24 research outputs found
Rhenium Complex with Noninnocent Dioxolene Ligand: Combined Experimental and ab Initio Study of [(3,5-di-<i>tert</i>-Bu<sub>2</sub>C<sub>6</sub>H<sub>2</sub>O<sub>2</sub>)ReCl<sub>3</sub>(OPPh<sub>3</sub>)]
Reaction of [ReOCl<sub>3</sub>(PPh<sub>3</sub>)<sub>2</sub>] with 3,5-di-<i>tert</i>-butyl-1,2-benzoquinone
(3,5-DTBQ) in hot toluene produces a new complex [(3,5-di-<i>tert</i>-Bu<sub>2</sub>C<sub>6</sub>H<sub>2</sub>O<sub>2</sub>)ĀReĀ(OPPh<sub>3</sub>)ĀCl<sub>3</sub>] (<b>1</b>), which was
isolated and characterized by elemental analysis, IR, UVāvis
spectroscopy, and cyclic voltammetry. In order to clarify the charge
state of rhenium and the coordinated dioxolene ligand, X-ray experiments
at 150 and 290 K were carried out. The CāO, CāC, and
ReāO bond distances at both 150 and 290 K fall between those
for semiquinolate (3,5-DTBSQ) and catecholate (3,5-DTBCat) forms;
an empirical āmetrical oxidation stateā of the dioxolene
ligand was estimated to be ā1.5. High-level <i>ab initio</i> calculations (SOC-CASSCF/NEVPT2) revealed a mixed valence nature
of the triplet ground state of complex <b>1</b> corresponding
to a superposition of the <i>Re</i><sup><i>IV</i></sup>ā<i>SQ</i> and <i>Re</i><sup><i>V</i></sup>ā<i>cat</i> forms. In agreement
with the high-level <i>ab initio</i> and DFT calculations,
the temperature dependence of the magnetic susceptibility (5ā300
K) is well described in the assumption of the triplet ground state,
with the anomalously large zero-field splitting (ZFS) arising from
the spināorbit coupling. According to the <i>ab initio</i> calculations, all absorption bands in the visible region of the
electronic absorptions spectrum are assigned to the LMCT bands, with
significant contribution of the intraligand transition in the most intense band
at 555 nm
Mixed Phenyl and Thiophene Oligomers for Bridging Nitronyl Nitroxides
The
synthesis of four nitronyl nitroxide (NN) biradicals is described
which are conjugatively linked through <i>p-ter</i>-phenyl
(PPP), <i>ter</i>-thiophene (TTT) and alternating phenylene
(P) and thiophene (T) units as PTP and TPT. We first utilized Suzuki
and Stille coupling reactions through protection and deprotection
protocols to synthesize these (NN) biradicals. Single crystals were
efficiently grown for radical precursors of <b>3</b>, <b>5</b>, <b>6</b>, <b>PPP-NNSi, PTP-NNSi</b>, and final
biradicals of <b>TTT-NN</b>, <b>TPT-NN</b>, and <b>PPP-NN</b>, whose structures and molecular packing were examined
by X-ray diffraction studies. As a result, much smaller torsions between
the NN and thiophene units (ā¼10Ā°) in <b>TTT-NN</b> and <b>TPT-NN</b> than for NN and phenyl units (ā¼29Ā°)
in <b>PPP-NN</b> were observed due to smaller hindrance for
a five vs a six membered ring. All four biradicals <b>TTT-NN</b>, <b>TPT-NN</b>, <b>PTP-NN</b>, and <b>PPP-NN</b> were investigated by EPR and optical spectroscopy combined with
DFT calculations. The magnetic susceptibility was studied by SQUID
measurements for <b>TTT-NN</b> and <b>TPT-NN</b>. The
intramolecular exchange interactions for <b>TPT-NN</b> and <b>TTT-NN</b> were found in good agreement with the ones calculated
by broken symmetry DFT calculations
Mixed Phenyl and Thiophene Oligomers for Bridging Nitronyl Nitroxides
The
synthesis of four nitronyl nitroxide (NN) biradicals is described
which are conjugatively linked through <i>p-ter</i>-phenyl
(PPP), <i>ter</i>-thiophene (TTT) and alternating phenylene
(P) and thiophene (T) units as PTP and TPT. We first utilized Suzuki
and Stille coupling reactions through protection and deprotection
protocols to synthesize these (NN) biradicals. Single crystals were
efficiently grown for radical precursors of <b>3</b>, <b>5</b>, <b>6</b>, <b>PPP-NNSi, PTP-NNSi</b>, and final
biradicals of <b>TTT-NN</b>, <b>TPT-NN</b>, and <b>PPP-NN</b>, whose structures and molecular packing were examined
by X-ray diffraction studies. As a result, much smaller torsions between
the NN and thiophene units (ā¼10Ā°) in <b>TTT-NN</b> and <b>TPT-NN</b> than for NN and phenyl units (ā¼29Ā°)
in <b>PPP-NN</b> were observed due to smaller hindrance for
a five vs a six membered ring. All four biradicals <b>TTT-NN</b>, <b>TPT-NN</b>, <b>PTP-NN</b>, and <b>PPP-NN</b> were investigated by EPR and optical spectroscopy combined with
DFT calculations. The magnetic susceptibility was studied by SQUID
measurements for <b>TTT-NN</b> and <b>TPT-NN</b>. The
intramolecular exchange interactions for <b>TPT-NN</b> and <b>TTT-NN</b> were found in good agreement with the ones calculated
by broken symmetry DFT calculations
Rhenium Complex with Noninnocent Dioxolene Ligand: Combined Experimental and ab Initio Study of [(3,5-di-<i>tert</i>-Bu<sub>2</sub>C<sub>6</sub>H<sub>2</sub>O<sub>2</sub>)ReCl<sub>3</sub>(OPPh<sub>3</sub>)]
Reaction of [ReOCl<sub>3</sub>(PPh<sub>3</sub>)<sub>2</sub>] with 3,5-di-<i>tert</i>-butyl-1,2-benzoquinone
(3,5-DTBQ) in hot toluene produces a new complex [(3,5-di-<i>tert</i>-Bu<sub>2</sub>C<sub>6</sub>H<sub>2</sub>O<sub>2</sub>)ĀReĀ(OPPh<sub>3</sub>)ĀCl<sub>3</sub>] (<b>1</b>), which was
isolated and characterized by elemental analysis, IR, UVāvis
spectroscopy, and cyclic voltammetry. In order to clarify the charge
state of rhenium and the coordinated dioxolene ligand, X-ray experiments
at 150 and 290 K were carried out. The CāO, CāC, and
ReāO bond distances at both 150 and 290 K fall between those
for semiquinolate (3,5-DTBSQ) and catecholate (3,5-DTBCat) forms;
an empirical āmetrical oxidation stateā of the dioxolene
ligand was estimated to be ā1.5. High-level <i>ab initio</i> calculations (SOC-CASSCF/NEVPT2) revealed a mixed valence nature
of the triplet ground state of complex <b>1</b> corresponding
to a superposition of the <i>Re</i><sup><i>IV</i></sup>ā<i>SQ</i> and <i>Re</i><sup><i>V</i></sup>ā<i>cat</i> forms. In agreement
with the high-level <i>ab initio</i> and DFT calculations,
the temperature dependence of the magnetic susceptibility (5ā300
K) is well described in the assumption of the triplet ground state,
with the anomalously large zero-field splitting (ZFS) arising from
the spināorbit coupling. According to the <i>ab initio</i> calculations, all absorption bands in the visible region of the
electronic absorptions spectrum are assigned to the LMCT bands, with
significant contribution of the intraligand transition in the most intense band
at 555 nm
Heteroligand oāSemiquinonato-Formazanato Cobalt Complexes
Two
novel heteroligand o-semiquinonato-formazanato cobalt complexes [CoĀ(3,6-SQ)Ā(Form)]
(<b>1</b>) and [CoĀ(3,6-SQ)<sub>2</sub>(Form)] (<b>2</b>) (3,6-SQ is 3,6-di-<i>tert</i>-butyl-o-benzosemiquinonate
radical anion; Form is 1,3,5-triphenylformazanate anion) were synthesized
and characterized in detail. The molecular structures of [CoĀ(3,6-SQ)Ā(Form)]
and [CoĀ(3,6-SQ)<sub>2</sub>(Form)] were determined by X-ray analysis.
Magnetic susceptibility measurements and spectroscopic studies have
shown that square-planar complex <b>1</b> is diamagnetic with
a residual paramagnetism due to antiferromagnetic exchange metalāligand.
Complex <b>2</b> includes cobaltĀ(III) in the low-spin state
and two anionic-radical o-semiquinonato and one formazanate ligand
Ferroceneā<i>o</i>āBenzosemiquinonato Tin(IV) Electron-Transfer Complexes
The interaction of
ferrocene with tinĀ(IV) <i>o</i>-benzosemiquinonato complexes
in acetonitrile results in a reversible electron transfer (ET) from
ferrocene to the redox-active ligand with the formation of electron-transfer
complexes [(3,6-Cat)ĀSnBr<sub>3</sub>]<sup>ā</sup>[Cp<sub>2</sub>Fe]<sup>+</sup> (<b>1</b>) and [(3,6-Cat)Ā(3,6-SQ)ĀSnCl<sub>2</sub>]<sup>ā</sup>[Cp<sub>2</sub>Fe]<sup>+</sup> (<b>2</b>), where 3,6-Cat is the 3,6-di-<i>tert</i>-butyl-catecholate
dianion and 3,6-SQ is the 3,6-di-<i>tert</i>-butyl-<i>o</i>-benzosemiquinonato radical anion. The ET process and the
solvent effect in the system āŖferroceneā<i>o</i>-benzosemiquinonato tinĀ(IV) complexesā« were investigated on
the basis of a combination of spectroscopic and X-ray diffraction
methods. The molecular structures of <b>1</b> and <b>2</b> were confirmed by X-ray analysis. Complex <b>2</b> demonstrates
the ferromagnetic coupling in the linear chain alternating Ā·Ā·Ā·D<sup>+ā¢</sup>A<sup>āā¢</sup>D<sup>+ā¢</sup>A<sup>āā¢</sup>Ā·Ā·Ā· motif
Ferroceneā<i>o</i>āBenzosemiquinonato Tin(IV) Electron-Transfer Complexes
The interaction of
ferrocene with tinĀ(IV) <i>o</i>-benzosemiquinonato complexes
in acetonitrile results in a reversible electron transfer (ET) from
ferrocene to the redox-active ligand with the formation of electron-transfer
complexes [(3,6-Cat)ĀSnBr<sub>3</sub>]<sup>ā</sup>[Cp<sub>2</sub>Fe]<sup>+</sup> (<b>1</b>) and [(3,6-Cat)Ā(3,6-SQ)ĀSnCl<sub>2</sub>]<sup>ā</sup>[Cp<sub>2</sub>Fe]<sup>+</sup> (<b>2</b>), where 3,6-Cat is the 3,6-di-<i>tert</i>-butyl-catecholate
dianion and 3,6-SQ is the 3,6-di-<i>tert</i>-butyl-<i>o</i>-benzosemiquinonato radical anion. The ET process and the
solvent effect in the system āŖferroceneā<i>o</i>-benzosemiquinonato tinĀ(IV) complexesā« were investigated on
the basis of a combination of spectroscopic and X-ray diffraction
methods. The molecular structures of <b>1</b> and <b>2</b> were confirmed by X-ray analysis. Complex <b>2</b> demonstrates
the ferromagnetic coupling in the linear chain alternating Ā·Ā·Ā·D<sup>+ā¢</sup>A<sup>āā¢</sup>D<sup>+ā¢</sup>A<sup>āā¢</sup>Ā·Ā·Ā· motif
Indirect Magnetic Exchange between <i>o</i>āIminosemiquinonate Ligands Controlled by Apical Substituent in Pentacoordinated Gallium(III) Complexes
A number of pentacoordinated gallium
complexes iSQ<sub>2</sub>GaR (<b>1</b>ā<b>7</b>) (R = Et (<b>1</b>), Me (<b>2</b>), N<sub>3</sub> (<b>3</b>), Cl (<b>4</b>), Br (<b>5</b>), I (<b>6</b>), NCS (<b>7</b>)) where iSQ is a radical anion of 4,6-di-<i>tert</i>-butyl-<i>N</i>-(2,6-diisopropylphenyl)-<i>o</i>-iminobenzoquinone were synthesized, and crystalline samples
of <b>1</b>ā<b>7</b> were characterized using magnetic
susceptibility measurements. The character of magnetic exchange interaction
between spins of <i>o</i>-iminosemiquinonate radicals was
found to be strongly influenced by the nature of the apical substituent.
The antiferromagnetic coupling is predominant when the apical position
is occupied by halogens or other tested inorganic anions, and the
value of exchange interaction parameter varies from ā99 to
ā176 K for R = I and NCS, respectively. In the case of alkyl
groups the ferromagnetic exchange prevails and, as the result, the
triplet ground state for pentacoordianted biradical compounds was
observed. Compounds <b>1</b>ā<b>7</b> demonstrate
a biradical X-band EPR spectrum in frozen toluene matrix. The molecular
structures of <b>4</b>, <b>6</b>, and <b>7</b> have
been established by single-crystal X-ray analysis. A computational
DFT UB3LYP/6-31GĀ(d,p) study was performed on complexes <b>1ā7</b> in order to understand the reason for changes in the magnetic behavior
of the related diradical gallium compounds. The calculations showed
that the magnetic behavior of the complexes with inorganic anions
is conditioned by the presence of antiferromagnetic exchange channel
formed as a consequence of overlapping between donor atomic orbitals
of iminoquinone with Ļ-orbitals of halogen atoms (<b>4</b>ā<b>6</b>) or nitrogen atom (<b>3</b>, <b>7</b>)
First Example of a Reversible Single-Crystal-to-Single-Crystal PolymerizationāDepolymerization Accompanied by a Magnetic Anomaly for a Transition-Metal Complex with an Organic Radical
The reaction of copperĀ(II) hexafluoroacetylacetonate
[CuĀ(hfac)<sub>2</sub>] with the stable nitronyl nitroxide 2-(1-ethyl-3-methyl-1<i>H</i>-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1<i>H</i>-imidazole-3-oxide-1-oxyl (L<sup>a</sup>) resulted in a
paired heterospin complex [[CuĀ(hfac)<sub>2</sub>]<sub>3</sub>(Ī¼-<i>O</i>,<i>N</i>-L<sup>a</sup>)<sub>2</sub>]Ā[CuĀ(hfac)<sub>2</sub>(<i>O</i>-L<sup>a</sup>)<sub>2</sub>]. The crystals
of the compound were found to be capable of a reversible single-crystal-to-single-crystal
(SCāSC) transformation initiated by the variation of temperature.
At room temperature, the molecular structure of [[CuĀ(hfac)<sub>2</sub>]<sub>3</sub>(Ī¼-<i>O</i>,<i>N</i>-L<sup>a</sup>)<sub>2</sub>]Ā[CuĀ(hfac)<sub>2</sub>(<i>O</i>-L<sup>a</sup>)<sub>2</sub>] is formed by the alternating fragments of the
pair complex. Cooling the crystals of the complex below 225 K caused
considerable mutual displacements of adjacent molecules, which ended
in a transformation of the molecular structure into a polymer chain
structure. A reversible topotactic polymerizationādepolymerization
coordination reaction actually takes place in the solid during repeated
coolingāheating cycles: [[CuĀ(hfac)<sub>2</sub>]<sub>3</sub>(Ī¼-<i>O</i>,<i>N</i>-L<sup>a</sup>)<sub>2</sub>]Ā[CuĀ(hfac)<sub>2</sub>(<i>O</i>-L<sup>a</sup>)<sub>2</sub>] ā CuĀ(hfac)<sub>2</sub>(Ī¼-<i>O</i>,<i>N</i>-L<sup>a</sup>)]<sub>ā</sub>. Polymerization
during cooling is the result of the anomalously great shortening of
intermolecular distances (from 4.403 Ć
at 295 K to 2.460 Ć
at 150 K; Ī<i>d</i> = 1.943 Ć
) between the terminal
Cu atoms of the trinuclear fragments {[[CuĀ(hfac)<sub>2</sub>]<sub>3</sub>(Ī¼-<i>O</i>,<i>N</i>-L<sup>a</sup>)<sub>2</sub>]} and the noncoordinated N atoms of the pyrazole rings
of the mononuclear {[CuĀ(hfac)<sub>2</sub>(<i>O</i>-L<sup>a</sup>)<sub>2</sub>]} fragments. When the low-temperature phase
was heated above 270 K, the polymer chain structure was destroyed
and the compound was again converted to the pair molecular complex.
The specifics of the given SCāSC transformation lies in the
fact that the process is accompanied by a magnetic anomaly, because
the intracrystalline displacements of molecules lead to a considerable
change in the mutual orientation of the paramagnetic centers, which,
in turn, causes modulation of the exchange interaction between the
odd electrons of the Cu<sup>2+</sup> ion and nitroxide. On the temperature
curve of Ļ<i>T</i>, this shows itself as a hysteresis
loop. The nontrivial character of the recorded spin transition during
the cooling of the sample below 225 K lies in the fact that the magnetic
moment abruptly increased. In contrast, heating the sample above 270
K led to a drastic decrease in Ļ<i>T</i>. This behavior
of Ļ<i>T</i> is caused by a stepwise change in the
character of the exchange interaction in the {>Nā<sup>ā¢</sup>OāCu<sup>2+</sup>āO<sup>ā¢</sup>āN<}
fragments. The lengthening of distances between the paramagnetic centers
on cooling below 225 K led to a transition from antiferromagnetic
to ferromagnetic exchange and, vice versa, the shortening of distances
between the paramagnetic centers during the heating of the heterospin
polymer above 270 K led to a transition from ferromagnetic exchange
to antiferromagnetic exchange
Ferroceneā<i>o</i>āBenzosemiquinonato Tin(IV) Electron-Transfer Complexes
The interaction of
ferrocene with tinĀ(IV) <i>o</i>-benzosemiquinonato complexes
in acetonitrile results in a reversible electron transfer (ET) from
ferrocene to the redox-active ligand with the formation of electron-transfer
complexes [(3,6-Cat)ĀSnBr<sub>3</sub>]<sup>ā</sup>[Cp<sub>2</sub>Fe]<sup>+</sup> (<b>1</b>) and [(3,6-Cat)Ā(3,6-SQ)ĀSnCl<sub>2</sub>]<sup>ā</sup>[Cp<sub>2</sub>Fe]<sup>+</sup> (<b>2</b>), where 3,6-Cat is the 3,6-di-<i>tert</i>-butyl-catecholate
dianion and 3,6-SQ is the 3,6-di-<i>tert</i>-butyl-<i>o</i>-benzosemiquinonato radical anion. The ET process and the
solvent effect in the system āŖferroceneā<i>o</i>-benzosemiquinonato tinĀ(IV) complexesā« were investigated on
the basis of a combination of spectroscopic and X-ray diffraction
methods. The molecular structures of <b>1</b> and <b>2</b> were confirmed by X-ray analysis. Complex <b>2</b> demonstrates
the ferromagnetic coupling in the linear chain alternating Ā·Ā·Ā·D<sup>+ā¢</sup>A<sup>āā¢</sup>D<sup>+ā¢</sup>A<sup>āā¢</sup>Ā·Ā·Ā· motif