Abstract
Extensive calculations of potential energy surfaces for parallel-displaced configurations of pyrrole–pyrrole systems have been carried out by the use of a dispersion-corrected density functional. System geometries associated with the energy minima have been found. The minimum interaction energy has been calculated as −5.38 kcal/mol. However, bonding boundaries appeared to be relatively broad, and stacking interactions can be binding even for ring centroid distances larger than 6 A. Though the contribution of the correlation energy to intermolecular interaction in pyrrole dimers appeared to be relatively small (around 1.6 smaller than it is in a benzene–benzene system), this system’s minimum interaction energy is lower than those calculated for benzene–benzene, benzene–pyridine and even pyridine–pyridine configurations. The calculation of the charges and energy decomposition analysis revealed that the specific charge distribution in a pyrrole molecule and its relatively high polarization are the significant source of the intermolecular interaction in pyrrole dimer systems.
Highlights
Non-covalent interactions (NCI) are inarguably of a great importance in chemical, catalytic and especially in biological systems
The understanding of their nature together with their interplaying and dependencies between different types of NCI is critical for harnessing their full potential in chemistry, especially when the precise control of the strength and geometry of intermolecular interactions is concerned, e.g. in the material improving processes and drug design strategy
That though M05-2X energies deviate relatively much from those obtained from CCSD(T)/complete basis set (CBS), the general energy dependencies between these two are similar
Summary
Non-covalent interactions (NCI) are inarguably of a great importance in chemical, catalytic and especially in biological systems. In order to identify an appropriate DFT functional for the PES study, the PES scan of the selected pyrrole–pyrrole model systems (Fig. 2) was performed at the CCSD(T)/ CBS level of theory using aug-cc-pVDZ and aug-cc-pVTZ basis sets [55] to obtain the MP2/CBS limit energy through the extrapolation scheme as described by Helgaker et al [56]: ECBS In order to find possible orbital interactions between the monomers in the studied dimers (e.g. associated with the creation of N–HÁÁÁp bond(s)), the electronic properties of the model dimer pyrrole systems with the energies corresponding to the energy minima on the PES maps (the global energy minimum and the selected local minima, Fig. 5)
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