Structure and properties of the sodium, potassium and calcium salts of 2-(2,3-dimethylphenyl)aminobenzoic acid

The mefenamic acid sodium, potassium, and calcium salts with general formulae [Na(mef)(H2O)2]n·nH2O, [K(mef)(H2O)]n and [Ca(mef)2(H2O)2]n·nH2O have been synthesised, studied by X-ray crystallography, 1H and 13C NMR and IR spectroscopy. The complex salts are air stable and soluble in water. During heating the Na and K complexes melt in the complexed water and next recrystallise in anhydrous form. In the solid state all salts create one-dimensional coordination polymers. The central atoms are five, six and seven coordinated, respectively, for Na, K and Ca complexes. In all structures exist OH⋯O, NH⋯O and CH⋯O hydrogen bonds. The vibrational analysis has been carried out for mefenamic acid and its three coordination polymer compounds on the basis of experimental results as well as quantum mechanical calculations. The theoretical and experimental vibrational frequencies are similar and reveal characteristic vibrations for all IR active oscillators. In the IR spectra of salts exist strong bands at ca. 1365 and 1600 cm−1 typical for carboxylate groups.