A Series of d10 Metal Clusters Constructed by 2,6-Bis[3-(pyrazin-2-yl)-1,2,4-triazolyl]pyridine: Crystal Structures and Unusual Luminescences

Five d10 transition-metal clusters, {[Zn15(2,6-Hbptp)­(2,6-bptp)7­(μ2-O)4­(μ2-OH)4­(HCOO)2­(NO3)­(H2O)2]·​20H2O} (1), {[Zn8(2,6-Hbptp)­(2,6-bptp)5­(μ3-O)2]·​(ClO4)·​7H2O} (2), {[Cd8(2,6-Hbptp)2­(2,6-bptp)4­(μ3-O)2]·​(NO3)2·​10H2O} (3), {[Ag7(2,6-Hbptp)­(2,6-bptp)3]·​4H2O·​CH3OH}n (4), and {[Ag6(2,6-Hbptp)2­(2,6-bptp)2]­[Ag6(2,6-Hbptp)2­(2,6-bptp)2]2·​30H2O·​4CH3OH} (5), based on bent ligand 2,6-bis­[3-(pyrazin-2-yl)-1,2,4-triazolyl]­pyridine (2,6-H2bptp) have been synthesized. Compound 1 exhibits a novel fanlike Zn15 cluster, which is the highest-nuclearity Zn cluster with 2,6-H2bptp reported thus far. In 2 or 3 (M = Zn/Cd), each ligand coordinates to three M2+ ions, to form an M8L6 cluster. The structure of compound 4 is a Ag6 cluster-based 1D chain, where each hexanuclear [Ag6(2,6-Hbptp)­(2,6-bptp)3]− cluster links its equivalent ones via sharing the Ag atom. Compound 5 contains two kinds of Ag6 clusters, and the alternating arrangement of them gives the final structure. It is worth mentioning that the Ag–Ag bond distances in 4 and 5 are relatively very short and suggest a closed-shell d10–d10 argentophilic interaction. The luminescence properties of compounds 1–5 have been researched at ambient and low temperatures. Interestingly, the emission intensities of 1–5 increase gradually upon cooling. A new strong emission band for 4 appears at 610 nm exhibiting red-orange luminescence. The low-energy emissions (620 nm) of 5 gradually blue shift to shorter wavelengths.