Theoretical studies on the interaction of the CO•••CO+ coupling system using density functional theory

Three hybrid density functional theory ( DFT) methods ( B3LYP ( Becke' s three-parameter Hybrid Functional using the Lee-Yang-Parr Correlation Function), B3P86 and B3PW91 ( Becke's three-parameter Hybrid Functional with Perdew86 and perdew/Wang91 Correlation Functions respectively)) and two appropriate basis sets (6-311 + G * and aug-cc-PVDZ) have been employed to investigate all the possible structures of the (COCO+)-C-... coupling system on the global potential energy surface. The results show that there are three relative stable complexes verified by none imaginary frequencies. Among them complexes A and B are co-plane structures except complex C and the subtle difference between complexes B and C is the dihedral of them. Complex A is the most stable structure through the comparison of the energies of three complexes. The orbital binding character using the population analysis and covalent bond orders between atoms within the AIM methodology is also calculated at B3LYP/6-311 + G * level. Then the precise interaction energies of the three complexes have been obtained through the corrections of the basis set superposition error ( BSSE) and the zero point vibration energy (ZPVE), and the full counterpoise procedure ( FCP) recommended by Boys and Bernardi has been applied for the BSSE correction. The results of the interactive energies are 252.47, 126.70, 127.12 kJ/mol for complexes A, B and C respectively, which are in agreement with the literature data reported before. Finally, we list the normal vibrational frequencies and corresponding IR intensity of the three complexes at B3LYP/6-311 + G * level. Moreover, the analytical figure of normal vibration frequencies for complex A is also displayed at the same time. All computations indicate that the interaction between CO and CO+ is strong and DFT methods can serve as an effective tool to predict the molecular geometry, thermodynamics and frequencies that are well close to the experimental values.