Synthesis, crystal structure and electron density analysis of a sulfanyl 2-pyridone analogue: Tautomeric preference and conformation locking by S···O chalcogen bonding

Abstract

The effect of intra-molecular chalcogen bonding involving S(sp3)···O(sp2) interaction in locking the molecular conformation has been investigated in 2-hydroxy-5-(4-methoxybenzoyl)-6-(methylsulfanyl)nicotinonitrile. The compound has been synthesized in a one-pot synthetic method and structurally characterized by NMR, FT-IR spectroscopic techniques and single crystal X-ray diffraction. The strength and n→σ∗ nature of the S···O interaction have been revealed by electron density topological analysis and second order perturbation energy estimation of orbital interaction. Among the two possible tautomers, the molecule prefers the relatively less stable one in the solid-state. A rare but robust hydroxyl-nitrile supramolecular synthon identified in the structure helps to understand this tautomeric preference.