Authors: Jingjuan Liu | Guolong Xing | Long Chen
Source: Accounts of Chemical Research (article, 2024-03-01)
Field: Chemistry — Inorganic Chemistry

2D Conjugated Metal–Organic Frameworks: Defined Synthesis and Tailor-Made Functions Conspectus2D conjugated metal-organic frameworks (2D -MOFs) have emerged as a class of graphene-like materials with fully π-conjugated aromatic structures. Their unique structural characteristics provide abundant physiochemical features, including regular nanochannels, high electrical conductivity, and customizable band gaps. Recent intensive research has significantly advanced this field, yet the exploration of 2D <i>c</i>-MOFs with enhanced features is limited by the availability of organic linkages and topologies. Designing novel ligands is essential for the construction of new 2D <i>c</i>-MOFs with high crystallinity, excellent conductivity, and tailor-made functions.In this Account, we summarize our recent contributions in fine-tuning the topology of 2D <i>c</i>-MOFs through precise ligand design, thereby giving them fantastic structures and tailor-made functions. First, we propose the concept of replacing planar ligands by nonplanar ligands on conductive MOF skeletons. The incorporation of nonplanar ligands improves the solubility of large π-conjugated organic molecules without interfering with the interlayer π-stacking. Our investigation discovered that conjugate polycyclic aromatics-based ligands can be synthesized through <i>in situ</i> Scholl reactions by means of oxidative cyclodehydrogenation of a nonplanar precursor ligand during the solvothermal synthesis process. Hence, fully conjugated 2D <i>c</i>-MOFs can be directly synthesized from nonplanar organic ligands, simplifying and diversifying the preparation of 2D <i>c</i>-MOFs. Accordingly, the design flexibility of the ligands expands the topological structures and pore types. By controlling the synthesis conditions, we can successfully induce either a rhombus or a kagome topology from a nonplanar <i>D</i><sub>2</sub> symmetric ligand. Moreover, by employing a ligand engineering strategy, we incrementally increase the number of coordination functional groups on a twisted hexabenzocoronene core, resulting in the formation of three distinct symmetric hydroxyl ligands. These ligands elicit diverse target topologies and pore sizes, resulting in variances in the coordination node density on the skeletons. This, in turn, leads to differences in electron transfer abilities, ultimately causing variations in the electrical conductivity and mobility. In addition, we employ a straightforward coupling method to incorporate redox components, such as salphen and pyrazine, into nonplanar ligands, facilitating the synthesis of 2D <i>c</i>-MOFs with highly active centers. This strategy confers upon the resulting frameworks substantial capacity for catalysis and energy storage, offering a good platform for elucidating the structure-property relationships at the molecular level. Moreover, the well-defined synthesis of 2D <i>c</i>-MOFs imparts them with specific properties, particularly in the fields of electrical, electrochemical, and spintronic applications. At the end, the primary challenges facing 2D <i>c</i>-MOFs in achieving tailor functions and their practical applications are proposed. This account is expected to evoke new inspirations and innovative research in the field of 2D c-MOFs, especially in emerging interdisciplinary research areas. Conjugated system ; Ligand (biochemistry) ; Stacking ; Materials science ; Topology (electrical circuits) ; Metal-organic framework ; Graphene ; Nanotechnology ; Molecule ; Combinatorial chemistry ; Chemistry ; Polymer ; Organic chemistry Metal-Organic Frameworks: Synthesis and Applications ; Covalent Organic Framework Applications ; Graphene research and applications