Thermodynamic Functions Of Complexation Research Articles

Lanthanides(III) and Silver(I) complex formation with triamines in DMSO: The effect of ligand cyclization

The thermodynamic functions of complexation between lanthanides(III) and 1,4,7-triazacyclononane (TACN) together with those of some of the above metal ions with the TACN-linear-analogue,N′-methyl-N′′-(2-(methylamino)ethyl)ethane-1,2-diamine (DMDIEN), are determined in dimethylsulphoxide (DMSO).The study aims to investigate the effect of ligand cyclization and methylation on the stability and nature of the complexes in non-aqueous solution. The stability constants of Ln3+/TACN complexes were obtained by means of potentiometric titrations at 298 K and I = 0.1 mol dm−3, using Ag+ as competitive ion. Ln3+-ligand complexation enthalpies were obtained by calorimetric titrations, extended also to the silver(I)-TACN system, whose thermodynamic data in DMSO are not published. Calorimetry was applied also to obtain simultaneously enthalpy values and stability constants of the Ln3+/DMDIEN systems, for which the difference in stabilities between Ag+ and Ln3+-DMDIEN complexes did not allow the competitive potentiometric method to work.The Ag+ ion forms mono- and poly-nuclear AgiLji+ complexes with TACN (i:j = 1:1, 1:2 and 2:3), whereas all lanthanide ions form with TACN both 1:1 complexes and 1:2, from Tb3+ to Lu3+. Only 1:1 species were detected for the Ln3+-DMDIEN systems. The 1:1 TACN complexes show an extra stability both with respect to those of DIEN and those of the linear analogue DMDIEN. Negative enthalpies favor the formation of all complexes, while entropies partially counteract the complexation. The results for TACN systems are compared with those here obtained for DMDIEN and for DIEN, reported previously. Density Functional Theory (DFT) calculations, carried out in presence of DMSO introduced as implicit solvent, were performed on some of the Ln3+ complexes with TACN and DIEN to provide insights into the structures and related solvation energies of the species formed in solution. Calculations support a tri-dentate coordination of both ligands. The effects of ligand methylation and cyclization on the stability constants, enthalpies and entropies of complex formation are discussed. The thermodynamic and DFT integrated data indicate that the trends of the thermodynamic functions concerning the complexation reactions of lanthanide ions in DMSO depend on the different solvation of the complexes.

Crystal structures, luminescent and thermal properties of lanthanide complexes with 3,4-dimethylbenzoic acid and 2,2′-bipyridine

Two lanthanide complexes [La(3,4-DMBA)3]n (1) and [Tb(3,4-DMBA)3(DIPY)2]2 (2) (where 3,4-DMBA = 3,4-dimethylbenzoate, DIPY = 2,2′-bipyridine) have been synthesized and then characterized. The single crystals of complexes 1 and 2 were obtained. Complex 1 adopts a distorted monocapped square antiprismatic molecular geometry, while complex 2 forms a distorted square antiprism. Complex 1 is stitched together by edge sharing through carboxylate ligands to form 1D chains along the b axis. The structure of complex 2 consists of 1D chains along the c axis by two kinds of π···π stacking interactions. Two complexes were characterized by elemental analysis, powder X-ray diffraction and IR spectra. The complex 2 shows typical green luminescence in the solid state. Thermal decomposition mechanisms of complexes were discussed by TG–DTG techniques. In the temperature range from 257.15 to 413.15 K, the molar heat capacities of the complexes were measured by DSC. The smoothed heat capacities and thermodynamic functions of complexes were calculated on the basis of fitted polynomial and thermodynamic equations.

Standard thermodynamic functions of complexation between copper(II) and glycine and L-histidine in aqueous solutions

The Cu2+–glycine–L-histidine system is studied calorimetrically at 298.15 K and an ionic strength of 0.2, 0.5, and 1.0 in aqueous solutions containing potassium nitrate. The standard thermodynamic parameters (Δr H°, Δr G°, Δr S°) of complexation processes are determined.

Copper(II) complexation with 1-methyl-2-mercaptoimidazole in 7 M HCl

The complexation of copper(II) with 1-methyl-2-mercaptoimidazole in 7 M HCl was potentiometrically studied. The compositions of complexes were determined, and their stepwise formation constants were calculated. The complexes were shown to become less stable with increasing temperature. The thermodynamic functions of complexation were estimated. The copper complexes were shown to surpass the rhenium complexes in stability.

Thermodynamic properties of o-semiquinonato complexes of cobalt, nickel, and copper in the range T → 0 to 350 K

The heat capacity of bis(3,6-di-tert-butyl-o-benzosemiquinonato)copper, (triethylarsine)bis(3,6-di-tert-butyl-o-benzosemiquinonato)nickel, and (triphenylphosphine)bis(3,6-di-tert-butyl-o-benzosemiquinonato)cobalt was determined in the range of 0 to 350 K by precision adiabatic vacuum calorimetry. The temperature dependences of magnetic moments were studied for the last two complexes. The G-transition in nickel complex, which is presumably caused by a loosening of the molecular degrees of freedom, was determined. The standard thermodynamic functions of complexes were calculated according to the obtained data: C p ○ , H○(T)-H○(0), S○(T), and G○(T)-H○(0) for the range of T → 0 to 350 K. It was concluded that our analysis of low-temperature heat capacity based on the Debye theory of the heat capacity of solids and the multifractal model confirms the chain-layer topologies of the structures of the investigated complexes.

Crystal structures and thermodynamic properties of lanthanide complexes with 2-chloro-4,5-difluorobenzoate and 1,10-phenanthroline

A series of lanthanide complexes with the 2-chloro-4,5-difluorobenzoate (2-cl-4,5-dfba) and 1,10-phenanthroline (phen), have been synthesized with the formulae of [La(2-cl-4,5-dfba)3phen]n·nH2O (1), [Nd(2-cl-4,5-dfba)3phenH2O]2 (2), [Ln(2-cl-4,5-dfba)3phen]2 (Ln=Eu (3), Ho (4)). The complexes are characterized by elemental analysis, infrared and fluorescent spectra and X-ray single-crystal diffraction. The structures of the four complexes are very different. Complex 1 is an infinite 1D chain polymeric structure formed by the asymmetric units with the mirror growth pattern. Each La3+ ion is coordinated to four bridging carboxylic groups, two tridentate chelating–bridging carboxylic groups, simultaneous with one phen molecule, giving the coordination number of nine. In the molecular structures of complexes 2 and 3, two Ln3+ ions are linked by four carboxyl groups, forming two binuclear molecules. In addition, each Nd3+ ion in complex 2 is bonded to one H2O molecule and one carboxyl group by monodentate mode, one phen molecule by bidentate chelating, and each Eu3+ ion is also chelated to one phen molecule and one carboxyl group in complex 3. And in complex 4, the Ho3+ ion yields a eight-coordinated distorted square anti-prism coordination geometry. The three-dimensional IR accumulation spectra of gaseous products for complexes 1 to 4 are analyzed and further authenticated the thermal decomposition processes with TG-DTG curves. The heat capacities of complexes 2 to 4 are measured and fitted to a polynomial equation by the least squares method on the basis of the reduced temperature x (x=[T−(Tmax+Tmin)/2]/[(Tmax−Tmin)/2]). Then the smoothed molar heat capacities and thermodynamic functions of complexes 2 to 4 are calculated. The fluorescence intensity of complex 3 is markedly improved as well.

Thermodynamics of sublimation of calix[4]arene complexes with solvent molecules

Some calix[4]arenes form complexes with solvent molecules, preserving the stoichiometric composition upon sublimation. The saturated vapor pressures of calix[4]arenes and their complexes with solvents were determined by the Knudsen effusion method in a wide temperature range. The changes in the standard thermodynamic functions of complexation in transfer from the condensed state to the gas phase were determined. It was found that the enthalpy term of the Gibbs energy of the complex formation increases with an increase in the conformational mobility of the ligand, and the entropy term increases as the ligand becomes less flexible and more rigid.

Rhenium(V) complexation with 3-ethyl-4-methyl-1,2,4-triazole-5-thiol in 6 M hydrochloric acid

The reversibility of the RSSR/RS redox system, where RS is 3-ethyl-4-methyl-1,2,4-Triazole-5-thiol (3-E-4-MTT) at a platinum electrode was established. The real potentials of the system in the temperature range of 273–338 K were determined. The real potentials of the systems comprising 1,2,4-triazolethiols and their oxidized species depend on the nature, positions, and number of alkyl radicals in the heterocyclic molecule. The stepwise formation constants of rhenium(V) oxochloro-3-ethyl-4-methyl-1,2,4-triazolethiol complexes in 6 M HCl at different temperatures were determined. The thermodynamic functions of complexation in the H2[ReOCl5]-3-E-4-MTT-6 M HCl system were estimated.

Correlation Analysis of the Solvent Effects on the Thermodynamic Functions of Complexation of Sodium and Potassium Ions with 18-Crown-6 Ether in Aqueous-Organic Solvents

The effect of dielectric and chemical (donor-acceptor interactions, cohesion energy density) properties of aqueous-organic solvents (water-methanol, water-2-propanol, water-acetonitrile, water-acetone, water-dioxane) on the thermodynamic functions of complexation of sodium and potassium cations with 18-crown-6 ether at 298 K was subjected to overall correlation analysis.

Microcalorimetric studies on the binding of some benzodiazepin derivatives to human serum albumin

The authors have employed a microcalorimetric method to study the nature of the interactions between several benzodiazepin molecules and human serum albumin. The thermodynamic functions of complexation have been determined at different pH, ionic strength and electrolyte support conditions. Both electrostatic and hydrophobic interactions have been demonstrated to exist in proportions which vary according to the drug's molecular structure.