Gholivand Khodayar, Valmoozi Ali A Ebrahimi, Mahzouni Hamid R
Department of Chemistry, Tarbiat Modares University, PO Box 14115-175, Tehran, Iran.
Acta Crystallogr B. 2013 Feb;69(Pt 1):55-61. doi: 10.1107/S0108768112048331. Epub 2012 Dec 20.
The bisphosphoramidate (C(6)H(5)O)(2)P(O)NH(CH(2))(4)NHP(O)(OC(6)H(5))(2) crystallizes in two polymorphs, one (ndl) with a needle habit from tetrahydrofuran (THF)/ethanol and another (prm) which forms prisms from H(2)O/ethanol. The molecules in the two forms differ from each other in some torsion angles and the orientation of the diaminobutane bridge, although the differences between the similar bond lengths are not significant for the two polymorphs. The geometry optimizations at the B3LYP/6-31+G* level for isolated molecules show that the two conformers which exist in the crystalline state also represent local gas-phase energy minima. The decrease in the N-H distance from the optimized to the crystal structures has been described in terms of the decrease in electron density (ρ) at the bond-critical point (b.c.p.) of the N-H bond path when the molecule participates in hydrogen bonding, comparing the results of atoms-in-molecules (AIM) and natural bond orbital (NBO) analyses for fully optimized structures ndl and prm with their hydrogen-bonded model clusters.
双磷酰胺酯（C(6)H(5)O)(2)P(O)NH(CH(2))(4)NHP(O)(OC(6)H(5))(2)）以两种多晶型形式结晶，一种（ndl）从四氢呋喃（THF）/乙醇中结晶成针状，另一种（prm）从水/乙醇中结晶成棱柱状。两种形式的分子在一些扭转角和二氨基丁烷桥的取向上彼此不同，尽管对于两种多晶型物，相似键长之间的差异并不显著。在B3LYP/6 - 31 + G*水平对孤立分子进行的几何优化表明，存在于晶体状态的两种构象异构体也代表局部气相能量最小值。当分子参与氢键形成时，通过比较完全优化结构ndl和prm及其氢键模型簇的分子中的原子（AIM）和自然键轨道（NBO）分析结果，从优化结构到晶体结构中N - H距离的减小已根据N - H键路径的键临界点（b.c.p.）处电子密度（ρ）的减小来描述。
