TREND OF STABILITIES OF ADDUCTS OF 4,4,4-TRIFLUORO-1-(2-THIENYL)-1,3-BUTANEDIONATES WITH PHENYLPYRIDINES OVER LANTHANOID SERIES

The formation constants of the adducts of 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionatolanthanoids(III) with 2-, 3-, and 4- phenylpyridines as well as the distribution constants and pK(a) of these pyridines were determined on the basis of data obtained by solvent extraction from a 0.1 mol/dm3 sodium perchlorate solution into chloroform containing TTA and/or pyridines. It has been found that the adduct formation constants(betaBAR) of a given lanthanoid(III) chelate increase along with increased pK(a) of the phenylpyridine, and that the constants do not change much from light to middle lanthanoids, and then decrease for heavy ones. The constants for the 2-phenylpyridine adduct are lower than expected, possibly reflecting a steric effect. The pattern of a plot of log betaBAR1 versus the atomic number is different from that with carboxylic acids and bidentate amines.