Manganese/Cerium Clusters Spanning a Range of Oxidation Levels and CeMng, Ce2Mn4, and Ce6Mn4 Nuclearities: Structural, Magneti, and EPR Properties.

The syntheses, structures, and magnetic properties are reported for three new Ce/Mn clusters with different Ce/Mn ratios: [Ce6Mn4O12(O2CMe)10(NO3)4(py)4] (py = pyridine) (1), [CeMngOg(O2CCH2tBu)12(DMF)14] (DMF = dimethylformamide) (2), and [Ce2Mn4O2(O2CMe)6(NO3)4(hmp)4] (3; hmp- is the anion of 2-(hydroxymethyl)pyridine). 1 and 2 were obtained from the reaction of CeIV with [Mn12O12(O2CMe)16(H2O)4] (MnIII8Mn(IV)4) and [MngO2(O2CCH2tBu)14tBuCH2CO2H)4] (MnII6MnIII2), respectively, whereas 3 resulted from the oxidation of MnII acetate with CeIV in the presence of hmpH. Cluster 1 possesses an unusual [Ce6Mn4O12]14+ core topology consisting of a [Ce6O8] face-capped octahedron, which is face-fused at each end to a [CeIV2MnIIIMnIVO4] cubane. Cluster 2 possesses a nonplanar, saddlelike loop of eight MnIII atoms bridged by eight µ3-O2- ions to a central CeIV atom. Cluster 3 is similar to 1 in possessing an octahedral core, but this is now a [Ce2Mn4] octahedron consisting of a CeIII atom on either side of a Mn4 parallelogram, with the metal atoms bridged by two µ4-O2- ions, the alkoxide arms of four hmp- groups, and six acetates. Clusters 1, 2, and 3 are thus at the CeIV6MnIII2MnIV2, CeIVMnIII8, and CeIII2MnIII4 oxidation levels, respectively. Variable-temperature, solid-state direct current (DC) and alternating current (AC) magnetization studies on 1-3 in the 5.0-300 K range revealed predominantly antiferromagnetic exchange interactions within the complexes. For 1, fitting of the DC data to the theoretical expression for a dinuclear MnIIIMnIV complex derived using the Van Vleck equation and an isotropic spin Hamiltonian (x = -2JŜi·Sj convention) gave a value for the exchange coupling parameter (J) of -60.4(7) cm-1 and a Landé factor g = 2.00(1), indicating an S = 1/2 ground state. For 2, both DC and AC data indicate an S = 0 ground state, which is unprecedented for a member of the CeMng family and now means members of the latter have been made that span the whole range of possible ground states from S = 0 to the maximum S = 16. Cluster 3 possesses an S = 0 ground state for its Mn4 fragment, with the paramagnetism remaining at low temperature coming from the weakly coupled Ce(III) centers. These three species are new additions to the Mn-Ce family of clusters and the broader class of 3d/4f molecular systems. [ABSTRACT FROM AUTHOR]