双接触蓝移氢键PH_2…Y的理论研究

Theoretical Study of the PH_2…Y Bifurcated Blue-Shifting Hydrogen Bond

运用量子化学从头算方法,在MP2/6-311++G(d,p),MP2/6-311++G(2df,2p),MP2/6-311++G(3df,3pd)和QCISD/6-311++G(d,p)水平上,研究了H2PF和H2POH作为质子给体与N2,HF,HCl与Cl-作为质子接受体的分子间双接触弯曲氢键PH2…Y.计算结果表明:6种复合物中都存在2个P—H…Y(Y=N,F,Cl,Cl-)氢键,P—H键收缩,伸缩振动频率增大,形成蓝移氢键.NBO分析表明,在这些复合物中,弯曲氢键的特殊结构使得分子间超共轭减小到可以忽略;质子接受体的电子密度没有转移到σ*(P—H)上,而是转移到了σ*(P—Z)(Z=F,O)上;存在一定程度的重杂化.Alabugin的超共轭与重杂化理论与Hobza的理论都能成功地解释这些蓝移氢键的形成.

Ab initio quantum mechanics methods were applied to investigate the PH2…Y bend hydrogen bonds in the complexes N2…H2PF, HF…H2PF, HC1…H2PF, N2…H2POH, HF…H2POH and C1…H2POH. The MP2 theory with four basis sets [6-311＋＋ G（d, p）, 6-311＋＋ G（2df, 2p）, 6-311 ＋＋ G （3dr, 3pd） and QCISD/6-311 ＋＋ G （d, p） ] and both the standard gradient and the counterpoise-corrected gradient techniques were used to optimize the geometries and analyze vibrational frequencies. Calculation indicated that there were two P-H…Y（Y=N, F, C1 and C1^-） hydrogen bonds in the six complexes and that P-H bond contracted with a concomitant blue shift of the corresponding IR stretching frequency. NBO （natural bond orbital）analysis showed that the hyperconjugation in a bend H-bond configuration was very small enough to be neglected in the complexes, that the electron density in the N, F, C1 and C1^- lone pair was transferred mainly to the σ^＊（P-F） antibonding orbital or σ^＊（P-O） antibonding orbital and that the character in the σ（P-H） orbital exhibited a small increase. Both the hyperconjugation theory of Ala-bugin and the view of Hobza can explain the formation of the PH2…Y bend hydrogen.