Spectroscopic, structural and theoretical studies of 2‐methyl‐4‐nitroaniline (MNA) crystal. Electronic transitions in IR

Abstract

Polarized FT-IR, Raman, neutron scattering (IINS), and UV-Vis-NIR spectra of 2-methyl-4-nitroaniline (MNA) crystal plates, powder, and solutions were measured in the 10-50 000 cm −1 range. The FT-IR spectrum of deuterated MNA (DMNA) in KBr pellet, the Raman spectrum of the DMNA powder as well as the EPR spectrum of the MNA powder were also recorded. Complete assignments of bands to normal vibrations have been proposed. Density functional theory (DFT) calculations of wavenumbers and potential energy distribution (PED) have been performed to strengthen the assignments. The analysis of vibrational and electronic spectra has revealed vibronic couplings in MNA molecules in solutions and in crystals. In the polarized FT-IR spectra of the crystal five unusually large bands are observed in MIR and NIR regions. Their origin is discussed in terms of N-H· · ·O, C-H· · ·O, C-H· · ·H-N hydrogen bonds, intermolecular charge transfers, electrostatic interactions, and ion radicals formation in the crystal. The role of a methyl group introduction to 4-nitroaniline is analyzed. The crystal structure of MNA at the room temperature was re-investigated.

Investigation of the linear and second-order nonlinear optical properties of molecular crystals within the local field theory

“…In isooctane (which is the solvent with the lowest polarity employed for its optical characterization) the energy of maximum absorption of the CT band is ∼3.80 eV. 38 Eq. (8) rather than the traditional TDHF method.…”

The revision of intermolecular interactions in 1,3‐dinitrobenzene crystal—the role of nitro groups in optical nonlinearity

“…The energy difference (Δν el ) between the forbidden A 1g → B 2u transition in the benzene molecule in the gas phase (38 089 cm −1 ) and the first electronic transition in 1,3‐dinitrobenzene has been calculated from the measured spectra. This parameter was proposed as the measure of optical nonlinearity in substituted benzenes63 and also served as the measure of vibronic couplings involving ICT and intermolecular CT 16, 64. It amounted approximately 4400 cm −1 for 1,3‐DNB in isooctane solution.…”

“…There has been an ongoing research in our laboratory on molecular crystals exhibiting nonlinear optical properties. The group of crystals under study contained substituted benzenes with nitro groups, such as 3‐nitroaniline,1–11 3‐nitrophenol,12–14 and 2‐methyl‐4‐nitroaniline 15, 16. The crystal of 1,3‐dinitrobenzene (Fig.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part III

“…Quite often, SERS was also employed to determine the orientation of the molecules on a metal surface. Such studies are compiled here for the following molecules: 1H-and 3H-imidazo [4,5-b]pyridine and their methyl derivatives, [113] copper(II) chloride and bromide compounds of KCuBr 3 , [114] 5,6-diméthyluracile, [115] [C(NH 2 ) 3 ] 2 M II (H 2 O) 4 (SO 4 ) 2 , M II = Mn, Cd and VO, [116] potassium trimethylsilanolate, [117] 2-aminopyridinium-4-hydroxybenzenosulfonate, [118] the H 4 I 2 O 10 2− ion in CuH 4 I 2 O 10 · 6H 2 O, [119] 2-amino-4,6-dihydroxypyrimidine, [120] 3 (or 4 or 6)-methyl-5-nitro-2-pyridinethiones, [121] 2-methyl-4-nitroaniline (MNA) crystal, [122] 2-amino-5-chloropyridinium hydrogen selenate, [123] the food dye amaranth, [124] transstilbene in the excited singlet state, [125] chloramphenicol, [126] oroxylin, [127] 4-fluoro-N-(2-hydroxy-4-nitrophenyl)benzamide, [128] phenanthridine, [129] 3,5 dichloro hydroxy benzaldehyde and 2,4 dichloro benzaldehyde. [130] Solid State (Minerals, Crystals, Linear Chains, Glasses, Ceramics and Disordered Materials) Minerals A great number of minerals have been studied during 2008 by the Frost group [131 -146] using both Raman and infrared spectroscopies: smithsonite, [131] the uranyl carbonate mineral voglite, [132] hydrotalcite with CO 3 2− and (MoO 4 ) 2− anions in the interlayer, [133] the uranyl phosphate minerals phosphuranylite and yingjiangite, [134] the uranyl carbonate mineral zellerite, [135] the molybdate-containing uranyl mineral calcurmolite, [136] the oxalate mineral wheatleyite Na 2 Cu 2+ (C 2 O 4 ) 2 ·2H 2 O, [137] the nickel silicate mineral pecoraite, [138] synthetic nesquehonite, [139] the uranyl mineral, compreignacite, K 2 [(UO 2 ) 3 O 2 (OH) 3 ] 2 ·7H 2 O, [140] the hydroxy nickel carbonate minerals nullaginite and zaratite, …”