Yan-Zhong Fan

A stable and porous iridium(III)-porphyrin metal–organic framework: synthesis, structure and catalysis

Self-assembly of a new metalloporphyrin tetracarboxylic ligand Ir(TCPP)Cl (TCPP = tetrakis(4-carboxyphenyl)porphyrin) with ZrCl4 in the presence of benzoic acid leads to the formation of a three-dimensional (3D) iridium(III)-porphyrin metal–organic framework (Ir-PMOF) with the formula of [(Zr6(μ3-O)8(OH)2(H2O)10)2(Ir(TCPP)Cl)3]·solvents (Ir-PMOF-1(Zr)), which possesses square-shaped channels of 1.9 × 1.9 nm2 (atom-to-atom distances across opposite Ir metal atoms) in three orthogonal directions as disclosed by the single-crystal X-ray diffraction analysis. Ir-PMOF-1(Zr) represents the first MOF bearing a self-supporting iridium-porphyrin catalytic framework, featuring high porosity and stability. The catalytic tests disclose that the activated Ir-PMOF-1(Zr) can promote O–H insertion with a turnover frequency (TOF) up to 4260 h−1. Ir-PMOF-1(Zr) can be recycled and reused for 10 runs without significant loss of catalytic activity, and the total turnover number (TON) for O–H insertion after 10 successive runs reaches 875.

Precise Modulation of the Breathing Behavior and Pore Surface in Zr-MOFs by Reversible Post-Synthetic Variable-Spacer Installation to Fine-Tune the Expansion Magnitude and Sorption Properties

To combine flexibility and modifiability towards a more controllable complexity of MOFs, a post-synthetic variable-spacer installation (PVSI) strategy is used to implement kinetic installation/ uninstallation of secondary ligands into/from a robust yet flexible proto-Zr-MOF. This PVSI process features precise positioning of spacers with different length, size, number, and functionality, enabling accurate fixation of successive breathing stages and fine-tuning of pore surface. It shows unprecedented synthetic tailorability to create complicated MOFs in a predictable way for property modification, for example, CO2 and R22 adsorption/separation, thermal/chemical stability, and extended breathing behavior.

A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium–palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h−1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

Ligand and Metal Effects on the Stability and Adsorption Properties of an Isoreticular Series of MOFs Based on T-Shaped Ligands and Paddle-Wheel Secondary Building Units

The synthesis of stable porous materials with appropriate pore size and shape for desired applications remains challenging. In this work a combined experimental/computational approach has been undertaken to tune the stability under various conditions and the adsorption behavior of a series of MOFs by subtle control of both the nature of the metal center (Co2+ , Cu2+ , and Zn2+ ) and the pore surface by the functionalization of the organic linkers with amido and N-oxide groups. In this context, six isoreticular MOFs based on T-shaped ligands and paddle-wheel units with ScD0.33 topology have been synthesized. Their stabilities have been systematically investigated along with their ability to adsorb a wide range of gases (N2 , CO2 , CH4 , CO, H2, light hydrocarbons (C1 -C4 )) and vapors (alcohols and water). This study has revealed that the MOF frameworks based on Cu2+ are more stable than their Co2+ and Zn2+ analogues, and that the N-oxide ligand endows the MOFs with a higher affinity for CO2 leading to excellent selectivity for this gas over other species.

Regio- and Enantioselective Photodimerization within the Confined Space of a Homochiral Ruthenium/Palladium Heterometallic Coordination Cage

The photoinduced regio- and enantioselective coupling of naphthols and derivatives thereof is achieved in the confined chiral coordination space of a RuII metalloligand based cage. The racemic or enantiopure cages encapsulate naphthol guests, which then undergo a regiospecific 1,4-coupling, rather than the normal 1,1-coupling, to form 4-(2-hydroxy-1-naphthyl)-1,2-napthoquinones; moderate stereochemical control is achieved with homochiral cages. The photoreactions proceed under both aerobic and anaerobic conditions but through distinct pathways that nevertheless involve the same radical intermediates. This unusual dimerization constitutes a very rare example of asymmetric induction in biaryl coupling by making use of coordination cages with dual functionality-photoredox reactivity and stereoselectivity.

Time controlled structural/packing transformation and tunable luminescence of Cd(II)-chloride-triBZ-ntb coordination assemblies: an experimental and theoretical exploration

In order to explore the supramolecular solid-state structural and packing transformations and the property tuning as a function of reaction time, a tripodal triBZ-ntb (4,4′,4′′-(2,2′,2′′-nitrilotris(methylene)tris(1H-benzo[d]imidazole-2,1-diyl)tris(methylene))tribenzonitrile) ligand was self-assembled with cadmium chloride by applying a hydrothermal method for differing reaction times. Three coordination structures were obtained, namely, [Cd(triBZ-ntb)Cl]2(CdCl4)·2H2O·2DMF (Cd5), [Cd(triBZ-ntb)Cl2]·3H2O (Cd10), and [Cd(triBZ-ntb)Cl]2(CdCl4)·2H2O (Cd20), and characterized by IR, EA, single crystal and powder X-ray diffraction methods. Cd5 and Cd20 have identical coordination monomers, [Cd(triBZ-ntb)Cl]+ and (CdCl4)2− counter anions, with a total metal-to-ligand ratio of 3 : 2, but with slightly different packing states. Meanwhile, the intermediate compound Cd10 is composed of only a neutral coordination unit [Cd(triBZ-ntb)Cl2], with a metal-to-ligand ratio of 1 : 1, by the additional coordination of one Cl− to the Cd(II) metal center. During the structural transformation process, the formation of (CdCl4)2− counter anions in Cd5 and Cd20 serves as an auxiliary “cabinet” for the storage of surplus Cd2+ metal ions. Theoretical study reveals the relative energy changes in the transformation processes. Furthermore, the switchable structures and packing states in these complexes result in tunable luminescent properties.

Nanoreactor Based on Macroporous Single Crystals of Metal‐Organic Framework

A sacrificial template strategy is developed for the synthesis of yolk-shell Au@ZIF-8 nanoreactor. The Au@ZIF-8 nanoreactor possesses single-crystalline metal-organic framework (MOF) shell with intrinsic monodisperse micropores and introduced macropores. In each of the macropores, one Au NP is encapsulated to form a nanoreactor unit. The quantity of the reactor units in the MOF shell can be readily regulated. Such structure features of the Au@ZIF-8 nanoreactor facilitate the size selectivity of reactants, the accessibility of Au nanoparticles to reactants, and the mass transfer of reactants and products. As a result, the Au@ZIF-8 nanoreactor delivers excellent size selectivity, enhanced conversion, and good cycling stability when used to catalyze the aerobic oxidation of alcohols with different molecular size.

Investigation of Binding Behavior Between Drug Molecule 5‐Fluoracil and M4L4 Type Tetrahedral Cages: Selectivity, Capture and Release

Two analogous M4 L4 -type tetrahedral cages (smaller: MOC-19; larger: MOC-22) were synthesized and investigated for their interactions with the anticancer drug 5-fluoracil (5-FU) by NMR spectroscopy, high-resolution electrospray-ionization mass spectrometry (HR-ESI-MS), and molecular simulation. The cages size and window are of importance for the host-guest binding, and consequently the smaller MOC-19 with a more suitable size of cavity window was found to have much stronger hydrogen-bond interactions with 5-FU. The porous nanoparticles of MOC-19 exhibited outstanding behavior for the controlled release of 5-FU in a simulated human body with liquid phosphate-buffered saline solution.

Catalytic Space Engineering of Porphyrin Metal-Organic Frameworks for Combined CO2 Capture and Conversion at a Low Concentration

Porous porphyrin metal-organic frameworks (PMOFs) provide promising platforms for studying CO2 capture and conversion (C3) owing to their versatility in photoelectric, catalytic, and redox activities and porphyrin coordination chemistry. Herein, we report the C3 application of two PMOFs by engineering the coordination space through the introduction of two catalytic metalloporphyrins doped with rhodium or iridium, Rh-PMOF-1 and Ir-PMOF-1, both of which can serve as heterogeneous catalysts for the chemical fixation of CO2 into cyclic carbonates with yields of up to 99 %. Remarkably, the catalytic reactions can effectively proceed under low CO2 concentrations and high yields of 83 % and 73 % can be obtained under 5 % CO2 in the presence of Rh-PMOF-1 and Ir-PMOF-1, respectively. The synergistic effect of the metalloporphyrin ligand and the Zr6 O8 cluster, in combination with the CO2 concentration effect from the pore space, might account for the excellent catalytic performance of Rh-PMOF-1 under low CO2 concentration. Recycling tests of Rh-PMOF-1 show negligible loss of catalytic activity after 10 runs.