Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Crystal structure, spectroscopic studies and quantum mechanical calculations of 2-[((3-iodo-4-methyl)phenylimino)methyl]-5-nitrothiophene
Graphical abstract
Introduction
Schiff’s bases (azomethines, imines) belong to a widely used group of organic intermediates important for the production of certain chemical specialties, e.g. pharmaceuticals, or additives to rubber. A basic reaction synthesis involves an aromatic amine and aldehyde [1], [2], [3].
Schiff bases are used as starting materials in the synthesis of important drugs, such as antibiotics and antiallergic, antiphlogistic and antitumor substances [4], [5], [6]. In this paper, we have characterized lots of physicochemical properties of the new thiophene containing compound. Over recent years, there has been an increasing interest in the chemistry of thiophenes because of their biological significance. Many of them have been widely investigated for therapeutic uses, especially as antifungal, antibacterial, anti-inflammatory, anticonvulsant, antiasthmatic and analgesic agents. They also were known to show anti-HIV, anti-proliferative, germicidal and D2 dopaminergic activities [7]. There are two characteristic properties of Schiff bases, viz. photochromism and thermochromism [8]. In general, Schiff bases display two possible tautomeric forms. The phenol-imine (OH) and the keto-amine (NH) forms. Depending on the tautomers, two types of intramolecular hydrogen bonds are observed in Schiff bases: OH⋯N in phenol-imine [9], [10] and NH⋯O in keto-amine tautomers [11], [12]. Another form of the Schiff base compounds is also known as zwitterion having an ionic intramolecular hydrogen bond (N+H⋯O−) and this form is rarely seen in the solid state [13], [14].
By means of increasing the development of computational chemistry in the past decade, the research of theoretical modeling of drug design, functional material design, etc. has become more mature than ever. Many important chemical and physical properties of biological and chemical systems can be predicted from the first principles by various computational techniques [15]. In recent years, density functional theory (DFT) has been a shooting star in theoretical modeling. The development of better and better exchange–correlation functionals made it possible to calculate many molecular properties with comparable accuracies to traditional correlated ab initio methods, with more favorable computational costs [16].
The most significant feature of the molecular structure, such as dipole moment, vibrational frequencies, electrostatic potentials, non-linear optical properties etc., are obtained by studies in the literature [17], [18], [19], [20]. In the past decade, by increasing development of computational chemistry, density functional theory (DFT) has been used extensively to calculate a wide variety of molecular properties such as equilibrium structure, charge distribution, UV–Visible, FTIR and NMR spectra, and provided reliable results which are in accordance with experimental data [21].
In the present study, a new Schiff base, 2-[((3-iodo-4-methyl)phenylimino)methyl]-5-nitrothiophene was derived from 5-nitro-2-thiophene-carboxaldehyde and 3-iodo-4-methylaniline (Fig. 1). The crystal structure of the title compound was determined by IR, UV–Vis and the single-crystal diffraction technique. In addition the molecular structure and geometry, the MEP map, the FMOs and the NLO properties for the title compound at the B3LYP, B3PW91 and PBEPBE methods with the 6-311G+(d,p) basis set were performed. These studies are precious for providing insight into molecular properties of Schiff base compounds.
Section snippets
Synthesis
The compound 2-[((3-iodo-4-methyl)phenylimino)methyl]-5-nitrothiophene was prepared by reflux a mixture of a solution containing 5-nitro-2-thiophene-carboxaldehyde (0.0135 g 0.88 mmol) in 20 ml ethanol and a solution containing 3-iodo-4-methylaniline (0.0199 g 0.88 mmol) in 20 ml ethanol. The reaction mixture was stirred for 1 h under reflux. The crystals of 2-[((3-iodo-4-methyl)phenylimino)methyl]-5-nitrothiophene suitable for X-ray analysis were obtained from ethylalcohol by slow evaporation (yield
3.1. Description of the crystal structure
The title compound crystallizes in the monoclinic space group P21/c with Z = 4 in the unit cell. The crystal structure parameters of the title compound are a = 7.8044(4) Å, b = 8.7804(3) Å, c = 19.4997(10) Å and β = 93.092°. The asymmetric unit in the crystal structure contains only one molecule. In the title compound, C12H9O2N2I1S1, the thiophene ring and the benzene ring are essentially planar, while the dihedral angle between the two rings is 1.03°(21). The length of the N2C5 double bond is 1.258 Å, which
Conclusions
The new Schiff base 2-[((3-iodo-4-methyl)phenylimino)methyl]-5-nitrothiophene has been studied using FT-IR, UV–Visible and X-ray crystallographic technique. The results of experimental studies are supported by some quantum mechanics calculations. The molecular structure and optimized geometry, the MEP map, the FMOs, the electronic absorption spectra, the harmonic vibrational frequencies and the NLO properties for the title compound have been calculated at the B3LYP, B3PW91 and PBEPBE methods
Acknowledgement
I’m greatly thankful for the considerable contributions of my dear advisor Prof. Dr. Şamil Işık (pass away, may god bless his soul.).
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