13 research outputs found
Proton-Coupled Electron Transfer in FerroceniumāPhenolate Radicals
Electron
and proton transfer (ET, PT) can be intimately coupled,
provided suitable redox and acid/base sites are available. The amide-linked
ferroceneāphenol <b>H-1</b> is deprotonated to the phenolate <b>[1]</b><sup><b>ā</b></sup> by phosphazene bases and
oxidized to the ferrocenium ion <b>[H-1]</b><sup><b>+</b></sup> by silver hexafluoroantimonate. Concomitant oxidation and
deprotonation yields the radical <b>[1]</b><sup><b>ā¢</b></sup>, featuring a characteristic near-IR absorption band. The ground
state of <b>[1]</b><sup><b>ā¢</b></sup> is best
described as the ferroceniumāphenolate zwitterion <b>[1b]</b><sup><b>ā¢</b></sup> with a dynamic dissymmetric NĀ·Ā·Ā·HĀ·Ā·Ā·O
hydrogen bond (PT). The ferroceniumāiminolate NĀ·Ā·Ā·HāO
tautomer <b>[1b]</b><sup><b>ā¢</b></sup><b>-NHOā²</b> can undergo a thermal structural rearrangement to the high-energy
OHĀ·Ā·Ā·O tautomer <b>[1b]</b><sup><b>ā¢</b></sup><b>-OHO</b>, while the amideāphenolate NāHĀ·Ā·Ā·O
tautomer <b>[1b]</b><sup><b>ā¢</b></sup><b>-NHO</b> is poised to optical electron transfer to yield the ferroceneāphenoxyl
valence isomer <b>[1a]</b><sup><b>ā¢</b></sup><b>-NHO</b> (<i>E</i><sub>op</sub> = 1.18ā1.19 eV)
Novel Iron(II) Microporous Spin-Crossover Coordination Polymers with Enhanced Pore Size
In this Communication, we report the synthesis and characterization
of novel Hofmann-like spin-crossover porous coordination polymers
of composition {FeĀ(L)Ā[MĀ(CN)<sub>4</sub>]}Ā·G [L = 1,4-bisĀ(4-pyridylethynyl)Ābenzene
and M<sup>II</sup> = Ni, Pd, and Pt]. The spin-crossover properties
of the framework are closely related to the number and nature of the
guest molecules included in the pores
Novel Iron(II) Microporous Spin-Crossover Coordination Polymers with Enhanced Pore Size
In this Communication, we report the synthesis and characterization
of novel Hofmann-like spin-crossover porous coordination polymers
of composition {FeĀ(L)Ā[MĀ(CN)<sub>4</sub>]}Ā·G [L = 1,4-bisĀ(4-pyridylethynyl)Ābenzene
and M<sup>II</sup> = Ni, Pd, and Pt]. The spin-crossover properties
of the framework are closely related to the number and nature of the
guest molecules included in the pores
Synthesis of Nanocrystals and Particle Size Effects Studies on the Thermally Induced Spin Transition of the Model Spin Crossover Compound [Fe(phen)<sub>2</sub>(NCS)<sub>2</sub>]
Surfactant-free
nanocrystals of the model spin-crossover compound [FeĀ(phen)<sub>2</sub>(NCS)<sub>2</sub>] (phen: 1,10-phenanthroline) have been synthesized
applying the reverse micelle technique. The morphology of the nanocrystals,
characterized by scanning electronic microscopy, corresponds to rhombohedric
platelets with dimensions ranging from 203 Ć 203 Ć 106 nm
to 142 Ć 142 Ć 74 nm. Variation of the concentration of the FeĀ(BF<sub>4</sub>)<sub>2</sub>Ā·6H<sub>2</sub>O salt in the synthesis has been found
to have little influence on the crystallite size. In contrast, the
solventāsurfactant ratio (Ļ) is critical for a good particle
growth. The spin transition of the nanocrystals has been characterized
by magnetic susceptibility measurements and MoĢssbauer spectroscopy.
The nanocrystals undergo an abrupt and more cooperative spin transition
in comparison with the bulk compound. The spin transition is centered
in the interval of temperature of 175ā185 K and is accompanied
by 8 K of thermal hysteresis width. The crystallite quality more than
the crystallite size is responsible for the higher cooperativity.
The magnetic properties of the nanocrystals embedded in organic polymers
such as polyethylene glycol, nujol, glycerol, and triton have been
studied as well. The spin transition in the nanocrystals is affected
by the polymer coating. The abrupt and first-order spin transition
transforms into a more continuous spin transition as a result of the
chemical pressure asserted by the organic polymers on the FeĀ(II) centers
Spin Crossover Star-Shaped Metallomesogens of Iron(II)
Three
new types of spin crossover (SCO) metallomesogens of Fe<sup>II</sup> based on symmetric tripod ligands and their magnetic and structural
properties are reported here. These were obtained by condensation
of trisĀ(2-aminoethyl)Āamin (tren) with the aldehyde derived from 3-alkoxy-6-methylpyridine
(<b>mpyN</b>, N (number of carbon atoms in <i>n</i>-alkyl chains) = 8, 18), 1-alkyl-1<i>H</i>-imidazole (<b>imN</b>, N = 4, 16, 18, 20, 22), or 1-alkyl-1<i>H</i>-benzimidazole (<b>bimN</b>, N = 6, 14, 16, 18, 20). A complex
derived from 1-octadecyl-1<i>H</i>-naphthoĀ[2,3-<i>d</i>]Āimidazole (<b>nim18</b>) retains the high spin state at any
temperature. Single crystals of the short-chain complexes were investigated
by a combination of X-ray crystallography, magnetic measurements and
MoĢssbauer spectroscopy. Generally, in comparison with the short-chain
complexes the long-chain complexes display more gradual SCO and undergo
a phase transition crystalāliquid crystal that is reflected
in their magnetic properties. Characterization by X-ray powder diffractometry
and differential calorimetry reveal formation of a smectic mesophase
upon melting
<i>Screw</i>-<i>Type</i> Motion and Its Impact on Cooperativity in BaNa<sub>2</sub>Fe[VO<sub>4</sub>]<sub>2</sub>
BaNa<sub>2</sub>FeĀ[VO<sub>4</sub>]<sub>2</sub> contains a JahnāTeller active ion (Fe<sup>II</sup>, 3d<sup>6</sup>, high-spin) in an octahedral coordination.
On the basis of a combination of temperature-dependent X-ray diffraction
and MoĢssbauer and Raman spectroscopies, we demonstrate the
coupling of lattice dynamics with the electronic ground state of Fe<sup>II</sup>. We identify three lattice modes combined to an effective
canted <i>screw</i>-<i>type</i> motion that drives
the structural transition around room temperature from the high-temperature
(<i>P</i>3Ģ
) via intermediate phases to the low-temperature
phase (<i>C</i>2/<i>c</i>). The dynamics of the
electronic ground state of FeĀ(II) are evident from MoĢssbauer
data with signatures of a motion-narrowed doublet above 320 K, a gradual
evolution of the <sup>5</sup>E<sub>g</sub> electronic state below
293 K, and finally the signature of the thermodynamically preferred
orbitally nondegenerate ground state (<sup>5</sup>A<sub>g</sub>) of
FeĀ(II) below 100 K. The continuous nature of the transition is associated
with the temperature-dependent phonon parameters derived from Raman
spectroscopy, which point out the presence of strong electronāphonon
coupling in this compound. We present a microscopic mechanism and
evaluate the collective component leading to the structural phase
transition
Spin Crossover in Fe(II)āM(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2āSubstituted Pyrazines
Discovery of spin-crossover
(SCO) behavior in the family of Fe<sup>II</sup>-based Hofmann clathrates
has led to a ānew rushā in the field of bistable molecular
materials. To date this class of SCO complexes is represented by several
dozens of individual compounds, and areas of their potential application
steadily increase. Starting from Fe<sup>2+</sup>, square planar tetracyanometalates
M<sup>II</sup>(CN)<sub>4</sub><sup>2ā</sup> (M<sup>II</sup> = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as
coligands we obtained a series of nine new Hofmann clathrate-like
coordination frameworks. X-ray diffraction reveals that in these complexes
Fe<sup>II</sup> ion has a pseudo-octahedral coordination environment
supported by four Ī¼<sub>4</sub>-tetracyanometallates forming
its equatorial coordination environment. Depending on the nature of
X and M, axial positions are occupied by two 2X-pyrazines (X = Cl
and M<sup>II</sup> = Ni (<b>1</b>), Pd (<b>2</b>), Pt
(<b>3</b>); X = Me and M<sup>II</sup> = Ni (<b>4</b>),
Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X
= I and M<sup>II</sup> = Ni (<b>7</b>), Pd (<b>8</b>),
Pt (<b>9</b>)), or, alternatively, two distinct Fe<sup>II</sup> positions with either two pyrazines or two water molecules (X =
Me and M<sup>II</sup> = Pt (<b>6</b>)) are observed. Temperature
behavior of magnetic susceptibility indicates that all compounds bearing
FeN<sub>6</sub> units (<b>1</b>ā<b>6</b>) display
cooperative spin transition, while Fe<sup>II</sup> ions in N<sub>5</sub>O or N<sub>4</sub>O<sub>2</sub> surrounding are high spin (HS). Structural
changes in the nearest Fe<sup>II</sup> environment upon low-spin (LS)
to HS transition, which include ca. 10% FeāN distance increase,
lead to the cell expansion. MoĢssbauer spectroscopy is used
to characterize the spin state of all HS, LS, and intermediate phases
of <b>1</b>ā<b>9</b> (see abstract figure). Effects
of a pyrazine substituent and M<sup>II</sup> nature on the hyperfine
parameters in both spin states are established
Spin Crossover in Fe(II)āM(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2āSubstituted Pyrazines
Discovery of spin-crossover
(SCO) behavior in the family of Fe<sup>II</sup>-based Hofmann clathrates
has led to a ānew rushā in the field of bistable molecular
materials. To date this class of SCO complexes is represented by several
dozens of individual compounds, and areas of their potential application
steadily increase. Starting from Fe<sup>2+</sup>, square planar tetracyanometalates
M<sup>II</sup>(CN)<sub>4</sub><sup>2ā</sup> (M<sup>II</sup> = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as
coligands we obtained a series of nine new Hofmann clathrate-like
coordination frameworks. X-ray diffraction reveals that in these complexes
Fe<sup>II</sup> ion has a pseudo-octahedral coordination environment
supported by four Ī¼<sub>4</sub>-tetracyanometallates forming
its equatorial coordination environment. Depending on the nature of
X and M, axial positions are occupied by two 2X-pyrazines (X = Cl
and M<sup>II</sup> = Ni (<b>1</b>), Pd (<b>2</b>), Pt
(<b>3</b>); X = Me and M<sup>II</sup> = Ni (<b>4</b>),
Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X
= I and M<sup>II</sup> = Ni (<b>7</b>), Pd (<b>8</b>),
Pt (<b>9</b>)), or, alternatively, two distinct Fe<sup>II</sup> positions with either two pyrazines or two water molecules (X =
Me and M<sup>II</sup> = Pt (<b>6</b>)) are observed. Temperature
behavior of magnetic susceptibility indicates that all compounds bearing
FeN<sub>6</sub> units (<b>1</b>ā<b>6</b>) display
cooperative spin transition, while Fe<sup>II</sup> ions in N<sub>5</sub>O or N<sub>4</sub>O<sub>2</sub> surrounding are high spin (HS). Structural
changes in the nearest Fe<sup>II</sup> environment upon low-spin (LS)
to HS transition, which include ca. 10% FeāN distance increase,
lead to the cell expansion. MoĢssbauer spectroscopy is used
to characterize the spin state of all HS, LS, and intermediate phases
of <b>1</b>ā<b>9</b> (see abstract figure). Effects
of a pyrazine substituent and M<sup>II</sup> nature on the hyperfine
parameters in both spin states are established
Spin Crossover in Fe(II)āM(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2āSubstituted Pyrazines
Discovery of spin-crossover
(SCO) behavior in the family of Fe<sup>II</sup>-based Hofmann clathrates
has led to a ānew rushā in the field of bistable molecular
materials. To date this class of SCO complexes is represented by several
dozens of individual compounds, and areas of their potential application
steadily increase. Starting from Fe<sup>2+</sup>, square planar tetracyanometalates
M<sup>II</sup>(CN)<sub>4</sub><sup>2ā</sup> (M<sup>II</sup> = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as
coligands we obtained a series of nine new Hofmann clathrate-like
coordination frameworks. X-ray diffraction reveals that in these complexes
Fe<sup>II</sup> ion has a pseudo-octahedral coordination environment
supported by four Ī¼<sub>4</sub>-tetracyanometallates forming
its equatorial coordination environment. Depending on the nature of
X and M, axial positions are occupied by two 2X-pyrazines (X = Cl
and M<sup>II</sup> = Ni (<b>1</b>), Pd (<b>2</b>), Pt
(<b>3</b>); X = Me and M<sup>II</sup> = Ni (<b>4</b>),
Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X
= I and M<sup>II</sup> = Ni (<b>7</b>), Pd (<b>8</b>),
Pt (<b>9</b>)), or, alternatively, two distinct Fe<sup>II</sup> positions with either two pyrazines or two water molecules (X =
Me and M<sup>II</sup> = Pt (<b>6</b>)) are observed. Temperature
behavior of magnetic susceptibility indicates that all compounds bearing
FeN<sub>6</sub> units (<b>1</b>ā<b>6</b>) display
cooperative spin transition, while Fe<sup>II</sup> ions in N<sub>5</sub>O or N<sub>4</sub>O<sub>2</sub> surrounding are high spin (HS). Structural
changes in the nearest Fe<sup>II</sup> environment upon low-spin (LS)
to HS transition, which include ca. 10% FeāN distance increase,
lead to the cell expansion. MoĢssbauer spectroscopy is used
to characterize the spin state of all HS, LS, and intermediate phases
of <b>1</b>ā<b>9</b> (see abstract figure). Effects
of a pyrazine substituent and M<sup>II</sup> nature on the hyperfine
parameters in both spin states are established
Spin Crossover in Fe(II)āM(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2āSubstituted Pyrazines
Discovery of spin-crossover
(SCO) behavior in the family of Fe<sup>II</sup>-based Hofmann clathrates
has led to a ānew rushā in the field of bistable molecular
materials. To date this class of SCO complexes is represented by several
dozens of individual compounds, and areas of their potential application
steadily increase. Starting from Fe<sup>2+</sup>, square planar tetracyanometalates
M<sup>II</sup>(CN)<sub>4</sub><sup>2ā</sup> (M<sup>II</sup> = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as
coligands we obtained a series of nine new Hofmann clathrate-like
coordination frameworks. X-ray diffraction reveals that in these complexes
Fe<sup>II</sup> ion has a pseudo-octahedral coordination environment
supported by four Ī¼<sub>4</sub>-tetracyanometallates forming
its equatorial coordination environment. Depending on the nature of
X and M, axial positions are occupied by two 2X-pyrazines (X = Cl
and M<sup>II</sup> = Ni (<b>1</b>), Pd (<b>2</b>), Pt
(<b>3</b>); X = Me and M<sup>II</sup> = Ni (<b>4</b>),
Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X
= I and M<sup>II</sup> = Ni (<b>7</b>), Pd (<b>8</b>),
Pt (<b>9</b>)), or, alternatively, two distinct Fe<sup>II</sup> positions with either two pyrazines or two water molecules (X =
Me and M<sup>II</sup> = Pt (<b>6</b>)) are observed. Temperature
behavior of magnetic susceptibility indicates that all compounds bearing
FeN<sub>6</sub> units (<b>1</b>ā<b>6</b>) display
cooperative spin transition, while Fe<sup>II</sup> ions in N<sub>5</sub>O or N<sub>4</sub>O<sub>2</sub> surrounding are high spin (HS). Structural
changes in the nearest Fe<sup>II</sup> environment upon low-spin (LS)
to HS transition, which include ca. 10% FeāN distance increase,
lead to the cell expansion. MoĢssbauer spectroscopy is used
to characterize the spin state of all HS, LS, and intermediate phases
of <b>1</b>ā<b>9</b> (see abstract figure). Effects
of a pyrazine substituent and M<sup>II</sup> nature on the hyperfine
parameters in both spin states are established