Titanium germanium antimonide, TiGeSb

TiGeSb adopts the PbFCl- or ZrSiS-type structure, with Ti atoms (4mm symmetry) centred within monocapped square antiprisms generated by the stacking of denser square nets of Ge atoms ( m2 symmetry) alternating with less dense square nets of Sb atoms (4mm symmetry).

TiGeSb adopts the PbFCl-or ZrSiS-type structure, with Ti atoms (4mm symmetry) centred within monocapped square antiprisms generated by the stacking of denser square nets of Ge atoms (4m2 symmetry) alternating with less dense square nets of Sb atoms (4mm symmetry).
The Natural Sciences and Engineering Research Council of Canada supported this work.

R. Lam and A. Mar
Comment After a report of the ternary antimonide ZrGeSb (Lam & Mar, 1997), the corresponding Ti and Hf analogues were later described in a conference proceeding, but full crystallographic details have not been forthcoming (Dashjav & Kleinke, 2002). The complete structure of TiGeSb, which is absent in the Ti-Ge-Sb phase diagram at 670 K (Kozlov & Pavlyuk, 2004) but was prepared here at 1273 K, is presented. Common to many equiatomic compounds of the formulation MAB (M = large transition-metal atom; A, B = main group atoms), TiGeSb adopts the PbFCl-or ZrSiS-type structure, among other names (Tremel & Hoffmann, 1987). Square nets of each type of atom, with the Ge net being twice as dense as the other two, are stacked along the c axis (Fig. 1). The Zr atoms are nine-coordinate, centred within monocapped square antiprisms. The Ge-Ge distances are 0.13 Å longer than the sum of the Pauling metallic radii (2.48 Å; Pauling, 1960), indicative of weak polyanionic bonding. The solid solutions ZrGe x Sb 1-x and HfGe x Sb 1-x (up to x = 0.2) form related orthorhombic PbCl 2 -type structures (Soheilnia et al., 2003), whereas TiGe x Sb 1-x adopts a NiAs-type structure (Kozlov & Pavlyuk, 2004).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(F 2 ) is used only for calculating Rfactors(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )