Crystal structure of a new lamellar compound:

The lamellar compound Ag12In12PS3 was synthesized from the elements, except for In which was introduced through In2S3, and heated in evacuated silica tubes for 1 week at 700°C. Its crystal structure has been solved from 820 independent reflections and 18 parameters, the least-squares refinement yielding R = 0.028. The crystal symmetry is trigonal, space group P31c, with lattice constants a = 6.182(2) Å, c = 12.957(2) Å, V = 428.8(4) Å3, and Z = 4. The structure is built up with S[Ag13In13(P2)13]S slabs with an AB-type sulfur sequence. All the cations are distributed orderly in the a-b planes, each of them forming a triangular lattice. The structural features of the studied compound and those of the MPX3 (M = transition metal; X = S, Se) are compared. In particular, the silver thermal factor is found to be by far the largest (4.2 Å2) and to be very anisotropic. In addition, the driving force for the ordered distribution nature of the cations in the M(I)12M(III)12PS3 materials is discussed, together with the origin and nature of the cuts in the magnetic zigzagging chains in Ag12Cr12PS3.