Electron-Rich Mo^IV ₃ -Polyoxomolybdates Resembling the Paratungstic Archetype

The first polyoxometalates (POMs) composed of Mo^IV , Mo^V ₂ , discrete d¹ -Mo^V and Mo^VI , [Mo^IV ₃ Mo^V ₆ Mo^VI ₄ O₃₂ (μ₂ -OH)(μ₃ -OH)py₉ ] (1), was prepared from the solvothermal partial oxidation of [Mo^IV ₃ O₂ (O₂ CCH₃ )₆ (H₂ O)₃ ]ZnCl₄ in a mixture of pyridine and water. The Mo^V =O adduct-free unit [H₂ Mo₁₂ O₃₃ py₉ ] presents the 11e-reduced Mo derivative of the paratungtic archetype. The use of methanol, ethanol, n-propyl alcohol and triglycol instead of water produced the isostructural [Mo^IV ₃ Mo^V ₆ Mo^VI ₄ O₃₂ (μ₃ -OH)(μ₂ -OR)py₉ ](R=CH₃ , 2; C₂ H₅ , 3; C₃ H₇ , 4; C₂ H₄ OH, 5), providing the first examples of Mo^IV ₃ -POMs containing bridging alkoxyl groups. The addition of [Cr^III Mo₆ O₂₄ ]^9- led to the substitution of {Mo^V =O}³⁺ with {Cr^III -py}³⁺ in the allomer [Mo^IV ₃ Mo^V ₅ Mo^VI ₄ Cr^III O₃₂ (μ-OH)₂ py₁₀ ] (6). Using a mixture of Mo₃ and MoW₂ precursors afforded W^VI -incorporated allomer [Mo^IV ₃ Mo^V ₆ Mo^VI W^VI ₃ O₃₂ (μ-OH)₂ py₉ ] (7). The complete substitution of Mo^VI with W^VI by using a mixture of the Mo₂ W, MoW₂ and W₃ precursors produced the diamagnetic [Mo^IV ₃ Mo^V ₆ W^VI ₄ O₃₃ (μ₃ -OH)py₉ ]^- (syn-8) resulting from the anti→syn conversion between the top and bottom M₃ triads concomitant with Mo^V -Mo^V bonding. Both anti-1-7 and syn-8 have been characterized by X-ray single crystal structural analyses. The spin distribution and magnetic interactions have been investigated by temperature-dependent magnetic susceptibility and DFT theoretical calculations. Heterogeneous hydrogen transfer catalysis has been examined by the Lewis catalysis field (LCF) theory.