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Two Mn70 torus-like molecules have been obtained from the alcoholysis in EtOH and 2-ClC2H4OH of [Mn12O12(O2CMe)16(H2O)4]·4H2O·2MeCO2H (1) in the presence of NBun4MnO4 and an excess of MeCO2H. The reaction in EtOH afforded [Mn70O60(O2CMe)70(OEt)20(EtOH)16(H2O)22] (2), whereas the reaction in ClC2H4OH gave [Mn70O60(O2CMe)70(OC2H4Cl)20(ClC2H4OH)18(H2O)22] (3). The complexes are nearly isostructural, each possessing a Mn70 torus structure consisting of alternating near-linear [Mn3(μ3-O)4] and cubic [Mn4(μ3-O)2(μ3-OR)2] (R = OEt, 2 R = OC2H4Cl, 3) subunits, linked together via syn,syn-μ-bridging MeCO2- and μ3-bridging O2- groups. 2 and 3 have an overall diameter of ∼4 nm and crystallize as highly ordered supramolecular nanotubes. Alternating current (ac) magnetic susceptibility measurements, performed on microcrystalline samples in the 1.8-10 K range and a 3.5 G ac field with oscillation frequencies in the 5-1500 Hz range, revealed frequency-dependent out-of-phase signals below ∼2.4 K for both molecules indicative of the slow magnetization relaxation of single-molecule magnets (SMMs). Single-crystal, magnetization vs field studies on both complexes revealed hysteresis loops below 1.5 K, thus confirming 2 and 3 to be new SMMs. The hysteresis loops do not show the steps that are characteristic of quantum tunneling of magnetization (QTM). However, low-temperature studies revealed temperature-independent relaxation rates below ∼0.2 K for both compounds, the signature of ground state QTM. Fitting of relaxation data to the Arrhenius equation gave effective barriers for magnetization reversal (Ueff) of 23 and 18 K for 2 and 3, respectively. Because the Mn70 molecule is close to the classical limit, it was also studied using a method based on the Néel-Brown model of thermally activated magnetization reversal in a classical single-domain magnetic nanoparticle. The field and sweep-rate dependence of the coercive field was investigated and yielded the energy barrier, the spin, the Arrhenius pre-exponential, and the cross-over temperature from the classical to the quantum regime. The validity of this approach emphasizes that large SMMs can be considered as being at or near the quantum-classical nanoparticle interface. © 2016 American Chemical Society. 55 7 3419 3430 Cited By :5

The syntheses, structures, and magnetic properties are reported of the mixed-metal complexes [Ce4Mn10O10(OMe) 6(O2-CPh)16(NO3)2(MeOH) 2(H2O)2] (1) and [Th6Mn 10O22(OH)2(O2CPh) 16-(NO3)2(H2O)8] (2), which were both prepared by the reaction of (NBun4) [Mn4O2(O2CPh)9(H2O)] (3) with a source of the heterometal in MeCN/MeOH. Complexes 1 and 2 crystallize in the monoclinic space group C2/c and the triclinic space group P1, respectively. Complex 1 consists of 10 MnIII, 2 CeIV, and 2 Ce IV atoms and possesses a very unusual tubular [Ce4Mn 10O10(OMe)6]18+ core. Complex 2 consists of 10 MnIV and 6 ThIV atoms and possesses a [Th6Mn10O22(OH)2]18+ core with the metal atoms arranged in layers with a 2:3:6:3:2 pattern. Peripheral ligation around the cores is provided by 16 bridging benzoates, 2 chelating nitrates, and either (i) 2 each of terminal H2O and MeOH groups in 1 or (ii) 8 terminal H2O groups in 2. Complex 1 is the largest mixed-metal Ce/Mn cluster and the first 3d/4f cluster with mixed-valency in its lanthanide component, while complex 2 is the first Th/Mn cluster and the largest mixed transition metal/actinide cluster to date. Solid-state dc and ac magnetic susceptibility measurements on 1 and 2 establish that they possess S = 4 and 3 ground states, respectively. Ac susceptibility studies on 1 revealed nonzero frequency-dependent out-of-phase (χM″) signals at temperatures below 3 K complex 2 displays no χM″ signals. However, single-crystal magnetization vs dc field scans at variable temperatures and variable sweep-rates down to 0.04 K on 1 revealed no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by hydrogen bonds involving CeIII-bound ligands. Complex 1 is thus concluded not to be a single-molecule magnet (SMM), and the combined results thus represent a caveat against taking such ac signals as sufficient proof of a SMM. © 2007 American Chemical Society. 46 8 3105 3115 Cited By :55

A new synthetic procedure has been developed in Mn cluster chemistry involving reductive aggregation of permanganate (MnO4-) ions in MeOH in the presence of benzoic acid, and the first products from its use are described. The reductive aggregation of NBun 4MnO4 in MeOH/benzoic acid gave the new 4MnIV, 8MnIII anion [Mn12O12(OMe)2(O 2CPh)16(H2O)2]2-, which was isolated as a mixture of two crystal forms (NBun 4)2[Mn12O12(OMe)2-(O 2CPh)16(H2O)2]·2H 2O·4CH2Cl2 (1a) and (NBu n4)2[Mn12O12(OMe) 2(O2CPh)16(H2O)2] ·2H2O·CH2Cl2 (1b). The anion of 1 contains a central [MnIV4(μ3-O) 2(μ-O)2(μ-OMe)2]6+ unit surrounded by a nonplanar ring of eight MnIII atoms that are connected to the central Mn4 unit by eight bridging μ3-O2- ions. This compound is very similar to the well-known [Mn12O12(O2CR)16(H 2O)4] complexes (hereafter called "normal Mn 12"), with the main difference being the structure of the central cores. Longer reaction times (∼2 weeks) led to isolation of polymeric [Mn(OMe)(O2CPh)2]n (2), which contains a linear chain of repeating [MnIII(μ-O 2CPh)2(μ-OMe)MnIII] units. The chains are parallel to each other and interact weakly through π-stacking between the benzoate rings. When KMnO4 was used instead of NBun 4MnO4, two types of compounds were obtained, [Mn 12O12(O2CPh)16(H2O) 4] (3), a normal Mn12 complex, and [Mn4O 2(O2CPh)8(MeOH)4]·2MeOH (4·2MeOH), a new member of the Mn4 butterfly family. The cyclic voltammogram of 1 exhibits three irreversible processes, two reductions and one oxidation. One-electron reduction of 1 by treatment with 1 equiv of l- in CH2Cl2 gave (NBun 4)[Mn12O12(O2CPh) 16(H2O)3]·6CH2Cl2 (5·6CH2Cl2), a normal Mn12 complex in a one-electron reduced state. The variable-temperature magnetic properties of 1, 2, and 5 were studied by both direct current (dc) and alternating current (ac) magnetic susceptibility measurements. Variable-temperature dc magnetic susceptibility studies revealed that (i) complex 1 possesses an S = 6 ground state, (ii) complex 2 contains antiferromagnetically coupled chains, and (iii) complex 5 is a typical [Mn12]- cluster with an S = 19/2 ground state. Variable-temperature ac susceptibility measurements suggested that 5 and both isomeric forms of 1 (1a,b) are single-molecule magnets (SMMs). This was confirmed by the observation of hysteresis loops in magnetization vs dc field scans. In addition, 1a,b, like normal Mn12 clusters, display both faster and slower relaxing magnetization dynamics that are assigned to the presence of Jahn-Teller isomerism. © 2005 American Chemical Society. 44 18 6324 6338

Four heterometallic, enneanuclear Mn8Ce clusters [Mn 8CeO8(O2CMe)12(H2O) 4] (4), [Mn8CeO8(O2CMe) 12(py)4] (5), [Mn8CeO8(O 2CPh)12(MeCN)4] [Mn8CeO 8(O2CPh)12(dioxane)4] (6), and [Mn8CeO8(O2CCHPh2) 12(H2O)4] (7) have been prepared by various methods. Their cores are essentially isostructural and comprise a nonplanar, saddlelike [MnIII8O8]8+ loop containing a central CeIV ion attached to the eight μ3-O2- ions. Peripheral ligation around the [Mn 8CeO8]12+ core is provided by eight μ- and four μ3-O2CR- groups. Terminal ligation on four MnIII atoms is provided by H2O in 4 and 7, pyridine in 5, and MeCN/dioxane in 6. Solid-state magnetic susceptibility studies, fits of dc magnetization vs field and temperature data, and in-phase ac susceptibility studies in a zero dc field have established that complexes 4, 5, and 7 possess S = 16, S = 4 or 5, and S = 6 ± 1 spin ground states, respectively, but in all cases there are very low-lying excited states. The large variation in the ground-state spins for this isostructural family is rationalized as due to a combination of weak exchange interactions between the constituent MnIII atoms, and the presence of both nearest-neighbor and next-nearest-interactions of comparable magnitudes. Magnetization vs applied dc field sweeps on single crystals of 4·4H2O and 7·4H2O·3MeCN·2CH2Cl2 down to 0.04 K have established that these two complexes are new single-molecule magnets (SMMs). The former also shows an exchange-bias, a perturbation of its single-molecule properties from very weak intermolecular interactions mediated by hydrogen-bonding interactions with lattice-water molecules of crystallization. © 2008 American Chemical Society. 47 11 4832 4843 Cited By :55

The syntheses of the first mixed-metal CeIVMnIV complexes are reported. [CeMn2O3(O2CMe)(NO 3)4(H2O)2(bpy)2]-(NO 3) (1 bpy = 2,2′-bipyridine) was obtained from the reaction of Mn(NO3)2·xH2O and bpy with (NH 4)2Ce(NO3)6 in a 1:1:2 molar ratio in 25% aqueous acetic acid. The complexes [CeMn6O9(O 2CR)9(X)(H2O)2]y+ (R = Me, X = NO3-, y = 0 (2) R = Me, X = MeOH, y = +1 (3) R = Et, X = NO3-, y = 0 (7)) were obtained from reactions involving a [Mn(O2CR)2]·4H2O/Ce IV ratio of ∼1:1.5 in concentrated aqueous carboxylic acid. A related reaction in less-concentrated aqueous acetic acid and in the presence of L (where L = 2-hydroxy-6-methylpyridine (mhpH), 2-pyrrolidinone (pyroH), or pyridine (py)) gave [Ce3Mn2O6(O 2CMe)6(NO3)2(L)a(H 2O)b] (L = mhpH, a = 4, b = 0 (4) L = pyroH, a = 2, b = 3 (5)) and {{(pyH)3[Ce3Mn2O6(O 2CMe)7.5(NO3)3]·(HO 2CMe)0.5·(H2O)2} 2(NO3)}n (6), respectively. Solid-state magnetic susceptibility (χM) data for compounds 1, , and 5 were fit to the theoretical χMT versus T expression for a Mn IV2 complex derived using the isotropic Heisenberg spin Hamiltonian (H = -2JŜ1Ŝ2) and the Van Vleck equation. The obtained fit parameters were (in the format J, g) 1, -45.7(3) cm-1, 1.95(5) 4, -0.40(10) cm-1, 2.0(1) and 5, -0.34(10) cm-1, 2.0(1), where J is the exchange interaction constant between the two MnIV ions. The data for compound 3 were fit by a matrix diagonalization method that gave J1 = -5.8 cm-1, J 2 = -0.63 cm-1, J3 ≈ 0, and g = 2.0(1), where J1 and J2 are the exchange interactions for the [MnIV2O2(O2-CMe)] and [Mn IV2O(O2CMe)2] units, respectively, and J3 for a uniform next-nearest-neighbor interaction. Theoretical estimates of the exchange constants in compounds 1 and 3 obtained with the ZILSH method were in excellent and good agreement, respectively, with the values obtained from fits of the magnetization data. The difference for 3 is assigned to the presence of the Ce4+ ion, and atomic bond indices obtained from the ZILSH calculations were used to rationalize the values of the various exchange constants based on metal-ligand bond strengths. © 2007 American Chemical Society. 46 23 9678 9691 Cited By :47