Molecular Engineering of Atomically Precise Silver Clusters into 2Dand 3D Framework Solids

Two- and three-dimensional (2D and 3D) atomically precise nanocluster (NC)-based metal-organic frameworks (MOFs)with properties richer than those of NCs themselves are emerging materials. However, fabricating such materials with good stability has not been easy. In this work, a facile synthetic strategy was employed for the creation of silver NC-MOFs starting from[Ag12(TBT)7(TFA)4(CH3CN)6]+, facilitated by heterocyclic amines,4,4 '-bipyridine (bpy) and pyrazine (pyz), via metal-metal and metal-sulfide rearrangement reactions, where TBT and TFA are tertiar-ybutylthiolate and trifluoroacetate, respectively. In one of the reactions, the pyz ligand facilitates the formation of a 2D framework with atrigonal crystal system, which exhibits high stability and emits bright green luminescence at low temperatures. Owing to its facile synthesis, good stability, efficient luminescence, uniform porosity, and layered structure, the resultant hexagonal 2D nanosheets can be efficiently exfoliated from parent crystals. The 2D nanosheets arestructurally similar to graphene. A top-down approach was employed for the exfoliation of stable 2D nanosheets with lateraldimensions in the range of 0.156 mu m. In another case, the bpy ligand induces the construction of a 3D framework with anorthorhombic crystal system. Owing to its interpenetrated ABmiddotmiddotmiddotAB structure, robustness, and efficient green luminescence at roomtemperature, the resultant 3D MOF is capable of functioning as a high-performance luminescent sensor for selective detection ofexplosive analogues, 2-nitrotoluene and 2,4-dinitrotoluene, with excellent recyclability. However, in the absence of the heterocyclicamines, a pristine AgNC was formed. Time-dependent density functional theory calculations were employed to understand the mechanism of energy transfer in AgNC-MOFs. Our strategy offers an unprecedented approach in which heterocyclic amines facilitate intramolecular rearrangement reactions, resulting in 2D and 3D atomically precise NC framework materials. This work not only demonstrates the creation of 2D and 3D materials but also provides new insights into the critical surface coordination chemistry controlled by heterocyclic amines for defining the morphology and properties of cluster frameworks.

Automated summary

This article presents a facile synthetic strategy for the fabrication of two- and three-dimensional atomically precise nanocluster-based metal-organic frameworks with good stability. These materials show rich properties and demonstrate high-performance luminescent sensing capabilities for explosive analogues. The study provides insights into surface coordination chemistry controlled by heterocyclic amines for defining the morphology and properties of cluster frameworks.