Issue 31, 2022

Tetranitro- and tetraamino-dibenzo[18]crown-6-ether derivatives: complexes for alkali metal ions, redox potentials, crystal structures, molecular sorption, and proton conducting behaviours

Abstract

Tetranitro-dibenzo[18]crown-6 (1) and tetraamino-dibenzo[18]crown-6 (2) are ion-recognition electron acceptor and electron donor molecules, respectively. The electron-accepting ability of 1 is lower than that of o-dinitorobenzene, whereas the electron-donating ability of 2 exceeds that of tetrathiafulvalene, a typical electron donor. The oxidation potential of 2 is drastically reduced by di-protonation at the two –NH2 sites under acidic conditions. Thermally annealed 1 exhibits gate-opened gas adsorption–desorption behaviors for CO2 at 200 K and N2 at 77 K. The central cavity of 1 can bind alkali metal ions (M) to form M(1) complexes for M = Na+, K+, Rb+, and Cs+; these crystallize into monomers (M = Na+ and K+), dimers (M = Rb+), and one-dimensional polymers (M = Cs+) in single crystals of [M(1)I]·nCH3CN. Multiple M+⋯O2N– axial coordination at the M+ site generates dimer and polymer networks in solids. Single crystals of [Na(2)(H2SO4)3nH2O and [K(2)(H2SO4)3nH2O were obtained by crystallization of 2 in the presence of Na+ and K+, respectively, in dilute H2SO4. The single crystals formed an ionic channel in the one-dimensional array of ⋯[(Na)0.25(2)]⋯H2O⋯[(H3O)0.25(2)]⋯H2O⋯, and the mixed protonated state of HSO4 and H2SO4 formed an O–H⋯O[double bond, length as m-dash] hydrogen-bonding network with the aid of additional H2O molecule occupation around the ionic channels. In contrast, the two oxygen atoms of HSO4 were axially coordinated to the K(2) complex, which isolated them from each other, and HSO4 and H2O occupied [K(2)(H2SO4)3]. These two hydrated crystals showed a proton conductivity (σH+) of ∼5 μS cm−1 at 310 K, while in the dehydrated crystals the σH+ values disappeared; furthermore, the motional freedom of the polar HSO4 was observed in the Debye-type dielectric relaxations.

Graphical abstract: Tetranitro- and tetraamino-dibenzo[18]crown-6-ether derivatives: complexes for alkali metal ions, redox potentials, crystal structures, molecular sorption, and proton conducting behaviours

Supplementary files

Article information

Article type
Paper
Submitted
27 Apr 2022
Accepted
23 Jun 2022
First published
29 Jun 2022

CrystEngComm, 2022,24, 5570-5579

Author version available

Tetranitro- and tetraamino-dibenzo[18]crown-6-ether derivatives: complexes for alkali metal ions, redox potentials, crystal structures, molecular sorption, and proton conducting behaviours

Y. Shimizu, T. Takeda, N. Hoshino and T. Akutagawa, CrystEngComm, 2022, 24, 5570 DOI: 10.1039/D2CE00582D

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