Tuning of carbon bonds by substituent effects: an ab initio study

An ab initio study, at the MP2/aug-cc-pVTZ level of theory, is performed to study sigma-hole bond in binary XH3C center dot center dot center dot CNY complexes, where X = CN, F, NO2, CCH and Y = H, OH, NH2, CH3, C2H5, Li. This type of interaction is labelled as 'carbon bond', since a covalently bonded carbon atom acts as the Lewis acid in these systems. The geometrical and energetic parameters of the resulting complexes are analysed in details. The interaction energies of these complexes are between -4.97 kJ/mol in (HCC) H3C center dot center dot center dot CNH and -23.07 kJ/mol in (O2N) H3C center dot center dot center dot CNLi. It is found that the electrostatic interaction plays a key role in the overall stabilisation of these carbon-bonded complexes. To deepen the understanding of the nature of the carbon-bonding, the molecular electrostatic potential, natural bond orbital, quantum theory of atoms in molecules and non-covalent interaction index analyses are also used. Our results indicate that the carbon bond is favoured over the C-H center dot center dot center dot C hydrogen bond in the all complexes considered and may suggest the possible important roles of the C center dot center dot center dot C interactions in the crystal growth and design. [GRAPHICS] .