Intercalation of decamolybdodicobaltate (III) anion in layered double hydroxides

Intercalation of decamolybdodicobaltate(III) anion ([Co2Mo10]) in a MgAl layered double hydroxide (LDH) was carried out by an anion exchange reaction using MgAl-OH LDHs (meixnerite) as precursors. The synthesis of pure and crystalline LDHs intercalated with [Co2Mo10] required trade-offs between different reaction conditions for the [Co2Mo10] anions and the LDH layers to be stable to hydrolysis reactions. In this work, these conditions for intercalation were achieved using meixnerite precursors of Al/(Mg + Al) molar ratios larger than 0.33, a reaction pH of about 4.7, and a nonaqueous medium (ethanol/water 40 vol %) at 353 K, with an exchange time of 1 h. The structure and composition of the intercalates were established by elemental analysis, powder X-ray diffraction, FTIR and Raman spectroscopies, thermal methods, rehydration experiments, SEM and TEM microscopies, and N-2 adsorption/desorption studies. Gallery heights of 0.74 and 0.97 nm were observed for the [Co2Mo10] intercalated LDHs, corresponding to two different anion orientations in the interlayers. The interlayer [Co2Mo10] is stable up to 523 K and the layer structure is stable up to 573 K, even though the morphology of the intercalated materials is retained up to 773 K.