Synthesis, crystal structure and vibrational properties of K_(0.38)TaPS_6 and Rb_(0.46)TaPS_6: chemical intercalation and deintercalation of the ternary TaPS_6 phase

摘要

The quaternary tantalum thiophosphates K_(0.38)TaPS_6 (1) and Rb_(0.46)TaPS_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 I4/acd (No. 142) with a = 15.920(2) A, c = 13.150(3) A, V = 3332.8(9) A~3 and Z = 16. Compound 2 crystallizes in the tetragonal space group I42d (No. 122) with a = 15.880(2) A, c = 13,156(2) A, V = 3317.7(5) A 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_6 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.