A new family of rare earth – strontium tellurite chlorides, SrLn4(TeO3)4Cl6 (Ln = Ce, Nd, Sm): Synthesis, crystal structures, possible polytypism, and crystal-chemical relationships.

An interaction of LnOCl and TeO 2 (Ln ​= ​Ce, Nd, Sm) in molten SrCl 2 results in a new family of layered quinary compounds, SrLn 4 (TeO 3) 4 Cl 6. Their monoclinic structures (P 2/ c) correspond to a novel structure type, build up by the alternation of [M 2 Ln 3 (TeO 3) 4 ] layers (M ​= ​Ln 0.5 Sr 0.5) and double halide sheets. New compounds are characterized by the modular type of the structures, while the presence of the twinning indicates the possible stacking disorder and polytypic character. An accurate analysis indicates that crystal structures belong to the OD ("order-disorder") family of category III with one types of nonpolar OD layers and can be described by the same OD family groupoid. Possible maximal degree order polytypes have been predicted and crystal chemical relationships among the oxyhalides of rare earth and lone-pair cations are briefly discussed. New compounds SrLn 4 (TeO 3) 4 Cl 6 (Ln ​= ​Ce, Nd, Sm) are characterized by layered OD ("order-disorder") structures with the corresponding twinning and polytypism. [Display omitted] • Single crystals of SrLn 4 (TeO 3) 4 Cl 6 (Ln ​= ​Ce, Nd, Sm) were synthesized. • The polytypism and OD-structures can be observed for these compounds. • The general features of the crystal chemistry and related tellurites are discussed in detail. [ABSTRACT FROM AUTHOR]