Volodymyr N. Kokozay

Heterometallic CoIII4FeIII2 Schiff Base Complex: Structure, Electron Paramagnetic Resonance, and Alkane Oxidation Catalytic Activity

The heterometallic complex [Co(4)Fe(2)OSae(8)]·4DMF·H(2)O (1) was synthesized by one-pot reaction of cobalt powder with iron chloride in a dimethylformamide solution of salicylidene-2-ethanolamine (H(2)Sae) and characterized by single crystal X-ray diffraction analysis, magnetic measurements, high frequency electron paramagnetic resonance (HF-EPR), and Mössbauer spectroscopies. The exchange coupling in the Fe(III)-Fe(III) pair is of antiferromagnetic behavior with J/hc = -190 cm(-1). The HF-EPR spectra reveal an unusual pattern with a hardly detectable triplet signal of the Fe(III) dimer. The magnitude of D (ca. 13.9 cm(-1)) was found to be much larger than in related dimers. The catalytic investigations disclosed an outstanding activity of 1 toward oxidation of cycloalkanes with hydrogen peroxide, under mild conditions. The most efficient system showed a turnover number (TON) of 3.57 × 10(3) with the concomitant overall yield of 26% for cyclohexane, and 2.28 × 10(3)/46%, respectively, for cyclooctane. A remarkable turnover frequency (TOF) of 1.12 × 10(4) h(-1) (the highest initial rate W(0) = 3.5 × 10(-4) M s(-1)) was achieved in oxidation of cyclohexane. Kinetic experiments and selectivity parameters led to the conclusion that hydroxyl radicals are active (attacking C-H bonds) species. Kinetic and electrospray ionization mass spectrometry (ESI-MS) data allowed us to assume that the trinuclear heterometallic particle [Co(2)Fe(Sae)(4)](+), originated from 1 in solution, could be responsible for efficient generation of hydroxyl radicals from hydrogen peroxide.

Heterometallic Cu/Co and Cu/Co/Zn complexes bearing rare asymmetric tetranuclear cores: synthesis, structures, and magnetic and catalytic properties toward the peroxidative oxidation of cycloalkanes.

The three novel heterometallic complexes [CuCo(III)Co(II)(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.55)(H(2)O)(0.45)](H(2)O)(0.45) (1), [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.74)(H(2)O)(0.26)](H(2)O)(0.26) (2), and [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(DMF)] (3) have been prepared using a one-pot reaction of copper powder with cobalt chloride (1) and zinc nitrate (2, 3) in a methanol (1, 2) or dimethylformamide (3) solution of N-methyldiethanolamine. A search of the Cambridge Structural Database shows that the tetranuclear asymmetric cores M(4)(μ(3)-X)(μ-X)(5) of 1-3 represent an extremely rare case of M(4)X(6) arrays. The magnetic investigations of 1 disclose antiferromagnetic coupling in a Co(II)-Cu(II)-Co(II) exchange fragment with J(Co-Cu)/hc = -4.76 cm(-1), J(Co-Co)/hc = -2.76 cm(-1), and D(Co)/hc = +34.3 cm(-1). Compounds 1-3 act as precursors for the mild peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone with overall yields up to 23%. The synthetic and structural features as well as the thermogravimetric behavior and electrospray ionization mass spectrometry data are discussed.

Self-assembly of the unique heterotrimetallic Cu/Co/M complexes possessing triangular antiferromagnetic {Cu2CoPb}2 and linear ferromagnetic {Cu2CoCd2} cores

Two novel heterotrimetallic octa-[Cu2CoPbCl4(L)4]2 (1) and pentanuclear [Cu2CoCd2Cl6(L)4(HOMe)2] (2) complexes have been prepared in one-pot reactions of zerovalent copper with metal chlorides in a methanol (for 1) or acetonitrile (for 2) solution of 2-(dimethylamino)ethanol (HL) in open air. The crystal structures of both compounds consist of discrete centrosymmetric heterotrimetallic molecules revealing triangular (1) and unique consecutive (2) arrangements of magnetic CuII(2)CoII cores. The complex 1 can be viewed as a dimer made up of tetranuclear Cu2CoPbCl4(L)4 units linked through the two micro(2)-Cl atoms. The molecular structure of 2 is a pentanuclear assembly containing the previously unknown Cu(micro-O)(2)Co(micro-O)(2)Cu core. The magnetic studies of 1 revealed an antiferromagnetic coupling (J(CoCu) = 37 cm(-1) and J(CuCu) = 87 cm(-1)) while 2 exhibits a weak ferromagnetic behavior (J(CoCu) = -3.2 cm(-1) and J(CuCu) = -14.2 cm(-1)). The correlations between magnetic behaviour and structures as well as synthetic features are also discussed.

Mixed-metal copper(II) and lead(II) complexes due to μ- and μ3-bridging alkoxo groups from 2-dimethylaminoethanol. Chains and layers in [CuPbCl2(Me2NCH2CH2O)2]n · n/2H2O and [CuPbI2(Me2NCH2CH2O)2]2

Abstract A number of mixed-metal complexes of CuII and PbII containing 2-dimethylaminoethanol (HL) is reported. The compounds were identified and characterized by chemical analyses and IR investigations. The crystal structure of [CuPbCl2L2]n·n/2H2O and [CuPbI2L2]2 were determined by X-ray crystallographic analysis. The metal complex motif of both compounds is a centrosymmetric tetranuclear dimer with square pyramidal coordination geometry around the Cu atom and highly distorted octahedral coordination to the Pb atom. The Cu and Pb atoms are bridged by alkoxide oxygens from L to form a Pb2Cu2O4 core which displays a flattened chair conformation. In the chloride complex tetranuclear units are connected successively via μ-chloro bridging between two Pb sites forming polymeric chains. In the iodide complex the I atom bonded to the Pb atom bridges to Cu and Pb atoms of adjacent complex molecules to produce a layer parallel to the bc plane.

Direct synthesis of an heterometallic {MnII3CrIII4} wheel by decomposition of Reineckes salt

A new heterometallic Mn/Cr molecular wheel complex has been synthesized using zerovalent manganese, Reineckes salt, ammonium thiocyanate and triethanolamine (H(3)tea) as starting materials. The compound [Mn(3)Cr(4)(NCS)(6)(Htea)(6)] (1) has been characterized in terms of its electrochemical, IR and EPR spectroscopic as well as its magnetic properties. The magnetic susceptibility and magnetization data were treated simultaneously during the optimization routine and resulted in J(Mn-Cr) = +0.43 cm(-1), J(Cr-Cr) = -4.75 cm(-1), J(Mn-Mn) = +1.78 cm(-1), g(eff) = 1.878 with the ground state S = 15/2.

Direct reaction of zerovalent copper with lead salts and an amino alcohol to form a heterotetranuclear mixed-anion polymeric complex

A direct reaction of zerovalent copper with PbCl2, Pb(SCN)2 and 2-dimethylaminoethanol (HL) in DMSO affords the heterotetranuclear mixed-anion polymeric complex [Cu2Pb2Cl3(NCS)L4]n, the first example of a compound containing N-bonded thiocyanate-bridging heterometal atoms.

Tris(2,2′-bipyridine-κ2N,N′)cobalt(III) tris­(oxalato-κ2O1,O2)ferrate(III) mono­hydrate

The title compound, [Co(C10H8N2)3][Fe(C2O4)3]·H2O, consists of two discrete tris(chelate) metal ions (CoIIIN6 and FeIIIO6 chromophores) and a water molecule. The structure is highly symmetrical; the CoIII and FeIII ions occupy positions with site symmetry 3.2. The coordination polyhedra of the metal atoms have a nearly octahedral geometry with noticeable trigonal distortions. The Co—N and Fe—O bond lengths are equal by symmetry, viz. 1.981 (2) and 1.998 (4) Å, respectively. The cations and anions are arranged alternately along their threefold rotation axes parallel to [001], forming chains that are packed in a hexagonal manner. The water molecules occupy voids between the chains. The crystal under investigation was an inversion twin.

Novel polynuclear CuII/CoII complexes constructed from one and two Cu2Co triangles with antiferromagnetic exchange coupling

The reaction of acetonitrile solutions of CoX2·2H2O (X = NCS, I, Br) and 2-dimethylaminoethanol (HL) with copper powder in air leads to the formation of new tri- and hexa-nuclear complexes [Cu2Co(NCS)3L3]·½CH3CN (1), [Cu2Co(μ3-OH)I2L3]2·4CH3CN (2) and [Cu2Co(μ3-OH)Br2L3]2·2CH3CN (3). X-Ray crystallographic analysis of 1 reveals a symmetrical triangular core with one Co and two Cu atoms. The amino alkoxo- and SNCS-bridges between metal centres result in copper–copper and copper–cobalt separations of 3.413(2) and 3.103(2) A, respectively. Additional intermolecular association occurs through the NCS groups bridging Co and Cu centres of adjacent complex molecules to give chains. In the solid-state structures of 2 and 3 two symmetry-related Cu2Co units are linked by amino alkoxo bridges to form a hexanuclear molecule with intermetallic distances ranging from 3.102(2)–3.260(2) (Cu⋯Co) to 3.287(3)–3.931(2) A (Cu⋯Cu). The triangular planes formed by two copper and one cobalt atoms bridged by oxygen atoms from L groups are capped by a μ3-hydroxide not found in the core of 1. The hexanuclear units show no significant intermolecular contacts in the solid state. Variable-temperature magnetic susceptibility studies performed on 1 and 2 in the temperature range 5–280 K gave satisfactory fits to the observed susceptibility data by assuming isotropic magnetic exchange interactions and using the appropriate spin Hamiltonians considering 1 as a trinuclear entity and 2 as a combination of two trinuclear entities. An antiferromagnetic spin exchange operates in the Cu2Co units of both complexes [JCuCu = 40.1(4) (1), 48.7(9) (2); JCuCo = 141(2) (1), 86.2(1.3) cm−1 (2)] while a weak ferromagnetic coupling is active between Cu and Co ions from different trinuclear entities in 2 (JCuCo′ = −8.0(4) cm−1).

Spectroscopic and Magnetostructural Evidence for the Formation of [Cu0.5Co0.5(H2Tea)X] Mixed-Crystal Compounds from Zerovalent Cu and Co Salts in the Presence of Triethanolamine (H3Tea -Triethanolamine; X = SCN, Cl)

Mixed crystals [Cu0.5Co0.5(H2Tea)(SCN)] (1), [Cu0.5Co0.5(H2Tea)Cl] (2) (H3Tea = triethanolamine) have been obtained by the open-air reaction of metallic copper with cobalt(II) chloride/cobalt(II) thiocyanate and triethanolamine in non-aqueous solvents, like dmf, dmso, CH3OH and CH3CN. The simultaneous presence of copper and cobalt in the mixed crystals was unambiguously determined by atomic absorption, EPR and electronic spectroscopy. Details of 1 have been studied structurally, and a preliminary report of the structure of 2 is also given. The mononuclear species 1 and 2 contain crystallographically indistinguishable Cu(II) and Co(II) ions in virtually identical trigonal bipyramidal sites. The molecules are linked together by O-H···O hydrogen bonds to give chains. The values of the temperature independent μeff of 3.50 and 3.48 μB for 1 and 2 (in the range of T = 20 - 280 K), respectively, agree with the 1:1 molar ratio of the metals in both samples.

[2-(Dimethyl­amino)­ethanol-κ2N,O][2-(dimethyl­amino)­ethano­lato-κ2N,O]iodidocopper(II)

The title compound, [Cu(C4H10NO)I(C4H11NO)], was obtained unintentionally as the product of an attempted synthesis of a Cu/Zn mixed-metal complex using zerovalent copper, zinc(II) oxide and ammonium iodide in pure 2-(dimethylamino)ethanol, in air. The molecular complex has no crystallographically imposed symmetry. The coordination geometry around the metal atom is distorted square-pyramidal. The equatorial coordination around copper involves donor atoms of the bidentate chelating 2-(dimethylamino)ethanol ligand and the 2-(dimethylamino)ethanolate group, which are mutually trans to each other, with four approximately equal short Cu—O/N bond distances. The axial Cu—I bond is substantially elongated. Intermolecular hydrogen-bonding interactions involving the –OH group of the neutral 2-(dimethylamino)ethanol ligand to the O atom of the monodeprotonated 2-(dimethylamino)ethanolate group of the molecule related by the n-glide plane, as indicated by the O⋯O distance of 2.482 (12) Å, form chains of molecules propagating along [101].