New Mixed-Valence Mn-6(II/III) Complexes Bearing Oximato and Azido Ligands: Synthesis, and Structural and Magnetic Characterization
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Lampropoulos, C.
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
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Lampropoulos, C.
(EN)
The combined use of the anion of methyl 2-pyridyl ketone oxime (mpko(-)) and azides (N-3(-)) in non-carboxylate Mn chemistry has afforded two new Mn-6 clusters, [Mn6O3(N-3)(3)-(mpko)(6)(H2O)(3)](ClO4)(2) (1) and [Mn(6)O3(N-3)(5)(mpko)(6)(H2O)] (2), which are mixed-valence (Mn-II, 5 Mn-III). The 1:1:1:1 reaction of Mn(ClO4)(2)center dot 6H(2)O, 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, solid-state 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.
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