Preparation, crystal structure and chemical bonding analysis of the new binary compounds Rh4Ga21 and Rh3Ga16

The two new binary compounds Rh4Ga21 (space group Cmca (Cmce), image, image, image, Pearson symbol oC136) and Rh3Ga16 (space group Ccca (Ccce), image, image, image, Pearson symbol oC76) were synthesised and their crystal structures were solved from single-crystal X-ray diffraction data. From a topological point of view, both these two crystal structures and the crystal structure of PdGa5 can be described either as inhomogeneous intergrowth structures containing three different kinds of segments, or as built up by layers of capped square antiprisms condensed via their capping atoms. Bonding analysis with bonding indicators revealed that the crystal structures of Rh4Ga21 and Rh3Ga16 have to be considered as framework polyanions formed by covalently bonded gallium atoms with embedded rhodium cations.