K4Ti3Te9 - A New Pseudo One-Dimensional Polyanionic Alkali Chalcogenometallate(IV)

Lustrous black needle shaped single crystals of K4Ti3Te9 were obtained by reacting K2Te with the corresponding elemental components at 1000 ◦C. K4Ti3Te9 is monoclinic, mP64, s. g. P21/c (No. 14), Z = 4 with a = 9.052(2), b = 8.088(1), c = 29.465(9) ° A, β= 92.35(1)◦. The crystal structure was determined from diffractometer data and refined to a conventional R value of 0.035 (2840 Fo’s, 146 variables). The compound contains undulating polyanionic chains built up by severely distorted TiTe6 octahedra sharing opposite faces which run parallel to [100] and are arranged in a hexagonal rod packing. The translation period comprises three octahedra. The most striking feature of this compound is the formation of two ditelluride groups per formula unit with unusually long Te-Te distances of 2.960(2) and 3.025(2) ° A, respectively. All other Te-Te distances start at 3.2 ° A. The nearest homonuclear neighbours of the two pairs are at 3.215(2) and 3.333(2) ° A apart. Ti-Te bond lengths range from 2.700(3) to 2.841(3) ° A with an average value of 2.772(4) ° A for all three crystallographically independent titanium atoms. The alkali cations are irregularly coordinated by 7 to 9 tellurium atoms.