A Supramolecular Aggregate of Four Exchange-Biased Single-Molecule Magnets (original) (raw)
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Chemical Science, 2016
The syntheses and properties of four magnetically-supramolecular oligomers of triangular Mn 3 units are reported: dimeric [Mn 6 O 2 (O 2 CMe) 8 (CH 3 OH) 2 (pdpd) 2 ] (3) and [Mn 6 O 2 (O 2 CMe) 8 (py) 2 (pdpd) 2 ](ClO 4) 2 (4), and tetrameric [Mn 12 O 4 (O 2 CR) 12 (pdpd) 6 ](ClO 4) 4 (R ¼ Me (5), t Bu (6)). They were all obtained employing 3-phenyl-1,5-di(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH 2), either in direct synthesis reactions involving oxidation of Mn II salts or in metathesis reactions with the preformed complex [Mn 3 O(O 2 CMe) 6 (py) 3 ](ClO 4) (1); complex 6 was then obtained by carboxylate substitution on complex 5. Complexes 3 and 4 contain two [Mn III 2 Mn II (m 3-O)] 6+ and [Mn III 3 (m 3-O)] 7+ units, respectively, linked by two pdpd 2À groups. Complexes 5 and 6 contain four [Mn III 3 (m 3-O)] 7+ units linked by six pdpd 2À groups into a rectangular tetramer [Mn III 3 ] 4. Solid-state dc magnetic susceptibility studies showed that the Mn 3 subunits in 3 and 4 have a ground-state spin of S ¼ 3/2 and S ¼ 2, respectively, while the Mn 3 subunits in 5 and 6 possess an S ¼ 6 ground state. Complexes 5 and 6 exhibit frequency-dependent out-ofphase (c 00 M) ac susceptibility signals indicating 5 and 6 to be tetramers of Mn 3 single-molecule magnets (SMMs). High-frequency EPR studies of a microcrystalline powder sample of 5$2CH 2 Cl 2 provided precise spin Hamiltonian parameters of D ¼ À0.33 cm À1 , |E| ¼ 0.03 cm À1 , B 0 4 ¼ À8.0 Â 10 À5 cm À1 , and g ¼ 2.0. Magnetization vs. dc field sweeps on a single crystal of 5$xCH 2 Cl 2 gave hysteresis loops below 1 K that exhibit exchange-biased quantum tunneling of magnetization (QTM) steps with a bias field of 0.19 T. Simulation of the loops determined that each Mn 3 unit is exchange-coupled to the two neighbors linked to it by the pdpd 2À linkers, with an antiferromagnetic inter-Mn 3 exchange interaction of J/k B ¼ À0.011 K (Ĥ ¼ À2JŜ i $Ŝ j convention). The work demonstrates a rational approach to synthesizing magneticallysupramolecular aggregates of SMMs as potential multi-qubit systems for quantum computing.
Inorganic Chemistry, 2002
2), respectively. Both compounds contain a novel pentadentate ligand, the dianion of (6-hydroxymethylpyridin-2-yl)-(6-hydroxymethylpyridin-2-ylmethoxy)methanol (LH 2 ), which is the hemiacetal formed in situ from the Mn-assisted oxidation of pdmH 2 . Complex 1 crystallizes in the monoclinic space group P2 1 /n with the following cell parameters at −160°C: a ) 16.6942(5) Å, b ) 13.8473(4) Å, c ) 20.0766(6) Å, ) 99.880(1)°, V ) 4572.27 Å 3 , and Z ) 2, R (R w ) ) 4.78 (5.25). Complex 2‚0.2MeCN crystallizes in the triclinic space group P1 h with the following cell parameters at −157°C: a ) 12.1312(4) Å, b ) 18.8481(6) Å, c ) 23.2600(7) Å, R ) 78.6887(8)°, ) 77.9596(8)°, γ ) 82.3176(8)°, V ) 5076.45 Å 3 , and Z ) 2, R (R w ) ) 4.12 (4.03). Both complexes are new structural types comprising distorted-cubane units linked together, albeit in two very different ways. In addition, complex 2 features three distinct binding modes for the chelating ligands derived from deprotonated pdmH 2 . Complexes 1 and 2 were characterized by variabletemperature ac and dc magnetic susceptibility measurements and found to possess spin ground states of 0 and 11/2, respectively. Least-squares fitting of the reduced magnetization data gave S ) 11/2, g ) 2.0, and D ) −0.11 cm -1 for complex 2, where D is the axial zero-field splitting parameter. Direct current magnetization versus field studies on 2 at <1 K show hysteresis behavior at <0.3 K, establishing 2 as a new single-molecule magnet. Magnetization decay measurements gave an effective barrier to magnetization relaxation of U eff ) 3.1 cm -1 ) 4.5 K. † Present address:
Inorganic Chemistry, 2002
The reactions of the Mn III 3 and Mn II Mn III 2 complexes [Mn 3 O(O 2 CEt) 6 (py) 3 ][ClO 4 ] and [Mn 3 O(O 2 CEt) 6 (py) 3 ] with pyridine-2,6-dimethanol (pdmH 2) afford the mixed-valence Mn II 6 Mn III 2 octanuclear complex [Mn 8 O 2 (py) 4 (O 2 CEt) 8 (L) 2 ][ClO 4 ] 2 (1) and the Mn II 7 Mn III 2 enneanuclear complex [Mn 9 (O 2 CEt) 12 (pdm)(pdmH) 2 (L) 2 ] (2), respectively. Both compounds contain a novel pentadentate ligand, the dianion of (6-hydroxymethylpyridin-2-yl)-(6-hydroxymethylpyridin-2-ylmethoxy)methanol (LH 2), which is the hemiacetal formed in situ from the Mn-assisted oxidation of pdmH 2. Complex 1 crystallizes in the monoclinic space group P2 1 /n with the following cell parameters at −160°C: a) 16.6942(5) Å, b) 13.8473(4) Å, c) 20.0766(6) Å,) 99.880(1)°, V) 4572.27 Å 3 , and Z) 2, R (R w)) 4.78 (5.25). Complex 2‚0.2MeCN crystallizes in the triclinic space group P1 h with the following cell parameters at −157°C: a) 12.1312(4) Å, b) 18.8481(6) Å, c) 23.2600(7) Å, R) 78.6887(8)°,) 77.9596(8)°, γ) 82.3176(8)°, V) 5076.45 Å 3 , and Z) 2, R (R w)) 4.12 (4.03). Both complexes are new structural types comprising distorted-cubane units linked together, albeit in two very different ways. In addition, complex 2 features three distinct binding modes for the chelating ligands derived from deprotonated pdmH 2. Complexes 1 and 2 were characterized by variabletemperature ac and dc magnetic susceptibility measurements and found to possess spin ground states of 0 and 11/2, respectively. Least-squares fitting of the reduced magnetization data gave S) 11/2, g) 2.0, and D) −0.11 cm-1 for complex 2, where D is the axial zero-field splitting parameter. Direct current magnetization versus field studies on 2 at <1 K show hysteresis behavior at <0.3 K, establishing 2 as a new single-molecule magnet. Magnetization decay measurements gave an effective barrier to magnetization relaxation of U eff) 3.1 cm-1) 4.5 K.
Journal of the American Chemical Society, 2015
Mn 3 O(O 2 CMe) 3 (dpd) 3/2 )] 2 (I 3 ) 2 has been obtained from the reaction of 1,3-di(pyridin-2-yl)propane-1,3dione dioxime with triangular [Mn III 3 O(O 2 CMe)(py) 3 ]-(ClO 4 ). It comprises two [Mn III 3 O] 7+ triangular units linked covalently by three dioximate ligands into a [Mn 3 ] 2 dimer. Solid state dc and ac magnetic susceptibility measurements reveal that each Mn 3 subunit of the dimer is a separate single-molecule magnet (SMM) with an S = 6 ground state and that the two SMM units are very weakly ferromagnetically exchange coupled. Highfrequency EPR spectroscopy on a single crystal displays signal splittings indicative of quantum superposition/entanglement of the two SMMs, and parallel studies on MeCN/toluene (1:1) frozen solutions reveal the same spectral features. The dimer thus retains its structure and inter-Mn 3 coupling upon dissolution. This work establishes that covalently linked molecular oligomers of exchange-coupled SMMs can be prepared that retain their oligomeric nature and attendant inter-SMM quantum mechanical coupling in solution, providing a second phase for their study and demonstrating the feasibility of using solution methods for their deposition on surfaces and related substrates for study.
MOF-like supramolecular network of Mn3 single-molecule magnets formed by extensive π-π stacking
Polyhedron, 2016
Dedicated to Malcolm H. Chisholm on the occasion of his 70 th birthday; an outstanding scientist and friend. ABSTRACT [Mn 3 O(dhb) 3 (mpko) 3 ](ClO 4) (4) has been obtained from the carboxylate substitution reaction of triangular [Mn 3 O(O 2 CMe) 3 (mpko) 3 ](ClO 4) (mpkoH = methyl(2-pyridyl)ketone oxime) with 3,5dihydroxybenzoic acid (dhbH). Complex 4 possesses an equilateral triangle [Mn 3 O] 7+ core with the dhband mpkoligands on opposite sides of the Mn 3 plane. All dhband mpkogroups are involved in π-π stacking interactions with those on neighboring Mn 3 molecules to give a 3-D supramolecular network resembling a metal-organic framework (MOF), with periodic voids resulting from a repeating unit comprising an [Mn 3 ] 8 rhombohedron. Variable-temperature, solidstate magnetic susceptibility studies in the 5.0-300 K temperature range reveal the predominance of antiferromagnetic inter-Mn 3 exchange couplings. Alternating current magnetic susceptibility studies on 4 show that the single-molecule magnet (SMM) behavior characteristic of [Mn 3 O(O 2 CR) 3 (mpko) 3 ] + complexes has been lost. This work demonstrates that constructing MOF-like networks from SMMs by weak interactions is feasible but that even these can
Inorganic Chemistry, 2009
The syntheses, crystal structures, and magnetochemical characterization are reported for two new Mn clusters, [Mn 7 O 3 (OH) 3 (O 2 CBu t) 7 (dmhmp) 4 ] (1) and [Mn 12 O 7 (OH)(OMe) 2 (O 2 CPh) 12 (dmhmp) 4 (H 2 O)] (2). They were obtained from the use of 2-(pyridine-2-yl)propan-2-ol (dmhmpH), a more bulky version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dmhmpH with MnCl 2 3 4H 2 O and NaO 2 CBu t in MeCN/MeOH led to the heptanuclear complex 1, whereas the analogous reaction with Mn(O 2 CPh) 2 gave dodecanuclear complex 2. Complexes 1 and 2 are both mixed-valent and are of unprecedented structural types. Complex 1 (Mn II , 6Mn III) can be described as the fusion of butterfly-like [Mn 4 (μ 3-O) 2 ] and tetrahedral [Mn 4 (μ 4-O)] units by the sharing of a common Mn atom. Complex 2 (3Mn II , 9Mn III) possesses a central [Mn 4 O 6 ] face-sharing incomplete dicubane, on either side of which is a tetrahedral [Mn 4 (μ 4-O)] unit attached to the oxide ions of the former. Solid-state dc and ac magnetic susceptibility measurements on 1 and 2 establish that they possess unusual S = 7/2 and 13/2 ground states, respectively. The ac susceptibility studies on 2 revealed nonzero frequency-dependent out-of-phase (χ M 00) signals at temperatures below 3 K, indicating a single-molecule magnet (SMM). Magnetization versus applied dc field sweeps on single crystals of 2 3 3CH 2 Cl 2 down to 0.04 K exhibited hysteresis, thus confirming complex 2 to be a new half-integer SMM.
Journal of the American Chemical Society, 2001
Single-molecule magnets (SMMs) are a recent discovery that promises access to the ultimate high-density memory storage device in which each bit of digital information is stored on a single molecule. Each independent molecule of a SMM possesses the ability to function as a magnetizable magnet below a critical temperature. 1 This is due to intrinsic intramolecular properties, that is, a large spin ground state, and a large and negative (easy axis type) magnetoanisotropy, rather than to intermolecular interactions and long-range ordering. The most well studied SMMs are the [Mn 12 O 12 (O 2 CR) 16 (H 2 O) x ] n-(n = 0-2) (8Mn III 4Mn IV for n = 0) complexes. 2,3,4 Evidence for the SMM behavior comes from frequency-dependent out-of-phase ac susceptibility signals (χ M ″) and magnetization hysteresis loops. In addition, oriented crystals of these species display steps in the hysteresis loops indicative of field-tuned quantum tunneling of the magnetization (QTM). 5 A substantial amount of effort has been dedicated to systematic variation of the carboxylate R group and solvate molecules of crystallization, which has recently led to the discovery of Jahn-Teller (JT) isomerism, 6 involving differing relative orientations of the JT elongation axes of the eight Mn III centers and resulting in significantly different magnetic behavior for the different JT isomers. This includes differing positions of the χ M ″ peaks and differing magnetization hysteresis plots, both of these effects reflecting different rates of magnetization relaxation.
One-Dimensional Chain of Tetranuclear Manganese Single-Molecule Magnets
Inorganic Chemistry, 2005
A one-dimensional chain of interconnected single-molecule magnets (SMMs) is obtained that consists of [Mn 4 (hmp) 6 ] 4+ units bridged by chloride ions. Slow magnetization relaxation is evident in the AC susceptibility data and in magnetization hysteresis measurements for [Mn 4 (hmp) 6 Cl 2 ] n (ClO 4 ) 2n . The magnetization hysteresis loops for this complex are similar to those for an SMM and show significant coercive field and steps at regular magnetic intervals. Spin-canted antiferromagnetic coupling due to misalignment of easy axes of neighboring Mn 4 units is also observed for this complex.
Molecular Wheels: New Mn 12 Complexes as Single-Molecule Magnets
Inorganic Chemistry, 2008
The preparation, structure and magnetic properties of three new wheel-shaped dodecanuclear manganese complexes, [Mn 12 (Adea) 8 (CH 3 COO) 14 ] · 7CH 3 CN (1 · 7CH 3 CN), [Mn 12 (Edea) 8 (CH 3 CH 2 COO) 14 ] (2) and [Mn 12 (Edea) 8 (CH 3 COO) 2 -(CH 3 CH 2 COO) 12 ] (3), are reported, where Adea 2and Edea 2are dianions of the N-allyl diethanolamine and the N-ethyl diethanolamine ligands, respectively. Each complex has six Mn(II) and six Mn(III) ions alternating in a wheel-shaped topology, with eight n-substituted diethanolamine dianions. All variable-temperature direct current (DC) magnetic susceptibility data were collected in 1, 0.1, or 0.01 T fields and in the 1.8-300 K temperature range. Heat capacity data, collected in applied fields of 0-9 T and in the 1.8-100 K temperature range, indicate the absence of a phase-transition due to long-range magnetic ordering for 1 and 3. Variable-temperature, variablefield DC magnetic susceptibility data were obtained in the 1.8-10 K and 0.1-5 T ranges. All complexes show out-of-phase signals in the AC susceptibility measurements, collected in a 50-997 Hz frequency range and in a 1.8-4.6 K temperature range. Extrapolation to 0 K of the in-phase AC susceptibility data collected at 50 Hz indicates an S ) 7 ground state for 1, 2, and 3. Magnetization hysteresis data were collected on a single crystal of 1 in the 0.27-0.9 K range and on single crystals of 2 and 3 in the 0.1-0.9 K temperature range. Discrete steps in the magnetization curves associated with resonant quantum tunneling of magnetization (QTM) confirm these complexes to be single-molecule magnets. The appearance of extra QTM resonances on the magnetic hysteresis of 1 is a result of a weak coupling between two Mn ions at opposite ends of the wheel, dividing the molecule into two ferromagnetic exchange-coupled S ) 7 / 2 halves. The absence of these features on 2 and 3, which behave as rigid spin S ) 7 units, is a consequence of different interatomic distances.