Noticeable characteristics of conventional and nonconventional hydrogen bonds in the binary systems of chalcogenoaldehyde and chalcogenocarboxylic acid derivatives.

Forty-eight stable structures of complexes formed between XCHZ and RCZOH (with X = H, F; R = H, F, Cl, Br, CH, NH; Z = O, S, Se, Te) were comprehensively investigated. It was found that the HZ-RZ complexes were more stable than the FZ-RZ ones, and their stability tendency decreased in the following order of Z: O > S > Se > Te. A predominant role of the electrostatic component was observed in XO-RO, while an outstanding contribution of the induction term was estimated in XS-RS, XSe-RSe, and XTe-RTe. A pivotal role of O compared to S, Se, and Te for improving the strength and characteristics of nonconventional C -H⋯O/S/Se/Te hydrogen bonds was proposed. The O-H⋯Z hydrogen bonds were much more stable than the nonconventional C -H⋯Z hydrogen bonds. Following complexation, the stretching frequency for C -H involving nonconventional C -H⋯Z hydrogen bonds gradually turned from the blue shift to red shift when one O of >C[double bond, length as m-dash]O in XCHO and RCOOH was substituted by S, Se, and Te, with R varying from the electron-withdrawing to electron-donating groups. A very large red-shift of the O-H⋯Z hydrogen bonds up to -535.4 cm and a C -H blue-shift of the nonconventional C -H⋯O hydrogen bonds reaching 86.9 cm were observed in this work. It was noted that the considerable decrease in the intramolecular electron density transfer to the *(C -H) orbitals significantly impacted on the blue-shift of the C -H bonds involving hydrogen bonds.