X-ray diffraction, vibrational and quantum chemical investigations of 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid

Structural and theoretical analysis of 2-chloro-4-nitroaniline and 2-methyl-6-nitroaniline salts

The crystal structures of five new salts of 2-chloro-4-nitroaniline (2Cl4na) and 2-methyl-6-nitroaniline (2m6na) with inorganic acids, namely, 2-chloro-4-nitroanilinium bromide, C₆H₆ClN₂O₂⁺·Br^- (1), 2-chloro-4-nitroanilinium hydrogen sulfate, C₆H₆ClN₂O₂⁺·HSO₄^- (2), 2-methyl-6-nitroanilinium bromide, C₇H₉N₂O₂⁺·Br^- (3), 2-methyl-6-nitroanilinium triiodide, C₇H₉N₂O₂⁺·I₃^- (4), and 2-methyl-6-nitroanilinium hydrogen sulfate, C₇H₉N₂O₂⁺·HSO₄^- (5), were determined by single-crystal X-ray diffraction. Theoretical calculations of the relaxed potential energy surface (rPES) revealed that the energy barriers for the rotation of the nitro group for isolated H2Cl4na⁺ and H2m6na⁺ cations are 4.6 and 11.6 kcal mol^-1, respectively. The ammonium group and respective anions form hydrogen bonds which are the most important interactions and are arranged in zero- (in 3), one- (in 1 and 4) or two-dimensional (in 2 and 5) networks. Hydrogen-bonding patterns were analyzed by means of mathematical relationships between graph-set descriptors and compared with previously reported nitroaniline salts. Hirshfeld surface analysis indicates that the nitro group plays a dominant role among the weak interactions, i.e. C-H...O(NO₂), NO₂...π(Ar) and O(NO₂)...π(NO₂). The frequency of the ν_sNO₂ vibration is correlated with the type of interaction in which the NO₂ group is involved. Analysis of the ν_sNO₂ band observed in the IR and Raman spectra allowed an assessment of its shift in the sequence (H2m6na)I₃ (4) < (H2m6na)HSO₄ (5) < (H2m6na)Br (3) < (H2Cl4na)Br (1) < (H2Cl4na)HSO₄ (2).

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.

Quantum chemical studies and spectroscopic investigations on 22-amino-3-methyl-5-nitropyridine by density functional theory

Quantum chemical calculations on energy and molecular structure of 2-amino-3-methyl-5-nitropyridine (2A3M5NP) have been attempted by implementing DFT/B3LYP method using 6-311G (d,p), 6-311G++ (d,p) and cc-pVTZ basis sets. The optimized geometry and the vibrational analysis for energetically most stable configuration, are carried out theoretically by using B3LYP/cc-pVTZ basis set. The computed vibrational frequencies were scaled by using scaling factors and compared with the experimental Fourier Transform Infra-Red (FTIR) solid phase spectrum in the region 4000-400 cm-1 and FT-Raman spectrum in the region 4000-100 cm-1. The complete vibrational assignments, analysis and correlation of fundamental modes of the compound have been carried out using the potential energy distribution (PED). The intramolecular charge transfer, hyperconjugative interaction of the compound is investigated from natural bonding orbital (NBO) analysis. The UV-Visible spectrum of 2A3M5NP was obtained with ethanol as a solvent. The electronic properties such as HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) energies are determined by B3LYP/cc-pVTZ basis set. The electronic absorption spectrum of the compound was studied from UV-Visible analysis by using time-dependent density functional theory (TD-DFT). The electron density distribution and chemical reactive sites of 2A3M5NP were analyzed from molecular electrostatic potential (MEP) analysis and frontier molecular orbital (FMO) analysis.

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).

Structural, vibrational and theoretical studies of anilinium trichloroacetate: new hydrogen bonded molecular crystal with nonlinear optical properties

In this work, we report a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of the potential nonlinear optical (NLO) material anilinium trichloroacetate. The FT-IR and FT-Raman spectra of the compound have been recorded together between 4000-80 cm(-1) and 3600-80 cm(-1) regions, respectively. The compound crystallizes in the noncentrosymmetric space group of monoclinic system. The optimized molecular structure, vibrational wavenumbers, IR intensities and Raman activities have been calculated by using density functional method (B3LYP) with 6-311++G(d,p) as higher basis set. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. DSC measurements on powder samples do not indicate clearly on the occurrence of phase transitions in the temperature 113-293 K. The Kurtz and Perry powder reflection technique appeared to be very effective in studies of second-order nonlinear optical properties of the molecule. The non-linear optical properties are also addressed theoretically. The predicted NLO properties of the title compound are much greater than ones of urea. In addition, DFT calculations of the title compound, molecular electrostatic potential, frontier orbitals and thermodynamic properties were also performed at 6-311++G(d,p) level of theory. For title crystal the SHG efficiency was estimated by Kurtz-Perry method to be d(eff)=0.70 d(eff) (KDP).