Photocatalysis of chloroform degradation by μ-dichlorotetrachlorodipalladate(II)

Unlike other chlorometallate complexes that catalyze the photodecomposition of haloalkanes through photodissociation of a chlorine atom, both PdCl 4 2 - and Pd 2 Cl 6 2 - catalyze chloroform decomposition through a process that appears to involve C–H bond breakage from an excited state association complex with chloroform. This would account for the greatly retarded rate of decomposition in CDCl3 and for the generation of CCl4 as a side product. In chloroform, Pd 2 Cl 6 2 - and PdCl 4 2 - are in slow equilibrium with each other. The rate for the conversion of Pd 2 Cl 6 2 - – PdCl 4 2 - in chloroform at 23 °C obeys the expression (0.03 M−1 s−1) [ PdCl 4 2 - ][Cl−]. The equilibrium constant, K = [ Pd 2 Cl 6 2 - ][Cl−]2/[ PdCl 4 2 - ]2, was estimated to be 3 × 10−3 M in CHCl3.