title: Strong and anisotropic superexchange in the single-molecule magnet (SMM) [MnIII(6)OsIII]3+: promoting SMM behavior through 3d-5d transition metal substitution.
abstract: The reaction of the in situ generated trinuclear triplesalen complex [(talent-Bu2)MnIII3(solv)n]3+ with (Ph4P)3[OsIII(CN)6] and NaClO4·H2O affords [MnIII6OsIII](ClO4)3 (= [{(talent-Bu2)MnIII3}2{OsIII(CN)6}](ClO4)3) in the presence of the oxidizing agent [(tacn)2NiIII](ClO4)3 (tacn =1,4,7-triazacyclononane), while the reaction of [(talent-Bu2)MnIII3(solv)n]3+ with K4[OsII(CN)6] and NaClO4·H2O yields [MnIII6OsII](ClO4)2 under an argon atmosphere. The molecular structure of [MnIII6OsIII]3+ as determined by single-crystal X-ray diffraction is closely related to the already published [MnIII6Mc]3+ complexes (Mc = CrIII, FeIII, CoIII, MnIII). The half-wave potential of the OsIII/OsII couple is E1/2 = 0.07 V vs Fc+/Fc. The FT-IR and electronic absorption spectra of [MnIII6OsII]2+ and [MnIII6OsIII]3+ exhibit distinct features of dicationic and tricationic [MnIII6Mc]n+ complexes, respectively. The dc magnetic data (μeff vs T, M vs B, and VTVH) of [MnIII6OsII]2+ are successfully simulated by a full-matrix diagonalization of a spin-Hamiltonian including isotropic exchange, zero-field splitting with full consideration of the relative orientation of the D-tensors, and Zeeman interaction, indicating antiferromagnetic MnIII–MnIII interactions within the trinuclear triplesalen subunits (JMn–Mn(1) = −(0.53 ± 0.01) cm–1, Ĥex = −2∑i<j JijŜi·Ŝj) as well as across the central OsII ion (JMn–Mn(2,cis) = −(0.06 ± 0.01) cm–1, JMn–Mn(2,trans) = −(0.15 ± 0.01) cm–1), while DMn = −(3.9 ± 0.1) cm–1. The μeff vs T data of [MnIII6OsIII]3+ are excellently reproduced assuming an anisotropic Ising-like OsIII–MnIII superexchange with a nonzero component JOs–Mn(aniso) = −(11.0 ± 1.0) cm–1 along the Os–Mn direction, while JMn–Mn = −(0.9 ± 0.1) cm–1 and DMn = −(3.0 ± 1.0) cm–1. Alternating current measurements indicate a slower relaxation of the magnetization in the SMM [MnIII6OsIII]3+ compared to the 3d analogue [MnIII6FeIII]3+ due to the stronger and anisotropic Mc–MnIII exchange interaction.
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld , Universitätsstraße 25, D-33615 Bielefeld, Germany.
authors.forename: Veronika
authors.initials: V
authors.lastname: Hoeke
authors.forename: Anja
authors.initials: A
authors.lastname: Stammler
authors.forename: Hartmut
authors.initials: H
authors.lastname: Bögge
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schnack
authors.forename: Thorsten
authors.initials: T
authors.lastname: Glaser