Mn II/III and Ce III/IV Units Supported on an Octahedral Molecular Nanoparticle of CeO 2 .

The preparation of three new heterometallic clusters [Ce 6 Mn 12 O 17 (O 2 CPh) 26 ] ( 1 ), [Ce 10 Mn 14 O 24 (O 2 CPh) 32 ] ( 2 ), and [Ce 23 Mn 20 O 48 (OH) 2 (tbb) 46 (H 2 O) 4 ](NO 3 ) 2 ( 3 ; tbb - = 4- t Bu-benzoate) is reported. They all possess unprecedented structures with a common feature being the presence of an octahedral Ce IV -oxo core: a Ce 6 in 1 , two edge-fused Ce 6 giving a Ce 10 bioctahedron in 2 , or a larger Ce 19 octahedron in 3 . Complex 1 is the first Ce 6 cluster with a central μ 6 -O 2- . 2 and the cation of 3 are molecular nanoparticles of CeO 2 (ceria) because they possess the fluorite structure of bulk ceria and are thus ultrasmall ceria nanoparticles in molecular form. The {Ce 19 O 32 } octahedral subunit of the cation of 3 had been predicted from density functional theory studies to be one of the stable fragments of the CeO 2 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 Mn 3 , two Mn 7 , and four Mn 5 units, respectively. This represents a clear structural similarity with composite (phase-separated) CeO 2 /MnO x mixtures where at high Ce:Mn ratios the Mn atoms segregate on the surface of CeO 2 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 Mn 3 unit with no interaction between the end Mn III 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).