Hydrogen-bonded assemblies of two-electron reduced mixed-valence [XMo ₁₂O₄₀] (X = P and Si) with p-phenylenediamines

Hydrogen-bonded assemblies of the two-electron reduced mixed-valence Keggin clusters [PMo₁₂O₄₀]^5- and [SiMo ₁₂O₄₀]^6- were obtained by the one-pot electron-transfer reactions between p-phenylenediamine (PPD) or 2,3,5,6-tetramethyl-PPD (TMPPD) (donors) and H⁺₃[PMo ₁₂O₄₀]^3- or H⁺₄[SiMo ₁₂O₄₀]^4- (acceptors) in CH₃CN. The redox states of the [PMo₁₂O₄₀]^5- and [SiMo ₁₂O₄₀]^6- clusters were confirmed by the redox titrations and electronic absorption measurements. In (HPPD⁺) ₃(H⁺)₂[PMo₁₂O₄₀] ^5-(CH₃CN)_3-6 (1), the N-H ∼ O hydrogen-bonded interactions between the monoprotonated HPPD⁺ (or diprotonated H2PPD²⁺) and the [PMo₁₂O₄₀] ^5- resulted in a windmill-like assembly and hydrophilic one-dimensional channels are formed with a cross-sectional area of 0.065 nm ², and these are filled by the CH₃CN molecules. Also, the CH₃CN molecules in salt 1 were removed by immersing the single crystals of 1 into H₂O, CH₃OH, and C₂H ₅OH solvents. In the compound, (HTMPPD⁺) ₆[SiMo₁₂O₄₀]^6-(CH ₃CN)₆ (2), the N-H ∼ O hydrogen-bonded interactions between the monoprotonated HTMPPD⁺ molecules and the [SiMo ₁₂O₄₀]^6- formed a "Saturn-ring"-like assembly. Each Saturn-ring was arranged into an hexagonally packed array via hydrogen-bonded and π-stacking interactions of HTMPPD⁺, while the CH₃CN solvent present in salt 2 are only found in the zero-dimensional isolated cavities.