Phase formation in the system Co<sup>2+</sup>–WO<sub>4</sub><sup>2−</sup>–H<sup>+</sup>–C<sub>3</sub>H<sub>7</sub>ON–H<sub>2</sub>O. Synthesis, crystal structure, and characterization of cobalt(II) decatungstate [Co(C<sub>3</sub>H<sub>7</sub>NO)<sub>5</sub>]<sub>2</sub>[W<sub>10</sub>O<sub>32</sub>]

<div><p>The phase formation processes of isopolytungstates in the systems Co<sup>2+</sup>––H<sup>+</sup>–DMF–H<sub>2</sub>O (DMF-dimethylformamide) with different acidities (<i>Z</i> = <i>ν</i>(H<sup>+</sup>)/<i>ν</i> = 1.14–1.60) have been studied. It was found that only cobalt(II) hepta-, para-, and decatungstates could be isolated from aqueous DMF solutions. The chemical and FTIR spectroscopic analysis of the products isolated from the system allowed determination of conditions of Co(II) decatungstate formation. Cobalt(II) decatungstate, [Co(C<sub>3</sub>H<sub>7</sub>NO)<sub>5</sub>]<sub>2</sub>[W<sub>10</sub>O<sub>32</sub>], was characterized by elemental and EDX spectral analysis, SEM, FTIR spectroscopy, thermal analysis, single-crystal X-ray diffraction, and by UV–vis spectroscopy analysis.</p></div>