Strong and Anisotropic Superexchange in the Single-Molecule Magnet (SMM) [MnIII6OsIII]3+: Promoting SMM Behavior through 3d–5d Transition Metal Substitution

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• 作者：Veronika Hoeke ; Anja Stammler ; Hartmut B?gge ; Jürgen Schnack ; Thorsten Glaser
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：January 6, 2014
• 年：2014
• 卷：53
• 期：1
• 页码：257-268
• 全文大小：683K
• ISSN：1520-510X

文摘

The reaction of the in situ generated trinuclear triplesalen complex [(talen^t-Bu₂)Mn^III₃(solv)_n]³⁺ with (Ph₄P)₃[Os^III(CN)₆] and NaClO₄路H₂O affords [Mn^III₆Os^III](ClO₄)₃ (= [{(talen^t-Bu₂)Mn^III₃}₂{Os^III(CN)₆}](ClO₄)₃) in the presence of the oxidizing agent [(tacn)₂Ni^III](ClO₄)₃ (tacn =1,4,7-triazacyclononane), while the reaction of [(talen^t-Bu₂)Mn^III₃(solv)_n]³⁺ with K₄[Os^II(CN)₆] and NaClO₄路H₂O yields [Mn^III₆Os^II](ClO₄)₂ under an argon atmosphere. The molecular structure of [Mn^III₆Os^III]³⁺ as determined by single-crystal X-ray diffraction is closely related to the already published [Mn^III₆M^c]³⁺ complexes (M^c = Cr^III, Fe^III, Co^III, Mn^III). The half-wave potential of the Os^III/Os^II couple is E_1/2 = 0.07 V vs Fc⁺/Fc. The FT-IR and electronic absorption spectra of [Mn^III₆Os^II]²⁺ and [Mn^III₆Os^III]³⁺ exhibit distinct features of dicationic and tricationic [Mn^III₆M^c]ⁿ⁺ complexes, respectively. The dc magnetic data (渭_eff vs T, M vs B, and VTVH) of [Mn^III₆Os^II]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 Mn^III鈥揗n^III interactions within the trinuclear triplesalen subunits (J_Mn鈥揗n⁽¹⁾ = 鈭?0.53 卤 0.01) cm^鈥?, 膜_ex = 鈭?鈭?sub>i<j J_ij艤_i路艤_j) as well as across the central Os^II ion (J_Mn鈥揗n^(2,cis) = 鈭?0.06 卤 0.01) cm^鈥?, J_Mn鈥揗n^(2,trans) = 鈭?0.15 卤 0.01) cm^鈥?), while D_Mn = 鈭?3.9 卤 0.1) cm^鈥?. The 渭_eff vs T data of [Mn^III₆Os^III]³⁺ are excellently reproduced assuming an anisotropic Ising-like Os^III鈥揗n^III superexchange with a nonzero component J_Os鈥揗n^(aniso) = 鈭?11.0 卤 1.0) cm^鈥? along the Os鈥揗n direction, while J_Mn鈥揗n = 鈭?0.9 卤 0.1) cm^鈥? and D_Mn = 鈭?3.0 卤 1.0) cm^鈥?. Alternating current measurements indicate a slower relaxation of the magnetization in the SMM [Mn^III₆Os^III]³⁺ compared to the 3d analogue [Mn^III₆Fe^III]³⁺ due to the stronger and anisotropic M^c鈥揗n^III exchange interaction.