Studies on the interaction between lanthanide ions and ligands in solid complexes of lanthanide hexacyanometalates .1. The thermal dehydration of lanthanide hexacyanocobaltate(III) hydrates, Ln[Co(CN)(6)]center dot nH(2)O (Ln=La to Lu; n=4,5), and yttrium hexacyanocobaltate(III) tetrahydrate

In the present paper, series complexes of lanthanide hexacyanocobaltates(III), Ln[Co(Cn)(6)]. nH(2)O, were prepared in the hope of gaining some insight into the relation of the crystal structure and thermal dehydrations of these complexes. The thermal dehydration of the complex was followed by means of TG-DTA, DSC and X-ray powder diffraction analysis. The dehydration mode was discussed by a proper combination of two factors which were contrary to each other, i.e. (1) increasing of the effective charge of Ln(3+) with decreasing of the ionic radius of Ln(3+), which enhances the interaction of Ln(3+)-OH2 bonds, and (2) decreasing of the ionic radius leading to a narrowing of the coordination sphere and then a mutual repulsion between the ligands, contributing to the instability of Ln(3+)-OH2 bonds. The experimental results suggested a possibility of the occurrence of a metastable phase of tetrahydrate complexes, formed immediately after the dehydration of one water molecule of their pentahydrate complexes.