Bridging Nitrate Groups in [Mn<sub>4</sub>O<sub>3</sub>(NO<sub>3</sub>)(O<sub>2</sub>CMe)<sub>3</sub>(R<sub>2</sub>dbm)<sub>3</sub>] (R = H, Et) and [Mn<sub>4</sub>O<sub>2</sub>(NO<sub>3</sub>)(O<sub>2</sub>CEt)<sub>6</sub>(bpy)<sub>2</sub>](ClO<sub>4</sub>): Acidolysis Routes to Tetranuclear Manganese Carboxylate Complexes
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New synthesis procedures are described to tetranuclear manganese carboxylate complexes containing the [Mn4O2]8+ or [Mn4O3X]6+ (X- = MeCO2-, F-, Cl-, Br-, NO3-) core. These involve acidolysis reactions of [Mn4O3(O2CMe)4(dbm)3] (1; dbm is the anion of dibenzoylmethane) or [Mn4O2(O2CEt)6(dbm)2] (8) with HX (X- = F-, Cl-, Br-, NO3-); high-yield routes to 1 and 8 are also described. The X- = NO3- complexes [Mn4O3(NO3)(O2CR)3(R‘2dbm)3] (R = Me, R‘ = H (6); R = Me, R‘ = Et (7); R = Et, R‘ = H (12)) represent the first synthesis of the [Mn4O3(NO3)]6+ core, which contains an unusual η1:μ3-NO3- group. Treatment of known [Mn4O2(O2CEt)7(bpy)2](ClO4) with HNO3 gives [Mn4O2(NO3)(O2CEt)6(bpy)2](ClO4) (15) containing a η1:η1:μ-NO3- group bridging the two body MnIII ions of the [Mn4O2]8+ butterfly core. Complex 7·4CH2Cl2 crystallizes in space group P212121 with (at −168 °C) a = 21.110(3) Å, b = 22.183(3) Å, c = 15.958(2) Å, Z = 4, and V = 7472.4(3) Å3. Complex 15· 3/2CH2Cl2 crystallizes in space group P21/c with (at −165 °C) a = 26.025(4) Å, b = 13.488(2) Å, c = 32.102(6) Å, β = 97.27(1)°, Z = 8, and V = 11178(5) Å3. Complex 7 contains a [Mn4(μ3-O)3(μ3-NO3)]6+ core (3MnIII, MnIV) as seen for previous [Mn4O3X]6+ complexes. Complex 15 contains a butterfly [Mn4(μ3-O)2]8+ core. 1H NMR spectra have been recorded for all complexes reported in this work and the various resonances assigned. All complexes retain their structural integrity on dissolution in chloroform and dichloromethane. Magnetic susceptibility (χM) data were collected on 12 in the 5−300 K range in a 10.0 kG (1 T) field. Fitting of the data to the theoretical χM vs T expression appropriate for a [Mn4O3X]6+ complex of C3v symmetry gave J34 = −23.9 cm-1, J33 = 4.9 cm-1, and g = 1.98, where J34 and J33 refer to the MnIIIMnIV and MnIIIMnIII pairwise exchange interactions, respectively. The ground state of the molecule is S = 9/2, as found previously for other [Mn4O3X]6+ complexes. This was confirmed by magnetization data collected at various fields and temperatures. Fitting of the data gave S = 9/2, D = −0.45 cm-1, and g = 1.96, where D is the axial zero-field splitting parameter.
