Molecular mechanics, quantum mechanics, potentiometric, and conductometric studies on the complexes of some rare earth metals with 5‐azorhodanine derivatives

Abstract

ABSTRACT:The geometry of metal ions (La 3ϩ , Ce 3ϩ , UO 2 2ϩ , and Th 4ϩ ) complexes with 5-azorhodanine derivatives was optimized at the level of molecular mechanics. Two stoichiometric ratios of metal to ligand (i.e., 1:1 and 1:2) were investigated. Tetracoordinate and hexacoordinate of each stoichiometric ratio have been studied. Effect of substitution in the ligand on the geometry of the complexes was discussed in the light of electron donating-accepting properties of these substituents. The influence of the nuclear effective charge of the central metal ions on the metal-ligand (M-L) bonding was discussed and the effect of the number of ligands on the M-L bond length was also discussed and correlated to the experimental results. The total energies of the different metal complexes were computed using the extended Huckel method. The effect of substituents in ligand, metal type, and stoichiometry of the complexes on the complex total energies were discussed. Stability constant of (La , and Th 4ϩ ) metal ions with 5-azorhodanine derivaties have been determined potentiometrically in 0.1 M KCl and 50% (v/v) ethanol-water mixture. The order of the stability constants of the formed complexes was found to be La 3ϩ Ͻ Ce 3ϩ Ͻ UO 2 2ϩ Ͻ Th 4ϩ . The influence of substituents on the stability of the complexes was examined on the basis of electron-repelling property of the substituent. The effect of temperature on the stability of the complexes formed was studied and the corresponding thermodynamic parameters (⌬G, ⌬H, and ⌬S) were derived and discussed. The stoichiometries of these complexes were determined conductometrically and indicated

Potentiometric and Thermodynamic Studies of Dissociation and Metal Complexation of 4-(3-Hydroxypyridin-2-ylimino)-4-phenylbutan-2-one

“…The calculated thermodynamic parameters of HPIB are given in Table . The data show: (i) the positive Δ H 0 for the dissociation follows the general pattern for ionization processes which is endothermic; 27 (ii) the negative Δ S 0 indicates that the total number of solvent molecules bound with the dissociated ligand is greater than that bonded to the undissociated form; and (iii) the large positive value of Δ G 0 indicates that the dissociation process is not spontaneous. ,, …”

“…Schiff bases are an important class of ligands and play an important role in the development of coordination chemistry as they readily form stable complexes with most transition metals. − It is well-known that some drugs exhibit increased activity when administered as metal complexes, − and several metal chelates have been shown to inhibit tumor growth . There have been several reports on metal complexes of the Schiff base ligands having a variety of applications including biological, clinical, analytical, and industrial in addition to their important roles in catalysis and organic synthesis. − In continuation of our earlier work, − we report herein the dissociation constant of the free ligand (HPIB), I, the stepwise stability constants of its complexes with Mn 2+ , Co 2+ , Ni 2+ , and Cu 2+ , and thermodynamic calculations from data obtained at different temperatures. Such work may help to explain the nature and driving forces for the interactions occurring in biological systems, such as metal−protein and metal−nucleic acid interactions.…”

“…To calculate the stability constants of metal chelates, the acid dissociation constant of the ligand was first determined from the titration curves for HCl in the presence and absence of the ligand. The average number of protons, n̄ A , associated with the HPIB at different pH values was calculated according to the method previously reported. , The formation curve for the proton−ligand systems showed that the free ligand has two dissociable protons ( −CHC(OH)− and the hydroxyl group hydrogen) which are characterized by p K H 2 and p K H 1 , respectively. Different computational methods 15,17 were applied to evaluate the dissociation constants.…”

“…The formation curves for the metal complexes were obtained by plotting the average number of ligands attached per metal ion ( n̄ ) vs the free ligand exponent (pL). The ( n̄ ) values were calculated according to the previously reported methods. , These curves were analyzed, and the successive stability constants were determined using different computational methods , and agree within 1 % error. According to the average values in Table , the following general remarks can be made:…”

“…FT-IR spectra were recorded as KBr discs with a Schimadzu 2000 FT-IR spectrophotometer. The apparatus, general conditions, and methods of calculation were the same as in previous investigations . The following mixtures were prepared and titrated potentiometrically at 298 K against standard 0.010 M NaOH in a 40 % (v/v) ethanol−water mixture: (i) 5.00 mL of 0.0l0 M HCl + 5.00 mL of 1.00 M KCl + 20.00 mL of ethanol; (ii) 5.00 mL of 0.010 M HCl + 5.00 mL of 1.00 M KCl + 15.00 mL of ethanol + 5.00 mL of 0.001 M ligand; (iii) 5.00 mL of 0.010 M HCl + 5.00 mL of l.00 M KCl + 15.00 mL of ethanol + 5.00 mL of 0.001 M ligand + 5.00 mL of 0.0002 M metal ion.…”