5-COORDINATED MIXED-LIGAND NICKEL(II) COMPLEXES - THERMODYNAMIC AND SPECTROSCOPIC STUDIES OF SOLVATOCHROMIC AND THERMOCHROMIC PROPERTIES

Five-coordinate Ni(II) complexes (Ni(beta-dike)(pmdt)X; beta-dike- = a cetylacetonate or benzoylacetonate, pmdt = N, N, N', N'', N''-pentamet hyldiethylenetriamine and X = BPh4- or NO3-) have been prepared and ch aracterized by vibrational and electron spectroscopy and by magnetic m easurements. BPh4- complexes are five-coordinate species in non-coordi nating solvents like DCE or NM. In solvents with stronger donor proper ties like DMF or DMSO, or in the case of NO3- complexes, octahedral sp ecies are formed. Spectrophotometric titration was used to evaluate eq uilibrium constants between five- and six-coordinated species. Reactio n enthalpies and entropies were measured. The latter was found to gove rn the overall fee energy changes. Steric factors appear to be importa nt when large amine molecules are coordinated to Ni(II).