N-Heterocyclic Carbene-based Low-Dimensional Metal-Organic Frameworks with Metal-Dependent Electronic Properties

The electronic structure of metal-organic frameworks (MOFs) is intimately linked to the selection of metals, organic ligands, and binding modes. The highly tunable lattice parameters in MOFs can give rise to non-trivial topological and quantum behaviors. Despite this, there is a paucity of experimental demonstrations of MOFs with unconventional binding modes, such as carbenes. Moreover, the electronic structures of carbene-based MOFs, relying on the unique metal-carbene d→π* back-donation bonding, have rarely been studied.

Surface-assisted synthesis enables atomically precise control of 1D MOFs chains and 2D MOFs lattices. Herein, we describe the on-surface synthesis of N-heterocyclic carbenes (NHC) linked lower dimensional MOFs featuring 1D linear and 2D honeycomb lattices, respectively, by low-temperature STM. Using scanning tunneling spectroscopy (STS) and lifting techniques, we demonstrate the electronic structures of the NHC-MOFs on Au(111) surface and potentially metallic features on monolayer KBr. First-principle DFT calculations corroborate the electronic structures of the NHC-MOFs. Our work suggests a new strategy to construct low-dimensional carbene-based MOFs on the design for prospective quantum materials.