Hydrogen-Bonded Assemblies of Two-Electron Reduced Mixed-Valence [XMo12O40] (X = P and Si) with p-Phenylenediamines

Hydrogen-bonded assemblies of the two-electron reduced mixed-valence Keggin clusters [PMo12O40]5– and [SiMo12O40]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[PMo12O40]3– or H+4[SiMo12O40]4– (acceptors) in CH3CN. The redox states of the [PMo12O40]5– and [SiMo12O40]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 nm2, 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 C2H5OH solvents. In the compound, (HTMPPD+)6[SiMo12O40]6–(CH3CN)6 (2), the N–H ∼ O hydrogen-bonded interactions between the monoprotonated HTMPPD+ molecules and the [SiMo12O40]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.