Theoretical Study On The Systems Of Planar Hyper-coordinated Boron/Silicide By Sulfur-bridging Platinum

Since the concept of planar tetracoordinate carbon（Pt C）was proposed in 1970,examples containing PtC have been continuously discovered through theoretical prediction and experimental preparation.The structure of these unclassical small molecules can be well stabilized by electronic or mechanical strategy.Therefore,the bonding model based on planar methane can be widely extended to the design of planar hypercoordinate structures of other elements.Small molecules with planar hypercoordinate configuration may extend to form planar materials,and they may possess unusual electromagnetic properties and unique catalytic functions.Our basic knowledge of planar hypercoordinate chemistry,the structure and electronic distribution characteristics will help promoting the future development of this field.In this thesis,the density functional theory（B3LYP）was used to sequentially study the structure and stability of the tetracoordinate boron molecule BPt4S4ⁿ（n=-2,-1,0）system formed by the sulfur bridging transition metal platinum as the global energy minima,as well as the tetracoordinate and pentacoordinate silicon molecules SiPt₄S₄^2-and SiPt₅S₅^-system.My study verifies that the most important factor for the stable planar hypercoordinate molecules is the multiple aromaticity of the system,and also proves the feasibility of introducing sulfur as a great bridging element into the planar design.It provides theoretical basis for experimentally capturing planar tetracoordinate boron molecules and planar hypercoordinate silicon molecules.The main research contents of this thesis are as follows:1.Studies have confirmed that the sulfur-bridging platinum forms stable tetracoordinate boron clusters BPt₄S₄ⁿ（n=-2,-1,0）system.The cluster structure search shows that the planar tetracoordinate boron（PtB）is contained in three charges.The structures of PtB are all global minimum point structures.At the B3LYP/def2-TZVP level,the boron atom has a strong interaction with the surrounding ligand platinum atom,forming a stable BPt₄ central nucleus;the surrounding Pt₄S₄ skeleton formed by sulfur-bridging platinum is also relatively strong.BPt₄S₄^-has better stability than BPt₄S₄^2-and BPt₄S₄,and has good thermodynamic and dynamic stability.Its excellent stability is reflected in its adiabatic detachment energy ADE,adiabatic electron affinities AEA,and nuclear-independent vertical chemical shift NICS value.CMOs and AdNDP orbitals show that the internal BPt₄ core in BPt₄S₄^-has double aromaticity（πandσ）,which indicates that the tetracoordinate boron cluster BPt₄S₄^-has extremely strong stability.It is inferred that it may be better to be detected in experiments and then applied.In the three charges,the electrons that gain and lose occur on the S atom while the electrons of the BPt₄ nucleus are not obviously affected,which explains why the clusters can form the Pt B structure in three charges.2.Studies have confirmed that the sulfur-bridging platinum forms stable tetracoordinate and pentacoordinate silicon clusters SiPt₄S₄^2-and SiPt₅S₅^-systems.At the B3LYP/def2-TZVP level,it was confirmed that the global minimum structure of SiPt₄S₄^2-contains planar tetracoordinate silicon（PtSi）,which has excellent thermodynamic and dynamic stability.CMOs and AdNDP orbital analyses show that the SiPt₄ core has double aromaticity.On the basis of PtSi,the size of the ring was further enlarged to construct a five-membered ring,and SiPt₅S₅^-with planar pentacoordinate silicon（PpSi）was proposed,which is also the global minimum structure on the potential energy surface.CMOs and AdNDP orbital analyses indicate that the SiPt5 core also has double aromaticity,further verifying the validity of multiple aromaticity for planar design.