CONTRIBUTIONS TO THE CRYSTAL-CHEMISTRY OF THALLIUM SULFOSALTS .2. TLSB3S5 - THE MISSING LINK OF THE LILLIANITE HOMOLOGOUS SERIES

TlSb3S5, known from the synthetic studies of the Tl2S-Sb2S3 phase syst em and the structure determination by GOSTOJIC, et al. (1982), represe nts the first known (3,3) homologue of the lillianite homologous serie s. With only monovalent and trivalent cations present, this compound a dds a new element to the spectrum of known lillianite compositions. Th e general chemical formula for such cases can be written as M+(N-1)/2M 3+(N+3)/2SN+2, where N represents the order of the homologue. In the c ase of TlSb3S5 (space group P2(1)/c) the departure from the ideal symm etry for lillianite homologues (Bbmm) is caused by ordering of short a nd long Sb - S bonds in the PbS-like slabs of the structure. This orde ring is based on ''crankshaft chains'' of short bonds formed in connec tion with the trapezoidal deformation of ideal PbS-like coordination p olyhedra and formation of the tightly-bonded double layers. In the pap er, these features are compared to the similar ones in Pb - (Sb,Ag) ho mologues of the lillianite series, as well as in TlSb5S8 that belongs to the sartorite homologous series. In all these cases, the specific s hort-bond arrangements are caused by the accommodation of tone electro n pairs of the atoms inside the PbS-like slabs of the structure.