Tetranuclear Copper Pyrazolate Adducts with 1,1′-Dimethyl-2,2’-bibenzimidazole: Influence of Structure on Photophysics

• Published in: Molecules (Basel, Switzerland) Switzerland), 2023-01, Vol.28 (3)
• Main Authors: Yakovlev, Gleb B, Titov, Aleksei A, Smol’yakov, Alexander F, Chernyadyev, Andrey Yu, Filippov, Oleg A, Shubina, Elena S
• Format: Article
• Language: English
• Subjects: Chemical properties; Copper; Physiological aspects; Pyrazoles; Silver compounds
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28031189

A reaction of a cyclic trinuclear copper(I) or silver(I) pyrazolate complex ([MPz][sub.3] , M = Cu, Ag) with 1,1′-dimethyl-2,2’-bibenzimidazole (L) leads to the formation of tetranuclear adducts decorated by one or two molecules of a diimine ligand, depending on the amount of the ligand added (0.75 or 1.5 equivalents). The coordination of two L molecules stabilizes the formation of a practically idealized tetrahedral four-metal core in the case of a copper-containing complex and a distorted tetrahedron in the case of a Ag analog. In contrast, complexes containing one molecule of diimine possess two types of metals, two- and three-coordinated, forming the significantly distorted central M[sub.4] cores. The diimine ligands are twisted in these complexes with dihedral angles of ca. 50–60°. A TD-DFT analysis demonstrated the preference of a triplet state for the twisted 1,1′-dimethyl-2,2’-bibenzimidazole and a singlet state for the planar geometry. All obtained complexes demonstrated, in a solution, the blue fluorescence of the ligand-centered (LC) nature typical for free diimine. In contrast, a temperature decrease to 77 K stabilized the structure close to that observed in the solid state and activated the triplet states, leading to green phosphorescence at ca. 500 nm. The silver-containing complex Ag[sub.4] Pz[sub.4] L exhibited dual emission from both the singlet and triplet states, even at room temperature.