Theoretical Studies On Some Transition-Metal And Hydrogen Bonding Complexes

Owing to the progress of chemistry theories and the computer technology, the computational chemistry is becoming more and more important. People can do computaional and modeling researches within high accuracy on the properties of chemical materials and dynamics of chemical reactions to gain more insights in comparison with the experimental results. On the other hand, reasonable designment of the structures, functions, and reactions of the chemical materials can be supplied through the high-level computations for the instructions in the experiments. In this dissertation, we study the chemical properties and reaction processes of transition metal complexes with ab initio methods, including geometry, electronic structure, chemical bond character, reaction processes and so on. Meanwhile, we also study the novel hydrogen bonding (HB) in the specific systems.In the first chapter, we introduce the basic concepts of ab initio methods and the theories used in our work. Firstly, we simply introduce the Hartree Fock theory and high level methods including electronic correlation energy, such as configuration interaction, multiple perturbation theory and coupled cluster theory. Secondly, we introduce the basic properties of density functional theory and its merits and weak points in computation. Then we introduce the quantum theory atoms in molecules (QTAIM) and natural bond orbital (NBO) theory including their basic concepts, properties and their application.In the second chapter, we study the stepwise protonation of dioxo manganese porphyrin. The first-principles density functional calculations combined with the NBO analyses are preformed to investigate the molecular structural and electronic properties of the complexes dioxo (1), oxo-hydroxo (2), oxo-aqua (3), and bishydroxo-manganese(V) porphyrin (4) in their ground states. The thermodynamic analyses for protonation processes, the natural atomic population analyses, and the characteristics of the bonding between Mn(V) and O atoms indicate that the O atom of the hydroxyl group in 2 is a stronger base site for proton attack. In chapter 3, we study the chemical reaction dynamics of propene over the V4O11-anion clusters by the first-principles calculations. We find that the main C3H6O product observed in the photocatalytic experiment can be identified as propylene oxide (PO). Acetone and propanal are the by-products. Another possible product C3H4O is assigned as acrolein. We propose the reaction mechanisms which involve oxygen, proton, and the negative charge transfer. An excellent cluster model of the heterogeneous catalysis is established for the activation of the molecular oxygen and the coadsorption of propene on vanadium oxide anion clusters, in which the higher selectivity to produce PO is demonstrated, moreover, the much higher conversion to PO is hopefully archived. We also discuss in detail about oxidation dynamics and reaction mechanisms of propene to acrolein on V4O11- anion cluster. This can give good instruction for the oxidation of propene to PO by controlling the production of the by-product acrolein.In chapter 4, the molecular structural and electronic properties of the compounds CH3CH2TiHx(x=1,2,3) and CH3CHTiHy(y=1,2), involvingβ-agostic interactions, are studied with the first-principles density functional calculations and NBO analyses. The bond type between C and Ti atoms influences bond angle∠CβCαTi, and the bond angle∠CβCαTi influences the bond length R(CpHp). For the compounds CH3CH2TiHx(x=1,2,3) and CH3CHTiHy(y=1,2), the length of R(CβHβ) have different influencing factors. In the compounds CH3CH2TiHx(x=1,2,3), hyperconjugative interaction E(2) from bonding orbital ofσCβHβto anti-bonding orbitals of the titanium atom (including nTi* andσTiH*) is predominated while rehybridization of Cβin the Cβ—Hβis minor; On the contrary, in the compounds CH3CHTiHy(y=1,2), the rehybridization is important. On the other hand, for CH3CH2TiHx(x=1,2,3), the different coordinates number does not influence the varying trend of R(CpHp), because they have the same orbital shape for nTi* in the hyperconjugative interactions. The same is for the compounds CH3CHTiHy(y=1,2) because of the similar rehybridization characteristics.In chapter 5, novel HB interaction between diborane andπ-orbitals and dihydrogen bonding (DHB) in the stabilization of the zwitterionic glycine are reported. In the first part, we found a new type of HB in the complexes C6H6…B2H6, C5H6…B2H6, and C4H4…B2H6 on the basis of QTAIM and NBO analyses combined with the high-level ab initio calculations. Compared with those of free monomer B2H6, the theoretical calculations predict red shifts for complexes C6H6…B2H6 and C5H6…B2H6, and blue shift for C4H4…B2H6; for the symmetric stretching vibrational modes of the bridging H-atoms, however, three blue shifts for C6H6…B2H6, C5H6…B2H6, and C4H4…B2H6, are predicted for the asymmetric stretching vibrational modes. To the best of our knowledge, no such blue-or red-shifted vibrations for these complexes have been studied prior to this work. Distinctly different from the local stretching vibrational mode of a single bond, the complexity and variety of the blue or red-shifted multiple-bond stretching vibrations will be a challenge toward a complete understanding of HB effects. In the second part, we study the stabilization of the four complexes between BH4- anions and glycine by ab initio methods. We find that BH4-anions can stabilize the zwitterionic glycine through DHB interaction. The dissociations of the complexes are endothermic and the DHBs are stronger than those previously reported. Both the experimental and theoretical efforts to explore the nature of the DHBs between amino acids and boron hydrides are making progress towards the understanding of the medical applications of boranes. On the other hand, the work presented herein enhances the feasibility of searching for the stable zwitterionic conformers of amino acids in gas-phase complexes.