4 years ago

A new Polyselenide with a novel Se78- unit: the Structure of Sr19-xPbxGe11Se44 with x = 5.0 and 6.4

Holger Kleinke, Abdeljalil Assoud
An unprecedented, planar Se78- unit with a threefold rotation axis was discovered in the new polyselenide Sr19-xPbxGe11Se44. Sr12.6Pb6.4Ge11Se44 crystallizes in the non-centrosymmetric hexagonal space group P63 with unit cell dimensions of a = b = 19.9867(2) Å, c = 12.0546(1) Å, V = 4170.28(7) Å3, with two formula units per cell. Its structure contains isolated [GeSe4] tetrahedra, [Ge2Se7] dimers and a novel, planar propeller-shaped Se78- unit. The latter is unprecedented, but reminiscent of the isoelectronic pyramidal Se78- and I7- units. It consists of a central Se atom, to which three Se2 pairs with a short Se-Se bond are attached via a longer Se-Se distance, resulting in the central Se atom having 120° bond angles, and the middle Se atoms approximately linear coordination with a 179° bond angle. It can thus be written as [Se(Se2)3]8-. We characterized this unit via Gaussian calculations in comparison to the pyramidal Se78- unit, which may be described also as [Se(Se2)3]8-. The solid-state material is a black semiconductor with an optical band gap of 1.8 eV, which supports the assignment of this charge.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201701180

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