Gholivand Khodayar, Mahzouni Hamid Reza
Department of Chemistry, Tarbiat Modares University, Tehran, Iran.
Acta Crystallogr B. 2011 Jun;67(Pt 3):238-43. doi: 10.1107/S0108768111010470. Epub 2011 Apr 13.
A phosphoric triamide with the formula (4-CH(3)-C(6)H(4)NH)P(O)(NC(4)H(8)O)(2) has been synthesized and characterized. X-ray crystallography at 120 K reveals that the title compound is composed of two symmetrically independent molecules in the solid state. Density functional theory (DFT) calculations reveal that two conformers A and B are very close to each other from an energy point of view. Thus there is equal chance that the presence of two conformers in the lattice may lead to hydrogen-bonded chains with an ABABAB arrangement. Hydrogen bonds of the type O(P)...H-N (O(P) being the phosphoryl O atom) are established between the two conformers with binding energies of -18.8 and -20.3 kJ mol(-1) (at B3LYP/6-31+G*). The electronic delocalization LP(O(P)) → σ*(N-H), LP(O(P)) being the lone pair of O(P), leads to a decrease in the strength of the N-H bond during hydrogen bonding between the conformers. The charge density (ρ) at the bond critical point (b.c.p.) of N-H decreases by ∼0.012-0.014 e Å(-3) when the molecule participates in hydrogen bonding. This may explain the red shift of the ν(N-H) stretching frequency from a single molecule in the gas phase to a hydrogen-bonded one in the solid state.
已合成并表征了一种分子式为(4-CH(3)-C(6)H(4)NH)P(O)(NC(4)H(8)O)(2)的磷酰胺。120 K下的X射线晶体学研究表明，该标题化合物在固态下由两个对称独立的分子组成。密度泛函理论(DFT)计算表明，从能量角度来看，两种构象异构体A和B彼此非常接近。因此，晶格中两种构象异构体的存在有同等机会形成ABABAB排列的氢键链。在两种构象异构体之间形成了O(P)...H-N型氢键（O(P)为磷酰基O原子），结合能为-18.8和-20.3 kJ mol(-1)（在B3LYP/6-31+G水平）。电子离域LP(O(P)) → σ(N-H)（LP(O(P))为O(P)的孤对电子）导致构象异构体之间形成氢键时N-H键强度降低。当分子参与氢键形成时，N-H键临界点(b.c.p.)处的电荷密度(ρ)降低约0.012 - 0.014 e Å(-3)。这可能解释了ν(N-H)伸缩频率从气相中的单个分子到固态中的氢键分子的红移现象。
