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Strontium Selenogermanate( III ) and Barium Selenogermanate( II , IV ): Synthesis, Crystal Structures, and Chemical Bonding
Author(s) -
Johrendt Dirk,
Tampier Markus
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/(sici)1521-3765(20000317)6:6<994::aid-chem994>3.0.co;2-h
Subject(s) - crystallography , chemistry , strontium , lone pair , barium , covalent bond , electron localization function , crystal structure , ionic bonding , atom (system on chip) , chemical bond , divalent , ternary operation , ion , valence (chemistry) , stoichiometry , natural bond orbital , inorganic chemistry , molecule , density functional theory , computational chemistry , electron , physics , organic chemistry , quantum mechanics , computer science , embedded system , programming language
The new selenogermanates Sr 2 Ge 2 Se 5 and Ba 2 Ge 2 Se 5 were synthesized by heating stoichiometric mixtures of binary selenides and the corresponding elements to 750 °C. The crystal structures were determined by single‐crystal X‐ray methods. Both compounds adopt previously unknown structure types. Sr 2 Ge 2 Se 5 ( P 2 1 / n , a =8.445(2) Å, b =12.302 Å, c =9.179 Å, β =93.75(3)°, Z =4) contains [Ge 4 Se 10 ] 8− ions with homonuclear Ge−Ge bonds ( d Ge−Ge =2.432 Å), which may be described as two ethane‐like Se 3 Ge−GeSeSe 2/2 fragments sharing two selenium atoms. Ba 2 Ge 2 Se 5 ( Pnma , a =12.594(3) Å, b =9.174(2) Å, c =9.160(2) Å, Z =4) contains [Ge 2 Se 5 ] 4− anions built up by two edge‐sharing GeSe 4 tetrahedra, in which one terminal Se atom is replaced by a lone pair from the divalent germanium atom. The alkaline earth cations are arranged between the complex anions, each coordinated by eight or nine selenium atoms. Ba 2 Ge 2 Se 5 is a mixed‐valence compound with Ge II and Ge IV coexisting within the same anion. Sr 2 Ge 2 Se 5 contains exclusively Ge III . These compounds possess electronic formulations that correspond to (Sr 2+ ) 2 (Ge 3+ ) 2 (Se 2− ) 5 and (Ba 2+ ) 2 Ge 2+ Ge 4+ (Se 2− ) 5 . Calculations of the electron localization function (ELF) reveal clearly both the lone pair on Ge II in Ba 2 Ge 2 Se 5 and the covalent Ge−Ge bond in Sr 2 Ge 2 Se 5 . Analysis of the ELF topologies shows that the Ge III −Se and Ge IV −Se covalent bonds are almost identical, whereas the Ge II −Se interactions are weaker and more ionic in character.