A Series of d<sup>10</sup> Metal Clusters Constructed by 2,6-Bis[3-(pyrazin-2-yl)-1,2,4-triazolyl]pyridine: Crystal Structures and Unusual Luminescences
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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.
