Synthesis and crystal structure of Pb₃[IO₃]₂Cl₄, a representative of a new iodate-chloride class of compounds

Abstract

Compound Pb₃[IO₃]₂Cl₄ (space group C12/c1), representing a new iodate-chloride class of compounds, is synthesized under hydrothermal conditions. Only two minerals, schwartzembergite Pb₃[IO₃]Cl₂O(OH) and seeligerite Pb₃[IO₃]Cl₃O, the structures of which are unknown, are close in composition to this compound. In the iodate-chloride studied, the pentavalent iodine atom has an umbrella-like coordination, which is typical of iodates and consists of three O atoms at short distances and the fourth O atom at a longer distance. [IO₄]³⁻ tetrahedra share edges to form pairs. Lead ions form layers parallel to the ab plane. Along the c axis, these layers alternate with layers of iodate groups. Pb atoms are coordinated by O atoms of iodate groups and Cl atoms. The coordination sphere of the Pb(1) atom contains a free sector which is directed to more distant halogen atoms and possibly accommodates the lone electron pair.