Polymorphism of anhydrous cadmium iodate structure of ε-Cd(IO3)2

The investigation of CdC2-HIO3 system, in aqueous and HNO3 solutions, revealed that anhydrous cadmium iodate presents a marked polymorphism. No less than four new Cd(IO3)(2) poly-morphs have been isolated and characterized, two of which showing second harmonic generation activity. Single crystals of epsilon-Cd(IO3)(2) are obtained by slowly evaporating, at 60 degrees C, a saturated solution of gamma-Cd(IO3)(2) in 30 % nitric acid. This compound crystallizes in the orthorhombic space group Pca2(1) [a = 17.581(2), b = 5.495(2), c = 11. 163(2) angstrom]. The basic structural unit can be described as the connection of two cadmium polyhedrons with a short metal - metal distance of 3.88 angstrom. These units are further linked through two other iodate bridges resulting in layers parallel to the (100) plane. The 3D linkage is ensured by short bonds of the fourth iodate group.