Soft Cations Research Articles

Ion–solvent interactions in mixtures of N-methyl-2-pyrrolidinone and N-methyl-2-thiopyrrolidinone

Electrochemical measurements of hard, borderline and soft cations such as Li+, Na+, K+, Tl+, Cu+, Ag+ and Cd2+ as well as studies on the redox behaviour of oxygen, perylene and tetrabutylammonium hexacyanoferrate have been carried out in mixtures of the hard oxygen donor solvent N-methyl-2-pyrrolidinone and the soft sulphur donor solvent N-methyl-2-thiopyrrolidinone. Soft cations were found to be strongly stabilized by N-methyl-2-thiopyrrolidinone, and significant changes in the redox potentials to more positive values could be observed only in solutions rich in N-methyl-2-pyrrolidinone. The opposite effect was observed for hard cations. These cations interacted strongly with N-methyl-2-pyrrolidinone, and the redox potentials remained more or less constant until a considerable excess of N-methyl-2-thiopyrrolidinone appeared. The behaviour of the redox systems, which included anionic species, namely O2/O–2 and Fe(CN)3–6/Fe(CN)4–6 was only slightly affected by changes in the solvent composition. Gibbs energies of transfer from N-methyl-2-pyrrolidinone into the solvent mixtures for Li+, Na+, K+, Cu+, Ag+, Tl+ and Cd2+ were calculated from the electrochemical data on the basis of the bis(biphenyl)chromium uptake. In addition to the studies on the changes in redox potentials, the solvent-induced shifts of the visible spectra of the solvatochromic dyes acetylacetonato(tetramethylethylenediamine)-copper(II) perchlorate, bis(cyano)bis(1,10-phenanthroline)iron(II), bis(cyano)bis(3,4,7,8-tetramethyl-1,10-phenanthroline)iron(II) and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridino)phenoxide were investigated. The results are interpreted on the basis of changes in the Lewis-type donor and acceptor properties of the solvent mixtures including the principle of hard and soft acids and bases.

Cation complexation with functionalized 9‐arylacridinium ions. Part II: Conformational and spectral response upon metal‐ion complexation

AbstractThe chromoionophoric behaviour of compound 1 in solution was studied in relation to the X‐ray structure of its complexes with Na+, Ba2+ and Ag+. Interaction between the metal ion and the “soft” nitrogen atom, which forms part of the aza crown ether of 1, is concluded to be of crucial importance. It is shown that in solution a soft cation such as Ag+ induces a greater special spectral shift than do hard cations of equal charge and almost the same size, such as Na+ and K+. Solid‐state structures of the Ag+ and Na+ complexes of 1 show a relatively short Ag+ ‐N distance and a relatively long Na+ ‐ N distance.Netherlands Organization for Chemical Research (SON) with financial aid from the Netherlands Organization for Scientific Research (NWO).

ChemInform Abstract: Synthetic, Spectroscopic, and X‐Ray Studies on Methylmercury(II) and Dimethylthallium(III) Complexes with Cyclopentanone Thiosemicarbazone.

AbstractIn order to compare the properties of the coordination modes of cyclopentanone thiosemicarbazone in complexes with soft cations, the compounds (III) and (V) are prepared (no yield given).

ChemInform Abstract: Recent Aspects of Single Ion Transfer Properties

Gibbs energies, entropies and enthalpies of transfer for several cations and anions from acetonitrile into various solvents formed the basis for investigations on general trends in the interactions of solvent molecules with positively and negatively charged ions. Gibbs energies of transfer for Na+, K+, Rb+, Cs+, Cuff T1+ and Ag+ obtained from different assumptions, experimental techniques and research groups together with a large number of recen ly pu lishe energies of transfer for Li+, Ba2+, Cu, Zn9+, Cd9+,GiHbgb5+ and Pb2+ based on the bis (bipheny1)chromium assumption - were employed to study the interactions of hard and soft donor solvents with hard, soft and borderline cations. Solvent effects on anions were deduced from the Gibbs energies of transfer for Cl', Br-, I- and SCN-. Parameters proposed to account for hard and soft donor properties or for acceptor properties of the solvents were compared with the Gibbs energies of transfer. Parameters representing hard donor properties of solvents correlated with Gibbs energies of transfers for cations into hard solvents, but transfer properties of soft and borderline cations into soft solvents called for a different solvent parameter. The Gibbs energies of transfer for anions related to such solvent parameters that characterized acceptor properties. The solvent induced changes in the Gibbs energies of transfer of hard and soft cations as well as the respective data for anions were explained within the framework of a donor-acceptor model of ion-solvent interactions, including the principle of hard and soft acids and bases. The current status on enthalpies and entropies of transfer is discussed.

Recent aspects of single ion transfer properties

Abstract

Hydrated metal halide structures and the HSAB concept

AbstractA review of ligand coordinatio in the structures of hydrates of the bivalent Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn and Cd halide salts is made. Differences in the type of environment around the Me2+ are satisfactorily explained using the HSAB (Hard and Soft Acids and Bases) concept: in all structures the tendency for a preferable combination hard cation — hard ligand and soft cation — soft ligand is proved. The paper demonstrates the possibilities of the HSAB concept to solve crystallochemical problems of the type of ligand coordination in the structures.

N-nitration of salts of primary nitramines by nitryl fluoride

1. A method has been developed for the N-nitration of the anions of primary nitramines with nitryl fluoride to N,N-dinitramines. 2. Bulky tetraalkylammonium cations in nitramine salts direct the attack of nitryl fluoride on the nucleophilic amine center of the ion, whereas the harder metal cations favor O-nitration. 3. In the nitration of nitramine anions by nitronium tetrafluoroborate, the opposite effect is observed with respect to the influence of the salt cation on the outcome of the reaction, i.e., bulky, soft cations favor O-nitration.

Polarographic and voltammetric investigations in N-methylpyrrolidinone(2) and N-methylthiopyrrolidinone(2)

Polarographic and voltammetric methods were employed to study the influence of N-methylpyrrolidinone(2) (NMP) and N-methylthiopyrrolidinone(2) (NMTP) towards a series of cations. In NMP reversible electrode reactions were observed for Na + , K + , Tl + , Zn 2+ , Cd 2+ , Cu 2+ , Ag + and irreversible reductions for Ba 2+ , Mn 2+ , Co 2+ and Ni 2+ . 0.1 mol l −1 tetraethylammoniumperchlorate solutions served as supporting electrolytes. Li + was not electroactive in the supporting electrolyte mentioned, but yielded an irreversible cathodic wave in tetra-n-butylammonium perchlorate. In NMTP, Li + , Na + , Tl + , Zn 2+ , Cd 2+ , Cu + and Ag + gave reversible cathodic waves on the DME, while Mn 2+ , Co 2+ and Ni 2+ were reduced in an irreversible electrode process. Bisbiphenylchromium iodide serving as a reference system throughout this study showed reversible behaviour in both solvents. A comparison of E 1/2 for given ions in both solvents showed a shift of about 0.5 V to more positive values in the case of a typically hard cation such as Na + whereas soft cations such as Ag + and Cu + shifted by more than 0.8 V to more negative values. The effects of these two solvents on the cations studied is discussed in terms of donor acceptor interactions between the cation and the solvent molecules with special respect to the changes caused by replacing the oxygen atom in NMP by a sulphur atom.

Polarographic and voltammetric investigations in N-methylpyrrolidinone(2) and N-methylthiopyrrolidinone(2)

Polarographic and voltammetric methods were employed to study the influence of N-methylpyrrolidinone(2) (NMP) and N-methylthiopyrrolidinone(2) (NMTP) towards a series of cations. In NMP reversible electrode reactions were observed for Na +, K +, Tl +, Zn 2+, Cd 2+, Cu 2+, Ag + and irreversible reductions for Ba 2+, Mn 2+, Co 2+ and Ni 2+. 0.1 mol l −1 tetraethylammoniumperchlorate solutions served as supporting electrolytes. Li + was not electroactive in the supporting electrolyte mentioned, but yielded an irreversible cathodic wave in tetra-n-butylammonium perchlorate. In NMTP, Li +, Na +, Tl +, Zn 2+, Cd 2+, Cu + and Ag + gave reversible cathodic waves on the DME, while Mn 2+, Co 2+ and Ni 2+ were reduced in an irreversible electrode process. Bisbiphenylchromium iodide serving as a reference system throughout this study showed reversible behaviour in both solvents. A comparison of E 1/2 for given ions in both solvents showed a shift of about 0.5 V to more positive values in the case of a typically hard cation such as Na + whereas soft cations such as Ag + and Cu + shifted by more than 0.8 V to more negative values. The effects of these two solvents on the cations studied is discussed in terms of donor acceptor interactions between the cation and the solvent molecules with special respect to the changes caused by replacing the oxygen atom in NMP by a sulphur atom.

Solvation of ions. XXII. Solvation of cations by hard N,N-dimethylformamide and soft N,N-dimethylthioformamide

The free energies of transfer of some univalent cations from N,N-dimethylformamide to N,N- dimethylthioformamide at 25� are Li+, 64.0; Na+, 50.2; K+, 37.2; Cs+, 23.4; TI+, -4.2 and Ag+, - 87.0 kJ g-ion-1. The values are based on the assumption of negligible liquid junction potential in an electrochemical cell. Certain ones of these values can be interpreted in terms of general interactions of hard and soft cations with hard and soft basic solvents. A linear free energy relationship, ΔGtr(M+) = mΔGtr(K+), is roughly obeyed by many cations for transfer to a variety of solvents. Deviations from this relationship, for example ΔGtr(Ag2+) to acetonitrile, ΔGtr (Ph4As+) to water and ΔGtr (Ag+) to N,N-dimethylthioformamide, allow specific solvation mechanisms to be detected.