Synthesis, crystal structure and vibrational properties of K 0.38TaPS 6 and Rb 0.46TaPS 6: chemical intercalation and deintercalation of the ternary TaPS 6 phase

Abstract

The quaternary tantalum thiophosphates K 0.38TaPS 6 ( 1) and Rb 0.46TaPS 6 ( 2) were synthesized by reacting TaS 2 with an in situ formed melt of A 2S 3 (A = K, Rb), P 2S 5 and S. Both structures are related to the basic tunnel structures of the known ternary compounds TaPS 6 and Ta 4P 4S 29. Compound 1 crystallizes in the tetragonal space group I 4 1 / a c d (No. 142) with a = 15.920 ( 2 ) Å , c = 13.150 ( 3 ) Å , V = 3332.8 ( 9 ) Å 3 and Z = 16 . Compound 2 crystallizes in the tetragonal space group I 4 ¯ 2 d (No. 122) with a = 15.880 ( 2 ) Å , c = 13.156 ( 2 ) Å , V = 3317.7 ( 5 ) Å 3 and Z = 16 . The crystal structures are built up by bicapped biprismatic [Ta 2S 12] units and [PS 4] tetrahedra. Each Ta atom is surrounded by eight S atoms in a bicapped trigonal environment. Two TaS 8 polyhedra share a rectangular face to form the dimeric [Ta 2S 12] unit. The [Ta 2S 12] biprisms are linked by sharing common edges with four tetradentate [PS 4] groups yielding a three-dimensional network with large and small channels which are occupied by the alkali metal ions. The alkali metal atoms can be removed via a redox reaction with electron/ion transfer using I 2 in acetonitrile as oxidizing agent. The effect of the intercalated alkali metal cations onto the lattice parameters is small, but the electron transfer from the cations to the host material leads to a significant shortening of the Ta Ta distances within the [Ta 2S 12] biprismatic units.