Modular assembly and phase study of two- and three-dimensional porous tin(IV) selenides

Abstract

The work presented focuses attention on a detailed powder and single crystal XRD structure analysis of materials that emerge successively in the hydrothermal synthesis of tetramethylammonium-templated porous tin(IV) selenides. Four phases have been identified in this system and three of them, orthorhombic and monoclinic polymorphs of two-dimensional porous layered TMA ₂ Sn ₃ Se ₇ (TMA=tetramethylammonium) plus a novel tetragonal three-dimensional open-framework TMA ₂ Sn ₅ Se ₁₀ O have been structurally characterized by single crystal XRD. The order of appearance and interconversion of these materials is shown to follow Oswald's law of successive reactions, which is further supported by Connolly surface calculations. In addition the thermal stability of the orthorhombic TMA ₂ Sn ₃ Se ₇ phase is explored by in situ variable temperature PXRD under nitrogen and in vacuum, from which it is determined that the structural integrity of the framework is retained up to the point of template removal around 250 and 300 °C, respectively. The accumulated knowledge that has emerged from this study and earlier work allows a modular assembly pathway to be proposed that can rationalize the formation of the observed phases.