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

Three magnesium based metal-organic frameworks, Mg-3(3,5-PDC)(3)(DMF)3 center dot DMF [1], Mg(3,5-PDC)(H2O) center dot(H2O) [3], and Mg-4(3,5-PDC)(4)(DMF)(2)(H2O)(2)center dot 2DMF center dot 4.5H(2)O [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 P2(1)/n, a = 12.3475(5) angstrom, b = 11.1929(5) angstrom, c = 28.6734(12) angstrom, beta = 98.8160(10)degrees, V = 3916.0(3) angstrom(3)] 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 angstrom x 4.6 angstrom 1-D channel. The channel contains coordinated and free DMF molecules. In compound 2 [space group C2/c, a = 9.964(5) angstrom, b = 12.0694(6) angstrom, c = 7.2763(4) angstrom, beta = 106.4970(6)degrees, V = 836.70(6) angstrom(3)], PDC connects isolated seven coordinated magnesium polyhedra into a layered structure. Compound 3 [space group P6(1)22, a = 11.479(1) angstrom, c = 14.735(3) angstrom, V = 1681.7(4) angstrom(3)] (previously reported) contains isolated magnesium octahedra connected by the organic linker with each other forming a 3D network. Compound 4 [space group P2(1)/c, a = 13.7442(14) angstrom, b = 14.2887(15) angstrom, c = 14.1178(14) angstrom, beta = 104.912(2)degrees, V = 2679.2(5) angstrom(3)] 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 surgace areas greater than 51.9 m(2)/g for compound 1.