A bi-polyoxometallate-based host-guest metal-organic framework.

Anionic POMs prefer to bond with positive metal cations instead of neutral or negative organic ligands. Therefore, it is challenging to synthesize POM-based MOFs, let alone bi-POM-based host-guest MOFs. In this work, an unprecedented bi-POM-based host-guest MOF, Na[Ni(enMe)(2)](4)[Ni(enMe)(2)(H2O)(2)](2){[Ni-6(mu(3)-OH)(3)(enMe)(3) (SIP)(1.5)(B-alpha-PW9O34)](2)[H3PNiW11O40]}center dot 5enMe center dot 33H(2)O (1), with Ni-6-capped [PW9O34] as the node of the host framework and Keggin-type [PNiW11O40] units as the guest was synthesized. 1 showed excellent chemical stability towards aqueous solutions of pH 2-12 at both ambient and boiling temperature, providing opportunities for its application in fresh water harvesting from air.