螺桨烷型分子BX[(CH_2)_n]_3和BX(CH_2)[CH(CH_2)_nCH](X=N,P)的结构和性质

采用密度泛函理论(DFT)研究了螺桨烷型分子BX(CH2)n]3和BX(CH2)CH(CH2)n CH](X=N,P;n=1-6)的结构、稳定性、化学键和电子光谱性质.计算结果表明这些分子都是稳定的.BX(CH2)n]3(X=N,P;n=1-6)的最高占据分子轨道(HOMO)和最低空分子轨道(LUMO)之间的能隙均大于5.20 eV,其中BNCH2]3和BPCH2]3的能隙超过7.0 eV,与C5H6的能隙(7.27 eV)很接近,BX(CH2)CH(CH2)n CH](X=N,P;n=1-6)的能隙在6.80 eV左右.所研究分子能量的二阶差分表明BN(CH2)3]3、BP(CH2)4]3及BX(CH2)CH(CH2)2CH](X=N,P)是最稳定的.BX(CH2)n]3的Wiberg键级表明除了BN(CH2)n]3(n=2和6)中不存在B―N键,其它化合物中B和N均形成了化学键,BP(CH2)n]3中除了BP(CH2)2]3不存在B―P键,其它的均存在.电子密度的拓扑分析表明N―B键属于离子键,而P―B键具有共价键特征.BX(CH2)n]3(X=N,P)的第一垂直激发能分别在191.1-284.8 nm和191.8-270.1 nm之间,BX(CH2)CH(CH2)n CH](X=N,P)的第一垂直激发能分别在190.5-199.7 nm和209.0-221.3 nm之间.

Structures and Properties of BX[(CH2)n]3 and BX(CH2)[CH(CH2)nCH] (X=N,P) with the [n.n.n]propellane Configuration

We have designed a family of novel molecules BX(CH₂)_n]₃ and BX(CH₂)CH(CH₂)_nCH] (X=N, P) with the n.n.n]propellane configuration (n=1-6). The structures, stabilities, chemical bonds, and electronic spectra of these structures were investigated using density functional theory (DFT). The calculated results indicate that all of these compounds are situated at minima on the potential energy surfaces. The energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of BN(CH₂)_n]₃ and BP(CH₂)_n]₃ (n=1-6) were in the range of 5.24-7.07 eV and 5.47-7.33 eV, respectively, and the energy gap of BXCH₂]₃ is close to that of C₅H₆. In addition, the energy gaps of BN(CH₂) CH(CH₂)_nCH] and BP(CH₂) CH(CH₂)_nCH] (n=1-6) are around 6.80 eV. To compare the relative stabilities of these compounds, we investigated the second-order differences of energies. The results indicate that BN(CH₂)₃]₃, BP(CH₂)₄]₃, and BX(CH₂)CH(CH₂)₂CH] (X=N, P) are more stable than the other structures. Moreover, based on the bond lengths, Wiberg bond indices, and charges of the two"inverted"atoms, it can be concluded that the bridgehead B and N(P) atoms in BN(CH₂)_n]₃ (n=2, 6) and BP(CH₂)₂]₃ do not form chemical bonds, while the two bridgehead atoms in the other compounds studied formed chemical bonds. Additionally, topological analysis of the electron density using the theory of atoms-in-molecules shows that the inverted N―B bonds in BN(CH₂)_n]₃ (n=3-5) are ionic bonds whereas the B―P bonds in BP(CH₂)_n]₃ (n=3-6) have covalent character. The vertical transition energies of BN(CH₂)_n]₃, BP(CH₂)_n]₃, BN(CH₂) CH(CH₂)_nCH], and BP(CH₂) CH(CH₂)_nCH] (n=1-6) range from 191.1 to 284.8 nm, 191.8 to 270.1 nm, 190.5 to 199.7 nm, and 209.0 to 221.3 nm, respectively.