A lanthanide metal-organic framework based on a custom-designed macrocyclic ligand

The lanthanum-based metal macrocyclic framework, MMCF-3, where the ligand is 1,4,7,10-tetraazacyclododecane-N,N′,N″,N′″-tetra-p-methylbenzoic acid, has been synthesized and characterized by powder X-ray diffraction, single crystal X-ray diffraction, and thermogravimetric analysis. MMCF-3 forms in closely packed 2-D sheets. In MMCF-3, the azamacrocyclic-based ligand coordinates tetradentate to four separate lanthanum ions via its carboxylate groups, leaving the macrocycle site unoccupied. The lanthanum ions are 10-coordinate with a distorted bi-capped square anti-prism coordination environment. The vacancy of the macrocycle site within the framework encourages the utilization of the framework as a cation receptor. The availability of these sites allows for the possibility to coordinate to newly introduced metals to produce heterometallic frameworks, which could exhibit intriguing properties.