Structural and electrochemical comparison of NIII in an N2S2 with two, and no axial and of a five coordinate nickel(II) complex

Article abstract of DOI:10.1002/cber.19961290708

Addition of two equivalents of benzyl bromide to [N,N′-bis{2-mercaptoethyl)-l,5-diazacyclooctane]nickel(II) (Ni-1) produced the green dibenzyl dithioether complex [Ni-l-Bzl₂Br₂] structurally characterized by X-ray crystallography as a sixcoordinate octahedral complex in a monoclinic crystal system and the P21/C space group. Benzylation of the methyl thioether/thiolate [(Ni-l-Me)⁺I^- yielded the mixed benzyl/methyl dithioether [(Ni-l-BzlMe)Br]!, structurally characterized by X-ray crystallography as a five-coordinate square pyramidal nickel(II) complex with a Ni-Br distance of 2.451 A. The complex crystallizes in the orthorhombic Cmca space group. The latter is the first nickel(II) pentacoordinate complex iso-lated for the N,N′-bis(2-mercaptoethyi)-1,5-diazacyclooctane (daco) ligand. Structural comparison of these two complexes with the square-planar dimethyl compound {Ni-l-Me₂]I₂ found an expansion of the N₂S₂ plane upon addition of axial ligands. The five-coordinate nickel complex showed a displacement of the Ni ion from the N₂S₂ plane by 0.43 A toward the axial bromide ligand, a common observation of pentacoordinate complexes of this ligand with metals such as Zn and Fe. Electrochemical studies as well as the X-ray crystal structures for complex (Ni-l-Bzl₂Br₂] and [(Ni-l-BzlMe)Br]I are presented and discussed in detail. VCH Veriagsgeseilschaft mbH, 1996.