Refinement of the crystal structure of dipotassium tricadmium(II) tetraselenide, K2Cd3Se4

Abstract

Cd3K2Se4, orthorhombic, Pnma (no. 62), a = 14.312(4) A, b = 10.604(3) A, c = 6.839(2) A, V = 1037.9 A, Z = 4, Rgt(F) = 0.027, wRref(F) = 0.065, T = 290 K. Source of material CdCl2 (0.020 g, 0.11mmol) andK2Se2 (0.078 g, 0.33mmol)were charged to a Pyrex tube with diameter of 9 mm under an argon atmosphere, and about 0.5 ml ethylenediamine was added as a solvent. While the solvent was being frozen, the Pyrex tube was evacuated (about 2.0 × 10 torr) and sealed with the use of a flame. The sealed tube was placed in a furnace and heated at 160 °C for 24 h, then cooled to room temperature. Yellow crystals were isolated and washed with diethyl ether several times (36 % yield, based on CdCl2 used). The compound is insoluble in water and common organic solvents. Discussion Ternary low-dimensional cadmium chalcogenides, A2Cd3Q4 (A = alkali metal; Q = S, Se, Te) were explored in particular to achieve the dimensional reduction in II-VI materials [1-2]. Dimensional reduction of CdQ by the incorporation of A2Q resembles size reduction of CdQ particles into the nanometer range [2]. Nanometer-sized CdQ materials have attracted extensive research efforts last two decades and are still garnering a lot of attention [3-5]. The title compound is the first example of A/Cd/Q (A = alkali metal; Q = S, Se, Te) ternary compounds to be prepared by a hydro (or solvo) thermal method. Until now, only the lattice parameters for K2Cd3Se4 were reported, no complete structure determination was made [1]. The title crystal structure is composed of two-dimensional anionic layers (Cd3Se4)n and charge-balancing cationsK, representing the same structure as the other analogues of A2Cd3Q4 (A = K, Q = S, Te; A = Rb, Q = S, Se) [1]. Other structurally characterized A2Cd3Q4 compounds are Rb2Cd3Te4 and Cs2Cd3Te4, which crystallize in K2Zn3O4 type and Cs2Zn3S4 type, respectively [6]. The (Cd3Se4)n layer spreads out along the crystallographic b and c axes, with the repeating unit of a Cd3Se4 cluster (figure, top). The Cd3Se4 cluster is geometrically shaped as a truncated cube with one corner missing and consists of three Cd(II)metal ions and four Semonoselenide ligands. In the truncated cube cluster, one Se atom could be regarded to be sitting on the apex and coordinating to the threeCdmetal atoms in the puckered 6-member ring Cd3Se3. Three-coordinated Cd atoms and two-coordinated Se atoms in the Cd3Se4 cluster are connected to Se andCd atoms of adjacent clusters to form a layered structure (figure, bottom). As a result, all Cd atoms are tetrahedrally coordinated and all Se atoms are triply coordinated. Tetrahedral coordination of Cd atoms is distorted as the ∠Se–Cd–Se angles are ranging from 95.8° to 140.3°, and trigonal pyramidal coordination of Se atoms is encountered with the ∠Cd–Se–Cd angles ranging from 73.6° to 108.1°. Z. Kristallogr. NCS 226 (2011) 157-158 / DOI 10.1524/ncrs.2011.0071 157 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: yellow plate, size 0.04 × 0.10 × 0.48 mm Wavelength: Mo K* radiation (0.7107 A) -: 208.42 cm−1 Diffractometer, scan mode: MacScience MXC3, '% 2!max: 55° N(hkl)measured, N(hkl)unique: 1207, 1207 Criterion for Iobs, N(hkl)gt: Iobs > 2 σ(Iobs), 1067 N(param)refined: 50 Programs: SHELXS-97, SHELXL-97 [7], ORTEP-3 [8] Table 1. Data collection and handling.