4 research outputs found
Antisymmetric Exchange in Triangular Tricopper(II) Complexes: Correlation among Structural, Magnetic, and Electron Paramagnetic Resonance Parameters
Two new trinuclear copperĀ(II) complexes, [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(daat)Ā(Hdat)<sub>2</sub>(ClO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>3</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·2H<sub>2</sub>O (<b>1</b>) and [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aaat)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·3H<sub>2</sub>O (<b>2</b>) (daat = 3,5-diacetylamino-1,2,4-triazolate,
Hdat = 3,5-diamino-1,2,4-triazole, and aaat = 3-acetylamino-5-amino-1,2,4-triazolate),
have been prepared from 1,2,4-triazole derivatives and structurally
characterized by X-ray crystallography. The structures of <b>1</b> and <b>2</b> consist of cationic trinuclear copperĀ(II) complexes
with a Cu<sub>3</sub>OH core held by three <i>N</i>,<i>N</i>-triazole bridges between each pair of copperĀ(II) atoms.
The copper atoms are five-coordinate with distorted square-pyramidal
geometries. The magnetic properties of <b>1</b> and <b>2</b> and those of five other related 1,2,4-triazolato tricopperĀ(II) complexes
with the same triangular structure (<b>3ā7</b>) (whose
crystal structures were already reported) have been investigated in
the temperature range of 1.9ā300 K. The formulas of <b>3ā7</b> are [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aaat)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>]Ā(NO<sub>3</sub>)<sub>2</sub>Ā·H<sub>2</sub>O (<b>3</b>), {[Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aat)<sub>3</sub>(Ī¼<sub>3</sub>-SO<sub>4</sub>)]Ā·6H<sub>2</sub>O}<sub><i>n</i></sub> (<b>4</b>), and [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aat)<sub>3</sub>AĀ(H<sub>2</sub>O)<sub>2</sub>]ĀAĀ·<i>x</i>H<sub>2</sub>O [A = NO<sub>3</sub><sup>ā</sup> (<b>5</b>), CF<sub>3</sub>SO<sub>3</sub><sup>ā</sup> (<b>6</b>), or ClO<sub>4</sub><sup>ā</sup> (<b>7</b>); <i>x</i> = 0 or 2] (aat =3-acetylamino-1,2,4-triazolate). The magnetic
and electron paramagnetic resonance (EPR) data have been analyzed
by using the following isotropic and antisymmetric exchange Hamiltonian: <i>H</i> = ā<i>J</i>[<i>S</i><sub>1</sub><i>S</i><sub>2</sub> + <i>S</i><sub>2</sub><i>S</i><sub>3</sub>] ā <i>j</i>[<i>S</i><sub>1</sub><i>S</i><sub>3</sub>] + <i>G</i>[<i>S</i><sub>1</sub> Ć <i>S</i><sub>2</sub> + <i>S</i><sub>2</sub> Ć <i>S</i><sub>3</sub> + <i>S</i><sub>1</sub> Ć <i>S</i><sub>3</sub>]. <b>1</b>ā<b>7</b> exhibit strong antiferromagnetic coupling
(values for both ā<i>J</i> and ā<i>j</i> in the range of 210ā142 cm<sup>ā1</sup>) and antisymmetric
exchange (<i>G</i> varying from to 27 to 36 cm<sup>ā1</sup>). At low temperatures, their EPR spectra display high-field (<i>g</i> < 2.0) signals indicating that the triangles present
symmetry lower than equilateral and that the antisymmetric exchange
is operative. A magneto-structural study showing a lineal correlation
between the CuāOāCu angle of the Cu<sub>3</sub>OH core
and the isotropic exchange parameters (<i>J</i> and <i>j</i>) has been conducted. Moreover, a model based on Moriyaās
theory that allows the prediction of the occurrence of antisymmetric
exchange in the tricopperĀ(II) triangles, via analysis of the overlap
between the ground and excited states of the local CuĀ(II) ions, has
been proposed. In addition, analytical expressions for evaluating
both the isotropic and antisymmetric exchange parameters from the
experimental magnetic susceptibility data of triangular complexes
with local spins (<i>S</i>) of <sup>1</sup>/<sub>2</sub>, <sup>3</sup>/<sub>2</sub>, or <sup>5</sup>/<sub>2</sub> have been
purposely derived. Finally, the magnetic and EPR results of this work
are discussed and compared with those of other tricopperĀ(II) triangles
reported in the literature
Nonanuclear Spin-Crossover Complex Containing Iron(II) and Iron(III) Based on a 2,6-Bis(pyrazol-1-yl)pyridine Ligand Functionalized with a Carboxylate Group
The synthesis and
magnetostructural characterization of [Fe<sup>III</sup><sub>3</sub>(Ī¼<sub>3</sub>-O)Ā(H<sub>2</sub>O)<sub>3</sub>[Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sub>6</sub>]Ā(ClO<sub>4</sub>)<sub>13</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CO)<sub>6</sub>Ā·(solvate) (<b>2</b>) are reported. This compound is obtained as a secondary product
during synthesis of the mononuclear complex [Fe<sup>II</sup>(bppCOOH)<sub>2</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub> (<b>1</b>). The single-crystal
X-ray diffraction structure of <b>2</b> shows that it contains
the nonanuclear cluster of the formula [Fe<sup>III</sup><sub>3</sub>(Ī¼<sub>3</sub>-O)Ā(H<sub>2</sub>O)<sub>3</sub>[Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sub>6</sub>]<sup>13+</sup>, which is formed by
a central Fe<sup>III</sup><sub>3</sub>O core coordinated to six partially
deprotonated [Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sup>+</sup> complexes.
Raman spectroscopy studies on single crystals of <b>1</b> and <b>2</b> have been performed to elucidate the spin and oxidation
states of iron in <b>2</b>. These studies and magnetic characterization
indicate that most of the ironĀ(II) complexes of <b>2</b> remain
in the low-spin (LS) state and present a gradual and incomplete spin
crossover above 300 K. On the other hand, the Fe<sup>III</sup> trimer
shows the expected antiferromagnetic behavior. From the structural
point of view, <b>2</b> represents the first example in which
bppCOO<sup>ā</sup> acts as a bridging ligand, thus forming
a polynuclear magnetic complex
Nonanuclear Spin-Crossover Complex Containing Iron(II) and Iron(III) Based on a 2,6-Bis(pyrazol-1-yl)pyridine Ligand Functionalized with a Carboxylate Group
The synthesis and
magnetostructural characterization of [Fe<sup>III</sup><sub>3</sub>(Ī¼<sub>3</sub>-O)Ā(H<sub>2</sub>O)<sub>3</sub>[Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sub>6</sub>]Ā(ClO<sub>4</sub>)<sub>13</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CO)<sub>6</sub>Ā·(solvate) (<b>2</b>) are reported. This compound is obtained as a secondary product
during synthesis of the mononuclear complex [Fe<sup>II</sup>(bppCOOH)<sub>2</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub> (<b>1</b>). The single-crystal
X-ray diffraction structure of <b>2</b> shows that it contains
the nonanuclear cluster of the formula [Fe<sup>III</sup><sub>3</sub>(Ī¼<sub>3</sub>-O)Ā(H<sub>2</sub>O)<sub>3</sub>[Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sub>6</sub>]<sup>13+</sup>, which is formed by
a central Fe<sup>III</sup><sub>3</sub>O core coordinated to six partially
deprotonated [Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sup>+</sup> complexes.
Raman spectroscopy studies on single crystals of <b>1</b> and <b>2</b> have been performed to elucidate the spin and oxidation
states of iron in <b>2</b>. These studies and magnetic characterization
indicate that most of the ironĀ(II) complexes of <b>2</b> remain
in the low-spin (LS) state and present a gradual and incomplete spin
crossover above 300 K. On the other hand, the Fe<sup>III</sup> trimer
shows the expected antiferromagnetic behavior. From the structural
point of view, <b>2</b> represents the first example in which
bppCOO<sup>ā</sup> acts as a bridging ligand, thus forming
a polynuclear magnetic complex
Nonanuclear Spin-Crossover Complex Containing Iron(II) and Iron(III) Based on a 2,6-Bis(pyrazol-1-yl)pyridine Ligand Functionalized with a Carboxylate Group
The synthesis and
magnetostructural characterization of [Fe<sup>III</sup><sub>3</sub>(Ī¼<sub>3</sub>-O)Ā(H<sub>2</sub>O)<sub>3</sub>[Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sub>6</sub>]Ā(ClO<sub>4</sub>)<sub>13</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CO)<sub>6</sub>Ā·(solvate) (<b>2</b>) are reported. This compound is obtained as a secondary product
during synthesis of the mononuclear complex [Fe<sup>II</sup>(bppCOOH)<sub>2</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub> (<b>1</b>). The single-crystal
X-ray diffraction structure of <b>2</b> shows that it contains
the nonanuclear cluster of the formula [Fe<sup>III</sup><sub>3</sub>(Ī¼<sub>3</sub>-O)Ā(H<sub>2</sub>O)<sub>3</sub>[Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sub>6</sub>]<sup>13+</sup>, which is formed by
a central Fe<sup>III</sup><sub>3</sub>O core coordinated to six partially
deprotonated [Fe<sup>II</sup>(bppCOOH)Ā(bppCOO)]<sup>+</sup> complexes.
Raman spectroscopy studies on single crystals of <b>1</b> and <b>2</b> have been performed to elucidate the spin and oxidation
states of iron in <b>2</b>. These studies and magnetic characterization
indicate that most of the ironĀ(II) complexes of <b>2</b> remain
in the low-spin (LS) state and present a gradual and incomplete spin
crossover above 300 K. On the other hand, the Fe<sup>III</sup> trimer
shows the expected antiferromagnetic behavior. From the structural
point of view, <b>2</b> represents the first example in which
bppCOO<sup>ā</sup> acts as a bridging ligand, thus forming
a polynuclear magnetic complex