Rapid and Simple Isolation of the Crystalline Molybdenum-Blue Compounds with Discrete and Linked Nanosized Ring-Shaped Anions: Na15[MoMoO462H14(H2O)70]0.5 [MoMoO457H14(H2O)68]0.5 · ca. 400 H2O and Na22[MoMoO442H14(H2O)58] · ca. 250 H2O

The blue mixed-crystal title compound Na₁₅[MoMoO₄₆₂H₁₄ (H₂O)₇₀]_0.5[MoMoO₄₅₇H₁₄ · (H₂O)₆₈]_0.5 · ca. 400 H₂O ≡ Na₁₅[ 1 a ]_0.5[ 1 b ]_0.5 · ca. 400 H₂O 1 , which crystallizes in the triclinic space group P 1 (a = 30.785(2), b = 32.958(2), c = 47.318(3) Å, α = 90.53(1), β = 89.86(1), γ = 96.85(1)°, V = 47665(6) ų, Z = 2, D_calc = 2.149 g cm^–3), precipitates within one day when an acidic (pH ≈ 1) aqueous solution of sodium molybdate (because of the extremely high solubility of the reaction product used in relatively high concentration) is reduced by sodium dithionite. 1 contains hitherto unknown pure molybdenum-oxide based, nanosized, ring-shaped, crystallographically independent cluster anions of the type {Mo₁₅₄} 1 a and {Mo₁₅₂} 1 b , the lacunary-type analogue of 1 a . Using the same reducing agent but in the presence of a reagent with a high affinity to the specific {Mo₂}-type building unit (also a leaving group) of 1 a , such as formic acid, the compound Na₂₂[MoMoO₄₄₂H₁₄(H₂O)₅₈] · ca. 250 H₂O 2 (space group P 1, a = 24.724(1), b = 35.726(2), c = 44.608(3) Å, α = 93.25(1), β = 93.51(1), γ = 106.72(1)°, V = 37552(4) ų, Z = 2, D_calc = 2.401 g cm^–3) is obtained in which the giant rings, having four missing {Mo₂} units compared to 1 a , are linked to chains. Until now, similar chain-type compounds could only be obtained using a non-well-defined synthetic method.