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Issue 41, 2012
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Structural influences on the exchange coupling and zero-field splitting in the single-molecule magnet [MnIII6MnIII]3+

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Abstract

A comprehensive synthetic, structural, mass spectrometrical, FT-IR and UV/Vis spectroscopic, electrochemical, and magnetic study on [MnIII6MnIII]3+ (= [{(talent-Bu2)MnIII3}2{MnIII(CN)6}]3+) is presented. The high stability of [MnIII6MnIII]3+ in solution allows the preparation of different salts and solvates: [MnIII6MnIII](BPh4)3·3MeOH·3MeCN·3Et2O (1), [MnIII6MnIII(MeOH)4](BPh4)3·5MeOH (2), [MnIII6MnIII(MeOH)6](BF4)3·9MeOH (3), [MnIII6MnIII(MeOH)6](PF6)2(OAc)·11MeOH (4), and [MnIII6MnIII(MeOH)6](lactate)3·5MeOH·10H2O (5). The molecular structure of [MnIII6MnIII]3+ is closely related to the already published [MnIII6Mc]3+ complexes (Mc = CrIII, FeIII, CoIII). ESI mass spectra exhibit the signal of the [{(talent-Bu2)MnIII3}2{MnIII(CN)6}]3+ trication. FT-IR spectra show the characteristic bands of the triplesalen ligand in [MnIII6Mc]3+ and the symmetric ν(C[triple bond, length as m-dash]N) vibration of the [MnIII(CN)6]3− unit at 2135 cm−1. UV/Vis spectra are dominated by intense transitions of the trinuclear MnIII3 triplesalen subunits above 20 000 cm−1. The electrochemical studies establish the occurrence of ligand-centered oxidations at ≈1.0 V vs. Fc+/Fc, an oxidation of the central MnIII at 0.78 V, and a series of reductions of the terminal MnIII ions between −0.6 and −1.2 V. AC magnetic measurements indicate single-molecule magnet (SMM) behavior for all compounds. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting with full consideration of the relative orientation of the D-tensors, and Zeeman interaction, taking into account the diamagnetic nature of the central MnIII at low temperatures as inferred from a previous ab initio study. The spin-Hamiltonian simulations indicate MnIII–MnIII interactions in the −0.37 to −0.70 cm−1 range within the trinuclear triplesalen subunits and in the −0.02 to +0.23 cm−1 range across the central MnIII ion, while DMn = −3.1 to −5.0 cm−1. The differences in the exchange parameters and the relaxation behavior of the [MnIII6MnIII]3+ compounds are rationalized in terms of subtle variations in the molecular structures, especially regarding the distortion of the central [MnIII(CN)6]3− core and the ligand folding. In comparison with the other [MnIII6Mc]3+ compounds, this allows us to establish some general magnetostructural correlations for this class of complexes.

Graphical abstract: Structural influences on the exchange coupling and zero-field splitting in the single-molecule magnet [MnIII6MnIII]3+

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Publication details

The article was received on 17 Jul 2012, accepted on 30 Aug 2012 and first published on 31 Aug 2012


Article type: Paper
DOI: 10.1039/C2DT31590D
Citation: Dalton Trans., 2012,41, 12942-12959
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    Structural influences on the exchange coupling and zero-field splitting in the single-molecule magnet [MnIII6MnIII]3+

    V. Hoeke, M. Heidemeier, E. Krickemeyer, A. Stammler, H. Bögge, J. Schnack and T. Glaser, Dalton Trans., 2012, 41, 12942
    DOI: 10.1039/C2DT31590D

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