Theoretical study on the cooperativity of hydrogen bonds in (HNC) 2⋯HF complexes

Abstract

Ab initio calculations at the MP2(FC)/aug-cc-pVDZ level have been used to study the systems HNC–HNC–HNC, HF–HNC–HNC, HNC–HNC–HF and HF–HNC–HNC–HF. The binding distances, dipole moments, frequency shifts and interaction energies in these systems have been analyzed to study the cooperativity of hydrogen bond in the systems. The results indicate that the cooperativity of hydrogen bond is larger when a HF molecule acts as a proton donor in the system. This is reflected in the shorter C⋯H distance, larger dipole moment, larger cooperative energy, greater shifts of the donor N–H bond and the acceptor N–C bond stretching frequencies, and larger cooperativity factor in HNC–HNC–HF system. We also compared the contribution of HF as the proton donor and acceptor to the cooperativity of hydrogen bond. The cooperative energy corresponds to 28.6% and 30.0% of the total interaction energy in HNC–HNC–HF and HF–HNC–HNC systems, respectively. It is found that the proton acceptor plays a little bigger contribution to the cooperativity of hydrogen bond. Many-body interaction analyses have also been performed for these systems.