STUDIES ON DIACETYLENE COMPLEXES WITH WATER AND AMMONIA

Ab initio calculations at second-order Moller-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 C-2v and C-3v symmetry for H2O and NH3, respectively. Unlike diacetylene-HF, the pi-complexes are found to be much weaker and for diacetylene-NH3 no stable pi-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 sigma-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.