Phase formation studies and crystal structure refinements in the MnII/TeIV/O/(H) system

Abstract

Systematic phase formation studies in the system MnII/TeIV/O/-(H) using either solid-state reactions between stoichiometric MnO:TeO2 mixtures or hydrothermal reactions under basic conditions led to crystal growth of two polymorphs (α-, γ-) of MnTeO3, Mn6Te5O16, Mn15(TeO3)14(OH)2 and Mn3(TeO3)2(OH)2. Although α-MnTeO3 and Mn6Te5O16 have been reported previously, crystal structure refinements were missing so far. Whereas α-MnTeO3 crystallizes in a unique structure (space group Pbca, Z=16), Mn6Te5O16 (Pnma, Z=4) is isotypic with its Co-homologue. The previously unknown phases γ-MnTeO3 (Pbca, Z=8), Mn15(TeO3)14(OH)2 ((Formula presented.), Z=3) and Mn3(TeO3)2(OH)2 (P63mc, Z=4) all have isotypic relationships, namely with ZnTeO3, Co15(TeO3)14F2 and M3(TeO3)2(OH)2 (M=Ni, Co), respectively. Common to all crystal structures of the five manganese(II) oxidotellurate(IV) phases is the presence of [MnO5] or [MnO6] polyhedra and isolated trigonal-pyramidal [TeO3] groups (except for one of the TeIV atoms in Mn6Te5O16 [TeO4] bisphenoids) as principal building units, which share corners and edges with the [MnO5/6] groups. The resulting three-dimensional frameworks are dominated by the influence of the stereochemically active 5 s2 electron lone pair situated at the TeIV atom, leading to the formation of channels or interstices. Quantitative comparisons between the corresponding isotypic crystal structures are given.