Assembly of photoluminescent [Cu_nI_n] (n = 4, 6 and 8) clusters by clickable hybrid [N,S] ligands

Three new 1,2,3-triazole-based NS ligands, 2-((4-((benzylthio)methyl)-1H-1,2,3-triazol-1-yl)methyl)pyridine (L1), 2-((4-(2-(cyclopentylthio)ethyl)-1H-1,2,3-triazol-1-yl)methyl)pyridine (L2) and 2-((4-(2-(cyclopentylthio)ethyl)-1H-1,2,3-triazol-1-yl)methyl)quinoline (L3) and the corresponding copper(i)-iodide complexes [Cu₄I₄(L1)₂] (1), [Cu₆I₆(L2)₂] (2) and [Cu₆I₆(L3)₂] (3A) have been prepared and characterized by single-crystal X-ray diffraction (XRD), powder XRD, photoluminescence spectroscopy and thermogravimetric analysis. Complexes 1, 2 and 3A exhibit stair-step [Cu_nI_n] (n = 4 and 6) cluster structures with supporting ligands L1, L2 and L3, respectively. Ligand L1 coordinates with a bidentate/monodentate binding mode in the [Cu₄I₄] cluster complex 1 using the pyridyl-triazole moiety and with a pendant -CH₂SCH₂Ph group. Increasing the length of the bridge from -CH₂- in L1 to -C₂H₄- in L2 and L3 engages the S donor and these ligands coordinate using a bidentate/monodentate/monodentate mode supporting larger [Cu₆I₆] cluster complexes 2 and 3A. A kinetic product [Cu₈I₈(L3)₂(CH₃CN)₂] (3B) was isolated from the reaction of L3 with CuI in CH₃CN and the single-crystal X-ray structure indicates a rare discrete stair-step [Cu₈I₈] core supported by two L3 and two coordinated CH₃CN solvates. The structure is further stabilized by intermolecular π⋯π stacking interactions in the lattice. Isolation of 1-3 provides a good demonstration of the use of multidentate and multifunctional hybrid ligands in supporting [Cu_nI_n] clusters of different sizes (n = 4, 6, 8). Ligands L1-L3 are blue emissive molecules. The corresponding complexes display strong blue (1 and 2) or remarkable yellow (3A) emissions between 500 and 700 nm in the solid state. The structures of sulfur-containing ligands and their copper-iodide complexes are described and discussed.