Del Bene Janet E, Alkorta Ibon, Elguero José
Department of Chemistry, Youngstown State University , Youngstown, Ohio 44555, United States.
J Phys Chem A. 2014 Oct 30;118(43):10144-54. doi: 10.1021/jp509353a. Epub 2014 Oct 20.
Ab initio MP2/aug'-cc-pVTZ calculations have been carried out on the pnicogen-bonded complexes H(n)F(5-n)P:N-base, for n = 0-5 and nitrogen bases NC(-), NCLi, NP, NCH, and NCF. The structures of these complexes have either C(4v) or C(2v) symmetry with one exception. P-N distances and interaction energies vary dramatically in these complexes, while F(ax)-P-F(eq) angles in complexes with PF5 vary from 91° at short P-N distances to 100° at long distances. The value of this angle approaches the F(ax)-P-F(eq) angle of 102° computed for the Berry pseudorotation transition structure which interconverts axial and equatorial F atoms of PF5. The computed distances and F(ax)-P-F(eq) angles in complexes F5P:N-base are consistent with experimental CSD data. For a fixed acid, interaction energies decrease in the order NC(-) > NCLi > NP > NCH > NCF. In contrast, for a fixed base, there is no single pattern for the variations in distances and interaction energies as a function of the acid. This suggests that there are multiple factors that influence these properties. The dominant factor appears to be the number of F atoms in equatorial positions, and then a linear F(ax)-P···N rather than H(ax)-P···N alignment. The acids may be grouped into pairs (PF5, PHF4) with four equatorial F atoms, then (PH4F, PH2F3) with F(ax)-P···N linear, and then (PH3F2 and PH5) with H(ax)-P···N linear. The electron-donating ability of the base is also a factor in determining the structures and interaction energies of these complexes. Charge transfer from the N lone pair to the σ* P-A(ax) orbital stabilizes H(n)F(5-n)P:N-base complexes, with A(ax) either F(ax) or H(ax). The total charge-transfer energies correlate with the interaction energies of these complexes. Spin-spin coupling constants (1p)J(P-N) for (PF5, PHF4) complexes with nitrogen bases are negative with the strongest bases NC(-) and NCLi but positive for the remaining bases. Complexes of (PH4F, PH2F3) with these same two strong bases and H4FP:NP have positive (1p)J(P-N) values but negative values for the remaining bases. (PH5, PH3F2) have negative values of (1p)J(P-N) only for complexes with NC(-). Values of (1)J(P-F(ax)) and (1)J(P-H(ax)) correlate with the P-F(ax) and P-H(ax) distances, respectively.
对pn键合配合物H(n)F(5 - n)P:N - 碱进行了从头算MP2/aug'-cc - pVTZ计算，其中n = 0 - 5，氮碱包括NC(-)、NCLi、NP、NCH和NCF。这些配合物的结构除了一个例外，具有C(4v)或C(2v)对称性。在这些配合物中，P - N距离和相互作用能变化很大，而与PF5形成的配合物中F(ax) - P - F(eq)角在短P - N距离时为91°，在长距离时为100°。这个角度的值接近为PF5的轴向和赤道F原子相互转换的Berry假旋转过渡结构计算的102°的F(ax) - P - F(eq)角。配合物F5P:N - 碱中计算得到的距离和F(ax) - P - F(eq)角与实验CSD数据一致。对于固定的酸，相互作用能按NC(-) > NCLi > NP > NCH > NCF的顺序降低。相反，对于固定的碱，距离和相互作用能随酸的变化没有单一模式。这表明有多个因素影响这些性质。主导因素似乎是赤道位置的F原子数量，然后是线性的F(ax) - P···N而不是H(ax) - P···N排列。酸可以分为四组，第一组是有四个赤道F原子的对（PF5，PHF4），然后是F(ax) - P···N为线性的（PH4F，PH2F3），再然后是H(ax) - P···N为线性的（PH3F 和PH5）。碱的给电子能力也是决定这些配合物结构和相互作用能的一个因素。从N孤对向σ* P - A(ax)轨道的电荷转移使H(n)F(5 - n)P:N - 碱配合物稳定，其中A(ax)为F(ax)或H(ax)。总电荷转移能与这些配合物的相互作用能相关。与氮碱形成的（PF5，PHF4）配合物的自旋 - 自旋耦合常数(1p)J(P - N)对于最强的碱NC(-)和NCLi为负，但对于其余碱为正。（PH4F，PH2F3）与这两个强碱以及H4FP:NP形成的配合物具有正的(1p)J(P - N)值，但对于其余碱为负。（PH5，PH3F2）只有与NC(-)形成的配合物的(1p)J(P - N)值为负。(1)J(P - F(ax))和(1)J(P - H(ax))的值分别与P - F(ax)和P - H(ax)距离相关。
