Influence of substituents and cooperativity in doubly hydrogen-bonded complexes of 2-pyridone and oxalic acid

We performed a systemic investigation of the substitution and cooperative effects on the O–H···O and N–H···O H-bonds in the complexes of 2-pyridone and its derivatives with oxalic acid. Generally, the electron-withdrawing substituent in 2-pyridone weakens the O–H···O H-bond but strengthens the N–H···O H-bond, while the opposite effect is for the electron-donating group. In addition, the substitution effect is associated with its substitution position in 2-pyridone. The total interaction energy of a chainlike trimer with oxalic acid as a middle molecule exhibits some additivity. When oxalic acid combines with two 2-pyridone/2-pyridinethione molecules, the O–H···O/S H-bond is weakened but the N–H···O H-bond is enhanced. When three oxalic acid molecules are linked by the double O–H···O H-bonds, one H-bond with the middle oxalic acid as the proton donor is weakened and the other H-bond with the middle oxalic acid as the proton acceptor is strengthened.