Three-Dimensional Co- and Mn-MOFs Containing a C-2h-Symmetric Terphenyl-3,3-dicarboxylate Linker and Their Magnetic Properties

Abstract

We report herein two new isostructural, three-dimensional (3D) MOFs with the general formula [M(3,3-tpdc)(dmf)] [M = Co-II (I), Mn-II (II)] resulting from the assembly of a metal ion and the C-2h-symmetric ditopic bridging ligand terphenyl-3,3-dicarboxylate (3,3-tpdc). Both isostructural MOFs crystallize in the monoclinic space group C2/c. The metal ion is coordinated by four O-carboxylate ((1):(1):mu(2)) and two mu(2)-O-dmf atoms in a distorted octahedral geometry. The metal centers are interconnected through bridging 3,3-tpdc and dmf ligands to form a 1D chain. The resulting 1D metal chains are further interconnected by 3,3-tpdc ligands to form 3D frameworks without porosity. The thermolabile dmf bridging ligands were easily removed by heating at 180 degrees C under vacuum for 5 h. The activated MOFs I and II exhibited very low gas uptake of N-2, CO2, and H-2 after removal of the dmf bridging ligands. The encapsulation of iodine guest molecules by the activated I and II was also investigated. The crystal structure of iodine-encapsulated II was also elucidated. The coordination environment of the Mn-II atom in II changed as a result of the loss of dmf bridging ligands. The as-prepared MOFs I and II exhibit weak antiferromagnetic interactions in their 1D metal chains; these magnetic interactions should mainly occur between the metal ions bridged by the short carboxylate-based ligand and dmf oxygen atoms. Thermal removal of the bridging dmf molecules led to a change in the MnMn distances in the 1D chains of II that also affected its magnetic properties.