Chemical Shift-mole Ratio Data Research Articles

1H-NMR study of the stoichiometry and stability of the Ba2+, Sr2+, Hg2+, Pb2+, K+, Ag+, and Tl+ complexes with a new macrocyclic diamide in acetonitrile–nitrobenzene solvent mixture

Proton NMR technique was utilized to study the complexation reactions of a new macrocycle diamide with Ba2+, Sr2+, Hg2+, Pb2+, K+, Ag+, and Tl+ ions in % 50 (w/w) acetonitrile–nitrobenzene binary mixture. In all the cases, the chemical shifts of the single NMR signals due to the –O–CH2–CH2–O– and Ph–O–CH2– groups of the ligand were determined at 300 K. The exchange between free form of the macrocycle (I) and its complexes was fast on the NMR time scale and just a single population average 1H signal was observed. Formation constants of the resulting 1:1 complexes were determined by computer fitting of the chemical shift–mole ratio data. The stabilities of the resulting 1:1 complexes varying in the order Ba2+ > Sr2+ > Hg2+ > Pb2+ > Ag+ > K+ > Tl+ were determined. For two singlet groups of ligand (I) (Ph–O–CH2– and –O–CH2–CH2–O–), the values of the formation constants which were obtained from data fitting were found to be similar, but shift of the signal for Ph–O–CH2– group was larger than for –O–CH2–CH2–O– group. The theoretical studies on the structures and the energetic data of the five conformers of ligand macrocycle (I) and the complexes with Ba2+, Sr2+, Hg2+, Pb2+, Ag+, K+, and Tl+ have been performed by DFT-B3LYP/6-31G* method for ligand (I) and QM-PM6 method for the complexes. The comparison of the experimental and theoretical data with respect to the formation constants and the structures of the complexes have shown good agreement.

Conductometric and 1H NMR studies of thermodynamics of complexation of Zn2+, Cd2+ and Pb2+ ions with tetrathia-12-crown-4 in dimethylsulfoxide-nitrobenzene mixtures

The complex formation between Zn2+, Cd2+ and Pb2+ ions with macrocyclic ligand, tetrathia12-crown-4 (12S4) was studied in dimethylsulfoxide (DMSO)–nitrobenzene binary mixtures at different temperatures using conductometric and 1H NMR methods. In all cases, 12S4 found to form 1:1 complexes with these cations. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the resulting molar conductance- and chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The stability of the resulting M2+-12S4 complexes found to decrease in the order Pb2+ > Cd2+ > Zn2+. The values of ∆H°, ∆S° and ∆G° for complexation reactions were evaluated from the temperature dependence of formation constants via van’t Hoff method. The obtained results revealed that, in all cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ∆H° and ∆S° are strongly depend on the nature of medium. There is also a linear relationship between all ΔH° and TΔS° values indicating the existence of entropy–enthalpy compensation in complexation of the three cations and ligand in the solvent systems studied.

Multinuclear magnetic resonance study of N-phenyl-aza-15-crown-5 complexes with lithium, sodium and caesium ions in nonaqueous solvents

Nuclear magnetic resonances of 7Li, 23Na and 133Cs nuclei were used to study the lithium, sodium and caesium ion complexes with N-phenyl-aza-15-crown-5 (PhA15C5) in nitromethane (NM), acetonitrile (AN) and AN–NM mixture solutions. The chemical shift data indicated that these cations form 1 : 1 cation : ligand complexes with PhA15C5. The formation constants of the resulting complexes were calculated from the computer fitting of the chemical shift–mole ratio data. The results show that the complex formation constants of PhA15C5 with these cations vary in the order of Na+ > Li+ ≫ Cs+. Complexation of the lithium ion was also studied in binary AN–NM mixtures. It was found that the stability of the resulting complexes increases by an increase in the amount of NM in the solvent mixture.

7Li-NMR study of the stoichiometry, stability and exchange kinetics of Li + ion with 12-Crown-4, 15-Crown-5 and cryptands C222, C221 and C211 in 50% ionic liquid–acetonitrile mixtures

7Li-NMR spectroscopy was used to study the complexation of Li + ion with 12C4, 15C5, C222, C221, C211 in acetonitrile (AN) and its 50% (wt/wt) mixtures with two new room temperature ionic liquids, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMim PF 6) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMim BF 4) at 298 K. Excluding the cases of Li +–C211 in all solvents and Li +–C221 in AN and 50% (wt/wt) AN–EMim PF 6, in other cases, the exchange between free and 1:1 complexed Li + was fast on the NMR time scale and only a single population average 7Li signal was observed. Formation constants of the resulting 1:1 complexes were evaluated by computer fitting of the chemical shift-mole ratio data and integration of two 7Li signals. All complexes in EMim PF 6 were found to be more stable than those in EMim BF 4. 7Li-NMR line-shape analysis was used to determine the kinetic parameters and the mechanism for the chemical exchange of Li + between the free and 1:1 complex with C221 in 50% (wt/wt) AN–EMim PF 6 mixtures solution. By comparing our study with the previous one, it is derived that, increasing the percentage of ion liquid in acetonitrile, changes the mechanism and decrease the exchange rate constant of Li + ion between free and complex sites.

Proton NMR probing of stoichiometry and thermodynamic data for the complexation of Na + and Li + ions with 15-Crown-5 in acetonitrile–nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Li + and Na + ions with 15-Crown-5 (15C5) in a number of binary acetonitrile (AN)–nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 15C5 was fast on the NMR timescale and only a single population average 1H signal was observed. The 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 AN in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of the formation constants. In all the solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. Finally, the experimental results were compared with theoretical ones that were obtained from molecular modeling methods. Based on our results, it is most probable that Li +–15C5 in solvent stays in a rather nesting complex form with greater Log K f values, but Na +–15C5 forms a complete perching complex form with lower Log K f values.

133Cs NMR Study of Cs+ Ion Complexes with Aza-18-crown-6, Diaza-18-crown-6 and Dibenzyldiaza-18-crown-6 in Binary Acetonitrile–Nitromethane Mixtures

Cesium-133 nuclear magnetic resonance spectroscopy was used as a sensitive probe to investigate the stoichiometry and stability of Cs+ ion complexes with aza-18-crown-6 (A18C6), diaza-18-crown-6 (DA18C6) and dibenzylediaza-18-crown-6 (DBzDA18C6) in different binary acetonitrile–nitromethane mixtures. In all cases, the exchange between free and complexed cesium ion was fast on the NMR time scale and only a single population average resonance was observed. The 133Cs chemical shift–mole ratio data indicated that the cesium ion forms 1:1 cation–ligand complexes with the investigated aza-crowns in all acetonitrile–nitromethane mixtures. The formation constants of the resulting complexes were evaluated from computer fitting of the chemical shift–mole ratio data. The stability of the resulting 1:1 complexes with Cs+ were found to vary in the order A18C6 > DBzDA18C6 > DA18C6. In all cases, there is the inverse relationship between the complex stability constants and the amount of acetonitrile in the mixed solvent.

133Cs NMR Study of Cs+ Ion Complexes with Dibenzo-24-crown-8, Dicyclohexano-24-crown-8 and Dibenzo-30-crown-10 in Binary Acetonitrile-Nitromethane Mixtures

Complexation of the cesium ion with the macrocyclic ligands: dibenzo-24-crown-8 (DB24C8), dicyclohexano-24-crown-8 (DC24C8) and dibenzo-30-crown-10 (DB30C10) was studied in binary acetonitrile-nitromethane mixtures by 133Cs NMR spectroscopy. The 133Cs chemical shift data indicated that the cesium cation forms 1:1 cation:ligand complexes with DB24C8 and DB30C10 but forms 2:1, 1:1 and 1:2 cation:ligand complexes with DC24C8 in acetonitrile-nitromethane mixtures. The formation constants of the complexes were calculated from the computer fitting of the chemical shift mole ratio data. The results show that the complex formation constants with the Cs+ cation vary in the order DC24C8>DB24C8∼DB30C10. It was found that the stability of the resulting complexes increases with increasing nitromethane concentration in the solvent mixture.

Proton NMR study of the stoichiometry, stability and thermodynamics of complexation of Rb+ ion with 18-crown-6 in binary dimethylsulfoxide–nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Rb+ ion with 18-crown-6 (18C6) in a number of binary dimethylsulfoxide (DMSO)–nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 18C6 was fast on the NMR time scale and only a single population average 1H signal was observed. The 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 DMSO in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of formation constants. In all solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. The ∆H° versus T∆S° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reaction.

A Proton NMR Study of the Stoichiometry and Stability of 18-Crown-6 Complexes with K+, Rb+ and Tl+ Ions in Binary Dimethyl Sulfoxide-Nitrobenzene Mixtures

Proton NMR spectroscopy was used to study the complexation reaction of 18-crown-6 (18C6) with K+, Rb+ and Tl+ ions in a number of binary dimethyl sulfoxide-nitrobenzene mixtures. In all cases, the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average 1H 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 dimethyl sulfoxide in the mixed solvent. It was found that, in all solvent mixtures used, Rb+ ion forms the most stable complex with 18-crown-6 in the series.

1H NMR studies of homo and mixed ligand complexes of Tl + ion with several polyazamacrocycles

Proton NMR was used as a probe to study the interaction of the Tl + ion with 9–18-membered macromonocyclic tri-, tetra-, and hexaamines in dimethylformamide (DMF) solution. A study of proton chemical shift of ligands as a function of Tl + ion to ligand mole ratio revealed that the complexation reactions occur in a stepwise manner. Formation of a 1:1 complex is followed by the addition of a second complexant molecule to form a homo-sandwich complex for triazamacrocycle ligands and a mixed ligand complex in the case of hexamethylhexacyclen (HMHCY) and 1,4,7-triazacyclononane ([9]aneN 3). The formation constants of resulting 1:1 and 1:2 (homo and mixed ligand sandwich) complexes in DMF solution were evaluated from computer fitting of the chemical shift-mole ratio data. The mixed ligand complexes may be more stable than the parent complex in which both ligands are the same. The influence of cavity size and substitution of methyl groups on nitrogen atoms of the macrocyclic ring the stability of the resulting complexes is discussed. The geometries of the tri- and tetraazamacrocycle ligands and their Tl + ion complexes were optimized by an ab initio method, and the calculated binding energies of resulting complexes were compared. Both the experimental and theoretical studies revealed that, in the presence of methyl groups, the stability of triazamacrocycle complexes with Tl + ion was decreased.

NMR Study of the Stoichiometry, Stability, and Ligand Interchange of Silver Ion-Hexathia-18-crown-6 Complex in Binary Dimethyl Sulfoxide Solvent Mixtures at 300 K

Proton NMR was used to study the complexation reaction between silver ion and hexathia-18-crown-6 in a number of binary mixed solvents of dimethyl sulfoxide with acetonitrile and methanol. Formation constants for the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. The influence of solvent composition on the stability of the resulting complex is discussed. The exchange kinetics of Ag+-hexathia-18-crown-6 in 70-30 wt.% dimethyl sulfoxide-acetonitrile and 75-25 wt.% dimethyl sulfoxide-methanol were studied by proton NMR line-shape analysis. In both solvent mixtures, the exchange of thiacrown ether between the free and complexed sites was found to proceed via a dissociative pathway. The exchange rates and the activation parameters Ea, Δ H‡, Δ S‡, and Δ G‡ for the ligand exchange were determined and the influence of solvent properties on these parameters discussed.

Lithium-7 and sodium-23 nmr studies of complexation of Li + and Na + ions with 1,10-phenanthroline, 2,2′-bipyridine and 8-hydroxyquinoline in some non-aqueous solutions

—NMR spectra of lithium-7 and sodium-23 were used to study the interactions of Li + and Na + ions with 1,10-phenanthroline, 2,2′-bipyridine and 8-hydroxyquinoline in nitromethane, nitrobenzene, acetonitrile and acetone solutions. The stoichiometry and stability of the resulting complexes were evaluated from non-linear least-squares fitting of the chemical shift-mole ratio data to appropriate equations. There is an inverse relationship between the stability of the complexes and the solvating ability of the solvents, as expressed by Gutmann donor numbers. In all solvents studied, Li + forms more stable complexes than Na + and, for each cation, the stability order of the resulting complexes is 1,10-phenanthroline > 2,2′-bipyridine > 8-hydroxyquinoline.

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.

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 1∶1 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 Ea, ΔH‡ and ΔS‡, 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.