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 
doi.orgNature Communicationsdoi.orgOpen 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 doi.orgNature Communicationsdoi.orgOpen source ↗.
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 doi.orgNature Communicationsdoi.orgOpen source ↗. The reaction first yields one-dimensional coordination polymers (1D CPs) equipped with covalent extension sites doi.orgNature Communicationsdoi.orgOpen source ↗. These intermediate linear polymers then undergo covalent self-assembly under controlled conditions to form two separate 2D MOCOF conformations doi.orgNature Communicationsdoi.orgOpen source ↗.
The team resolved the atomic structures and analyzed the multi-step crystallization sequence by leveraging three-dimensional electron diffraction doi.orgNature Communicationsdoi.orgOpen source ↗. The experimental data showed that the targeted porous crystalline networks exhibit high structural order across their layers doi.orgNature Communicationsdoi.orgOpen source ↗.
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 doi.orgNature Communicationsdoi.orgOpen 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 doi.orgNature Communicationsdoi.orgOpen source ↗.
Prior to this work, characterization challenges had left the reaction trajectory of metal-organic covalent frameworks unresolved doi.orgNature Communicationsdoi.orgOpen source ↗. 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 doi.orgNature Communicationsdoi.orgOpen source ↗.
