), [Re(NO)Br4(μ-nic)Mn(dmphen)(H2O)2]·dmphen (4), [Re(NO)Br4(μ-nic)Cu(bipy)2] (5) [Re(NO)Br4(μ-nic)Cu(dmphen)2] (5′) (NBu4+ = tetra-n-butylammonium cation, Hnic = 3-pyridinecarboxylic acid, dmphen = 2,9-dimethyl-1,10-phenanthroline, bipy = 2,2′-bipyridine) have been prepared and the structures of 1–5 determined using single crystal X-ray diffraction. The structure of 1 consists of [Re(NO)Br4(Hnic)]− anions and NBu4+ cations. Each Re(ii) is six-coordinate with four bromide ligands, a linear nitrosyl group and a nitrogen atom from the Hnic molecule, in a distorted octahedral surrounding. The structures of 2–5 are made up of discrete heterodinuclear Re(ii)M(ii) units where the fully deprotonated [Re(NO)Br4(nic)]2− entity acts as a didentate ligand through the carboxylate group towards the [Ni(dmphen)2]2+ (2), [Co(dmphen)2]2+ (3), [Mn(dmphen)(H2O)2]2+ (4) and [Cu(bipy)2]2+ (5) fragments, the Re–M separation across the nic bridge being 7.8736(8) (2), 7.9632(10) (3), 7.7600(6) (4) and 8.2148(7) Å (5). The environment of the Re(ii) ion in 2–5 is the same as that in 1 and all M(ii) are six-coordinate in highly distorted octahedral surroundings, the main source of the distortion being due to the reduced bite of the chelating carboxylate. The magnetic properties of 1–5′ were investigated in the temperature range 1.9–300 K. 1 behaves as a quasi-magnetically isolated spin doublet with very weak antiferromagnetic interactions through space Br…Br contacts. Its magnetic susceptibility data were successfully modeled through a deep analysis of the influence of the ligand field, spin–orbit coupling, tetragonal distortion and covalence effects as variable parameters. Compounds 2–5′ exhibit weak antiferromagnetic interactions. The intramolecular exchange pathway in this family being discarded because of the symmetry of magnetic orbitals of the Re(ii) ion (dxy) precludes any spin delocalization on the bridging nic orbitals, the observed magnetic interactions are most likely mediated by π–π type interactions between the peripheral ligands which occur in them. Only in the case of 4, short through space Br…Br contacts of ca. 4.03 Å (values larger than 5.5 Å in 2, 3 and 5) could be involved in the exchange coupling. [ABSTRACT FROM AUTHOR]

The synthesis, crystal structure and preliminary magnetic characterization of a new heterobimetallic [MnSTACKABOVEII/ABOVEBELOW5/BELOW/STACKCuSTACKABOVEII/ABOVEBELOW5/BELOW/STACK] wheel containing a flexible bis-oxamate type ligand are described. This decanuclear compound exhibits a relatively strong intra-wheel antiferromagnetic interaction leading to a ground spin state S = 10. [ABSTRACT FROM AUTHOR]

Two new two-dimensional homometallic compounds {[M2(bpm)(ox)2]n·5nH2O} with M = Co(ii) (1) and Zn(ii) (2) and the mononuclear nickel(ii) complex [Ni(bpm)2(ox)]·2H2O (3) [bpm = 2,2′-bipyrimidine and ox = oxalate] have been prepared and structurally characterized. 1 and 2 are isostructural compounds whose structures are made up of oxalate-bridged M(ii) cations cross-linked by bis-bidentate bpm molecules to afford a honeycomb layered network extending in the crystallographic ab plane. The layers are eclipsed along the crystallographic c axis and show graphitic-like interactions between the bpm rings. The three-dimensional supramolecular network deriving from such interactions is characterized by hexagonal-shaped channels extending in the same direction. Each M(ii) ion in 1 and 2 is tris-chelated with four oxygen atoms from two oxalate groups and two bpm-nitrogen atoms building a distorted octahedral surrounding. The reduced values of the angles subtended by the bis-chelating bpm [77.69(8) (1) and 76.59(8)° (2)] and oxalate [79.69(6) (1) and 80.01(5)° (2)] are the main factors accounting for this distortion. The values of the metal–metal separation through bridging bpm are 5.6956(7) (1) and 5.7572(9) Å (2), whereas those across the bis-bidentate oxalate are 5.4306(4) (1) and 5.4058(5) Å (2). 3 is a neutral mononuclear nickel(ii) complex where each metal ion is six-coordinate with four nitrogen atoms from two bpm ligands in a cis arrangement and two oxalate-oxygen atoms building a somewhat distorted octahedral surrounding. The values of the angles subtended at the nickel(ii) ion by bpm and oxalate are 78.14(4) and 80.95(5)°, respectively. The magnetic properties of 1 have been investigated in the temperature range 1.9–295 K. They are typical of an overall antiferromagnetic coupling with a maximum of the magnetic susceptibility at 22.0 K. The analysis of the susceptibility data of 1 through an effective spin Hamiltonian allowed a satisfactory simulation in the temperature range 10–295 K with the best-fit parameters λ = −110 cm−1, α = 1.1, ☋Δ☋ = 400 cm−1, Jox = −11.1 cm−1 and Jbpm = −5.0 cm−1. The values of the antiferromagnetic coupling through bpm and ox in 1 have also been supported by electronic structure calculations based on Density Functional Theory (DFT) and they compare well with those reported in the literature for bpm-bridged dicobalt(ii) complexes and oxalate-bridged cobalt(ii) chains. [ABSTRACT FROM AUTHOR]

The ligand 3-chloro-6-dipicolylamino-1,2,4,5-tetrazine (Cl-TTZ-dipica) 1, prepared by the direct reaction between 3,6-dichloro-1,2,4,5-tetrazine and di(2-picolyl)-amine, afforded a series of four neutral transition metal complexes formulated as [Cl-TTZ-dipica-MCl2]2, with M = Zn(ii), Cd(ii), Mn(ii) and Co(ii), when reacted with the corresponding metal chlorides. The dinuclear structure of the isostructural complexes was disclosed by single crystal X-ray analysis, clearly indicating the formation of [MII–(μ-Cl)2MII] motifs and the involvement of the amino nitrogen atom in semi-coordination with the metal centers, thus leading to distorted octahedral coordination geometries. Moreover, the chlorine atoms, either coordinated to the metal or as a substituent on the tetrazine ring, engage respectively in specific anion–π intramolecular and intermolecular interactions with the electron-poor tetrazine units in the solid state, thus controlling the supramolecular architecture. Modulation of the emission properties is observed in the case of the Zn(ii) and Cd(ii) complexes when compared to the free ligand. A striking difference is observed in the magnetic properties of the Mn(ii) and Co(ii) complexes. An antiferromagnetic coupling takes place in the dimanganese(ii) compound (J = −1.25 cm−1) while the Co(ii) centers are ferromagnetically coupled in the corresponding complex (J = +0.55 cm−1), the spin Hamiltonian being defined as H = −JSA·SB. [ABSTRACT FROM AUTHOR]

Two types of oxalato-bridged heterometallic 3d–4f dodeca- and hexanuclear compounds have been obtained by connecting six bi- and, respectively, trinuclear moieties through oxalato bridges arising from the slow decomposition of the l-ascorbic acid. [ABSTRACT FROM AUTHOR]

A polyazamacrocycle formed from two tris(2-aminoethyl)amine units connected by 1H-pyrazole units shows unique hexanuclear Cu(ii) complexes by combination of two binuclear Cu(ii) cryptand complexes through pyrazolate moieties belonging to both cryptands. The formation of these dimeric entities has been proven both in solution by potentiometric studies and mass spectroscopy and in the solid state by X-ray diffraction of crystals of three different batches of formulae [Cu6(H-3L)2(H2O)2](TsO)6·22H2O (2), [Cu6(H-3L)2(NO3)2](NO3)4·2H2O (3) and [Cu6(H-3L)2Cl2]Cl4·(C4H5N3O2)2·14.35H2O (4). The hexanuclear unit in 2 and 4 can be viewed like three magnetically independent binuclear complexes with J = −366(3) cm−1, g = 2.08(1) for 2 and J = −360(3) cm−1, g = 2.07(1) for 4. [ABSTRACT FROM AUTHOR]

A novel two-dimensional coordination polymer of the formula [Co(dca)2(atz)2]n (1) resulted from assembling trans-bis(2-amino-1,3,5-triazine)cobalt(ii) motifs by dicyanamide spacers. Variable-temperature dc and ac magnetic susceptibility measurements of 1 show that the high-spin cobalt(ii) ions act as single ion magnets (SIMs). [ABSTRACT FROM AUTHOR]

The reaction of 8-quinolinol-2-carboaldoxime (LH2) with NiII and LnIII salts afforded the heterometallic decanuclear compounds [Ni8Dy2(μ3-OH)2(L)8(LH)2(H2O)6](ClO4)2·16H2O (1), [Ni8Gd2(μ3-OH)2(L)8(LH)2-(H2O)4(MeOH)2](NO3)2·12H2O (2), [Ni8Ho2(μ3-OH)2(L)8(LH)2(H2O)4(MeOH)2](ClO4)2·2MeOH·12H2O (3) and [Ni8Tb2 (μ3-OH)2(L)8(LH)2(MeOH)4(OMe)2]·2CH2Cl2·8H2O (4). While compounds 1-3 are dicationic, compound 4 is neutral. These compounds possess an S-shaped architecture and comprise a long chain of metal ions bound to each other. In all the complexes, the eight NiII and two LnIII ions of the multimetallic ensemble are hold together by two μ3-OH, eight dianionic (L2-) and two monoanionic oxime ligands (LH-) whereas compound 4 has two μ3-OH, eight dianionic (L2-), two monoanionic oxime ligands (LH-) and two terminal methoxy (MeO-) ligands. The central portion of the S-shaped molecular wire is made up of an octanuclear NiII ensemble which has at its two ends the LnIII caps. Magnetic studies on 1-4 reveal that the magnetic interactions between neighboring metal ions are negligible at room temperature. On the other hand, at lower temperatures in all the compounds anti-ferromagnetic interactions seem to be dominated. Analysis of the magnetic data for the GdIII derivative indicates NiII-NiII anti-ferromagnetic interactions and GdIII-NiII ferromagnetic interactions at low temperatures. A theoretical density functional study on the magnetic behavior of the GdIII derivative suggests that while the weak ferromagnetic interaction between GdIII and NiII is in line with the expectation of the magnetic interactions between orthogonal d and f orbitals, antiferromagnetic NiII-NiII interactions are related to the wide Ni-O-Ni angles (~102°) and quasi-planar conformation of the Ni2O2 core. [ABSTRACT FROM AUTHOR]

Clickable ligands like N,N'-bis((pyridin-2-yl)methyl)prop-2-yn-1-amine (L¹) and N-((1-methyl-1H-imidazol-2-yl)methyl)-N-(pyridin-2-ylmethyl)prop-2-yn-1-amine (L²) have been used to synthesise a series of manganese(II) complexes for grafting onto appropriate solid supports. These ligands mimic the 2-His-1-carboxylate facial chelation present in the active site of the manganese-dependent dioxygenase (MndD), while the alkyne side function allows grafting of the ligand onto an azido-functionalised support using "click chemistry" methodologies. Such synthetic analogues of the MndD crystallise in the solid state as double halide or pseudohalide-bridged dinuclear manganese(II) complexes of the general formula [Mn2(μ-X)2X2L2] [L = L¹ with X = Cl (1), Br (2), and N3 (3); L = L2 with X = N3 (4)]. Complexes 1-4 are characterised by a weak magnetic exchange interaction between the two high-spin MnII ions through the two X- bridges (J in the range of -0.059 to +5.30 cm-1, H = -J·SMn1·SMn2 with SMn1 = SMn2 = 5/2). A new magneto-structural correlation of superexchange bis(μ1,1-azido)dimanganese(II) complexes has been proposed using both structural parameters, the Mn-N-Mn bridging angle and the Mn-Nazido distance. In MeOH-EtOH solution the dimeric species are present together with few percents of mononuclear manganese(II) complexes as evidenced by electron paramagnetic resonance (EPR) spectroscopy. Grafting the complexes onto mesoporous silica of MCM-41 type stabilises both dimers and monomers in the nanopores of the solid. [ABSTRACT FROM AUTHOR]

Four novel Re(ii) complexes of formula NBu4[Re(NO)Br4(L)] [NBu4+ = tetra-n-butylammonium cation and L = pyridine (1), pyrazine (2), pyrimidine (3), pyridazine (4)] have been prepared by a substitution reaction involving NBu4[Re(NO)Br4(EtOH)] and L. Their crystal structures have been determined by single crystal X-ray diffraction. They are all mononuclear complexes whose structure is made up of [Re(NO)Br4L]− anions and NBu4+ cations. Each Re(ii) ion is six-coordinate with four bromide ligands, a linear nitrosyl group and one monodentate nitrogen donor L building a tetragonally distorted octahedral surrounding. The Re–Br bond distances cover a narrow range [2.5048(8)–2.5333(5) Å] and they are longer than the Re–NO [1.688(15)–1.736(3) Å] and Re–N bonds [2.219(4)–2.234(3) Å]. The magnetic properties of 1–4 have been investigated in the temperature range 1.9–295 K. They behave like quasi magnetically isolated spin doublets with very weak antiferromagnetic interactions through intermolecular Br…Br contacts. Their magnetic properties are discussed through a deep analysis of the influence of the ligand field, spin–orbit coupling, tetragonal distortion and covalence effects. The values of the temperature-independent paramagnetism for 1–4 are also substantiated and compared to those previously reported in related systems. [ABSTRACT FROM AUTHOR]

Using a (2-pyridyl)ethylamine-appended carboxylate ligand a new cluster [CuII7(L)4(μ3-OH)2(H2O)2(DMF)2][ClO4]4·4H2O (1) [L(2-): N-{CH2CH2(2-pyridyl)}(CH2CH2CO2)2] is synthesized, as a result of ‘coordination-driven self-assembly’. The structure of 1is unique and consists of a centrosymmetric carboxylato- and hydroxo-bridged heptanuclear copper(ii) cation, with body-centred anti-prismatic topology. The four crystallographically independent copper(ii) centres differ markedly in their coordination geometry. In addition to establishing cluster authenticity, the structural analysis of 1discloses two notable features. The existence of {CuII3(μ3-OH)}5+core and H-bonded metal-coordinated carboxylate and water unit, with water acting as a proton donor. Both of these features have biological implications. Magnetic measurements reveal that in this unprecedented cluster the net magnetic-exchange is antiferromagnetic. The different types of magnetic-exchange coupling constants (Jvalues) considered for magnetic data analysis appear to adopt a variety of values depending on the specific geometric parameters associated with two interacting copper(ii) centres. Notably, for 1a good agreement between the Jvalues obtained from DFT calculations at the B3LYP level of theory and from the experimental data is achieved. [ABSTRACT FROM AUTHOR]

Three MnIII–MIII(M = Cr and Fe) dinuclear complexes have been obtained by assembling [MnIII(SB)(H2O)]+and [MIII(AA)(CN)4]−ions, where SB is the dianion of the Schiff-base resulting from the condensation of 3-methoxysalicylaldehyde with ethylenediamine (3-MeOsalen2−) or 1,2-cyclohexanediamine (3-MeOsalcyen2−): [Mn(3-MeOsalen)(H2O)(µ-NC)Cr(bipy)(CN)3]·2H2O (1), [Mn(3-MeOsalen)(H2O)(µ-NC)Cr(ampy)(CN)3][Mn(3-MeOsalen)(H2O)2]ClO4·2H2O (2) and [Mn(3-MeOsalcyen)(H2O)(µ-NC)Fe(bpym)(CN)3]·3H2O (3) (bipy = 2,2′-bipyridine, ampy = 2-aminomethylpyridine and bpym = 2,2′-bipyrimidine). The [M(AA)(CN)4]−unit in 1–3acts as a monodentate ligand towards the manganese(iii) ion through one of its four cyanide groups. The manganese(iii) ion in 1–3exhibits an elongated octahedral stereochemistry with the tetradentate SB building the equatorial plane and a water molecule and a cyanide-nitrogen atom filling the axial positions. Remarkably, the neutral mononuclear complex [Mn(3-MeOsalen)(H2O)2]ClO4co-crystallizes with the heterobimetallic unit in 2. The values of the MnIII–MIIIdistance across the bridging cyanide are 5.228 (1), 5.505 (2) and 5.265 Å (3). The packing of the neutral heterobimetallic units in the crystal is governed by the self-complementarity of the [Mn(SB)(H2O)]+moieties, which interact each other through hydrogen bonds established between the aqua ligand from one fragment with the set of phenolate- and methoxy-oxygens from the adjacent one. The magnetic properties of the three complexes have been investigated in the temperature range 1.9–300 K. Weak antiferromagnetic interactions between the MnIIIand MIIIions across the cyanido bridge were found: JMnM= −5.6 (1), −0.63 (2) and −2.4 cm−1(3) the Hamiltonian being defined as H= −JSMn·SM. Theoretical calculations based on density functional theory (DFT) have been used to substantiate both the nature and magnitude of the exchange interactions observed and also to analyze the dependence of the magnetic coupling on the structural parameters within the MnIII–N–C–MIIImotif in 1–3. [ABSTRACT FROM AUTHOR]

Two new digadolinium(iii) complexes with monocarboxylate ligands, [Gd2(pac)6(H2O)4] (1) and [Gd2(tpac)6(H2O)4] (2) (Hpac = pentanoic acid and Htpac = 3-thiopheneacetic acid), have been prepared and their structures determined by X-ray diffraction on single crystals. Their structures consist of neutral and isolated digadolinium(iii) units, containing six monocarboxylate ligands and four coordinated water molecules, the bridging skeleton being built by a μO(1):κ2O(1)O(2) framework. This structural pattern has already been observed in the parent acetate-containing compound [Gd2(ac)6(H2O)4]·4H2O (3) whose structure and magnetic properties were reported elsewhere (L. Cañadillas-Delgado, O. Fabelo, J. Cano, J. Pasán, F. S. Delgado, M. Julve, F. Lloret and C. Ruiz-Pérez, CrystEngComm, 2009, 11, 2131). Each gadolinium(iii) ion in 1and 2is nine-coordinated with seven carboxylate-oxygen atoms from four pac (1)/tpac (2) ligands and two water molecules (1and 2) building a distorted monocapped square antiprism. The values of the intramolecular gadolinium–gadolinium separation are 4.1215(5) (1), 4.1255(6) (2) and 4.1589(3) Å (3) and those of the angle at the oxo-carboxylate bridge () are 113.16(13) (1), 112.5(2) (2) and 115.47(7)° (3). Magnetic susceptibility measurements in the temperature range 1.9–300 K reveal the occurrence of a weak intramolecular antiferromagnetic interaction [J= −0.032(1) (1) and −0.012(1) cm−1(2), the Hamiltonian being defined as = −JSA·SB] in contrast with the intramolecular ferromagnetic coupling which occurs in 3(J= +0.031(1) cm−1). The magneto–structural data of 1–3show the relevance of the geometrical parameters at the μO(1):κ2O(1)O(2) bridge on the nature of the magnetic coupling between two gadolinium(iii) ions. [ABSTRACT FROM AUTHOR]

Two isostructural heterometallic trinuclear oxalato-bridged complexes of formula C4[MCr2(ox)6(H2O)2]·nH2O (C+= 4-aminopyridinium; ox2−= oxalate dianion; M2+= Mn2+, n= 3, 1; M2+= Co2+, n= 3.25, 2) have been synthesized by using direct self-assembly methods combining C3[Cr(ox)3] and the chloride salts of the corresponding metal ion. The crystal structures of both compounds have been resolved by single-crystal X-ray diffraction. They crystallize in the C2/cspace group [a= 11.5113(15) Å, b= 20.250(3) Å, c= 21.810(4) Å, β= 100.447(10)°, V= 5161.6(3) Å3, and Z= 4 for 1, and a= 11.4334(16) Å, b= 20.243(2) Å, c= 21.805(3) Å, β= 101.113(9)°, V= 4951.9(11) Å3, and Z= 4 for 2]. The structures of 1and 2consist of discrete linear [MCr2(ox)6]4−bimetallic trinuclear units, pyridinium cations and crystallization water molecules. The linear trinuclear unit is built from a central trans-diaquametal(ii), linked to two Cr(ox)3]3−entities by oxalate bridges. One of the oxalate ions is coordinated to the central metal ion whereas the other two oxalate ligands are non-bridging. In the crystal, intermolecular hydrogen bonds involving oxalate ligands, water molecules and pyridinium cations, build a complex three-dimensional network. Variable-temperature magnetic susceptibility measurements for 1and 2indicate a weak ferromagnetic interaction (J= +1.16 and +2.62/+2.70 cm−1for 1and 2, respectively) between the two terminal CrIII(SCr= 3/2) and the central high-spin MnII(SMn= 5/2) and CoII(SCo= 3/2) ions. The nature and the amplitude of the exchange interaction are rationalized using DFT calculations and orbital interpretations. [ABSTRACT FROM AUTHOR]

The preparation, crystal structures and magnetic properties of the heterobimetallic complexes of formula [MnIII(n-MeOsalen)(H2O)(μ-CN)FeIII(bpym)(CN)3]·mH2O with n= m= 3 (1) and n= 4 and m= 2 (2) [n-MeOsalen2−= N,N′-ethylenebis(n-methoxysalicylideneiminate) dianion and bpym = 2,2′-bipyrimidine] are reported. 1and 2are dinuclear neutral species where the cyano-bearing low-spin unit [FeIII(bpym)(CN)4]−acts as a monodentate ligand towards the [MnIII(SB)(solv)x]+entity (SB = tetradentate Schiff-base) through one of its four cyano groups. Adjacent heterobimetallic units are interlinked through hydrogen bonds involving the coordinated water molecule of one dinuclear unit and the phenolate oxygen atoms of the neighbouring one to afford pairs of dimers with values of the interdimer MnMn distance of 4.925(20) (1) and 5.0508(25) Å (2). The analysis of the magnetic data of 1and 2in the temperature range 1.9-300 K shows the coexistence of weak ferro- [J= +2.95 (1) and +3.88 cm−1(2)] and antiferromagnetic interactions [j= -1.91 (1) and -0.70 cm−1(2)] through the single cyano bridge and hydrogen bonds, respectively (the Hamiltonian being of the type = J[Fe·Mn+ Fe′·Mn′] −jMn·Mn′). Theoretical calculations using methods based on density functional theory (DFT) have been used to substantiate the nature and magnitude of the magnetic coupling observed in 1and 2and also to analyze the dependence of the magnetic coupling on the structural parameters for the Fe–C–N–Mn skeleton. An extension of the calculations to selected examples of heterobimetallic FeIII–C–N–MnIIIcompounds with a different number of cyano groups on the low-spin iron(iii) precursor has been carried out allowing us to illustrate the influence of the symmetry of the magnetic orbital of the iron center on the magnetic coupling in this heterobimetallic unit. [ABSTRACT FROM AUTHOR]

Homo- and heterometallic octanuclear complexes of formula Na2{[Cu2(mpba)3][Cu(Me5dien)]6}(ClO4)6·12H2O (1), Na2{[Cu2(Mempba)3][Cu(Me5dien)]6}(ClO4)6·12H2O (2), Na2{[Ni2(mpba)3][Cu(Me5dien)]6}(ClO4)6·12H2O (3), Na2{[Ni2(Mempba)3][Cu(Me5dien)]6}(ClO4)6·9H2O (4), {[Ni2(mpba)3][Ni(dipn)(H2O)]6}(ClO4)4·12.5H2O (5), and {[Ni2(Mempba)3][Ni(dipn)(H2O)]6}(ClO4)4·12H2O (6) [mpba = 1,3-phenylenebis(oxamate), Mempba = 4-methyl-1,3-phenylenebis(oxamate), Me5dien = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine, and dipn = dipropylenetriamine] have been synthesized through the “complex-as-ligand/complex-as-metal” strategy. Single-crystal X-ray diffraction analyses of 1, 3, and 5show cationic MII2M′II6entities (M, M′ = Cu and Ni) with an overall double-star architecture, which is made up of two oxamato-bridged MIIM′II3star units connected through three meta-phenylenediamidate bridges between the two central metal atoms leading to a binuclear metallacryptand core of the meso-helicate-type. Dc magnetic susceptibility data for 1–6in the temperature range 2–300 K have been analyzed through a “dimer-of-tetramers” model [H= −J(S1A·S3A+ S1A·S4A+ S1A·S5A+ S2B·S6B+ S2B·S7B+ S2B·S8B) −J′S1A·S2B, with S1A= S2B= SMand S3A= S4A= S5A= S6B= S7B= S8B= SM′]. The moderate to strong antiferromagnetic coupling between the MIIand M′IIions through the oxamate bridge in 1–6(−JCu–Cu= 52.0–57.0 cm−1, −JNi–Cu= 39.1–44.7 cm−1, and −JNi–Ni= 26.3–26.6 cm−1) leads to a non-compensation of the ground spin state for the tetranuclear MIIM′II3star units [SA= SB= 3SM′−SM= 1 (1and 2), 1/2 (3and 4), and 2 (5and 6)]. Within the binuclear MII2meso-helicate cores of 1–4, a moderate to weak antiferromagnetic coupling between the MIIions (−J′Cu–Cu= 28.0–48.0 cm−1and −J′Ni–Ni= 0.16–0.97 cm−1) is mediated by the triple m-phenylenediamidate bridge to give a ground spin singlet (S= SA−SB= 0) state for the octanuclear MII2CuII6molecule. Instead, a weak ferromagnetic coupling between the NiIIions (J′Ni–Ni= 2.07–3.06 cm−1) operates in the binuclear NiII2meso-helicate core of 5and 6leading thus to a ground spin nonet (S= SA+ SB= 4) state for the octanuclear NiII8molecule. Dc magnetization data for 5reveal a small but non-negligible axial magnetic anisotropy (D= −0.23 cm−1) of the S= 4 NiII8ground state with an estimated value of the energy barrier for magnetization reversal of 3.7 cm−1(U= −DS2). Ac magnetic susceptibility data for 5show an unusual slow magnetic relaxation behaviour at low temperatures which is typical of “cluster glasses”. The temperature dependence of the relaxation time for 5has been interpreted on the basis of the Vogel–Fulcher law for weakly interacting clusters, with values of 2.5 K, 1.4 × 10−6s, and 4.0 cm−1for the intermolecular interaction parameter (T0), the pre-exponential factor (τ0), and the effective energy barrier (Ueff), respectively. [ABSTRACT FROM AUTHOR]

The preparation, crystal structures and magnetic properties of the copper(ii) complexes of formula [Cu2(tppz)(H2O)2(CF3SO3)4] (1), [Cu(tppz)(CrO4)]n·3nH2O (2) and [Cu4(tppz)4(H2O)4(MoO4)2](CF3SO3)4·7H2O (3) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine] are reported. Complex 1is a dinuclear species where tppz adopts a bis-tridentate bridging mode with an intramolecular copper–copper separation of 6.5221(6) . Each copper(ii) ion in 1has an elongated octahedral geometry with three tppz nitrogen atoms and a water molecule in the equatorial positions and two triflate oxygen atoms occupying the axial sites. Complex 2is a uniform copper(ii) chain where the copper atoms are bridged by two oxygen atoms of the chromate group (μ1,2-CrO4), the value of the intrachain metal–metal separation being 4.2614(5) . Each copper(ii) ion in 2exhibits a somewhat distorted square pyramidal geometry with three nitrogen atoms from a tridentate tppz ligand and a chromate oxygen atom in the basal plane and an oxygen atom of a symmetry-related chromate group in the apical position. Complex 3is a cyclic tetranuclear compound where peripheral [Cu(tppz)(H2O)]2+units are connected through two molybdate groups, each one adopting the μ1,1,2-MoO4bridging mode. Regular alternating five [Cu(1) and Cu(4)] and six [Cu(2) and Cu(3)] coordinated copper(ii) ions occur in 3with distorted square pyramidal CuN3O2and elongated octahedral CuN3O3surroundings, respectively. The four copper atoms in 3have in common the presence of a molybdate-oxygen and three tppz-nitrogen atoms in the basal [Cu(1) and Cu(4)]/equatorial [Cu(2) and Cu(3)] planes and a water molecule in the apical [Cu(1) and Cu(4)]/one axial [Cu(2) and Cu(3)] positions whereas the remaining axial position is occupied by a molybdate-oxygen [Cu(2) and Cu(3)]. The shorter intramolecular copper–copper separation is 3.371(1) [Cu(2)Cu(3)], the other ones varying in the range 5.537(1)–6.301(1) . The investigation of the magnetic properties of 1–3in the temperature range 1.9–295 K has shown the occurrence of intermediate antiferro- [J= −48.0(1) cm−1with = −J1·2(1)], weak ferro- [J= +0.28(1) cm−1with = −JΣii·i+I(2)] and coexistence of weak ferro- and antiferromagnetic interactions [J1= +2.38(2) cm−1, J2= +0.56(2) cm−1and J3= −1.53(2) cm−1with = −J1(2·3) + J2(1·3+ 2·4) + J3(1·2+ 3·4) (3)] between the copper(ii) ions across bis-tridentate tppz (1), μ1,2-CrO4(2), di-μ1,1-MoO4and μ1,2-MoO4(3) bridges. The values of the magnetic interactions are analyzed in terms of simple orbital symmetry considerations and compared with those reported for parent systems. [ABSTRACT FROM AUTHOR]