ic7020269_si_006.cif (69.83 kB)
Employment of 2,6-Diacetylpyridine Dioxime as a New Route to High Nuclearity Metal Clusters: Mn6 and Mn8 Complexes
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posted on 2008-02-04, 00:00 authored by Theocharis C. Stamatatos, Brian S. Luisi, Brian Moulton, George ChristouThe employment of the anion of 2,6-diacetylpyridine dioxime (dapdoH2) as a pentadentate chelate in transition
metal cluster chemistry is reported. The syntheses, crystal structures, and magnetochemical characterization are
described for [Mn6O2(OMe)2(dapdo)2(dapdoH)4](ClO4)2 (1), [Mn6O2(OMe)2(dapdo)2(dapdoH)4][Ca(NO3)4] (2), and
[Mn8O4(OH)4(OMe)2(N3)2(dapdo)2(dapdoH)2(H2O)2] (3). The reaction of [Mn3O(O2CMe)6(py)3](ClO4) with 3 equiv of
dapdoH2 (with or without 2 equiv of NEt3) in MeOH gave 1. The same cation, but with a [Ca(NO3)4]2- anion, was
found in complex 2, which was obtained from the reaction in MeOH between Mn(NO3)2, Ca(NO3)2, and dapdoH2
in the presence of NEt3. In contrast, addition of NaN3 to several reactions comprising MnCl2, dapdoH2, and NEt3
in MeOH gave the octanuclear complex 3. Complexes 1−3 all possess rare topologies and are mixed-valence:
2MnII, 4MnIII for 1 and 2, and 2MnII, 6MnIII for 3. The core of the cation of 1 and 2 consists of two edge-sharing
Mn4 tetrahedra at the center of each of which is a μ4-O2- ion. Peripheral ligation is provided by two μ-OMe-, four
μ-dapdoH-, and two μ3-dapdo2- groups. The core of 3 consists of two [MnIIMnIII3(μ3-O)2]7+ “butterfly” units linked
together by one of the μ3-O2- ions, which thus becomes μ4. Peripheral ligation is provided by four μ-OMe-, two
μ-OH-, two μ-dapdoH-, and two μ4-dapdo2- groups. Variable-temperature, solid-state dc and ac magnetization
studies were carried out on complexes 1−3 in the 5.0−300 K range; the data for 1 and 2 are identical. Fitting of
the obtained magnetization versus field (H) and temperature (T) data by matrix diagonalization and including only
axial anisotropy (zero-field splitting, D) established that 1 possesses an S = 5 ground state with D = −0.24 cm-1.
For 3, low-lying excited states precluded obtaining a good fit from the magnetization data, and the ground state
was instead determined from the ac data, which indicated an S = 1 ground state for 3. The combined work
demonstrates the ligating flexibility of pyridyl-dioxime chelates and their usefulness in the synthesis of new polynuclear
Mnx clusters without requiring the co-presence of carboxylate ligands.
