Structure, formation, and dynamics of Mo(12) and Mo(16) 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 Mo(2)O(2)S(2) dioxothio cation has been investigated. Three new molybdenum rings, Mo(12)O(12)S(12)(OH)(12)(TerP) (Mo(12)TerP), Mo(16)O(16)S(16)(OH)(16)(H(2)O)(4)(PDA)(2) (Mo(16)(PDA)(2)), and Mo(16)O(16)S(16)(OH)(16)(H(2)O)(2)(IsoP)(2) (Mo(16)(IsoP)(2)) 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 ((1)H 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-)/Mo(2)O(2)S(2) system gave rise to equilibrium, involving mono-templated Mo(12)IsoP and bis-templated Mo(16)(IsoP)(2) ions. Thermodynamic parameters have been determined and showed that the driving-force for the formation of the Mo(16)(IsoP)(2) is entropically governed. However, whatever the conditions (temperature, proportion of reactants), the PDA(2-)/Mo(2)O(2)S(2) system led only to a single compound, the Mo(16)(PDA)(2) 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) and Mo(16)(PDA)(2) ions.