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Electron Transfer in Pnicogen Bonds

机译:Pnicogen键中的电子转移

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摘要

As a new type of noncovalent interactions, pnicogen bond between a VA group element (N, P, and As) and an electron donor (Lewis base) has grabbed attention in recent several years. Here we employ the block-localized wave function (BLW) based energy decomposition scheme to probe the bonding nature in a series of substituted phosphines X_nPH_(3-n) complexed with ammonia. As the BLW method can derive the optimal monomer orbitals in a complex with the electron transfer among monomers quenched, we can effectively examine the HOMO-LUMO interaction in these pnicogen bonding systems. Among various energy components, electron transfer energy together with the polarization energy dominates the pnicogen bonding energy. Although usually it is assumed that the electron transfer from ammonia to substituted phosphines occurs in the form of n→ σ~*(XP) hyperconjugative interaction, we identify a kind of new pathway when X = NO_2 and CN, i.e., n → dπ~*, which results from the interaction between the π orbital of cyano or nitro substituent and d orbitals on P. But still this picture of electron transfer using a single pair of orbitals is greatly simplified, as the electron density difference (EDD) maps corresponding to the overall electron transfer processes show the accumulation of electron density on the P side opposite to the X-P bond, with insignificant or even negligible gain of electron density on the substituent group side. Thus, the EDD maps tend to support the concept of σ-hole in pnicogen bonds.
机译:作为一种新型的非共价相互作用,VA组元素(N,P和As)与电子供体(Lewis碱)之间的成虫原键近年来受到关注。在这里,我们采用基于块局部波函数(BLW)的能量分解方案来探究一系列与氨络合的取代膦X_nPH_(3-n)的键合性质。由于BLW方法可以通过淬灭单体之间的电子转移来推导复合物中的最佳单体轨道,因此我们可以有效地检查这些pogenogen键合系统中的HOMO-LUMO相互作用。在各种能量成分中,电子转移能和极化能一起主导着微纤维原的键合能。尽管通常假定电子从氨到取代的膦的转移是以n→σ〜*(XP)超共轭相互作用的形式发生的,但是当X = NO_2和CN时,我们确定了一种新的途径,即n→dπ〜 *是由氰基或硝基取代基的π轨道与P上的d轨道之间的相互作用产生的。但是,由于使用了一对电子,电子传递的电子密度差(EDD)对应于整个电子转移过程表明,电子密度在与XP键相对的P侧积累,而在取代基侧的电子密度增加不明显,甚至可忽略不计。因此,EDD图倾向于支持pogenogen键中σ-孔的概念。

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