Direct Synthesis of Two-Dimensional SnSe and SnSe2 through Molecular Scale Preorganization

Two-dimensional tin monoselenide (SnSe) and tin diselenide (SnSe2) materials were efficiently produced by the thermolysis of molecular compounds based on a new class of seleno-ligands. Main group metal chalcogenides are of fundamental interest due to their layered structures, thickness-dependent modulation in electronic structure, and small effective mass, which make them attractive candidates for optoelectronic applications. We demonstrate here the synthesis of stable tin selenide precursors by in situ reductive bond cleavage in the dimeric diselenide ligand (SeC2H4N(Me)C2H4Se)2 in the presence of SnCl4. New molecular precursors [SnIV(SeC2H4N(Me)C2H4Se)2], [SnIVCl2(SeC2H4N-(Me)C2H4Se)], and [SnIV(SC2H4N(Me)C2H4S)(SeC2H4N(Me)C2H4Se)] were thoroughly characterized by multinuclear magnetic resonance studies and single-crystal X-ray diffraction analysis that revealed the Sn(IV) center to be octahedrally coordinated by two tridentate dianionic chelating ligands or trigonally pyramidally coordinated by one chelating ligand and two chlorido ligands. Preorganization of metal-selenium bonds in both compounds offered direct and reproducible synthetic access to two-dimensional tin chalcogenides (SnSe and SnSe2) via simple adjustment of the pyrolysis temperature. Additionally, SnSe2 and SnSxSe2-x particles could be successfully synthesized by microwave-assisted decomposition of the molecular precursors, which was unambiguously corroborated by both experimental and computational analyses that explained the formation of a selenium rich SnSxSe2-x phase from a single molecular precursor containing both Sn-Se and Sn-S bonds.