Theoretical Studies Of Structures, Interactions And Properties In Some Hydrogen Bonds And Other Interaction Systems

Hydrogen bond is one of the most important interactions encountered in gas, liquid, and solid phases. It plays a crucial role in chemistry, physics and biology. The theoretical studies were performed on the structures, interactions and properties of some representative systems containing hydrogen bond and other interactions in this thesis. The results obtained on new structures and intermolecular interactions may be valuable for improving our understanding of the nature of intermolecular interaction, and enriching our knowledge of hydrogen bonds and other weak intermolecular interactions. There are five main aspects included in this thesis: (1) Ab initio study of the interaction hyperpolarizabilities of HCN-HF and HNC-HF complexes: The effects of the intermolecular interaction on dipole moment (μ), the mean (α) and anisotropy (?α) of the polarizability, the first and second hyperpolarizabilities (βand γrespectively) of HCN-HF and HNC-HF complexes have been calculated using finite-field approximate approach. The augmented correlation consistent basis sets x-aug-cc-pVXZ (x = s, d, t; X = D, T, Q) are employed to study the effects of the basis sets. With the d-aug-cc-pVTZ basis set, the electric properties are obtained at the coupled-cluster theory with single, double substitutions and perturbatively linked triple excitations CCSD(T) level. For the saturated molecules HF dimer, the βvalue is about 1/4 of the sum of two monomers. For the dimer HCN-HF containing π-bond, the βvalue is about 3/5 of the sum of two monomers. Similar to the organic systems, the existence of π-bond obviously enhances the first hyperpolarizability of the hydrogen-bonded dimer. The electron correlation effects for those electric properties are discussed. The value of each electric property calculated for HCN-HF is less than that for HNC-HF. The μ= 2.2918 a.u., α= 23.186 a.u., ?α=14.393 a.u., β= -6.03 a.u. and γ= 2553.4 a.u. for HCN-HF; μ= 2.3338 a.u., α= 24.383 a.u., ?α= 14.875 a.u., β= 7.60 a.u. and γ= 3049.3 a.u. for HNC-HF. The electric properties comes from the interaction parts are: μint = 0.3908 a.u.(17.1 %), αint = 0.181 a.u.(0.8 %), ?αint = 4.300 a.u.(29.9 %), βint = 6.02.(-99.8 % ) a.u. and γint = -492.0 a.u.(-19.3 %) for HCN-HF; μint = 0.4080 a.u.(17.5 %), αint = -0.084 a.u.(0.3 %), ?αint = 5.041 a.u.(33.9 %), βint = -7.20 a.u. (-94.7 % ) and γint = -931.7 a.u.(-30.6 %) for HNC-HF. The data above indicate significant effect of intermolecular interaction on the electric properties. The estimated electron correlation corrections are βcorr = 6.59 a.u., γcorr = 549.2 a.u. for HCN-HF and βcorr = -9.49 a.u., γcorr = 1056.5 a.u. for HNC-HF, which show large electron correlation effects in the electric properties of intermolecular interaction systems. (2) DFT (Density functional theory) study on structures and interaction hyperpolaribilities of NH3-HCl-(H2O) n (n = 0 ~ 4) clusters: The optimized structures of NH3-HCl-(H2O)n (n = 0 ~ 4) clusters have been obtained by B3LYP/d-aug-cc-PVDZ method. It is found that, in the structure for n = 1 proton transfer occurs. It is different from the results by smaller basis sets from the references [Chem. Phys. Lett. 1998, 287, 549, J. Phys. Chem. A 1998, 102, 5117, Chem. Phys. Lett. 1999, 313, 366], in which it is concluded that theproton transfer occurs in the NH3-HCl-(H2O)n (n = 0 ~ 4) clusters only for n=2. Using the optimized structures, the static dipole moments (μ), polarizabilities (α) and the first hyperpolarizabilities (β) of the clusters were calculated and the basis set effects on the physical properties (μ, αand β) were also studied with aug-cc-pVDZ, aug-cc-pVDZ+BF, aug-cc-pVTZ, d-aug-cc-pVDZ, t-aug-cc-pVDZ basis sets. The solvent effects on the electric properties of the NH3–HCl cluster are as follows: the μand βvalue reduce, and the αvalue increases with the number of water molecules. For the NH3-HCl, the properties (μ, αand β) all increase with the strength of proton transfer, which is related to the solvent effects of water molecules. Consequently, the proton transfer is brought forward as a new factor in influencing electric properties. (3) Proton transfer of the NH3-HCl by only one molecule catalyze: The smallest units with proton transfer occurring were studied. The proton transfer in NH3-HCl by only one molecule catalyze was studied using MP2 method with the large 6-311++G(2d,2p) basis set. The 18 structures are obtained for the smallest units, NH3-HCl-A trimers, for which the proton transfer maybe occurred. The final results show that the proton transfers have occurred in the 15 cyclic shape structures for A = H2SO4, H2SO3, HCOOH (a), HF, H2O2, HNO3, HNO2 (a), CH3OH, HCl, HNC, H2O, HNO2 (b), NH3, HCOOH (b) and HCHO, and not occurred in another 3 trimer structures for A = HCN, H2S and PH3. These results show that the proton transfer occurs from HCl to NH3 when catalyst molecule A (acidic, neutral or basic) not only as a proton donor strongly donates the proton to the Cl atom but as an acceptor strongly accepts the proton from the NH3 molecule in the cyclic H-bond structure. In this work, a proton circumfluence model is proposed to explain the mechanism of the proton transfer. We find that, for the trimer, when the sum of two hydrogen bond lengths (R = R1 + R2) is shorter than 5.0 ?, the molecule A has the ability of catalyzing the proton transfer. In addition, we also find that the interactionenergy Eint between NH3-HCl and A is nearly related to the extent (RH1-Cl) of proton transfer, that is, the interaction energy Eint increases with the proton transfer. (4) Ab Initio study on three hydrogen atoms interaction in the dimers BH3-HY (HY = HCCH, HCCF, HCN, HCl and HNC): The new geometrical structures of BH3-HCCH, BH3-FCCH BH3-HCN, BH3-HCl and BH3-HNC dimers were optimized at the MP2/aug-cc-pVTZ level, and the five dimers are the smallest structures including three hydrogen atoms interaction. Each structure of these dimers has C2v symmetry, except BH3-HCl. With aug-cc-pVTZ basis set the interaction energies Eint between three hydrogen atoms were calculated at seven levels of theory [HF, MP2, MP3, MP4(SDQ), MP4(SDTQ), CCSD and CCSD(T) ]. In the BH3-HY (HY = HCCH, HCCF, HCN, HCl and HNC) the largest interaction energy Eint is -1.73 kcal/mol (BH3-HNC, the corresponding RH1···H2 is the shortest, 2.207?), the smallest interaction energy Eint is -0.72 kcal/mol (BH3-HCCH, the corresponding RH1···H2 is the longest, 2.523?). The interaction between three hydrogen atoms is rather weak; it is a very weak intermolecular hydrogen-bonded interaction. (5) Single electron donor-acceptor bonds in the methyl radical complexes H3C-BH3, H3C-AlH3 and H3C-BF3: an ab initio study: A new kind of donor-acceptor complexes between methyl radical H3C and YZ3 (YZ3 = borane BH3, alane AlH3 and boron trifluoride BF3) molecules is predicted and intermolecular single electron donor-acceptor bonds in these methyl radical complexes are found. The optimized structures and harmonic vibrational frequencies (all real) of those methyl radical complexes are obtained by MP2/aug-cc-pVDZ approach. The single electron bond lengths of H3C-BH3, H3C-AlH3 and H3C-BF3 complexes are 2.181 ?, 2.594 ? and 2.823 ?, respectively. The intermolecular single electron donor-acceptor bond energies are calculated by the CCSD(T)/aug-cc-pVDZ method with Counterpoise...