Synthesis, characterization and properties of nickel(II)pseudohalide complexes of types [Ni(pap)₂(X)₂], [Ni(pap)₂(X)]₂(Y)₂ and [Ni(pap)(N₃)₂]_n [pap=2-(phenylazo)pyridine; X=N₃^ˉ, NCSˉ, NCOˉ; Y=ClO₄ˉ, PF₆ˉ]

Abstract

2474-2479Three different types of nickel(II)pseudohalide compounds, viz. red-brown [Ni(pap)2(X)2] [pap=2-(phenylazo)pyridine; X=N3ˉ, 1; NCSˉ, 2; NCOˉ 3], greenish-brown [Ni(pap)2(X)]2(Y)2  (X= N3ˉ , Y=ClO4ˉ, 4; X= N3ˉ  , Y=PF6ˉ , 5; X=NCOˉ, Y=ClO4ˉ, 6; X= NCOˉ, Y= PF6ˉ, 7) and brownish-green, [Ni(pap)(N3)2]n (8) have been prepared and characterised on the basis of microanalytical, spectroscopic, magnetic, electrochemical and other physicochemical properties. In IR, v(N=N) stretching frequency is observed at considerably lower frequencies (-1370 cm-1) than the free ligand value (1425 cm-1) indicating substantial Ni (II)→ pap π-back bonding and in electronic spectra, the MLCT bands show characteristic lower energy shifts in going from mono- to polynuclear compounds via dinuclear ones. Room temperature magnetic measurements show uniformly two-electron paramagnetism for each nickel(II) ion in these complexes. Electrochemical electron transfer study reveals nearly- reversible responses corresponding to NiIII/NiII couple in acetonitrile solutions. On the negative side of SCE, multiple ligand reductions pertaining to azo reductions are observable