Investigations On Structures And Stability Of Boron-Rich B-H And B-O Binary Clusters

Cluster is a new type of materials between microscopic particles and macroscopic solid matters. It is a transition state from the microscopic to macroscopic and reflects the initial state of condensed matter. With the rapid development of computer technology and the constant improvement of quantum chemistry, computational chemistry is widely used in structure prediction and propertity ananlysis of novel clusters. It becomes a new way to investigate the clusters. The design and study of boron clusters has been attracted considerable attention in recent years. A large number of the boron hydride clusters, which boron atoms are less or equal to hydrogen atoms, have been reported in many literatures, but the understanding about boron-rich boron hydride clusters were rare. At the same time, its rule of structural changes and utility value are still uncertain. Based on density functional theory, wave function theory and H/BO isolobal analogy, a systemic theoretical investigation on their structures and properties of the new boron-rich hydride clusters B19Hn0/-(n=0-2,4) and corresponding boron-oxyen cluster Bi9(BO)4-has been performed in this thesis. The main contents and conclusions of this paper are as follows:1. The results of systemic DFT and ab initio method showed that PBEO and TPSSh had a very close relative energy, but displayed a little difference with B3LYP calculations. Further precision energy calculation CCSD(T) confirmed that PBEO and TPSSh were more suitable for studying the boron-rich hydride clusters B19Hn0/-(n=0-2,4).2. Based on bare boron cluster B190/-, we searched for the global mininum of B29Hn0/-(n2=1,2) using two ways:programs and manual building. What’s more, the structural optimizations and vibarational analyses were performed using the hybrid density functional theory (DFT) methods of B3LYP、X3LYP、PBEO and TPSSh. At last, the low energy isomers of B19Hn0/-(n=1,2) were determined and their structures and properties were discussed in this paper.3. In neutral boron clusters B19Hn(n=0-2), the most stable structure of boron skeleton exhibited a small change from B19 to B19H. When the B19H was hydrogenated to B19H2, its boron skeleton had a large deformation. The boron skeleton of original stable structure became second. For anion boron hydride clusters B19Hn-(n=0-2), the structure of boron framework from the second bare boron did not change much.4. The possibility of hydride generation about B19Hn0/-(n=1,2) in the view of thermodynamics was analyzed. Compared with B19H to B19H2, the results revealed that it was more easily from B19 to B19H for the neutral boron clusters B19Hn(n=0-2). On the contrary, in anion boron hydride clusters B19Hn0/-(n=0-2), B19H2- was easier generated than B19H-.5. The UV-Vis spectra of the neutral boron-rich hydride clusters B19Hn(n=0-2) were simulated. In the UV-Vis spectra, it was observed that the spectra had some red shift from B19(Cs,2A’) to B19H(C1,1A) and blue shift from B19H(C1,1A) to B19H2(Cs,2A"). In additon, the electron detachment energies of anions were predicted and the photoelectron spectrum (PES) of B19H-(Cs,2A’) and B19H2-(Cs,2A-) were also simulated in theory.6. There was a little effect on the boron skeleton when bare boron B19-was hydrogenated to B19H4-. Their delocalized π orbitals almost did not change. Based on the thermodynamic principle, there was less chance that the bare boron B19- was hydrogenated to B19H4- directly.7. Searching for the global minimum of B19H4-, many tortuous planar double-chain structures were found. Thus, we suspected that the long double-chain structures became unstable with the increase of born atoms and might fold various regular polygons, which were similar to the cycloolefins in hydrocarbons. Thereby, a new relationship between boron hydride clusters and hydrocarbons would be established.8. According to the H/BO isolobal analogy, the boron-oxyen cluster B19(BO)4- corresponding boron-rich hydride clusters B19H4- was also discussed. From the analysis of bond length, it was indicated that BO group formed a σ bond with boron skeleton., The number of delocalized π orbitals in the B19(BO)4- was more than B19H4". It was proved that the boronyl(B=O) had a strong binding, indirectly.