NMR study of the stoichiometry,stability and exchange kinetics of complexation reaction between Pb2+ ion and 18-crown-6 in binary acetonitrile-water mixtures

Proton NMR was used to study the complexation reaction between lead ion and 18-crown-6 in a number of binary acetonitrile-water mixtures. Formation constant for the resulting 11 complexes in different solvent mixtures was determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and amount of water in the mixed solvent. The dissociative kinetics of the complex was studied by proton line-shape analysis. The Arrhenius plots showed a distinct isokinetic temperature at about 25°C at which the decomplexation rate is more or less independent of the solvent composition. the complexation rate and the activation parameters E _a , H and S, for the exchange have been determined and found to be strongly solvent dependent. There is actually a linear relationship between the mole fraction of acetonitrile in the mixed solvent and logarithm of the stability constant as well as activation parameters.     

Reverse Schreinemakers Method for Experimental Analysis of Mixed-Solvent Electrolyte Systems

A method based on Schreinemakers’s tie-line theory of 1893 is derived for determining the composition and phase amounts in solubility experiments for multi-solvent electrolyte systems. The method uses the lever rule in reverse compared to Schreinemakers’s wet residue method, and is therefore called the reverse Schreinemakers (RS) method. The method is based on simple mass balance principles similar to the wet residues method. It allows for accurate determination of the mixed-solvent phase composition even though part of the solvent may precipitate as complexes between solvent and salt. Discrepancies from determining the composition of salt mixtures by pH titration are discussed, and the derived method significantly improves the obtained result from titration. Furthermore, the method reduces the required experimental work needed for analysis of phase composition. The method is applicable to multi-solvent systems and may be used for the determination of solid-phase compositions, similar to Schreinemakers’s original “rest” method. An example calculation is presented for the Na₂CO₃-NaHCO₃-MEG-H₂O system.     

Copper Phthalocyanine‐Functionalized Graphitic Carbon Nitride: A Hybrid Heterostructure toward Photoelectrochemical and Photocatalytic Degradation Applications

In this work, alcian blue 8GX (AB), a copper(II) phthalocyanine derivative, was employed to functionalize graphitic carbon nitride (g‐C₃N₄) for the preparation of a highly efficient photocatalyst. The approach relies on a facile AB‐assisted ethanol/water mixed‐solvent exfoliation of bulk g‐C₃N₄. The as‐prepared g‐C₃N₄/AB hybrid possesses significantly enhanced solution dispersibility and photoelectrochemical performance resulting from the synergistic effect between g‐C₃N₄ and AB, which involves the optimization of intimate interfacial contact, extension of light absorption range, and enhancement of charge‐transfer efficiency. This synergy contributes enormously to the photocatalytic degradation of rhodamine 6G (R6G) under light irradiation.     

NMR STUDY OF EXCHANGE KINETICS OF THE LITHIUM ION WITH CRYPTAND C222 IN BINARY ACETONITRILE-NITROMETHANE MIXTURES

Abstract

The exchange kinetics of the lithium ion with cryptand C222 were studied in acetonitrile-nitromethane mixtures by lithium-7 NMR line-shape analysis. In all solvent mixtures used, and over the entire temperature range studied, the chemical exchange of the Li⁺ ion between the solvated and complexed sites was found to occur via a bimolecular mechanism. The activation parameters E_a, δH?, δS? and δG? for the exchange have been determined. The free energy barrier for the exchange process appears to be nearly independent of the binary mixture composition. The results confirm the preferential solvation of the lithium ion with acetonitrile in the binary mixed solvent systems used.     

An NMR study of the stoichiometry and stability of lithium ion complexes with 12-crown-4, 15-crown-5 an 18-crown-6 in binary Acetonitrile-Nitrobenzene mixtures

Proton NMR spectroscopy was used to study the complexation reaction between lithium ion and 12-crown-4, 15-crown-5 and 18-crown-6 in a number of binary acetonitrile-nitrobenzene mixtures. In all cases the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average¹H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of acetonitrile in the mixed solvent. It was found that, in all solvent mixtures used, 15-crown-5 forms the most stable complex with Li⁺ ion in the series.