H-Bond donor parameters for cations. Issue 23 (16th May 2019)

• Record Type: Journal Article
• Authors: Pike, Sarah J.; Lavagnini, Ennio; Varley, Lisa M.; Cook, Joanne L.; Hunter, Christopher A.
• Is Part Of: Chemical science. Volume 10:Issue 23(2019)
• Page Start: 5943
• Page End: 5951
• Publication Date: 2019-05-16
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c9sc00721k
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Parameters that provide a quantitative description of the free energy of interaction of cations with any H-bond acceptor in any solvent have been experimentally determined. Abstract : UV/Vis absorption and NMR spectroscopy titrations have been used to investigate the formation of complexes between cations and neutral H-bond acceptors in organic solvents. Complexes formed by two different H-bond acceptors with fifteen different cations were studied in acetone and in acetonitrile. The effects of water and ion pairing with the counter-anion were found to be negligible in the two polar solvents employed for this study. The data were used to determine self-consistent H-bond donor parameters ( α ) for a series of organic and inorganic cations; guanidinium, primary, tertiary and quaternary ammonium, imidazolium, methylpyridinium, lithium, sodium, potassium, rubidium and caesium. The results demonstrate the transferability of α parameters for cations between different solvents and different H-bond acceptor partners, allowing reliable prediction of cation recognition properties in different environments. Lithium and protonated nitrogen cations form the most stable complexes, but the α parameter is only 5.0, which is similar to the neutral H-bond donor 3-trifluoromethyl, 4-nitrophenol ( α = 5.1). Quaternary ammonium is the weakest H-bond donor investigated with an α value of 2.7, which is comparable to an alcohol. The α parameters for alkali metal cations decrease down the group from 5.0 (Li + ) to 3.5 (Cs + ).