Theoretical Studies On Structures And Properties Of Hydrogen Bond And Halogen Bond In Some Dimers

(1) The optimized structures of CH2O-HF, CH2O-H2O, CH2O-NH3, and CH2O-CH4.with all real frequencies were obtained by the MP2 level and four basis bets (6-311G(d,p), 6-31+G(d,p), 6-311++G(2d,2p), and 6-311++G(3df,3pd). The structures of CH2O-HF, CH2O-H2O, and CH2O-NH3 are cycle-shaped. This is because there is a larger bend of their σhydrogen bonds O???H-Y (Y= F, O, N). The results show that the larger bend of σhydrogen bond is caused by a secondary weak interaction. The secondary weak interaction is named π-type hydrogen bond in this paper, and The bend of σ-type H-bond O???H-Y (Y= F, O, N) is illustrated and interpreted by the attractive interaction of a chemically intuitive π-type hydrogen bond. The π-type hydrogen bond is the interaction between one of the H atoms of CH2O and lone pair(s) on the F atom in HF, the O atom in H2O, or the N atom in NH3. By contrast with π-type hydrogen bond in dimers saturated molecule, the π-type hydrogen bond is a new type in π-type hydrogen bond. For CH2O-CH4, because there is not a π-type hydrogen-bond to bend its linear hydrogen bond, the structure of CH2O-CH4 is a non-cyclic shaped. The interaction energy of hydrogen bonds and the π-type H-bond are calculated and discussed at the CCSD(T) /6-311++G(3df,3pd) level. (2) By the counterpoise-correlated potential energy surface method (interaction energy optimization), five structures of C2H4-nFn?HF (n=0, 1, 2) dimers with all real frequencies have been obtained at MP2/aug-cc-pVDZ level. The structure and π-Hydrogen bond of dimer has been changed by the influence of F substituent effect, obviously. By contrast with the π-Hydrogen bond of C2H4-HF, the π-Hydrogen bonds of C2H4-nFn?HF (n=1, 2) are elongated by F substituent effect. For C2H3F-HF, g-C2H2F2-HF, cis-C2H2F2-HF, the π-Hydrogen bonds are further deformed. These changes (elongate, shift and deformation) of π-Hydrogen bond mainly come from deformation of π-electron cloud of C=C bond. The densities of π-electron cloud have deviated or shifted slightly from the molecular vertical plane passing through C=C bond, so the π-Hydrogen bond is also sloped or shifted. The π-Hydrogen bond of C2H3F-HF, g-C2H2F2-HF, and cis-C2H2F2-HF are bent by the π-type H-bond in the dimers. The F substituent effect added the electron correlation contribution of interaction energy. Intermolecular interaction energies of the dimers are calculated to be -3.9 for C2H4-HF, -2.8 for C2H3F-HF, -2.1 for g-C2H2F2-HF, -1.6 for cis-C2H2F2-HF, -1.3 kcal/mol for trans-C2H2F2-HF, at CCSD (T)/aug-cc-pVDZ level. (3) The dimers C2H4-nFn-ClF (n=0, 1, 2) are proper model as investigating of π-halogen bond kind in the paper. Using the counterpoise-correlated potential energy surface method (interaction energy optimization), the C2V, C2, C1, Cs and Cs stationary structures of the...