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UiO-66 is a benchmark metal-organic framework that holds great promise for the design of new functional materials. In this work, we perform two-dimensional infrared measurements on polycrystalline membranes of UiO-66 grown on c-sapphire substrates. We study the symmetric and antisymmetric stretch vibrations of the carboxylate groups of the terephthalate linker ions and find that these vibrations show a rapid energy exchange and a collective vibrational relaxation with a time constant of 1.3 ps. We also find that the symmetric vibration of the carboxylate group is strongly coupled to a vibration of the aromatic ring of the terephthalate ion. We observe that the antisymmetric carboxylate vibrations of different terephthalate linkers show rapid resonant (Förster) energy transfer with a time constant of ∼1 ps.

Magnetic properties of new d-f cyanido-bridged 1D assemblies [RE(pzam)(3)(H(2)O)W(CN)(8)]·H(2)O (RE(III) = Gd, 1, Tb, 2, Dy, 3; pzam = pyrazine-2-carboxamide) were studied by temperature- and field-dependent magnetization measurements. No evidence for 3D interchain magnetic ordering is found above 2 K. Multiconfiguration ab initio calculations and subsequent modeling afforded simulation of the weak zero-field splitting effect in 1 and discussion of magnetic anisotropy in the f units of compounds 2 and 3. A semiquantitative corroboration with the experimental magnetic measurements is presented, performing the simulation of magnetic susceptibility vs temperature and magnetization vs field variation. The association into molecular and supramolecular architectures is analyzed by means of energy decomposition subsequent to the DFT calculations on idealized molecular models extracted from the experimental chain structure.

We present and develop alternative catalysts for biomass conversion and specifically lignin conversion into aromatics. Unlike the conventional CoMo and NiMo formulations, our catalysts can convert low-sulfur feedstocks. A set of five magnesia–alumina mixed oxides were screened in the hydrodealkylation of alkyl phenyl ethers as lignin model compounds. The typical selectivity to phenol is 30–75 %. Interestingly, we saw that the more basic the catalyst, the higher the selectivity for phenol. The results concur with the formation of phenoxide (PhO–) and RH3+ fragments on the catalyst surface. These can then react with H+ and H– species formed by the hydrogen dissociation on the MgO surface, giving phenol and hydrocarbons. We conclude that magnesia–alumina mixed oxides are attractive candidates for catalyzing lignin breakdown. These catalysts are highly stable, inexpensive, and readily available.

A combination of density functional theory (DFT) calculations and Mössbauer spectroscopy has been used to determine that the magnetic easy-axis is coincident with its crystallographic c-axis in [Fe(pca)(2)(py)(2)] x py, where pac is the 2-pyrazinecarboxylate ligand. This easy-axis bisects the approximately axial O-Fe-O coordination axes of molecules adjacent to each other along the b-axis. In {[Fe(pca)(2)(H(2)O)] x H(2)O}(n) the easy magnetic axis is not coincident with any of its crystallographic axes nor with the Fe-O(water) coordination axis, but is coincident with one of the Fe...Fe axes in the crystal structure. The DFT calculations, which use the B3LYP functional and the 6-311++G(d,p) basis set, yield s-electron probability densities and electric field gradient tensors for the iron(II) ion that are in excellent agreement with the observed iron-57 Mössbauer spectral isomer shifts and quadrupole interactions. The gas phase results are very similar for calculations based either on the X-ray structures of the two complexes or on their optimized structures; the optimized structures indicate that the iron to ligand bond distances increase in the absence of any solid-state lattice interactions. The results of a normal coordinate vibrational mode analysis of the two optimized structures are compared with the observed infrared spectra.

New mononuclear compounds of the ligand 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-dione (H2L) with Cu(II) and several lanthanoid(III) ions, where Ln(III) = Pr, Nd, Eu, Gd, have been synthesized and characterized by spectroscopic methods and X-ray crystal structure determinations. In all compounds, the ligand coordinates in a bidentate chelating manner, using the diketone function. In the [Cu(HL)2], the coordination geometry of Cu(II) ion is slightly distorted square-planar; two strong intramolecular (OH⋯O) hydrogen-bonding interactions are established between the phenolate group and the neighboring ketone function. The lanthanoid(III) compounds have the general formula [Ln(HL)3(CH3OH)2] · CH3OH · 2H2O; the lanthanoid(III) ion (Ln) is eight-coordinated and the coordination geometry is based on a distorted square-antiprism. In addition to the intramolecular hydrogen bonding (OH⋯O), intermolecular hydrogen-bonding interactions are also present between the coordinated methanol molecule and the non-coordinated methanol molecule giving rise to a three-dimensional network.

The synthesis, crystal structure, and magnetic properties of three new manganese(III) clusters are reported, [Mn 3(mu 3-O)(phpzH) 3(MeOH) 3(OAc)] (1), [Mn 3(mu 3-O)(phpzMe) 3(MeOH) 3(OAc)].1.5MeOH (2), and [Mn 3(mu 3-O)(phpzH) 3(MeOH) 4(N 3)].MeOH (3) (H 2phpzH = 3(5)-(2-hydroxyphenyl)-pyrazole and H 2phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole). Complexes 1- 3 consist of a triangle of manganese(III) ions with an oxido-center bridge and three ligands, phpzR (2-) (R = H, Me) that form a plane with the metal ions. All the complexes contain the same core with the general formula [Mn 3(mu 3-O)(phpzR) 3] (+). Methanol molecules and additional bridging ligands, that is, acetate (complexes 1 and 2) and azide (complex 3), are at the terminal positions. Temperature dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between manganese(III) ions in 1 and 3, while both antiferromagnetic and ferromagnetic intramolecular interactions are operative in 2.

A novel linear bis(chlorido)-bridged Cu(II) compound with the ligand 7-azaindole (abbreviated as Haza) have been synthesized and fully characterized by spectroscopy, EPR and X-ray structure analysis. The geometry around the Cu(II) ion in the compound [Cu–μ-Cl2(Haza)2]n, is distorted octahedral with the basal plane formed by two chloride anions with a Cu–Cl distance of 2.286(1) A and two nitrogen atoms of two trans-chelating Haza ligands with a Cu–N distance of 2.042(4) A. The apical positions is formed by two chloride anions of a neighbouring unit at a distance of 3.143(2) A. The Cu–Cl–Cu angle is 90.09(5)°, while the Cu–Cu distance is 3.8890(8) A. The EPR powder spectrum appears as rhombic, displaying some extra features which were assigned to the differences in orientation of chains in the lattice, as their intensity appears to decrease on powdering. The magnetic susceptibility measurements, recorded from 5 to 300 K, agree with a very weak antiferromagnetic interaction in a chain with J = −2.6 cm−1.

Iron complexes of two ligands, HphoxCOOH and HphoxiPr, have been synthesized and characterized by crystal structure analyses. The complexes (HNEt3)2[Fe(phoxCOO)2](ClO4) and [Fe(phoxiPr)3] are reported. Reactions of the ligands rac-HphoxCOOH and rac-HphoxiPr with iron(II) or iron(III) perchlorate result in the formation of iron(III) complexes with pseudo-octahedral geometry around the metal center. The iron complex obtained from rac-HphoxCOOH crystallized in the centrosymmetric space group Cmca. The two ligands are bound in a tridentate manner generating a meridional coordination with both dianionic ligands on a metal center having the same chirality; due to the center of symmetry the complex with opposite chirality is also present. The complex (HNEt3)2[Fe(phoxCOO)2](ClO4) is the first accurate structural model of the iron complex of a siderophore analog commonly observed in mycobactins. The three didentate ligands in the complex [Fe(phoxiPr)3] are bound with like atoms in a meridional manner to the metal center. The metal ion is surrounded by two ligands of the same chirality and one ligand of opposite chirality (ie. RRS or SSR); due to the presence of a center of symmetry both isomers are present in the crystal structure. The complex (HNEt3)2[Fe(phoxCOO)2](ClO4) shows promising activity in the oxidation of alkanes, such as toluene, ethylbenzene and cumene, while the complex [Fe(phoxiPr)3] does not show any catalytic activity in alkane oxidations under the conditions tested. The complex (HNEt3)2[Fe(phoxCOO)2](ClO4) is reasonably efficient in the conversion of H2O2 to oxidation products.

Item does not contain fulltext The reactions of pyridine-2,6-dicarboxamide with europium(III) and terbium(III) triflates led to the formation of mononuclear complexes of formula [Ln(pcam)(3)](CF3SO3)(3) (Ln = Eu 1, Tb 2; pcam stands for pyridine-2,6-dicarboxamide). From single-crystal X-ray diffraction analysis, the complexes were found to be isomorphous and isostructural. The [Ln(pcam)(3)](3+) cations and triflate counterions are connected by intermolecular hydrogen bonds, resulting in a 3D network structure. Both the europium(III) and terbium(III) complexes exhibit efficient ligand sensitized luminescence in the visible region with lifetimes of 1.9 ms and 2.2 ms, respectively, in the solid state. (c) 2006 Elsevier B.V. All rights reserved.

A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature. The sensing mechanism in the europium-doped compound Tb0.95Eu0.05HL (H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) is based not only on phonon-assisted energy transfer from Tb(III) to Eu(III) centers, but also on phonon-assisted energy migration between neighboring Tb(III) ions. It shows good performance in a wide temperature range, especially in the range 4-50 K, reaching a sensitivity up to 31% K(-1) at 4 K.

Design and synthesis of cyanido-bridged d–f molecular assemblies, often accessible via self-assembly of anionic building-block [M(CN)6]3− and lanthanide ions in the presence of blocking ligands, is of significant utility in the preparation of molecule-based magnets. The ability of the cyanido ligand to link various metal ions leads to a wide diversity of structural architectures ranging from discrete polynuclear complexes to fascinating three-dimensional networks. In this review, examples of cyanido-bridged d–f polynuclear complexes are discussed in terms of their structures, and their magnetic properties. It is shown that the efforts to synthesize d–f cyanido-bridged assemblies have lead to a great variety of supramolecular architectures created by the interplay of coordinative, hydrogen bonding, and π–π stacking interactions. Furthermore, the magnetic properties of these assemblies will be discussed in terms of the magnetic exchange coupling between lanthanide(III) and transition metal ions.

The synthesis and characterization is reported of four new iron(III) complexes, [Fe(L1)](ClO4) (1), [Fe(L1)](BF4) (2), [Fe(L2)](ClO4) (3), [Fe(L2)](BF4) (4) with the N4O2-donor hexadentate Schiff-base ligands (L1 = N,N′,N″,N‴-1,5,8,12-tetraazadodecane-bis(salicylaldiminato), L2 = N,N′,N″,N‴-1,5,8,12-tetraazadodecane-bis(3-methoxysalicylaldiminato)) obtained from salicylaldehyde, or a 3-methoxysalicylaldehyde. The iron(III) complexes have been prepared with different counter ions, i.e., ClO 4 - and BF 4 - , and characterized by different experimental techniques: X-ray crystallography, IR, ligand field spectroscopy, EPR, cyclic voltammetry, and magnetic susceptibility measurements. The molecular structure of the complexes is built up by complex cations [Fe(L1)]+ or [Fe(L2)]+ and counter anions ClO 4 - or BF 4 - , and has been proven by X-ray diffraction on single crystals for 1, 3 and 4. In all cases, the coordination geometry around the iron(III) ion is distorted octahedral with the iron to phenoxo oxygen bonds being trans to each other. In the crystal lattice, the mononuclear entities are organized into infinite 1D chains due to the hydrogen-bonding interactions involving the secondary amine functions and one oxygen/fluorine atom of a counter anion. In acetonitrile, all complexes exhibit a quasi-reversible one-electron reduction process Fe(III) → Fe(II), with half-wave potential E1/2 = −0.5 V. The EPR spectra of 1–4 clearly indicate a low-spin d5 (S = 1/2) electronic configuration with a rhombic symmetry. In all cases, the temperature dependent magnetic properties (5–300 K) agree with the presence of one unpaired electron (S = 1/2) and with moderate orbital contribution due to the orbitally degenerate electronic ground state (2T2g) of the octahedral iron(III) complexes.

The copper(II) polymeric complex {[Cu(pzca)(CH3CN)3](ClO4)2 AE H2O}n (1) (pzca stands for 2-pyrazine carboxamide) has been synthesized and characterized by X-ray crystal structure determination. The copper(II) ion has an elongated octahedrally geometry due to the coordination of three donor atoms from two different pzca ligands and one acetonitrile molecule in the equatorial plane and two acetonitrile molecules in axial positions. The pzca ligand acts as a tridentate with a pyrazine bridge between two Cu(II) ions leading to a Cu Cu separation of 6.7852 A ˚ . Adjacent chains are linked through hydrogen-bonding interactions to generate a twodimensional layer structure. 2005 Elsevier B.V. All rights reserved.

The synthesis, X-ray structure, spectroscopic and magnetic properties of a zig-zag formato-bridged chain complex with the formula [Cu(dpyam)(μ-O2CH)(OH2)]n(NO3)n (1) (in which dpyam = di-2-pyridylamine) is described. The geometry of the copper(II) ion is distorted square pyramidal with a basal plane consisting of two nitrogen atoms of the dpyam ligand (Cu–N distances 1.987(3) and 2.010(3) A) and two oxygen atoms of two different formato ligands (Cu–O distances 1.974(2) and 1.975(2) A). A coordinated water molecule occupies the axial position at a distance of 2.222(3) A. The copper atoms are bridged unsymmetrically by a formato anion in a syn-anti arrangement, resulting in a polymeric zig-zag chain structure. The magnetic susceptibility measurements (5–280 K) agree with a very weak ferromagnetic chain interaction between the Cu centres with a J value of 0.75 cm−1.

A new Cu(II) chain compound, [Cu(1,10-phenanthroline)(μ-HPO4)(H2O)2]n 1 has been synthesized hydrothermally and structurally characterized by elemental analysis, IR, EPR spectrum and single-crystal X-ray diffraction. The Cu(II) ion is tetragonally coordinated with a phen ligand and two aqua ligands in the equatorial plane (Cu–N distance 2.006(2) A and Cu–O distance 1.969(2) A) and hydrogenphosphates as axial ligands (Cu–O distance 2.470(2) A), thereby forming a linear chain. The crystal lattice is formed from antiparallel chains, kept together by relatively strong phosphate–water H-bonds (intra- and intermolecular) with O⋯O contacts of 2.615(3) and 2.672(3) A and by interpenetrated stacking of the phen ligands with other chains. The magnetic susceptibility measurements (5–300 K) agrees with a weak antiferromagnetic chain interaction between the Cu centers with J value of −5.86 cm−1.

The preparation of a new tridentate N2O-donor ligand N-(2-pyridylmethyl)-3-methoxysalicylaldiminato (HL) is described, together with the corresponding copper(II) complexes [Cu(L)X] (X = Cl−, Br−). The compounds were characterized by elemental analysis, spectral, magnetic and crystallographic studies. In both compounds, the local molecular structure of the Cu(II) ion involves a square-planar CuN2OX chromophore, consisting of a deprotonated phenolate oxygen, an imine nitrogen, the pyridine nitrogen and X. In the solid state, π–π stacking interactions are dominantly present, involving the pyridine and phenolate rings of neighboring molecules, which lead to a one-dimensional arrangement with alternating short and long Cu ⋯ Cu distances of [3.720, 4.599 A] for the bromo complex and of [3.698, 4.696 A] for the chloro complex. The temperature-dependent magnetic measurements and EPR data of polycrystalline samples, as well as of frozen solutions in CHCl3 show that there is no observable exchange interaction between the Cu ions. The EPR parameters (g∥, A∥) agree with a perfect planar geometry, just as found in the X-ray analysis.

Two new Zn(II) complexes, [Zn(dap)Cl 2 ] ( 1 ) and [Zn(dap) 2 Cl 2 ] ( 2 ) (dap stands for 2,3-diaminopyridine), were prepared and spectroscopically and crystallographically characterized. In both compounds, the zinc(II) atom has a pseudo-tetrahedral ZnN 2 Cl 2 coordination environment. Compound 1 adopts a three-dimensional structure built up from [Zn(dap)Cl 2 ] n zig-zag chains, which are linked by N–H⋯Cl hydrogen bonds. In compound 2 the dap is monodentate coordinating via the pyridine nitrogen; the mononuclear tetrahedral [Zn(dap) 2 Cl 2 ] units are linked into two-dimensional sheets through extensive N–H⋯Cl hydrogen bonding. Inter-sheet π–π interactions connect them into a three-dimensional network.

In this study an unusual dinuclear bis-chloride bridged Mn(II) compound, [Mn(μ-Cl)(biz)2]2Cl2 (in which biz = 2,2′-bi-imidazoline), has been described and characterised. Also the magnetic susceptibility and EPR investigations are made. The distorted octahedral geometry around the Mn(II) ion is formed by four nitrogen atoms of two dichelating biz ligands and two bridging chloride atoms. The lattice is further stabilised by hydrogen bonds between uncoordinating N atoms of the ligand and the coordinating and uncoordinating chloride atoms. Magnetic susceptibility measurements reveal a weak ferromagnetic interaction between the two high-spin Mn(II) ions of J = 0.33 cm−1.

The crystal structure of [Cu(nhep)Cl]2 (Hnhep=1-(2-hydroxyethyl)-pyrazole) shows both copper(II) ions to be in a slightly distorted square-planar CuO2NCl environment with the copper(II) ions bridged by the oxygen atoms of the dehydronated ligands. The Cu2O2 core has an asymmetric geometry with a Cu…Cu distance of 3.055 A. The EPR and magnetic susceptibility measurements indicate the presence of a very strong antiferromagnetic coupling between the copper ions, which results in essential diamagnetic behavior.

N-(3-methoxypropyl)-N-(pyridin-2-ylmethyl)amine (abbreviated as mppma) and its complex [Mn(μ-Cl)2(mppma)]n have been synthesized. Single-crystal X-ray diffraction analysis has revealed that in the complex, mppma acts as a didentate ligand bound to the Mn(II) ion through two nitrogen atoms; [MnCl2(mppma)] units are connected by double chloride bridges to form one-dimensional zigzag chains of edge-sharing distorted MnCl4(mppma) octahedra. The temperature-dependent magnetic susceptibility data have been explained with Fisher model, with parameters J=−0.25 cm−1 and g=1.99, indicating weak antiferromagnetic coupling.

The reaction of trans -[Ni(ampy) 2 (NO 3 ) 2 ] ( 1 ) (ampy=2-aminomethylpyridine) with K 3 [Fe(CN) 6 ] affords a cyano-bridged bimetallic system, [Ni(ampy) 2 ] 3 [Fe(CN) 6 ] 2 ·6H 2 O ( 2 ). The crystal structure of compound 1 has been solved. It crystallizes in the monoclinic space group P 121/ c 1 and consists of neutral mononuclear entities with the nickel atom located on an inversion center. The nickel atom exhibits a (pseudo)octahedral stereochemistry with the two nitrato ligands coordinated in trans positions. The NiN bond distances vary from 2.0690(15) to 2.0811(15) A, while the trans -NiO distances are 2.1665(13) A. The cryomagnetic investigation of compound 1 reveals an intermolecular ferromagnetic coupling ( θ =+3.7 K), which is mediated by the ππ stacking interactions between the mononuclear entities. Compound 2 is a soft ferromagnet with T c =7.5 K and a coercive field of 330 G at 2 K.

The reaction of [Cu(dien)(H2O)](NO3)2 with K3[Co(CN)6] leads to the cyano-bridged heteropolynuclear complex, [{(Cu(dien))2Co(CN)6}n][Cu(dien)(H2O)Co(CN)6]n·5nH2O, {Cu3Co2}, whose crystal structure has been solved. The structure consists of two distinct ionic units, namely one-dimensional cationic chains [{(Cu(dien))2Co(CN)6}n]n+, and discrete binuclear anionic entities [(H2O)(dien)Cu–NC–Co(CN)5]−. The cryomagnetic investigation of the title compound reveals a very weak antiferromagnetic coupling between the Cu(II) ions within the cationic chain (J=−1.02 cm−1, g=2.14). The complete elimination of the water molecules from the isomorphous {Cu3Co2}, {Cu3Fe2} and {Cu3Cr2} complexes causes the modification of the magnetic properties. The most dramatic one is observed with the Cu(II)–Fe(III) system, where the magnetic behavior changes from ferro- to antiferromagnetic. The dehydrated chromium derivative preserves the ferromagnetic coupling, which is observed at lower temperatures (below 30 K) in comparison with the parent compound (below 150 K).

The synthesis and characterization of two Fe-Gd systems based on bpca(-) (Hbpca = bis(2-pyridilcarbonyl)amine) as bridging ligand is presented, taking the systems as a case study for structure-property correlations. Compound 1, [Fe(LS)(II)(μ-bpca)(2)Gd(NO(3))(2)(H(2)O)]NO(3)·2CH(3)NO(2), is a zigzag polymer, incorporating the diamagnetic low spin Fe(LS)(II) ion. The magnetism of 1 is entirely determined by the weak zero field splitting (ZFS) effect on the Gd(III) ion. Compound 2 is a Fe(III)-Gd(III) dinuclear compound, [Fe(LS)(III)(bpca)(μ-bpca)Gd(NO(3))(4)]·4CH(3)NO(2)·CH(3)OH, its magnetism being interpreted as due to the antiferromagnetic coupling between the S(Fe) = ½ and S(Gd) = 7/2 spins, interplayed with the local ZFS on the lanthanide center. In both systems, the d-f assembly is determined by the bridging capabilities of the ambidentate bpca(-) ligand, which binds the d ion by a tridentate moiety with nitrogen donors and the f center by the diketonate side. We propose a spin delocalization and polarization mechanism that rationalizes the factors leading to the antiferromagnetic d-f coupling. Although conceived for compound 2, the scheme can be proposed as a general mechanism. The rationalization of the weak ZFS effects on Gd(III) by multiconfiguration and spin-orbit ab initio calculations allowed us to determine the details of the small but still significant anisotropy of Gd(III) ion in the coordination sites of compounds 1 and 2. The outlined methodologies and generalized conclusions shed new light on the field of gadolinium coordination magnetochemistry.

The new d-f cyanido-bridged 1D assembly [Nd(pzam)(3)(H2O)Mo(CN)(8)]center dot H2O was prepared by self-assembly of pyrazine-2-carboxamide (pzam), Nd(NO3) center dot nH(2)O and (Bu3NH)(3)[Mo(CN)(8)] center dot 4H(2)O in acetonitrile. X-ray crystallographic studies indicate that the complex comprises chains of alternating, cyanido-bridged [Nd(pzam)(3)(H2O)](3+) and Mo(CN)(8)](3) fragments. The magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (>= 0.3 K). Below approximate to 10 K the Nd(III) moment is well approximated by an effective spin S = 1/2, with anisotropic g-tensor. The exchange coupling between the Nd(III) and the Mo(V) spins S = 1/2 along the structural chains is found to be ferromagnetic, with J/k(B) = 1.8 +/- 0.2 K and approximately XY (planar) anisotropy. No evidence for 3D interchain magnetic ordering is found. A comparison with magneto-structural data of other cyanido-bridged complexes involving the Nd(III) ion is presented. (c) 2008 Elsevier B.V. All rights reserved.

"Reaction of H(2)phpzR (R = H, Me, Ph; H(2)phpzH = 3(5)-(2-hydroxyphenyl)pyrazole, H(2)phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole, and H(2)phpzPh = 3(5)-(2-hydroxyphenyl)-5(3)-phenylpyrazole)) with MnCl2 center dot 2H(2)O or MnBr2 center dot 4H(2)O in an acetonitrile-methanol mixture and in the presence of a small quantity of triethylatnine affords the compounds [Mn(HphpzR)(2)Cl] (R = H (1), Me (3), and Ph (5) and [Mn(HphpzR)(2)Br] (R = H (2), Me (4), and Ph (6)). This new family of compounds 1-6 with a library of phenol-pyrazole-based ligands was structurally characterized. All compounds are mononuclear manganese(III) coordination compounds in which the manganese(III) ion has a square-pyramidal geometry. In compounds 1-4 intermolecular hydrogen bonds are present between the N-H group of the pyrazole ring of a mononuclear entity and the halogen of a neighboring molecule, thus forming ladder-like chains. The presence of two crystallographically independent molecules in the unit cell of 5 and 6 precludes formation of ID structure and instead gives rise to a 2D structure with the independent molecules aligned in a face-to-face manner. Low-temperature magnetization studies evidence the presence of antiferromagnetic interactions between the manganese(III) ions in all compounds. Detailed temperature-dependent susceptibility and magnetic specific heat measurements on compounds 1 and 2 show the presence of antiferromagnetic S = 2 chains, the magnetic interaction being described by the anisotropic Heisenberg model with a predominantly planar (XY) type of crystal field anisotropy. In addition, the magnetic specific heat data evidence the occurrence of long-range magnetic ordering between chains in 1 and 2 below about 1.5 K. Compounds 3-6 show weaker antiferromagnetic interactions as compared with 1 and 2."

The synthesis, crystal structures, as well as the magnetic properties, of two new 1D polymeric Mn(II) compounds containing the ligand dicyanamide (dca), with the general formula [Mn(II)(dca)2(L)2]n (where L = C2H5OH and 2-aminopyrimidine (abbreviated as ampym)) are reported. The Mn(II) ions in the compounds [Mn(dca)2(C2H5OH)2]n (1), and [Mn(dca)2(ampym)2]n (2) possess an octahedral geometry. The octahedron of (1) is formed by four nitrogen atoms of four different dca molecules with a Mn–N distance of 2.217(2) A and two oxygen atoms of two trans-ethanol molecules with a Mn–O distance of 2.216(3) A. The Mn–Mn distance is 7.506 A. The octahedron of (2) is formed by four nitrogen atoms of four different dca molecules with a Mn–N distance of 2.2193(13) A and two nitrogen atoms of two trans-ampym molecules with a Mn–N distance of 2.3191(18) A. The Mn–Mn distance is 7.580 A. Magnetic susceptibility measurements of (2) revealed that a very weak antiferromagnetic interaction (J = −0.22 cm−1) is present between the metal atoms, as was expected, since the Mn–Mn distance is very large and the magnetic interaction must take place via the dca ligands.

Item does not contain fulltext Three new complexes of 5-methyl-2-pyrazinecarboxylate (Hmpca) with cobalt(II), [Co(mpca)(2)(H2O)(2)], nickel(II), [Ni(mpca)(2)(H2O)(2)] and iron(III) [Fe(mpca)(2)(OH)](2) center dot 2H(2)O, have been synthesized and characterized by spectroscopic techniques, X-ray crystallography and low-temperature magnetic measurements in the range 5-300 K. The molecular structures of [Co(mpca)(2)(H2O)(2)] (1) and [Ni(mpca)(2)(H2O)(2)](2) comprise mononuclear complexes of cobalt(II) and nickel(II), with distorted octahedral coordination environments. In both cases, the mononuclear entities are linked through hydrogen-bonding and pi-pi stacking interactions to form two-dimensional network structures. The molecular structure of [Fe(mpca)(2)(OH)](2) center dot 2H(2)O (3) consists of a symmetric bis(mu-hydroxido)-diiron(III) core. The geometry around the two iron(III) ions is pseudo-octahedral due to the coordination of two mpca(-) ions in a bidentate chelating manner and of two bridging hydroxide ions. Adjacent dinuclear Fe-2(OH)(2) molecules are linked together via hydrogen-bonding and pi-pi stacking interactions, thus forming a two-dimensional network. Variable-temperature magnetic susceptibility data suggest that weak intermolecular antiferromagnetic interactions are effective in 1 and 2, while intramolecular antiferromagnetic interactions (J = -21.2 cm(-1)) between the two iron(III) ions are operative in 3. The spectroscopic and magnetic properties of the complex [Cu(mpca)(2)(H2O)] center dot 3H(2)O (4) are in agreement with the earlier reported mononuclear structure. (C) 2006 Elsevier Ltd. All rights reserved.

The reaction of Cu(ClO 4 ) 2 · 6H 2 O with dpa (in which dpa = N , N -bis(pyridin-2-ylmethyl)amine) in the presence of CH 3 COOH results in the formation of a linear chain copper(II) complex, {[Cu(dpa)(CH 3 COO)](ClO 4 ) · 0.5THF} n ( 1 ), containing syn–anti acetato bridges. The copper(II) atoms display a slightly distorted square-pyramidal geometry with a N 3 O 2 chromophore group and with Cu–O distances of 1.950(2), 2.388(3) A and Cu–N distances which vary from 1.984(3) to 1.998(3) A. The intra chain Cu⋯Cu separation is 4.039 A. The EPR spectra of solid 1 shows at RT an unresolved S = 1/2 signal with g ⊥ of 2.06 and g ∥ of 2.24; the frozen solution EPR has values of g ⊥ of 2.04, g ∥ of 2.26 and A ∥ of 17.9 mT, typical for a CuN 3 O(O) chromophore. The magnetic susceptibility measurements (5–300 K) agree with a very weak ferromagnetic chain interaction between the Cu centres with a J value of 0.21 cm −1 .

The synthesis and characterization of two new bis(l-alkoxo)-bridged dinuclear iron(III) complexes with the ligands 1-(2hydroxyethyl)-pyrazole (Hnhep) and 1-(2-hydroxyethyl)-3,5-dimethylpyrazole (Hnhed), [Fe(nhep)Cl2(EtOH)]2 (1) and [Fe(nhed)Cl2]2 (2) are reported. The crystal structures of both complexes reveal the presence of centrosymmetric dinuclear units. In compound 1, the iron(III) center has a coordination number of six, with a slightly distorted octahedral geometry. In compound 2, the bulkier nhed ligand, with methyl groups at the 3- and 5-positions of the pyrazole ring, leads to a coordination number of five at the iron(III) center in a distorted square pyramidal geometry. The magnetic properties of both complexes have been investigated in the range 2–300 K and indicate the presence of fairly weak antiferromagnetic exchange interactions between iron(III) ions (J1 = � 10.04 cm � 1 for 1 and J2 = � 12.5 cm � 1 for 2). The inactivity of both complexes in the cyclohexane hydroxylation appears to be partly due to the presence of the strong iron(III)–chloride bond that does not allow exchange with the reactant molecules. � 2004 Published by Elsevier Ltd.

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The preparation of the tetradentate dianionic ligand N,N′-bis(3,5-di-t-butylsalicylidene)-4,5-dimethyl-1,2-phenylenediamine [H2L] is described, together with the corresponding uranium complex [UO2(L)CH3OH]. H2L has been found to selectively bind to a representative actinide ( UO 2 2 + ) rather than to lanthanum (La3+) due to its cavity size. Both the free ligand and uranyl complex were characterized by elemental analysis, spectroscopic methods and single-crystal X-ray diffraction. The crystal structure of [UO2(L)CH3OH] complex show that uranyl cation adopts a distorted pentagonal bipyramidal conformation, with two imine nitrogen atoms, two phenolic oxygen atoms and a methanol oxygen in the coordination sphere, together with two trans oxo groups. The oxo groups have a (O–U–O, 176.85(15)°) angle consistent with linear coordination and U–O bond lengths of 1.786(4) and 1.805(4) A. The difference in the bond distances can be ascribed to the existence of a hydrogen bond between one uranyl oxygen and the O–H of a methanol of neighboring molecule. This complex has one of the highest solubilities in organic solvents of all uranium compounds, making it a potential candidate for applications in solvent extraction.

Two molecule-based magnets, [Mn(2)(tea)Mo(CN)(7)].H(2)O, 1, and [Mn(2)(tea)Mo(CN)(7)], 2 (tea stands for triethanolamine), formed with the 4d ion building block, [Mo(CN)(7)](4)(-), Mn(II) ions, and an additional ligand, tea, have been prepared and structurally characterized by single-crystal X-ray analyses. Whereas 1 is obtained by a self-assembling process in solution, compound 2 is quantitatively formed through a smooth thermal treatment of 1. Their magnetic properties revealed that these compounds exhibit magnetic ordering at T(c) = 75 and 106 K respectively for compounds 1 and 2. The difference for their critical temperature is attributed to the geometry of the coordination sphere of a Mn(II) site found to be square-pyramidal for 1 and tetrahedral for 2.

The reaction between K3[Fe(CN)6] and [Mn(MAC)(H2O)2]Cl2·4H2O (MAC=2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) in a water/methanol mixture affords a pentanuclear complex with the formula [{Mn3(MAC)3(H2O)2}{Fe(CN)6}2]·6H2O·2CH3OH (1), whose crystal structure has been solved. It consists of discrete [MnIIFeIIIMnIIFeIIIMnII] entities. The three {Mn(MAC}2+ moieties are connected by two [Fe(CN)6]3− anions, each one involving two cis cyano bridging groups. The manganese ions display a distorted pentagonal–bipyramidal geometry, with the macrocyclic ligand forming the equatorial plane. The axial positions are occupied by two nitrogen atoms arising from the cyano bridges, for the central manganese atom, and by one aqua ligand and one nitrogen atom from the cyano bridge, for the terminal manganese atoms. The cryomagnetic properties of 1 have been investigated and reveal a new case of irregular spin-state structure.