Luminescent Ag^I−Cu^I Heterometallic Hexa-, Octa-, and Hexadecanuclear Alkynyl Complexes

A series of Ag^I−Cu^I heteronuclear alkynyl complexes were prepared by reaction of polymeric (MC⋮CC₆H₄R-4)_n (M = Cu^I or Ag^I; R = H, CH₃, OCH₃, NO₂, COCH₃) with [M‘₂(μ-Ph₂PXPPh₂)₂(MeCN)₂](ClO₄)₂ (M‘ = Ag^I or Cu^I; X = NH or CH₂). Heterohexanuclear complexes [Ag₄Cu₂(μ-Ph₂PNHPPh₂)₄(C⋮CC₆H₄R-4)₄](ClO₄)₂ (R = H, 1; CH₃, 2) were afforded when X = NH, and heterooctanuclear complexes [Ag₆Cu₂(μ-Ph₂PCH₂PPh₂)₃(C⋮CC₆H₄R-4)₆(MeCN)](ClO₄)₂ (R = H, 3; CH₃, 4; OCH₃, 5; NO₂, 6) were isolated when X = CH₂. Self-assembly reaction between (MC⋮CC₆H₄COCH₃-4)_n and [M‘₂(μ-Ph₂PCH₂PPh₂)₂(MeCN)₂](ClO₄)₂, however, gave heterohexadecanuclear complex [Ag₆Cu₂(μ-Ph₂PCH₂PPh₂)₃(C⋮CC₆H₄COCH₃-4)₆]₂(ClO₄)₄ (7). The heterohexanuclear complexes 1 and 2 show a bicapped cubic skeleton (Ag₄Cu₂C₄) consisting of four Ag^I and two Cu^I atoms and four acetylide C donors. The heterooctanuclear complexes 3−6 exhibit a waterwheel-like structure that can be regarded as two Ag₃Cu(C⋮CC₆H₅)₃ components put together by three bridging Ph₂PCH₂PPh₂ ligands. The heterohexadecanuclear complex 7 can be viewed as a dimer of heterooctanuclear complex [Ag₆Cu₂(μ-Ph₂PCH₂PPh₂)₃(C⋮CC₆H₄COCH₃-4)₆](ClO₄)₂ through the silver and acetyl oxygen (Ag−O = 2.534 (4) Å) linkage between two waterwheel-like Ag₆Cu₂ units. All of the complexes show intense luminescence in the solid states and in fluid solutions. The microsecond scale of lifetimes in the solid state at 298 K reveals that the emission is phosphorescent in nature. The emissive state in compounds 1−5 is likely derived from a ³LMCT (C⋮CC₆H₄R-4 → Ag₄Cu₂ or Ag₆Cu₂) transition, mixed with a metal cluster-centered (d → s) excited state. The lowest lying excited state in compounds 6 and 7 containing electron-deficient 4-nitrophenylacetylide and 4-acetylphenylacetylide, respectively, however, is likely dominated by an intraligand ³[π → π*] character.