The preparation, properties, crystal lattice and thermal decomposition reactions of cobalt malonate dihydrate

Abstract

Cobalt malonate dihydrate crystallizes in the monoclinic system, the dimensions of the unit cell are reported. On heating, two molecules of water are lost at ∼400 K to give the anhydrous salt which is amorphous to X-rays. At higher temperatures (520K) the initial stages of carboxylate decomposition obey the zero-order kinetic equation to 30% reaction. Thereafter, there is a marked diminution in rate of the vacuum reaction but kinetic behaviour is sensitive to the gases present; the influences of reaction products, of carbon monoxide and of oxygen have been investigated quantitatively. Form these observations we conclude that the decomposition of cobalt malonate proceeds by an autocatalytic mechanism, through the nucleation and growth of an ill-crystallized mixture of product phases. The rate of reactions at the reactant-product contact surface are controlled, to some extent, by available gaseous molecules which may participate in equilibria at the interface and at active surfaces of the residual phases.