Huseyin Isci

Polymerisation of bis(trichlorophenolato)tri(pyridine)nickel(II) and bis(trihalophenolato)di(pyridine)nickel(II) complexes in solid state

Abstract The synthesis of five-coordinated bis(trihalophenolato)tri(pyridine)nickel(II) and four-coordinated bis(trihalophenolato)di(pyridine)nickel(II) complexes from an aqueous solution and their characterisation by FT-IR, X-ray, DSC and elemental analysis is described. The thermal polymerisation of these complexes was carried out in the solid state and in the melt. Structural analyses were performed using 1 H NMR, 13 C NMR and FT-IR spectroscopic analyses. T g s were determined by differential thermal analysis and the molecular weights by viscometric method.

Electrochemistry of Acetate-, Carbonate-, Sulfate-, and Dihydrogenphosphate-Bridged Dirhodium(II) Complexes

Complexes, [Rh2(B-B)4L2]n (B-B = CH3COD2 , L = CH3CN, H2O, Cl-, Br-, SCN-; B-B = CO2-3 , SO2-4 , H2PO4̄, L =H2O, Cl-, Br-, SCN-) were prepared and their cyclic voltammograms (CV) and electronic absorption spectra were measured in solution. The CV of the complexes exhibits a reversible one-electron transfer from a metal-based orbital. Constant potential electrolysis at the oxidation peak potential of [Rh2(O2CCH3)4(NCCH3)2] in acetonitrile yielded [Rh2(O2CCH3)4(NCCH3)2]+, a mixed valent Rh(II)DRh(III) cation complex. The formation of the mixed valent complex was monitored by measuring electronic absorption spectra of the solution in situ during the oxidative electrolysis. The reductive electrolysis of the mixed valent complex solution, in the same electrolysis cell, yielded the original electronic absorption spectrum of the starting complex. The changes in the oxidation and reduction potentials of the complexes with different axial ligands, L = H2O, Cl-, Br-, SCN-, are correlated to the relative energy changes of HOMO and LUMO of the complexes, which indicates the metal-axial ligand σ- and π-bonding interactions. Spectroscopic and CV data indicate that the degree of σ-interaction is Cl- > Br- > SCN-, and that of π-interaction is Br- > SCN- > Cl-.

Low-temperature Spectroelectrochemistry of Tetraethylammonium Tris(ethylxanthato)nickelate(II) and Bis(ethylxanthato)nickel(II) Complexes

One-electron constant potential electrolysis of tetraethylammonium tris(ethylxanthato)nickelate(II), (NEt 4 )[Ni(S 2 COEt) 3 ] and bis(ethylxanthato)nickel(II), Ni(S 2 COEt) 2 , at their lowest oxidation peak potentials, were followed by in situ UV-VIS spectrophotometry, in acetonitrile at 253 K. In both cases [Ni III (S 2 COEt) 3 ] complex formed and detected by its electronic absorption and EPR spectra. [Ni III (S 2 COEt) 3 ] slowly disproportionated to Ni(S 2 COEt) 2 and the dimer of the oxidized ethylxanthate ligand, (S 2 COEt) 2 , with a second-order rate law.

Crystal structure of bis(pyridine)bis(2,4,6-tribromophenolato)cobalt(II), C22H14Br6CoN2O2

Source of material: To a 100 ml aqueous solution of 20 mmol C0SO4 7H2O and 40 mmol pyridine, a solution of 40 mmol NaOH and 40 mmol 2,4,6-tribromophenol in 100 ml water was added gradually. The purple precipitate was filtered, washed and dried in vacuo. This residual crude product was crystallized from a mixture of toluene (3 ml), pyridine (0.12 ml) and 25 ml hexane. All non-Η atoms were refined with anisotropic thermal parameters. H atoms were placed geometrically 0.9S À from the parent C atoms. For all H atoms a riding model was used with Uiso(H) = 1.3Ueq(C). This type of complexes with general formula [ML2(TXP)2] (M = transition metal; L = neutral nitrogen donor ligand and TXP = 2,4,6-trihalophenolato) are known since the turn of this century (see refs. 1, 2). Thermal decomposition of these complexes yields the formation of polydihalophenyleneoxides. The mechanism of this polymerization reaction is not clear. Thermal decomposition of Co(Py)2(TXP)2 in the solid state, also resulting in polydihalophenyleneoxide, have been observed in this laboratory. This structure determination was conducted to contribute to the understanding of polymerization. The coordination around the Co atom is a distorted tetrahedron, involving two phenoxy O atoms and two pyridine Ν atoms. The two Co—O distances are equal (1.914(7) Â] and the C o N bond lengths are the same [2.073(8) À and 2.091(9) Λ] within experimental errors. The bond angles around Co atom range from 95.1(3)° to 104.5(3)°. The Co-Br distance [3.120(2) Â] is too long to be considered as secondary interaction. The tribromophenolate has a flexibility to twist about t h e C O bond (average torsion 28(1)°), so that the Co—Br interaction is minimized. The average C o O C angle is 135.7(5)° which is also a result of steric hinderances. The dihedral angle between the pyridine rings is 79.1(2)° while the corresponding angle between the phenol rings has a value of 81.8(3)°. The dihedral angles between the pyridine and phenol rings are 72.9(2)° and 87.1(3)°. The closest intermolecular contact [2.906(1) Â] is between Br(4) and H(5)(l-x, -y, -z ) . Some of the 2,4,6-trichlorophenolate complexes with Fe, Co, Ni, Cu and Ag involve chelation through oxygen and chlorine donor atoms (see ref. 3) which is not observed in the title compound.

Electrochemical and Chemical Oxidation of K(C2H5OCS2), [Ni(C2H5OCS2)D And [N(C2H5)4][Ni(C2H5OCS2)3]

Electrochemical and chemical oxidation of (Et-Xan−), [Ni(Et-Xan-2] and [Ni(Et-Xan)3]− (Et-Xan− = C2H5OCS2 −) have been studied by Cyclic Voltammetry and in situ UV-Vis spectroscopy in acetonitrile at room temperature. Cyclic Voltammograms (CV) of Et-Xan− and Ni(Et-Xan)2 display one (0.00 V) and two (0.35 and 0.80 V) irreversible oxidation peaks, respectively, referenced to Ag/Ag+(0.10 M) electrode. However, CV of Ni(Et-Xan)3 − displays one reversible (-0.15 V) and two irreversible (0.35, 0.80 V) oxidation peaks, respectively, referenced to Ag/Ag+ electrode. The products of constant potential electrolysis at the first oxidation peak potentials of Et-Xan” and [Ni(Et-Xan>2] are the dimer of the oxidized ligand, (Et- Xan-2 and Ni2+ (sol); and that of Ni(Et-Xan)3]− are (Et-Xan)2 and [Ni(Et-Xan)2]. Chemical oxidation of Et-Xan− and [Ni(Et-Xan)3]− with iodine to (Et-Xan)2 and (Et- Xan)2/[Ni(Et-Xan)2], were also achieved. The oxidized ligand in the dimer form can be reduced to Et-Xan− with CN− in solution. Our data do not support the formation of Ni(III) species at any oxidation stage.