Experimental and Theoretical Studies of Dimers Stabilized by Two Chalcogen Bonds in the Presence of a N···N Pnicogen Bond.

Abstract

The structure of the 5,6-dichloro-2,1,3-benzoselenadiazole homodimer, obtained by adding the ligand, 4,5-dichloro-o-phenylenediamine, to the methanolic solution of SeCl4, was determined by X-ray crystallography, augmented by Fourier transform infrared, Raman, and NMR spectroscopy. The binding motif involves a pair of Se···N chalcogen bonds, with a supplementary N···N pnicogen bond. Quantum calculations provide assessments of the strengths of the individual interactions as well as their contributing factors. All together, these three bonds compose a total interaction energy between 5.4 and 16.8 kcal/mol, with the larger chalcogen atom associated with the strongest interactions. Replacement of the Se atoms by S and Te analogues allows analysis of the dependence of these forces on the nature of the chalcogen atom. Calculations also measure the importance to the binding of the presence of a second N atom on each diazole unit as well as the substituted phenyl ring to which it is fused.