Fredrickson Takagi Rie, Johnsson Mats, Lidin Sven
Inorganic Chemistry, Stockholm University, Stockholm, Sweden.
Chemistry. 2008;14(11):3434-41. doi: 10.1002/chem.200701527.
Compounds containing lone-pair elements such as Te(IV) 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-Ba(2)Cu(2)Te(4)O(11)Br(2) (I) and Ba(2)Cu(2)Te(4)O(11-delta)(OH)(2delta)Br(2) (II, delta approximately equal to 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 C_1 (equivalent to P_1), with unit cell parameters (at 120 K) of a=10.9027(9), b=15.0864(7), c=9.379(2) A, beta=106.8947 degrees . It is layered and built from [TeO(3)E] tetrahedra, [TeO(3+1)E] trigonal bipyramids (where E is the lone pair of Te(IV)), [CuO(4)] squares and irregular [BaO(10)Br] 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 X$\bar 1$(alphabetagamma)0 with the vector q approximately equal to1/16 c*.
从结构角度来看，含有孤对元素（如Te(IV)）的化合物非常有趣，因为孤对非键合区域会形成低维几何排列。我们通过固态反应合成了两种具有这些特征的新化合物——Ba₂Cu₂Te₄O₁₁Br₂（I）和Ba₂Cu₂Te₄O₁₁₋ₓ(OH)₂ₓBr₂（II，x约等于0.57），它们属于AE-M-Te-O-X（AE = 碱土金属，M = 过渡金属，X = 卤化物）化合物家族。初步的单晶X射线分析表明化合物I结晶于正交晶系，但精修尝试并不令人满意。对倒易晶格的进一步检查发现了系统的、非晶体学的消光，这表明存在孪晶。实际上，该结构为三斜晶系，空间群为C₁（等同于P₁），晶胞参数（在120 K时）为a = 10.9027(9)，b = 15.0864(7)，c = 9.379(2) Å，β = 106.8947°。它是层状结构，由[TeO₃E]四面体、[TeO₃₊₁E]三角双锥（其中E是Te(IV)的孤对电子）、[CuO₄]正方形和不规则的[BaO₁₀Br]多面体构成。化合物II的晶体结构与I具有相同的基本结构，但含有额外的氧，可能以OH基团的形式存在。卫星峰的出现表明该O位点上的有序排列产生了非公度调制，主要影响Br和Te。化合物II的调制结构在三斜超空间群X$\bar 1$(αβγ)0中解析，矢量q约等于1/16 c*。
