The Influence of Aryl Substituents on the Supramolecular Structures and Photoluminescence of Cyclic Trinuclear Pyrazolato Copper(I) Complexes

Cyclic trinuclear complexes with group 11 metal(I) ions are fascinating and important to coordination chemistry. One of the ligands known to form these cyclic trinuclear complexes is pyrazolate, which is a bridging ligand that coordinates many transition metal ions in a Npz-M-Npz linear mode (Npz = pyrazolyl nitrogen atom). In these group 11 metal(I) ions, copper is the most abundant metal. Therefore, polynuclear copper(I) complexes are very important in this field. The cyclic trinuclear copper(I) complex [Cu(3,5-Ph₂pz)]₃ (3,5-Ph₂pz^- = 3,5-diphenyl-1-pyrazolate anion) was reported in 1988 as a landmark complex, but its photoluminescence properties have hitherto not been described. In this study, we report the photoluminescence and two different polymorphs of [Cu(3,5-Ph₂pz)]₃ and its derivative [Cu(3-Me-5-Phpz)]₃ (3-Me-5-Phpz^- = 3-metyl-5-phenyl-1-pyrazale anion). The substituents in [Cu(3-Me-5-Phpz)]₃ cause smaller distortions in the solid-state structure and a red-shift in photoluminescence due to the presence of intermolecular cuprophilic interactions.