MP2-CM Studies On The Mechanism Of The "Concerted Breaking And Stepwise Making" Rearrangement Of Hydrogen-bond Networks In Water Hexamer

Study on?H₂O?₆ in gas phase has important significance for understanding the properties of water in liquid and solid phase,as well as uncovering the essential problems in the field of atmospheric physics and chemistry and life science.The insight of the rearrangement dynamics of the ever-changing and complex hydrogen-bond networks is the core issue for these studies.Recently,Richardson et al reported a new phenomenon of concerted breaking of two hydrogen-bonds in water hexamer prism.This research has caused widespread concern.The dynamic mechanism and the whole reaction pathways of the rearrangement of hydrogen-bond networks are important to understand the rearrangement process and to investigate other water clusters.However,the detailed process of the concerted breaking of two hydrogen-bonds at molecular level has not been reported.In the simulation of Al?H₂O?₆³⁺aqueous solution system,the explicit water molecules are added to simulate the short-range solvent effect.However,due to the large number of local minimum structures caused by the number and arrangement of the explicit water molecules,there is no uniform method for adding the explicit water molecules.Chiral substances are widely exist in environment and living organisms.The coordination of Al???and organic ligand molecules in the way of 1:2 or 1:3 can form different chiral complexes.At the molecular level,the information about the static structure and dynamic water exchange reaction of chiral complexes is important for understanding the similarity and chiral enantiomers of chiral compounds.In this dissertation,the key issues mentioned above are investigated.There are four chapters as follows:1.MP2-CM studies on the mechanism of the "Concerted breaking and stepwise making" rearrangement of hydrogen-bond networks in water hexamer.The "concerted breaking and stepwise making" dynamic reaction pathways for the rearrangement of hydrogen-bond networks in water hexamer prism are simulated by M???ller-Plesset second order perturbation theory?MP2?combined with cluster model?CM?at aug-cc-pVDZ level.Other three typical species including the chiral isomer of?H₂O?₆,?D2O?6 as well as?H218O?6 are also investigated.For the first time,the pathways for concerted hydrogen-bonds breaking reactions of a two-step mechanism are obtained.The first step is the concerted breaking of two hydrogen-bonds and making of one of the hydrogen-bonds,denoted as "-2+1" process,which is the rate-determining step.The second step is the making of another hydrogen-bond,denoted as "?1 "process.The whole reaction pathways combine a bifurcation with a double flip,corresponding to the permutation P =?A D??B F??C E??1 8 2 7??3 11??4 12??5 9??610?.The activation single-point energy calculated by CCSD?T?/aug-cc-pVDZ agrees well with the previous report.All the results of other eight possible rotation modes related to the rearrangement prove that the geared pathway of "-2+1"/"+1" processes is the most feasible pathway,and then,antigeared pathway is also feasible.2.Density functional theory studies on the solvent effects in Al?H₂O?₆³⁺Water-exchange reactions-The number and arrangement of outer-sphere water molecules.Density functional theory?DFT?calculations combined with cluster model?CM?are performed at B3LYP/6-311+G?d,p?level for investigating the solvent effects in Al?H₂O?₆³⁺ water-exchange reactions.The "One-by-one" method is proposed to obtain the most representative number and arrangement of explicit H₂O in the second hydration sphere.First,all the possible ways to locate one explicit H₂O in second sphere?Nm' = 1?based on the gas phase structure?Nm'=0?are examined,and the optimal pathway?with the lowest energy barrier?for Nm' = 1 is determined.Next,more explicit H₂O are added one by one until the inner-sphere is fully hydrogen bonded.The optimal pathways with Nm' = 0?7 are obtained finally.The structural and energetic parameters as well as the lifetimes of transition states are compared with the results obtained with "Independent-minimum" method and "Independent-average" method,and all three methods show that the pathway with Nm' = 6 may be representative.Our results give a new idea for finding the representative pathway for water-exchange reactions in other hydrated metal ion systems.3.Density functional theory studies on the properties of aluminium-oxalate and aluminium-maltolate chiral complexes.Density functional theory?DFT?calculations combined with cluster model?CM?are performed at B3LYP/6-311+G?d,p?level for investigating the aluminium-organic chiral complexes.Using both aluminium-oxalate and aluminium-maltolate complexes as examples,systematic studies on the static and dynamic properties of chiral aluminium-organic complexes are conducted:?1?The static configurations for one pair of aluminium-oxalate and three pairs of aluminium-maltolate chiral complexes are optimized to obtain their static structure parameters and energetic parameters,as well as spectroscopic properties,based on the gas phase-supermolecule-polarizable continuum model?GP-SM-PCM?;?2?Ten possible water-exchange reaction pathways are obtained with GP-SM?PCM?model,and the water-exchange rate constants are predicted;?3?The chirality inversion pathway for aluminium-oxalate is simulated with GP-SM?PCM?model using Berny algorithm,and the activation barrier is obtained.4.Investigation of the properties of chiral tris-oxalate-Al???complexes by the density functional theory.Density functional theory?DFT?combined with the cluster model?CM?and the polarizable continuum model?PCM?at the level of B3LYP/6-311+G?d,p?are used to obtain the static configurations of chiral tris-oxalate-Al???(Al?ox?₃^3-).The structural and energetic parameters,NMR,IR and VCD spectroscopy,frontier molecular orbitals and electrostatic potential characteristics of the chiral isomers are compared.The results show that the structural and energetic parameters as well as the NMR shifts are basically the same.The IR of chiral Al?ox?₃^3-is the same but their VCD are basically equal in intensity but opposite in sign?mirror images of each other?.However,there are obvious differences in the frontier molecular orbitals.The results give insight into the similarity in physicochemical properties and the enantiomeric characteristics on the Licrostructure of the chiral Al?ox?₃^3-.