Acta Crystallographica Section E

Structure Reports Online

Volume 63, Part 7 (July 2007)

inorganic compounds

 

A polymorph of K₄Ge₄Se₁₀

A. Choudhury, S. Strobel and P. K. Dorhout

Abstract: A new monoclinic polymorph, -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 -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.

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