AXIAL LIGATION OF COPPER(2) BIS(T-BUTYLACETOACETOACETATE) BY PYRIDINE DONORS . THERMODYNAMICS AND SOLVENT EFFECTS

Equilibrium constants and enthalpies for 1:1 adduct formation of copper(II) bis (t-butylacetoacetate), Cu(t-Buoac)2, with a series of pyridine donors have been measured in cyclohexane by calorimetric and spectrophotometric methods. Agreement between the two methods was found to be good. The equilibrium constants and enthalpies were found to correlate linearly with the corresponding shift in methanol OH stretching frequency, except for 2-methylpyridine, where a steric effect is proposed. Calorimetric studies in benzene, carbon tetrachloride, and chloroform have shown the thermodynamics of adduct formation with pyridine to be solvent dependent. Equilibrium constants and enthalpies decreased with change in solvent in the order C6H12 > C6H6 > CC14 > CHCl3. The epr parameters for Cu(t-Buoac)2 are solvent dependent. The (a) values increase in the order C6H12 < CC14 < C6H6 < CHCl3, which is contrasted with the large decrease in 〈a〉 observed in donor solvents. Infrared spectra of copper(II) bis(trifluoroacetylacetonate) and copper(II) bis(trifluoroacetylacetonate)-pyridine show that upon adduct formation the pyridine ring vibrational frequencies increase and that the metal-oxygen stretching frequency decreases. © 1969, American Chemical Society. All rights reserved.