Studies on diacetylene complexes with water and ammonia

Ab initio calculations at second-order Møller-Plesset (MP2) level with a 6–31G∗∗ basis set have been carried out on diacetylene complexes with H2O and NH3. The equilibrium structures are symmetric with C2v and C3v symmetry for H2O and NH3. respectively. Unlike diacetylene-HF, the π-complexes are found to be much weaker and for diacetylene-NH3 no stable π-complex has been detected. The hydrogen bond lengths at MP2 level are a little shorter than the experimental values. The hydrogen bond lengths at SCF level are in close agreement with experiment. The diacetylene σ-complexes are more stable than the corresponding acetylene complexes. The diacetylene complexes possess a larger induced dipole moment than the acetylene complexes, and the ratio is found to be in agreement with experiment.