Structure, Formation, and Dynamics of Mo₁₂ and Mo₁₆ Oxothiomolybdenum Rings Containing Terephtalate Derivatives

Abstract

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)](2+) dioxothio cation has been investigated. Three new molybdenum rings, [Mo(12)O(12)S(12)(OH)(12)(TerP)](2-) ([Mo(12)TerP](2-)), [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(4)(PDA)(2)](4-) ([Mo(16)(PDA)(2)](4-)), and [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(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 ((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)](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-)/[Mo(2)O(2)S(2)](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.

Polyoxothiomolybdenum Wheels as Anionic Receptors for Recognition of Sulfate and Sulfonate Anions

“…[15] In contrast to the standard structures of polyoxometalates, these compounds are characterized by a host-guest self-adaptability. The selfassembly process can be controlled by templating agents, mainly anionic groups such as phosphates [16,17] metalates, [18] or polycarboxylates, [19][20][21][22][23] which are encapsulated covalently as guests in the adapted central cavity. In the presence of halides, supramolecular assemblies based on hydrogen bonding with water molecules within the cavity of the ring were evidenced in the solid state and in solution, thus highlighting anionic recognition properties for this class of compounds.…”

Characterization and catalytic performance of {Mo2O2S2}-based oxothiomolybdenum cyclic clusters supported on mesoporous SBA-15

“…As for Mo 12 S 12 BDC/SBA-15, the weight loss before 398°C attributed to the adsorbed solvent, lattice water molecules, coordinated water and six constitutive water molecules (from the sixteen OH bridging groups). And for Mo 12 BTC/SBA-15, loss of about adsorbed water and lattice water between room temperature and 270°C, six constitutive water molecules (from the 12 OH bridging groups) between 270 and 430°C [9]. So the lattice water, coordinated water and constitutive water molecules of the clusters may be lost in the catalytic procedure from 200°C to 320°C, however, the IR spectra (Figs.…”

“…Consequently, the four Mo atoms which connected to carboxylate groups retain an octahedral environment, whereas, the other eight Mo atoms display square-pyramidal arrangements (Fig. S1b) [9]. The structure of Mo 12 BTC can be described as a dodecanuclear ring encapsulated with a benzenetricarboxylate anion, each carboxylate group bridging two Mo centers (Fig.…”

“…The structure of Mo 12 BTC can be described as a dodecanuclear ring encapsulated with a benzenetricarboxylate anion, each carboxylate group bridging two Mo centers (Fig. S1c) [9,12]. (200) planes of ordered hexagonal mesoporous materials (Fig.…”

“…Cyclic [Mo 2 O 2 S 2 ]-based molybdenum clusters displayed flexible and adaptable cyclic oxothiomolybdenum rings exhibiting an open inner available cavity [9]. The encapsulated ligands should also have an influence upon the hydrodesulfurization (HDS) process.…”