New Chalcogenogermanates with Adamantane Type Complex Anions: Preparation and Crystal Structures of K4Ge4S10, Rb4Ge4S10, Rb4Ge4Se10 and Cs4Ge4Se10

The title compounds were obtained by reacting stoichiometric quantities of the corresponding dialkalimonochalcogenide, germanium powder and chalcogen at 1073 K. The four compounds are isostructural, crystallizing in space group C2/c, Z=4 with K4Ge4S10: a=15.161(3), b=15.198(2), c=8.760(2)Ä, beta=105.36(3)?, Rb4Ge4S10: a=15.282(7), c=9.390(7)Ä, beta=105.79(2)? and Cs4Ge4Se10: a=16.348(9), b=16.49(1), c=9.771(3)Ä, beta=107.10(3)?. Their crystal structures were solved and refined from single crystal diffractometer data (MoKalpha radiation) obtained at 294 K. They are characterized by the formation of discrete adamantane-like complex anions [Ge4Q10](4-) which are arranged in slabs parallel to (010). Mean Ge-S bond lengths are 2.202Ä for K4Ge4S10 and 2.186Ä for Rb4Ge4S10 while the mean Ge-Se bond length in both selenides amounts to 2.332(3)Ä. Terminal and bridging Ge-Q bonds differ by at least 0.1Ä. The atomic arrangement corresponds to that of Tl4Ge4S10