NUCLEAR MAGNETIC RESONANCE STUDIES OF LIGAND-EXCHANGE PROCESSES .I. LIGAND-EXCHANGE EQUILIBRIA FOR SOME GALLIUM(3) BETA-DIKETONATES

The ligand-exchange equilibria that are established in Ga(acac)3-Ga(bzbz)3 and Ga(acac )3-Ga(hfac )3 mixtures, where acac = acetylacetonate, bzbz = dibenzoylmethanate, and hfac = hexafluoroacetylacetonate, have been studied by proton nmr spectroscopy. Equilibrium constants for formation of each mixed-ligand complex from the parent Complexes have been determined in benzene solution. For formation of Ga(acac)2(bzbz) and Ga(acac)(bzbz)2, the equilibrium constants, extrapolated to 25°, are only ca. 20% smaller than the values expected for a random statistical distribution of ligands. Within experimental error, enthalpy changes ate zero or nearly zero and entropy changes are equal to the values expected for a statistical distribution of ligands. In the Ga(acac)3-Ga(hfac)3 system, the mixed-ligand complexes are very strongly favored at the expense of the parent complexes, the equilibrium constants being ca. 400 times larger than statistical values. The deviations from statistical behavior are due almost entirely to enthalpy effects. © 1969, American Chemical Society. All rights reserved.