3D Racemic Microporous Frameworks and 3D Chiral Supramolecular Architectures Based on Evans–Showell-Type Polyoxometalates Controlled by the Temperature

Four new architectures containing [Co₂Mo₁₀H₄O₃₈]^6– polyoxoanion, [Ln­(H₂O)₇]­[Ln­(H₂O)₅]­[Co₂Mo₁₀H₄O₃₈]·5H₂O (Ln = Gd <b>1</b>; Tb <b>2</b>), and (NH₄)₃[Ln­(H₂O)₆]­[Co₂Mo₁₀H₄O₃₈]·6H₂O (Ln = Gd <b>3</b>; Tb <b>4</b>) have been synthesized at different temperatures and characterized by elemental analysis, IR and Raman spectroscopy, TG analysis, powder X-ray diffraction and single crystal X-ray diffraction. Isostructural compounds <b>1</b> and <b>2</b> obtained at the higher temperature (85 °C), are built up of Evans–Showell-type polyoxoanions [Co₂Mo₁₀H₄O₃₈]^6–, respectively, linked by Gd³⁺ or Tb³⁺ cations to form a 3D racemic framework with 1D zigzag channels. From the topological point of view, the 3D net is a rare binodal 4-connected SrAl₂ (sra) topology. As far as we know, compounds <b>1</b> and <b>2</b> represent the first examples of 3D architectures based on Evans–Showell-type polyoxometalate. Interestingly, the stable 3D microporous compounds exhibit selective adsorption ability: adsorbing water and methanol, as well as excellent photocatalytic activity for organic dye degradation under visible light irradiation. When the reaction temperature was decreased to room temperature (25 °C), two chiral species <b>3</b> and <b>4</b> were obtained, with a monosupporting structure composed of one [Co₂Mo₁₀H₄O₃₈]^6– polyoxoanion and one [Ln­(H₂O)₆]³⁺ unit. These chiral monosupporting motifs can be connected by strong hydrogen-bonding interactions to form a 3D chiral supramolecular architecture. They crystallize in the chiral space group <i>P</i>2₁, as conglomerates of two enantiomerically pure crystals. Their absolute configurations were determined by the Flack parameters and solid-state circular dichroism spectroscopy