Pillar-Layered Metal-Organic Frameworks Based on a Hexaprismane [Co6(μ3-OH)6] Cluster: Structural Modulation and Catalytic Performance in Aerobic Oxidation Reaction.

Embedding a functional metal-oxo cluster within the matrix of metal-organic frameworks (MOFs) is a feasible approach for the development of advanced porous materials. Herein, three isoreticular pillar-layered MOFs (Co6-MOF-1-3) based on a unique [Co6(μ3-OH)6] cluster were designed, synthesized, and structurally characterized. For these Co6-MOFs, tuning of the framework backbone was facilitated due to the existence of second ligands, which results in adjustable apertures (8.8 to 13.4 Å) and high Brunauer-Emmett-Teller surfaces (1896-2401 m2 g-1). As the [Co6(μ3-OH)6] cluster has variable valences, these MOFs were then utilized as heterogeneous catalysts for the selective oxidation of styrene and benzyl alcohol, showing high conversion (>90%) and good selectivity. The selectivity of styrene to styrene oxide surpassed 80% and that of benzyl alcohol to benzaldehyde was up to 98%. The calculated TOF values show that the increase of reaction rate is positively correlated with the enlargement of pore sizes in these MOFs. Further, a stability test and cycling experiment proved that these Co6-MOFs have well-observed stability and recyclability.