Programmable Metal Arrangements in Metal-Organic Polyhedra and Frameworks

The preparation of regioisomers of small molecules is routine, but an analogous concept of positional isomerism is absent for extended materials. Crystalline frameworks such as zeolites and metal-organic frameworks (MOFs) can furnish well-defined active sites for heterogeneous catalysis, but their arrangement cannot be tuned in isolation. Here we show that a mobility-tuned synthesis approach permits selective synthesis of multiple different “structomers”, which are isostructural and compositionally identical but which feature different metal arrangements. High-fidelity access to each targeted metal arrangement was confirmed by operationally facile electron paramagnetic resonance analysis and validated by mass spectrometry. The performance of Rh centers in propene hydrogenation catalysis differs substantially for different metal arrangements within the framework, even though all Rh centers have identical primary coordination environments. For properties that depend on metal distances, structomer-selective synthesis thus presents a new paradigm for fundamental study and performance optimization.