Theoretical Studies On The Nature Of Metal-Metal Bond In Metal Cluster Compounds

The chemistry of metal cluster compound is a new branch of science which develope onthe basis of organometallic chemistry and inorganic complexes chemistry. The study of metalcluster compound has the great theoretical meaning to the development of biochemistry,synthetic chemistry, inorganic chemistry and organometallic chemistry. Meanwhile, the studyof metal cluster compound has extensive using prospect in catalytic and materials science.In this thesis, we studied the metal-metal bonding characteristics. The nature ofmetal-metal bonding have been studied within the framework of the ‘atoms in molecules’（AIM） theory and using ‘electron localization function’（ELF） analysis. All calculations arecarried out using the Gaussian03program package. The topological analysis of electrondensity of molecule have been studied using AIMALL program and TOPMOD program. Themain contents are the following aspects:1. The nature of M-M bonding in Na2[Arx^*MMArx^*] and H2[Arx^*MMArx^*]（M=Al,Ga; Arx^*=C₆H₃-2,6-（C₆H₅）₂） was investigated and compared within the framework of the‘atoms in molecules’（QTAIM） theory and using ‘electron localization function’（ELF）analysis. The calculated results show that Na2[Arx^*MMArx^*] and H2[Arx^*MMArx^*] havedifferent structural and electronic features. In Na2[Arx^*MMArx^*], the M-M interaction is anon-classical triple bond, which consists of a distorted σ bond, a Ï€ bond and a “slipped” Ï€bond. The contribution of sodium atoms to the short M-M bond length is considerable and theheart of the molecule is a M2Na2cluster rather than a simple M-M bond. InNa2[Arx^*MMArx^*], in which the two sodium atoms are substituted by two hydrogen atoms,the M-M bond is replaced by two3-center,2-electron（3c-2e） M-H-M bridged bonding. Thebulky ligands play important stabilizing roles in both Na2[Arx^*MMArx^*] andH2[Arx^*MMArx^*].2. The nature of chemical bonding and metalloaromaticity of Na₂[（MArx′）₃]（M=B, Al,Ga） have been studied within the framework of the ‘atoms in molecules’（AIM） theory andusing ‘electron localization function’（ELF） analysis. The Ï€ electrons of the studied systemswere separated from the total electron density and analyzed. The calculated results indicatethat there are noncovalent weak interactions between the sodium atom and the M3（M=B, Al,Ga） ring, between the sodium atom and the terminal phenyl group on each Arx′, and betweenthe terminal phenyl groups on Arx′in Na₂[（MArx′）₃]. The bulky ligands and sodium atomsplay important stabilizing roles in the studied complexes. Moreover, the contribution ofsodium atoms to the short M-M bond is significant. The Ï€ electrons analysis shows that Na₂[（MArx′）₃] is metalloaromatic and the metalloaromaticity gradually decreases in the orderM=B, Al, Ga.3. The nature of Zn-Zn bonding in Arx′ZnZnArx′, Arx′Zn（μ-H）₂ZnArx′,Arx′Zn（μ-H）（μ-Na）ZnArx′and Arx′Zn（μ-Na）₂ZnArx′（Arx′=C₆H₃-2,6-（C₆H₅）₂） wasinvestigated and compared using ‘electron localization function’（ELF） analysis and ‘naturalbond orbital’（NBO） analysis. In Arx′ZnZnArx′, the Zn-Zn bond is formed mainly by theoverlap of the Zn4s orbitals, but is different from a normal σ bond. The Zn-Zn bond ischaracterized by a ring shaped region of localized electrons. In Arx′Zn（μ-H）₂ZnArx′,Arx′Zn（μ-H）（μ-Na）ZnArx′and Arx′Zn（μ-Na）₂ZnArx′, the introduction of hydrogen andsodium atoms weakens the strengh of Zn-Zn bond. And Zn-Zn bond in Arx′Zn（μ-Na）2ZnArx′was stronger than Zn-Zn bond in Arx′Zn（μ-H）（μ-Na）ZnArx′, Arx′Zn（μ-H）2ZnArx′. There are3c-2e （Zn-H-Zn/Zn-Na-Zn） bonds in Arx′Zn（μ-H）₂ZnArx′, Arx′Zn（μ-H）（μ-Na）ZnArx′andArx′Zn（μ-Na）₂ZnArx′.The innovations in the thesis:1. The ELF program has been improved in order to calculate various physics parametersof basins, such as various energy density （Lagrangian kinetic density Gc, the virial energydensity Vcand the total energy density Hc）. The improved ELF program is helpful to furtherunderstand the nature of chemical bond.2. The metal-metal bond of group13and transition metal is investigated using ‘electronlocalization function’（ELF） analysis. The population in various basin is calculated, thetwo-dimensional ELF contours, three-dimensional ELF iso-surfaces are described and thenature of metal-metal bond is investigated.3. The Ï€ electrons of the studied systems are separated from the total electron density andanalyzed. The molecular graph of the Ï€ electron density are described. Meanwhile, the Ï€electrons are investigated using ELF analysis and discuss the metalloaromaticity of thestudied systems.