Distinctive coordination behavior of a pyrazole imine-oxime compound towards Co(II) and Ni(II)

The polytopic Schiff base 5-methyl-1H-pyrazole-3-carboxylic acid 2-(hydroxyimino-1-methyl-propylidene)-hydrazide (H(2)L)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 [Co(2)(1κN(2):2κN(2)-L) (1κN(3):2κO(1)-HL)(2)](NO(3))(2) (1). With the Ni(II) precursor, H(2)L was hydrolyzed to N′,N˝-butane-2,3-diylidenebis (5-methyl-1H-pyrazole-3-carbohydrazide) (H(2)L(1)) which bound the metal cation in a tetradentate N(3)O(1) fashion leading to the neutral square planar complex [Ni(κN(3)O(1)-L(1))]·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 H(2)L into H(2)L(1) has been investigated by ESI-MS.