Thiourea complexes of zinc, cadmium and mercuric perchlorates, fluoborates and trifluoroacetates; their stability and composition studied by paper chromatography, using 35S-thiourea

Abstract

Solid thiourea complexes of zinc, cadmium and mercuric perchlorates, fluoborates and trifluoroacetates were prepared from water or ethanol media. The metal: thiourea ratio in the complexes was determined by titration using a high frequency method. The solid complexes, to which an equivalent amount of 35S-labelled thiourea was added, were eluted on Whatman No. 1 paper with a ketone [acetone (Ac), methylethylketone (MEK), acetylacetone (AcAc)] containing 5–20% of 5 M - Na X ( X = ClO 4 −, BF 4 −, CF 3COO −) aqueous solution. The complexed and the free thiourea exchange immediately and completely and, with these eluents, a definite complex and the free thiourea migrate in compact spots on the strip. The metal: thiourea ratio of the migrating complex was determined by measuring the activities of the two spots. The number of thiourea molecules per metal atom in the migrating complex increases from Zn to Cd to Hg in accordance with their increasing sulphur affinity. The thiourea R f values chiefly depend on the solvent and on the anion present in the eluting mixture in the sequence: ClO 4 −, MEK > CF 3COO −, Ac ⩾ ClO 4 −, Ac > CF 3COO −, MEK. The R f values are always greater for perchlorates than for the more complexing trifluoroacetates.