Structural, theoretic and spectroscopic analysis of 2-methyl-5-nitroaniline salts with various inorganic acids.

Crystal structures of six new salts of 2-methyl-5-nitroaniline with inorganic acids [(H2Me5NA)Br, (H2Me5NA)I, (H2Me5NA)NO3, (H2Me5NA)Cl, (H2Me5NA)HSO4 and (H2Me5NA)I3·0.5H2O] are determined by single-crystal X-ray diffraction. The most important hydrogen-bonding patterns are formed by the ammonio group and respective anions composing 1D or 2D networks. The patterns are analysed using the graph-set approach and mathematical interrelations between graph-set descriptors are shown for comparative purposes. Analysis of IR spectra enables the strength of hydrogen bonds in the crystals to be assessed. The frequency of N-H and O-H stretching vibrations and NH3 group libration indicates that the strongest hydrogen bonds are present in (H2Me5NA)HSO4, whereas the weakest ones occur in (H2Me5NA)I3·0.5H2O. Hirshfeld surface analysis reveals that apart from obvious N-H...anion hydrogen bonds, the molecules are also connected to each other by exclusive C-H...ONO2 interactions. The opposite occurs in the crystal structure of 2-methyl-4-nitroaniline salts, where a variety of ONO2...π(N)NO2 non-hydrogen bonding interactions are observed.