Spectroscopic studies of the 1:1 adduct of N-methylmorpholinium-acetate with hydrobromic acid in the crystalline and gaseous state

The 1:1 complex of N-methylmorpholinium-acetate, MMB, with hydrobromic acid (1) has been investigated by single-crystal X-ray analysis, infrared spectroscopy and theoretical calculations. The proton-transfer complex has been observed in the crystalline state, with the COOH⋯Br hydrogen bond with the O⋯Br distance of 3.107(2) Å. In the structure optimized at the B3LYP/6-311++G(d,p) levels of theory the proton is closer to the bromide anion, with the BrH⋯OOC distance of 3.069 Å. The potential energy distributions (PED) have been used for the assignments of IR bands. The experimental and theoretical infrared spectra have been discussed.