Polynuclear manganese complexes with the dicarboxylate ligand m-phenylenedipropionate:: A hexanuclear mixed-valence (3MnIII, 3MnIV) complex

The dicarboxylate group m-phenylenedipropionate (mpdp(2-)) has been used for the synthesis of four new Mn compounds of different nuclearities and oxidation states: [Mn2O(mpdp)(bpy)(2)(H2O)(MeCN)](ClO4)(2) (3), [Mn3O(mpdp)(3)(py)(3)](ClO4) (4), [Mn3O(mpdp)(3)(py)(3)] (5), and [Mn6O7(mpdp)(3)(bpy)(3)](ClO4) (6). Compound 3 (2Mn(III)) contains a [Mn-2(mu-O)](4+) core, whereas 5 (Mn-II 2Mn(III)) and 4 (3Mn(III)) contain the [Mn-3(mu(3)-O)](6+,7+) core, respectively. In all three compounds, the mpdp(2-) ligand is flexible enough to adopt the sites occupied by two monocarboxylates in structurally related compounds, without noticeable distortion of the cores. Variable-temperature magnetic susceptibility studies establish that 3 and 5 have ground-state spin values of S = 0 and S = 1/2, respectively. Compound 6 is a highly unusual 3Mn(III), 3Mn(IV) trapped-valent compound, and it is also a new structural type, with six Mn atoms disposed in a distorted trigonal antiprismatic topology. Its electronic structure has been explored by variable-temperature measurements of its dc magnetic susceptibility, magnetization vs field response, and EPR spectrum. The magnetic data indicate that it possesses an S = 3/2 ground state with an axial zero-field splitting parameter of D = -0.79 cm(-1), and this conclusion is supported by the EPR data. The combined results demonstrate the ligating flexibility of the mpdp(2-) ligand and its usefulness in the synthesis of a variety of Mn-x species.