The title compounds were studied by TG, DTA, DSC, IR and absorption spectroscopy. The complexes go through dehydration (70–200°C), an irreversible exothermic process (in air or N2 atmosphere, 250–300°C) and decomposition to a mixture of oxides and carbonates (385–700°C). The exothermic process occurs without weight loss and corresponding heats of reaction fall in the range 0–26 kJ/mol. The absorption spectrum of the Nd complex in the range 5000–6000 Å was employed to monitor perturbations in the coordination sphere of Nd3+ arising from the exothermic process. Involvement of the Nd3+ cation is implied and the heats of reaction show a close relationship to the radii of Ln3+. The interpretation of these data was made with the aid of valuable structural information obtained previously.