Coinage metal(I) clusters based on a flexible P,P′(N,N′)2-ligand: colorful phosphorescence, abnormal thermal quenching behavior and anticounterfeiting application

Unprecedented pseudosymmetric CuI, AgI and AuI clusters with pronounced metallophilic Au–X (X = Cu, Ag, Au) or Ag–Ag contacts have been assembled using 1,2-bis[bis(pyridin-2-ylmethyl)phosphino]ethane (L), an innovative P,P′(N,N′)2- ligand. Its interaction with AuCl/KPF6, AuI or (AuC≡CPh)n yields complexes of the type [Au2L2]2+, [Au2I2L2] and [Au2(C≡CPh)2L]x (x = 2 or n), respectively. The reaction of Lwith AgPF6 affords a [Ag4L2]4+ cluster, while the treatment with AgNO3 leads to a nine-nuclear [Ag9L3(NO3)3]6+ cluster. The latter was transformed into a heterometallic [Au2Ag4L2(NO3)2(H2O)]4+ cluster by treatment with [Au(tht)Cl]. Sequential reaction of L with Au(I) halides and [Cu(MeCN)4]PF6 provides heterometallic [Au2Cu4(μ2-Cl)2L2]4+ and [Au2Cu4L2I2(MeCN)4]4+ ensembles. Most of the title clusters exhibit a charge transfer photoluminescence in the green to orange region with the quantum efficiencies up to an impressive 77%. Surprisingly, the [Au2Cu4L2I2(MeCN)4]4+ cluster shows an abnormal (negative) thermal quenching of the luminescence, which is unprecedented for Au(I) derivatives. The practical utility of the designed clusters was demonstrated by their application as innovative vapor-responsive emission inks for advanced anticounterfeiting.