LAUSR

The polytopic Schiff base 5-methyl-1H-pyrazole-3-carboxylic acid 2-(hydroxyimino-1-methyl-propylidene)-hydrazide (H2L)was synthesized by the condensation of 5-methyl pyrazole-3-carbohydrazide and 3-(hydroxyimino)butan-2-one and its coordination ability was tested against cobalt (II) and nickel (II) nitrates. The ligand exhibited two different binding modes to form a unique binuclear triply bridged Co(III) cationic complex [Co2(1κN2:2κN2-L) (1κN3:2κO1-HL)2](NO3)2 (1). With the Ni(II) precursor, H2L was hydrolyzed to N′,N˝-butane-2,3-diylidenebis (5-methyl-1H-pyrazole-3-carbohydrazide) (H2L1) which bound the metal cation in a tetradentate N3O1 fashion leading to the neutral square planar complex [Ni(κN3O1-L1)]·MeOH (2·MeOH). Complexes 1 and 2 were characterized by IR, NMR, UV-Vis and single crystal X-ray crystallography. The probable mechanism for the Ni(II) mediated transformation of H2L into H2L1 has been investigated by ESI-MS.