Comparative study of the hydrogen-bonded complexes of phenol and o-cyanophenol with CO: Ab initio and DFT approachs

The structures, stability and vibrational spectra of the hydrogen-bonded complexes of carbon monoxide (CO) with phenol and o-cyanophenol (syn and anti) have been studied using ab initio and DFT calculations. Full geometry optimization has been performed for the studied complexes by DFT (BLYP/6-311++G(d,p)) calculations. The calculations show that the hydrogen-bond formation of carbon monoxide (CO) with phenol and o-cyanophenol (syn and anti) leads to the following stable structures: C6H5OH…CO (1A); C6H5OH…OC (1B); (syn) o-CNC6H4OH…CO (2A-syn); (syn) o-CNC6H4OH…OC (2B-syn); (anti) o-CNC6H4OH…CO (2A-anti) and (anti) o-CNC6H4OH…OC (2B-anti). Having in mind the corrected values of the dissociation energy, the studied hydrogen-bonded complexes can be ordered according their stability as follows: 2A-anti > 2A-syn > 1A > 2B-anti > 1B > 2B-syn. The predicted red-shifts for the νOH vibration with the B3LYP/6-311++G(d,p) calculations for the structures 1A (−46 cm−1), 2A-syn (−60 cm−1) and 2A-anti (−73 cm−1) are in very good agreement with the experimentally observed. The magnitudes of the wavenumber shifts are indicative of relatively weak OH…C hydrogen-bonded interactions. The calculations predict an increase of the IR intensity of the νOH vibration in the complexes 1A, 2A-anti and 2A-syn up to five times.