Synthesis, X-ray crystal structure and cation binding properties of a tetrahomodioxacalix[4]arene tetraester

Treatment of p-t-butyltetrahomodioxacalix[4]arene with ethyl bromoacetate yields a tetraester derivative (4) whose crystal and molecular structure have been determined and whose ion binding properties have been assessed by phase transfer and stability constant measurements. Colorless transparent triclinic crystals (obtained from methoxyethanol) C₆₂H₈₄O₁₄, a = 10.347(2), b = 11.583(2), c = 13.448(3) Å, α = 72.04(2), β = 86.50(2)°, γ = 81.23(2)°, space group {Mathematical expression}, Z = 1, Mo K_α radiation λ = 0.70930 Å. Refinement was carried out using 2221 reflections with I > 1.5 σ(I). The complexation properties resemble those of calix[6]arene hexaester (6), although weaker, with a preference for the larger alkali cations. Ca²⁺ and Ba²⁺; though not extracted, are more strongly complexed than alkali cations. Eu³⁺ is better complexed than Na⁺.