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

The work presented focuses attention on a detailed powder and single crysta l XRD structure analysis of materials that emerge successively in the hydro thermal synthesis of tetramethylammonium-templated porous tin(Iv) selenides . Four phases have been identified in this system and three of them, orthor hombic and monoclinic polymorphs of two-dimensional porous layered TMA,Sn,S e, (TMA = tetramethylammonium) plus a novel tetragonal three-dimensional op en-framework TMA(2)Sn(5)Se(10)O have been structurally characterized by sin gle crystal XRD. The order of appearance and interconversion of these mater ials is shown to follow Oswald's law of successive reactions, which is furt her supported by Connolly surface calculations. In addition the thermal sta bility of the orthorhombic TMA(2)Sn(3)Se(7) phase is explored by in situ va riable temperature PXRD under nitrogen and in vacuum, from which it is dete rmined that the structural integrity of the framework is retained up to the point of template removal around 250 and 300 degrees C, respectively. The accumulated knowledge that has emerged from this study and earlier work all ows a modular assembly pathway to be proposed that can rationalize the form ation of the observed phases.