A strong Nsingle bondH…Br vibrational behaviour studied through X-ray, vibrational spectra and quantum chemical studies in an isomorphous crystal: 2-Nitroanilinium bromide

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Highlights

  • Comparative studies of theoretical and experimental vibrational spectra of the 2-nitroanilinium bromide.

  • Theoretical bond lengths and bond angles were slightly deviated from the experimental values.

  • Theoretical wavenumber numbers were showed good agreement with the experimental values.

  • Number of modes calculated from the factor group method is match with the theoretical method.

  • Atomic charge analysis is also attempted.

Abstract

A needle shaped transparent light brown crystals of 2-nitroanilinium bromide were successfully synthesized and crystallized from an aqueous mixture by slow evaporation technique. Single crystal XRD studies confirm the crystalline phase of this isomorphous compound which contains a positively charge 2-nitroanilinium cation and a negatively charged bromide anion. The solid phase FT-IR and FT-Raman spectra of the compound have been recorded in the range of 4000–400 cm−1. The observed modes are correlated by the factor group theory analysis and different IR and Raman active species were identified. Geometrical optimisations were carried out and harmonic vibrational wave numbers were computed for the minimum energy molecular structure at RHF level invoking 6-311++G(d,p) and SDD basis sets. Optimised molecular geometry was compared with the crystallographic data. The calculated wavenumbers were compared with the experimental values. The Nsingle bondH vibrational bands are shifted from its normal range and the shifting is associated with the influence of the intermolecular hydrogen bonds in the crystal. A strong intensity peak in theoretical and corresponding band in experimental confirms the presence of Nsingle bondH…Br interaction as predicted in crystalline state.

Graphical abstract

A needle shaped transparent light brown crystals of 2-nitroanilinium bromide were successfully synthesized and crystallized from an aqueous mixture by slow evaporation technique. Single crystal XRD studies confirm the crystalline phase of this isomorphous compound which contains a positively charge 2-nitroanilinium cation and a negatively charged bromide anion. The solid phase FT-IR and FT-Raman spectra of the compound have been recorded in the range of 4000–400 cm−1. The observed modes are correlated by the factor group theory analysis and different IR and Raman active species were identified. As a striking feature of the structure, the evident for the intermolecular Nsingle bondH…Br hydrogen bonding interaction between the cation and anion is observed in both the methods which gives out a sharp peak in spectral intensity which is correlated with the experimental results.

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Introduction

Aniline and its related structures are widely studied because of its importance in many pharmaceutical, electro-optical and several other social applications. Also Aniline is an important raw material for many industrial uses such as dyes, oil paints, rubber and plastics. Aniline has been widely studied for use in electrical conduction, electroluminescence and rechargeable batteries and anti corrosion applications [1], [2], [3].

In most of the cases, the applications are ensued due to the intermolecular interactions especially hydrogen bonds which has its importance in the areas of molecular recognition, crystal engineering research and supramolecular chemistry. Understanding of these non-covalent interactions has proved to be the most valuable because of its strength and directional properties [4]. The strength and directionality of hydrogen bonding interactions is responsible for solid state formation and other physical properties of the system [5]. The nitro substituted anilines are interesting candidates for the design of supramolecular structures as it contains both donor (NH2) and acceptor groups (NO2) for hydrogen bonding interactions. 2-Nitroaniline exists in three phases, viz., α-, β- & γ-polymorphs [6], [7]. Based on the above facts, we are interested on the specificity of recognition of the compound with other inorganic/organic acids. Hence, the present work is attempted here for the crystallization of 2-nitroaniline with hydrobromic acid by experimental and theoretical method.

Section snippets

Preparation

Crystals of 2-nitroanilinium bromide (2NABR) were synthesized from an aqueous mixture of 2-nitroaniline and hydrobromic acid with a stoichiometric ratio of 1:1 at room temperature by slow evaporation. After 10 days, needle-shaped and light brown crystals of 2-nitroanilinium bromide were obtained. The quality of the crystals is improved by recrystallization.

Density measurement

The density of the crystal was measured by sink and swim method (flotation technique) using a liquid mixture of carbon tetrachloride and

Factor group analysis

The title compound, (C6H7N2O2)+·Br (2NABR), crystallizes in the centrosymmetric space group Pbca or D2h15 in the orthorhombic system. The crystal has eight formula units per unit cell. A single-crystal X-ray diffraction study of the title compound predicts that the asymmetric part of the unit cell contains one 2-nitroanilinium cation and a bromide anion. Factor group analysis [12] of the title compound gives rise to 380 genuine normal modes of vibrations (excluding acoustic modes). These

Conclusion

A needle shaped light brown crystals of 2-nitroainlinium bromide were successfully crystallized. Single crystal XRD studies confirm that the asymmetric part contains a cation and an anion. Further, the packing of crystal is achieved through Nsingle bondH…O and Nsingle bondH…Br interactions. The FT-IR and FT-Raman spectra of the crystals and their detailed vibrational assignments were given with high degree of accuracy. The computed wavenumbers were compared with the corresponding measured wavenumbers. Theoretically

Acknowledgement

One of the authors S.A. thanks the Department of Science and Technology, SERB for the financial support of this work in the form of Fasttrack Research Project scheme.

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    Present address: Department of Physics, DMI Engineering College, Aralvaimozhi – 627105, India.

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