Single-crystal X-ray study of Ba2Cu2Te 4O11Br2 and its incommensurately modulated superstructure companion

Rie Fredrickson Takagi, Mats Johnsson, Sven Lidin

Research output: Contribution to journalArticlepeer-review

Abstract

Compounds containing lone-pair elements such as TeIV are very interesting from the structural point of view, as the lone-pair nonbonding regions create low-dimensional geometrical arrangements. We have synthesized two new compounds with these features - Ba2Cu2Te 4O11Br2 (I) and Ba2Cu 2Te4O11-δ(OH)Br 2 (II, δ ≈ 0.57) - as members of the AE-M-Te-O-X (AE = alkaline-earth metal, M = transition metal, X = halide) family of compounds by solid-state reactions. Preliminary single-crystal X-ray analysis indicated that compound I crystallizes in the orthorhombic system, but attempts at refinement proved unsatisfactory. Closer inspection of the reciprocal lattice revealed systematic, non-crystallographic absences that indicate twinning. The structure is in fact triclinic, space group C1̄ (equivalent to P1̄), with unit cell parameters (at 120 K) of a= 10.9027(9), b = 15.0864(7), c = 9.379(2) Å, β=106.8947°. It is layered and built from [TeO3E] tetrahedra, [TeO3+1E] trigonal bipyramids (where E is the lone pair of TeIV), [CuO4] squares and irregular [BaO 10Br] polyhedra. The crystal structure of II shows the same basic structure as I but contains additional oxygen, probably in the form of OH groups. The presence of satellites reveals that ordering on this O site creates an incommensurate modulation, primarily affecting Br and Te. The modulated structure of II was solved in the triclinic superspace group X1̄(αβγ)0 with the vector q ≈ 1/16 c*.

Original languageEnglish
Pages (from-to)3434-3441
Number of pages8
JournalChemistry - A European Journal
Volume14
Issue number11
DOIs
Publication statusPublished - 2008 Apr 7
Externally publishedYes

Free keywords

  • Alkaline earth metals
  • Layered compounds
  • Solid-state reactions
  • Structure elucidation
  • Tellurium

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