Synthesis and characterization of two distinct structural types of coordination polymers are reported with 1, 2, 4, 5-benzenetetracarboxylate (btec) ligands associated with lanthanides (Ln) Ce (III), La (III), and Pr (III) for compounds 1-3, and Dy (III) and Yb (III) for compounds 4-5. The two structures are built from the connection of lanthanide centers with the linkers to construct a 3D framework composed of 1D tunnels encapsulating dimethylammonium and water in (CH3) 2NH2Ln (btec) 00b72H2O (1-3) or dimethylammonium only in (CH3) 2NH2Ln (btec) (H2O) (4-5). These two atomic arrangements differ by the occurrence of infinite chains of edge-sharing LnO9 units and, the presence of trapped water species in 1-3, instead of dinuclear carboxylate-bridged 2 × LnO8 units and, bonded aquo species to Ln centers in 4-5. The dehydration process was investigated for compound 1. Removal of water induces a crystalline phase transition related to the shrinkage of the 3D network to form (Ln (btec) · (CH3) 2NH2, noted 1'). Elucidation of the mechanism is provided by combining water adsorption measurements with GCMC calculations. This transformation shows a relative flexibility of the network (cell volume variation of -6%) reminiscent of the breathing effect reported in the MOF such as the MIL-53 series. The anhydrous phase 1' is able to adsorb reversibly water as experienced with the measurement of water vapor isotherms.
Flament et al. (Wed,) studied this question.