Structural and Selective Gas Adsorption Studies of Polyoxometalate and Tris(ethylenediamine) Cobalt(III) Based Ionic Crystals

Seven new ionic solids built on polyoxometalate anions and [Co(en)3]3+ cations, namely, [Co(en)3Mo8O26(H3O)(Cl)](DMF)4(H2O) (Co-Mo8-DMF), [α-PW12O40][Co(en)3]·6DMF (Co-W12P-DMF), [α-PW12O40][Co(en)3]·6DEF (Co-W12P-DEF), [α-PMo12O40][Co(en)3]·5.5DMF (Co-Mo12P-DMF), [α-PMo12O40][Co(en)3]·6DEF (Co-Mo12P-DEF), [α-SiW12O40][Co(en)3]3/2[Cl]1/2·6DMF·3H2O (Co-W12Si-DMF), and [α-SiW12O40][Co(en)3]·6DEF (Co-W12Si-DEF), have been synthesized from nonaqueous (DMF/DEF) media and characterized by single-crystal X-ray diffraction. We attempt to understand if [Co(en)3]3+ cations used in these reaction systems play a crucial role in controlling the assembly of these crystals. These ionic solids, after removal of the DMF or DEF molecules, are found to exhibit size selective H2 adsorption properties over N2. The amount of hydrogen adsorption was influenced by POM anion types and their orientations. CoMo12P-DEF has the highest (0.9 wt %) H2 uptake, and CoW12P-DEF has the lowest (0.4 wt %) uptake among the series when the adsorbate pressure approached 1 atm.