A Structural Approach to the Strength Evaluation of Linear Chalcogen Bonds

The experimental structural features of chalcogen bonding (ChB) interactions in over 34,000 linear fragments R–Ch⋯A (Ch = S, Se, Te; R = C, N, O, S, Se, Te; A = N, O, S, Se, Te, F, Cl, Br, I) were analyzed. The bond distances d(R–Ch) and the interaction distances d(Ch⋯A) were investigated, and the functions δ(R–Ch) and δ(Ch⋯A) were introduced to compare the structural data of R–Ch⋯A fragments involving different Ch atoms. The functions δ(R−Ch) and δ(Ch⋯A) were calculated by normalizing the differences between the relevant bond d(R–Ch) and ChB interaction d(Ch⋯A) distances with respect to the sum of the relevant covalent (r(cov)R + r(cov)Ch) and the van der Waals (vdW) radii (r(vdW)Ch + r(vdW)A), respectively. A systematic comparison is presented, highlighting the role of the chalcogen involved, the role of the R atoms covalently bonded to the Ch, and the role of the A species playing the role of chalcogen bond acceptor. Based on the results obtained, an innovative approach is proposed for the evaluation and categorization of the ChB strength based on structural data.