Synthesis and Crystal Structure of Binuclear and Pentanuclear Nickel(II) Complexes Containing 4-(salicylaldiminato)antipyrine Schiff base

The new title binuclear Ni (II) compound  (1) and the novel pentanuclear Ni (II) cluster {[   } (2) are formed from the reaction of an asymmetric Schiff base ligand L (L = 4-(salicylaldiminato)antipyrine) with Ni .4  in the former or Ni(ClO₄)₂.6H₂O in presence of malonate in the later.  Complex (1) consists of ( ]⁺ cation) and one uncoordinated tetraphenylborate anion.  The cation adopts a distorted octahedral arrangement around each metal center.  In the binuclear unit both Ni(II) ions are linked through two phenolate (µ₂-O) oxygen atoms of L, and two oxygen atoms of a  bridging carboxylate group. Each Ni (II) coordinates to four oxygen atoms at the basal plane, two oxygen atoms from two bridging phenolate groups, one from pyrazolone ring and the last of an aqua molecule, and at the axial positions to a bridging carboxylate-O atom and an azomethine nitrogen atom.  In the pentanuclear cluster (2) consisting of [ ]⁺² cation and two tetraphenylborate anions, the core of the cation is assembled by four [Ni( )] units, linked to the central Ni-ion by two bridging water molecules. The resulting coordination sphere for the external symmetry related nickel ions is a pseudo octahedron.  The central Ni-atom unusually adopts dodecahedron geometry through its coordination to eight bridging water molecules. In complex (1) each Ni-atom is coordinated to one tridentate L ligand and in complex (2) each [Ni ( )] unit is coordinated to two bidentate L ligands.  Inter-and intramolecular hydrogen bonds are present in both crystal structures.