Crystal Structures of Ce(IV) Nitrates with Bis(2-pyrrolidone) Linker Molecules Deposited from Aqueous Solutions with Different HNO 3 Concentrations.

We investigated the molecular and crystal structures of Ce(IV) compounds deposited under different [HNO] with bis(2-pyrrolidone) linker molecules having a -1,4-cyclohexyl bridging moiety (L). As a result, we found that, after loading L, Ce(IV) in HNO(aq) exclusively provides one of different crystalline phases, (HL)[Ce(NO)] or [Ce(μ-O)-(NO)(L)] 2D MOF, depending on [HNO]. The former has been obtained at [HNO] = 4.70-9.00 M and is isomorphous with the analogous (HL)[An(NO)] we reported previously. In contrast, the deposition of the latter phase at the lower [HNO] conditions (1.00-4.30 M) demonstrates that hydrolysis and oxolation of Ce proceed even below pH 0 to provide a [Ce-O-Ce] unit included in this compound. These different Ce(IV) phases are exchangeable with each other under soaking in HNO(aq), implying that chemical equilibria of dissolution/deposition of these crystalline phases and hydrolysis and oxolation of Ce and its complexation with NO occur in parallel. Indeed, such coordination chemistry of Ce(IV) in HNO(aq) was well corroborated by O NMR, Raman, and IR spectroscopy.