Short hydrogen bonds in 2,4-dinitrobenzoic acid complexed with pyridine

•Short hydrogen bonds are investigated in two complexes between 2,4-DNBA and pyridine.•Spectroscopy with neutrons is used to identify OH and NH stretch vibrations.•DFT calculations aid in the assignment of modes connected to short hydrogen bonds.•Single crystal XRD is used to determine the structure of the two complexes.•The composition of the complexes is determined with chemical analysis (CHN).

The aim of this work was to describe the vibrations connected with the short hydrogen bonds of differing geometries in 2,4-dinitrobenzoic acid and in 2,4-dinitrobenzoic acid complexed in two ratios with pyridine. All three compounds contain short hydrogen bonds either between two acid molecules (OH⋯O bond) or between acid and pyridine (NH⋯O bonds) or both. We selectively deuterated the proton of the 2,4-dinitrobenzoic acid molecule involved in the proton transfer to aid in the assignment of the H-bond protonic modes. The compounds have been characterized with single crystal X-ray diffraction, CHN elemental analysis, FT-IR and IINS spectroscopy. We show that our combination of analytical methods with DFT calculations represents a fruitful approach to observe the relationship between the geometries of hydrogen bonds and their dynamics.

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