Substituent Effect on Chalcogen Bonding in 5-Substituted Benzo[c][1,2,5]selenadiazoles and Their Copper(II) Complexes: Experimental and Theoretical Study

In parallel to the nature of the chalcogen atom (Ch) and nucleophile (Nu), the strength and directionality of chalcogen bonding (ChB) are also dependent on the electron donor or acceptor character of the functional group (R) at angle R-ChNu. Although Hammett's para-substituent constant (sigma(p)) can be used for the quantitative description of substituent effects, herein, we found that due to participation of the substituents in various types of intermolecular interactions, there is no linear relationship between the sigma(p) of the substituent in R (X = -CH3, -H, -F, -Cl, -Br, and -NO2) and the experimental SeN distance or angle N-SeN angle in 5-substituted benzo[c][1,2,5]selenadiazoles and their copper(II) complexes. Such a relationship is also not observed theoretically, which is rationalized by taking into consideration the formation of intramolecular hydrogen and chalcogen bonds in the Cu complexes. The chalcogen bonds have been analyzed using the quantum theory of "atoms in molecules" combined with the noncovalent interaction plot and energy decomposition analysis.