Cerium(IV) Hexanuclear Clusters from Cerium(III) Precursors: Molecular Models for Oxidative Growth of Ceria Nanoparticles

Abstract

Reactions of cerium(III) nitrate, Ce(NO3 )3 ⋅6 H2 O, with different carboxylic acids, such as pivalic acid, benzoic acid, and 4-methoxybenzoic acid, in the presence of a tridentate N,N,N-donor ligand, diethylenetriamine (L(1) ), under aerobic conditions yielded the corresponding cerium hexamers Ce6 O8 (O2 CtBu)8 (L(1) )4 (1), Ce6 O8 (O2 CC6 H5 )8 (L(1) )4 (2), and Ce6 O8 (O2 CC6 H4 -4-OCH3 )8 (L(1) )4 (3). Hexamers 1, 2, and 3 contain the same octahedral Ce(IV) 6 O8 core, in which all interstitial oxygen atoms are connected by μ3 -oxo bridging ligands. In contrast, treatment of the Ce(IV) precursor (NH4 )2 Ce(NO3 )6 (CAN) with pivalic acid and the ligand L(1) under the same conditions afforded Ce6 O4 (OH)4 (O2 CtBu)12 (L(1) )2 (4), exhibiting a deformed octahedral Ce(IV) 6 O4 (OH)4 core containing μ3 -oxo and μ3 -hydroxo moieties in defined positions. In contrast to the formation of 1-3, the use of N-methyldiethanolamine (L) in the reaction with Ce(NO3 )3 ⋅6 H2 O and pivalic acid afforded a previously reported Ce(III) dinuclear cluster, Ce2 (O2 CtBu)6 L2 , even in the presence of dioxygen. ESI-MS analysis of the reaction mixture clearly indicated the importance of the ligand L(1) in promoting oxidation of the Ce(III) aggregates, [Cen (O2 CtBu)3n (L(1) )2 ], which is necessary for the formation of Ce(IV) hexamers.

Self‐Assembly of Hexanuclear Lanthanide Carboxylate Clusters of Three Architectures

“…Thus, we have firstly observed[17a] the synthesis of Ce 6 L 4 with stable fluorite‐like core by a direct redox reaction between Ce(NO 3 ) 3 , Hpiv and deta with molar ratio 1:3:5 in acetonitrile media in air (Scheme ). Later, similar solvate Ce 6 L 4 · 2CH 3 CN has been reported by Mathey et al…”

“…There are two structures of Ce 6 L 4 being reported in the present work, Ce 6 O 8 (piv) 8 (deta) 4 and Ce 6 O 8 (piv) 8 (deta) 4 · 0.7CH 3 CN. Additionally, the structure of Ce 6 O 8 (piv) 8 (deta) 4 · 2CH 3 CN was reported earlier . All of three structures are comprised of the same isolated centrosymmetric molecules Ce 6 O 8 (piv) 8 (deta) 4 with octahedral {Ce 6 (µ 3 ‐O) 8 } core, in contrast to distorted {Ce 6 (µ 3 ‐O) 4 (µ 3 ‐OH) 4 } core observed in related structures of Ce 6 O 4 (OH) 4 (piv) 12 (deta) 2 and Ce 6 O 4 (OH) 4 (piv) 12 .…”

“…Additionally, the structure of Ce 6 O 8 (piv) 8 (deta) 4 · 2CH 3 CN was reported earlier . All of three structures are comprised of the same isolated centrosymmetric molecules Ce 6 O 8 (piv) 8 (deta) 4 with octahedral {Ce 6 (µ 3 ‐O) 8 } core, in contrast to distorted {Ce 6 (µ 3 ‐O) 4 (µ 3 ‐OH) 4 } core observed in related structures of Ce 6 O 4 (OH) 4 (piv) 12 (deta) 2 and Ce 6 O 4 (OH) 4 (piv) 12 . Three Ce (4+) ions, Ce1, Ce2, and Ce3, together with the symmetrically related ones, form an almost ideal octahedron with Ce–Ce distances being equal to 3.6 Å and 5.0 Å.…”

“…This solid state transformation requires the rearrangement of Ln 6 L 4 molecules. Although having, in general, similar molecular structures, the compounds Pr 6 L 4 · 2C 6 H 6 , Gd 6 L 4 · 4CH 3 CN , Ce 6 L 4 · 2CH 3 CN, Ce 6 L 4 · 0.7CH 3 CN and Ce 6 L 4, differ in packing organization.…”

“…The notation of atoms for the previously reported Ce 6 L 4 · 2CH 3 CN was made uniform with the structures being reported in this paper for clarity.…”