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On Oxohalogeno Niobates(V) M 2 [Nb 3 O 5 X 7 ] ( M = NH 4 , K, Rb, Cs; X = Cl, Br) – New Members of a Compound Family with a Layered Structure
Author(s) -
Beck Johannes,
Bordinhão Jairo,
Kusterer Christian
Publication year - 2007
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.200600382
Subject(s) - orthorhombic crystal system , monoclinic crystal system , crystallography , alkali metal , lattice energy , crystallization , crystal structure , chemistry , ampoule , materials science , organic chemistry
The reaction of alkali chlorides M Cl with NbOCl 3 yields melts which on cooling solidify under crystallization. In the case of KCl / NbOCl 3 , the pink coloured regulus was investigated by powder‐XRD and shown to be biphasic, consisting of K[NbOCl 4 ] (primitive orthorhombic lattice, a = 13.467(2); b = 7.9362(8); c = 14.041(2) Å) and K 2 [NbOCl 5 ] ( F centred cubic lattice, a = 9.8291(2) Å). To a small amount vapour phase transport occurs and colourless crystals of M 2 [Nb 3 O 5 Cl 7 ] ( M = K, Rb, Cs) are deposited in the colder parts of evacuated glass tubes containing molten mixtures of M Cl and NbOCl 3 or M Cl, Nb 2 O 5 and NbCl 5 in a temperature gradient of 500 °C to 450 °C for some days. Green crystals of (NH 4 ) 2 [Nb 3 O 5 Br 7 ] are obtained as a by‐product in the reaction of NH 4 Br with NbOBr 3 in sealed ampoules at temperatures of 300 °C. All compounds are isotypic and belong to the M 2 [Nb 3 O 5 X 7 ] structure type of which (NH 4 ) 2 [Nb 3 O 5 Cl 7 ] was already known ( Schweda , 1997) (monoclinic, C 2/ c , Z = 4, (NH 4 ) 2 [Nb 3 O 5 Br 7 ] a = 17.8488(6), b = 8.8581(3), c = 11.3376(4) Å, β = 110.572(2)°; K 2 [Nb 3 O 5 Cl 7 ] a = 16.7346(3), b = 8.8558(2), c = 11.0623(3) Å, β = 112.661(1)°; Rb 2 [Nb 3 O 5 Cl 7 ] a = 16.794(14), b = 8.873(5), c = 11.032(8) Å, β = 111.33(6)°; Cs 2 [Nb 3 O 5 Cl 7 ] a = 17.233(6), b = 8.928(3), c = 11.092(3), β = 109.36(2)°). The structures consist of niobium‐centred NbO 3 Cl 3 and NbO 4 Cl 2 octahedra, which share common edges to form a two‐dimensional network of the composition ${\rm [(Nb_{3}O_{5}} X_{7})^{2-}]^{2}_{\infty}$ ( X = Cl, Br). These anionic layers are stacked with the cations located between them. The monovalent cations are coordinated exclusively by halogen atoms and have the coordination number ten in form of “edshammar polyhedra”.