26 research outputs found
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 (L<sup>1</sup>–L<sup>3</sup>) using cobalt(II) salts. Our efforts have resulted in the formation
of 10 novel compounds, formulated as [Co<sub>2</sub>(L<sup>1</sup>)<sub>2</sub>Cl<sub>4</sub>]·2MeCN (<b>1</b>·2MeCN),
Co<sub>2</sub>(L<sup>1</sup>)<sub>2</sub>Br<sub>4</sub> (<b>2</b>), [Co(L<sup>2</sup>)Cl<sub>2</sub>]·MeCN (<b>3</b>·MeCN), Co(L<sup>2</sup>)Cl<sub>2</sub> (<b>4</b>), [Co<sub>2</sub>(L<sup>2</sup>)<sub>2</sub>Br<sub>4</sub>]·2MeCN
(<b>5</b>·2MeCN), [Co(L<sup>2</sup>)<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>]·2MeCN (<b>6</b>·2MeCN),
[Co<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>Cl<sub>4</sub>]·2MeCN
(<b>7</b>·2MeCN), Co<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>Cl<sub>4</sub> (<b>8</b>), Co<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>Br<sub>4</sub> (<b>9</b>), and Co(L<sup>3</sup>)<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub> (<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<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms
Three
new heterometallic complexes with formulas of [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<b>1</b>), [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OH)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>]·4H<sub>2</sub>O (<b>2</b>), and [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(mdea)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<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<sup>III</sup> ions occupying
the “body” position and two diamagnetic low-spin Co<sup>III</sup> 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<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>} 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<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms
Three
new heterometallic complexes with formulas of [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<b>1</b>), [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OH)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>]·4H<sub>2</sub>O (<b>2</b>), and [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(mdea)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<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<sup>III</sup> ions occupying
the “body” position and two diamagnetic low-spin Co<sup>III</sup> 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<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>} 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<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms
Three
new heterometallic complexes with formulas of [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<b>1</b>), [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OH)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>]·4H<sub>2</sub>O (<b>2</b>), and [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(mdea)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<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<sup>III</sup> ions occupying
the “body” position and two diamagnetic low-spin Co<sup>III</sup> 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<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>} 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 Bi<sub>2</sub><sup>3–</sup> 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<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>}‑Acetylacetonate Complexes with Multiple Relaxation Mechanisms
Three
new heterometallic complexes with formulas of [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<b>1</b>), [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OH)<sub>2</sub>(teaH)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>]·4H<sub>2</sub>O (<b>2</b>), and [Dy<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(mdea)<sub>2</sub>(acac)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] (<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<sup>III</sup> ions occupying
the “body” position and two diamagnetic low-spin Co<sup>III</sup> 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<sup>III</sup><sub>2</sub>Co<sup>III</sup><sub>2</sub>} 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<sup>III</sup><sub>2</sub>Ln<sup>III</sup><sub>2</sub>} 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<sup>III</sup> ions in
the [Cr<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(mdea)<sub>2</sub>(O<sub>2</sub>CPh)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] single-molecule magnet (SMM)
by the trivalent Pr, Nd, Gd, Tb, Ho, and Er lanthanide ions. The parent
{Cr<sub>2</sub>Dy<sup>III</sup><sub>2</sub>} compound displayed an
anisotropy barrier to magnetization reversal of 53 cm<sup>–1</sup>, 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<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>} complex. When Ln<sup>III</sup> = Pr, a complete loss of SMM behavior is found, but when Ln<sup>III</sup> = 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<sup>III</sup> = Tb and Ho, SMM behavior
is clearly revealed with anisotropy barriers of 44 and 36 cm<sup>–1</sup>, 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 {Cr<sub>2</sub>Dy<sub>2</sub>} example is lost. The {Cr<sub>2</sub>Tb<sub>2</sub>} and {Cr<sub>2</sub>Ho<sub>2</sub>} 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<sup>III</sup><sub>2</sub>Ln<sup>III</sup><sub>2</sub>} 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<sup>III</sup> ions in
the [Cr<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>(OMe)<sub>2</sub>(mdea)<sub>2</sub>(O<sub>2</sub>CPh)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>] single-molecule magnet (SMM)
by the trivalent Pr, Nd, Gd, Tb, Ho, and Er lanthanide ions. The parent
{Cr<sub>2</sub>Dy<sup>III</sup><sub>2</sub>} compound displayed an
anisotropy barrier to magnetization reversal of 53 cm<sup>–1</sup>, 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<sup>III</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>} complex. When Ln<sup>III</sup> = Pr, a complete loss of SMM behavior is found, but when Ln<sup>III</sup> = 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<sup>III</sup> = Tb and Ho, SMM behavior
is clearly revealed with anisotropy barriers of 44 and 36 cm<sup>–1</sup>, 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 {Cr<sub>2</sub>Dy<sub>2</sub>} example is lost. The {Cr<sub>2</sub>Tb<sub>2</sub>} and {Cr<sub>2</sub>Ho<sub>2</sub>} 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<sup>ttt</sup>)<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (Cp<sup>ttt</sup> = C<sub>5</sub>H<sub>2</sub><sup>t</sup>Bu<sub>3</sub>-1,2,4, <b>1-Dy</b>) remains mysterious, thus
we envisaged that analysis of a series of [Ln(Cp<sup>ttt</sup>)<sub>2</sub>]<sup>+</sup> (Ln = lanthanide) cations could shed light on
these properties. Herein we report the synthesis and physical characterization
of a family of isolated [Ln(Cp<sup>ttt</sup>)<sub>2</sub>]<sup>+</sup> cations (<b>1-Ln</b>; Ln = Gd, Ho, Er, Tm, Yb, Lu), synthesized
by halide abstraction of [Ln(Cp<sup>ttt</sup>)<sub>2</sub>(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<sup>ttt</sup>)<sub>2</sub>]<sup>+</sup> 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