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···O interactions, one by O–H···S, one by O–H···π, and one with an unusual, dual interaction of O–H···S and C–H···O. The O–H···π interaction was found to have the lowest overall energy at multiple levels of theory (B3LYP, B3LYP-GD3BJ, B97-D3, M05-2X, ωB97X-D, and MP2). Analysis of matrix isolation FTIR spectra indicated that the primary experimental geometry was a complex where water interacts through C–H···O at the α 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···O and O–H···π). These atypical differences are explored in our findings.

Weakly-bound complexes containing aromatic species have been the subject of study for many years. Here, a study of the weakly-bound complexes of thiophene (C 4 H 4 S) with water will be presented. In this study, matrix isolation FTIR and computational methods were used to examine stable 1:1 complexes of thiophene : water (Tp:H 2 O). Multiple density functional theories along with MP2 calculations were used to find four stable geometries. Two geometries can be described by C−H•••O interaction, one by O−H•••π interaction, and one by O−H•••S interaction. These geometries were found to be within 10 kJ/mol of each other by all computational methods. Matrix isolation FTIR experiments identified several peaks that were not associated with isolated water or thiophene, implying the bands are due to weakly-bound complexes of the two. In addition to normal water, D 2 O and HDO complexes with thiophene were also observed. Possible interpretations of the experimental and computational results will be presented. Comparisons to the structure of furan (C 4 H 4 O) : water a will also be discussed.