Del Bene Janet E
Department of Chemistry, Youngstown State University, Youngstown, OH 44555, USA.
J Phys Chem A. 2007 Jun 28;111(25):5509-14. doi: 10.1021/jp0711491. Epub 2007 Jun 1.
Ab-initio MP2/aug'-cc-pVTZ calculations have been performed to determine the structures and binding energies of proton-bound complexes stabilized by N-H+-P hydrogen bonds and to investigate the nature of the proton-transfer coordinate in these systems. Double minima are found only when the difference between the protonation energies of the N and P bases is less than about 4 kcal/mol. The isomer in which the protonated nitrogen base is the donor lies lower on the potential surface and also has a greater binding energy relative to the corresponding isolated monomers. Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) calculations have been employed to obtain one- and two-bond spin-spin coupling constants across these hydrogen bonds. Two-bond coupling constants (2h)J(N-P) correlate with N-P distances, irrespective of whether the donor ion is N-H+ or P-H+. One-bond coupling constants (1)J(N-H) and (1h)J(H-P) for complexes stabilized by N-H+...P hydrogen bonds correlate with corresponding distances, but similar correlations are not found for (1)J(P-H) and (1h)J(H-N) for complexes with P-H+...N hydrogen bonds. Negative values of (1h)K(H-N) and (1h)K(H-P) indicate that the hydrogen bonds in these complexes are traditional. Comparisons are made with complexes stabilized by N-H+-N and P-H+-P hydrogen bonds.
已进行从头算MP2/aug'-cc-pVTZ计算，以确定由N-H⁺-P氢键稳定的质子结合复合物的结构和结合能，并研究这些体系中质子转移坐标的性质。仅当N和P碱的质子化能之差小于约4千卡/摩尔时，才会发现双势阱。质子化氮碱作为供体的异构体在势能面上位置更低，相对于相应的孤立单体也具有更大的结合能。已采用运动方程耦合簇单双激发（EOM-CCSD）计算来获得这些氢键上的一键和二键自旋-自旋耦合常数。二键耦合常数(²h)J(N-P)与N-P距离相关，无论供体离子是N-H⁺还是P-H⁺。由N-H⁺...P氢键稳定的复合物的一键耦合常数(¹)J(N-H)和(¹h)J(H-P)与相应距离相关，但对于具有P-H⁺...N氢键的复合物，(¹)J(P-H)和(¹h)J(H-N)未发现类似的相关性。(¹h)K(H-N)和(¹h)K(H-P)的负值表明这些复合物中的氢键是传统的。并与由N-H⁺-N和P-H⁺-P氢键稳定的复合物进行了比较。
