AN AB-INITIO STUDY OF HYDROGEN-BONDED COMPLEXES OF PYRIDONE WITH WATER

Ab initio calculations have been carried out at the MP2/6-31+G(d,p) level of theory to determine the equilibrium structures of complexes formed between pyridone and water. Two equilibrium H2O:pyridone structures have been found: complex I, a bridging structure in the N-H and C=O region in which a single water molecule is both a proton donor and proton acceptor; and complex II, in which a single water molecule is a proton donor to pyridone at the carbonyl oxygen trans to N-H. The equilibrium structure of a bridging (H2O)(2):pyridone complex in the N-H and C=O region also has been determined. The electronic binding energies of these complexes at MP2/cc-pVTZ+//MP2/6-31+G(d,p) are 12.0, 8.4, and 18.7 kcal/mol, respectively, leading to room temperature binding enthalpies of 10.2, 6.7, and 16.8 kcal/mol, respectively. Comparisons are made between the theoretical results and recent experimental results on the H2O:pyridone complex I and the (H2O)(2):pyridone complex.