Countercomplementarity and strong ferromagnetic coupling in a linear mixed mu-acetato, mu-hydroxo trinuclear copper(II) complex. Synthesis, structure, magnetic properties, EPR, and theoretical studies

The structural and magnetic data of the trinuclear compound [Cu3(L)2(CH3COO)2(OH)2(dmf)2] (HL = N-(2-methylpyridyl)toluensulfonylamide) are reported. The compound crystallizes in the monoclinic system, space group P2(1)/n (no. 14), with a = 11.6482(6) A, b = 13.5772(6) A, c = 13.5306(7) A, alpha = 90 degrees, beta = 92.859(5) degrees, gamma = 90 degrees, and Z = 2. The three copper atoms form an exact linear arrangement. Neighboring coppers are connected by a hydroxo bridge and a bidentate syn-syn carboxylato group. The coordination spheres of the terminal copper atoms are square pyramidal with a dmf molecule as the apical ligand. The central copper has a regular square planar geometry. The mixed bridging by a hydroxide oxygen atom and a bidentate carboxylato group leads to a noncoplanarity of the adjacent basal coordination planes with a dihedral angle of 51.96(9) degrees. Susceptibility measurements (2-300 K) reveal a strong ferromagnetic coupling, J = 93(6) cm-1, in the mixed-bridged moiety leading to a quartet ground state that is confirmed by the EPR spectra. The ferromagnetic exchange coupling is discussed using DFT calculations on model compounds that have shown a countercomplementary effect of the hydroxo and acetate bridges.     

Self-assembly and characterization of copper 3,4-pyridinedicarboxylate complexes based on a variety of polynuclear hydroxo clusters

Self-assembly of copper(ii) ion, 3,4-pyridinedicarboxylate (PDC), and 1,10-phenanthroline (phen) under basic conditions at 100 °C affords four PDC linked copper(ii) complexes, [Cu(4)(μ(2)-OH)(3)(μ(3)-OH)(PDC)(phen)(4)](n)·n(PDC)·11.5 nH2O (1), [Cu(4)(μ(2)-OH)(2)(μ(3)-OH)(2)(PDC)(phen)(4)](n)·n(PDC)· 11.5 nH(2)O (2), [Cu(8)(μ(2)-OH)(2)(μ(3)-OH)(6)(PDC)(2)(phen)(8)]·2(PDC)·23 H(2)O (3), and [Cu(3.5)(μ(2)-OH)(3) (PDC)(2)(phen)](n) (4). 1-4 are copper hydroxo complexes, and 1, 2 and 3 co-crystallized from the one-pot reaction. X-ray single crystal diffraction analyses indicate that complexes 1 and 2 are linkage isomers and contain tetranuclear copper cluster cores with different geometry, and that PDC links the cluster core to form a one-dimensional chain. Complex 3 is a discrete step-like octanuclear copper hydroxo cluster complex. The involvement of hydroxo and phen in the coordination makes some coordination sites of PDC idle, which leads to rich hydrogen bonds and π-π interactions in complexes 1, 2 and 3. Complex 4 contains two types of copper hydroxo cluster cores: chair-like tetranuclear and linear trinuclear units, and the cluster cores are linked by PDC to a double-layer metal-organic framework. Magnetic properties of 1, 3 and 4 were investigated. The results reveal that complexes 3 and 4 exhibit strong antiferromagnetic interactions whereas ferromagnetic coupling is predominant for complex 1. The magnetic properties are analyzed in connection with their structures.     

Binuclear copper(II) oxidation products from copper(I) complexes with tridentate ligands. Magnetostructural characterization

The bis-pyridine tridentate ligands (6-R-2-pyridylmethyl)-(2-pyridylmethyl) benzylamine (RDPMA, where R = CH(3), CF(3)), (6-R-2-pyridylmethyl)-(2-pyridylethyl) benzylamine (RPMPEA, where R = CH(3), CF(3)), and the bidentate ligand di-benzyl-(6-methyl-2-pyridylmethyl)amine (BiBzMePMA) have been synthesized and their copper(I) complexes oxidized in a methanol solution to afford self-assembled bis-micro-methoxo-binuclear copper(II) complexes (1, 2, 4, 6) or hydroxo- binuclear copper(II) complexes (3). Oxidation of the nonsubstituted DPMA (R = H) in dichloromethane gives a chloride-bridged complex (5). The crystal structures for [Cu(MeDPMA)(MeO)](2)(ClO(4))(2) (1), [Cu(RPMPEA)(MeO)](2)(ClO(4))(2) (for 2, R= Me, and for 4, R = CF(3)), [Cu(BiBzMePMA)(MeO)](2)(ClO(4))(2) (6), [Cu(FDPMA)(OH)](2)(ClO(4))(2) (3), and [Cu(DPMA)(Cl)](2)(ClO(4))(2) (5) have been determined, and their variable-temperature magnetic susceptibility has been measured in the temperature range of 10-300 K. The copper coordination geometries are best described as square pyramidal, except for 6, which is square planar, because of the lack of one pyridine ring in the bidentate ligand. In 1-4 and 6, the basal plane is formed by two pyridine N atoms and two O atoms from the bridging methoxo or hydroxo groups, whereas in 5, the bridging Cl atoms occupy axial-equatorial sites. Magnetic susceptibility measurements show that the Cu atoms are strongly coupled antiferromagnetically in the bis-methoxo complexes 1, 2, 4, and 6, with -2J > 600 cm(-)(1), whereas for the hydroxo complex 3, -2J = 195 cm(-)(1) and the chloride-bridged complex 5 shows a weak ferromagnetic coupling, with 2J = 21 cm(-)(1) (2J is an indicator of the magnetic interaction between the Cu centers).     

Mono-, di- and trinuclear 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)-containing copper(II) complexes: syntheses, crystal structures and magnetic properties

Three new copper(ii) complexes of formula [Cu(tppz)(NCO)(2)].0.4H(2)O (1), [Cu(2)(tppz)Br(4)](2) and [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)].7H(2)O (3)[tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; C(5)O(5)(2-) = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione] have been synthesised and structurally characterized by X-ray diffraction methods. The structure of complex is made up of neutral [Cu(tppz)(NCO)(2)] mononuclear units and uncoordinated water molecules. The mononuclear units are grouped by pairs to give a rather short copper-copper distance of 3.9244(4) angstroms. The structure of complex 1 consists of neutral tppz-bridged [Cu(2)(tppz)Br(4)] dinuclear units, the copper-copper separation across tppz being 6.6198(1) angstroms. The dinuclear units are further connected through weak, double out-of-plane Cu-Br...Cu bridges [Br(1)...Cu(1a) 4.0028(17) angstroms] creating tetranuclear entities, the copper-copper separation through this interaction being 4.3299(21) angstroms. The structure of complex 3 is built of neutral [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)] trinuclear units and uncoordinated water molecules. Tppz and one of the croconate groups act as bridging ligands, the former exhibiting the bis-terdentate coordination mode and the latter adopting an unusual asymmetrical bis-bidentate bridging mode through three adjacent oxygen atoms. The other two croconate groups exhibit the bidentate coordination mode. The intramolecular copper-copper separations are 6.5417(9)(across tppz) and 4.3234(9) angstroms (through bis-bidentate croconato). The magnetic properties of 2 and 3 have been investigated in the temperature range 1.9-300 K. The magnetic behaviour of complex 2 is that of an antiferromagnetically coupled copper(II) dimer (J = -40.9 cm(-1), the Hamiltonian being H = -JS(A).S(B)). In the case of compound , the chi(M) T vs. T plot is typical of an overall antiferromagnetic coupling with a low-lying spin doublet being fully populated at T < 10 K. The values of the intramolecular antiferromagnetic interactions in 3 are -19.9 (across tppz) and -32.9 cm(-1)(through bridging croconato). Density functional type calculations were performed on model dinuclear fragments of 3 in order to analyze the efficiency of the exchange pathways involved and also to substantiate the coupling parameters.     

A trinuclear copper(II) cryptate and its μ3-CO3 cascade complex: thermodynamics, structural and magnetic properties

The 2,4,6-triethylbenzene-capped hexaamine macrobicycle with pyridyl spacers (pyr) was able to coordinate three copper(II) ions within its cavity. Potentiometric studies performed at 298.2 K in MeOH/H(2)O (50:50 v/v) and at ionic strength 0.10 mol dm(-3) in KNO(3) revealed that trinuclear species predominate in solution from pH 5.0, the hydroxo complexes being the main species, which start forming at unusual very low pH values. The single-crystal X-ray determination of the trinuclear complex showed that the three copper centres have square-planar geometry, arranged in an almost equilateral triangle, and have carbonate bridging the three metal centres. The presence of carbonate resulted from fixation of atmospheric CO(2). The present study represents the first μ(3)-CO(3)-bridged trinuclear copper(II) complex located in the interior of a macrobicyclic cavity. The magnetic data of [Cu(3)(pyr)(μ(3)-CO(3))]·(ClO(4))(4) showed ferromagnetic intramolecular interactions [J=3.80 cm(-1), based on the Hamiltonian H=-J(S(1)S(2)+S(2)S(3)+S(1)S(3))] yielding a spin quartet, S=3/2, ground state. Density functional calculations on the experimental geometry of the trinuclear complex showed that the ferromagnetic nature of the magnetic coupling can be attributed to the syn-anti conformation of the carbonato bridge, and a magneto-structural correlation, based on the different conformations (syn-anti, syn-syn and anti-anti), is presented. The interesting properties observed, namely the lowering of the pK(a) of coordinated water molecules to unusual values and the good fit of the carbonate anion between the copper centres, derive from the special architecture of pyr.     

Ferromagnetic coupling in a 1D coordination polymer containing a symmetric [Cu(mu1,1-N3)2Cu(mu1,1-N3)2Cu]2+ core and based on an organic ligand obtained from the solid state

Addition of rctt-tetrakis(2-pyridyl)cyclobutane (2,2'-tpcb) in a Cu(II)/N(3)- solution afforded the 1D coordination polymer [Cu(3)(N(3))(6)(2,2'-tpcb)(DMF)(2)](n) (1). The ligand 2,2'-tpcb serves as a tetradentate bis-chelating ligand by linking linear [(DMF)Cu(mu(1,1)-N(3))(2)Cu(N(3))(2)(mu(1,1)-N(3))(2)Cu(DMF)] trinuclear units to produce a zigzag chain. Within each centrosymmetric trinuclear unit there exist two irregularly asymmetric end-on double azido-bridged [Cu(mu(1,1)-N(3))(2)Cu](2+) cores, while one of the largest Cu-Nazide-Cu angles is observed. Magnetic susceptibility data, measured from 2 to 300 K, show bulk moderate ferromagnetic coupling within the magnetically isolated trinuclear units. These data were fitted to the appropriate equation derived from the Hamiltonian H = -J(1)(S(A1)S(B) + S(A2)S(B)) - J(2)S(A1)S(A2), giving the parameters J1 = +70(3) cm(-1), J2 = -3(2) cm(-1), g = 2.12(1), with an intertrimer interaction parameter theta = -0.74(2) K. The coupling constants were correlated with the structural parameters. Density functional calculations reproduce very well the experimental J values and show that ferromagnetism for this complex is mainly due to the topology of the magnetic orbitals and the different coordination spheres of two neighboring Cu(II) atoms, resulting in a small overlap of the orbitals possessing the unpaired electrons.     

Fine-tuning of copper(I)-dioxygen reactivity by 2-(2-pyridyl)ethylamine bidentate ligands

Copper(I)-dioxygen reactivity has been examined using a series of 2-(2-pyridyl)ethylamine bidentate ligands (R1)Py1(R2,R3). The bidentate ligand with the methyl substituent on the pyridine nucleus (Me)Py1(Et,Bz) (N-benzyl-N-ethyl-2-(6-methylpyridin-2-yl)ethylamine) predominantly provided a (mu-eta(2):eta(2)-peroxo)dicopper(II) complex, while the bidentate ligand without the 6-methyl group (H)Py1(Et,Bz) (N-benzyl-N-ethyl-2-(2-pyridyl)ethylamine) afforded a bis(mu-oxo)dicopper(III) complex under the same experimental conditions. Both Cu(2)O(2) complexes gradually decompose, leading to oxidative N-dealkylation reaction of the benzyl group. Detailed kinetic analysis has revealed that the bis(mu-oxo)dicopper(III) complex is the common reactive intermediate in both cases and that O[bond]O bond homolysis of the peroxo complex is the rate-determining step in the former case with (Me)Py1(Et,Bz). On the other hand, the copper(I) complex supported by the bidentate ligand with the smallest N-alkyl group ((H)Py1(Me,Me), N,N-dimethyl-2-(2-pyridyl)ethylamine) reacts with molecular oxygen in a 3:1 ratio in acetone at a low temperature to give a mixed-valence trinuclear copper(II, II, III) complex with two mu(3)-oxo bridges, the UV-vis spectrum of which is very close to that of an active oxygen intermediate of lacase. Detailed spectroscopic analysis on the oxygenation reaction at different concentrations has indicated that a bis(mu-oxo)dicopper(III) complex is the precursor for the formation of trinuclear copper complex. In the reaction with 2,4-di-tert-butylphenol (DBP), the trinuclear copper(II, II, III) complex acts as a two-electron oxidant to produce an equimolar amount of the C[bond]C coupling dimer of DBP (3,5,3',5'-tetra-tert-butyl-biphenyl-2,2'-diol) and a bis(mu-hydroxo)dicopper(II) complex. Kinetic analysis has shown that the reaction consists of two distinct steps, where the first step involves a binding of DBP to the trinuclear complex to give a certain intermediate that further reacts with the second molecule of DBP to give another intermediate, from which the final products are released. Steric and/or electronic effects of the 6-methyl group and the N-alkyl substituents of the bidentate ligands on the copper(I)-dioxygen reactivity have been discussed.     

A three-dimensional ferromagnet based on linked copper-azido clusters

Two novel three-dimensional coordination polymers [Cu(6)(N(3))(12)(N-Eten)(2)](n) (1) (N-Eten=N-ethylethylenediamine) and {[Cu(9)(N(3))(18)(1,2-pn)(4)].H(2)O}(n) (2) (1,2-pn=1,2-diaminopropane) have been synthesized by the self-assembly reactions of Cu(NO(3))(2).3H(2)O, NaN(3) and small diamine ligands. Their molecular structures were determined by single-crystal X-ray diffraction. Complex 1 is composed of a neutral 3D coordination framework based on unprecedented hexanuclear copper(ii) clusters which features three types of bridging modes for azide (mu-1,1, mu-1,3 and mu-1,1,3). Complex 2 is a novel 3D coordination polymer featuring octanuclear copper-azido clusters and [Cu(diamine)(2)](2+) units which are linked by azido bridges. Magnetic studies for complex show ferromagnetic ordering at 3.5 K, where the azido bridges mediate ferromagnetic coupling between adjacent Cu(II) ions. The magnetic data for 1 were fitted to a uniform hexanuclear copper model which yielded g=2.21, J=6.26 cm(-1), zJ'=0.39 cm(-1). Complex 2 shows ferromagnetic coupling in the octanuclear unit and antiferromagnetic interaction between neighboring units.     

含樟脑衍生物氰基桥联双金属配合物的合成、结构及磁性质

采用樟脑衍生物为配体，分别合成了氰基桥联Cu(Ⅱ)-Fe(Ⅲ)-Cu(Ⅱ)三核配合物[{Cu(D,L-La)₂}₂Fe(CN)₆](ClO₄) (1)和Mn(Ⅲ)-Fe(Ⅲ)双核配合物[Mn(D,L-Lb)(DMF)(Tp)Fe(CN)₃]·(H₂O)₆ (2)。晶体结构分析表明，化合物1中Cu(Ⅱ)离子处于五配位的配位环境，分别和1个D-La，1个L-La及[Fe(CN)₆]^3-中的1个氰基配位，2个Cu(Ⅱ)离子通过[Fe(CN)₆]^3-桥联。通过分子间氢键作用，化合物1形成二维超分子网络结构。化合物2中，[(Tp)Fe(CN)₃]^-通过其中的1个氰基与[Mn(D，L-Lb)]⁺桥联，其中Mn(Ⅲ)离子为六配位，分别和四齿配体Lb的2个氧原子和2个氮原子、DMF的1个氧原子及[(Tp)Fe(CN)₃]^-中的氰基氮原子配位。磁性研究表明，在化合物1中，Cu(Ⅱ)离子与Fe(Ⅲ)离子之间表现出铁磁相互作用，用哈密顿函数H=-2J(S₁·S₂+S₂·S₃)对其χ_MT-T曲线进行拟合，得到1的朗日因子g为2.190，交换常数J为0.55 cm^-1。     

Syntheses and structures of isoindoline complexes of Zn(II) and Cu(II): an unexpected trinuclear Zn(II) complex

Deprotonation of the tridentate isoindoline ligand 1,3-bis[2-(4-methylpyridyl)imino]-isoindoline, 4'-MeLH, and reaction with hydrated zinc(II) perchlorate produces an unexpected trinuclear Zn(II) complex, [Zn(3)(4'-MeL)(4)](ClO(4))(2).5H(2)O (1), whereas reaction with hydrated copper(II) perchlorate in methanol produces the expected mononuclear product, [Cu(4'-MeL)(H(2)O)(2)]ClO(4) (2). X-ray diffraction shows that the trinuclear Zn(II) complex (1) contains a linear zinc backbone, and the arrangement of ligands about the outer chiral zinc(II) atoms is helical. The two terminal zinc ions exhibit approximate C(2) site symmetry, with tetrahedral coordination by two pyrrole and two pyridyl nitrogen atoms of the potentially tridentate isoindoline ligands. The central zinc ion exhibits approximate tetrahedral symmetry, with coordination by four pyridyl nitrogen atoms of four different isoindoline ligands. Pyridyl-pyrrole intramolecular pi-stacking interactions contribute to the stability of the trinuclear cation. The structure of the mononuclear copper(II) complex cation in 2 is best described as a distorted trigonal bipyramid. The isoindoline anion binds Cu(II) in both axial positions and one of the equatorial positions; water molecules occupy the other two equatorial positions.     

X-Ray Diffraction Study on Manganese(II) Complexes with Thiophene-2-Carboxylate and Furan-3-Carboxylate Ligands

Abstract

Mn(II) cations in the crystals of trisaquobis(μ-thiophen-2-carboxylato-O,O′)(thiophen-2-carboxylato-O)manganese(II) monohydrate are bridged by oxygen atoms donated by bidentate carboxylic groups of two thiophen-2-carboxylate ligands. In addition, each Mn(II) ion is coordinated by an oxygen atom of a monodentate carboxylic group of this ligand and three oxygen atoms of water molecules. The coordination around the Mn(II) cation is octahedral. The bridging of the ligands results in molecular ribbons propagating in the c-direction of the crystal held together by C?H…O hydrogen bonds. The crystal structure of diaquobis(μ-furan-3-carboxylato-O,O′)di(μ-furan-3-carboxylato-O,O)(μ-aqua-O)manganese(II) consists of dinuclear structural units. In each molecule Mn(II) cations are O,O′ bridged by oxygen atoms of bidentate carboxylic groups of two furan-3-carboxylate ligands and have a water located between the Mn cations. The units are O,O′ bridged to Mn(II) ions located in adjacent units by bidentate oxygen atoms, forming molecular ribbons extending in the c-direction. Octahedral coordination around each Mn(II) ion is completed by two water molecules. The octahedra around two adjacent metal ions in the unit share a common apex - the bridging oxygen atom of the water molecule. The ribbons are held together by C?H…O hydrogen bonds between furan ring oxygen atoms and the carbon atoms of adjacent furan rings.     

The first mu3-oxalato-bridged copper complex with tridentate Schiff base ligand N-ethyl-N'-salicylidene-1,2-diaminoethane: synthesis,structure, and magnetic properties

The first mu(3)-oxalato-bridged copper(II) complex, [[Cu(3)(L)(3)(mu(3)-C(2)O(4))][Cu(L)(H(2)O)](ClO(4))(2)] x 0.5(H(2)O) x 0.5(CH(3)OH), where HL = N-ethyl-N'-salicylidene-1,2-diaminoethane, has been synthesized and characterized by variable-temperature magnetic susceptibility measurement. The complex exhibits ferromagnetic coupling between the oxalato-bridged copper atoms and antiferromagnetic coupling between the oxygen-bridged copper atoms.     

Ferromagnetic coupling in trinuclear, partial cubane Cu(II) complexes with a micro(3)-OH core: magnetostructural correlations

Three new trinuclear copper(II) complexes, [(CuL(1))(3)(micro(3)-OH)][ClO(4)](2).3 H(2)O (1), [(CuL(2))(3)(micro(3)-OH)][ClO(4)](2).H(2)O (2), and [(CuL(3))(3)(micro(3)-OH)][ClO(4)](2).7 H(2)O (3) have been synthesized from the three tridentate Schiff bases HL(1), HL(2), and HL(3) (HL(1)=6- aminomethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one, HL(2)=6-aminoethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one, and HL(3)=6-aminodimethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one). They have been characterized by X-ray crystallography and IR and UV spectroscopy, and their magnetic properties have been investigated. All the compounds contain a partial cubane [Cu(3)O(4)] core consisting of the trinuclear unit [(CuL)(3)(micro(3)-OH)](2+), perchlorate ions, and water molecules. In each of the complexes, the copper atoms are five-coordinate with a distorted square-pyramidal geometry except complex 1, in which one of the Cu(II) of the trinuclear unit is weakly coordinated to one of the perchlorate ions. Magnetic measurements performed in SQUID MPMS-XL7 using polycrystalline samples at an applied field of 2 kOe indicate a global intramolecular ferromagnetic coupling. Magnetostructural correlations have been calculated on the basis of theoretical models without symmetry restriction. Continuous shape measurements are an appropriate tool for establishing the degree of distortion of the Cu(II) from square-planar geometry. Structural, theoretical, and experimental magnetic data indicate that the higher the degree of distortion, the greater the ferromagnetic coupling.     

Helical-chain copper(II) complexes and a cyclic tetranuclear copper(II) complex with single syn-anti carboxylate bridges and ferromagnetic exchange interactions

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.     

Crystal structure of 4,4-bipyridine-containing complexes of copper(II) nitrate with 1-[(2-Hydroxyethylimino)methyl]naphthalen-2-ol and 2-[(2-hydroxyethylimino)methyl]phenol

The crystal structures of (μ-4,4-bipyridine)-di(nitrato-1-[(2-hydroxyethylimino)methyl]naphthalen-2-olocopper (I) and catena-di(μ-4,4’-bipyridine)di(μ-4,4’-bipyridine)-di(nitrato-2-[2-(hydroxyethylimino) methyl]phenolocopper)diaquacopper(II) nitrate (II) were determined. In the crystal of I, each of the two copper atoms coordinates a singly deprotonated tridentate azomethine molecule, a nitrate ion, and bipyridine, which functions as a bridge between the central atoms. The copper coordination polyhedron is a slightly distorted tetragonal pyramid with the base formed by the imine and bipyridine nitrogen atoms and the phenol and alcohol oxygen atoms. The axial site in the pyramid is occupied by the oxygen atom of the monodentate nitrate groups. In the trinuclear structure II with C₂ crystal chemical symmetry, the terminal coordination unit is composed through copper coordination of monodeprotonated 2-[2-(hydroxyethylimino)methyl]phenol, bipyridine, and the nitrate anion. In the crystal, the trinuclear molecules form infinite ribbons along the z axis in which the pyridine molecules perform the bridging function. The central copper atom has an octahedral configuration formed by the nitrogen atoms of four 4,4’-bipyridine molecules and oxygen of two water molecules.     

π-π Stacking and ferromagnetic coupling mechanism on a binuclear Cu(II) complex

The ferromagnetic couplings were observed in an unpublished crystal that consists of binuclear copper(II) complexes, namely, [Cu(2)(μ(1,3)-SCN)(2)(PhenOH)(OCH(3))(2)(HOCH(3))(2)] (PhenOH = 2-hydroxy-1,10-phenanthroline), and in the binuclear complex Cu(ii) ion assumes a distorted octahedral geometry and thiocyanate anion functions as a μ(1,3)-SCN(-) equatorial-axial (EA) bridging ligand. The analysis for the crystal structure indicates that there are three types of magnetic coupling pathways, in which two pathways involve π-π stacking between the adjacent complexes and the third one is the μ(1,3)-SCN(-) bridged pathway. The fitting for the data of the variable-temperature magnetic susceptibilities shows that there is a ferromagnetic coupling between adjacent Cu(II) ions with J = 50.02 cm(-1). Theoretical calculations reveal that the two types of π-π stacking resulted in ferromagnetic couplings with J = 4.16 cm(-1) and J = 2.75 cm(-1), respectively, and the bridged thiocyanate anions pathway led to a weaker ferromagnetic interaction with J = 0.88 cm(-1). The theoretical calculations also indicate that the ferromagnetic coupling sign from the two types of π-π stacking does not accord with McConnell I spin-polarization mechanism. The analysis for the Wiberg bond indexes that originate from the π-π stacking atoms indicates that the Wiberg bond indexes are relevant to the associated magnetic coupling magnitude and the Wiberg bond index is one of the key factors that dominates the associated magnetic coupling magnitude.     

Influence of the anions on the structure and magnetic properties of a series of bis(μ-diphenoxo)-bridged linear trinuclear copper(II) complexes: an experimental and theoretical study

The reaction of H(2)L (N,N'-dimethyl-N,N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-ethylenediamine) with different copper salts, in methanol and using a H(2)L/Cu = 2 : 3 molar ratio, led to four new bis(μ-diphenoxo)-bridged Cu(3) complexes of general formula [{Cu(S)(μ-L)}(2)Cu(H(2)O)(2n)]X(2) (S = CH(3)OH, n = 1 and X = BF(4)(-) for (1) or ClO(4)(-) for (2); S = Br(3)(-) anion and n = 1 without any X species for (3); S = H(2)O, n = 0 and X = NO(3)(-) for (4)). The use in the same reaction conditions of 4,4'-bipyridine (4,4'-bipy) as connector led to the chain complex [{Cu(μ-4,4'-bipy)(0.5)(μ-L)}(2)Cu(H(2)O)(2n)](ClO(4))(2)·17H(2)O (5). The structure of the centrosymmetric trinuclear unit in (1)-(5) consists of two [Cu(L)] fragments connected through two phenoxo bridging groups to the central copper(II) ion giving rise to a linear arrangement of the copper(II) ions, where the ligand acts in a compartmental form wrapping the metal centre with a N(2)O(2) tetradentate bridging mode. The coordination polyhedron of the symmetrically related external copper atoms exhibits a geometry very close to square-pyramidal, whereas the central copper(II) atom displays either a tetragonally elongated octahedral geometry or a square-planar geometry. Owing to the steric hindrance promoted by the methoxy groups at the phenyl rings, the whole Cu(3) structure is not planar but folded along the line connecting the phenoxo bridging oxygen atoms of the same ligand. Temperature dependence of the magnetic susceptibility of complexes (1)-(5) was measured, showing strong antiferromagnetic interactions between the central and external atoms through the bis(μ-phenoxo) groups. DFT calculations were also performed (a) to support the experimental values of the coupling constant (J(1)) between the nearest-neighbouring copper atoms, (b) to determine the magnitude of the interactions between next-nearest copper(II) atoms (J(2)) and (c) to study magneto-structural correlations for this kind of bis(μ-diphenoxo) trinuclear copper(II) complex.     

Covalent linkage of the type-2 and type-3 structural mimics to model the active site structure of multicopper oxidases: synthesis and magneto- structural properties of two angular trinuclear copper(II) complexes

Two new angular trinuclear copper(II) complexes of formulation [Cu(3)(HL)LL'](ClO(4)), where L' is imidazole (Him, 1) or 1-methylimidazole (1-MeIm, 2) and H(3)L is a Schiff base obtained from the condensation of salicylaldehyde and 1,3-diaminopropan-2-ol (2:1 mole ratio), are prepared from a reaction of [Cu(2)L(mu-Br)] and [Cu(HL)] in the presence of L' and isolated as perchlorate salts. The crystal structures of 1 and 2 consist of a trinuclear copper(II) unit formed by the covalent linkage of monomeric type-2 mimic and dimeric type-3 mimic precursor complexes to give an angular arrangement of the metal atoms in the core which is a model for the active site structure of blue multicopper oxidases. In 1 and 2, the coordination geometry of two terminal copper atoms is distorted square-planar. The central copper has a distorted square-pyramidal (4 + 1) geometry. The mean Cu...Cu distance is approximately 3.3 A. The complex has a diphenoxo-bridged dicopper(II) unit with the phenoxo oxygen atoms showing a planar geometry. In addition, the complex has an endogenous alkoxo-bridged dicopper(II) unit showing a pyramidal geometry for the oxygen atom. The 1:1 electrolytic complexes show a d-d band at 607 nm. Cyclic voltammetry of the complexes in MeCN containing 0.1 M TBAP using a glassy carbon working electrode displays a Cu(3)(II)/Cu(2)(II)Cu(I) couple near -1.0 V (vs SCE). The variable temperature magnetic susceptibility measurements in the range 300-18 K show antiferromagnetic coupling in the complexes giving magnetic moments of approximately 3.0 mu(B) at 300 K and approximately 2.1 mu(B) at 18 K for the tricopper(II) unit. The experimental susceptibility data are theoretically fitted using a model with Heisenberg spin-(1)/(2) Hamiltonian for a trimer of spin-(1)/(2) copper(II) ions having two exchange parameters involving the alkoxo-bridged dicopper(II) (J1) and the diphenoxo-bridged dicopper(II) (J2) units, giving J1 and J2 values of -82.7, -73 cm(-1) for 1 and -98.3, -46.1 cm(-1) for 2, respectively. The structural features indicate a higher magnitude of anitiferromagnetic coupling in the alkoxo-bridged unit based on the greater value of the Cu-O-Cu angle in comparison to the diphenoxo-bridged unit. The core structures of 1 and 2 compare well with the first generation model complexes for the active site structure of multicopper oxidases in the oxidized form. The crystal structure of 1 exhibits a lamellar structure with a gap of approximately 7 A containing water molecules in the interlamellar space. Complex 2 forms a hexanuclear species due to intermolecular hydrogen bonding interactions involving two trimeric units. The crystal packing diagram of 2 displays formation of a three-dimensional framework with cavities containing the perchlorate anions.     

Magnetic properties and molecular structures of binuclear (2-pyrazinecarboxylate)-bridged complexes containing Re(IV) and M(II) (M = Co, Ni)

Three novel Re(iv) compounds, the mononuclear complex Bu(4)N[ReBr(5)(Hpyzc)] (1) and the heterobimetallic complexes [ReBr(5)(mu-pyzc)M(dmphen)(2)].2CH(3)CN [M = Co (2), Ni (3)] (Hpyzc = 2-pyrazinecarboxylic acid, dmphen = 2,9-dimethyl-1,10-phenanthroline), have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. The structure of 1 consists of [ReBr(5)(Hpyzc)](-) complex anions and tetrabutylammonium cations, Bu(4)N(+). The Re(iv) is surrounded by five bromide anions and a N-donor Hpyzc monodentate ligand, in a distorted octahedral environment. The structures of 2 and 3 consist of dinuclear units [ReBr(5)(mu-pyzc)M(dmphen)(2)], with the metal ions linked by a pyzc bridge ligand, being bidentate toward M(II) and monodentate toward Re(IV). The environment of Re(IV) is the same as in 1, whereas M(II) is six-coordinate, being surrounded by four nitrogen atoms of two bidentate dmphen ligands and one oxygen atom and one nitrogen atom of the pyzc anion. The magnetic properties of 1-3 were investigated in the temperature range 2.0-300 K. 1 shows the expected magnetic behavior for a mononuclear Re(IV) complex with a weak intermolecular antiferromagnetic coupling at low temperatures. The bimetallic complexes exhibit an intramolecular ferromagnetic coupling between Re(IV) and the M(II) ion (Co, Ni).