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.