Oligonuclear homo- and mixed-valence manganese complexes based on thiophene- or aryl-carboxylate ligation: Synthesis, characterization and magnetic studies

Mixed-valence trinuclear manganese compounds [Mn3O(O2CTh)(6)(L)(x)(H2O)y]center dot n(solvent) (Th = thiophene, 1 center dot CH3CN: L = pyridine (py), x = 3, y = 0, n = 1, solvent = CH3CN; 1 center dot similar to H2O: L = py, x = 3, y = 0, n = similar to 1, solvent = H2O; 2: L = py, x = 2, y = 1, n = 0.25, solvent = CH3CN; 3: L = 3-Mepy, x = 2, y = 1, n = 0) containing a [(MnMn2III)-Mn-II(mu(3)-O)](6+) core have been prepared. Homo-valence tetranuclear manganese complexes (NBu4n)[Mn4O2(O2CAr)(9)(L)] (4 center dot ThCO2H center dot CH2Cl2: Ar = -Th, L = EtOH; 6: Ar = -Ph, L = H2O; 7: Ar = -Ph-p-Me, L = H2O; 8 center dot CH2Cl2: -Ph-3,5-Me-2, no L) with a [Mn-4(III)(mu(3)-O)(2)](8+) core and [(MnMn3O2)-Mn-II-O-III(O2CTh)(7)(bpy)(2)] (5) were synthesized, structurally and magnetically characterized. Compounds 1-3 were obtained by comproportionation of Mn-II(O2CMe)(2)center dot 4H(2)O with (NBu4n) (MnO4)-O-VII in aprotic pyridine (1) or aprotic/protic py/EtOH (2) or Mepy/EtOH (3) solvent mixtures. Clusters 4-8 were synthesized by comproportionation of Mn-II(O2CAr)(2)center dot xH(2)O/ArCOOH with (NBu4n)(MnO4)-O-II in EtOH/CH3CN. X-ray structural characterization of the 2-thiophenecarboxylate (ThCO2-) containing compounds 1 center dot CH3CN, 1 center dot similar to 2H(2)O and 4 center dot ThCO2H center dot CH2Cl2 revealed a thiophene ring disorder about the (O-2)C-C(Th) bond so that the S atom and opposite (5-)CH group are distributed over two ring positions each. The MnII atom in the approximately isosceles triangular [(MnMn2III)-Mn-II(mu(3)-O)](6+) cores in 1 could be clearly assigned from bond valence sum calculations and bond distances. The [Mn-4(mu(3)-O)(2)](8+) core in the anionic complexes in the structures of 4 center dot ThCO2H center dot CH2 Cl-2 and 8 center dot CH2Cl2 has an all Mn-III oxidation level and butterfly-like arrangement. The magnetic properties of 4-8 were investigated by variable temperature magnetic susceptibility and magnetization measurements. Similar magnetic behavior was observed for the [Mn-4(III)(mu(3)-O)(2)](8+) butterfly-core compounds 4, 6-8, with antiferromagnetic interactions between pairs of manganese ions with amplitude of similar to 14.5 cm(-1) and similar to 4.6 cm(-1) for the Mn-b center dot center dot center dot Mn-b and Mn-b center dot center dot center dot Mn-w coupling, respectively (b = body, w = wing). Changing the Ar-ligand size in [Mn4O2(O2CAr)(9)(L)](-) does not have a significant effect on the magnetic properties of these butterfly clusters. (c) 2013 Elsevier B.V. All rights reserved.