The [Ag25Cu4H8Br6(CCPh)12(PPh3)12]3+ : Ag13H8 silver hydride core protected by [CuAg3(CCPh)3(PPh3)3]+ motifs

Abstract

Copper alkynyl complexes [CuAg₃(CCAr)₃(PPh₃)₃]⁺ (Ar = Ph, p-C₆H₄Me), in which three Ag(PPh₃) units are bound among three CCAr arms of trigonal-planar [Cu(CCAr)₃]²⁻, were selected as a protecting unit to cover the metal core of an atomically precise core–shell-type cluster. First, the formation of the protecting unit through the reaction of Cu(NCMe)₄(PF₆) with Ag(CCAr) and PPh₃ in a 1 : 3 : 3 ratio was confirmed. The reaction gave dimeric [CuAg₃(CCAr)₃(PPh₃)₃]₂²⁺, in which the two planar [CuAg₃(CCAr)₃(PPh₃)₃]⁺ units were stacked. Next, core–shell-type clusters were synthesized by adding NaBH₄ and Et₄NX (X = Cl, Br) to a solution similar to that used to prepare the protecting unit. The trigonal-planar protecting units nicely formed core–shell-type Ag nanoclusters formulated as [Ag₁₃H₈X₆{CuAg₃(CCAr)₃(PPh₃)₃}₄]³⁺ (X = Cl, Ar = p-C₆H₄Me; X = Br, Ar = p-C₆H₄Me; X = Br, Ar = Ph). Their crystal structures revealed that the four [CuAg₃(CCAr)₃(PPh₃)₃]⁺ units are linked by six halogen ions to form a tetrahedral cage that accommodates a polyhydride–Ag cluster formulated as Ag₁₃H₈⁵⁺. As a concrete proof of the existence of the polyhydride, deuterated analogs Ag₁₃D₈⁵⁺ were synthesized and subsequently characterized by high-resolution electrospray-ionization mass spectrometry measurements.