Hafnium germanium telluride

The title hafnium germanium telluride, HfGeTe4, has been synthesized by the use of a halide flux and structurally characterized by X-ray diffraction. HfGeTe4 is isostructural with stoichiometric ZrGeTe4 and the Hf site in this compound is also fully occupied. The crystal structure of HfGeTe4 adopts a two-dimensional layered structure, each layer being composed of two unique one-dimensional chains of face-sharing Hf-centered bicapped trigonal prisms and corner-sharing Ge-centered tetrahedra. These layers stack on top of each other to complete the three-dimensional structure with undulating van der Waals gaps.

The title hafnium germanium telluride, HfGeTe 4 , has been synthesized by the use of a halide flux and structurally characterized by X-ray diffraction. HfGeTe 4 is isostructural with stoichiometric ZrGeTe 4 and the Hf site in this compound is also fully occupied. The crystal structure of HfGeTe 4 adopts a two-dimensional layered structure, each layer being composed of two unique one-dimensional chains of facesharing Hf-centered bicapped trigonal prisms and cornersharing Ge-centered tetrahedra. These layers stack on top of each other to complete the three-dimensional structure with undulating van der Waals gaps.

Structure Reports Online
ZrGeTe 4 (Lee et al., 2007) and the detailed descriptions of this structural type have been given previously.
The Hf atom is surrounded by six Te atoms in a trigonal prismatic manner. The vertices of two base sides of the prism are composed of six Te atoms. Atoms Te1, Te2, and Te3 form a triangle that is isosceles and the short Te1-Te2 distance (2.739 (1) Å) is typical of (Te-Te) 2pair (Furuseth et al., 1973). An additional Te4 and Ge atoms cap two of the rectangular faces of the trigonal prism to complete the bicapped trigonal prismatic coordination. These trigonal prisms share their triangular faces to form an infinite chain, ∞ 1 [HfGeTe 4 ] along the a axis. The Ge atom is surrounded by three Te and one Hf atoms in distorted tetrahedral fashion. These tetrahedra share their corners through the Te4 atom to form an infinite chain.
These bicapped trigonal prismatic and the tetrahedral chains are fused through Hf-Ge bonds to form a double chain and finally these chains are linked along the c axis to complete the two-dimensional layer. These layers then stack on top of each other to form the three-dimensional structure with undulating van der Waals gaps shown in Fig. 1.

Experimental
HfGeTe 4 was prepared from a reaction of Hf(CERAC 99.8%), Ge(CERAC 99.999%), and Te(CERAC 99.95%) in an elemental ratio of 1:1:4 in the presence of KCl(Aldrich 99.99%) as flux. The mass ratio of reactants and flux was 1:3. The starting materials were placed in a fused-silica tube. The tube was evacuated to 10 -3 Torr, sealed, and heated to 973 K at a rate of 15 K/hr, where it was kept for 72 hrs. The tube was cooled at a rate of 10 K/hr to 373 K and the furnace was shut off. Air-and water-stable metallic shiny needle-shaped crystals were isolated after the flux was removed with water. Qualitative analysis of the crystals with an EDAX-equipped scanning electron microscope indicated the presence of Hf, Ge, and Te. No other element was detected.

Refinement
Refinement with the positional parameters taken from the ZrGeTe 4 structure (Lee et al., 2007) gave the value of the Flack parameter (Flack, 1983) of x=0.96 (4) (wR2=0.128), which suggests that the absolute structure should be incorrect. Refinement of the inverse structure which is in agreement with the selected setting of this work leads to x=-0.02 (6) and significantly better reliability factor (wR2=0.054). The structure was standardized by means of the program STRUCTURE TIDY (Gelato supplementary materials sup-2 & Parthé, 1987). The nonstoichiometry of the Hf site in the title compound was checked by refining the occupancy and anisotropic displacement parameters of Hf while those of the other atoms were fixed. With the nonstoichiometric model, both parameter were not changed significantly and the residuals (wR2, R1 indices) remained the same. The highest peak(1.55 e/Å -3 ) and the deepest hole (-2.00 e/ Å -3 ) are 0.98 Å and 0.78 Å from the atom Hf, respectively.    (3) Te4 v -Ge-Hf iv 123.85 (4)