Theoretical Design Of Species With The Planar Penta-and Hexa-coordinate Carbon

With the rapid development of quantum chemical methods, chemists have begun to explore the non-classical bonding structures. The planar carbon chemistry has opened up a new direction of the carbon chemistry. Over the past decade, a number of compounds with the planar tetracoordinate Carbon(ptC) have been characterized experimentally and explored computationally. The concept of ptC was extended to planar pentacoordinate and hexacoordinate Carbon (ppC and phC), even hypercoordinate arrangements with other main group atoms or transition metals. To further extend the investigation of planar carbon chemistry, scientists tend to search more molecules with planar hypercoordinate centers. For the easy realization purpose, these molecules had better to be the global minima. In this thesis, the ab initio has been used to investigate systematically a series of ppC and phC molecules. We designed and analyzed the new ppC or phC global minima, and probed the species of CB3X2q preliminary in this paper.This work consists of five chapters:Chapter One:We intend to briefly introduce development and deficiencies in planar carbon chemistry, based on which we point out what we will do in this thesis.Chapter Two:We are going to introduce the theoretical background and the computational methods related to this work.Chapter Three:With the phC species CB62" as the starting point, we used the scheme of isoelectronic substitution to design the new phC species D3h CO3Li3+, CN3Be3+, and C4B3+. We then investigated their stability both thermodynamically and kinetically. We found that phC structure of C4B3+was the high energy isomer, which centainly can not be realized experimentally; that of CO3Li3+was the distinct global minimum, which can be realized experimentally as the thermodynamically stable isomer; the CN3Be3+was the second lowest isomer, but the ab initio molecular dynamic simulation and the ring-open reaction studies suggest it can be realized experimentally as the kinetically stable isomer.Chapter Four:Similar to Charpter Three, the isoelectronic substitution was used once again in this Charpter. Starting from the global minimum ppC species CAl5+, we designed the first dinaionic ppC species C2v CAl2Be32-and its salt complex C2v LiCAl2Be3-in this thesis. In combination with DFT and high-level ab initio calculations (CCSD(T)), the extensive exploration on their potential energy surfaces indicates that they are both the global minima. Compared to CAl2Be32-, the geometrical and electronic structures of corresponding ppC core in LiCAl2Be3-do not vary obviously, but the stability of whole molecule is improved significantly. We think the ppC dianion C2v CAl2Be32" is possible to detect directly in the gas-phase experiments, but it can be detected as its salt complex C2v LiCAl2Be3-more easily.Chapter Five:Based on our understanding to the structural units employed to design the ppC molecular families (the Hyperenes), we designed in this thesis a new family of Hyperenes CB3X2q (q=±1). We found that most of the main group elements can be the proper candidate for the "X" atom in CB3X2q (q=±1). Though the exploration on their potential energy surface suggest that the global minima of most of the CB3X2q (q=±1) have the planar pentacoordinate boron (ppB) structures, there had exceptions:the global minima of CB3X2-(X=Be, Mg, Ca) had the ppC or quasi-ppC structures. Although effort on realizing CB3Be2-may be deterred because of the poisonous of Be element, CB3X2-(X=Mg, Ca) may be the good target for experimental realization of new ppC species.