Manganese/Cerium Clusters Spanning a Range of Oxidation Levels and CeMn8, Ce2Mn4, and Ce6Mn4 Nuclearities: Structural, Magnetic, and EPR Properties

• Published in: Inorganic chemistry 2014-07, Vol.53 (13), p.6805-6816
• Main Authors: Lampropoulos, Christos, Thuijs, Annaliese E, Mitchell, Kylie J, Abboud, Khalil A, Christou, George
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic500617f

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), [CeMn8O8­(O2CCH2 t Bu)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] (MnIII 8MnIV 4) and [Mn8O2­(O2CCH2 t Bu)14­( t BuCH2CO2H)4] (MnII 6MnIII 2), 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 [CeIV 2MnIII­MnIVO4] 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 CeIV 6MnIII 2MnIV 2, CeIVMnIII 8, and CeIII 2MnIII 4 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 (ℋ = −2JŜ i ·Ŝ j 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 CeMn8 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 CeIII centers. These three species are new additions to the Mn–Ce family of clusters and the broader class of 3d/4f molecular systems.