Water-Water and Water-Solute Interactions in Microsolvated Organic Complexes

A structural study of microsolvated clusters of beta-propiolactone (BPL) formed in a pulsed molecular jet expansion is presented. The rotational spectra of BPL-(H2O)(n) (n=1-5) adducts have been analyzed by broadband microwave spectroscopy. Unambiguous identification of the structures has been achieved using isotopic substitution and experimental measurements of the cluster dipole moment. The observed structures are discussed in terms of the different intermolecular interactions between water molecules and between water and BPL, which include n-pi* interactions involving the lone pairs of electrons on water oxygen atoms and the antibonding orbital of the BPL carbonyl group. The changes induced in the structures of the water hydrogen-bonding network by complexation to BPL indicate that water clusters adopt specific configurations to maximize their links to solute molecules.