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

Anionic POMs prefer to bond positive metal cations instead of neutral or negative organic ligands. Therefore, it is challenging to synthesize POM-based MOF, 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{[Ni6(μ3-OH)3(enMe)3 (SIP)1.5(B-α-PW9O34)]2[H3PNiW11O40]}∙5enMe∙33H2O (1), with Ni6-capped [PW9O34] as node of the host framework and Keggin-type [PNiW11O40] unit as the guest was synthesized. 1 showed excellent chemical stability towards pH 2 ~ 12 aqueous solutions at both ambient and boiling temperature, providing opportunities for its application in fresh water harvesting form air.