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A Polyselenide with a Novel Se 7 8– Unit: the Structure of Sr 19– x Pb x Ge 11 Se 44 with x = 5.0 and 6.4
Author(s) -
Assoud Abdeljalil,
Kleinke Holger
Publication year - 2017
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201701180
Subject(s) - chemistry , crystallography , bond length , atom (system on chip) , formula unit , molecular geometry , unit (ring theory) , band gap , tetrahedron , crystal structure , molecule , physics , condensed matter physics , mathematics education , mathematics , organic chemistry , computer science , embedded system
An unprecedented, planar Se 7 8– unit with a threefold rotation axis was discovered in the new polyselenide Sr 19– x Pb x Ge 11 Se 44 . Sr 12.6 Pb 6.4 Ge 11 Se 44 crystallizes in the non‐centrosymmetric hexagonal space group P 6 3 with unit cell dimensions of a = b = 19.9867(2) Å, c = 12.0546(1) Å, V = 4170.28(7) Å 3 , with two formula units per cell. Its structure contains isolated [GeSe 4 ] tetrahedra, [Ge 2 Se 7 ] dimers, and a novel, planar propeller‐shaped Se 7 8– unit. The latter is unprecedented, but reminiscent of the isoelectronic pyramidal Se 7 8– and I 7 – units. It consists of a central Se atom, to which three Se 2 pairs with a short Se–Se bond are attached through a longer Se–Se distance, resulting in a central Se atom featuring 120° bond angles, and bridging Se atoms featuring an approximately linear coordination with a 179° bond angle. It can thus be written as [Se(Se 2 ) 3 ] 8– . We characterized this unit using Gaussian calculations in comparison to the pyramidal Se 7 8– unit, which may be described also as [Se(Se 2 ) 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.