Mn^II/III and Ce^III/IV Units Supported on an Octahedral Molecular Nanoparticle of CeO₂

Abstract

The preparation of three new heterometallic clusters [Ce6Mn12O17(O2CPh)26] (1), [Ce10Mn14O24(O2CPh)32] (2), and [Ce23Mn20O48(OH)2(tbb)46(H2O)4]­(NO3)2 (3; tbb– = 4-tBu-benzoate) is reported. They all possess unprecedented structures with a common feature being the presence of an octahedral CeIV–oxo core: a Ce6 in 1, two edge-fused Ce6 giving a Ce10 bioctahedron in 2, or a larger Ce19 octahedron in 3. Complex 1 is the first Ce6 cluster with a central μ6-O2–. 2 and the cation of 3 are molecular nanoparticles of CeO2 (ceria) because they possess the fluorite structure of bulk ceria and are thus ultrasmall ceria nanoparticles in molecular form. The {Ce19O32} octahedral subunit of the cation of 3 had been predicted from density functional theory studies to be one of the stable fragments of the CeO2 lattice, but has never been previously synthesized in molecular chemistry. Around the Ce/O core of 1–3 is an incomplete monolayer of Mn n ions disposed as four Mn3, two Mn7, and four Mn5 units, respectively. This represents a clear structural similarity with composite (phase-separated) CeO2/MnO x mixtures where at high Ce:Mn ratios the Mn atoms segregate on the surface of CeO2 phases. Variable-temperature dc and ac magnetic susceptibility studies have revealed S = 2, S = 1/2, and S = 3/2 ground states for 1–3, respectively. Fitting of the 5.0–300 K dc data for 1 to a two-J model for an asymmetrical V-shaped Mn3 unit with no interaction between the end MnIII ions gave an excellent fit with the following values: J 1 = 5.2(3) cm–1, J 2 = −7.4(3) cm–1, and g = 1.96(2).

Semiempirical Magnetostructural Correlation for High-Nuclearity MnIII-Oxo Complexes: Accommodation of Different Relative Jahn–Teller Axis Orientations

“…[Ce 6 Mn 12 O 17 (O 2 CPh) 26 ] consists of a diamagnetic {Ce 6 O 9 } core with four isostructural, noninteracting {Mn 3 (μ-O 2− ) 2 } (10) units (Figure 13) attached to the surface. 40 Lowtemperature dc and ac susceptibility data reveal that each Mn 3 unit has an S = 2 ground state. Pertinent metric parameters and obtained J MSC are listed in Table 11; the Mn 1 Mn 3 pair is not monoatomically bridged (instead by an η 1 / η 1 -benzoate), so the MSC is not applicable.…”

“…We probe this point with a low-symmetry Mn 3 cluster that is a scalene triangle and thus a 3- J system. [Ce 6 Mn 12 O 17 (O 2 CPh) 26 ] consists of a diamagnetic {Ce 6 O 9 } core with four isostructural, noninteracting {Mn 3 (μ-O 2– ) 2 } ( 10 ) units (Figure ) attached to the surface . Low-temperature dc and ac susceptibility data reveal that each Mn 3 unit has an S = 2 ground state.…”

Synthesis and Characterization of Cerium-Oxo Clusters Capped by Acetylacetonate

“…For example, Gupta et al characterized [Ce 6 Mn 12 O 17 (O 2 CPh) 26 ], which consisted of four {Mn 3 (μ 3 -O) 2 } surrounding a Ce IV 6 core. 93 Likewise, Thuijs et al reported [Ce 3 Mn 8 O 8 (O 2 CPh) 18 (HO 2 CPh) 2 ] for which the central position in the cluster core was occupied by Ce IV and the surface was composed of two Ce III and eight Mn III sites. 94 Nonetheless, it is important to note that this is not the only arrangement observed.…”