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Evidence is presented which indicates that chelating ability may be greatly altered by changing the steric requirements of the ligand. A series of formation constants was measured for three beta-diketones. Thermodynamic values could not be obtained but relative concentration constants were. The constants obtained were correlated with each other and with the basicity of the reagent toward a proton. Each correlation indicated that the formation constants for the copper chelates of diisobutyrylmethane and dipivaloytmethane were low and exhibited large separation factors. However, relatively small separation factors were found for metal chelates which do not form square planar complexes. A simple method for determining the extent of enolization of beta-diketones and the kinetics of enolization is presented. The method makes uses of spectrophotometric measurements in the ultraviolet region. Correlations were observed between the pKa of the chelating agent, the kinetics of enolization, and the kinetics of hydrolysis of corresponding esters. Variations in the pKa and enol content were explained on the basis of steric effccts. A procedure for the separaticn of lithium from other alkali metal ions was developed, making use of the selectivity of dipivaloylmethane. The theoretical implications of this selectivity are discussed. Correlation of formation constants with a doublemore » basicity scale is reveiwed. It is suggested that when using such correlations a chelate effect be taken into account. The application of the Edward and Hammett equation to formation constants is discussed. (auth)« less

STERIC EFFECTS ON THE FORMATION CONSTANT OF METAL CHELATES OF BETA- DIKETONES