PUB - Publikationen an der Universität Bielefeld

A comprehensive synthetic, structural, mass spectrometrical, FT-IR and UV/Vis spectroscopic, electrochemical, and magnetic study on [(Mn6MnIII)-Mn-III](3+) (= [{(talen(t-Bu2)) Mn-3(III)}(2){Mn-III(CN)(6)}](3+)) is presented. The high stability of [(Mn6MnIII)-Mn-III](3+) in solution allows the preparation of different salts and solvates: [(Mn6MnIII)-Mn-III](BPh4)(3)center dot 3MeOH center dot 3MeCN center dot 3Et(2)O (1), [(Mn6MnIII)-Mn-III(MeOH)(4)](BPh4)(3)center dot 5MeOH (2), [(Mn6MnIII)-Mn-III(MeOH)(6)](BF4)(3)center dot 9MeOH (3), [(Mn6MnIII)-Mn-III(MeOH)(6)](PF6)(2)(OAc)center dot 11MeOH (4), and [(Mn6MnIII)-Mn-III(MeOH)(6)](lactate)(3)center dot 5MeOH center dot 10H(2)O (5). The molecular structure of [(Mn6MnIII)-Mn-III](3+) is closely related to the already published [Mn(6)(III)Mc](3+) complexes (M-c = Cr-III, Fe-III, Co-III). ESI mass spectra exhibit the signal of the [{(talen(t-Bu2))Mn-3(III)}(2){Mn-III(CN)(6)}](3+) trication. FT-IR spectra show the characteristic bands of the triplesalen ligand in [Mn(6)(III)Mc](3+) and the symmetric nu(C N) vibration of the [Mn-III(CN)(6)](3-) unit at 2135 cm(-1). UV/Vis spectra are dominated by intense transitions of the trinuclear Mn-3(III) triplesalen subunits above 20 000 cm(-1). The electrochemical studies establish the occurrence of ligand-centered oxidations at approximate to 1.0 V vs. Fc(+)/Fc, an oxidation of the central Mn-III at 0.78 V, and a series of reductions of the terminal Mn-III 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 Mn-III at low temperatures as inferred from a previous ab initio study. The spin-Hamiltonian simulations indicate Mn-III-Mn-III 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 Mn-III ion, while D-Mn = -3.1 to -5.0 cm(-1). The differences in the exchange parameters and the relaxation behavior of the [(Mn6MnIII)-Mn-III](3+) compounds are rationalized in terms of subtle variations in the molecular structures, especially regarding the distortion of the central [Mn-III(CN)(6)](3-) core and the ligand folding. In comparison with the other [(Mn6Mc)-M-III](3+) compounds, this allows us to establish some general magnetostructural correlations for this class of complexes.