Crystallographic isomorphism (S,Tl) in the structure of TlHg6S4Br5

Crystallographic analysis of the known structure of TlHg6S4Br5 reveals that the Tl+ cation occupies the S2-site, centering the cubic Br subcells in the unit cell. The analysis shows that Tl is located in one sublattice with Br and S anions, and the Hg cationic sublattice, which has a relatively small size and large amount of vacant sites, is coordinated with the anionic one due to the selective site occupation in the former. An algorithm is considered for calculating the compositions with a given proportion of large monovalent cations substituting for S.