Tetranuclear Copper(I) and Silver(I) Pyrazolate Adducts with 1,1′-Dimethyl-2,2’-bibenzimidazole: Influence of Structure on Photophysics

Abstract

A reaction of a cyclic trinuclear copper(I) or silver(I) pyrazolate complex ([MPz]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 M4 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 Ag4Pz4L exhibited dual emission from both the singlet and triplet states, even at room temperature.

Exploring the Interaction of Pyridine-Based Chalcones with Trinuclear Silver(I) Pyrazolate Complex

“…2.1 Å in a free [AgPz]3)[53]. The corresponding Ag…O and Ag…N bonds are in a similar range compared to the complexes of silver(I) pyrazolates with carbonyl compounds or diimines[42,43,45,46].…”

“…. N bonds are in a similar range compared to the complexes of silver(I) pyrazolates with carbonyl compounds or diimines[42,43,45,46].Inorganics 2023, 11, x FOR PEER REVIEW 5 of 13 chelated one silver atom in the trinuclear core. The Ag1…O1 and Ag1…N7 bonds are 2.611(3) and 2.403(4) Å, respectively.…”

“…From another hand, trinuclear metal pyrazolates form stable complexes with boron hydrides or halide substituents/ligands [33][34][35][36][37]. Interaction of this class of compound with P-or N-donor Inorganics 2023, 11, 175 2 of 13 ligands allows the rearrangement of the central core with the formation of di-, tri-, tetra-, or pentanuclear cores [15,[38][39][40][41][42][43][44]. Our studies of the host-guest complexes of the macrocyclic coinage metal pyrazolates with ketones or isocoumarines possess their coordination via the oxygen atom of the C=O group and demonstrate the formation of 1:1 complexes in the solution.…”