Redetermination of Ba2CdTe3 from single-crystal X-ray data

The previous structure determination of the title compound, dibarium tritelluridocadmate, was based on powder X-ray diffraction data [Wang & DiSalvo (1999 ▶). J. Solid State Chem. 148, 464–467]. In the current redetermination from single-crystal X-ray data, all atoms were refined with anisotropic displacement parameters. The previous structure report is generally confirmed, but with some differences in bond lengths. Ba2CdTe3 is isotypic with Ba2 MX 3 (M = Mn, Cd; X = S, Se) and features 1 ∞[CdTe2/2Te2/1]4− chains of corner-sharing CdTe4 tetrahedra running parallel [010]. The two Ba2+ cations are located between the chains, both within distorted monocapped trigonal–prismatic coordination polyhedra. All atoms in the structure are located on a mirror plane.

The previous structure determination of the title compound, dibarium tritelluridocadmate, was based on powder X-ray diffraction data [Wang & DiSalvo (1999). J. Solid State Chem. 148,[464][465][466][467]. In the current redetermination from singlecrystal X-ray data, all atoms were refined with anisotropic displacement parameters. The previous structure report is generally confirmed, but with some differences in bond lengths. Ba 2 CdTe 3 is isotypic with Ba 2 MX 3 (M = Mn, Cd; X = S, Se) and features 1 1 [CdTe 2/2 Te 2/1 ] 4À chains of cornersharing CdTe 4 tetrahedra running parallel [010]. The two Ba 2+ cations are located between the chains, both within distorted monocapped trigonal-prismatic coordination polyhedra. All atoms in the structure are located on a mirror plane.
In comparison with the previous structure model on basis of powder X-ray data (Wang & DiSalvo, 1999), the most important improvement of the current redetermination is reflected in the higher precision of the atomic coordinates and the use of anisotropic displacemenet parameters for all atoms. Although the coordination spheres of Cd and the two Ba atoms can still be described as a distorted CdTe 4 tetrahedron and two distorted monocapped trigonal BaTe 7 prisms, respectively, the results of the redetermination indicate some differences in terms of Cd-Te and Ba-Te bond lengths (mean σ for the bond length of the powder model in the range 0.003 Å; 0.0006 for the current model). For example, the longest Ba-Te bonds are 3.6722 (8) and 3.6796 (8) Å for Ba1 and Ba2. The previous powder study revealed distances of 3.638 (5) and 3.500 (5) Å, respectively.

Experimental
The title compound was synthesized through a high temperature metal flux reaction. All starting elements were handled inside an Argon-filled glove box with controlled oxygen and moisture levels below 0.1 p.p.m.. The reaction conditions were optimized as follows: Ba, Cd, Te and Bi in a molar ratio of 2:1:3:10 were loaded in an alumina crucible, which were subsequently flame-sealed in a fused silica tube. The reactants were heated quickly to 973 K and allowed to dwell at this temperature for 20 h. After a slow cooling process down to 773 K at a rate of 5 K/h and the removal of the Bi flux by centrifugation, high-quality single crystals of Ba 2 CdTe 3 were obtained.

Refinement
The full occupancies for all sites were verified by freeing the site occupation factor for an individual atom, while other remaining parameters were kept fixed. This proved that all positions are fully occupied with corresponding deviations from full occupancy within 3σ. The residual electron densities show a maximum peak of 1.44 e/Å 3 and a minimum hole of -1.27 e/Å 3 , which are 0.86 and 0.81 Å from Te3 and Te2, respectively.

Figure 1
View of the structure of Ba 2 CdTe 3 along the b-axis. The barium, cadmium and tellurium atoms are plotted as purple, green and red ellipsoids, respectively. Ellipsoids are drawn at the 90% probability level. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.