A novel mixed-coordination cobalt(III)complex:synthesis and structure of Co(III)(mpp)(Hmpp)(n-Bu3P)2

Complex Co(III)(mpp)(Hmpp) (n-Bu₃P)₂ (1. H₂mpp= 2-mercapto-3-pyridinol) was obtained from the reaction of CoCl₂ with H₂mpp, n·Bu₃P and Na metal in EtOH. The Co atom in a distorted octahedral geometry is coordinated with donor atoms N, O, P and S. The two H₂mpp ligands form two different chelate rings with the Co(III) ion: one 5-membered and the other one 4-membered, while the two n-Bu₃P ligands are in the axial positions with the angle P(1)-Co-P(2) of 176.1:     

Synthesis and characterization of tetrahedrally and octahedrally coordinated mixed-valence Co(II)/Co(III) complex with thiosemicarbazone-based ligand

Synthesis, characterization, and X-ray crystal structure for a mixed-valence binuclear Co(II)/Co(III) complex with the dianionic dithiolate form of a pentadentate ligand 2,6-diacetylpyridinebis(thiosemicarbazone) are reported. A new synthetic methodology has been employed replacing usual cobalt(II) salts by [Co(NH₃)₅Cl]Cl₂ as a precursor. The coordination geometry of cobalt(II), CoN₂S₂, was found to be distorted tetrahedral, whereas the cobalt(III) coordination sphere, CoN₄S₂, is slightly distorted octahedral. The magnetic behavior and molar conductivity of the complex are in agreement with the mixed-valence state.     

Dinuclear Co(II)Co(III) mixed-valence and Co(III)Co(III) complexes with N- and O-donor ligands: characterization and water oxidation studies

The tridentate ligand N-methyl-N,N-bis(2-pyridylmethyl)amine (L) has been employed to synthesize a dinuclear Co(II)Co(III) mixed-valence complex containing μ-methoxo and μ-carboxylato bridging ligands, [LCo(II)(μ-carboxylato)bis(μ-methoxo)Co(III)L](ClO(4))(2). In this complex, the two pseudo-octahedral Co centers have an identical ligand environment, yet the average Co-N and Co-O bond distances at the two Co ions differ significantly. Electrochemical, spectroscopic, and magnetic susceptibility measurements confirm that it belongs to a localized Class II mixed-valence system, despite the presence of a short Co···Co distance of 3.021 ?. Oxidation of this Co(II)Co(III) complex leads to formation of the corresponding Co(III)Co(III) complex that was characterized structurally and spectroscopically. In addition, dinuclear and trinuclear μ-hydroxo Co(III) complexes have been obtained in the presence of phosphate anions and absence of methanol, respectively, suggesting that an additional bridging ligand is needed to stabilize the Co(III)bis(μ-hydroxo)Co(III) fragment. Moreover, the ability of the mixed-valence Co(II)Co(III) complex and the three related Co(III) complexes to electrocatalytically oxidize water was also investigated. The observed limited water oxidation catalytic ability for these systems suggests that a multinuclear Co cluster and/or presence of O-rich ligands may be needed for the generation of efficient molecular Co-based water oxidation catalysts.     

Photomagnetic effect in a cyanide-bridged mixed-valence {Fe(II)2Fe(III)2} molecular square

The self-assembly of [Fe(III)(Tp)(CN)(3)](-) and [Fe(II)(bik)(2)(S)(2)](2+) affords the cyanide-bridged mixed valence {Fe(III)(2)Fe(II)(2)}(2+) molecular square, which exhibits a photomagnetic effect under laser light irradiation at low temperature and also shows thermal spin-state conversion near ambient temperature.     

Assembly of a two-dimensional oxalate-bridged heterometallic Co(II)(3)Cr(III)(2) coordination polymer

Reaction of CoCl(2).4H(2)O with Ag(3)[Cr(ox)(3)] (3 : 2 mol/mol) in methanol gives rise to an oxalate-bridged complex [Co(MeOH)(2)](3)[Cr(ox)(3)](2).6MeOH that consists of a rare cloverleaf-like layered structure (12,3-net). Ferromagnetic coupling is operative between the adjacent metal ions through the oxalate bridges.     

Formation of unusual molecular rectangles and squares containing low spin and high spin Co(II) and Fe(II) centers

The ditopic carbohydrazide and thiocarbohydrazide based ligands H?L1 and H?L2 react with Co(II)(OAc)? to produce the homoleptic Co(II) molecular rectangles 1 and 2, containing either a mixture of high spin and low spin Co(II) sites or exclusively low spin Co(II) centers, respectively, with two mono-deprotonated ligands in a syn-conformation, and the other two doubly-deprotonated ligands in an anti-arrangement. The Co(II) centers are bridged by μ-O/S and μ-N-N groups, respectively. Magnetic susceptibility measurements indicate weak antiferromagnetic coupling between metal centers in 1 and 2, with room temperature magnetic moments of 6.6 and 3.4 μ(B), respectively, in good agreement with two S = 3/2 and two S = 1/2 centers for 1 and four S = 1/2 centers for 2. Reaction of H?L1 and H?L2 with Fe(II)(CF?SO?)? in the presence of a base leads to the formation of μ-O/S bridged homoleptic molecular squares 3 and 4, with the Fe(II) centers in high spin and low spin configurations, respectively at room temperature, as indicated from X-ray structural data and magnetic susceptibility measurements. However, in 3 one Fe(II) site undergoes spin crossover to a low spin state at about 150 K, while 4 stays diamagnetic in the full 2-300 K temperature range. Electrochemistry of 4 showed four distinct reversible red-ox waves associated with step-by-step one electron processes in the molecular square [-0.643 (ΔE(p) = 81 mV), -0.278 (ΔE(p) = 70 mV), +0.565 (ΔE(p) = 65 mV), ~1.1 V], associated with the Fe(II)/Fe(III) red-ox couples.     

Spectroelectrochemical studies on mixed-valence states in a cyanide-bridged molecular square, [Ru(II)(2)Fe(II)(2)(mu-CN)(4)(bpy)(8)](PF6)(4).CHCl(3).H(2)O

A cyanide-bridged molecular square of [Ru(II) (2)Fe(II) (2)(mu-CN)(4)(bpy)(8)](PF(6))(4).CHCl(3).H(2)O, abbreviated as [Ru(II) (2)Fe(II) (2)](PF(6))(4), has been synthesised and electrochemically generated mixed-valence states have been studied by spectroelectrochemical methods. The complex cation of [Ru(II) (2)Fe(II) (2)](4+) is nearly a square and is composed of alternate Ru(II) and Fe(II) ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru(II) (2)Fe(II) (2)](PF(6))(4) in acetonitrile showed four quasireversible waves at 0.69, 0.94, 1.42 and 1.70 V (vs. SSCE), which correspond to the four one-electron redox processes of [Ru(II) (2)Fe(II) (2)](4+) right arrow over left arrow [Ru(II) (2)Fe(II)Fe(III)] (5+) right arrow over left arrow [Ru(II) (2)Fe(III) (2)](6+) right arrow over left arrow [Ru(II)Ru(III)Fe(III) (2)](7+) right arrow over left arrow [Ru(III) (2)Fe(III) (2)](8+). Electrochemically generated [Ru(II) (2)Fe(II)Fe(III)](5+) and [Ru(II) (2)Fe(III) (2)](6+) showed new absorption bands at 2350 nm (epsilon =5500 M(-1) cm(-1)) and 1560 nm (epsilon =10 500 M(-1) cm(-1)), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fe(II) to Fe(III) and from Ru(II) to Fe(III) ions, respectively. The electronic interaction matrix elements (H(AB)) and the degrees of electronic delocalisation (alpha(2)) were estimated to be 1090 cm(-1) and 0.065 for the [Ru(II) (2)Fe(II)Fe(III) (2)](5+) state and 1990 cm(-1) and 0.065 for the [Ru(II) (2)Fe(III) (2)](6+) states.     

Ground- and excited-state properties of the mixed-valence complex [(NH3)5Ru(III)NCRu(II)(CN)5]-

A computational study of the ground- and excited-state properties of the mixed-valence complex [(NH 3) 5Ru (III)NCRu (II)(CN) 5] (-) is presented. Employing DFT and TDDFT calculations for the complex in the gas phase and in aqueous solution, we investigate the vibrational and electronic structure of the complex in the electronic ground state as well as the character of the electronically excited states. The relevance of the various excited states for the intervalence metal-metal charge-transfer process in the complex is analyzed based on the change of charge density, spin density, and dipole moment upon photoexcitation as well as by a Mulliken-Hush analysis. Furthermore, those intramolecular modes, which are important for the charge-transfer process, are identified and characterized.     

Structural and magnetic investigations of the mixed-valence Fe(II,III) two-dimensional layer complex, [Fe2(II) Fe2(III)(HCOO)10(C6H7N)6]n.

The structure of the complex, [Fe2(II)Fe2(III)(HCOO)10(C6H7N6)n, (1) exhibits a neutral two-dimensional layer network of alternating iron(II) and iron(III) ions, bridged equatorially by formate groups. All iron atoms are octahedrally coordinated, with iron(III) coordinating axially to one gamma-picoline and one formate group, while the iron(II) centers interact axially with two gamma-picoline groups, above and below the layer plane. The complex crystallizes in the triclinic space group P1 at all studied temperatures [at 120 K, the cell dimensions are: a = 10.228(1), b = 12.071(1), c = 12.072(1) A, alpha = 89.801(2), beta = 71.149(2), gamma = 73.371(2) degrees]. An intralayer antiferromagnetic exchange interaction of J = -2.8 cm(-1) between iron(II) and iron(III) was observed in the magnetic studies. Decreasing the temperature to close to 20 K causes a magnetic-ordering phenomenon to occur and a low-temperature phase with a long-range antiferromagnetic spin orientation appears. The magnetic phase transition was confirmed by M?ssbauer spectroscopic studies at temperatures above and below the critical temperature. Structural information of 1 from synchrotron X-ray diffraction data collected at room temperature and 16 K suggests that the antiferromagnetic ordering is caused by an enhanced pi-pi interaction between chi-picoline groups from adjacent layers.     

New rhodium(II)-rhodium(III) dinuclear complexes with 2-aminopyridine bridges

Summary The syntheses of the complexes [Rh₂(ap)₄X] (ap = the heterocyclic anion of 2-aminopyridine; X = Cl or Br) are described. The complexes have been characterized on the basis of elemental analysis, i.r., e.s.r. and electronic absorption spectra, and magnetic susceptibility measurements. The 2-aminopyridine anion behaves as bridging ligand, coordinatingvia the pyridine and amine nitrogen atoms in a way analogous to that in the dinuclear rhodium(II) carboxylates.     

Binuclear platinum(II) complex with thiocarbamide bridges

A binuclear complex, diamminedithiocarbamide-μ-diamminedithiocarbamideplatinum(II) nitrate, was prepared by the reaction of tetrathiocarbamideplatinum(II) and diaquadiammineplatinum(II) nitrates. The composition and structure of the prepared complex were determined by elemental analysis, conductometry, and cryoscopy.     

Reaction of superoxo Co(III) complex with quinones formation of a semiquinone Co(III) complex

The superoxo complex [Co(CN)₅O₂]^3- was found to act as a reducing agent towards quinones. One-electron reduction took place with $\text{o}$-quinones whereas two-electrons reduction with $\text{p}$-quinones. 3,5-Di-$\text{t}$-butyl-$\text{o}$-benzoquinone gave the corresponding semiquinone Co(III) complex quantitatively.     

Dinuclear [Co(II)(NCMe)5Co(II)(NCS)4] possessing octahedral and tetrahedral Co(II) sites

The structural and magnetic properties of dinuclear [Co(II)(NCMe)(5)Co(II)(NCS)(4)]·MeCN have been investigated. The structure consists of an octahedral Co(II)(NCMe)(5) center connected to a tetrahedral Co(II)(NCS)(4) center bridged by a μ(1,3)-NCS(-) ligand. The bridging NCS(-) weakly couples the pair of S = (3)/(2) Co(II) spin sites, as evidenced by the magnetic data being best fit by the Curie-Weiss expression with θ = -15.5 K.     

Slow magnetic relaxation in a mixed-valence Mn(II/III) Complex: [MnII2(bispicen)2(mu 3-Cl)2Mn(III)(Cl4Cat)2Mn(III)(Cl4Cat)2(H2O)2] infinity

A layered mixed-valence manganese complex, [Mn(II)(2)(bispicen)(2)(mu(3)-Cl)(2)Mn(III)(Cl(4)Cat)(2)Mn(III)(Cl(4)Cat)(2)(H(2)O)(2)](infinity), is synthesized and characterized structurally. It displays a slow magnetic relaxation and hysteresis effect.     

A novel hexanuclear mixed oxidation state Cu(II)(4)Cu(I)(2) cluster complex exhibiting weak ferromagnetic exchange

The complex [(PAH)(4)Cu(II)(4)Cu(I)(2)Br(10)] (1) (PAH = picolinamide hydrazone) containing a Cu(II)(4)Cu(I)(2) hexanuclear cluster, with two well-separated Cu(II)(2) dinuclear centers, results from a redox reaction involving a hydrolytically unstable ligand, salicilyl picolinamide hydrazone, and CuBr(2) in aqueous acetonitrile. The Cu(II) centers are axially bridged via long bromine contacts, leading to ferromagnetic exchange (2J = 4.04 cm(-)(1)). Density functional calculations have been carried out, giving a comparable singlet-triplet splitting energy. 1 crystallizes in the triclinic system, space group Ponemacr;, with a = 9.253(3) A, b = 18.159(3) A, c = 7.199(5) A, alpha = 91.31(3) degrees, beta = 107.35(4) degrees, gamma = 104.22(2) degrees, and Z = 2.     

一个新型分子铁磁体: 氰根桥联的铜(II)-铁(III)配合物

合成和表征了一个新的分子磁体,氰根桥联的杂化型异金属配合物[Cu(en)]~3[Fe(CN)~6]~2.3H~O(en为乙二胺)。变温磁化率、零场冷却磁化强度(ZFCM)、场冷却磁化强度(FCM)和磁滞回线测量表明铜铁离子间存在着铁磁性相互作用,其铁磁相变温度为T~c=11.0K,矫顽力为20×10^-^4T,剩磁为1.70×10^-^1cm^3.mol^-^1.T。该化合物为杂化型铜(II)-铁(III)普鲁士蓝类中具有铁磁相变温度的首例。     

Synthesis and crystal structure of ionic multicomponent complex: ([Cr(I)(PhH)(2)].+))(2)[Co(II)TPP(C(60)(CN)(2))]-[C(60)(CN)(2)](.-).3(o-C(6)H(4)Cl(2)) containing C(60)(CN)(2).- radical anion and sigma-bonded diamagnetic Co(II)TPP(C(60)(CN)(2)) -anion

The ionic multicomponent complex complex: ([Cr(I)(PhH)(2)].+))(2)[Co(II)TPP(C(60)(CN)(2))]-[C(60)(CN)(2)](.-).3(o-C(6)H(4)Cl(2)) (Co(II)TPP: cobalt (II) tetraphenylporphyrin; Cr(PhH)(2): bis(benzene)chromium; o-C(6)H(4)Cl(2): o-dichlorobenzene) containing CoTPP(C(60)(CN)(2)- anion and C(60)(CN)(2).- radical anion was obtained. The complex has the cage structure with channels, which accommodate Cr(I)(PhH)(2)(.+) and o-C(6)H(4)Cl(2) molecules. For the first time the sigma-bonding of Co(II)TPP to the fullerene radical anion with the essentially shortened Co.C(C(60)(CN)(2)) contact of 2.282 A is observed. The sigma-bonding results in the diamagnetism of Co(II)TPP(C(60)(CN)(2))(-) anion. The nonbonded C(60)(CN)(2)(.-) radical anion retains both the C(2)(v)symmetry and the shape of the molecule. The length of the C(triple bond)N bonds is 1.141 and 1.152 A.     

Synthesis and magnetic properties of 3-D [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr,Fe, Co)

Three-dimensional network structures of [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr, Fe, Co) composition have been formed and their magnetic properties characterized. [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr, Fe, Co) have nu(CN) IR absorptions at 2138, 2116, and 2125 cm(-1) and have body-centered unit cells (a = 13.34, 13.30, and 13.10 A, respectively) with -M-Ctbd1;N-Ru=Ru-Ntbd1;C-M- linkages along all three Cartesian axes. [Ru(II/III)(2)(O(2)CMe)(4)](3)[Cr(III)(CN)(6)] magnetically orders as a ferrimagnet (T(c) = 33 K) and has an unusual constricted hysteresis loop.