NICKEL(II) CHELATES OF UNSATURATED AROYLHYDRAZONES AND THEIR REACTIONS WITH PYRIDINES

The reactions of nickel(II) acetate with cinnamaldehyde- and benzalace tone-aroylhydrazones (2) (R' = H or CH3) afforded green octahedral par amagnetic NiL(2).2H(2)O chelates, where L refers to the mononegative b identate ligand. Upon dehydration of these chelates, brown and yellow square-planar diamagnetic complexes (alpha-series) were isolated, resp ectively. The in situ reactions of cinnamaldehyde and aroylhydrazines in the presence of nickel(II) acetate gave diamagnetic orange complexe s with the planar arrangement around the nickel(II) ion (beta-series). Based on the IR and W spectral data trans-geometry was assigned for t he brown and yellow alpha-series and cis-geometry for the orange beta- series. Both the brown or yellow and orange forms behave differently c owards pyridine. Their crystallization from pyridine solutions led to the isolation of stable bis- and tetrakis(pyridine) adducts, respectiv ely. The stability constants and the thermodynamic parameters for the adduct formation reactions of the orange NiL(2) chelates with py, 3-Me py and 4-Mepy have been evaluated.