Twenty stable geometrical structures of RCHSe∙∙∙nH2Z (R = H, F, Cl, Br, CH3; n = 1, 2; Z = O, S) were observed on potential surface energy. The strength of complexes increases in the order of substituted derivatives H < F < Cl < Br < CH3. The O–H∙∙∙O H‐bond is ca. four times stronger than the S–H∙∙∙S counterpart while Csp2–H∙∙∙S bond strength is about half of the Csp2–H∙∙∙O bond strength. This work reveals that a contraction of the Csp2–H bond length and an increase of its stretching frequency upon complexation are induced as replacing an H atom in H2CSe by CH3, and an inverse trend is observed in the case of F/Cl/Br halogen substitution. In addition, magnitude of Z–H bond elongation accompanied by a decrease of its stretching frequency increase in the order of substitution of F ~ Cl ~Br < H < CH3, following complexation. For RCHSe∙∙∙H2Z binary system, when H2O molecule is substituted by H2S, the Csp2–H blue‐shift in Csp2–H∙∙∙Z H‐bond is decreased, while the Z–H red‐shift in the Z–H∙∙∙Se H‐bond is increased, and an inverse change is detected in the case of ternary system. When adding one H2O molecule to the binary system, the Csp2–H blue‐shift of Csp2–H∙∙∙Z for H/CH3‐substituted derivatives is increased, while an increase in the Csp2–H red‐shift of Csp2–H∙∙∙Z H‐bond is observed for F/Cl/Br‐substituted derivatives.

Eight stable structures of nHCHO∙∙∙nH2O (n=1-3) were observed on potential surface energy at the MP2/aug-cc-pVDZ level of theory. All complexes were mainly stabilized by O-H∙∙∙O hydrogen bond and an additional contribution of Csp2-H∙∙∙O one. The larger positive cooperativity when adding H2O as compared to HCHO molecule is the most important factor in complex stabilization. The obtained results show that the O-H∙∙∙O is red-shifting hydrogen bond while Csp2-H∙∙∙O belongs to blue-shifting hydrogen bond. It is remarkable that an addition of H2O/HCHO into the binary system leads a Csp2-H bond contraction and an increase of its stretching frequency in Csp2-H∙∙∙O hydrogen bond, in which the larger marnitude of its blue-shifting enhancement is found as adding H2O molecule. This result is mainly governed by a decrease of electron density at σ*(Csp2-H) orbital and an increase in the s-character percentage of the Csp2 (Csp2-H).