Metal-Organic Frameworks from Dipodal and Tripodal Silicon-Centered Tetrahedral Ligands

Six metal-organic frameworks from organic systems with tetrahedral geometry have been prepared and their crystal structures solved. The organic portions contain different central atoms (M = S, C, Si), a common binding group (4-carboxyphenyl), and a sterically variable series of nonbinding groups (H, =O, CF3, phenyl, and tolyl). Five of these systems are dipodal, with two carboxyphenyl groups, and one is tripodal, with three. Dipodal systems with small, nonbinding groups produced two-dimensional, layered structures with medium void percentages. The nonbinding groups are positioned away from the voids. Dipodal systems with large (aryl), nonbinding groups produced three-dimensional networks with larger void percentages. The nonbinding aryl groups are directed into the voids, where they line the surfaces. The single tripodal case produced a two-dimensional, layered structure with a high void percentage. The pore sizes and shapes are tailored by and for the nonbinding groups.