(Kanazawa University) A Japanese research team led by Kanazawa University studied host-guest interactions in vanadate clusters. V12 is a spherical bowl that hosts small molecules in its interior. The team created empty (guest-free) V12 for the first time. One of the 12 units of VO5 was found to flip inwards to fill the void vacated by the guest. Empty V12 could absorb CO2 but rejected CO, offering a way to separate these molecules for CO2 capture.