Field-Induced Xy And Ising Ground States In A Quasi-Two-Dimensional S=1/2 Heisenberg Antiferromagnet

High field specific heat up to 35 T, C-p, and magnetic susceptibility, chi, measurements were performed on the quasi-two-dimensional (2D) Heisenberg antiferromagnet [Cu(pyz)(2)(pyO)(2)](PF6)(2). While no C-p anomaly is observed down to 0.5 K in zero magnetic field, the application of field parallel to the crystallographic ab-plane induces a lambda-like anomaly in C-p, suggesting Ising-type magnetic order. On the other hand when the field is parallel to the c-axis, C-p and chi show evidence of XY-type antiferromagnetism. This dependence upon the field orientation occurs because the extreme two-dimensionality allows the intrinsic (zero field) spin anisotropy to dominate the interlayer coupling, which has hitherto masked such effects in other materials

Experimental realization of field-induced XY and Ising ground states in a quasi-2D S=1/2 Heisenberg antiferromagnet

High field specific heat, Cp, and magnetic susceptibility, \c{hi}, measurements were performed on the quasi-two dimensional Heisenberg antiferromagnet [Cu(pyz)2(pyO)2](PF6)2. While no Cp anomaly is observed down to 0.5 K in zero magnetic field, the application of field parallel to the crystallographic ab-plane induces a lambda-like anomaly in Cp, consistent with Ising-type magnetic order. On the other hand, when the field is parallel to the c-axis, Cp and \c{hi} show evidence of XY-type antiferromagnetism. We argue that it is a small but finite easy-plane anisotropy in quasi-two dimensional [Cu(pyz)2(pyO)2](PF6)2 that allows the unusual observation of field induced XY and Ising-type magnetic states.Comment: 4 figure

Record High Single-Ion Magnetic Moments Through 4f(n)5d(1) Electron Configurations in the Divalent Lanthanide Complexes [(C5H4SiMe3)3Ln]⁻.

The recently reported series of divalent lanthanide complex salts, namely [K(2.2.2-cryptand)][Cp'3Ln] (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm; Cp' = C5H4SiMe3) and the analogous trivalent complexes, Cp'3Ln, have been characterized via dc and ac magnetic susceptibility measurements. The salts of the complexes [Cp'3Dy](-) and [Cp'3Ho](-) exhibit magnetic moments of 11.3 and 11.4 μB, respectively, which are the highest moments reported to date for any monometallic molecular species. The magnetic moments measured at room temperature support the assignments of a 4f(n+1) configuration for Ln = Sm, Eu, Tm and a 4f(n)5d(1) configuration for Ln = Y, La, Gd, Tb, Dy, Ho, Er. In the cases of Ln = Ce, Pr, Nd, simple models do not accurately predict the experimental room temperature magnetic moments. Although an LS coupling scheme is a useful starting point, it is not sufficient to describe the complex magnetic behavior and electronic structure of these intriguing molecules. While no slow magnetic relaxation was observed for any member of the series under zero applied dc field, the large moments accessible with such mixed configurations present important case studies in the pursuit of magnetic materials with inherently larger magnetic moments. This is essential for the design of new bulk magnetic materials and for diminishing processes such as quantum tunneling of the magnetization in single-molecule magnets

Record High Single-Ion Magnetic Moments Through 4f(n)5d(1) Electron Configurations in the Divalent Lanthanide Complexes [(C5H4SiMe3)3Ln]⁻.

The recently reported series of divalent lanthanide complex salts, namely [K(2.2.2-cryptand)][Cp'3Ln] (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm; Cp' = C5H4SiMe3) and the analogous trivalent complexes, Cp'3Ln, have been characterized via dc and ac magnetic susceptibility measurements. The salts of the complexes [Cp'3Dy](-) and [Cp'3Ho](-) exhibit magnetic moments of 11.3 and 11.4 μB, respectively, which are the highest moments reported to date for any monometallic molecular species. The magnetic moments measured at room temperature support the assignments of a 4f(n+1) configuration for Ln = Sm, Eu, Tm and a 4f(n)5d(1) configuration for Ln = Y, La, Gd, Tb, Dy, Ho, Er. In the cases of Ln = Ce, Pr, Nd, simple models do not accurately predict the experimental room temperature magnetic moments. Although an LS coupling scheme is a useful starting point, it is not sufficient to describe the complex magnetic behavior and electronic structure of these intriguing molecules. While no slow magnetic relaxation was observed for any member of the series under zero applied dc field, the large moments accessible with such mixed configurations present important case studies in the pursuit of magnetic materials with inherently larger magnetic moments. This is essential for the design of new bulk magnetic materials and for diminishing processes such as quantum tunneling of the magnetization in single-molecule magnets

Varying the Lewis Base Coordination of the Y2N2Core in the reduced dinitrogen complexes {[(Me3Si)2N]2(L)Y}2(μ-η2:η2-N2) (L = benzonitrile, pyridines, triphenylphosphine oxide, and trimethylamine N-oxide)

The effect of the neutral donor ligand, L, on the Ln2N2 core in the (N═N)2– complexes, [A2(L)Ln]2(μ-η2:η2-N2) (Ln = Sc, Y, lanthanide; A = monoanion; L = neutral ligand), is unknown since all of the crystallographically characterized examples were obtained with L = tetrahydrofuran (THF). To explore variation in L, displacement reactions between {[(Me3Si)2N]2(THF)Y}2(μ-η2:η2-N2), 1, and benzonitrile, pyridine (py), 4-dimethylaminopyridine (DMAP), triphenylphosphine oxide, and trimethylamine N-oxide were investigated. THF is displaced by all of these ligands to form {[(Me3Si)2N]2(L)Y}2(μ-η2:η2-N2) complexes (L = PhCN, 2; py, 3; DMAP, 4; Ph3PO, 5; Me3NO, 6) that were fully characterized by analytical, spectroscopic, density functional theory, and X-ray crystallographic methods. The crystal structures of the Y2N2 cores in 2–5 are similar to that in 1 with N–N bond distances between 1.255(3) Å and 1.274(3) Å, but X-ray analysis of the N–N distance in 6 shows it to be shorter: 1.198(3) Å

Cocrystallization of (μ‑S₂)^2– and (μ-S)^2– and Formation of an [η²‑S₃N(SiMe₃)₂] Ligand from Chalcogen Reduction by (N₂)^2– in a Bimetallic Yttrium Amide Complex

The reactivity of the (N₂)^2– complex {[(Me₃Si)₂N]₂Y­(THF)}₂(μ-η²:η²-N₂) (<b>1</b>) with sulfur and selenium has been studied to explore the special reductive chemistry of this complex and to expand the variety of bimetallic rare-earth amide complexes. Complex <b>1</b> reacts with elemental sulfur to form a mixture of compounds, <b>2</b>, that is the first example of cocrystallized complexes of (S₂)^2– and S^2– ligands. The crystals of <b>2</b> contain both the (μ-S₂)^2– complex {[(Me₃Si)₂N]₂Y­(THF)}₂(μ-η²:η²-S₂) (<b>3</b>) and the (μ-S)^2– complex {[(Me₃Si)₂N]₂Y­(THF)}₂(μ-S) (<b>4</b>), respectively. Modeling of the crystal data of <b>2</b> shows a 9:1 ratio of <b>3</b>:<b>4</b> in the crystals of <b>2</b> obtained from solutions that have 1:1 to 4:1 ratios of <b>3</b>/<b>4</b> by ¹H NMR spectroscopy. The addition of KC₈ to samples of <b>2</b> allows for the isolation of single crystals of <b>4</b>. The [S₃N­(SiMe₃)₂]⁻ ligand was isolated for the first time in crystals of [(Me₃Si)₂N]₂Y­[η²-S₃N­(SiMe₃)₂]­(THF) (<b>5</b>), obtained from the mother liquor of <b>2</b>. In contrast to the sulfur chemistry, the (μ-Se₂)^2– analogue of <b>3</b>, namely, {[(Me₃Si)₂N]₂Y­(THF)}₂(μ-η²:η²-Se₂) (<b>6</b>), can be cleanly synthesized in good yield by reacting <b>1</b>, with elemental selenium. The (μ-Se)^2– analogue of <b>4</b>, namely, {[(Me₃Si)₂N]₂Y­(THF)}₂(μ-Se) (<b>7</b>), was synthesized from Ph₃PSe

Record High Single-Ion Magnetic Moments Through 4f^<i>n</i>5d¹ Electron Configurations in the Divalent Lanthanide Complexes [(C₅H₄SiMe₃)₃Ln]⁻

The recently reported series of divalent lanthanide complex salts, namely [K­(2.2.2-cryptand)]­[Cp′₃Ln] (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm; Cp′ = C₅H₄SiMe₃) and the analogous trivalent complexes, Cp′₃Ln, have been characterized via dc and ac magnetic susceptibility measurements. The salts of the complexes [Cp′₃Dy]⁻ and [Cp′₃Ho]⁻ exhibit magnetic moments of 11.3 and 11.4 μ_B, respectively, which are the highest moments reported to date for any monometallic molecular species. The magnetic moments measured at room temperature support the assignments of a 4f^<i>n</i>+1 configuration for Ln = Sm, Eu, Tm and a 4f^<i>n</i>5d¹ configuration for Ln = Y, La, Gd, Tb, Dy, Ho, Er. In the cases of Ln = Ce, Pr, Nd, simple models do not accurately predict the experimental room temperature magnetic moments. Although an <i>LS</i> coupling scheme is a useful starting point, it is not sufficient to describe the complex magnetic behavior and electronic structure of these intriguing molecules. While no slow magnetic relaxation was observed for any member of the series under zero applied dc field, the large moments accessible with such mixed configurations present important case studies in the pursuit of magnetic materials with inherently larger magnetic moments. This is essential for the design of new bulk magnetic materials and for diminishing processes such as quantum tunneling of the magnetization in single-molecule magnets

Record High Single-Ion Magnetic Moments Through 4f^<i>n</i>5d¹ Electron Configurations in the Divalent Lanthanide Complexes [(C₅H₄SiMe₃)₃Ln]⁻

The recently reported series of divalent lanthanide complex salts, namely [K­(2.2.2-cryptand)]­[Cp′₃Ln] (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm; Cp′ = C₅H₄SiMe₃) and the analogous trivalent complexes, Cp′₃Ln, have been characterized via dc and ac magnetic susceptibility measurements. The salts of the complexes [Cp′₃Dy]⁻ and [Cp′₃Ho]⁻ exhibit magnetic moments of 11.3 and 11.4 μ_B, respectively, which are the highest moments reported to date for any monometallic molecular species. The magnetic moments measured at room temperature support the assignments of a 4f^<i>n</i>+1 configuration for Ln = Sm, Eu, Tm and a 4f^<i>n</i>5d¹ configuration for Ln = Y, La, Gd, Tb, Dy, Ho, Er. In the cases of Ln = Ce, Pr, Nd, simple models do not accurately predict the experimental room temperature magnetic moments. Although an <i>LS</i> coupling scheme is a useful starting point, it is not sufficient to describe the complex magnetic behavior and electronic structure of these intriguing molecules. While no slow magnetic relaxation was observed for any member of the series under zero applied dc field, the large moments accessible with such mixed configurations present important case studies in the pursuit of magnetic materials with inherently larger magnetic moments. This is essential for the design of new bulk magnetic materials and for diminishing processes such as quantum tunneling of the magnetization in single-molecule magnets

Varying the Lewis Base Coordination of the Y₂N₂ Core in the Reduced Dinitrogen Complexes {[(Me₃Si)₂N]₂(L)Y}₂(μ-η²:η²-N₂) (L = Benzonitrile, Pyridines, Triphenylphosphine Oxide, and Trimethylamine <i>N</i>-Oxide)

The effect of the neutral donor ligand, L, on the Ln₂N₂ core in the (NN)^2– complexes, [A₂(L)­Ln]₂(μ-η²:η²-N₂) (Ln = Sc, Y, lanthanide; A = monoanion; L = neutral ligand), is unknown since all of the crystallographically characterized examples were obtained with L = tetrahydrofuran (THF). To explore variation in L, displacement reactions between {[(Me₃Si)₂N]₂(THF)­Y}₂(μ-η²:η²-N₂), <b>1</b>, and benzonitrile, pyridine (py), 4-dimethylaminopyridine (DMAP), triphenylphosphine oxide, and trimethylamine <i>N</i>-oxide were investigated. THF is displaced by all of these ligands to form {[(Me₃Si)₂N]₂(L)­Y}₂(μ-η²:η²-N₂) complexes (L = PhCN, <b>2</b>; py, <b>3</b>; DMAP, <b>4</b>; Ph₃PO, <b>5</b>; Me₃NO, <b>6</b>) that were fully characterized by analytical, spectroscopic, density functional theory, and X-ray crystallographic methods. The crystal structures of the Y₂N₂ cores in <b>2</b>–<b>5</b> are similar to that in <b>1</b> with N<i>–</i>N bond distances between 1.255(3) Å and 1.274(3) Å, but X-ray analysis of the N<i>–</i>N distance in <b>6</b> shows it to be shorter: 1.198(3) Å