Assembly of Keggin-/Dawson-type Polyoxotungstate Clusters with Different Metal Units and SeO₃^2– Heteroanion Templates

Using a pH-dependent synthetic approach, the combination of different simple metal salts or metal coordination complexes with SeO₃^2– heteroanion templates was employed to synthesize five distinct assemblies of Keggin-/Dawson-type tungstoselenites: (C₂H₈N)₁₀KNa­[(α-SeW₉O₃₄)­{Zr­(H₂O)}­{WO­(H₂O)}­(WO₂)­(SeO₃)­{α-SeW₈O₃₁Zr­(H₂O)}]₂­·14H₂O (<b>1</b>) at pH = 1.3; (C₂H₈N)₁₀KNa₅­[(Se₂W₁₈O₆₀)₂­(μ₂-O)₄]­·12H₂O (<b>2</b>) at pH = 2.5; (C₂H₈N)₄Na₄­[Se₂W₁₈O₆₂­(H₂O)₂]­·13H₂O (<b>3</b>) at pH = 3.6; (C₂H₈N)₄­K₃Na₁₀­[(α-SeW₉O₃₃)₂­{Ce₂(CH₃COO)­(H₂O)₃W₃O₆}­(α-Se₂W₁₄O₅₂)]·26H₂O (<b>4</b>) at pH = 4.5; K₁₀Na₅­[(α-SeW₉O₃₃)₂­{Ce₂(H₂O)₄W₃O₆}­{α-Se₂W₁₄O₅₁(OH)}]­·24H₂O (<b>5</b>) at pH = 4.5. All five compounds were characterized by single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric, UV/vis spectroscopy, and ESI-MS. Moreover, their electrochemical properties were investigated. Keggin-type polyoxoanion of <b>1</b> remains the first reported Zr-containing tungstoselenites based on {α-SeW₉} building blocks. X-ray analysis revealed that the 4d metal Zr centers have seven- and eight-coordinated modes, and SeO₃^2– acts as the templates as well as the linkers. With the increasing of the pH, Dawson-type polyoxoanions of <b>2</b> and <b>3</b> based on the first reported basic lacunary {α-Se₂W₁₄} building blocks are obtained by using 3d-4f metal coordination complexes. Polyoxoanions of <b>4</b> and <b>5</b> remain similar structures stabilized by the 4f metal Ce centers at pH = 4.5 and that contain the basic Keggin-type {α-SeW₉} and Dawson-type {α-Se₂W₁₄} building blocks in <b>1</b>–<b>3</b> at the same time, presenting the mixed multiple lacunary building blocks being combined into the single polyoxoanion architecture. Furthermore, the density functional theory calculations have been performed on polyoxoanions of <b>1</b> and <b>5</b> as the representatives to investigate their electronic properties