A new salen base 5-(phenylazo)-N-(2-amino pyridine) salicyliden Schiff base ligand: synthesis, experimental and density functional studies on its crystal structure, FTIR, 1H NMR and 13C NMR spectra

Synthesis of Amidoalkyl Naphthols in PEG-400 as a Green and Efficient Solvent and Theoretical Study of their Spectroscopic Properties

Abstract:

An efficient synthesis of amidoalkyl naphthols from the multicomponent reaction of 2- naphthol, aromatic aldehydes, and benzamide derivatives using PEG-400 as an environmentally friendly solvent is described. The main advantage of this protocol is that the benzamide derivatives with low reactivity, such as 4-nitro benzamide, can react effectively. Also, the molecular structure, IR, and 13C NMR spectra of the synthesized compounds are also investigated theoretically. Density functional theory (DFT) calculations at the B3LYP level of theory are carried out to locate optimized geometries and calculate vibrational normal modes and 13C NMR chemical shifts. These calculations enable us to assign the observed FT-IR and 13C NMR peaks to the corresponding vibrational motions and 13C atoms, respectively.

A spectrophotometric study of impact of solvent, substituent and cross-conjugation in some 4-aminoantipyrine based Schiff bases

The influences of substituent and solvent polarity on the electronic transition of seven different 4-aminoantipyrine based Schiff bases have been investigated in 14 solvents of different polarity. Reichardt'sE_T(30) scale has been used to propose a quantitative approach towards the relative stability of the electronic ground and excited state species. The Schiff bases can sense the polarity changes of the solvents and accordingly there appear three categories of solvents: non-polar, dipolar aprotic and polar protic. The first two categories of solvents induce negative solvatochromism and the third one induces positive solvatochromism in the molecules. Cross conjugation and geometrical configuration have been proposed to play an important role in the extent of electronic transition of the Schiff bases in various solvent media. Out of various substituent effects, field effect and resonance significantly influence the electronic environment of the compounds, as evidenced from the regression models involving change in UV-Vis absorption wavelengths ¹HNMR chemical shifts and IR frequencies.

Synthesis, Structural Characterization and Antimicrobial Activity of Cu(II) and Fe(III) Complexes Incorporating Azo-Azomethine Ligand

We are reporting a novel azo-azomethine ligand, HL and its complexes with Cu(II) and Fe(III) ions. The ligand and its complexes are characterized by various physico-chemical techniques using C,H,N analyses, FT-IR, ¹H-NMR, ESI-MS and UV-Vis studies. TGA analyses reveal complexes are sufficiently stable and undergo two-step degradation processes. The redox behavior of the complexes was evaluated by cyclic voltammetry. Furthermore, the ligand and its complexes were tested for antimicrobial activity against bacterial and fungal strains by determining inhibition zone, minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). The complexes showed moderate antimicrobial activity when tested against Gram +ve and Gram −ve bacterial strains. To obtain insights into the structure of ligand, DFT studies are recorded. The results obtained are quite close to the experimental results. In addition, the energy gap, chemical hardness, softness, electronegativity, electrophilic index and chemical potential were calculated using HOMO, LUMO energy value of ligand.

Synthesis, characterization, solvatochromism and biological properties of 2,2'-((1E,1'E)-((1,2,5-oxadiazole-3,4-diyl)bis (azanylylidene))bis(methan-ylylidene))bis(4-(phenyldiazenyl)phenol)

Azo-azomethine dyes 2-((4-amino-1,2,5-oxadiazol-3-ylimino)methyl)-4-(phenyl diazenyl)phenols (2a-h) have been synthesized by condensation reaction of 3,4-diamino-1,2,5-oxadiazole with 2-hydroxy-5-[(E)-(aryldiazenyl)]benzaldehyde (1a-h) in methanol. The structures of dyes have been characterized by elemental analysis, mass, IR, UV-Vis, 1H and 13С NMR spectroscopy. UV-Vis absorption spectra indicated enol-keto tautomeric and positive solvatochromism in compounds 2a-h which is dependent on the substitution, solvent, pH and environment temperature. The synthesized compounds were investigated for their in vitro antioxidant activity by diphenylpicrylhydrazyl assay. Compounds substituted with electron donating groups, such as, alkyl and methoxy groups showed moderate antioxidant activity. The in vitro antibacterial activity of all compounds was determined by disk diffusion method. The test compounds showed varying degree of inhibition against B. cereus and S. aureus strains.

Conformation of azo-bridge in 3,3'-dinitro-2,2'-azobipyridine and its 4,4'(or 5,5' or 6,6')-dimethyl-derivatives: vibrational studies and DFT quantum chemical calculations

Syntheses of 3,3'-dinitro-2,2'-azobipyridine and 4,4' (or 5,5' or 6,6')-dimethyl-3,3'-dinitro-2,2'-azobipyridine have been described. Molecular structures of these compounds have been determined and compared, to the basic compound, azobipyridine, reported by us earlier. The conformation of the azo-bond and other structural data are discussed in terms of substitution place of methyl chromophore. Fourier transform IR and Raman spectra of these compounds have been measured and analysed. The 6-311G (2d,2p) basis set with the B3LYP functional have been used to discuss the space conformation and dynamics of the studied compounds.

Spectroscopy and solvatochromism studies along with antioxidant and antibacterial activities investigation of azo-azomethine compounds 2-(2-hydroxyphenylimino)methyl)-4-phenyldiazenyl)phenol

The azo-azomethine compounds 2-(2-hydroxyphenylimino)methyl)-4-phenyldiazenyl)phenol (2a-d) were prepared from the reaction of 2-aminophenol with 2-hydroxy-5-(aryldiazenyl)benzaldehyde (1a-d). The structures of all compounds were then characterized by elemental analysis, mass, infrared, UV-vis, (1)H and (13)C NMR spectroscopy. The electronic absorption spectra indicated enol-keto tautomeric and positive solvatochromism in compounds (2a-d), which is dependent on the substitution, nature of solvent, pH and environment temperature. The compounds (2a-d) were also evaluated for antibiotic activities by disc diffusion method. Compounds 2a and 2b exhibited antibacterial activities against Staphylococcus aureus and Bacillus cereus, but 2c and 2d were found to have no remarkable antibacterial activity. All the compounds (2a-d) also showed antioxidant activity as determined by 1,1-diphenyl-2-picryl-hydrazyl (DPPH) method.

Combined experimental and theoretical studies on the X-ray crystal structure, FT-IR, 1H NMR, 13C NMR, UV-Vis spectra, NLO behavior and antimicrobial activity of 2-hydroxyacetophenone benzoylhydrazone

A Schiff base ligand, 2-hydroxyacetophenone benzoylhydrazone (HL) was synthesized and fully characterized with FT-IR, elemental analyses, UV-Vis, (1)H NMR and (13)C NMR spectra. DFT calculations using B3LYP/6-31+G(d,p) and PW91/DZP are performed to optimize the molecular geometry. Optimized structures are used to calculate FT-IR, UV-Vis, (1)H NMR and (13)C NMR spectra of the compound. Also the energies of the frontier molecular orbitals (FMOs) have been determined. The results obtained from the optimization and spectral analyses are in good agreement with the experimental data. To investigate non-linear optical properties, the electric dipole moment (μ), polarizability (α) and molecular first hyperpolarizability (β) were computed. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the compound can be a good candidate of nonlinear optical materials. In addition, the minimal inhibitory concentration (MIC) of this compound against Staphylococcus aureus, and Candida albicans was determined.

Spectroscopic and solvatochromism studies along with antioxidant and antibacterial activities investigation of 2-((2-mercaptophenylimino)methyl)-4-(phenyldiazenyl)phenol

The condensation reaction of 2-hydroxy-5-(aryldiazenyl)benzaldehyde (1a-d) with 2-aminothiophenole affored Schiff base compounds 2-((2-mercaptophenylimino)methyl-4-(-aryldiazenyl)phenol (2a-d). The structures of compounds (2a-d) were characterized by elemental analysis, mass, infrared, UV-vis and NMR spectroscopy. The 2a-d shows enol-keto tautomeric and positive solvatochromism. The antibacterial activities of 2a-d were also evaluated by disc diffusion method. Compound 2b displayed activity against Staphylococcus aureus and Bacillus cereus, 2a and 2c were active against B. cereus but 2d did not exhibit activity against the tested organisms. Among the tested compounds, 2b showed the best antioxidant properties as evaluated by free radical scavenging activity on 1,1-diphenyl-2-picryl-hydrazyl and ferric reducing power determination.

Synthesis and characterization of an azo dibenzoic acid Schiff base and its Ni(II), Pb(II), Zn(II) and Cd(II) complexes

The new Schiff base 4,4'-(1E,1'E)-(3,3'-(1E,1'E)-(pyridine-2,6-diylbis(azan-1-yl-1-ylid ene))bis(methan-1-yl-1-ylidene)bis(4-hydroxy-3,1-phenylene))bis(diazene-2,1-diyl)dibenzoic acid (1) was prepared from the condensation reaction of 2,6-diaminopyridine with 4-((3-formyl-4-hydroxyphenyl)diazenyl)benzoic acid in methanol. The compound 1 is potentially an N, O multidentate chelating ligand which could form stable complexes with metal ions in 1:1 up to 1:3mol ratio of metal to ligand. The 1:1 complexes of Schiff base 1 with Ni(II), Pb(II), Zn(II) and Cd(II) have been synthesized by its condensation reaction with appropriate salts of metal ions. Structures of Schiff base (1) as well as its complexes with abovementioned metal ions were characterized by elemental analysis, mass, IR, UV-vis., (1)H and (13)С NMR spectroscopy.

FT-IR, FT-Raman, NMR studies and ab initio-HF, DFT-B3LYP vibrational analysis of 4-chloro-2-fluoroaniline

The Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectra of 4-chloro-2-fluoroaniline (CFA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been investigated with the help of ab initio and density functional theory (DFT) methods. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the Gauge including atomic orbital (GIAO) method. The first order hyperpolarizability (β(0)) of this novel molecular system and related properties (β, α(0) and Δα) of CFA are calculated using B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) methods on the finite-field approach. The calculated results also show that the CFA molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The result confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The HOMO-LUMO energies UV-vis spectral analysis and MEP are performed by B3LYP/6-311++G(d,p) approach. A detailed interpretation of the infrared and Raman spectra of CFA is also reported based on total energy distribution (TED). The difference between the observed and scaled wave number values of the most of the fundamentals is very small.

A new Schiff base compound N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone): synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, 1H NMR and 13C NMR spectra

The Schiff base compound, N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone) (NDHA) is synthesized through the condensation of 2-hydroxylacetophenone and 2,2-dimethyl 1,3-amino propane in methanol at ambient temperature. The yellow crystalline precipitate is used for X-ray single-crystal determination and measuring Fourier transform infrared (FTIR), UV-visible, (1)H NMR and (13)C NMR spectra. Electronic structure calculations at the B3LYP, PBEPBE and PW91PW91 levels of theory are performed to optimize the molecular geometry and to calculate the FTIR, (1)H NMR and (13)C NMR spectra of the compound. Time-dependent density functional theory (TDDFT) method is used to calculate the UV-visible spectrum of NDHA. Vibrational frequencies are determined experimentally and compared with those obtained theoretically. Vibrational assignments and analysis of the fundamental modes of the compound are also performed. All theoretical methods can well reproduce the structure of the compound. The (1)H NMR and (13)C NMR chemical shifts calculated by all DFT methods are consistent with the experimental data. However, the NMR shielding tensors computed at the B3LYP/6-31+G(d,p) level of theory are in better agreement with experimental (1)H NMR and (13)C NMR spectra. The electronic absorption spectrum calculated at the B3LYP/6-31+G(d,p) level by using TD-DFT method is in accordance with the observed UV-visible spectrum of NDHA. In addition, some quantum descriptors of the molecule are calculated and conformational analysis is performed and the results were compared with the crystallographic data.