Experimental and theoretical identification of C3O2 center dot center dot center dot H2O and C3O2 center dot center dot center dot NH3 complexes: Pre-reactive intermediates of a 1,4 nucleophilic addition

The structure and energy properties of the H2O/C3O2 (D2O/C3O2) and NH3/C3O2 ((NH3)-N-15/C3O2) 1:1 complexes have been investigated in solid argon matr ices with FT-infrared spectroscopy and ab initio calculations at the MP2/6- 31G** level. These complexes trapped in argon matrices are characterized by a large shift of the upsilon(CCO) stretching modes to lower frequencies. P redicted frequency shifts for the T-Nu shaped structure were found to be in good agreement with the observed complex vibrational frequency shifts. The se complexes are indicative of a nucleophilic attack of the oxygen (or nitr ogen) atom on the C4 atom of the C3O2 moiety. At the same time, we observe very short intermolecular distances between the O1 oxygen atom of the subox ide subunit and the hydrogen atom of H2O (D2O), or NH3 ((NH3)-N-15), lying in the C3O2 plane (2.77 and 2.96 Angstrom for H2O (D2O) and NH3 ((NH3)-N-15 ), respectively). These values are indicative of a hydrogen bond between th ese atoms. Examination of the T-Nu complex structures shows for the C3O2 su bunit the pinching of the CCC (-22 degrees and -26 degrees for H2O and NH3, respectively) and the CCO valence bond angles (-3 degrees for H2O and NH3) . The geometries of the complexes and the structural modifications of the c omplex's suboxide moiety suggest pre-reactive intermediates of an 1,4 nucle ophilic addition.