Contains The Theoretical Study Of Plane Four-coordinate And Five-coordinate Carbon Boron Carbon Compounds

In this paper,the structures,stabilities,bonding properties and aromaticities of the three types of boron-carbon compounds containing the planar tetracoordinate carbon(ptC) and planar pentacoordinate carbon(ppC) have been investigated by the density functional theory B3LYP.The first type of compounds contain ptC and ppC without the limit of symmetrical planes;the second type of compounds are contain two ptCs in one molecule;and the third type one are crown ethers structures containing multi-ptC.1.The boron-carbon compounds with ptC and ppC without the limit of symmetrical planesThe boron and carbon compounds containing the ptC and ppC have been investigated by the density functional theory B3LYP with 6-311+G^** basis set.These novel compounds are formed by assembling three types of stable molecules C₃B₂H₄,CB₄H₂ and CB₅H₂,together with -CHCH- units. The bonding properties,spectroscopic properties,and the aromaticity of these novel boron and carbon compounds have been obtained.The results show that these compounds with lowest energy are stable.Moreover,they contain ptCs and ppCs without the limit of symmetrical planes.The calculated WBIs indicate that all of the structures in this paper are follow the octet rule.2.The compounds with double ppCs in one moleculeUsing B3LYP/6-311+G^** method,the initial structures boron-carbon clusters C_2+nB_10-n(n=0-10) with double ppCs were optimized.And their vibrational frequencies are calculated at the same level. The results showed that the most stable C_2+nB_10-n(n=0-2) clusters contain two ppCs,the C_2+nB_10-n (n=3-6) clusters with the lowest energy contain one ppC,while the lowest energy C_2+nB_10-n(n=7-10) clusters have no ppC.In addition,only the C_2+nB_10-n(n=0-2) clusters do not include dangling bonds, and theÏ€electron of the C_2+nB_10-n(n=0-2) clusters are 6,7 and 8,respectively.The calculated NICS(0) indicate that the strong aromaticity locates at the centers of some three-numbered rings.3.The crown ethers containing muli-ptCWe optimized the structures of tetra-C₃B₂H₂-16-crown-4,penta-C₃B₂H₂-20-crown-5 and hexa-C₃B₂H₂ -24-crown-6 at the B3LYP/6-31G^** level,and their vibrational frequencies are also calculated.They contain four,five and six the ptCs,respectively and their symmetries are D_4h,D_5h and D_6h,respectively.The smallest frequencies of the three molecules are 31,23 and 14cm^-1, respectively and the energy gaps are 5.03,4.98 and 4.68eV,respectively,which show that the three compounds are stable.Their first vertical electronic excitation energies are 286.2,279.1 and 293.0 nm,respectively.The NICS(0) of the center of three-membered rings of the three compounds are -32.42,-30.96 and -29.79 ppm,which the three-membered rings have strong aromaticity,while the center of the molecules are antiaromatic.