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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Topological Analysis of Chemical Bonding in Cyclophosphazenes
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Topological Analysis of Chemical Bonding in Cyclophosphazenes

机译：环磷腈中化学键的拓扑分析

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Chemical bonding in the cyclophosphazenes is studied from the point of view of th.e quantum theory of Atoms in Molecules (AIM). To that end, HF/6-3lG** ab initio calculations are done on a collection of (NPXV3 derivatives for a wide set of -X substituents, and its electron density , p(T), and pair density, p(2)(fJ,rv, are obtained and analyzed. The (NP)_3 ring geometry and bonding properties are basically maintained along the cyclotriphosppazenes. The PN distance and the bond critical point properties (electron density, Laplacian, etc.) lie between those of XNPX3, formally a double NP bond, and those of X2NPX4, formally a single NP bond, b(:ing much closer to the former than to the latter. The Laplacian of the electron density shows the PN bond to be highly polar, with a clear tendency of the P atoms to lose almost all of their five valence electrons, and a significant concentration of charge along the PN line, even though within the N basin. The charge on the ring N basins, Q(N), remains almost invariant, -2.3 e, in all cyclotriphosphazenes, whereas the charge of the ring P basin, Q(P), varies from +2.9 to +4.0 e, depending on the electronegativity of the -X group. There is an inverse correlation between Q(P) and the PN distance, the more electronegative -X groups shrinking the (NP)3 ring,more, even though only slightly. The partition of the pair densities indicates that some 0.63 electron pairs are shared between each P and its two N neighbors in the ring, this value being typical of a polar but largely ionic bonding situation. The three N atoms in the ring share 0.20 electron pairs perN-N group, a small but significant amount, even though no bond path line occurs linking them. The three-dimensional contour surfaces of V2p clearly depict the molecular regions having a Lewis basic or acidic character. Ring N atoms behave as weak Lewis bases, whereas ring P atoms are preferred sites for a nucleophilic attack tending to remove, perhaps ionically, a -X group. These topological properties do explain the chemistry of cyclophosphazenes and agree well with the available experimental densities. The AIM analysis supports the main conclusions froin the traditional Dewar's model of phosphazenes. .
机译：从分子中的原子量子理论（AIM）的角度研究了环磷腈中的化学键合。为此，对一组广泛的-X取代基（NPXV3衍生物）及其电子密度p（T）和对密度p（2）进行了HF / 6-3lG **从头算的计算。 （fJ，rv，的获得和分析。）（NP）_3环的几何形状和键合性质基本上沿着环三膦保持。PN距离和键合临界点性质（电子密度，拉普拉斯等）位于XNPX3的之间形式为双NP键，而X2NPX4形式为单NP键，b（：比前者更接近前者。电子密度的拉普拉斯算子表明PN键是高极性的，具有清晰的P原子几乎失去所有五个价电子的趋势，并且即使在N盆中，也沿PN线有显着的电荷浓度。环N盆上的电荷Q（N）几乎不变， -2.3 e，在所有环三磷腈中，而环P盆的电荷Q（P）从+2.9到+4不等。 0 e，取决于-X基团的电负性。 Q（P）与PN距离之间呈反比关系，负电性的-X基团越收缩（NP）3环，甚至越小。对密度的分配表明，环中的每个P和它的两个N邻居之间共享约0.63个电子对，该值是极性但主要是离子键合情况的典型值。环中的三个N原子每个N-N基团共享0.20个电子对，尽管它们之间没有键合路径键合，但数量很少但数量可观。 V2p的三维轮廓表面清楚地描绘了具有路易斯碱性或酸性特征的分子区域。环N原子的行为像弱的Lewis碱，而环P原子是亲核攻击的首选位点，趋于从离子上除去-X基团。这些拓扑性质确实说明了环磷腈的化学性质，并与可用的实验密度很好地吻合。 AIM分析支持基于传统杜瓦磷腈模型的主要结论。 。

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