Solvent effects on vibrational spectra of hydrogen-bonded complexes of propanedinitrile (malononitrile) and dimethyl sulfoxide (DMSO): Ab initio and DFT studies

The hydrogen-bonded complexes malononitrile-dimethyl sulfoxide (DMSO) (1:1; 1:2) have been studied extensively by ab initio and DFT (B3LYP) calculations with different basis sets. The most stable structures of the complexes are established. The vibrational spectra of the complexes have been predicted by ab initio and B3LYP calculations and the solvent effects on the vibrational spectrum of malononitrile are evaluated. In agreement with the experiment, the calculations show that the moderately strong O…C-H hydrogen bonds are formed between malononitrile and DMSO that lead to the substantial changes in the vibrational characteristics (vibrational frequencies and IR intensities) for νsym(CH2) and νas(CH2) in malononitrile. The predicted frequency shift with B3LYP/6-311++G(d,p) calculations for νsym(CH2) is −98 cm−1 and for νas(CH2) is −53 cm−1, while the experimentally observed shifts are in the range: from −51 to −81 cm−1. The IR intensity for νsym(CH2) increases upon hydrogen bonding at the higher extent in comparison with the IR intensity of νas(CH2).