Measuring spin ... spin interactions between heterospins in a hybrid [2]rotaxane

Use of molecular electron spins as qubits for quantum computing will depend on the ability to produce molecules with weak but measurable interactions between the qubits. Here we demonstrate use of pulsed EPR spectroscopy to measure the interaction between two inequivalent spins in a hybrid rotaxane molecule

Exploring the Coordination Capabilities of a Family of Flexible Benzotriazole-Based Ligands Using Cobalt(II) Sources

In this study we focus on the coordination chemistry of a family of three flexible benzotriazole-based ligands (L¹–L³) using cobalt­(II) salts. Our efforts have resulted in the formation of 10 novel compounds, formulated as [Co₂(L¹)₂Cl₄]­·2MeCN (<b>1</b>·2MeCN), Co₂(L¹)₂Br₄ (<b>2</b>), [Co­(L²)­Cl₂]­·MeCN (<b>3</b>·MeCN), Co­(L²)­Cl₂ (<b>4</b>), [Co₂(L²)₂Br₄]­·2MeCN (<b>5</b>·2MeCN), [Co­(L²)₂(NO₃)₂]­·2MeCN (<b>6</b>·2MeCN), [Co₂(L³)₂Cl₄]­·2MeCN (<b>7</b>·2MeCN), Co₂(L³)₂Cl₄ (<b>8</b>), Co₂(L³)₂Br₄ (<b>9</b>), and Co­(L³)₂(NO₃)₂ (<b>10</b>). The structures have been well characterized through X-ray crystallography, Fourier transform-infrared spectroscopy, electrospray ionization mass spectrometry, powder X-ray diffraction, elemental analysis, and thermogravimetric analysis studies. The compounds show a large structural variety depending on synthetic parameters (ratio, temperature, and metal salt) and the ligand selection (various conformations in each ligand). When tuned appropriately, these factors drastically affect dimensionality, metal geometry, and the nuclearity of the final product, resulting in a range of zero-dimensional dimers (<b>1</b>, <b>3</b>, <b>5</b>, <b>8</b>, <b>9</b>), one-dimensional (<b>2</b>, <b>7</b>, <b>10</b>), and two-dimensional (<b>4</b>, <b>6</b>) coordination polymers. A temperature-induced single-crystal-to-single-crystal transformation of compound <b>3</b>–<b>4</b> is additionally reported. The magnetic properties of representative compounds (<b>4</b>, <b>7</b>, <b>9</b>) are subject to large changes with only minor structural variations, suggesting that tetrahedral Co­(II) nodes in coordination polymers or metal–organic frameworks could function as sensitive reporters of small changes in the local environment

Single-Molecule Magnetism in Three Related {Co^III₂Dy^III₂}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms

Three new heterometallic complexes with formulas ­of ­[Dy^III₂­Co^III₂­(OMe)₂­(teaH)₂­(acac)₄­(NO₃)₂]­ (<b>1</b>),­ [Dy^III₂Co^III₂­(OH)₂­(teaH)₂­(acac)₄­(NO₃)₂]­·4H₂O (<b>2</b>), and [Dy^III₂­Co^III₂­(OMe)₂­(mdea)₂­(acac)₄­(NO₃)₂] (<b>3</b>) were characterized by single-crystal X-ray diffraction and by dc and ac magnetic susceptibility measurements. All three complexes have an identical “butterfly”-type metallic core that consists of two Dy^III ions occupying the “body” position and two diamagnetic low-spin Co^III ions occupying the outer “wing-tips”. Each complex displays single-molecule magnet (SMM) behavior in zero applied magnetic field, with thermally activated anisotropy barriers of 27, 28, and 38 K above 7.5 K for <b>1</b>–<b>3</b>, respectively, as well as observing a temperature-independent mechanism of relaxation below 5 K for <b>1</b> and <b>2</b> and at 3 K for <b>3</b>, indicating fast quantum tunneling of magnetization (QTM). A second, faster thermally activated relaxation mechanism may also be active under a zero applied dc field as derived from the Cole–Cole data. Interestingly, these complexes demonstrate further relaxation modes that are strongly dependent upon the application of a static dc magnetic field. Dilution experiments that were performed on <b>1</b>, in the {Y^III₂Co^III₂} diamagnetic analog, show that the slow magnetic relaxation is of a single-ion origin, but it was found that the neighboring ion also plays an important role in the overall relaxation dynamics

Single-Molecule Magnetism in Three Related {Co^III₂Dy^III₂}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms

Three new heterometallic complexes with formulas ­of ­[Dy^III₂­Co^III₂­(OMe)₂­(teaH)₂­(acac)₄­(NO₃)₂]­ (<b>1</b>),­ [Dy^III₂Co^III₂­(OH)₂­(teaH)₂­(acac)₄­(NO₃)₂]­·4H₂O (<b>2</b>), and [Dy^III₂­Co^III₂­(OMe)₂­(mdea)₂­(acac)₄­(NO₃)₂] (<b>3</b>) were characterized by single-crystal X-ray diffraction and by dc and ac magnetic susceptibility measurements. All three complexes have an identical “butterfly”-type metallic core that consists of two Dy^III ions occupying the “body” position and two diamagnetic low-spin Co^III ions occupying the outer “wing-tips”. Each complex displays single-molecule magnet (SMM) behavior in zero applied magnetic field, with thermally activated anisotropy barriers of 27, 28, and 38 K above 7.5 K for <b>1</b>–<b>3</b>, respectively, as well as observing a temperature-independent mechanism of relaxation below 5 K for <b>1</b> and <b>2</b> and at 3 K for <b>3</b>, indicating fast quantum tunneling of magnetization (QTM). A second, faster thermally activated relaxation mechanism may also be active under a zero applied dc field as derived from the Cole–Cole data. Interestingly, these complexes demonstrate further relaxation modes that are strongly dependent upon the application of a static dc magnetic field. Dilution experiments that were performed on <b>1</b>, in the {Y^III₂Co^III₂} diamagnetic analog, show that the slow magnetic relaxation is of a single-ion origin, but it was found that the neighboring ion also plays an important role in the overall relaxation dynamics

Single-Molecule Magnetism in Three Related {Co^III₂Dy^III₂}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms

Three new heterometallic complexes with formulas ­of ­[Dy^III₂­Co^III₂­(OMe)₂­(teaH)₂­(acac)₄­(NO₃)₂]­ (<b>1</b>),­ [Dy^III₂Co^III₂­(OH)₂­(teaH)₂­(acac)₄­(NO₃)₂]­·4H₂O (<b>2</b>), and [Dy^III₂­Co^III₂­(OMe)₂­(mdea)₂­(acac)₄­(NO₃)₂] (<b>3</b>) were characterized by single-crystal X-ray diffraction and by dc and ac magnetic susceptibility measurements. All three complexes have an identical “butterfly”-type metallic core that consists of two Dy^III ions occupying the “body” position and two diamagnetic low-spin Co^III ions occupying the outer “wing-tips”. Each complex displays single-molecule magnet (SMM) behavior in zero applied magnetic field, with thermally activated anisotropy barriers of 27, 28, and 38 K above 7.5 K for <b>1</b>–<b>3</b>, respectively, as well as observing a temperature-independent mechanism of relaxation below 5 K for <b>1</b> and <b>2</b> and at 3 K for <b>3</b>, indicating fast quantum tunneling of magnetization (QTM). A second, faster thermally activated relaxation mechanism may also be active under a zero applied dc field as derived from the Cole–Cole data. Interestingly, these complexes demonstrate further relaxation modes that are strongly dependent upon the application of a static dc magnetic field. Dilution experiments that were performed on <b>1</b>, in the {Y^III₂Co^III₂} diamagnetic analog, show that the slow magnetic relaxation is of a single-ion origin, but it was found that the neighboring ion also plays an important role in the overall relaxation dynamics

Taming Super-Reduced Bi₂^3– Radicals with Rare Earth Cations

Here, we report the synthesis of two new sets of dibismuth-bridged rare earth molecules. The first series contains a bridging diamagnetic Bi22– anion, (Cp*2RE)2(μ-η2:η2-Bi2), 1-RE (where Cp* = pentamethylcyclopentadienyl; RE = Gd (1-Gd), Tb (1-Tb), Dy (1-Dy), Y (1-Y)), while the second series comprises the first Bi23– radical-containing complexes for any d- or f-block metal ions, [K(crypt-222)][(Cp*2RE)2(μ-η2:η2-Bi2•)]·2THF (2-RE, RE = Gd (2-Gd), Tb (2-Tb), Dy (2-Dy), Y (2-Y); crypt-222 = 2.2.2-cryptand), which were obtained from one-electron reduction of 1-RE with KC8. The Bi23– radical-bridged terbium and dysprosium congeners, 2-Tb and 2-Dy, are single-molecule magnets with magnetic hysteresis. We investigate the nature of the unprecedented lanthanide–bismuth and bismuth–bismuth bonding and their roles in magnetic communication between paramagnetic metal centers, through single-crystal X-ray diffraction, ultraviolet–visible/near-infrared (UV–vis/NIR) spectroscopy, SQUID magnetometry, DFT and multiconfigurational ab initio calculations. We find a πz* ground SOMO for Bi23–, which has isotropic spin–spin exchange coupling with neighboring metal ions of ca. −20 cm–1; however, the exchange coupling is strongly augmented by orbitally dependent terms in the anisotropic cases of 2-Tb and 2-Dy. As the first examples of p-block radicals beneath the second row bridging any metal ions, these studies have important ramifications for single-molecule magnetism, main group element, rare earth metal, and coordination chemistry at large

Single-Molecule Magnetism in Three Related {Co^III₂Dy^III₂}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms

Three new heterometallic complexes with formulas ­of ­[Dy^III₂­Co^III₂­(OMe)₂­(teaH)₂­(acac)₄­(NO₃)₂]­ (<b>1</b>),­ [Dy^III₂Co^III₂­(OH)₂­(teaH)₂­(acac)₄­(NO₃)₂]­·4H₂O (<b>2</b>), and [Dy^III₂­Co^III₂­(OMe)₂­(mdea)₂­(acac)₄­(NO₃)₂] (<b>3</b>) were characterized by single-crystal X-ray diffraction and by dc and ac magnetic susceptibility measurements. All three complexes have an identical “butterfly”-type metallic core that consists of two Dy^III ions occupying the “body” position and two diamagnetic low-spin Co^III ions occupying the outer “wing-tips”. Each complex displays single-molecule magnet (SMM) behavior in zero applied magnetic field, with thermally activated anisotropy barriers of 27, 28, and 38 K above 7.5 K for <b>1</b>–<b>3</b>, respectively, as well as observing a temperature-independent mechanism of relaxation below 5 K for <b>1</b> and <b>2</b> and at 3 K for <b>3</b>, indicating fast quantum tunneling of magnetization (QTM). A second, faster thermally activated relaxation mechanism may also be active under a zero applied dc field as derived from the Cole–Cole data. Interestingly, these complexes demonstrate further relaxation modes that are strongly dependent upon the application of a static dc magnetic field. Dilution experiments that were performed on <b>1</b>, in the {Y^III₂Co^III₂} diamagnetic analog, show that the slow magnetic relaxation is of a single-ion origin, but it was found that the neighboring ion also plays an important role in the overall relaxation dynamics

A Family of {Cr^III₂Ln^III₂} Butterfly Complexes: Effect of the Lanthanide Ion on the Single-Molecule Magnet Properties

We report the synthesis of several heterometallic 3d–4f complexes which result from the replacement of the Dy^III ions in the [Cr^III₂Dy^III₂­(OMe)₂­(mdea)₂­(O₂CPh)₄­(NO₃)₂] single-molecule magnet (SMM) by the trivalent Pr, Nd, Gd, Tb, Ho, and Er lanthanide ions. The parent {Cr₂Dy^III₂} compound displayed an anisotropy barrier to magnetization reversal of 53 cm^–1, with magnetic hysteresis observed up to 3.5 K and with large coercive fields at low temperatures (2.7 T at 1.8 K). Magnetic studies for the new complexes revealed significantly different static and dynamic magnetic behavior in comparison to the parent {Cr^III₂Dy^III₂} complex. When Ln^III = Pr, a complete loss of SMM behavior is found, but when Ln^III = Nd or Er, frequency-dependent tails in the out-of-phase susceptibility at low temperatures are observed, indicative of slow magnetic relaxation, but with very small anisotropy barriers and fast relaxation times. When Ln^III = Tb and Ho, SMM behavior is clearly revealed with anisotropy barriers of 44 and 36 cm^–1, respectively. Magnetic hysteresis is also observed up to 2.5 and 1.8 K (0.003 T/s) for the Tb and Ho complexes, respectively. A large loss of the magnetization is, however, observed at zero-field, and as a result, the large coercivity which is present in the {Cr₂Dy₂} example is lost. The {Cr₂Tb₂} and {Cr₂Ho₂} complexes are rare examples of Tb- and Ho-based SMMs which reveal both slow relaxation in the absence of a static dc field (ac susceptibility) and open hysteresis loops above 1.8 K

A Family of {Cr^III₂Ln^III₂} Butterfly Complexes: Effect of the Lanthanide Ion on the Single-Molecule Magnet Properties

We report the synthesis of several heterometallic 3d–4f complexes which result from the replacement of the Dy^III ions in the [Cr^III₂Dy^III₂­(OMe)₂­(mdea)₂­(O₂CPh)₄­(NO₃)₂] single-molecule magnet (SMM) by the trivalent Pr, Nd, Gd, Tb, Ho, and Er lanthanide ions. The parent {Cr₂Dy^III₂} compound displayed an anisotropy barrier to magnetization reversal of 53 cm^–1, with magnetic hysteresis observed up to 3.5 K and with large coercive fields at low temperatures (2.7 T at 1.8 K). Magnetic studies for the new complexes revealed significantly different static and dynamic magnetic behavior in comparison to the parent {Cr^III₂Dy^III₂} complex. When Ln^III = Pr, a complete loss of SMM behavior is found, but when Ln^III = Nd or Er, frequency-dependent tails in the out-of-phase susceptibility at low temperatures are observed, indicative of slow magnetic relaxation, but with very small anisotropy barriers and fast relaxation times. When Ln^III = Tb and Ho, SMM behavior is clearly revealed with anisotropy barriers of 44 and 36 cm^–1, respectively. Magnetic hysteresis is also observed up to 2.5 and 1.8 K (0.003 T/s) for the Tb and Ho complexes, respectively. A large loss of the magnetization is, however, observed at zero-field, and as a result, the large coercivity which is present in the {Cr₂Dy₂} example is lost. The {Cr₂Tb₂} and {Cr₂Ho₂} complexes are rare examples of Tb- and Ho-based SMMs which reveal both slow relaxation in the absence of a static dc field (ac susceptibility) and open hysteresis loops above 1.8 K

Synthesis and Electronic Structures of Heavy Lanthanide Metallocenium Cations

The origin of 60 K magnetic hysteresis in the dysprosocenium complex [Dy­(Cp^ttt)₂]­[B­(C₆F₅)₄] (Cp^ttt = C₅H₂^tBu₃-1,2,4, <b>1-Dy</b>) remains mysterious, thus we envisaged that analysis of a series of [Ln­(Cp^ttt)₂]⁺ (Ln = lanthanide) cations could shed light on these properties. Herein we report the synthesis and physical characterization of a family of isolated [Ln­(Cp^ttt)₂]⁺ cations (<b>1-Ln</b>; Ln = Gd, Ho, Er, Tm, Yb, Lu), synthesized by halide abstraction of [Ln­(Cp^ttt)₂(Cl)] (<b>2-Ln</b>; Ln = Gd, Ho, Er, Tm, Yb, Lu). Complexes within the two families <b>1-Ln</b> and <b>2-Ln</b> are isostructural and display pseudo-linear and pseudo-trigonal crystal fields, respectively. This results in archetypal electronic structures, determined with CASSCF-SO calculations and confirmed with SQUID magnetometry and EPR spectroscopy, showing easy-axis or easy-plane magnetic anisotropy depending on the choice of Ln ion. Study of their magnetic relaxation dynamics reveals that <b>1-Ho</b> also exhibits an anomalously low Raman exponent similar to <b>1-Dy</b>, both being distinct from the larger and more regular Raman exponents for <b>2-Dy</b>, <b>2-Er</b>, and <b>2-Yb</b>. This suggests that low Raman exponents arise from the unique spin-phonon coupling of isolated [Ln­(Cp^ttt)₂]⁺ cations. Crucially, this highlights a direct connection between ligand coordination modes and spin-phonon coupling, and therefore we propose that the exclusive presence of multihapto ligands in <b>1-Dy</b> is the origin of its remarkable magnetic properties. Controlling the spin-phonon coupling through ligand design thus appears vital for realizing the next generation of high-temperature single-molecule magnets