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

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Abstract
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.

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