Trinuclear-based Copper(I) Pyrazolate Polymers: Effect of Trimer π-Acid···Halide/Pseudohalide Interactions on the Supramolecular Structure and Phosphorescence

Under different situations, solvothermal reactions of 3,5-diethyl-4-(4-pyridyl)-pyrazole (HL) with CuX or CuX₂ (X = Cl, Br, I, and SCN) afforded five copper(I) coordination polymers, {CuX[CuL]₃·solvent}_n (X = Cl, 1; Br, 2; I, 3; X = SCN and solvent = MeCN, 4) and {Cu₂I₂[CuL]₃}_n (5). X-ray diffraction analyses show that all the complexes have trinuclear [CuL]₃ (referred as Cu₃) secondary building units featuring planar nine-membered Cu₃N₆ metallocycles with three peripheral pyridyl groups as connectors, which are further linked by CuX or Cu₂X₂ motifs to generate single- or double-strand chains. Interestingly, the Cu(I) atoms within the Cu₃ units in 1−5 behave as coordinatively unsaturated π-acid centers to contact soft halide/pseudohalide X atoms of CuX and Cu₂X₂ motifs, which lead to novel sandwich substructures of [(Cu₃)(Cu₂X₂)(Cu₃)] (X = Br, I, and SCN) in 2−4. In addition, both the π-acid [Cu₃]···X contacts and intertrimer Cu···Cu interactions contribute to the one-dimensional (1D) double-strand and 2D/3D supramolecular structures of 1−5. All of these complexes exhibit high thermostability and bright solid-state phosphorescence upon exposure to UV radiation at room temperature. The emissions arise from the mixtures of metal-centered charge transfer, metal to ligand charge transfer, and halide-to-ligand charge transfer excited states, and can be tuned by intermolecular π-acid [Cu₃]···halide/pseudohalide contacts.