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_covR + r_covCh) and the van der Waals (vdW) radii (r_vdWCh + r_vdWA), 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.