Hydrogen bond cooperativity effects in cyclic and ladder cyanamide oligomers using density functional theory method

The hydrogen bond cooperativity effects in cyclic and ladder oligomers of cyanamide are studied using density functional theory (DFT) method. Among different levels of theory used here, the geometrical parameters for cyanamide monomer at B3LYP/aug-cc-pvdz level are in excellent agreement with the experimental determinations. Cyclic oligomers are found to be more stable than the ladder, and the hydrogen bonds in the former are stronger than those in the latter. The hydrogen bond cooperativity effects are discussed in terms of the strength of hydrogen bonds, energy per hydrogen bond, excess energy, inter- and intra-molecular distances and vibrational frequencies. The positive and negative hydrogen bond cooperativity effects are found for the cyclic and ladder oligomers, respectively. We also report hyperpolarizabilities for these oligomers.