Luminescent polymorphic aggregates of trinuclear Cu(i)–pyrazolate tuned by intertrimeric Cu⋯NPy weak coordination bonds

Abstract

Five luminescent polymorphic aggregates of trinuclear Cu(I)–pyrazolate, namely [anti-Cu₃L₃]₂ (1), [syn-Cu₃L₃·C₂H₅OH]₂ (2), [anti-Cu₃L₃·C₂H₅OH]_n (3), [anti-Cu₃L₃·0.5C₇H₈]_n (4) and [syn-Cu₃L₃·C₈H₁₀]_n (5) (HL = 4-(pyridin-4-ylthio)-3,5-dimethyl-1H-pyrazole), were reported. The trimeric Cu₃L₃ fragments present syn- and anti-conformations dependent on the dangled direction of 4-pyridyl groups on the two sides of the Cu₃Pz₃ plane (Pz = pyrazolate). Intertrimeric N_Py⋯Cu weak coordination bonds associate these Cu₃L₃ fragments together to form dimeric or polymeric structures, which are further stabilized by crystallized solvent molecules or intertrimeric Cu⋯Cu interactions. The solvated complexes (3–5) may be transformed into the unsolvated complex 1 by evacuation of the crystallized solvents upon heating. All these complexes emit from green to yellow under UV irradiation, which originated from the triplet excited states of metal to ligand charge transfer (³MLCT) mixed with intertrimeric Cu⋯Cu interactions. This work provides a novel kind of supramolecular aggregate based on Cu₃Pz₃ beyond the classical π-acid⋯base adducts and metallophilicity-dependent dimers/oligomers.