Electric field-induced assembly of monodisperse polyhedral metal-organic framework crystals

Monodisperse polyhedral metal-organic framework (MOF) particles up to 5 μm in size, large enough to enable in situ optical imaging of particle orientation, were synthesized by the strategy of simultaneous addition of two capping ligands with different binding strength during crystallization. Upon dispersing them in ethylene glycol and applying AC electric field, the particles facets link to form linear chains. We observe well-regulated crystal orientation not only for rhombic dodecahedra all of whose facets are equivalent, but also for truncated cubes with nondegenerate facets. After removing the electric field, chains disassemble if their facets contain even modest curvature, but remain intact if their facets are planar. This assembly strategy offers a general route to fabricate oriented polyhedral crystal arrays of potential interest for new applications and functions.