For CoMo6O24@NU1K, after 125°C heating in Ar overnight to remove physisorbed water, the sharp band of NU1K, peaking at ∼3750 cm -1 and associated with an O-H stretch for 3-hydroxo ligands, is replaced with a broad band maximizing at 3667 cm -1 for CoMo6O24@NU1K, while the formate-associated band at 2745 cm -1 disappears (Figure ). Thus, we infer that formate anions are displaced by POM anions. The protons of the four 3-hydroxos are the most acidic of the sixteen protons ideally offered by each ligated node. Their loss, as implied by the disappearance of the IR peak at 3750 cm -1 , suggests Bronsted acid/base or other interactions with the installed POMs.