A new theoretical analysis of the cooperative effect in T-shaped hydrogen complexes of CnHm∙∙∙HCN∙∙∙HW with n = 2, m = 2 or 4, and W = F or CN.

In this theoretical work, a new idea about cooperativity in intermolecular clusters of CnHm∙∙∙HCN∙∙∙HW stabilized by hydrogen bonds composed by lone-electron pairs (nitrogen) and π clouds (C = C and C ≡ C) as proton acceptors is developed. The structural study and vibrational analysis have pointed out deformations in the intermolecular clusters caused by the HW terminal proton-donor, in which if W = fluorine the largest perturbation occurs. On the contrary, the HCN molecule is considered an intermolecular mediator because its structure is practically unaltered upon the formation of the trimolecular complexes. In order to understand the real contribution of the proton-donor either mediator (HCN) or terminal (HW with W = CN or F), a chemometric analysis was performed uniquely to discover which interaction plays a key role in the collapse of the cooperative effect. The formation of strongest interactions leads to more drastic variations in the energy distribution. In this way, the application of the quantum theory of atoms in molecules (QTAIM) has been extremely important because the hydrogen bond strengths followed by indiciums of covalence were predicted, and therefore the cooperative effect could be understood at last.