New mixed-valence Mn6II/III complexes bearing oximato and azido ligands: Synthesis, and structural and magnetic characterization

Abstract

The combined use of the anion of methyl 2-pyridyl ketone oxime (mpko -) and azides (N3-) in non-carboxylate Mn chemistry has afforded two new Mn6 clusters, [Mn6O 3(N3)3(mpko)6(H2O) 3](ClO4J2 (1) and [Mn6O3(N3) 5(mpko)6(H2O)] (2), which are mixed-valence (MnII, 5 MnIII). The 1:1:1:1 reaction of Mn(C1O 4)2·6H2O, mpkoH, NaN3 and NEt3 in MeOH gave the cationic complex 1, while a similar reaction using additional NaO2CMe led instead to the neutral complex 2. The structurally unprecedented cores of the two cages are very similar, and contain the six Mn ions in a topology comprising three vertex-sharing oxide-centered triangles bridged by two end-on azides. Variable-temperature, solidstate dc and ac magnetization studies were carried out for 1 and 2 in the 1.8-300 K range. The data reveal S = 5/2 ground states for both complexes, and fitting of magnetization vs. field (H) and temperature (T) data by matrix diagonalization for 1 gave S = 5/2, D = -1.4(3) cm-1, and g = 1.99(1), where D is the axial zero-field splitting (ZFS) parameter. The combined results demonstrate the versatility of 2-pyridyl ketone oxime anions in the presence of suitable ancillary ligands, such as azides, for the synthesis of new Mn clusters, without requiring the co-presence of carboxylate ligands. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.