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

Abstract

Unprecedented Cu^I, Ag^I and Au^I 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 (AuCCPh)_n yields complexes of the type [Au₂L₂]²⁺, [Au₂I₂L₂] and [Au₂(CCPh)₂L]_x (x = 2 or n), respectively. The reaction of L with 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.