Structural Prediction And Bonding Analysis Of Transition Metals

In recent decades, the transition metals have attracted much attention. Hg is the transition metal, its electronic configuration is 5d106s2. In this thesis, the geometric structures of (HgS)n(n=1-16,20) clusters has been optimized and its properties has been analyzed at first; secondly, for the experimentally produced [Pd2(CO)2Cl4]2- and Pd4(CO)4(OAc)4 cluster, we investigate their properties and bonding style.The main works are listed as follows:1、Secondary Bonding Networks in small (HgS)n Clusters:a Theoretical InvestigationLow-lying isomers of mercury sulfide (HgS)n (n=1-16,20) clusters are located by unbiased global search method combining the genetic algorithm with density functional theory. The global minimum structures of mercury sulfide clusters are found to be monotonous rings up to n=8, and multiple rings at n≥9, much different from any other 1:1 clusters. The (HgS)n clusters have large HOMO-LUMO energy gaps (greater than 3.0 eV at n≥3). S…Hg secondary bonds are found between the rings in multiple-ring structures, where direct evidences for the S…Hg secondary bonding networks in the multiple-ring structures are given by noncovalent interaction index analysis. Energy level of the S-Hg secondary bonding is about 0.2 eV, which is the key role for the stability of multiple-ring structures. Such a secondary bond is due to the strong relativistic effects of Hg and may be the reason for the novel geometric properties of (HgS)n clusters.2、A new bonding feature between transition metals:Synergistic bonding in Pd clustersA unique bonding pattern is found in the experimentally produced [Pd2(CO)2Cl4]2- and Pd4(CO)4(OAc)4 clusters. Previously, it is believed that Pd-Pd single bonds (～2.70A) exist in the Pd2C2 diamond units of the clusters. However, we found that bonding orbitals cannot be formed directly between two Pd atoms due to the symmetry of d orbitals. Instead, orbitals of neighboring atoms are borrowed to form an eight-center two-electron (8c-2e) bond. Such a bonding feature is not viewed before and is defined as synergistic bonding.