A Theoretical Investigation On Borospherenes And Transition-metal-doped Boron Nanoclusters

Theoretical chemical calculations can help to better investigate the structures and properties of novel nanoclusters.In recent years,boron nanomaterials have attracted much attention.Persistent joint photoelectron spectroscopy(PES)and first-principles theory(FPT)investigations by Lai-Sheng Wang and co-workers in the past two decades have revealed the structures and bonding of boron nanoclusters Bn-in the size range between n=3-42.Theoretical and experimental studies have also shown that transition metal doping is an effective approach to stabilize boron clusters and modify their structures and properties.The structure and properties of metal-doped boron nanomaterials form a new area of research in boron chemistry Based on the latest developments in boron clusters,we have performed in this thesis an in-depth investigation on the structures and binding of borospherenes and transition metal doped boron nanoclusters at first-principles theory level.The following are the main contents and results of this thesis1.Cage-like borospherene B39+:The recently observed axially chiral C3/C2 B39-have attracted considerable attention in chemistry and materials science.Based on extensive global minimum searches and first-principles theory calculations,we predict the existence of two cage-like Cs B39+ structures which possess five hexagonal and heptagonal faces and one filled hexagon on the surface and follow the bonding pattern of ?+? double delocalization with 12 delocalized ? bonds over a?-skeleton,adding a new member to the borospherene family2.From B39-to Nin?B39-(n=1-6):Blocking the "W-X-M" transformation by transition-metal doping:The "W-X-M" transformation in cage-like borospherenes was firstly defined in the axially chiral C3/C2 B39-.Based on extensive first-principles theory calculations,we present the possibility of Nin?B39-complexes(n=1-6)by doping Ni atoms into the axially chiral B39-.It is found that Nin?B39-all contain planar or quasi-planar heptacoordinate Ni(phNi)centers in?7-B7 heptagons.And Nin?B39--(n=1-4)possess the universal bonding pattern of?+? double delocalization on the boron frameworks by detailed bonding analyses,each phNi forms two effective 8c-2e ?-coordination bonds between Ni and the ?7-B7 heptagon around it.Extensive molecular dynamics simulations show that,when n=1-4,the transformation temperature of Nin?B39-increases with the number of Ni atoms.However,Nin?B39-(n=5,6)are not stable even at the room temperature.More interestingly,the transformation of Ni?B39-involves two simultaneous "W-X-M" processes and the corresponding barrier is higher than that of B39-.In other words,the Ni dopant anchors the heptagons and then block the"W-X-M" transformation of B39-in some extent3.Half-sandwich aromatic boron clusters NiB10,NiB11-,NiB12 and NiB13+:Planar or quasi-planar C2v B10,C2v B11-,C3v B12 and C2v B13+ are known to be boron analogs of benzene.Extensive global minimum searches and first-principles theory investigations performed herein indicate that doping these aromatic boron clusters with a nickel atom generates the closed-shell half-sandwich C2v NiB10,Cs NiB11-,C3v NiB12,and Cs NiB13+ which are all well-defined global minima of the systems with the coordination numbers of CN=10,11,12 and 13,respectively.Detailed bonding analyses indicate that these clusters follow the universal ? plus ? double delocalization coordination bonding patterns.Molecular dynamics simulations show that NiB11-behaves like a Wankel motor at room temperature with the B3 inner wheel rotating almost freely inside the quasi-rotating B8 outer bearing,while NiB10,NiB 12,and NiB13+ fluctuate at much higher temperatures4.La-Doped Cage-like La3&[B2@Bi7]-and La3&[B2@B18]-with a B2 Core Sandwiched Inside:The results of extensive first-principles theory calculations show that the global minima structures of La3B19-and La3B20-are cage-like structures with a B2 Core Sandwiched Inside,which are the first cage-like coreshell structures found in the lanthanide boron binary cluster.C2v La3&[B2@B17]-and D3h La3&[B2@B18]-exhibit the high thermodynamic and dynamical stabilities and are possible to be characterized in experiments.