Ligand-Directed Dimensionality Control over Zr-Based Metal-Organic Materials: From an Extended Framework to a Discrete Metal-Organic Cage and Macrocycle

Different from extensively documented zirconium-cluster-based frameworks, discrete molecular assemblies based on zirconium hexanuclear clusters have scarcely been reported, mainly due to the lack of control over the connectivity of clusters. In this work, we propose a new strategy for controlling the highly connected Zr clusters and report two unprecedented discrete Zr-based metal-organic systems, a {Zr72} metal-organic cage (IAM-5) based on Zr12 clusters and a {Zr24} metal-organic macrocycle (IAM-6) based on Zr6 clusters. Structural analyses reveal that the combination of a unique bowl-shaped geometry, deliberately controlled bridging angles, and conformational flexibility brings a characteristic coordination geometry to the ligand, with significant effects and controls on the connectivities of Zr clusters as low as 4 for Zr12 nodes in IAM-5 and 2 for Zr6 nodes in IAM-6, consequently directing the formation of discrete rather than extended structures.