Abstract:
Interaction energy (E-int) values of a variety of hydrogen, halogen, and dihydrogen bonded complexes in the weak, medium, and strong regimes have been computed using W1BD, MP2, M06L density functional theory, and hybrid methods MP4//MP2, MP4//M06L, and CCSD(T)//MP2. W1BD level E-int and CCSD(T) results reported in the literature show very good agreement (mean absolute deviation=0.19 kcal/mol). MP2 underestimates E-int while M06L shows accurate behavior for all except halogen and charge-assisted hydrogen bonds. MP4//MP2, MP4//M06L, and CCSD(T)//MP2 yield E-int very close to those obtained from W1BD. The high accuracy energy data at MP4/MP2 is used to study the effect of a cation (Li+, NH4+) on the E-int. The cation enhances electron donation from the donor to noncovalent bonding region leading to substantial enhancement in E-int (approximate to 141-566% for Li+ and approximate to 105-539% for NH4+) and promotes a noncovalent bond in the weak regime to medium regime and that in the medium regime to strong regime.
