Two 2D Layered P₄Mo₆ Clusters with Potential Bifunctional Properties: Proton Conduction and CO₂ Photoreduction

Two hourglass-type molybdophosphate hybrids with the formulas [Cd(H₂O)₂DABT]₄[Cd(H₇P₄Mo₆O₃₁)₂]·19H₂O (1) and (C₂H₅OH)(C₃H₅N₂)₆[Co₃(H₆P₄Mo₆O₃₁)₂]·H₂O (2) (DABT= 3,3'-diamino-5,5'-bis(1H-1,2,4-triazole)) have been successfully designed and synthesized via a hydrothermal method. Structure analysis revealed that the inorganic moieties in compounds 1 and 2 are made up of hourglass-type {M[P₄Mo₆]₂} (M = Cd/Co) structure, which were constructed by two (P₄Mo₆) units with single transition metal (TM) (Cd/Co) atom as the central metal. The {M[P₄Mo₆]₂} (M = Cd/Co) structures were then further connected by TM to constitute a 2D layered structure. Surprisingly, under the condition of 60 °C and 98% RH, compounds 1 and 2 exhibited excellent proton conductivity of 1.35 × 10^-3 and 3.78 × 10^-3 S cm^-1, respectively. Furthermore, compound 2 can act as heterogeneous catalyst for CO₂ photoreduction, which indicates that it may be a bifunctional POM-based material with great promise.