Structure, formation, and dynamics of Mo12 and Mo16 oxothiomolybdenum rings containing terephtalate derivatives

The influence of rigid or semirigid dicarboxylate anions, terephtalate (TerP(2-)), isophtalate (IsoP(2-)), and phenylenediacetate (PDA(2-)) on the self-condensation process of the [Mo2O2S2](2+) dioxothio cation has been investigated. Three new molybdenum rings, [Mo12O12S12(OH)(12)(TerP)](2-) ([Mo(12)TerP](2-)), [Mo16O16S16(OH)(16-) (H2O)(4)(PDA)(2)](4-) ( [Mo-16(PDA)(2)](4-)), and [Mo16O16S16(OH)(16)(H2O)(2)(IsoP)(2)](4-) ([Mo-16(IsoP)(2)](4-)) have been isolated and unambiguously characterized in the solid state by single-crystal X-ray studies and in solution by various NMR methods and especially by diffusion-correlated NMR (H-1 DOSY) spectroscopy, which was shown to be a powerful tool for the characterization and speciation of templated molybdenum ring systems in solution. Characterization by FT-IR and elemental analysis are also reported. The dynamic and thermodynamic properties of both the sixteen-membered rings were studied in aqueous medium. Specific and distinct behaviors were revealed for each system. The ISop(2-)/[Mo2O2S2](2+) system gave rise to equilibrium, involving mono-templated [Mo(12)IsoP](2-) and bis-templated [Mo-16(IsoP)(2)](4-) ions. Thermodynamic parameters have been determined and showed that the driving-force for the formation of the [Mo-16(IsoP)(2)](4-) is entropically governed. However, whatever the conditions (temperature, proportion of reactants), the PDA(2-)/[Mo2O2S2](2+) system led only to a single compound, the [Mo-16(PDA)(2)](4-) ion. The latter exhibits dynamic behavior, consistent with the gliding of both the stacked aromatic groups. Stability and dynamics of both Mo-16 rings was related to weak hydrophobic or pi-pi stacking inter-template interactions and inner hydrogen-bond network occurring within the [Mo-16(IsoP)(2)](4-) and [Mo-16(PDA)(2)](4-) ions.