EFFECT OF OUTER-SPHERE HYDRATION ON LIQUID-LIQUID PARTITION OF TRIS-BETA-DIKETONATES OF 3D METAL-IONS

Partition coefficients for tris-acetylacetonates and tris-2,4-hexanedi onates of trivalent Sc, Ti, Cr, Mn, Co and Ga between heptane and wate r were determined. It has been found that the partition coefficients, including the values for Fe and V chelates reported in the literature, decrease with decreasing metal to oxygen distance in the chelate mole cule. The observed relationship has been explained by the effect of th e central metal ion on the distribution of electron density in the bet a-diketonate ligand. The decrease in the metal-oxygen distance in the metal(III) beta-diketonates increases the electron density on ligand o xygen atoms, which in turn strengthens hydrogen bonds between the oxyg ens and water molecules. The increased strength of the hydrogen bond d ecreases the partition coefficient.