Cooperativity between Intermolecular Hydrogen and Carbon Bonds in ZY···CH 3 CN/CH 3 NC···HX Trimers (ZY = H 2 O, H 2 S, HF, HCl, HBr, NH 3 , and H 2 CO; HX = HF, HCl, and HBr).

Hydrogen-bonding and carbon-bonding interactions are widespread in nature. We studied the cooperativity between these interactions in 42 trimeric complexes ZY···CH 3 CN/CH 3 NC···HX, where ZY molecules are H 2 O, H 2 S, HF, HCl, HBr, NH 3 , and H 2 CO, and HX molecules are HF, HCl, and HBr. Acetonitrile (CH 3 CN) and isoacetonitrile (CH 3 NC) act as hydrogen bond acceptors as well as carbon bond donors in these trimers. Various theoretical methods, such as electronic structure calculations, quantum theory of atoms in molecule (QTAIM), natural bond orbital (NBO), and reduced density gradient analysis, are employed to study these trimers, and the results are compared with the corresponding ZY···CH 3 CN/CH 3 NC and CH 3 CN/CH 3 NC···HX dimers. Electronic structure calculations are performed at the second-order Mo̷ller-Plesset perturbation theory using the 6-311++G(2d,2p) basis set. We show that both the interactions act synergistically in these trimers leading to an increase in their bond strength as compared to the strength in the individual dimers. The cooperative energies for these trimers are in the range of 0.69 to 3.22 kJ/mol. It is seen that the carbon bonds benefit more from the cooperativity than the hydrogen bonds. The trends of cooperativity and correlations of interaction energies and cooperative energies with relevant QTAIM and NBO parameters are reported.