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Mixed Valence Tungsten (IV, V) Compounds with Layered Structures (Part IV): Syntheses, Crystal Structures, and Conductivity of Bi X 2 [W 2 O 2 X 6 ] ( X = Cl, Br)
Author(s) -
Schieweling Marcel,
Daniels Jörg,
Beck Johannes
Publication year - 2012
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201200227
Subject(s) - tungsten , crystallography , monoclinic crystal system , triclinic crystal system , crystal structure , bismuth , valence (chemistry) , chemistry , conductivity , electrical resistivity and conductivity , tungsten compounds , metal , materials science , physics , organic chemistry , quantum mechanics
The reaction of metallic bismuth with either tungsten tetrachlorideoxide WOCl 4 at 650 K or tungsten tetrabromideoxide WOBr 4 at 670 K, respectively, leads to Bi X 2 [W 2 O 2 X 6 ] ( X = Cl, Br) as black, lustrous crystal needles. The crystal structure determinations (triclinic, P $\bar{1}$ ) show the two isotypic structures to be closely related to Hg 0.55 [W 2 O 2 Cl 6 ] with the presence of 1D‐polymeric W 2 O 2 X 6 double strands. Dinuclear [Bi 2 X 4 ] 2+ cations are embedded in the host structure via secondary W– X ··· Bi bonds. Unlike the other members of the M y [W 2 O 2 X 6 ] structure family, which crystallize monoclinic and show crystallographic equivalent tungsten atoms, Bi X 2 [W 2 O 2 X 6 ] has independent tungsten sites. Nevertheless, an assignment of an individual oxidation state to the tungsten atoms within the W 2 group (W–W 2.8321(4) Å for X = Cl, 2.8985(4) Å for X = Br) is not possible and a dynamic intervalent state W(IV, V) is assumed. Electrical conductivity measurements for BiCl 2 [W 2 O 2 Cl 6 ] show semi‐conductive behavior with a very small band gap of 70 meV and a high conductivity of around 0.5 Ω –1 cm –1 at temperatures above 220 K. A temperature dependence of the activation energy of charge transport is present and interpreted by the Varshni model.