Chemists synthesize single-crystal 2D metal-organic covalent organic frameworks
Researchers produced single-crystal 2D MOCOFs in the laboratory, confirming a coordination-directed assembly mechanism.
A research team from The Hong Kong Polytechnic University, Nankai University, Hong Kong Baptist University, and City University of Hong Kong has developed two single-crystal two-dimensional metal-organic covalent organic frameworks (MOCOFs), designated PUMC-1 and PUMC-2 nature.com
Nature Communicationsnature.comOpen source ↗. According to a study published in Nature Communications, the work expands the structural dimensionality of MOCOFs, which were previously limited to a few three-dimensional architectures, and clarifies whether their network growth is governed by coordination or covalent pathways.
Structural assembly and characterization
To construct the porous frameworks, the researchers utilized two distinct sub-building units: tetrakis(4-aminophenyl) porphyrin and cobalt(II) trans-A₂B₂ porphyrin. The reaction first yields one-dimensional coordination polymers (1D CPs) equipped with covalent extension sites. These intermediate linear polymers then undergo covalent self-assembly under controlled conditions to form two separate 2D MOCOF conformations.
The team resolved the atomic structures and analyzed the multi-step crystallization sequence by leveraging three-dimensional electron diffraction. The experimental data showed that the targeted porous crystalline networks exhibit high structural order across their layers.
Synthesis pathway and mechanism
The authors observed that the identical 2D MOCOFs could also be produced directly via a one-pot synthesis combining the same precursor monomers nature.com
Nature Communicationsnature.comOpen source ↗. Generating the exact same single-crystal frameworks through both stepwise and one-pot methods provided direct experimental evidence that the framework formation follows a coordination-directed covalent assembly mechanism.
Prior to this work, characterization challenges had left the reaction trajectory of metal-organic covalent frameworks unresolved. The synthesis of PUMC-1 and PUMC-2 establishes a verifiable coordination-directed route for fabricating lower-dimensional hybrid crystalline architectures, broadening design strategies within reticular chemistry.
