Ultrathin 2D coordination polymer nanosheets by surfactant-mediated synthesis

Low-dimensional nanostructures offer a host of intriguing properties which are distinct from those of the bulk material, owing to size-confinement effects and amplified surface areas. Here, we report on the scalable, bottom-up synthesis of ultrathin coordination polymer nanosheets via surfactant-mediated synthesis and subsequent exfoliation. Layers of a two-dimensional (2D) zinc coordination polymer are self-assembled in the interlamellar space of a reverse microemulsion mesophase into stacks of nanosheets interleaved with cethyltrimethylammonium bromide (CTAB) at regular intervals, thus giving rise to a lamellar hybrid mesostructure with a lattice period of ~8 nm and an underlying highly crystalline substructure. The basic structural motif is composed of 2D acetato-benzimidazolato-zinc layers of tetrahedrally coordinated zinc joined together by anionic acetate and benzimidazolate ligands. The hierarchical structure was studied by PXRD, TEM, EDX, EELS, AFM, and solid-state NMR spectroscopy, revealing a high level of order on both the atomic and mesoscale, suggesting fairly strong interactions along the organic-inorganic hybrid interface. Exfoliation of the hybrid material in organic solvents such as THF and chloroform yields sheet- and belt-like nanostructures with lateral sizes between 10's and 100's of nanometers and a height of about 10 nm measured by AFM, which precisely maps the basal spacing of the lamellar mesostructure; further exfoliation results in nanobelts with minimum sizes around 4 nm. Finally, the sheetlike nanostructures behave as morphological chameleons, transforming into highly regular multiwalled coordination polymer nanotubes upon treatment with organic solvents.