Structural overview and structure–property relationships of iodoplumbate and iodobismuthate

This review discusses the main structural features of the inorganic of the iodoplumbate and iodobismuthate moieties according to the aggregation and connections of the primary MI6 octahedron building unit. The cation effect, ligand effect and hetero metal–iodine bonding effect are summarized. The aggregation density of the inorganic moiety (ADIM) is an important structural parameter that is related to the solid-state properties. An empirical r value is thus defined as r = Σ(Nμn-I)/n, where Nμn-I means the number of n-fold-coordinated I atoms per building unit and n = 1–6; M/r value as M/r = M:r (M = the number of metal centers per building unit). The M/r value–anionic structure relationship and M/r value–band gap correlation are described. Several interesting optical, thermal and ferroelectric properties that are related to the dimensionality, composition, configuration, distortion, and bonding are discussed in detail.