A polymorph of K₄Ge₄Se₁₀

Abstract

A new monoclinic polymorph, β-K4Ge4Se10 (tetra­potassium deca­selenidotetra­germanate), that crystallizes in space group P21/c has been isolated. The structure contains isolated super-tetra­hedral adamantane [Ge4Se10]4− clusters identical to those in the known K4Ge4Se10 polymorph (P21/m), held together in in the crystal structure by ionic inter­action with the K+ ions. The adamantane unit, [Ge4Se10]4−, is formed by corner-sharing of four GeSe4 tetra­hedra, with average Ge—Se distances of 2.378 and 2.281 Å for (Ge—Se)endo and (Ge—Se)exo, respectively. There are four crystallographically distinct K+ ions in β-K4Ge4Se10 having coordination numbers of 5, 7 and 8 (× 2), with K—Se distances in the range 2.986 (2)–3.888 (1) Å, while the coordination numbers of the three unique K+ ions in the known K4Ge4Se10 (P21/m) vary between 5 and 7. Besides the differences in coordination numbers of K+ ions, the two polymorphs also exhibit a different packing of the adamantane units.