Nickel(II) chelates of unsaturated aroylhydrazones and their reactions with pyridines

Abstract

The reactions of nickel(II) acetate with cinnamaldehyde- and benzalacetone- aroylhydrazones( 2) (R′ = H or CH 3) afforded green octahedral paramagnetic NiL 2·2H 2O chelates, where L refers to the mononegative bidentate ligand. Upon dehydration of these chelates, brown and yellow square-planar diamagnetic complexes (α-series) were isolated, respectively. The in situ reactions of cinnamaldehyde and aroylhydrazines in the presence of nickel(II) acetate gave diamagnetic orange complexes with the planar arrangement around the nickel(II) ion (β-series). Based on the IR and IV spectral data trans-geometry was assigned for the brown and yellow α-series and cis-geometry for the orange β-series. Both the brown or yellow and orange forms behave differently towards pyridine. Their crystallization from pyridine solutions led to the isolation of stable bis- and tetrakis- (pyridine) adducts, respectively. The stability constants and the thermodynamic parameters for the adduct formation reactions of the orange NiL 2 chelates with py, 3-Mepy and 4-Mepy have been evaluated.