Del Bene Janet E, Alkorta Ibon, Elguero José
Department of Chemistry, Youngstown State University , Youngstown, Ohio 44555, United States.
J Phys Chem A. 2014 Mar 27;118(12):2360-6. doi: 10.1021/jp500915c. Epub 2014 Mar 19.
Ab initio MP2/aug'-cc-pVTZ calculations have been carried out in search of equilibrium structures with P···Cl pnicogen bonds or halogen bonds on the potential energy surfaces H2FP:ClY for Y = F, NC, Cl, CN, CCH, CH3, and H. Three different types of halogen-bonded complexes with traditional, chlorine-shared, and ion-pair bonds have been identified. Two different pnicogen-bonded complexes have also been found on these surfaces. The most electronegative substituents F and NC form only halogen-bonded complexes, while the most electropositive substituents CH3 and H form only pnicogen-bonded complexes. The halogen-bonded complexes involving the less electronegative groups Cl and CN are more stable than the corresponding pnicogen-bonded complexes, while the pnicogen-bonded complexes with CCH are more stable than the corresponding halogen-bonded complex. Traditional halogen-bonded complexes are stabilized by charge transfer from the P lone pair to the Cl-A σ* orbital, where A is the atom of Y directly bonded to Cl. Charge transfer from the Cl lone pair to the P-F σ* orbital stabilizes pnicogen-bonded complexes. As a result, the H2FP unit becomes positively charged in halogen-bonded complexes and negatively charged in pnicogen-bonded complexes. Spin-spin coupling constants (1X)J(P-Cl) for complexes with traditional halogen bonds increase with decreasing P-Cl distance, reach a maximum value for complexes with chlorine-shared halogen bonds, and then decrease and change sign when the bond is an ion-pair bond. (1p)J(P-Cl) coupling constants across pnicogen bonds tend to increase with decreasing P-Cl distance.
开展了从头算MP2/aug'-cc-pVTZ计算，以在势能面H2FP:ClY（Y = F、NC、Cl、CN、CCH、CH3和H）上寻找具有P···Cl氮族元素键或卤键的平衡结构。已识别出三种不同类型的具有传统键、氯共享键和离子对键的卤键复合物。在这些势能面上还发现了两种不同的氮族元素键复合物。电负性最强的取代基F和NC仅形成卤键复合物，而电正性最强的取代基CH3和H仅形成氮族元素键复合物。涉及电负性较小的基团Cl和CN的卤键复合物比相应的氮族元素键复合物更稳定，而与CCH形成的氮族元素键复合物比相应的卤键复合物更稳定。传统卤键复合物通过从P孤对向Cl-A σ轨道的电荷转移而稳定，其中A是Y中直接与Cl键合的原子。从Cl孤对向P-F σ轨道的电荷转移使氮族元素键复合物稳定。结果，H2FP单元在卤键复合物中带正电，在氮族元素键复合物中带负电。具有传统卤键的复合物的自旋-自旋耦合常数(1X)J(P-Cl)随着P-Cl距离的减小而增加，对于具有氯共享卤键的复合物达到最大值，然后在键为离子对键时减小并改变符号。跨越氮族元素键的(1p)J(P-Cl)耦合常数倾向于随着P-Cl距离的减小而增加。
