It was found that the binding energy values calculated by B3LYP differ
significantly from the same calculated at M06-2X (Table 1). This might
be due to the contribution of long-range dispersion interaction which is
known to play an important role in stabilizing weak H-bonded complexes.
Therefore, geometry optimization, frequency calculation and single point
counterpoise correction have been carried out using ωB97X-D functional
and 6-311++G** basis set. Further, counterpoise corrected single point
energy calculation has been performed using M06-2X functional and
6-311++G** basis set for geometries optimized at ωB97X-D/6-311++G**
level of theory given in Table 1. Here, the stabilization energy
obtained at this level was close to what was predicted by
ωB97X-D/6-311++G** level of theory. Therefore throughout the manuscript
stabilization energy calculated at ωB97X-D/6-311++G** level has been
used for study the molecular cluster. Natural bond orbital and atoms in
molecules calculations have been carried out using ωB97X-D functional
and 6-311++G** to corroborate with the energetic and geometric findings.
All the geometry optimization, normal mode frequency and natural bond
orbital (NBO)60calculation have been carried out using
Gaussian1661 suite of
program where as topological analysis was performed using AIM 2000
software package.62Throughout the manuscript, all the binding energy values mentioned are
counterpoise corrected values calculated at ωB97X-D/6-311++G** level of
theory, unless otherwise mentioned.
Results and discussion:
In this work, we have investigated the intermolecular C-H···O H-bond
formed between two CHD molecules and how they undergo modifications with
increasing size of CHD clusters from dimer to hexamer. In order to do
so, we have focused on the geometric, energetic and electronic features
of the C-H—O H-bonds and subsequently tried to quantify the extent
of cooperativity (both positive and negative) exerted by them.