PUB - Publikationen an der Universität Bielefeld

The reaction of the tris(tetradentate) triplesalen ligand H(6)talen(t-Bu2), which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn-II salts under aerobic conditions affords, in situ, the trinuclear Mn-III triplesalen complexes [(talen(2)(t-Bu)){Mn-III(solv)(n)}(3)](3+). These can be used as molecular building blocks in the reaction with [Fe(CN)(6)](3-) as a hexaconnector to form the heptanuclear complex [{(talen(2)(t-Bu)){Mn-III(solv)(n)}(3)}(2){Fe-III(CN)(6)}](3+) ([(Mn6FeIII)-Fe-III](3+)). The regular ligand folding observed in the trinuclear triplesalen complexes preorganizes the three metal ions for the reaction of three facially coordinated nitrogen atoms of a hexacyanometallate and provides a driving force for the formation of the heptanuclear complexes [(M6Mc)-M-t](n+) (M-t, terminal metal ion of the triplesalen building block; Me, central metal ion of the hexacyanometallate) by molecular recognition, as has already been demonstrated for the single-molecule magnet [(Mn6CrIII)-Cr-III](3+)center dot [{(talen(2)(t-Bu))(Mn-III(MeOH))(3)}(2){Fe-III(CN)(6)}][Fe-III(CN)(6)] (1) was characterized by single-crystal X-ray diffraction, FTIR, ESI- and MALDI-TOF-MS, Mossbauer spectroscopy, and magnetic measurements. The molecular structure of [(Mn6FeIII)-Fe-III](3+) is overall identical to that of [(Mn6CrIII)-Cr-III](3+) but exhibits a different ligand folding of the Mn-III salen subunits with a helical distortion. The Mossbauer spectra demonstrate a stronger distortion from octahedral symmetry for the central [Fe(CN)(6)](3-) in comparison to the ionic [Fe(CN)(6)](3-). At low temperatures in zero magnetic fields, the Mossbauer spectra show magnetic splittings indicative of slow relaxation of the magnetization on the Mossbauer time scale. Variable-temperature-variable-field and yen versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction taking into account the relative orientation of the D tensors. Satisfactory reproduction of the experimental data has been obtained for parameters sets J(Mn-Mn) = -(0.85 +/- 0.15) cm(-1), J(Fe-Mn) = +(0.70 +/- 0.30) cm(-1), and D-Mn = -(3.0 +/- 0.7) cm(-1). Comparing these values to those of [Mn Cr-III(6)III](3+) provides insight into why [(Mn6FeIII)-Fe-III](3+) is not a single-molecule magnet.