Reversed-phase liquid chromatographic retention of geometrical isomers of tris(β-diketonato)—chromium(III) and tris(β-diketonato)—cobalt(III) : Comparison with liquid—liquid partition in a dodecane—(methanol—water) system

Abstract

The retention of the fac and mer isomers of chromium(III) and cobalt(III) complexes with eight asymmetrical β-diketones in the octadecyl-bonded silica (ODS)—(methanol—water) system was studied. The retention order for two geometrical isomers depends on the structure of the complexing β-diketone; the retention order, fac< mer, is found for complexes of the β-diketones which possess a fluorinated functional group in each molecule, whereas the reverse order is found for complexes of β-diketones without a fluorinated moiety. The capacity factors ( k′) of the chromium(III) complex isomers were compared with their partition coefficients ( P) between dodecane and methanol—water of an identical composition to the mobile phase used in the chromatographic separation. It was found that the transfer of a complex from a methanol—water phase occurs more easily to ODS than to dodecane. The retention sequence for the fac and mer isomers of each metal complex is the same as the increasing order of P values. The difference in k′ between the mer and fac isomers is smaller than the difference in the P value.