Carbon-13 nuclear magnetic resonance spin-lattice relaxation study of di-2-pyridyl dichalcogenides, Py2X2 (X = S, Se, Te)

Abstract Carbon-13 NMR relaxation times ( T 1 ) were determined for di(2-pyridyl) dichalcogenides, Py 2 X 2 (X = S, Se, Te). The experimental data were fitted to a model of anisotropic reorientation of a rigid body using the extended relaxation equation and assuming a diffusion model for reorientation and a dipole-dipole mechanism for relaxation. The fitting procedure was carried out for conformers with dihedral angles (CXXC) of approximately 90°, and angles of rotation of the pyridyl rings of 0,0; 180,0; and 180,180. All the conformers have the pyridyl rings in the planes formed by the CXX groups. The calculations produced a best fit for these conformers. According to these results, the di(2-pyridyl) dichalcogenides could be present in solution as a mixture of three rigid conformers characterized by the relative position of the two nitrogen atoms (syn-syn, syn-anti, anti-anti) with respect to the dichalcogen group.