Hydrogen bonding in ionic systems of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) with 4-cyanophenol: ab initio and DFT studies of their structures

The structures of the hydrogen-bonded systems of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) with one and two 4-cyanophenol molecules have been investigated employing ab initio and DFT calculations at different basis sets. The calculations show that the optimised structures of the studied systems are cyclic. The calculated values of the dissociation energy and the changes of the atomic charges upon hydrogen bonding for the studied hydrogen-bonded systems confirm their ionic structures. The hydrogen bonding of TBD with one and two 4-cyanophenol molecules leads to changes in the structural (bond lengths and angles) and vibrational (vibrational frequencies and infrared intensities) characteristics of the monomers. It was established that the TBD molecule is considerably deformed upon hydrogen bonding, while the deformation of the 4-cyanophenol molecules is smaller. The ab initio and DFT predicted vibrational spectra for the complexes TBD: 4-cyanophenol (1:1 and 1:2) demonstrate the ionic character of the forming hydrogen-bonded systems.