NEW TERNARY HAFNIUM TELLURIDES HF8TE6M (M=MN, FE) CONTAINING M-CENTERED TETRAKAIDECAHEDRA

The synthesis of the new ternary hafnium tellurides Hf8Te6M (M = Mn, Fe) is reported. The single-crystal structure of the Mn-containing compound has been determined. Hf8Te6Mn crystallizes in the orthorhombic space group Pmmn (No. 59) with lattice parameters a = 25.816 (4) angstrom, b = 3.7614 (6) angstrom, c = 7.605 (2) angstrom (Z = 2); the lattice parameters for the Fe analog show a slight shortening of the b axis: a = 25.815 (5) angstrom, b = 3.7309 (7) angstrom, c = 7.598 (1) angstrom. The Hf8Te6M structure possesses tricapped trigonal-prismatic Hf clusters centered by M. The trigonal prism dimensions are such that Hf-Hf contacts between triangular faces are long (3.761 angstrom) and the triangular faces themselves are isosceles (d(Hf-Hf): 2 x 3.160 angstrom, 3.565 angstrom). The Te atoms are 4-, 5-, and 6-coordinate with respect to Hf and serve to sheath the metal framework to produce large Te-lined cavities within the structure. Resistivity measurements between 77 and 250 K show Hf8Te6Mn to be metallic as predicted by band-structure calculations. The same calculations also indicate that Hf-M bonding is of overriding importance in stabilizing these metal-metal bonded structures. There is no significant Te-Te bonding.