Spectroscopic and structural studies on metal halide complexes of 4-vinylpyridine

Fourier transform infrared spectra (4000–400 cm⁻¹) are reported for metal(II) halide 4-vinlypridine complexes of the following stoichiometries: [MX₂(4-vipy]_n (n=4, M=Ni, X=Cl or Br; n=2, M=Cd, X=Cl, Br or I) and assignment are given for all the observed bands. These spectra were compared with X-ray powder diffraction patterns of complexes. It is shown that the proposed structures for these complexes derived from FTIR spectra are consistent with the X-ray powder diffraction measurements and the elemental analysis results. Coordination effect on 4-vinylpyridine has also been investigated.     

DFT study of solvent effects on 3-hydroxy-2-quinoxalinecarboxylic acid tautomers

By using the combination of density functional theory (DFT) B3LYP/6-311++G(d,g) within polarized continuum (PCM) model, solvent effects on 3-hydroxy-2-quinoxalinecarboxylic acid (3HQC) tautomers were investigated. Geometrical parameters, vibrational frequencies, electronic and energetic properties, and the nucleus-independent chemical shifts (NICS) were calculated in benzene, diethyl ether, and water. It has been seen that these molecular features of 3HQC are mostly solvent dependent.     

Theoretical and FT-IR, FT-Raman studies of nipecotamide and its tautomers, isomers

The structure, conformers, energies and vibrational spectra of the important nipecotamide molecule have been characterized by FT-IR (mid-IR, far-IR), FT-Raman spectroscopy and by DFT calculations. The structure is optimized by B3LYP/6-311++G(d,p) calculations. All vibrational frequencies assigned in detail with the help of total energy distribution (TED). The calculated vibrational wavenumbers were compared with IR and Ra experimental data. In the most stable tautomer (NT-1), the piperidine ring adopts the chair conformation and the amide group is in the axial orientation and is stabilized by an intramolecular N-H…O hydrogen bond of 4.37 Å.     

Spectroscopic and structural studies on dichlorobis(nicotinamide)zinc(II)

ZnCl₂(C₆H₆N₂O)₂ complex was prepared and investigated. The stoichiometry of this complex was derived from the results of elemental analysis and infrared spectroscopic studies. The crystal and molecular structure of the complex was also crystallographically characterized, to obtain a certain structure. The Zn(II) atom is coordinated by two chloride ligands and two N atoms from the nicotinamide ligands, in a distorted tetrahedral coordination environment, with Zn-N distances 2.058(3) and 2.057(4) Å, Zn-Cl distances of 2.221(1) and 2.209(1) Å and N-Zn-N and Cl-Zn-Cl angles of 101.8(1) and 121.81(5)°, respectively.     

Removal of Cu(II), Zn(II) and Co(II) ions from aqueous solutions by adsorption onto natural bentonite

In this study, the removal of Cu(II), Zn(II) and Co(II) ions from aqueous solutions using the adsorption process onto natural bentonite has been investigated as a function of initial metal concentration, pH and temperature. In order to find out the effect of temperature on adsorption, the experiments were conducted at 20, 50, 75 and 90 °C. For all the metal cations studied, the maximum adsorption was observed at 20 °C. The batch method has been employed using initial metal concentrations in solution ranging from 15 to 70 mg L⁻¹ at pH 3.0, 5.0, 7.0 and 9.0. A flame atomic absorption spectrometer was used for measuring the heavy metal concentrations before and after adsorption. The percentage adsorption and distribution coefficients (K _d) were determined for the adsorption system as a function of adsorbate concentration. In the ion exchange evaluation part of the study, it is determined that in every concentration range, adsorption ratios of bentonitic clay-heavy metal cations match to Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich (DKR) adsorption isotherm data, adding to that every cation exchange capacity of metals has been calculated. It is shown that the bentonite is sensitive to pH changes, so that the amounts of heavy metal cations adsorbed increase as pH increase in adsorbent-adsorbate system. It is evident that the adsorption phenomena depend on the surface charge density of adsorbent and hydrated ion diameter depending upon the solution pH. According to the adsorption equilibrium studies, the selectivity order can be given as Zn²⁺>Cu²⁺>Co²⁺. These results show that bentonitic clay hold great potential to remove the relevant heavy metal cations from industrial wastewater. Also, from the results of the thermodynamic analysis, standard free energy ΔG ⁰, standard enthalpy ΔH ⁰ and standard entropy ΔS ⁰ of the adsorption process were calculated.     

HF and DFT studies of the structure and vibrational spectra of 8-hydroxyquinoline and its mercury(II) halide complexes

The geometry, frequency and intensity of the vibrational bands of 8-hydroxyquinoline (8-HOQ) were obtained by HF and density functional theory (DFT) with BLYP and B3LYP functionals and 6-31G(d) as the basis set. The optimized bond lengths and bond angles are in good agreement with the X-ray data. The vibrational spectra of 8-HOQ which is calculated by the HF and DFT methods, reproduces the vibrational wavenumbers and intensities with an accuracy, which allows reliable vibrational assignments. Complexes of the type Hg(8-HOQ)X(2) [where X = Cl , Br] have been studied in the 4000-200 cm(-1) region, and assignment of all the observed bands were made. The analysis of the infrared spectra indicates that there are some structure-spectra correlations.     

A quantum chemical investigation on methylated pyridines

The structural features of the methylated pyridine series have been studied by quantum chemical methods. The aromatic character of these molecules is derived from the frontier molecular orbital energies, harmonic oscillator model of aromaticity (HOMA), and nucleus independent chemical shift (NICS) values. Hybrid density functional theory with 6-311++G(d,p) basis set was employed for all calculations.     

Reversible film formation from nano-sized PNIPAM particles below glass transition

Reversible film formation process from nano-sized Poly(N-isopropylacrylamide) (PNIPAM) microgel particles were studied during heating-cooling cycles at various rates. Photon transmission technique was used and transmitted photon intensity I _tr was monitored during heating–cooling cycles. The increase and decrease in I _tr during heating and cooling was explained with the void closure and void reconstruction processes, and the corresponding activation energies were measured. It was observed that PNIPAM microgels required less energy during reconstruction of voids than their closure.     

A combined experimental and theoretical study on 8-hydroxy-2-quinolinecarboxylic acid

The mid-IR and Raman spectra of 8-hydroxy-2-quinolinecarboxylic acid (8HQC) were recorded. These spectra were interpreted with the help of B3LYP/6–311 ++G(d,p) calculations and potential energy distribution (PED) analysis. As a result of the calculations, seven tautomers were determined among many stable conformations. The experimental spectra were concordant with the theoretical data of one tautomer. In the functional group region overtone and combination bands were detected and assigned. In addition, because of several peaks in the IR spectrum, it was proposed that the 8HQC exhibits dimerization in condensed phase. Possible dimeric forms of 8HQC were evaluated at the same level of theory, and it has been seen that the calculation results confirm the above proposal. ¹H and ¹³C NMR chemical shifts of 8HQC have been calculated, and compared with the experimental data. The frontier molecular orbital properties and the atomic charges were also theoretically obtained and presented.