Search

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4′-carboxyl-2,2′:6′,2″-terpyridine and terpyepy = 4′-[(2-pyridin-4-yl)ethynyl]-2,2′:6′,2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel–nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9–200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to −6.0 (1) and −4.7 cm−1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0–5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

The slow magnetic relaxation for CoII cations in an unusual axial bipyramidal environment and psudo-spin 1/2 has been explored, showing a Direct plus Raman relaxation mechanism.

Two Ni12-multicubane topologies {Ni12W30} and {Ni12W27} have been synthesized. Magnetometry and homogeneous catalytic studies probing their properties as hydrogen evolution photocatalysts clearly distinguish {Ni12W30} and {Ni12W27} from Ni4 cubanes.

The metal ion, countercation and crystallization solvent control the packing of bis(dithiooxalato-k2S,S′)metallate(ii) complex anions in the solid state.

A mononuclear octahedral cobalt(ii) complex based on a unique benzothiadiazole-ortho-vanillin ligand shows slow relaxation of the magnetization under applied dc magnetic fields.

The coexistence of field-induced blockage of the magnetization and significant magnetocaloric effects in the low-temperature region occurs in a mononuclear holmium(III) diethylenetriamine-N,N,N′,N″,N″-pentaacetate complex, whose gadolinium(III) analogue is a commercial MRI contrast agent. Both properties make it a suitable candidate for cryogenic magnetic refrigeration, thus enlarging the variety of applications of this simple class of multifunctional molecular nanomagnets., A mononuclear holmium(III) complex is proposed as a new prototype of a multifunctional molecular nanomagnet for the physical implementation of cryomagnetic refrigeration near the strategically relevant hydrogen liquefaction temperature. Significant magnetocaloric effects occur in a wide temperature range just above the field-induced magnetization blockage.

We report two Ni

Field-induced SMM behaviour in a series of tetrahedral 1,2-disubstituted benzimidazole cobalt(ii) complexes and their catalytic properties for an eco-friendly cycloaddition of CO2 with epoxides.

Two new complexes [CoIII2CoII(μ-OL)2(μ-OOCCH3)2(μ-N3)2(N3)2]·Et2O (1·Et2O) and [NiII5(μ-OL)4(μ-OOCCH3)2(OOCCH3)2(μ-N3)2]·CH3CN (2) (HOL = 2-((2-(pyridin-2-yl)ethylamino)methyl)phenol) have been synthesized and characterized by elemental analysis, IR, and UV/Vis spectroscopy. Structural analysis revealed that 1 is a discrete trinuclear and 2 is a discrete pentanuclear coordination complex. In complex 1, terminal metal (CoIII) is in a distorted octahedral MN4O2 environment where coordination is satisfied by two nitrogen atoms and one oxygen atom of the ligand, and an oxygen atom from the acetate group and two nitrogen atoms from azide (one each from the bridging and terminal ones). The central metal (CoII) is also in a distorted octahedral MN2O4 environment where coordination is satisfied by two oxygen atoms from the phenoxo bridge, two oxygen atoms from the acetate bridge and two nitrogen atoms from the azide bridge. In complex 2, each Ni is in a distorted octahedral MN2O4/MN3O3 environment where coordination is satisfied by different donor atoms (amine, pyridine, acetate, phenolate and azide). Direct current (DC) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 1·Et2O and 2 were carried out in the temperature range of 1.8–300 K. The magnetic behaviour of 1·Et2O indicates the presence of magnetic anisotropy of the cobalt(II) ion. The magnetic data of 2 reveal the coexistence of antiferromagnetic and ferromagnetic interactions within the Ni5 unit. Theoretical calculations made from the crystal structures reveal a very good agreement with the experimental findings.

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 P 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 A. 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.

The coexistence of field-induced slow magnetic relaxation and moderately large magnetocaloric efficiency in the supra-Kelvin temperature region occurs in the 2D compound [GdIII2(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.

The cobalt(II)-mediated self-assembly of the potentially tris(chelating)

Mono-, di-, tri-, and tetranuclear compounds of nickel(II) of formula [Ni(dppn)3](NCS)2·0.5dppn (1), [{Ni(dppn)(NCS)}2(μ-dppn)(μ-NCS)]NCS (2), [Ni3(dppn)2(N3)2(μ-dppn)2(μ-N3)2](ClO4)2·CH3CH2OH·2H2O...

In this work we describe the preparation, spectroscopic, thermal and structural characterization, and cryomagnetic investigation of four new polymorphic derivatives of the [M2(H2mpba)3]2– mesocate ...

We report the preparation, spectroscopic characterisation, crystal structure determination and cryomagnetic investigation of three cobalt(II) complexes of formula trans-[Co(bim)4(NCS)2] (1), [Co(bim)2(NCO)2] (2) and [Co(bim)2(N3)2]n (3) (bim = 1-benzylimidazole). The structure of 1 is made up of neutral [Co(bim)4(NCS)2] mononuclear units, where the cobalt(II) ion is six-coordinate with four monodentate bim ligands in equatorial positions and two N-thiocyanato groups in the axial sites building a slightly compressed octahedron. In contrast to 1, each cobalt(II) ion in 2 is four-coordinate with two imidazole-nitrogen atoms from two bim molecules and two N-cyanato ligands describing a slightly distorted tetrahedral geometry, the value of Okuniewski's structural parameter being 0.925. The structure of 3 consists of uniform chains of cobalt(II) ions connected by double end-to-end azido bridges in equatorial positions with two trans-coordinated bim molecules occupying the axial sites. The Co–Nbim bond lengths in 3 are ca. 0.06 A shorter than the Co–Nazido distances, the value of the tetragonality parameter being 1.03. The intrachain cobalt–cobalt separation is 5.361(1) A, a value which is much shorter than the shortest interchain one (ca. 12.4 A). Detailed solid state ac and dc magnetic studies show that 1 and 2 are field-induced single-ion magnets with D = +88.6 (1) and −6.8 cm−1 (2). Q-band EPR spectrometry measurements for polycrystalline samples of 1 and 2 confirm the signs of D and reveal the occurrence of a strong (1)/low (2) low asymmetry in the g-tensors. Theoretical calculations by CASSCF/NEVPT2 support the results from magnetometry and EPR for 1 and 2. The values of the spin reversal barrier which were obtained from the corresponding Arrhenius plots cover the ranges 48.0–50.2 cm−1 (1) and 25.9–27.2 and 11.5–13.1 cm−1 for the high- and low-temperature relaxation processes (2). Compound 3 exhibits an overall antiferromagnetic behaviour with a maximum of the magnetic susceptibility at ca. 70 K, the intrachain antiferromagnetic coupling being J = −26.5 cm−1 (the spin Hamiltonian being defined as ). This value is of the same nature and its size compares well with those reported for the scarce examples of this type of cobalt(II) chain.

Thermal-assisted spin crossover and field-induced slow magnetic relaxation coexist in the solid state for the mononuclear cobalt(II) complex with the non-innocent 2,6-bis(N-4-methoxyphenylformimidoyl)pyridine ligand. One-electron oxidation of the paramagnetic low-spin CoII ion (SCo = 1/2) to the diamagnetic low-spin CoIII ion (SCo = 0) leads to the electroswitching of the slow magnetic relaxation in acetonitrile solution.

Construction of efficient multifunctional materials is one of the greatest challenges of our time. We herein report the magnetic and catalytic characterization of dinuclear [CoIIICoII(HL1)2(EtOH)(H2O)]Cl·2H2O (1) and trinuclear [CoIIICoII2(HL2)2(L2)Cl2]·3H2O (2) mixed valence complexes. Relevant structural features of the complexes have been mentioned to correlate with their magnetic and catalytic properties. Unique structural features, especially in terms of significant distortions around the CoII centre(s), prompted us to test both spin–orbit coupling (SOC) and zero field splitting (ZFS) methodologies for the systems. The positive sign of D values has been established from X-band EPR spectra recorded in the 5–40 K temperature range and reaffirmed by CAS/NEVPT2 calculations. ZFS tensors are also extracted for the compounds along with CoIIGaIII and CoIIZnIICoIII model species. Interestingly, 1 shows slow relaxation of magnetization below 6.5 K in the presence of a 1000 Oe external dc field with two relaxation processes (Ueff = 37.0 K with τ0 = 1.57 × 10−8 s for the SR process and Ueff = 7 K with τ0 = 1.66 × 10−6 s for the FR process). As mixed valence cobalt complexes with various nuclearities are central to the quest for water oxidation catalysts, we were prompted to explore their features and to our surprise, water oxidation ability has been realized for both 1 and 2 with significant nuclearity control.

Two novel mixed valence CoII–CoIII complexes, namely [CoIICoIII(L1)(ab)(mb)2(H2O)]·dmf (1) and [CoIII2CoII(L2)4(H2O)4]·2H2O (2) [H2L1 = (E)-2-((1-hydroxybutan-2-ylimino)methyl)-6-methoxyphenol, ab = 2-amino-butan-1-ol anion, mb = p-methyl benzoate, H2L2 = 3-((2-hydroxy-3-methoxy-benzylidene)-amino)-propionic acid, and dmf = N,N-dimethyl-formamide], were synthesized and characterized by single crystal X-ray diffraction and magnetic studies at low temperature. The structure determination reveals that both complexes belong to the monoclinic system with P21/c (1) and I2/a (2) space groups. Complex 1 is a dinuclear CoIIICoII compound with distorted octahedral cobalt centers showing different coordination environments. In 2, a bent trinuclear CoIII2CoII complex, the coordination environments around the two terminal CoIII sites are alike, whereas they are different in the central CoII ion. Alternating current/direct current (ac/dc) magnetic studies revealed that both complexes show field-induced slow magnetic relaxation. The dc magnetic susceptibility and magnetization data were analyzed with the following Hamiltonianwhere D and E are the axial and rhombic zero-field splitting (zfs) parameters, respectively, and a good agreement between experimental and simulated results was found using the parameters g⊥ = 2.585, g∥ = 2.437, D = +98.1 cm−1, E/D = 0.008 and F = 8.2× 10−5 for 1 and g⊥ = 2.580, g∥ = 2.580, D = +55.4 cm−1, and E/D = 0.000 for 2.

Polyoxometalates (POMs) provide rigid and highly symmetric coordination sites and can be used as a strategy for the stabilization of magnetic ions. Herein, we report a new member of the Keggin archetype, the Cr-centered Keggin anion [α-CrW12O40]5– (CrW12), with the unusual tetrahedral coordination of CrIII reported for the first time in POMs conferring unattended magnetic properties. POM chemistry has recently presented excellent examples of single-molecule and single-ion magnets (SMMs and SIMs) as well as molecular spin qubits; however, the majority of POM-based SIMs reported to date contain lanthanoid ions. CrW12, as the first example of a chromium(III) SIM, exhibits slow relaxation of magnetization and quantum tunneling with a single-ion magnetic behavior even above 10 K with an energy barrier for the reversal of the magnetization of 3.0 K. The first 3d-metal SIM based on a nonlacunary Keggin anion is the foundation for a new research area in POM chemistry.

International audience; We describe herein the first examples of six-coordinate CoII single-ion magnets (SIMs) based on the β-diimine Mebik ligand [Mebik = bis(1-methylimidazol-2-yl)ketone]: two mononuclear [CoII(Rbik)2L2] complexes and one mixed-valence {CoIII2CoII}n chain of formulas [CoII(Mebik)(H2O)(dmso)(μ-NC)2CoIII2(μ-2,5-dpp)(CN)6]n·1.4nH2O (3) [L = NCS (1), NCSe (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine (3)]. Two bidentate Mebik molecules plus two monodentate N-coordinated pseudohalide groups in cis positions build somewhat distorted octahedral surroundings around the high-spin cobalt(II) ions in 1 and 2. The diamagnetic [CoIII2(μ-2,5-dpp)(CN)8]2− metalloligand coordinates the paramagnetic [CoII(Mebik)(H2O)(dmso)]2+ complex cations in a bis-monodentate fashion to afford neutral zigzag heterobimetallic chains in 3. Ab initio calculations, and cryomagnetic dc (2.0–300 K) and ac (2.0–12 K) measurements as well as EPR spectroscopy for 1–3 show the existence of magnetically isolated high-spin cobalt(II) ions with D values of 59.84–89.90 (1), 66.32–93.90 (2) and 70.40–127.20 cm−1 (3) and field-induced slow relaxation of the magnetization, being thus new examples of SIMs with transversal magnetic anisotropy. The analysis of their relaxation dynamics reveals that the relaxation of the magnetization occurs by the Raman (with values of the n parameter covering the range 6.0–6.8) and direct spin-phonon processes.

We report the unique heterobimetallic dodecanuclear oxamate-based {CoII6CuII6} nanowheel obtained using an environmentally friendly synthetic protocol. The effective Hamiltonian methodology employed herein allows the rationalisation of magnetic isotropic or anisotropic metal clusters, being a significant advance for future studies of exciting properties only observed at low and ultralow temperatures.

Electrocrystallization of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) organic donor in the presence of the [Fe(ClCNAn)3]3– tris(chlorocyananilato)ferrate(III) paramagnetic anion in different stoichiometric ratios and solvent mixtures afforded two different hybrid systems formulated as [BEDT-TTF]4[Fe(ClCNAn)3]·3H2O (1) and [BEDT-TTF]5[Fe(ClCNAn)3]2·2CH3CN (2) (An = anilato). Compounds 1 and 2 present unusual structures without the typical segregated organic and inorganic layers, where layers of 1 are formed by Λ and Δ enantiomers of the anionic paramagnetic complex together with mixed-valence BEDT-TTF tetramers, while layers of 2 are formed by Λ and Δ enantiomers of the paramagnetic complex together with dicationic BEDT-TTF dimers and monomers. Compounds 1 and 2 show semiconducting behaviors with room-temperature conductivities of ca. 6 × 10–3 S cm–1 (ambient pressure) and 1 × 10–3 S cm–1 (under applied pressure of 12.1 GPa), respectively, due to strong dimerization between the donors. Magnetic measurements performed on compound 1 indicate weak antiferromagnetic coupling between high-spin FeIII (SFe = 5/2) and mixed-valence radical cation diyads (BEDT-TTF)2+ (Srad = 1/2) mediated by the anilate ligands, together with an important Pauli paramagnetism typical for conducting systems., This work was supported in France by the CNRS, the University of Angers, the RFI Regional LUMOMAT project ASCO-MMM (grant to A.A.). The work in Italy was supported by the Fondazione di Sardegna-Convenzione triennale tra la Fondazione di Sardegna e gli Atenei Sardi, Regione Sardegna-L.R. 7/2007 annualità 2016-DGR 28/21 del 17.05.2015 “Innovative Molecular Functional Materials for Environmental and Biomedical Applicatons” (grant to S.A.S.) and INSTM. M.J.O. acknowledges support from the Ministerio Español de Ciencia e Innovación (Project CTQ2016-75068P) and Unidad de Excelencia María de Maeztu (Project MDM-2015-0538). Work at Bellaterra (Spain) was supported by the Spanish MICIU through Grant PGC2018-096955-B-C44 and the MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2015-0496 as well as by Generalitat de Catalunya (2017SGR1506).

Thin films of an anionic oxamato-bridged cobalt(II)–copper(II) 3D MOF have been growth at 120 °C in DMSO through a one-pot reaction from Co(NO3)2·6H2O and (Me4N)2[Cu(2,6-Et2pa)2]·6H2O (2,6-Et2pa = N-2,6-diethylphenyloxamate) over Si(111) surfaces functionalized with carboxylic acid terminating groups. These heterobimetallic CoII2CuII3 MOF thin films (2) of about ten nanometers thickness show a ferrimagnetically ordered phase below ca. 10 K with a relatively large magnetic hysteresis similar to that of the bulk material of formula (Me4N)2[Co2Cu3(2,6-Et2pa)6]·5H2O (1).

A leitmotiv in the field of molecular magnetism is the study of the electron exchange (EE) magnetic interactions among distant metal centers through the corresponding bridging ligands in polynuclear coordination compounds. The present review provides a historical perspective on the use of dinuclear copper(II) complexes with either simple inorganic or extended organic bridging ligands as experimental and theoretical models for the fundamental research on the relative importance of the spin delocalization and spin polarization mechanisms of the EE interaction across σ- and π-type orbital pathways. Particular focus is placed on the work by Professor Miguel Julve, outstanding researcher and an excellent teacher, best friend and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th anniversary.

Two novel compounds, {[Cr(pyim)(ox)2]2Mn}n·2nCH3OH (1) and {[Cr(pyim)(ox)2]2Co(H2O)2}·7.5H2O (2) [pyim = 2-(2′-pyridyl)imidazole and H2ox = oxalic acid], were synthesized by using the mononuclear chromium(III) complex PPh4[Cr(pyim)(ox)2]·H2O (PPh4+ = tetraphenylphosphonium) as metalloligand towards the fully solvated manganese(II) (1) and cobalt(II) (2) ions as perchlorate salts. The structure of 1 consists of neutral double chains, with diamond-shaped units sharing the manganese(II) ions with the two other corners being occupied by the chromium(III) ions. The two metal centres in 1 are connected by bis-bidentate oxalate groups, each [CrIII(pyim)(ox)2]− unit being bound to two manganese(II) ions through its two oxalate ligands. Complex 2 is a centrosymmetric trinuclear compound where two outer [CrIII(pyim)(ox)2]− units act as bidentate ligands through one of their two oxalate groups towards the inner trans-diaquacobalt(II) entity. The values of the chromium(III)–manganese(II) (1) and chromium(III)–cobalt(II) (2) separation across the oxalate bridge are 5.5233(14) [Cr(1)…Mn(1)], 5.5735(14) [Cr(1)…Mn(1b)] and 5.3681(11) A [Cr1⋯Co(1)]. The investigation of the magnetic properties of 1 and 2 in the temperature range 1.9–300 K reveals the occurrence of significant ferromagnetic interactions between the chromium(III) and the high-spin manganese(II) (1)/cobalt(II) (2) across the oxalate bridge. Monte Carlo simulations were used to evaluate the intrachain magnetic interaction in 1. Simple molecular orbital analysis of the exchange interactions in 1 and 2 identify the σ- and π-type pathways involving the d(x2 − y2) (Mn and Co)/d(xy) (Cr) and d(xz) (Cr)/d(yz) (Mn and Co) pairs of orthogonal magnetic orbitals as the main individual contributions accounting for the overall ferromagnetic couplings in these compounds.

Three dimanganese(iii) complexes have been synthesised and fully characterised by standard spectroscopic methods and spectroelectrochemistry. Each MnIII ion is chelated by a salen type ligand (H2L), but there is variation in the bridging group: LMn(OOCCH[double bond, length as m-dash]CHCOO)MnL, LMn(OOCC6H4COO)MnL, and LMn(OOCC6H4C6H4COO)MnL. X-ray diffraction revealed an axial compression of each six-coordinate high-spin d4 MnIII ion, which is a Jahn-Teller-active ion. Temperature dependent magnetic susceptibility and variable temperature-variable field (VTVH) magnetisation measurements, as well as high-frequency and -field EPR (HFEPR) spectroscopy were used to accurately describe the magnetic properties of the complexes, not only the single-ion spin Hamiltonian parameters: g-values and zero-field splitting (ZFS) parameters D and E, but also the exchange interaction constant J between the two ions, which has been seldom determined for a di-MnIII complex, particularly when there is more than a single bridging atom. Quantum chemical calculations reproduced well the electronic and geometric structure of these unusual complexes, and, in particular, their electronic absorption spectra along with the spin Hamiltonian and exchange parameters.

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-HN type interactions into supramolecular chains, which are further interconnected into supramolecular 2D motifs by C-Hπ 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.

Two mononuclear cobalt(II) complexes, with the formulas [Co(2,6-dfba)2(bpp)2(H2O)2]n (1) and [Co(2,6-dfba)2(bpe)2(H2O)2]n (2) (2,6-Hdfba = 2,6-difluorobenzoic acid, bpp = 1,3-bis(4-pyridyl)propane, bpe = 1,2-bis(4-pyridyl)ethylene), have been synthesized by combining Co(II) ions with benzoate derivatives and two homogeneous N-donor ligands, respectively. Constrained by the analogous CoN2O4 coordination spheres, the discretely hexa-coordinated Co(II) cores in both complexes display stretched octahedral geometries. The equatorial environments in both complexes are identical, whereas the axial sites are finely modulated by the different chemical natures of the terminal N-donor ligands. The combined analyses of the magnetic data, the high-frequency electron paramagnetic resonance (HF-EPR) and the ab initio calculations unveil large easy-plane magnetic anisotropies for both complexes (D = +53.19 and +65.67 cm−1 for 1 and 2, respectively), which function as field-induced single-ion magnets (SIMs) with effective barriers (Ueff) of 45.34 (1) and 57.97 K (2). This work demonstrates how fine-tuning the coordination microenvironment of metal ions results in a non-negligible manipulation of their magnetic anisotropy.

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.

The use of the cyanide-bearing dicobalt(III) complex (PPh 4 ) 2 [Co 2 III (m-2,5-dpp)(CN) 8 ] as a metalloligand towards [Mn(salen)(H 2 O)]ClO 4 afforded the heterobimetallic two-dimensional compound of formula [{Mn III (salen)} 2 {(m-NC) 4 Co 2 III (m-2,5-dpp)(CN) 4 }] n (1) [PPh 4 + = teraphenylphosphonium cation, 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine and H 2 salen = N,N’ -ethylenebis(salicylideneimine)] whose structure has been determined by single crystal X-ray diffraction. Compound 1 exhibits a neutral brick-wall structure, where each [Co 2 III (m-2,5-dpp)(CN) 8 ] 2- unit adopts a tetrakis-monodentate bridging mode towards four {Mn III (salen)} + fragments through four of its eight cyanide ligands. Each cobalt(III) ion is six-coordinate with one pyrazine- and one pyridine-nitrogen atoms of the 2,5-dpp molecule and four cyanide-carbon atoms describing a somewhat distorted octahedral surrounding. The two crystallographically independent manganese(III) ions are also six-coordinate in an elongated octahedral environment with two imino-nitrogen and two phenoxo-oxygen atoms occupying the equatorial positions and two cyanide-nitrogen atoms filling the axial sites. Variable-temperature direct- (1.9-300 K) and alternating-current (2.0-5.0 K) magnetic measurements of 1 show the occurrence of magnetically isolated manganese(III) ions with a local negative zero-field splitting ( D = -5.87 cm -1 ) and slow magnetic relaxation, this compound being a new example of field-induced Single-Ion Magnet (SIM). The analysis of the ac magnetic data of 1 under an applied dc field 5000 G reveals that the value of the energy barrier ( E a ) to reverse the magnetization direction and that of the pre-exponential factor (t 0 ) are 10.8 cm -1 and 2.7 x 10 -8 s, respectively. These values compare well with those reported for the few examples of manganese(III)-based SIMs nowadays.

International audience; Molecular magnetism has made a long journey, from the fundamental studies on through-ligand electron exchange magnetic interactions in dinuclear metal complexes with extended organic bridges to the more recent exploration of their electron spin transport and quantum coherence properties. Such a field has witnessed a renaissance of dinuclear metallacyclic systems as new experimental and theoretical models for single-molecule spintronics and quantum computing, due to the intercrossing between molecular magnetism and metallosupramolecular chemistry. The present review reports a state-of-the-art overview as well as future perspectives on the use of oxamato-based dicopper(II) metallacyclophanes as promising candidates to make multifunctional and multiresponsive, single-molecule magnetic (nano)devices for the physical implementation of quantum information processing (QIP). They incorporate molecular magnetic couplers, transformers, and wires, controlling and facilitating the spin communication, as well as molecular magnetic rectifiers, transistors, and switches, exhibiting a bistable (ON/OFF) spin behavior under external stimuli (chemical, electronic, or photonic). Special focus is placed on the extensive research work done by Professor Francesc Lloret, an outstanding chemist, excellent teacher, best friend, and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th birthday.

International audience; A mononuclear iron(III) porphyrin compound exhibiting unexpectedly slow magnetic relaxation, which is a characteristic of single-ion magnet behaviour, is reported. This behaviour originates from the close proximity (approximate to 550 cm(-1)) of the intermediate-spinS=3/2 excited states to the high-spinS=5/2 ground state. More quantitatively, although the ground state is mostlyS=5/2, a spin-admixture model evidences a sizable contribution (approximate to 15 %) ofS=3/2 to the ground state, which as a consequence experiences large and positive axial anisotropy (D=+19.2 cm(-1)). Frequency-domain EPR spectroscopy allowed them(S)= |+/- 1/2⟩->|+/- 3/2⟩ transitions to be directly accessed, and thus the very large zero-field splitting in this 3d(5)system to be unambiguously measured. Other experimental results including magnetisation, Mossbauer, and field-domain EPR studies are consistent with this model, which is also supported by theoretical calculations.

Construction of efficient multifunctional materials is one of the greatest challenges of our time. We herein report the magnetic and catalytic characterization of dinuclear [CoIIICoII(HL1)2(EtOH)(H2O)]Cl·2H2O (1) and trinuclear [CoIIICoII2(HL2)2(L2)Cl2]·3H2O (2) mixed valence complexes. Relevant structural features of the complexes have been mentioned to correlate with their magnetic and catalytic properties. Unique structural features, especially in terms of significant distortions around the CoII centre(s), prompted us to test both spin-orbit coupling (SOC) and zero field splitting (ZFS) methodologies for the systems. The positive sign of D values has been established from X-band EPR spectra recorded in the 5-40 K temperature range and reaffirmed by CAS/NEVPT2 calculations. ZFS tensors are also extracted for the compounds along with CoIIGaIII and CoIIZnIICoIII model species. Interestingly, 1 shows slow relaxation of magnetization below 6.5 K in the presence of a 1000 Oe external dc field with two relaxation processes (Ueff = 37.0 K with τ0 = 1.57 × 10-8 s for the SR process and Ueff = 7 K with τ0 = 1.66 × 10-6 s for the FR process). As mixed valence cobalt complexes with various nuclearities are central to the quest for water oxidation catalysts, we were prompted to explore their features and to our surprise, water oxidation ability has been realized for both 1 and 2 with significant nuclearity control.

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.

A primary goal of molecular spintronics is detecting the response of the spins from a single magnetic molecule to an external stimulus and, eventually, being able to implement logic quantum memory capabilities for information data storage and processing applications in quantum computation. Having this in mind, a novel hexanuclear oxamatocopper(II) complex of formula {[Cu2(naba)2][Cu(pmdien)]4}(ClO4)4·8H2O (2) [naba = N,N'-1,5-naphthalenebis(oxamate) and pmdien = N,N,N’,N”,N”-pentamethyldiethylenetriamine] has been prepared by the reaction of stoichiometric amounts of (nBu4N)4[Cu2(naba)2] · 4H2O (1) (nBu4N+ = tetra-n-butylammonium cation) and [Cu(pmdien)](ClO4)2 (1:4 molar ratio) in water. 2 exhibits a ladder-like “dimer-of-trinuclears” structure featuring a photoactive dicopper(II) naphthalenophane core acting as inverse coordination centre (centroligand) towards four peripheral [Cu(pmdien)]2+ groups through the outer amidate/carboxylate oxygen atoms of the oxamato fragments. 2 undergoes a unique magnetic photoswitching ON/OFF behaviour upon UV light irradiation because of an intramolecular (“pseudo-bimolecular”) photocycloaddition of the two facing naphthalene spacers through the more reactive carbon atoms at the 1,4 and 1’,4’ positions of the benzene rings to afford the putative [4 + 4] cycloaddition product c-2. Hence, the two oxamato-bridged S = 1/2 CuII3 linear units antiferromagnetically coupled within the CuII6 precursor (2, ON state) become magnetically uncoupled in the corresponding [4 + 4] photocycloaddition product (c-2, OFF state) [jeff = –2.13 (2) and 0 cm−1 (c-2); H = – jeffSA.SB with SA = SB = 1/2]. This new example of inverse coordination complex constitutes thus a potential candidate to molecular magnetic photoswitch in the “bottom-up” approach to nanometer-scale spintronic and quantum computing devices.

Molecular magnetism has travelled a long way from the pioneering studies on electron exchange and double exchange or spin crossover and valence tautomerism in small oligonuclear complexes, from mono- to di- and tetranuclear species, to the current investigations about magnetic anisotropy and spin dynamics or quantum coherence of simple mono- or large polynuclear complexes, behaving as switchable bistable molecular nanomagnets for potential applications in information data storage and processing. In this review, we focus on the origin and development of the research in the field of molecular magnetism from a coordination chemistry viewpoint, which dates back to the establishment of magnetochemistry as a novel discipline among the molecular sciences. This overview is conceived as an attempt to orientate coordination chemists regarding their role in the future direction that molecular magnetism will undergo in its further evolution toward molecular spintronics and quantum computation. A particular emphasis will be given to some selected recent advances in single-molecule spintronic circuitry and quantum computing devices based on the large class of multiresponsive and multifunctional magnetic metal complexes to stimulate the progress in the field of molecular magnetism.

In the series described in this work, the hydrothermal synthesis led to oxidation of the 5-methyl-pyrazinecarboxylate anion to the 2,5-pyrazinedicarboxylate dianion (2,5-pzdc) allowing the preparation of three-dimensional (3D) lanthanide(III) organic frameworks of formula {[Ln2(2,5-pzdc)3(H2O)4]·6H2O}n [Ln = Ce (1), Pr (2), Nd (3), and Eu (4)] and {[Er2(2,5-pzdc)3(H2O)4]·5H2O}n (5). Single-crystal X-ray diffraction on 1–5 reveals that they crystallize in the triclinic system, P1 space group with the series 1–4 being isostructural. The crystal structure of the five compounds are 3D with the lanthanide(III) ions linked through 2,5-pzdc2– dianions acting as two- and fourfold connectors, building a binodal 4,4-connected (4·648)(426282)-mog network. The photophysical properties of the Nd(III) (3) and Eu(III) (4) complexes exhibit sensitized photoluminescence in the near-infrared and visible regions, respectively. The photoluminescence intensity and lifetime of 4 were very sensitive due to the luminescence que...