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 3 ] with bis(2-pyrrolidone) linker molecules having a trans -1,4-cyclohexyl bridging moiety (L). As a result, we found that, after loading L, Ce(IV) in HNO 3 (aq) exclusively provides one of different crystalline phases, (HL) 2 [Ce(NO 3 ) 6 ] or [Ce 2 (μ-O)-(NO 3 ) 6 (L) 2 ] n 2D MOF, depending on [HNO 3 ]. The former has been obtained at [HNO 3 ] = 4.70-9.00 M and is isomorphous with the analogous (HL) 2 [An(NO 3 ) 6 ] we reported previously. In contrast, the deposition of the latter phase at the lower [HNO 3 ] conditions (1.00-4.30 M) demonstrates that hydrolysis and oxolation of Ce 4+ proceed even below pH 0 to provide a [Ce-O-Ce] 6+ unit included in this compound. These different Ce(IV) phases are exchangeable with each other under soaking in HNO 3 (aq), implying that chemical equilibria of dissolution/deposition of these crystalline phases and hydrolysis and oxolation of Ce 4+ and its complexation with NO 3 - occur in parallel. Indeed, such coordination chemistry of Ce(IV) in HNO 3 (aq) was well corroborated by 17 O NMR, Raman, and IR spectroscopy.