Synthesis, characterization and properties of mono-, di- and polynuclear nickel(II) pseudohalide complexes containing bidentate Schiff bases. X-ray structure of [Ni(Ni,Np)₂(NCS)₂] [Ni,Np = N-((pyridin-2-yl)benzylidene) benzylamine]

Abstract

Three different types of nickel(II) pseudohalide compounds, [Ni(Ni,Np)₂(X)₂] [Ni,Np = N-((pyridin-2-yl)benzylidene) benzylamine; X = N₃⁻, 1; X = NCS⁻, 2; X = NCO-, 3], [Ni(Ni,Np)₂(X)]₂(Y)₂ [X = N₃⁻, Y = ClO4⁻, 4; X = N₃⁻, Y = PF6⁻, 5; X = NCO⁻, X = ClO4⁻, 6; X = NCO⁻, Y = PF6⁻, 7] and [Ni(Ni,Np)(N₃)2]n (8) have been prepared and characterized using microanalytical, spectroscopic and other physicochemical results. Single crystal X-ray study of one of the mononuclear compounds, [Ni(Ni,Np)₂(NCS)₂] (2) has been done. Structural analysis reveals that the metal center in 2 adopts a distorted octahedral geometry with an NiN6 chromophore coordinated through four N atoms of two bidentate L units and two N atoms of terminal thiocyanate in mutual cis orientation. The mononuclear units in 2 are engaged in intermolecular weak C-H…S hydrogen bonding to give a 1D chain. Electrochemical electron transfer study reveals nearly-reversible responses to NiIII/NiII couple in acetontrile solutions. High-energy intraligand 1(π-π *) fluorescence at room temperature and intraligand ³ (π-π*) phosphorescence in glassy solutions (MeOH at 77 K) are seen in all the complexes.