Synthesis and Structural Characterization of Magnesium Based Coordination Networks in Different Solvents

Three magnesium based metal–organic frameworks, Mg3(3,5-PDC)3(DMF)3·DMF [1], Mg(3,5-PDC)(H2O)·(H2O) [3], and Mg4(3,5-PDC)4(DMF)2(H2O)2·2DMF·4.5H2O [4], and a 2-D coordination polymer, [Mg(3,5-PDC)(H2O)2] [2] [PDC = pyridinedicarboxylate], were synthesized using a combination of DMF, methanol, ethanol, and water. Compound 1 [space group P21/n, a = 12.3475(5) Å, b = 11.1929(5) Å, c = 28.6734(12) Å, β = 98.8160(10)°, V = 3916.0(3) Å3] consists of a combination of isolated and corner-sharing magnesium octahedra connected by the organic linkers to form a 3-D network with a 12.2 Å × 4.6 Å 1-D channel. The channel contains coordinated and free DMF molecules. In compound 2 [space group C2/c, a = 9.964(5) Å, b = 12.0694(6) Å, c = 7.2763(4) Å, β = 106.4970(6)°, V = 836.70(6) Å3], PDC connects isolated seven coordinated magnesium polyhedra into a layered structure. Compound 3 [space group P6122, a = 11.479(1) Å, c = 14.735(3) Å, V = 1681.7(4) Å3] (previously reported) contains isolated magnesium octahedra connected by the organic linker with each other forming a 3D network. Compound 4 [space group P21/c, a = 13.7442(14) Å, b = 14.2887(15) Å, c = 14.1178(14) Å, β = 104.912(2)°, V = 2679.2(5) Å3] also exhibits a 3D network based on isolated magnesium octahedra with square cavities containing both disordered DMF and water molecules. The structural topologies originate due to the variable coordination ability of solvent molecules with the metal center. Water molecules coordinate with the magnesium metal centers preferably over other polar solvents (DMF, methanol, ethanol) used to synthesize the coordination networks. Despite testing multiple desolvation routes, we were unable to measure BET surface areas greater than 51.9 m2/g for compound 1.