UNUSUAL COORDINATION OF TRIPODAL NN3S3 DONOR LIGAND WITH NICKEL(II) -SINGLE-CRYSTAL X-RAY STRUCTURE OF H2CH2N(CH2CH2N=CH(C4H3S))(2))(CH3CN)(H2O)](PF6)(2)

Reaction of Ni(acetate)(2).6H(2)O with a potentially heptentate Schiff base ligand, tris[4-(2-thienyl)-3-aza-3-butenyl]amine [(thiophene),tr en], resulted in the formation of an unexpected octahedral Ni-II compl ex with an NiN4 core and the remaining two coordination sites occupied by solvent molecules; An X-ray crystal structure of the complex estab lished the unusual cleavage at one of the three alpha-imino bonds and revealed that it deviates from the usual mono-capped trigonal prismati c coordination polyhedron designed for this type of complex. The compl ex molecule has an approximate plane of symmetry(C-s) rather than the three-fold axis (C-3) normally observed for this type of complex and i s the first example where the apical 'unique' nitrogen approaches the Ni-II as closely as the other three nitrogens of the ligand.