New triclinic modification of lead iodate Pb(IO₃)₂: Synthesis and crystal structure

Abstract

A new triclinic modification of lead iodate Pb(IO₃)₂ (space group $C\bar 1$) is obtained under hydrothermal conditions. The crystal structure is determined without preliminary knowledge of the chemical formula. [IO₃]⁻ groups, which are characteristic of pentavalent iodine, have a typical umbrella-like configuration. The new phase has a more complex structure than the known orthorhombic modification. The arrangement of heavy Pb and I atoms follows a’ = a/3 pseudoperiodicity. In the layers of two types that form sheets parallel to the ab plane, Pb and I atoms have different coordinations. A polytypic nature of the new modification is responsible for the one-dimensional disordering along the a axis as well as different variants of layer alternation. It is possible to obtain crystals of acentric and polar derivatives of the centrosymmetric phase that will be promising for application.