SPECTROSCOPIC AND THERMODYNAMIC STUDIES ON SOLVATOCHROMIC NICKEL(II) COMPLEXES

The solvatochromic and thermochromic behaviour of a series of mixed Ni(II) complexes with unsubstituted and substituted beta-diketones and diamines in the solvents 1,2-dichloroethane (DCE), acetonitrile (An), acetone (AC), n-butanol (n-BuOH), formamide (FA), N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and pyridine (PY) has been studied and characterized on the basis of electronic spectra. Spectrophotometric methods have been used to evaluate equilibrium constants and their enthalpic and entropic terms for the formation of Ni(beta-dik)(diam)L+ and Ni(beta-dik)(diam)L2+. Increasing donor strength of the donor-solvents (L) and (or) increasing electronwithdrawing parameters of the substituents at the beta-diketone and the diamine ligands lead to increasing formation constants, paralleled by relative increase in the stability of the five-coordinated species Ni(beta-dik)(diam)L+. The results are discussed in terms of the extended donor-acceptor concept.