The use of phosphonates for constructing 3d-4f clusters at high oxidation states: synthesis and characterization of two unusual heterometallic CeMn complexes

The use of phosphonic acids in the synthesis of mixed-metal CeMn complexes has led to the formation of two phosphonate complexes with unusual topologies: [Ce2Mn6O6(OH)(5)(t-BuPO3)(6)(O2CMe)(3)]center dot 53H(2)O (1 center dot 53H(2)O) and [Ce22Mn12O34(MePO3)(12)(O2CMe)(33)(OMe)(6)(NO3)(H2O)(12)](n) (2). The two mixed-metal CeMn complexes were both prepared from a reaction system containing Mn(O2CMe)(2) and (NH4)(2)[Ce(NO3)(6)] with similar procedures except for using different phosphonic acids (tert-butylphosphonic acid and methylphosphonic acid, respectively) as coligands. Both complexes possess rare topology of triangular type, with compound 1 being a 0D discrete cluster, whereas, compound 2 is a 1D polymer. The octanuclear core of complex 1 is composed of three symmetry equivalent distorted cubanes {(Ce2Mn2O2)-Mn-IV-O-IV(OH)(2)} sharing a trigonal-bipyramidal unit {Ce-2(IV)(OH)(3)} in the centre. Compound 2 is a one-dimensional chain polymer of identical Ce22Mn12O34 units linked together by NO3- and MeCO2-groups, while the Ce22Mn12O34 unit is constituted by two centrosymmetric (Ce9Ce2Mn6O17)-Ce-IV-Mn-III-O-IV subunits, which features three identical distorted cubanes {(Ce2Mn2O4)-Mn-IV-O-IV} connecting to a central trigonal-bipyramidal unit {(Ce3O2)-O-IV}, and two additional Ce-III ions capping the top and bottom of the central trigonal bipyramid by six MePO32- ligands. Complexes 1 and 2 are the first high-nuclearity Mn/Ln aggregates reported to date using phosphonates as ligands. Magnetic susceptibility measurements reveal that compound 1 displays dominant ferromagnetic interactions between the adjacent metal ions with the best fit parameters for the exchanges are J(1) = 6.186 cm(-1), J(2) = 4.172 cm(-1), and with a result of S = 9 ground state confirmed by the M versus HT-1 data, which indicates the spins of all the six Mn-IV ions in the cluster are parallel to each other. In contrast, the data for 2 reveals overall antiferromagnetic couplings within the cluster and a resulting S = 6 ground state. Both the in-phase signal chi'T-M and out-of-phase signal chi ''(M) of the two complexes exhibit frequency-dependent below approximate 3 K.