Synthesis, structure, electrochemistry and magnetism of cobalt-, nickel- and zinc-containing [M4(OH)3(H2O)2(α-SiW10O36.5)2]13− (M = Co2+, Ni2+, and Zn2+)

Abstract

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW₉O₃₄]¹⁰⁻ with cobalt(II), nickel(II) and zinc(II) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M₄-containing heteropolytungstates [M₄(OH)₃(H₂O)₂(α-SiW₁₀O_36.5)₂]¹³⁻ (M = Co²⁺ (1), Ni²⁺ (2), and Zn²⁺ (3)). Polyanions 1–3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, and thermogravimetric and elemental analyses. Electrochemical studies showed that the Co²⁺ ions in 1 can be oxidized to Co³⁺ and the CVs of the W^VI centers of the polyanions feature well-defined and chemically reversible reduction waves. Magnetic measurements on 1 and 2 showed paramagnetism with complex ferromagnetic and antiferromagnetic interactions. A model was presented for extracting the exchange constants for the magnetic exchange interaction.