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

Abstract

Using a pH-dependent synthetic approach, the combination of different simple metal salts or metal coordination complexes with SeO32– 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 (1) at pH = 1.3; (C2H8N)10KNa5[(Se2W18O60)2(μ2-O)4]·12H2O (2) at pH = 2.5; (C2H8N)4Na4[Se2W18O62(H2O)2]·13H2O (3) at pH = 3.6; (C2H8N)4K3Na10[(α-SeW9O33)2{Ce2(CH3COO)(H2O)3W3O6}(α-Se2W14O52)]·26H2O (4) at pH = 4.5; K10Na5[(α-SeW9O33)2{Ce2(H2O)4W3O6}{α-Se2W14O51(OH)}]·24H2O (5) 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 1 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 SeO32– acts as the templates as well as the linkers. With the increasing of the pH, Dawson-type polyoxoanions of 2 and 3 based on the first reported basic lacunary {α-Se2W14} building blocks are obtained by using 3d-4f metal coordination complexes. Polyoxoanions of 4 and 5 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 1–3 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 1 and 5 as the representatives to investigate their electronic properties.