Luminescent Cu₄I₄–Cu₃(Pyrazolate)₃ Coordination Frameworks: Postsynthetic Ligand Substitution Leads to Network Displacement and Entanglement

Abstract

Six daughter complexes based on two-dimensional (2-D) luminescent Cu₄I₄-Cu₃Pz₃ (Pz = pyrazolate) coordination networks, which exhibit an uncommon Cu₄I₄L₃L' (L = pyridine; L' = acetonitrile, pyridine, pyrazine, 1,4-diazabicyclo[2.2.2]octane, triphenylphosphine, none) local configuration, were prepared through a postsynthetic modification method starting from a parent complex (L' = NH₃). This work has successfully implemented the single-site substitution of Cu₄I₄-based coordination frameworks, which have rarely been reported for isolated Cu₄I₄-type compounds, by taking advantage of the solvent-assisted ligand substitution strategy recently developed in metal-organic framework (MOF) chemistry. Such a procedure not only resulted in the variation of local geometry in the Cu₄I₄ units but also led to interlayer network displacement and entanglement. Particularly, an interesting topological transformation (from 2-D to 2-D → 3-D interpenetration) occurred when linear bidentate linkers (e.g., pyrazine and 1,4-diazabicyclo[2.2.2]octane) are inserted between the 2-D layers. Moreover, the variation in the L' sites can effectively tune the emission colors, ranging from green to orange (λ_em^max 540-605 nm at room temperature). The photoluminescence origins are tentatively assigned to be a mixture of ³MLCT and ³XLCT, different from that of the well-studied isolated Cu₄I₄-type complexes.