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 similar to O hydrogen-bonded interactions between the monoprotonated HPPD+ (or diprotonated H2PPD(2+)) 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 C2H5OH solvents. In the compound, (HTMPPD+)(6)[SiMo12O40](6-) (CH3CN)(6) (2), the N-H similar to 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 pi-stacking interactions of HTMPPD+, while the CH3CN solvent present in salt 2 are only found in the zero-dimensional isolated cavities.