Investigations On Medium-sized Boron Clusters And Their Metal-doped Complexes

With the rapid development of computational chemistry,theoretical calculations exhibit unique advantages in predicting and exploring the structures and properties of novel clusters.Because of the similarities and differences in the structures and properties of boron and carbon,researches on boron and boron-based nanomaterials have attracted much attention from chemists and materials scientists in recent years.In this thesis,we present a joint first-principles theory calculations and photoelectron spectroscopy(PES)study on the geometric structures,bonding mode and spectral properties of the size-selected boron clusters B26-/0and metal-doped boron clusters Ni B13+/-.The main contents of this thesis are as follows:1.Experimental and theoretical studies on the smallest planar boron cluster B26- with a hexagonal vacancyThe study of geometric and spectral properties of the Bn- monoanions is mainly based on the combination of theoretical calculations and experiment currently.The Bn-(n=3-25,27-30)clusters have been systematically investigated both experimentally and theoretically and have all been proved to be planar or quasi-planar in their global minima and the B27-is the first cluster with a hexagonal hole in the experiment(13)In this size range,only B26-cluster has remained unknown due to its complicated PES spectrum and potential energy surface.Based on the analysis of the photoelectron spectrum of B26-and the rigorous theoretical calculations and the extensive global searches,we investigated the geometric structures,bonding pattern and spectral properties of this cluster.We calculated the relative energy of the selected isomers at the PBE0 and CCSD(T)levels,the TD-PBE0 method was used to simulate photoelectron spectra and compared with experimental data.It is found that at least three isomers(I,II,III)with different geometric characteristics in the gas phase contribute to the measured photoelectron spectroscopy.Isomer I is the most stable structure in Gibbs free energy at finite temperatures and is found to be the major isomer in the experiment,indicating that B26-is the smallest 2D boron cluster with a hexagonal hole at the geometric center.The ground state VDE of isomer III could be used to explain the distinct spectral feature of the experimental spectrum,which has a pentagonal hole and is found to be a minor species.Isomer II is the global minimum in total energy at 0 K.It may also contribute to the observed spectrum.Isomer I can be viewed as an all-boron ?-analog of the polycyclic hydrocarbon C17H11+.2.Theoretical investigations on half-sandwich NiB13+ and perfect planar Ni B13- complexesSmaller boron clusters are known to be planar or quasi-planar which may serve as inorganic ligands to form new complexes with transition metals.Earlier theoretical studies of metal-doped boron clusters indicate that metal atoms have important influence on the structures,bonding and other properties of boron clusters.The global minimal structure of B13+ possesses three inner boron atoms and ten boron atoms at the outer ring(B3-B10 structure),similar to benzene.Unbiased global searches combined with the high level of quantitative calculations show that NiB13+ tends to from a half-sandwich structure,with Ni lying above the bowl-shaped B13 ligand which consists of a quasi-planar B4 unit as inner ring and B9 unit as outer ring(B4-B9 structure),similar to the experimentally known half-sandwich structures of Co B12- and RhB12-.NiB13- monoanion,on the other hand,possesses a perfect planar Ni?B13- structure with an octacoordinate Ni center,similar to the global minimum of Co?B18- reported in the literature.It is the smallest Ni-doped heteroborophene-typed cluster.