Interaction of Polar Substrates with Transition Metal Substituted Keggin-Type Heteropolyanions [X(H₂O)W₁₁SiO₃₉]⁶⁻(X=Co²⁺, Mn²⁺) Pillared in a Mg-Al Hydrotalcite-Like Clay

<jats:title>Abstract</jats:title><jats:p>The intercalation of Keggin-type [X(H<jats:sub>2</jats:sub>O)W<jats:sub>11</jats:sub>SiO<jats:sub>39</jats:sub>]<jats:sup>6−</jats:sup>(X=Co<jats:sup>2+</jats:sup>, Mn<jats:sup>2+</jats:sup>) heteropolyanions by aqueous anion exchange of 10 Å in a synthetic hydrotalcite-like Mg<jats:sub>2</jats:sub>Al(OH)<jats:sub>6</jats:sub>(NO<jats:sub>3</jats:sub>) results in products with interlayer spacing of ca. 10 Å. The layered array of the product and the integrity of the intercalated heteropolyanion are stable below 623 K in air as examined by XRD and IR analyses, respectively. UV-vis Diffuse Reflectance spectroscopy indicates that the water ligand in the intercalated [Co(H<jats:sub>2</jats:sub>O)W<jats:sub>11</jats:sub>SiO<jats:sub>39</jats:sub>]<jats:sup>6−</jats:sup> can be removed by thermal evacuation at 473 K leaving a coordinatively unsaturated site (in the transition metal) which reversibly coordinates water,methanol, ethanol or ammonia. ESR analysis of the intercalated [Mn(H<jats:sub>2</jats:sub>O)W<jats:sub>11</jats:sub>SiO<jats:sub>39</jats:sub>]<jats:sup>6−</jats:sup> shows that the shape of a signal at g = 2.00, arising from six-coordinated Mn<jats:sup>2+</jats:sup> strongly depends on adsorption-desorption of the water ligand.</jats:p>