High Spin Molecules: Unusual Magnetic Susceptibility Relaxation Behavior of a Dodecanuclear Manganese Aggregate in Two Oxidation States

Tsai, Hui-Lien; Eppley, Hilary J.; Vries, N. De; Folting, Kirsten; Christou, George; Hendrickson, David N.

doi:10.1080/10587259508031877

Cited by 15 publications

(16 citation statements)

References 9 publications

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“…One area in which high-spin molecules are encountered on a relatively frequent basis is manganese cluster chemistry. ,, Spin values of S ≤ 12 have been observed; for calibration, the largest S value observed to date in a molecular species is S ≈ 33 / 2 in a cocrystallized mixture of Fe 17 and Fe 19 clusters . We and others have reported several Mn x clusters with S values ≥ 4, ,,,, and some of these have also proven to be single-molecule magnets. In this paper, we describe two new Mn 6 clusters of formula [Mn 6 O 4 X 4 (R 2 dbm) 6 ] (X = Cl - , Br - ).…”

Section: Introductionmentioning

confidence: 88%

“…These include the topological arrangement of the paramagnetic ions, the nature (ferromagnetic or antiferromagnetic) of the inter-ion exchange interactions, and the presence of spin frustration effects from the presence of competing interactions of comparable magnitude. In addition, it has recently become apparent that a relatively large ground-state S value is one of the necessary requirements for molecules to be able to exhibit the new phenomenon of single-molecule magnetism. − Another requirement is a significant magnetoanisotropy as reflected in the zero-field splitting (ZFS) parameter D , which needs also to be negative. The development of synthetic procedures to new examples of high-spin molecules is thus of continuing interest.…”

Section: Introductionmentioning

confidence: 99%

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High-Spin Molecules: Hexanuclear Mn^III Clusters with [Mn₆O₄X₄]⁶⁺ (X = Cl^-, Br^-) Face-Capped Octahedral Cores and S = 12 Ground States

et al. 1999

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Reaction of R2dbmH (R = H, Me, Et; dbmH is dibenzoylmethane) with MnCl3 (generated in situ from MnCl2 and MnO4 -) in MeCN yields the five-coordinate, square-pyramidal complexes [MnCl(R2dbm)2] (R = H, 1; Me, 4; Et, 7). The same reaction with MnBr2 yields [MnBr(R2dbm)2] (R = H, 2; Me, 5; Et, 8). Slow hydrolysis of 4 or 7 in CH2Cl2/MeCN over two weeks gives [Mn6O4Cl4(R2dbm)6] (R = Me, 9; Et, 11); the crystal structure of 9 reveals a novel [Mn6(μ3-O)4(μ3-Cl)4]6+ core comprising an octahedron whose faces are capped by O2- or Cl- ions. Similar slow hydrolysis of 5 or 8 gives [Mn6O4Br4(R2dbm)6] (R = Me, 10; Et, 12); the crystal structure of 10 is identical with that of 9 except for the Br--for-Cl- substitution. The 1H NMR spectra of 1−12 in CDCl3 show paramagnetically shifted and broadened R2dbm resonances. The spectra are as expected for retention of the solid-state structures, the Mn6 complexes exhibiting effective T d solution symmetry with no evidence of fragmentation to [MnX(R2dbm)], [Mn(R2dbm)3], or any other species. The effective magnetic moment (μeff) per Mn6 for 9/12 slowly increases from 16.01/16.73 μ B at 320/300 K to a maximum of 24.37/24.60 μ B at 30.1/40.0 K, and then decreases to 13.69/13.86 μ B at 2.00 K. Fitting of the data to the theoretical equation derived for a octahedron gives (for 9/12) J cis = 8.6/8.5 cm-1 and g = 1.97/1.98 with J trans and TIP held fixed at 0 cm-1 and 1200 × 10-6 cm3 mol-1, respectively. These values indicate a S = 12 ground state. Fitting of magnetization vs field data collected in the 2.00−15.0 K and 0.500−50.0 kG ranges confirmed S = 12 ground states with D ≈ 0 cm-1.

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Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

High-Spin Molecules: Hexanuclear Mn^III Clusters with [Mn₆O₄X₄]⁶⁺ (X = Cl^-, Br^-) Face-Capped Octahedral Cores and S = 12 Ground States

et al. 1999

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“…Single-molecule magnets now include the present Mn 4 complex 6 , one Fe 8 complex, and several Mn 12 complexes. − These molecules range in size from ∼10 to ∼20 Å in diameter. It will be instructive to identify larger molecules with ground states with an even higher spin than S = 10 and/or greater magnetic anisotropies.…”

Section: Concluding Commentsmentioning

confidence: 99%

“…Taft et al and Papaefthymiou employed Mössbauer spectroscopy to demonstrate the superparamagnetic behavior of Fe 12 and Fe 16 Mn molecular complexes. One family of single-molecule magnets is [Mn 12 O 12 (O 2 CR) 16 (H 2 O) x ], where R is CH 3 ( 1 ) − with x = 4, R is Et ( 2 ) − with x = 3 and R is Ph ( 3 ) − with x = 4. An [Mn 12 ] - salt, PPh 4 [Mn 12 O 12 (O 2 CEt) 16 (H 2 O) 4 ] ( 4 ), has also been reported to be a single-molecule magnet. − All of these Mn 12 complexes exhibit magnetic hysteresis loops.…”

Section: Introductionmentioning

confidence: 99%

“…One family of single-molecule magnets is [Mn 12 O 12 (O 2 CR) 16 (H 2 O) x ], where R is CH 3 ( 1 ) − with x = 4, R is Et ( 2 ) − with x = 3 and R is Ph ( 3 ) − with x = 4. An [Mn 12 ] - salt, PPh 4 [Mn 12 O 12 (O 2 CEt) 16 (H 2 O) 4 ] ( 4 ), has also been reported to be a single-molecule magnet. − All of these Mn 12 complexes exhibit magnetic hysteresis loops. A second family of Mn clusters with a [Mn IV Mn III 3 O 3 X] 6+ core has been reported to display frequency-dependent out-of-phase magnetic susceptibility peaks, a property indicative of the slow magnetic relaxation of single-molecule magnets. − Finally, Barra et al.…”

Section: Introductionmentioning

confidence: 99%

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Resonant Magnetization Tunneling in the Trigonal Pyramidal Mn^IVMn^III₃Complex [Mn₄O₃Cl(O₂CCH₃)₃(dbm)₃]

et al. 1998

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The trigonal pyramidal complex [Mn4O3Cl(O2CCH3)3(dbm)3], where dbm- is the monoanion of dibenzoylmethane, functions as a single-molecule magnet. High-field EPR data are presented for an oriented microcrystalline sample to characterize the electronic structure of the MnIVMnIII 3 complex. These data show that the complex has a S = 9/2 ground state, experiencing axial zero-field splitting (DŜ z 2) with D = −0.53 cm-1 and a quartic zero-field splitting (B 4 0Ô4 0)with B 4 0 = −7.3 × 10-5 cm-1. Magnetization versus external magnetic field data were collected for an oriented single crystal in the 0.426−2.21 K range. At temperatures below 0.90 K hysteresis is seen. Steps are seen on each hysteresis loop. This is clear evidence that each MnIVMnIII 3 complex functions as a single-molecule magnet that is magnetizable. Furthermore, the steps on the hysteresis loops are due to resonant magnetization quantum mechanical tunneling. In response to an external field each molecule reverses its direction of magnetization not only by being thermally activated over a potential-energy barrier, but by the magnetization tunneling through the barrier. Additional evidence for resonant magnetization tunneling was found in the change in the temperature at which the out-of-phase ac magnetic susceptibility is observed as a function of an external dc field. The results of magnetization relaxation experiments carried out in the 0.394−0.700 K range are presented. These data are combined with the ac susceptibility data taken at higher temperatures to give an Arrhenius plot of the logarithm of the magnetization relaxation rate versus inverse absolute temperature. The temperature-dependent part of this plot gives an activation barrier of 11.8 K. Below 0.6 K the relaxation rate is independent of temperature with a rate of 3.2 × 10-2 s-1. This S = 9/2 single-molecule magnet exhibits a tunneling of its direction of magnetization at a rate of 3.2 × 10-2 s-1 in the 0.394−0.600 K range. Thus, resonant magnetization tunneling is seen for a half-integer-spin (S = 9/2) ground-state magnet in the absence of an external magnetic field. The transverse component of the small magnetic field from the nuclear spins is probably the origin of this tunneling.

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Cluster-Based Single-Molecule Magnets

Milios

Winpenny

2014

Structure and Bonding

107

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High Spin Molecules: Unusual Magnetic Susceptibility Relaxation Behavior of a Dodecanuclear Manganese Aggregate in Two Oxidation States

Cited by 15 publications

References 9 publications

High-Spin Molecules: Hexanuclear Mn^III Clusters with [Mn₆O₄X₄]⁶⁺ (X = Cl^-, Br^-) Face-Capped Octahedral Cores and S = 12 Ground States

High-Spin Molecules: Hexanuclear Mn^III Clusters with [Mn₆O₄X₄]⁶⁺ (X = Cl^-, Br^-) Face-Capped Octahedral Cores and S = 12 Ground States

Resonant Magnetization Tunneling in the Trigonal Pyramidal Mn^IVMn^III₃Complex [Mn₄O₃Cl(O₂CCH₃)₃(dbm)₃]

Cluster-Based Single-Molecule Magnets

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High Spin Molecules: Unusual Magnetic Susceptibility Relaxation Behavior of a Dodecanuclear Manganese Aggregate in Two Oxidation States

Cited by 15 publications

References 9 publications

High-Spin Molecules: Hexanuclear MnIII Clusters with [Mn6O4X4]6+ (X = Cl-, Br-) Face-Capped Octahedral Cores and S = 12 Ground States

High-Spin Molecules: Hexanuclear MnIII Clusters with [Mn6O4X4]6+ (X = Cl-, Br-) Face-Capped Octahedral Cores and S = 12 Ground States

Resonant Magnetization Tunneling in the Trigonal Pyramidal MnIVMnIII3Complex [Mn4O3Cl(O2CCH3)3(dbm)3]

Cluster-Based Single-Molecule Magnets

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High-Spin Molecules: Hexanuclear Mn^III Clusters with [Mn₆O₄X₄]⁶⁺ (X = Cl^-, Br^-) Face-Capped Octahedral Cores and S = 12 Ground States

High-Spin Molecules: Hexanuclear Mn^III Clusters with [Mn₆O₄X₄]⁶⁺ (X = Cl^-, Br^-) Face-Capped Octahedral Cores and S = 12 Ground States

Resonant Magnetization Tunneling in the Trigonal Pyramidal Mn^IVMn^III₃Complex [Mn₄O₃Cl(O₂CCH₃)₃(dbm)₃]