3D Metal–Organic Framework Based on a Lower-Rim Acid-Functionalized Calix[4]arene: Crystal-to-Crystal Transformation upon Lattice Solvent Removal

A rare three-dimensional (3D) calix[4]­arene-based metal–organic framework (calixMOF) {[Pb₂@L]·2DMF}_n (1) was obtained by the solvothermal reaction between a lower-rim acid-functionalized calix[4]­arene (H₄L) and Pb­(NO₃)₂ in N,N-dimethylformamide; 1 exhibited ths topology, in which Pb­(II) atoms accommodated inside the calixarene unit adopted hemidirected coordination geometry. Interestingly, upon the removal of guest solvent molecules, the 3D framework of 1 readily converted to a shrunken 3D framework [Pb₂@L]_n (1a) via a single-crystal to single-crystal transformation. However, the resolvation of the guest molecules was not observed when 1a was immersed into DMF at room temperature or at 110 °C. Furthermore, 1a exhibited interesting CO₂ sorption behavior: Its CO₂ isotherm curves exhibited looped patterns of linear adsorption and nonlinear desorption. The thermal behavior and solid-state photoluminescence properties of 1 and 1a were also reported.