Khairia M. Al-Ahmary

Spectroscopic studies and molecular orbital calculations on the charge transfer reaction between DDQ and 2-aminopyridine

Charge transfer complex formation between 2-aminopyridine (donor, 2AP) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (acceptor, DDQ) has been studied spectrophotometrically in acetonitrile (CH3CN). The newly formed CT-complex has reddish brown color and is characterized by the appearance of new absorption bands in the 375-650 nm regions where acceptor and donor do not have any absorption. Maximum and constant absorbance of the complex was obtained after 10 min at 20 °C with 1 mL 5×10(-3) M DDQ in CH3CN. Based on photometric titration method, the stoichiometry of the formed CT-complex was found to be 1:1 [(2AP)(DDQ)]. Minimum-maximum absorbances method has been applied to estimate the formation constant of the complex where it recorded large value confirming its high stability. Molecular orbital calculations utilizing GAMESS computations were carried out in order to record changes in the electronic structure and molecular geometry of the formed CT-complex. In addition, the infrared vibrational frequencies of the complex were computed and compared with experimental results.

Spectroscopic characterization of hydrogen-bonded proton transfer complex between 4-aminopyridine with 2,6-dichloro-4-nitrophenol in different solvents and solid state

Proton transfer reaction between the proton donor 2,6-dichloro-4-nitrophenol (DCNP) with the proton acceptor 4-aminopyridine (4APy) has been investigated spectrophotometrically in different solvents included the aprotic solvent acetonitrile (MeCN), the protic one methanol (MeOH) and a mixture consists of 50% acetonitrile+50% dichloroethane (ANDC). The proton transfer complex is produced instantaneously with deep yellow color and absorption maxima in the range 395-425nm. The composition of the complex was characterized spectrophotometrically to be 1:1 in all solvent proving that the solvent has no effect on the complex stoichiometry. The proton transfer formation constant has been estimated by using Benesi-Hildebrand equation where the highest value was recorded in the mixture ANDC. This proofs the high stability of the complex in less polar solvent as a result of the high stability of the complex ground state. The solid complex has been synthesized and characterized by elemental analysis to be 1:2 [(proton donor) (proton acceptor)2]. The obtained solid complex was analyzed by infrared spectroscopy where two broad bands at 3436 and 2500cm(-1) characterized for asymmetric NHN(+) hydrogen bond were identified. Molecular modeling utilizing GAMESS computations as a package of ChemBio3D Ultra12 program was carried out where asymmetric NHN(+) was explored with NN bond distance 2.77Å. The computations showed a difference in molecular geometry of the complex compared with reactants especially bond lengths, bond angles and distances of close contact.

Spectrophotometric study of the proton transfer equilibrium between 2-aminopyridine with 2,4-dinitrophenol in methanol

2-Aminopyridine (2AP) reacts instantaneously with 2,4-dinitrophenol (DNP) in methanol to form yellow proton transfer (PT) complex at absorption maxima from 362–402 nm. The molecular composition of the PT-complex has been identified by Jobs and photometric titration methods to be 1 : 1. The PT-complex formation constant (K PT) and molecular extinction coefficient (ε) were estimated by using Benesi–Hildebrand equation. They recorded high values confirming high stability of the formed complex. The stability of the formed complex was interpreted based on the formation of bifurcated and cooperative hydrogen bonds. On the basis of the rapidity of the PT-reactions, a simple and accurate spectrophotometric method for determination 2AP was proposed. Beers law was obeyed in the concentration range 2–56 µg mL−1 with excellent correlation coefficients (0.99). Furthermore, the recovery percentage recorded 100.93%.

Spectroscopic characterization of charge transfer complexes of 2,3-diaminopyridine with chloranilic acid and dihydroxy-p-benzoquinone in polar solvent

Charge transfer (CT) complexes formed between 2,3-aminopyridine (2,3-DAP) as electron donor with the π-electron acceptors chloranilic acid (CHA) and dihydroxy-p-benzoquinone (DHBQ) were investigated spectrophotometrically in ethanol. Minimum-maximum absorbance method has been used for estimating the formation constants of the charge transfer reactions (KCT). Jobs method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes and they showed that 1:1 complexes were produced. The molar extinction coefficient (ε), oscillator strength (f), dipole moment (μ), charge transfer energy (ECT), ionization potential (IP) and the dissociation energy (W) of the formed complexes were estimated, they reached acceptable values suggesting the stability of the formed CT-complexes. The solid CT-complexes were synthesized and characterized by elemental analyses, (1)H NMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.

Spectrophotometric study on the charge-transfer reaction between 4-aminopyridine with 2,5-dihydroxy-p-benzoquinone in methanol and the binary mixture 50% acetonitrile + 50% 1,4-dioxane (v/v)

Charge-transfer (CT) reaction between 4-aminopyridine (4APy) as the electron donor with 2,5-dihydroxy-p-benzoquinone (DHBQ) as the electron acceptor has been investigated spectrophotometrically in methanol (MeOH) and a binary mixture composed of 50% acetonitrile and 50% 1,4-dioxane (v/v) (ANDI). The composition of the complex has been investigated utilising Jobs and photometric titration methods to be 1:1. Benesi–Hildebrand equation has been applied to estimate the formation constant of the CT reaction (K CT) and the molecular extinction coefficient (ϵ) where they reached high values confirming high stability of the produced complex. The solid CT complex (4APy–DHBQ) was isolated, and elemental analysis proved its formation in 1:1 ratio. A spectral study on the formed complex has been carried out using infrared and 1H NMR measurements, where it included hydrogen bonding beside CT.

Spectrophotometric study on the charge transfer reaction between 2-amino-4-methylpyridine with chloranilic acid in polar solvents

ABSTRACT Charge transfer (CT) complexes formed between 2-amino-4-methylpyridine as electron donor, chloranilic acid as electron acceptor was investigated spectrophotometrically in acetonitrile (AN), methanol (MeOH) and binary mixture of acetonitrile 50% + methanol 50% (MeOH-AN). Minimum–maximum absorbance method has been used for estimating the formation constants of the CT reactions (KCT). Job’s method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes, and they showed that 1:1 complexes were produced. The molar extinction coefficient (e), oscillator strength (f), dipole moment (l), CT energy (ECT), ionisation potential (IP) and the dissociation energy (W) of the formed complexes were estimated; they reached acceptable values suggesting the stability of the formed CT complexes. The solid CT complexes were synthesised and characterised by elemental analyses, 1H NMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.

Synthesis and spectroscopic studies of charge transfer complex between dihydroxy-p-benzoquinone and 4-dimethylaminopyridine in different solvents

Charge transfer (CT) complex formation between 4-dimethylaminopyridine (4-DMAP) as the electron donor and 2,5-dihydroxy-p-benzoquinone (DHBQ) as the π-electron acceptor has been investigated spectrophotometrically in methanol (MeOH), ethanol (EtOH) and acetonitrile (AN). The stoichiometry of the complex has been identified by Job’s and photometric titration methods to be 1:1. The Benesi–Hildebrand equation has been applied to estimate the formation constant (KCT) and molecular extinction coefficient (ε). It was found that the value of KCT is larger in AN than in MeOH and EtOH. The thermodynamic parameters are in agreement with the KCT values in that the enthalpy of formation (−ΔH) has a larger value both in EtOH and MeOH than in AN, suggesting higher stability of the complex in EtOH. The complex formed between 4-DMAP and DHBQ has been isolated as a solid and characterised using elemental analysis, FTIR and 1H NMR measurements. Moreover, it has been found that the formed complex involves proton transfer in addition to CT.

Retention profile of cadmium and lead ions from aqueous solutions onto some selected local solid sorbents

Abstract Adsorption of cadmium (Cd2+) and lead (Pb2+) ions on the surface of different samples collected from five regions in Saudi Arabia has been studied. For each experiment, measured amounts of soil (25-300 mg) were shaken with 50 mL of Cd2+ and Pb2+ aqueous solutions. Free Cd2+ and Pb2+ were measured periodically by atomic absorption spectrometer. Varied parameters were pH, initial concentrations, contact time and endogenous ions (Ca2+ and Mg2+). Results indicated that adsorption increases by increasing contact time and initial concentrations . Adsorption was not significant at pHs lower than 6.0 and increases over pH range between 6.0 and 10. Adsorption of Cd2+ and Pb2+ decreases in presence of high concentrations of Ca2+ and Mg2+ which is explained by competitive phenomena between ions on active sites on soil.

Charge transfer complex between 2,3-diaminopyridine with chloranilic acid. Synthesis, characterization and DFT, TD-DFT computational studies

New charge transfer complex (CTC) between the electron donor 2,3-diaminopyridine (DAP) with the electron acceptor chloranilic (CLA) acid has been synthesized and characterized experimentally and theoretically using a variety of physicochemical techniques. The experimental work included the use of elemental analysis, UV-vis, IR and 1H NMR studies to characterize the complex. Electronic spectra have been carried out in different hydrogen bonded solvents, methanol (MeOH), acetonitrile (AN) and 1:1 mixture from AN-MeOH. The molecular composition of the complex was identified to be 1:1 from Jobs and molar ratio methods. The stability constant was determined using minimum-maximum absorbances method where it recorded high values confirming the high stability of the formed complex. The solid complex was prepared and characterized by elemental analysis that confirmed its formation in 1:1 stoichiometric ratio. Both IR and NMR studies asserted the existence of proton and charge transfers in the formed complex. For supporting the experimental results, DFT computations were carried out using B3LYP/6-31G(d,p) method to compute the optimized structures of the reactants and complex, their geometrical parameters, reactivity parameters, molecular electrostatic potential map and frontier molecular orbitals. The analysis of DFT results strongly confirmed the high stability of the formed complex based on existing charge transfer beside proton transfer hydrogen bonding concordant with experimental results. The origin of electronic spectra was analyzed using TD-DFT method where the observed λmax are strongly consisted with the computed ones. TD-DFT showed the contributed states for various electronic transitions.

Spectroscopic characterisation and structural modelling of new hydrogen-bonded charge transfer complex between picric acid and 3-aminoquinoline

ABSTRACT New charge transfer hydrogen-bonded (HBCT) complex between the electron donor 3-aminoquinoline with the electron acceptor picric acid has been synthesised and characterised experimentally and theoretically using a variety of physicochemical techniques. The experimental work included the use of UV–vis, IR and 1H NMR studies to characterise the complex in different hydrogen-bonded solvents. The studied reaction proceeded based on 1:1 stoichiometric ratio and the stability constant recorded high values. The solid complex was prepared and characterised by elemental analysis that confirmed its formation in 1:1. Both IR and NMR studies supported the existence of proton and charge transfers in the formed complex. In complemented with experimental results, molecular modelling using DFT using 31–6G(d,p) basis set was carried out in the gas phase where the existence of both charge and hydrogen transfers was reconfirmed in the obtained complex in full consistency with experimental results.