Metal-organic layers (MOLs) represent an emerging class of tunable and functionalizable two-dimensional materials. In this work, the scalable solvothermal synthesis of self-supporting MOLs composed of [Hf6O4(OH)4(HCO2)6] secondary building units (SBUs) and benzene-1,3,5-tribenzoate (BTB) bridging ligands is reported. The MOL structures were directly imaged by TEM and AFM, and doped with 4'-(4-benzoate)-(2,2',2''-terpyridine)-5,5''-dicarboxylate (TPY) before being coordinated with iron centers to afford highly active and reusable single-site solid catalysts for the hydrosilylation of terminal olefins. MOL-based heterogeneous catalysts are free from the diffusional constraints placed on all known porous solid catalysts, including metal-organic frameworks. This work uncovers an entirely new strategy for designing single-site solid catalysts and opens the door to a new class of two-dimensional coordination materials with molecular functionalities.

Metal-organic frameworks (MOFs) with light-harvesting building blocks designed to mimic photosynthetic chromophore arrays in green plants provide an excellent platform to study exciton transport in networks with well-defined structures. A step-by-step exciton random hopping model made of the elementary steps of energy transfer between only the nearest neighbors is usually used to describe the transport dynamics. Although such a nearest neighbor approximation is valid in describing the energy transfer of triplet states via the Dexter mechanism, we found it inadequate in evaluating singlet exciton migration that occurs through the Förster mechanism, which involves one-step jumping over longer distance. We measured migration rates of singlet excitons on two MOFs constructed from truxene-derived ligands and zinc nodes, by monitoring energy transfer from the MOF skeleton to a coumarin probe in the MOF cavity. The diffusivities of the excitons on the frameworks were determined to be 1.8 × 10(-2) cm(2)/s and 2.3 × 10(-2) cm(2)/s, corresponding to migration distances of 43 and 48 nm within their lifetimes, respectively. "Through space" energy-jumping beyond nearest neighbor accounts for up to 67% of the energy transfer rates. This finding presents a new perspective in the design and understanding of highly efficient energy transport networks for singlet excited states.

Pyridinium has been shown to be a cocatalyst for the electrochemical reduction of CO 2 on metal and semiconductor electrodes, but its exact role has been difficult to elucidate. In this work, we create cooperative cobaltprotoporphyrin (CoPP) and pyridine/pyridinium (py/pyH + ) catalytic sites on metal−organic layers (MOLs) for an electrocatalytic CO 2 reduction reaction (CO 2 RR). Constructed from [Hf 6 (μ 3 -O) 4 (μ 3 -OH) 4 (HCO 2 ) 6 ] secondary building units (SBUs) and terpyridine-based tricarboxylate ligands, the MOL was postsynthetically functionalized with CoPP via carboxylate exchange with formate capping groups. The CoPP group and the pyridinium (pyH + ) moiety on the MOL coactivate CO 2 by forming the [pyH + -− O 2 C-CoPP] adduct, which enhances the CO 2 RR and suppresses hydrogen evolution to afford a high CO/ H 2 selectivity of 11.8. Cooperative stabilization of the [pyH + -− O 2 C-CoPP] intermediate led to a catalytic current density of 1314 mA/mgCo for CO production at −0.86 V RHE , which corresponds to a turnover frequency of 0.4 s −1 .