Crystal structures of bis(2-methoxy-3-pyridyl) diselenide and bis(2-methoxy-3-pyridyl) ditelluride: an investigation by X-ray crystallography and DFT calculations

Abstract

We determined, using single-crystal X-ray diffraction, crystal structures of bis(2-methoxy-3-pyridyl) diselenide and bis(2-methoxy-3-pyridyl) ditelluride. The diselenide crystallizes in the monoclinic system (P21/c), while the ditelluride preferers the orthorhombic system (Pccn). In molecules of these compounds, the pyridine rings are almost perpendicular. Torsion angles (α) centered on the covalent bond between the two chalcogen atoms are 87.05(7)° and −96.1(1)° for the diselenide and ditelluride, respectively. In the crystal structure of the diselenide, the pyridine rings establish π•••π stacking interactions at centroid-centroid distances of 3.66 Å. The crystal structure of the ditelluride can be described as layers with a ladder type-shape stacked by π•••π interactions between the pyridine rings. Geometries of isolated molecules were optimized using the PBE0 density functional coupled with Grimme's D3 dispersion correction. The crystal structures of the diselenide and ditelluride were optimized at the same level of theory. The agreement between theoretical and experimental structures is excellent. Structurally similar diselenide and ditelluride molecules pack differently because of the stronger dispersion interaction between and pyridine rings and dichalcogenide bridges in the ditelluride in comparison to the diselenide. Our models indicate that a polymorph of the diselenide isostructural to the ditelluride is very close in the energy to the polymorph observed in the experiment while a polymorph of the ditelluride isostructural to the diselenide is less favorable energetically.