Synthesis and characterization of Ag(I) alkynyl nanoclusters utilizing Mo^VI-anchored thiacalix[4]arene metalloligands: Application in electrocatalytic CO₂ reduction

The utilization of metalloligands as building blocks for assembling heteronuclear metallocages or heterometallic coordination polymers has garnered increasing attention, yet its utilization for assembling Ag(I) alkynyl nanoclusters remains limited. In this study, we present the synthesis of two new Ag(I) alkynyl nanoclusters, namely, Mo₂Ag₈ and Mo₂Ag₁₂, employing a Mo^VIO₂R-anchored (R = O or OEt) thiacalix[4]arene (TC4A) as a metalloligand. Through detailed structural analyses, their distinct sandwich geometries were revealed. Mo₂Ag₈ features a square Ag₄(^tBuC≡C)₄ core enclosed between two {MoAg₂–TC4A} units, with two MoO₂(OEt) units suspended on each side. Mo₂Ag₁₂ features a hexagonal Ag₆(^tBuC≡C)₆ core sandwiched between two {MoAg₃–TC4A} units, with two MO₃ units acting as oxygen anion templates, directly interacting with Ag(I) ions. In addition, we demonstrated the electrocatalytic application of Ag–Mo bimetallic clusters for CO₂ reduction. The catalytic analysis results show that the binding mode of MO₃ units considerably influences the electrochemical CO₂ reduction activity and competitive hydrogen evolution reaction activity of the clusters. Notably, Mo₂Ag₁₂ achieved an impressive Faradaic efficiency of 60.85% for CO production at a voltage of −0.8 V (vs. RHE).