Theoretical Investigations On Structures And Properties Of B-O And B-Au Clusters

One of the main tasks of computational chemistry is to predict the structures and properties of novel clusters. Computational chemistry also provides new directions for synthetical chemistry and material science. The proposal of isolobal analogy by Hoffmann in 1981 has promoted the development of cluster chemistry since then. This thesis focuses on the isolobal analogies between-BO,-BS, Au atom and H atom based on intensive theoretical investigations on the binary boron oxide, boron sulfur, and boron gold clusters which are of great significance for the development of boron clusters.A systematic density functional theory and wave function theory investigation on the geometrical structure, electronic structure, bonding character and thermodynamic stabilities of B-O, B-S, B-Au and Al-Au clusters has been performed in this thesis. The adiabatic and vertical detachment energies of the concerned anions have been calculated to facilitate their future experimental characterizations. The main contents and results are as follows:1 Theoretical Investigations on Structures and Properties of Boron-rich Boron-Oxide clusters (B5O4-/0)A density functional theory and wave function theory investigation on the geometrical and electronic structures of B5O40/- clusters has been performed. B5O4- anion proves to possess a perfect tetrahedral ground state of Td B(BO)4- (1A1) analogous to BH4- with four equivalent-BO terminals around the B center, while B5O4 neutral favors a slightly off-planed Cs B(BO)4 (2A') which contains three-BO terminals and one-O-bridge. An intramolecular BO radical transfer occurs from Td B(BO)4 to Cs B(BO)4 when one electron is detached from the anion. The one-electron detachment energies of the B(BO)4- anion and the characteristic stretching vibrational frequencies of-B=O groups at about 2000 cm-1 have been calculated to facilitate future experimental characterization of these clusters. A neutral B(BO)4-Li+ ion-pair is formed when a countercation Li+ is incorporated. Tetrahedral B5O4- is a stable structure unit as evidence by the calculated structural parameters and dipole moment. Therefore, B5O4-, which behaves like a superatom, can be used as a building block to construct new solid state materials.2 Theoretical Investigations on Structures and Stabilities of Oxygen-rich Boron-Oxide clusters (B2O4-/0, B3O4-/0, B3O5-/0 and B3O6-/0)The structures and stabilities of the oxygen-rich B2O4-/0, B3O4-/0, B3O5-/0, and B3O6-/0 binary clusters have been investigated for the first time at both DFT-B3LYP and CCSD(T)//B3LYP levels. The ground-state structures of the anions and their neutrals appear to be much different, with the triangular BO3 unit, terminal-BO, and bridging-O-coexisting and competing with one another. The preference of BO3 planar triangles in O-rich microclusters agrees with the structural character of the glassy B2O3 which represents the most stable boron oxide in the bulk. The results obtained for O-rich boron clusters invite experimental confirmations.3 Theoretical Investigations on Structures and Stabilities of Boron-Sulfur clusters (B4S20/-/2- and B5S40/-)A density functional theory investigation on the geometrical and electronic properties of B4S20/-/2-(B2(BS)20/-/2-) and B5S40/- (B(BS)40/-) clusters has been performed in this work. Both the doublet B2(BS)2-([S=B-B(?)B-B=S]-) (D∞h,2Πu) and singlet B2(BS)22- ([S=B-B=B-B=S]2-) (S∞h,1Σg+) proved to have perfect linear ground-state structures containing a multiply bonded BB core (B(?)B or B=B) terminated with two BS groups, while Td B(BS)4- turned out to possess a perfect tetrahedral B center directly corrected to four BS groups, similar to the corresponding boron hydride molecules of D∞h B2H2-, D∞h B2H22-, and Td BH4-, respectively. B4S2 and B5S4 neutrals, however, appeared to be much different:they favor a planar fan-shaped C2v B4S2 (a di-S-bridged B4 rhombus) and a planar kite-like C2v B5S4 (a di-S-bridged B3 triangle bonded to two BS groups), respectively. One-electron detachment energies and symmetrical stretching vibrational frequencies are calculated for D∞h B2(BS)2- and Td B(BS)4- monoanions to facilitate their future characterizations. Neutral salts of B2(BS)2Li2 with a elusive B=B triple bond and B(BS)4Li containing a tetrahedral B- center are predicted possible to be targeted in future experiments.4 Theoretical Investigations on Structures and properties of Boron-Gold clusters (B2Aun-/0 (n=1,2,3,5)) and Aluminum-Gold clusters (Al2Aun-/0 (n=1,3,5))A systematic density functional theory and wave function theory investigation on the geometrical and electronic structures of the electron-deficient diboron aurides B2Aun-/0 (n=1,3,5) and their mixed analogues B2HmAun-(m+n=3,5) has been performed in this chapter. Ab initio theoretical evidences strongly suggest that bridging gold atoms exist in the ground states of C2v B2Au-(1A1), C2 B2Au3-(1A), C2v B2Au3(2B1), C2v B2Au5-(1A1), and Cs B2Au5(2A") which all prove to possess a B-Au-B three-center-two-electron (3c-2e) bond. For B2HmAun- (m+n=3,5) mixed anions, bridging B-Au-B units appear to be favored in energy over bridging B-H-B, as demonstrated by the fact that the Au-bridged C2v B2H2Au- (1A1), Cs B2HAu2- (1A'), and C, B2HAu4- (1A) lie clearly lower than their H-bridged counterparts Cs B2H2Au-(1A'), C2 B2HAu2-(1A), and C2v B2HAu4- (1A1), respectively. Orbital analyses indicate that Au 6s makes about 92-96% contribution to the Au-based orbitals in these B-Au-B 3c-2e interactions, while Au 5d contributes 8-4%. The adiabatic and vertical detachment energies of the concerned anions have been calculated to facilitate their future experimental characterizations. We have done a compare research on Al2Aun-/0 (n=1,3,5) clusters at DFT-B3LYP, finding that although there is bridging Al-Au-Al units in AlAu clusters, the ground state structures are different from B-Au systems. Au 6s makes more than 98% contribution to the Au-based hybridized orbitals, while Au 5d contributes less than 2%.The geometrical and electronic structures of B2Au20/-/2- have also been explored. Their ground states proved to cantain a multiply bonded BB core, in the forms of linear Au-B=B-Au and chained[Au-B三B-Au]- and [Au-B≡B-Au]2-.