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Mixed‐Valence Thallium(I, III) Bromides The Crystal Structure of α—Tl 2 Br 3
Author(s) -
Ackermann Rupprecht,
Hirschle Christian,
Rotter Heinz W.,
Thiele Gerhard
Publication year - 2002
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 - 10.1002/1521-3749(200212)628:12<2675::aid-zaac2675>3.0.co;2-4
Subject(s) - monoclinic crystal system , crystallography , thallium , octahedron , valence (chemistry) , crystal structure , chemistry , crystal twinning , materials science , inorganic chemistry , microstructure , organic chemistry
Thallium sesquibromide Tl 2 Br 3 is dimorphic. Scarlet coloured crystals of α‐Tl 2 Br 3 were obtained by reactions of aqueous solutions of TlBr 3 and Tl 2 SO 4 in agarose gel. In case of rapid crystallisation of hydrous TlBr 3 /TlBr solutions and from TlBr/TlBr 2 melts ß‐Tl 2 Br 3 is formed as scarlet coloured, extremely thin lamellae. The crystal structures of both forms are very similar and can be described as mixed‐valence thallium(I)‐hexabromothallates(III) Tl 3 [TlBr 6 ]. In the monoclinic unit cell of α‐Tl 3 [TlBr 6 ] (a = 26.763(7) Å; b = 15.311(6) Å; c = 27.375(6) Å; β = 108.63(2)°, Z = 32, space gr. C2/c) the 32 Tl III ‐cations are found in strongly distorted octahedral TlBr 6 groups. The 96 Tl I cations are surrounded either by four or six TlBr 6 groups with contacts to 8 or 9 Br neighbors. Crystals of β‐Tl 3 [TlBr 6 ] by contrast show almost hexagonal metrics (a = 13.124(4) Å, b = 13.130(4) Å, c = 25.550(7) Å, γ = 119.91(9)°, Z = 12, P2 1 /m). Refinements of the parameters revealed structural disorder of TlBr 6 units, possibly resulting from multiple twinning. Both structures are composed of Tl 2 [TlBr 6 ] — and Tl 4 [TlBr 6 ] + multilayers, which alternate parallel (001). The structural relationships of the complicated structures of α‐ and β‐Tl 3 [TlBr 6 ] to the three polymorphous forms of Tl 2 Cl 3 as well as to the structures of monoclinic hexachlorothallates M 3 TlCl 6 (M = K, Rb) and the cubic elpasolites are discussed.