Cadmium sulfite hexahydrate revisited

The present structural revision of the title compound, tetra-cadmium tetra-sulfite hexa-hydrate, [Cd(4)(SO(3))(4)(H(2)O)(5)]·H(2)O, is a low-temperature upgrade (T = 100 K and R = 0.017) of the original room-temperature structure reported by Kiers & Vos [Cryst. Struct. Commun. (1978). 7, 399-403; T = 293 K and R = 0.080). The compound is a three-dimensional polymer with four independent cadmium centres, four sulfite anions and six water mol-ecules, five of them coordinated to two cadmium centres and the remaining one an unbound solvent mol-ecule which completes the asymmetric unit. There are two types of cadmium environment: CdO(8) (through four chelating sulfite ligands) and CdO(6) (by way of six monocoordinated ligands). The former groups form planar arrays [parallel to (001) and separated by half a unit cell translation along c], made up of chains running along [110] and [10], respectively. These chains are, in turn, inter-connected both in an intra-planar as well as in an inter-planar fashion by the latter CdO(6) polyhedra into a tight three-dimensional framework. There is, in addition, an extensive network of hydrogen bonds, in which all 12 water H atoms act as donors and eight O atoms from all four sulfite groups and two water mol-ecules act as acceptors.