Investigations On Geometrical Structures And Bonding Characteristics Of Boron-Containing Binary Clusters

Along with the rapid development of computer technology and computational methodologies, theoretical computation has become an important way for predicting and studying the structures and characteristics of novel clusters. Recently, pure boron and boron-containing binary clusters have attracted wide attention. However, the rules on structures and properties of the boron-containing binary clusters are not clear. A systematic density functional theory and wave function theory investigation on the geometrical structure, electronic structures, bonding characteristics, thermodynamic stabilities and spectrum characteristics of boron containing binary clusters, such as boron hydrides, boron oxides and boron-gold has been performed in this thesis. We aim to provide a theoretical basis for their experimental and applied researches.1. Terminal η1-Au and Bridging η2-Au in Boron-gold and Carbon-gold ClustersAn ab initio theoretical investigation on the geometrical, electronic structures and photoelectron specctroscopies (PES) of BAun-/0(n=1-4) clusters has been performed. Density functional theory (DFT) and coupled cluster method (CCSD(T)) calculations indicate that BAun-/0(n=1-4) clusters with n η1-Au possess similar geometrical structures and bonding patterns with the corresponding boron hydrides BHn-/0(n=1-4). Natural resonant theory (NRT) analyses showed that the B-Au interactions in BAun-/0clusters (n=2-4) are mainly covalent. The PES spectra of the BAun-anions and the Au-B stretching vibrations of the BAun neutrals (n=1-4) are simulated. The investigation on BAu4-unit served as the building block provides a theoretical basis for the synthesis of LiBAu4and other [BAu4]--containing inorganic solids.A systematic density functional theory investigation on C2Aun+(n=1,3,5) and C2Aun (n=2,4,6) indicates that gold atoms serve as terminal η1-Au in the chain-like Cs C2Au+(C=C-Au+) and D∞h C2Au2(Au-C=C-Au) and as bridging η2-Au in the side-on coordinated C2v C2Au3+([Au-C=C-Au]Au+) and Cs C2HAu2+([Au-C=C-Au]Au+). However, when the number of gold atoms reaches four, they form stable gold triangles (-Au3) in the head-on coordinated C2v C2Au4(Au-C=C+Au3) and the side-on coordinated C2v C2Au5+([Au-C=C-Au]Au3+. The high stability of Au3triangles originates from the fact that an equilateral D3h Au3+cation possesses a completely delocalized three-center-two-electron (3c-2e) σ bond and therefore is σ-aromatic in nature. The extension from H/Au analogy to H/Au3analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials.2. Planar π-aromatic C3h B6H3+, C2v B10H5-and π-antiaromatic C2h B8H4Extensive structural searches and wave function theory calculations have been performed for B2nHn(n=3,4,5). We predict the existence of the perfectly planar triangle C3h B6H3+, the double-chain C2h B8H4and the planar C2v B10H5-which are the inorganic analogues of cyclopropene cation D3h C3H3+, cyclobutadiene D2h C4H4, and cyclopentadiene D5h C5H5-in both geometrical and electronic structures, respectively. Here, a vertex-sharing B3triangle in planar boron hydride clusters is equivalent to a C atom in the well-known hydrocarbon clusters. Detailed adaptive natural density partitioning (AdNDP) and the nucleus independent chemical shifts (NICS) analyses further unravel the bonding patterns and overall aromaticity of C3h B6H3+, C2h B8H4and C2v B10H5-.3. Aromatic Double-Chain Conjugated D2h B4H2, C2h B8H2and C2h B12H2Based upon comprehensive theoretical investigations and known experimental observations, we predict the existence of the aromatic double-chain (DC) planar D2h B4H2, C2h B8H2and C2h B12H2which all appear to be the lowest-lying isomers of the systems at DFT level. These conjugated aromatic borenes turn out to be the boron hydride analogues of the conjugated ethylene D2h C2H4,1,3-butadiene C2h C4H6, and1,3,5-hexatriene C2h C6H8, respectively, indicating that a B4rhombus in B2nH2borenes (n=2,4,6) is equivalent to a C=C double bond unit in the corresponding CnHn+2hydrocarbons. Detailed canonical molecular orbital (CMO), AdNDP, and electron localization function (ELF) analyses unravel the bonding patterns of these novel borene clusters and indicate that they are all overall aromatic in nature with the formation of islands of both σ-and π-aromaticity. The double-chain planar or quasi-planar C2v B3H2-, C2B5H2-, and C2h B6H2with one delocalized π orbital, C2v B7H2-, C2B9H2-, and C2h B10H2with two delocalized π orbitals, and C2v B11H2-with three delocalized π orbitals are found to be analogous in π-bonding to D2h B4H2, C2h B8H2, and C2h B12H2, respectively. The results obtained in this work enrich the analogous relationship between hydroborons and their hydrocarbon counterparts and help to understand the high stability of all-boron nanostructures which favor the formation of double-chain substructures.Theoretical evidences strongly suggest that the ground states of the BnA20/-(n=8,9; A=Au and BO) all can be obtained by connecting two terminal η1-Au or η1-BO to the corner B atoms. The distributions of the localized π bonds of the B8and B9skeleton have not been changed by the terminal η1-Au or η1-BO. The Au/H and H/BO analogy all still exist in BnA20/-(n=8,9; A=H,Au and BO). The BO group exists as stable unit in the boron-rich boron oxide.4. B2A60/-(A=BO and BS) Clusters with Bridging η2-BO or η2-BSThe investigation on the geometrical and electronic properties of B2(BO)60/-and B2(BS)60/-have been performed by density functional theory (DFT) using the B3LYP and BP86methods, for comparison of their predicted structures with those of the well known B2H6. Similar to H atoms in the corresponding boranes, both BO and BS units can serve as terminal and bridging groups in D2h B2(BO)60/-and B2(BS)60/-,respectively. As analogues of diborane (B2H6), D2h B2(BO)6and B2(BS)6with two bridging η2-BO or η2-BS groups are the most interesting candidates possible to be targeted in future experiments. AdNDP analyses further unravel the bonding patterns. Different from that of classical D3d B2H6-,D2h B2(BO)6-and B2(BS)6-with two bridging η2-BO or η2-BS groups are more stable than their corresponding D3d structures. The IR spectra and UV-vis spectra of D2h B2(BO)6and B2(BS)6have been simulated to facilitate their future experimental characterizations. The boronyl pattern we proposed builds a clear structural link between boron oxides or boron sulfides and boron hydrides.5. Boroxine B3O3X3(X=H and BO) Clusters and Their Transition-metal Sandwich CompoundsBased upon extensive density functional theory calculations, molecular analyses and natural resonance theory (NRT) analyses, we predict the existence of the perfectly planar D3h B6O6(1,1A1’) we prefer to as boronyl boroxine which is the ground states of the systems and the boron oxide analogue of benzene D6h C6H6.A density functional theory investigation on half-sandwich-type C3v B3O3X3Cr, full-sandwich-type D3d [B3O3X3]2Cr, and triple-decker complexes [B3O3X3]3Cr2(X=H, BO) containing B3O3H3or B3O3(BO)3ligands has been performed. Both B3O3H3and B3O3(BO)3units serve as robust inorganic ligands in B3O3X3Cr,[B3O3X3]2Cr and [B3O3X3]3Cr2(X=H, BO) complex series. Effective d-π coordination interactions between the partially filled3d orbitals of the transition-metal center and the delocalized π orbitals of the B3O3X3(X=H, BO) ligands help maintain the stabilities of the complexes. The sandwich structural pattern developed in this work expands the structural domain of transition-metal complexes by introducing new inorganic B3O3H3and B3O3(BO)3with a B3O3core into traditional sandwich-type structures and may be extended to form [B3O3X3]nCrn-1(X=H, BO) multi-decker (n≥4) liner wires.