Structure and ionic conductivity of the octahydrate of tetralithium salt of calix[4]arenesulfonic acid

Abstract

Octahydrate of tetralithium salt of calix[4]arenesulfonic acid was isolated for the first time. The crystal structure of the salt was determined by X-ray diffraction analysis. Compound crystallized in a triclinic syngony, P, a = 11.8752(5) Å, b = 12.2144(4) Å, c = 13.2972(6) Å, α = 97.241(3)°, β = 99.345(4)°, γ = 90.658(3)°, V = 1886.96(13) ų, Z = 2, R₁ = 0.0407, T = 150 K. The presence of 8 water molecules in the structure was confirmed by STA. According to the IR spectroscopy data upon lithiation, the contours of the ν_s(SO₃) and ν_as(SO₃) bands became symmetric and narrower, which was explained by the disappearence of contacts between the sulfonic groups and the H₅O₂⁺ cations compared with calix[4]arenesulfonic acid. Lithium ions were qualitatively determined from the maximum of the stretching vibration band of the Li–O bond at ∼400 cm⁻¹. The participation of H₂O molecules coordinated by Li cations in the formation of a network of hydrogen bonds with oxygen atoms of sulfogroups was determined by the maximum of the stretching band ν(OH) belonging to these molecules at 3452 cm⁻¹ in the spectrum. The intense band at 3148 cm⁻¹ referred to the ν(OH) stretching vibration of the C–OH group. The dependence of the conductivity of the tetralithium salt of calix[4]arenesulfonic acid in a wide range of humidity has been investigated. It was shown that with the gradual replacement of protons in calix[4]arenesulfonic acid, the conductivity decreased from 10⁻⁴–10⁻² S cm⁻¹ in acid in the ambient humidity range of 10–60 rel% down to 10⁻⁷–10⁻⁴ S cm⁻¹ for the tetralithium salt of calixarenesulfonic acid in a wide range of humidity 10–95 rel%.