MnIII-NiII-MnIII linear-type trinuclear complexes bridged by oximate groups were selectively synthesized by the assembly reaction of [Mn2(5-Rsaltmen)2(H2O) 2](ClO4)2 (5-Rsaltmen2- = N,N′-(1,1,2,2-tetramethylethylene) bis(5-R-salicylideneiminate); R = Cl, Br) with [Ni(pao)2(phen)] (pao- = pyridine-2-aldoximate; phen = 1,10-phenanthroline) in methanol/ water: [Mn2(5-Rsaltmen) 2Ni(pao)2(phen)](ClO4)2 (R = Cl, 1; R = Br, 2). Structural analysis revealed that the [MnIII-ON-Ni II-NO-MnIII] skeleton of these trimers is in every respect similar to the repeating unit found in the previously reported series of 1D materials [Mn2(saltmen)2Ni(pao)2(L 1)2](A)2 (L1 = pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole; A = ClO4-, BF4-, PF6-, ReO4 -). Recently, these 1D compounds have attracted a great deal of attention for their magnetic properties, since they exhibit slow relaxation of the magnetization (also called single-chain magnet (SCM) behavior). This unique magnetic behavior was explained in the framework of Glauber's theory, generalized for chains of ferromagnetically coupled anisotropic spins. Thus, in these 1D compounds, the [MnIII-ON-NiII-NO-Mn III] unit was considered as an ST = 3 anisotropic spin. Direct-current magnetic measurements on 1 and 2 confirm their ST = 3 ground state and strong uniaxial anisotropy (D/kB ≈ -2.4 K), in excellent agreement with the magnetic characteristic deduced in the study on the SCM series. The ac magnetic susceptibility of these trimers is strongly frequency-dependent and characteristic of single-molecule magnet (SMM) behavior. The relaxation time τ shows a thermally activated (Arrhenius) behavior with τ0 ≈ 1 × 10-7 s and Δeff/ kB ≈ 18 K. The effective energy barrier for reversal of the magnetization Δeff is consistent with the theoretical value (21 K) estimated from |D|ST2. The present results reinforce consistently the interpretation of the SCM behavior observed in the [Mn 2(saltmen)2Ni(PaO)2(L1) 2](A)2 series and opens new perspectives to design single-chain magnets.
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