Hydrogen bonding in isomorphous 2-methyl-4-nitroanilinium bromide and iodide

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...O_NO2 interactions. The opposite occurs in the crystal structure of 2-methyl-4-nitroaniline salts, where a variety of O_NO2...π(N)_NO2 non-hydrogen bonding interactions are observed.

Comparison of hydrogen bonds and diverse weak interactions of the nitro group in 2-methyl-4-nitroanilinium nitrate, bisulfate and two hexafluoridosilicates: elementary graph-set approach

Crystal structures of (H2m4na)NO₃ (1), (H2m4na)HSO₄ (2), (H2m4na)₂SiF₆ (3) and (H2m4na)₂SiF₆·2H₂O (4), where 2m4na = 2-methyl-4-nitroaniline, are presented. Two layers of interactions occur in the structures, N-H...O/F hydrogen bonds and interactions with the nitro group. Although diverse, hydrogen-bonding patterns are compared with each other by means of interrelations among elementary graph-set descriptors and descriptors of hydrogen-bonding patterns. Using mathematical relations, the gradual expansion of the ring patterns was shown in the crystal structures. Parallel and perpendicular arranged nitro groups form weak π(N)_NO2...π(O)_NO2 and π(N)_NO2...O_NO2 interactions, respectively. The π_NO2...π_ring interaction has an impact to the stabilization of parallel oriented nitro groups. Generally, weak interactions constructed by the nitro group occur in the studied crystals as follows: π(N)_NO2...π(O)_NO2, π_ring...π_ring, C-H...O (1); π(N)_NO2...π(O)_NO2, π(N)_NO2...O_NO2 (2); π(N)_NO2...π(O)_NO2, π(N)_NO2...O_NO2 (3); C-H...O (4).

Hydrogen bonding in 4-nitrobenzene-1,2-diamine and two hydrohalide salts

The structures of 4-nitrobenzene-1,2-diamine [C6H7N3O2, (I)], 2-amino-5-nitroanilinium chloride [C6H8N3O2(+)·Cl(-), (II)] and 2-amino-5-nitroanilinium bromide monohydrate [C6H8N3O2(+)·Br(-)·H2O, (III)] are reported and their hydrogen-bonded structures described. The amine group para to the nitro group in (I) adopts an approximately planar geometry, whereas the meta amine group is decidedly pyramidal. In the hydrogen halide salts (II) and (III), the amine group meta to the nitro group is protonated. Compound (I) displays a pleated-sheet hydrogen-bonded two-dimensional structure with R2(2)(14) and R4(4)(20) rings. The sheets are joined by additional hydrogen bonds, resulting in a three-dimensional extended structure. Hydrohalide salt (II) has two formula units in the asymmetric unit that are related by a pseudo-inversion center. The dominant hydrogen-bonding interactions involve the chloride ion and result in R4(2)(8) rings linked to form a ladder-chain structure. The chains are joined by N-H···Cl and N-H···O hydrogen bonds to form sheets parallel to (010). In hydrated hydrohalide salt (III), bromide ions are hydrogen bonded to amine and ammonium groups to form R4(2)(8) rings. The water behaves as a double donor/single acceptor and, along with the bromide anions, forms hydrogen bonds involving the nitro, amine, and ammonium groups. The result is sheets parallel to (001) composed of alternating R5(5)(15) and R6(4)(24) rings. Ammonium N-H···Br interactions join the sheets to form a three-dimensional extended structure. Energy-minimized structures obtained using DFT and MP2 calculations are consistent with the solid-state structures. Consistent with (II) and (III), calculations show that protonation of the amine group meta to the nitro group results in a structure that is about 1.5 kJ mol(-1) more stable than that obtained by protonation of the para-amine group. DFT calculations on single molecules and hydrogen-bonded pairs of molecules based on structural results obtained for (I) and for 3-nitrobenzene-1,2-diamine, (IV) [Betz & Gerber (2011). Acta Cryst. E67, o1359] were used to estimate the strength of the N-H···O(nitro) interactions for three observed motifs. The hydrogen-bonding interaction between the pairs of molecules examined was found to correspond to 20-30 kJ mol(-1).

Bis(2-methyl-4-nitro-anilinium) tetra-chloridomercurate(II)

The title compound, (C₇H₉N₂O₂)₂[HgCl₄], self-assembles into cationic organic bilayers containing the 2-methyl-4-nitro­anilinium cations, sandwiched between anionic inorganic layers built up by the distorted tetra­hedral [HgCl₄]²⁻ groups. The organic sheets are inter­linked through weak C—H⋯O hydrogen bonds, while they inter­act with the anionic part via strong charge-assisted N⁺—H⋯Cl—Hg hydrogen bonds. The [HgCl₄]²⁻ anions are bis­ected by a mirror plane passing through the metal and two of the chloride ions.