Employment of methyl 2-pyridyl ketone oxime in manganese non-carboxylate chemistry: MnII2MnIV and MnII 2MnIII6 complexes
Date
2009Author
Stoumpos, Constantinos C.Stamatatos, Theocharis C.
Sartzi, H.
Roubeau, O.
Tasiopoulos, Anastasios J.
Nastopoulos, Vassilios
Teat, S. J.
Christou, George
Perlepes, Spyros P.
ISSN
1477-9226Source
Dalton TransactionsIssue
6Pages
1004-1015Google Scholar check
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The employment of the anion of methyl 2-pyridyl ketone oxime (mpko -) as a tridentate chelating/bridging ligand in manganese chemistry is described. The inorganic anion (Br-, ClO4-) used in the reaction affects the identity of the product. The reaction of MnBr2 and one equivalent of mpkoH in the presence of a base affords [Mn3(OMe)2(mpko)4Br2] (3), which is mixed-valence (2MnII, MnIV). The central MnIV atom in each of the two, crystallographically independent, centrosymmetric molecules is coordinated by four oximate oxygen atoms belonging to the η1:η1:η1:μ mpko- ligands, and two η1:μ MeO- groups, while six coordination at each terminal MnII atom is completed by four nitrogen atoms belonging to the 'chelating' part of two mpko- ligands, and one Br- ion. The MnII atoms have trigonal prismatic coordination geometry. The reaction of Mn(ClO4)2· 6H2O, mpkoH and OH- (1:2:1) in MeOH gives [Mn 8O4(OMe)(mpko)9(mpkoH)](ClO4) 4 (4), which is also mixed-valence (2MnII, 6Mn III) and possesses the novel [Mn8(μ3-O) 4(μ-OMe)(μ-OR″)2]11+ core. The latter possesses a U-shaped sequence of four fused {MnIIMn III2(μ3-O)}6+ triangular units, with a MnIII-MnIII edge being shared between the central triangles. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on complexes 3 and 4. The dc susceptibility data for 3 in the 5.0-300 K range have been fit to a model with two J values, revealing weak ferromagnetic MnII⋯MnIV (J = +3.4 cm -1) and MnII⋯MnII (J′ = +0.3 cm-1) exchange interactions. Fitting of the magnetization vs. H/T data by matrix diagonalization and including only axial anisotropy (ZFS, D) gave ground state spin (S) and D values of S = 13/2, D = +0.17 cm-1 for 3 and S = 3, D = -0.09 cm-1 for 4. The combined work demonstrates the usefulness of mpko- in the preparation of interesting Mn clusters, without requiring the co-presence of carboxylate ligands. © The Royal Society of Chemistry 2009.