Ti insertion in the MTe5 (M = Zr, Hf) structure type: Hf0.78Ti0.22Te5

The group 5 mixed-metal telluride, Hf0.78Ti0.22Te5 (hafnium titanium pentatelluride), is isostructural with the binary phases HfTe5 and ZrTe5 and forms a layered structure extending parallel to (010). The layers are made up from chains of bicapped metal-centered trigonal prisms and zigzag Te chains. The metal site (site symmetry m2m) is occupied by statistically disordered Hf [78.1 (5)%] and Ti [21.9 (5)%]. In addition to the regular Te—Te pair [2.7448 (13) Å] forming the short base of the equilateral triangle of the trigonal prism, an intermediate Te⋯Te separation [2.9129 (9) Å] is also found. The classical charge balance of the compound can be described as [M 4+][Te2−][Te2 2−][Te2 0] (M = Hf, Ti). The individual metal content can vary in different crystals, apparently forming a random substitutional solid solution (Hf1-xTix)Te5, with 0.15 ≤ x ≤ 0.22.

The group 5 mixed-metal telluride, Hf 0.78 Ti 0.22 Te 5 (hafnium titanium pentatelluride), is isostructural with the binary phases HfTe 5 and ZrTe 5 and forms a layered structure extending parallel to (010). The layers are made up from chains of bicapped metal-centered trigonal prisms and zigzag Te chains. The metal site (site symmetry m2m) is occupied by statistically disordered Hf
Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO; data reduction: RAPID-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND3 (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 1999).  (DiSalvo et al., 1981). The Ti analogue of this phase is desired to study the relationship between structure and properties. However, efforts to find TiTe 5 have not been successful despite numerous attempts (Furuseth et al., 1973). Indeed, no Ti analogue of the MTe 8 polyhedra found in MTe 5 (Furuseth et al., 1975) has been observed up to now. During attempts to synthesize new metal tellurides, we found the new Ti-containing mixed-metallic phase Hf 0.78 Ti 0.22 Te 5 .
The title compound is isostructural with HfTe 5 and ZrTe 5 . Detailed descriptions of this structural type have been reported previously (Furuseth et al., 1973). A view of the structure down the a axis is given in Fig. 1, which shows the Two Te3 (site symmetry m..) atoms outside the rectangular faces of the prism are connected to the neighboring Te3 to form the infinite zigzag Te chain. Finally, the MTe 5 layer is formed by the alternate linking of these chains (Fig. 2).
The structure shows a wide range of Te···Te interactions. In the prism, the Te2-Te2 pair (2.7448 (13) Å) forming the short base of the equilateral triangle exhibits a regular Te-Te bond, Te 2 2-(e.g. discussed by Pell & Ibers, 1996) the Hf: Ti ratio is 80: 20. The composition of the compound was determined by single-crystal X-ray diffraction.

Refinement
The statistically disordered nature of the M site in the title compound was checked by refining the anisotropic displacement parameters (ADPs). When the model was refined assuming HfTe 5 or TiTe 5 , the displacement parameters of the metal site were very large and small, respectively. In both cases the reliability indices were rather high (wR2 > 0.127).
In the refined mixed-metal model, the ADPs of the metal atoms are comparable with those of the other atoms and the residuals were reduced significantly (wR2 = 0.068). The remaining highest and lowest electron densities are found 0.81 and 0.77 Å from atom Te1.

Computing details
Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND3 (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 1999).    (14) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. 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 > 2σ(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.