SPECTROSCOPIC, THERMODYNAMIC AND QUANTUM-MECHANICAL STUDIES ON SOLVATOCHROMIC MIXED-LIGAND COPPER(II)-CHELATES

Coordination of donor solvent molecules to square planar Cu(acac)(tmen )+ (acac- = acetylacetonate, tmen = tetramethylethylenediamine) leads to a continuous shift of the d-d absorption band which is used to esti mate donor numbers for a series of amines. Spectrophotometric methods are used to evaluate formation constants, enthalpies and entropies of formation for the consecutive coordination of one or two solvent molec ules to the square planar Cu(acac)(tmen)+ complex. The results are com pared with those of the corresponding Ni(II) chelate showing larger fo rmation constants than the copper(II) system. Quantum mechanical calcu lations were carried out within the CNDO/2 framework and related to ex perimental data. With increasing charge on the Cu atom, formation cons tants and ESR g values are increased.