Structural and electronic properties of K2Ni3S4, a pseudo-two dimensional compound with a honeycomb-like arrangement

Air sensitive single crystals of K2Ni3S4 have been synthesized by reaction of 1Ni,2K(2)S and 4S in an evacuated silica tube at 750 degrees C for 6 days. The structure was solved in the Fddd space group with a = 5.723(2) Angstrom, b = 10.040(3) Angstrom and c = 26.059(7) Angstrom. The refinement led to R(F) = 0.038 (R(wF), = 0.045) for 23 variables and 392 reflections. The crystal structure can be described along the c-axis as the succession of [Ni,S-4(2-)] infinite layers separated by two alkali metal cation slabs. In the [Ni3S42-] layers, the nickel atoms are in sulfur square planar coordination. The (NiS4) square planes are linked together by edge sharing in such a way as to define a honeycomb network. Despite the occurrence of short S ... S contacts perpendicular to the slabs, electrical measurements and tight-binding band structure calculations suggest the classical overall charge balance (K2Ni3S4-II)-Ni-I-S-II.