H-Bond donor parameters for cations.

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 (?) 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 ? 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 ? parameter is only 5.0, which is similar to the neutral H-bond donor 3-trifluoromethyl,4-nitrophenol (? = 5.1). Quaternary ammonium is the weakest H-bond donor investigated with an ? value of 2.7, which is comparable to an alcohol. The ? parameters for alkali metal cations decrease down the group from 5.0 (Li⁺) to 3.5 (Cs⁺).

SUBMITTER: Pike SJ 

PROVIDER: S-EPMC6566073 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature