Synthetic and magnetic studies of a dodecanuclear cobalt wheel

Brechin, Euan K.; Cador, Olivier; Caneschi, Andréa; Cadiou, Cyril; Harris, Steven G.; Parsons, Simon; Vonci, Michele; Winpenny, Richard E. P.

doi:10.1039/b205721m

Cited by 106 publications

(48 citation statements)

References 10 publications

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“…The dc magnetic susceptibility (c M ) measurements in the 2-320 K range at 1000 Oe ( Figure 2) showed a c M T value of 35.98 cm 3 K mol À1 at 295 K, similar to that of a Co 12 wheel. [14] This value is much higher than that expected for 12 isolated spin-only S i = 3/2 ions (22.5 cm 3 K mol À1 with g Co = 2), which is attributed to the orbital contribution of Co II , which is known to be significant in an octahedral field.…”

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confidence: 65%

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A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co₁₂ Supercluster

et al. 2007

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For single-molecule magnet (SMM) behavior, molecular clusters require Ising magnetoanisotropy (D mol < 0) and a large ground-state spin multiplicity.[1] These requirements result in a high thermal barrier (U) to magnetization relaxation. Such clusters elicit intense interest in both chemistry and physics owing to behavior that is intermediate between that of a simple paramagnet (or classical bulk magnet) and that of a quantum/classical system, [2] which heralds applications in quantum devices.[3] The development of SMMs is often determined by serendipitous assembly. [2,4] However, the synthesis of molecular clusters with SMM-type behaviors presents a formidable challenge because of the difficulties in assembling predetermined structures with predictable magnetic properties. [4] The Mn 12 and Fe 8 clusters and their derivatives [2,4] are the most widely studied of homo-and heterometallic SMM systems, [4][5][6] and only very few cobalt-based SMMs are known. [7] One reason may be the difficulty in synthesizing cobalt clusters that display a large spin and molecular anisotropy. Because Co II has an exceptionally large D ion > 0 (a characteristic known to dominate molecular anisotropy), [8] only a limited number of high-nuclearity clusters are known for cobalt compared with manganese and iron. [4, 7c] Previous investigations implied that an alkoxido-bridged metal-cubane structure probably favors ferromagnetic coupling through m 3 -O bridges, in which orthogonal hard-axis alignment of four single-ion spins (D ion > 0) may result in a negative D mol value for the clusters. [7a, 8] As 2-(hydroxymethyl)pyridine (hmp) can furnish a cubane-like M 4 O 4 motif, [9] we chose the analogous (1H-benzimidazol-2-yl)methanol (Hbm) to serve as a chelating/bridging ligand to bring (Figure 1).[10] The cubane subunit is constructed by four Co II ions and four alkoxido oxygen atoms of m 3 -h 1 :h 3 -bm ligands.The Co1 and Co2 atoms in distorted octahedral N 2 O 4 environments are complexed by two O,N-chelating sites, one bm m 3 -alkoxido oxygen atom, and one EtOH ligand. The Co3 and Co4 atoms both form distorted CoO 6 octahedra with three alkoxido groups, two acetate groups, and one nitrate group. The cuboidal core is distorted with all the Co-O-Co angles in the range (98 AE 4)8 (Table S1 in the Supporting Information) for Co···Co dominant ferromagnetic exchange. [7a,b] Similar to the hmp analogue, the Co···Co distances vary from 3.034 to 3.243 . A Jahn-Teller distortion of the four d 7 Co 2+ ions lowers the symmetry of the cubes to S 4 . In addition to the central m 6 -NO 3 À bridge, six syn-syn acetate ligands also interconnect neighboring cubane units in the supercluster. Five discrete NO 3 À ions balance the overall positive charge of the cluster. There are no significant intermolecular interactions. A space-filling plot of 1 reveals that the cluster has an approximate trefoil shape with a diameter of about 2.0 nm ( Figure S1 in the Supporting Information). High coordination numbers of nitrate, a weak ligand, to transition met...

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“…In the low-temperature limit the effective spin S T of the molecule may be equal to 12 1/2 = 6. [14] We note that this is an oversimplified picture, as the S T classification is applicable only in the case of isotropic exchange. The gradual decrease of c M T below 2 K is best ascribed to the large anisotropy of the Co II centers.…”

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confidence: 98%

A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co₁₂ Supercluster

et al. 2007

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“…There exist a large family of ferric wheels with a different even number ( 6 8 10 12 18 N = , , , , ) of iron atoms [109][110][111][112][113][114][115][116][117][118][119]. Besides the ferric ones, there have been reports on wheels with other transition metal ions such as an eight membered Cr(III) wheel [120], a Cu(II) [121,122], a Co(II) [123], a Mn(II) [124] and a 24 membered Ni(II) wheel [125]. The latter structure contains the largest so far number of transition metal ions in a wheel-like structure.…”

Section: Ferric Wheelsmentioning

confidence: 97%

Density functional studies of molecular magnets

Postnikov

Kortus

Pederson

2006

Physica Status Solidi (b)

110

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PACS 71.15.Mb, 75.50.XxAfter a general introduction into the field of molecular magnets the discussion focuses on a more specific description of their most important representative species, single-molecule magnets incorporating transition metal ions. We overview traditional model approaches for the phenomenological description of such systems and outline some ways used to parameterize the corresponding models from experiment and from first-principle calculations. The latter can be either multi-determinantal quantum chemical schemes or those based on the density functional theory. In particular we discuss Heisenberg exchange parameters and magnetic anisotropy constants. As a practical example, an introduction into problems and properties of some single-molecule magnets which gained much attention within last years, namely Mn 12 -acetate, "Fe 8 " and "V 15 " systems, is given. This introduction into systems is followed by a critical comparison of calculation schemes based on the density functional theory that are particularly well suited for the study of molecular magnets. For the above systems we select some benchmark results, obtained by different methods. Finally, we outline our recent progress in the study of other single-molecule magnets, including sixmembered "ferric wheels", "ferric stars" and "Ni 4 " molecules, which we studied with the use of firstprinciples methods SIESTA and NRLMOL.

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“…Other 3D metal-ion cyclic cages, such as Ni 24 , [5] Fe 18 [6] , and Co 12 wheels, [7] and so forth, with interesting properties have also been found. However, to the best of our knowledge, large cage structures involving copper(II) ions are relatively rare.…”

Section: Introductionmentioning

confidence: 96%

Self‐Assembly of High‐Nuclearity Copper Cages: Tricorne Cu₂₁ and Saddlelike Cyclic Cu₁₆

Bai¹,

Tangoulis²,

Huang³

et al. 2009

Chemistry A European J

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Reaction of cupric salts with H(2)Rppz (R = H, Me; H(2)ppz = 3-(2-hydroxyphenyl)pyrazole; H(2)Meppz = 3-(2-hydroxy-5-methylphenyl)pyrazole) in the presence of sodium azide and triethylamine as bases gave two high-nuclearity copper cage compounds [HNEt(3)](2)[Cu(21)(CH(3)CN)(2)(H(2)O)(mu(2)-N(3))(6)(mu(3)-N(3))(2)(ppz)(18)](H(2)O)(3)(EtOH)(2) (1) and [Cu(16)(EtOH)(2)(H(2)O)(2)(Meppz)(16)]9.5 H(2)O (2), respectively. X-ray crystallographic studies revealed that molecular skeletons of 1 and 2 are unique tricorne Cu(21) and saddlelike cyclic Cu(16) aggregates, respectively. The magnetic properties studies showed overall antiferromagnetic interactions in 1 and 2. Quantum Monte Carlo simulations by using a 3-J model for 1 and a 2-J model for 2 were performed, which indicated that the magnetic couplings within the triangular copper units in 1 are ferromagnetic and those between other copper ions are antiferromagnetic, whereas in 2 all magnetic couplings between adjacent copper ions are exclusively antiferromagnetic.

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Synthetic and magnetic studies of a dodecanuclear cobalt wheel

Abstract: The synthesis, structural characterisation and preliminary magnetic studies of a Co12 wheel are reported; the magnetic investigations reveal that the electronic ground state has a spin S = 6, which corresponds to ferromagnetic interactions between the twelve Co(II) ions.

Cited by 106 publications

References 10 publications

A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co₁₂ Supercluster

A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co₁₂ Supercluster

Density functional studies of molecular magnets

Self‐Assembly of High‐Nuclearity Copper Cages: Tricorne Cu₂₁ and Saddlelike Cyclic Cu₁₆

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Synthetic and magnetic studies of a dodecanuclear cobalt wheel

Abstract: The synthesis, structural characterisation and preliminary magnetic studies of a Co12 wheel are reported; the magnetic investigations reveal that the electronic ground state has a spin S = 6, which corresponds to ferromagnetic interactions between the twelve Co(II) ions.

Cited by 106 publications

References 10 publications

A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co12 Supercluster

A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co12 Supercluster

Density functional studies of molecular magnets

Self‐Assembly of High‐Nuclearity Copper Cages: Tricorne Cu21 and Saddlelike Cyclic Cu16

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A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co₁₂ Supercluster

A Single‐Molecule‐Magnetic, Cubane‐Based, Triangular Co₁₂ Supercluster

Self‐Assembly of High‐Nuclearity Copper Cages: Tricorne Cu₂₁ and Saddlelike Cyclic Cu₁₆