Synthesis and crystal structure determination of three layered-type thiophosphate compounds KMP2S7 (M = Cr, V, In)

Three new thiophosphates KMP2S7 (M = Cr, V and In) have been synthesized and their structure determined from twinned crystals through X-ray diffraction experiments. The three compounds crystallize in the monoclinic system, space group C2 and Z = 2, with the following lattice parameters: KCrP2S7, a = 8.5146(6), b = 9.5848(6), c = 6.3052(5) Å, β = 97.981(8)°, V = 509.59(6) Å3; KInP2S7, a = 8.7506(9),b = 9.9685(9), c = 6.3151(8) Å, β = 98.906(13)°, V = 544.2(2) Å3; KVP2S7, a = 8.5553(6), b = 9.5765(5), c = 6.3323(4) Å, β = 98.630(8)°, V = 512.8(1) Å3. For each compound, the structure determination was carried out taking into account the two twin domain sets (rejecting only the partially overlapping reflections) down to R = 3.08%, R = 3.20%, and R = 3.08% (2σ level) for KCrP2S7, KInP2S7, and KVP2S7, respectively. The two-dimensional structures, built from bitetrahedral [P2S7] units sharing edges and corners with [MS6] octahedra, are isotypic to the structure of RbVP2S7, with the same nonharmonic behavior of the alkali metal.