Evidence of C-H•••O Interactions in the Thiophene:Water Complex

An analysis of the 1:1 complex of thiophene and water is presented. In this study, computation and matrix isolation Fourier transform infrared spectroscopy (FTIR) were used to determine stable complexes of thiophene and water. Computational studies found six, low-energy complexes that were differentiated by the interaction present. Three complexes were characterized by C-H center dot center dot center dot O interactions, one by O-H center dot center dot center dot S, one by O-H center dot center dot center dot pi, and one with an unusual, dual interaction of O-H center dot center dot center dot S and C-H center dot center dot center dot O. The O-H center dot center dot center dot pi interaction was found to have the lowest overall energy at multiple levels of theory (B3LYP, B3LYP-GD3BJ, B97-D3, MO5-2X, omega B97X-D, and MP2). Analysis of matrix isolation FTIR spectra indicated that the primary experimental geometry was a complex where water interacts through C-H center dot center dot center dot O at the alpha carbon position of the thiophene ring. This experimental result is not in line with other related complexes (furan:water and thiophene:methanol) where the complex formed through more standard interactions (e.g., O-H center dot center dot center dot O and O-H center dot center dot center dot pi). These atypical differences are explored in our findings.