Three-Dimensional Co(II)-Metal–Organic Frameworks with Varying Porosities and Open Metal Sites toward Multipurpose Heterogeneous Catalysis under Mild Conditions

Abstract

In recent years, heterogeneous catalysis has become one of the most active domains in the research of metal–organic frameworks (MOFs). Here, two three-dimensional (3D) Co(II)-MOFs with open metal sites and exposed azo functionality on the MOF backbone have been constructed via mixed ligand assembly. Both the MOFs, 1 {[Co2(1,4-NDC)2(L)(H2O)2(μ2-H2O)]·(DMF)2(H2O)}n and 2 {[Co(fma)(L)(H2O)2]·S}n [1,4-NDC = 1,4-naphthalene dicarboxylic acid, fma = fumaric acid, L = 3,3′-azobis pyridine and S = disordered solvents] exhibit 3D frameworks with metal-bound aqua ligands. These metal-bound aqua ligands, as well as the lattice solvent molecules, could simply be removed upon activation affording the desolvated frameworks 1a and 2a respectively maintaining the original crystallinity with a varying number of open metal sites. Although crystallographic analysis revealed a porous structure for both the MOFs (34.4% and 14.3% void volume for 1 and 2, respectively), 1 showed a permanently microporous nature with a Brunauer–...