2 research outputs found
The Series of Molecular Conductors and Superconductors ET<sub>4</sub>[AFe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]·PhX (ET = bis(ethylenedithio)tetrathiafulvalene; (C<sub>2</sub>O<sub>4</sub>)<sup>2–</sup> = oxalate; A<sup>+</sup> = H<sub>3</sub>O<sup>+</sup>, K<sup>+</sup>; X = F, Cl, Br, and I): Influence of the Halobenzene Guest Molecules on the Crystal Structure and Superconducting Properties
An extensive series of radical salts formed by the organic
donor bis(ethylenedithio)tetrathiafulvalene
(ET), the paramagnetic tris(oxalato)ferrate(III) anion [Fe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]<sup>3–</sup>, and halobenzene
guest molecules has been synthesized and characterized. The change
of the halogen atom in this series has allowed the study of the effect
of the size and charge polarization on the crystal structures and
physical properties while keeping the geometry of the guest molecule.
The general formula of the salts is ET<sub>4</sub>[A<sup>I</sup>Fe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]·G with A/G = H<sub>3</sub>O<sup>+</sup>/PhF (<b>1</b>); H<sub>3</sub>O<sup>+</sup>/PhCl
(<b>2</b>); H<sub>3</sub>O<sup>+</sup>/PhBr (<b>3</b>),
and K<sup>+</sup>/PhI (<b>4</b>), (crystal data at room temperature:
(<b>1</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.3123(2) Å, <i>b</i> = 20.0205(3) Å, <i>c</i> = 35.2732(4) Å, β
= 92.511(2)°, <i>V</i> = 7275.4(2) Å<sup>3</sup>, <i>Z</i> = 4; (<b>2</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.2899(4)
Å, <i>b</i> = 20.026(10) Å, <i>c</i> = 35.411(10) Å, β = 92.974°, <i>V</i> =
7287(4) Å<sup>3</sup>, <i>Z</i> = 4; (<b>3</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.2875(3) Å, <i>b</i> = 20.0546(15)
Å, <i>c</i> = 35.513(2) Å, β = 93.238(5)°, <i>V</i> = 7315.0(7) Å<sup>3</sup>, <i>Z</i> = 4;
(<b>4</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.2260(2) Å, <i>b</i> = 19.9234(2) Å, <i>c</i> = 35.9064(6) Å, β
= 93.3664(6)°, <i>V</i> = 7302.83(18) Å<sup>3</sup>, <i>Z</i> = 4). The crystal structures at 120 K evidence
that compounds <b>1</b>–<b>3</b> undergo a structural
transition to a lower symmetry phase when the temperature is lowered
(crystal data at 120 K: (<b>1</b>) triclinic, space group <i>P</i>1̅ with <i>a</i> = 10.2595(3) Å, <i>b</i> = 11.1403(3) Å, <i>c</i> = 34.9516(9) Å,
α = 89.149(2)°, β = 86.762(2)°, γ = 62.578(3)°, <i>V</i> = 3539.96(19) Å<sup>3</sup>, <i>Z</i> =
2; (<b>2</b>) triclinic, space group <i>P</i>1̅
with <i>a</i> = 10.25276(14) Å, <i>b</i> =
11.15081(13) Å, <i>c</i> = 35.1363(5) Å, α
= 89.0829(10)°, β = 86.5203(11)°, γ = 62.6678(13)°, <i>V</i> = 3561.65(8) Å<sup>3</sup>, <i>Z</i> =
2; (<b>3</b>) triclinic, space group <i>P</i>1̅
with <i>a</i> = 10.25554(17) Å, <i>b</i> =
11.16966(18) Å, <i>c</i> = 35.1997(5) Å, α
= 62.7251(16)°, β = 86.3083(12)°, γ = 62.7251(16)°, <i>V</i> = 3575.99(10) Å<sup>3</sup>, <i>Z</i> =
2; (<b>4</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.1637(3) Å, <i>b</i> = 19.7251(6) Å, <i>c</i> = 35.6405(11) Å, β
= 93.895(3)°, <i>V</i> = 7128.7(4) Å<sup>3</sup>, <i>Z</i> = 4). A detailed crystallographic study shows
a change in the symmetry of the crystal for compound <b>3</b> at about 200 K. This structural transition arises from the partial
ordering of some ethylene groups in the ET molecules and involves
a slight movement of the halobenzene guest molecules (which occupy
hexagonal cavities in the anionic layers) toward one of the adjacent
organic layers, giving rise to two nonequivalent organic layers at
120 K (compared to only one at room temperature). The structural transition
at about 200 K is also observed in the electrical properties of <b>1</b>–<b>3</b> and in the magnetic properties of <b>1</b>. The direct current (dc) conductivity shows metallic behavior
in salts <b>1</b>–<b>3</b> with superconducting
transitions at about 4.0 and 1.0 K in salts <b>3</b> and <b>1</b>, respectively. Salt <b>4</b> shows a semiconductor
behavior in the temperature range 300–50 K with an activation
energy of 64 meV. The magnetic measurements confirm the presence of
high spin <i>S</i> = 5/2 [Fe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]<sup>3–</sup> isolated monomers together with a Pauli
paramagnetism, typical of metals, in compounds <b>1</b>–<b>3</b>. The magnetic properties can be very well reproduced in
the whole temperature range with a simple model of isolated <i>S</i> = 5/2 ions with a zero field splitting plus a temperature
independent paramagnetism (Nα) with the following parameters: <i>g</i> = 1.965, |<i>D</i>| = 0.31 cm<sup>–1</sup>, and Nα = 1.5 × 10<sup>–3</sup> emu mol<sup>–1</sup> for <b>1</b>, <i>g</i> = 2.024, |<i>D</i>| = 0.65 cm<sup>–1</sup>, and Nα = 1.4 × 10<sup>–3</sup> emu mol<sup>–1</sup> for <b>2</b>, and <i>g</i> = 2.001, |<i>D</i>| = 0.52 cm<sup>–1</sup>, and Nα = 1.5 × 10<sup>–3</sup> emu mol<sup>–1</sup> for <b>3</b>
The Series of Molecular Conductors and Superconductors ET<sub>4</sub>[AFe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]·PhX (ET = bis(ethylenedithio)tetrathiafulvalene; (C<sub>2</sub>O<sub>4</sub>)<sup>2–</sup> = oxalate; A<sup>+</sup> = H<sub>3</sub>O<sup>+</sup>, K<sup>+</sup>; X = F, Cl, Br, and I): Influence of the Halobenzene Guest Molecules on the Crystal Structure and Superconducting Properties
An extensive series of radical salts formed by the organic
donor bis(ethylenedithio)tetrathiafulvalene
(ET), the paramagnetic tris(oxalato)ferrate(III) anion [Fe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]<sup>3–</sup>, and halobenzene
guest molecules has been synthesized and characterized. The change
of the halogen atom in this series has allowed the study of the effect
of the size and charge polarization on the crystal structures and
physical properties while keeping the geometry of the guest molecule.
The general formula of the salts is ET<sub>4</sub>[A<sup>I</sup>Fe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]·G with A/G = H<sub>3</sub>O<sup>+</sup>/PhF (<b>1</b>); H<sub>3</sub>O<sup>+</sup>/PhCl
(<b>2</b>); H<sub>3</sub>O<sup>+</sup>/PhBr (<b>3</b>),
and K<sup>+</sup>/PhI (<b>4</b>), (crystal data at room temperature:
(<b>1</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.3123(2) Å, <i>b</i> = 20.0205(3) Å, <i>c</i> = 35.2732(4) Å, β
= 92.511(2)°, <i>V</i> = 7275.4(2) Å<sup>3</sup>, <i>Z</i> = 4; (<b>2</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.2899(4)
Å, <i>b</i> = 20.026(10) Å, <i>c</i> = 35.411(10) Å, β = 92.974°, <i>V</i> =
7287(4) Å<sup>3</sup>, <i>Z</i> = 4; (<b>3</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.2875(3) Å, <i>b</i> = 20.0546(15)
Å, <i>c</i> = 35.513(2) Å, β = 93.238(5)°, <i>V</i> = 7315.0(7) Å<sup>3</sup>, <i>Z</i> = 4;
(<b>4</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.2260(2) Å, <i>b</i> = 19.9234(2) Å, <i>c</i> = 35.9064(6) Å, β
= 93.3664(6)°, <i>V</i> = 7302.83(18) Å<sup>3</sup>, <i>Z</i> = 4). The crystal structures at 120 K evidence
that compounds <b>1</b>–<b>3</b> undergo a structural
transition to a lower symmetry phase when the temperature is lowered
(crystal data at 120 K: (<b>1</b>) triclinic, space group <i>P</i>1̅ with <i>a</i> = 10.2595(3) Å, <i>b</i> = 11.1403(3) Å, <i>c</i> = 34.9516(9) Å,
α = 89.149(2)°, β = 86.762(2)°, γ = 62.578(3)°, <i>V</i> = 3539.96(19) Å<sup>3</sup>, <i>Z</i> =
2; (<b>2</b>) triclinic, space group <i>P</i>1̅
with <i>a</i> = 10.25276(14) Å, <i>b</i> =
11.15081(13) Å, <i>c</i> = 35.1363(5) Å, α
= 89.0829(10)°, β = 86.5203(11)°, γ = 62.6678(13)°, <i>V</i> = 3561.65(8) Å<sup>3</sup>, <i>Z</i> =
2; (<b>3</b>) triclinic, space group <i>P</i>1̅
with <i>a</i> = 10.25554(17) Å, <i>b</i> =
11.16966(18) Å, <i>c</i> = 35.1997(5) Å, α
= 62.7251(16)°, β = 86.3083(12)°, γ = 62.7251(16)°, <i>V</i> = 3575.99(10) Å<sup>3</sup>, <i>Z</i> =
2; (<b>4</b>) monoclinic, space group <i>C</i>2/<i>c</i> with <i>a</i> = 10.1637(3) Å, <i>b</i> = 19.7251(6) Å, <i>c</i> = 35.6405(11) Å, β
= 93.895(3)°, <i>V</i> = 7128.7(4) Å<sup>3</sup>, <i>Z</i> = 4). A detailed crystallographic study shows
a change in the symmetry of the crystal for compound <b>3</b> at about 200 K. This structural transition arises from the partial
ordering of some ethylene groups in the ET molecules and involves
a slight movement of the halobenzene guest molecules (which occupy
hexagonal cavities in the anionic layers) toward one of the adjacent
organic layers, giving rise to two nonequivalent organic layers at
120 K (compared to only one at room temperature). The structural transition
at about 200 K is also observed in the electrical properties of <b>1</b>–<b>3</b> and in the magnetic properties of <b>1</b>. The direct current (dc) conductivity shows metallic behavior
in salts <b>1</b>–<b>3</b> with superconducting
transitions at about 4.0 and 1.0 K in salts <b>3</b> and <b>1</b>, respectively. Salt <b>4</b> shows a semiconductor
behavior in the temperature range 300–50 K with an activation
energy of 64 meV. The magnetic measurements confirm the presence of
high spin <i>S</i> = 5/2 [Fe(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]<sup>3–</sup> isolated monomers together with a Pauli
paramagnetism, typical of metals, in compounds <b>1</b>–<b>3</b>. The magnetic properties can be very well reproduced in
the whole temperature range with a simple model of isolated <i>S</i> = 5/2 ions with a zero field splitting plus a temperature
independent paramagnetism (Nα) with the following parameters: <i>g</i> = 1.965, |<i>D</i>| = 0.31 cm<sup>–1</sup>, and Nα = 1.5 × 10<sup>–3</sup> emu mol<sup>–1</sup> for <b>1</b>, <i>g</i> = 2.024, |<i>D</i>| = 0.65 cm<sup>–1</sup>, and Nα = 1.4 × 10<sup>–3</sup> emu mol<sup>–1</sup> for <b>2</b>, and <i>g</i> = 2.001, |<i>D</i>| = 0.52 cm<sup>–1</sup>, and Nα = 1.5 × 10<sup>–3</sup> emu mol<sup>–1</sup> for <b>3</b>