3 research outputs found
Multifunctional One-Dimensional Rhodium(I)–Semiquinonato Complex: Substituent Effects on Crystal Structures and Solid-State Properties
Two
new one-dimensional (1D) rhodium(I)–semiquinonato complexes
formulated as [Rh(3,6-DBSQ-4,5-PDO)(CO)<sub>2</sub>]<sub>∞</sub> (<b>4</b>; 3,6-DBSQ-4,5-PDO<sup>•–</sup> = 3,6-di-<i>tert</i>-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato)
and [Rh(3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN))(CO)<sub>2</sub>]<sub>∞</sub> (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)<sup>•–</sup> = 3,6-di-<i>tert</i>-butyl-4,5-(<i>N</i>,<i>N</i>′-diethylenediamine)-1,2-benzosemiquinonato) were
synthesized to explore the nature of the unusual structural phase
transition and magnetic and conductive properties recently reported
for [Rh(3,6-DBSQ-4,5-(MeO)<sub>2</sub>)(CO)<sub>2</sub>]<sub>∞</sub> (<b>3</b>; 3,6-DBSQ-4,5-(MeO)<sub>2</sub><sup>•–</sup> = 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato).
Their crystal structures and magnetic and conductive properties were
investigated. Compounds <b>4</b> and <b>5</b> comprise
neutral 1D chains of complex molecules stacked in a staggered arrangement
with fairly short average Rh–Rh distances of 3.06 Å for <b>4</b> and 3.10 Å for <b>5</b>. These distances are
similar to those for <b>3</b> (3.09 Å); however, the molecules
of <b>5</b> are strongly dimerized in the 1D chain. Compound <b>4</b> undergoes a first-order phase transition at <i>T</i><sub>trs</sub> = 229.1 K, and its magnetic properties drastically
change from antiferromagnetic coupling in the room-temperature (RT)
phase to strong ferromagnetic coupling in the low-temperature (LT)
phase. In addition, compound <b>4</b> exhibits a long-range
ordering of net magnetic moments originating from the imperfect cancellation
of antiferromagnetically coupled spins between the ferromagnetic 1D
chains at <i>T</i><sub>N</sub> = 10.9 K. Furthermore, this
compound exhibits an interesting crossover from a semiconductor with
a small activation energy (<i>E</i><sub>a</sub> = 31 meV)
in the RT phase to a semiconductor with a large activation energy
(<i>E</i><sub>a</sub> = 199 meV) in the LT phase. These
behaviors are commonly observed for <b>3</b>. Alternating current
susceptibility measurements of <b>4</b>, however, revealed a
frequency-dependent phenomenon below 5.2 K, which was not observed
for <b>3</b>, thus indicating a slow spin relaxation process
that possibly arises from the movements of domain walls. In contrast,
compound <b>5</b>, which possesses a strongly dimerized structure
in its 1D chain, shows no sign of strong ferromagnetic interactions
and is an insulator, with a resistivity greater than 7 × 10<sup>7</sup> Ω cm
Multifunctional One-Dimensional Rhodium(I)–Semiquinonato Complex: Substituent Effects on Crystal Structures and Solid-State Properties
Two
new one-dimensional (1D) rhodium(I)–semiquinonato complexes
formulated as [Rh(3,6-DBSQ-4,5-PDO)(CO)<sub>2</sub>]<sub>∞</sub> (<b>4</b>; 3,6-DBSQ-4,5-PDO<sup>•–</sup> = 3,6-di-<i>tert</i>-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato)
and [Rh(3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN))(CO)<sub>2</sub>]<sub>∞</sub> (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)<sup>•–</sup> = 3,6-di-<i>tert</i>-butyl-4,5-(<i>N</i>,<i>N</i>′-diethylenediamine)-1,2-benzosemiquinonato) were
synthesized to explore the nature of the unusual structural phase
transition and magnetic and conductive properties recently reported
for [Rh(3,6-DBSQ-4,5-(MeO)<sub>2</sub>)(CO)<sub>2</sub>]<sub>∞</sub> (<b>3</b>; 3,6-DBSQ-4,5-(MeO)<sub>2</sub><sup>•–</sup> = 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato).
Their crystal structures and magnetic and conductive properties were
investigated. Compounds <b>4</b> and <b>5</b> comprise
neutral 1D chains of complex molecules stacked in a staggered arrangement
with fairly short average Rh–Rh distances of 3.06 Å for <b>4</b> and 3.10 Å for <b>5</b>. These distances are
similar to those for <b>3</b> (3.09 Å); however, the molecules
of <b>5</b> are strongly dimerized in the 1D chain. Compound <b>4</b> undergoes a first-order phase transition at <i>T</i><sub>trs</sub> = 229.1 K, and its magnetic properties drastically
change from antiferromagnetic coupling in the room-temperature (RT)
phase to strong ferromagnetic coupling in the low-temperature (LT)
phase. In addition, compound <b>4</b> exhibits a long-range
ordering of net magnetic moments originating from the imperfect cancellation
of antiferromagnetically coupled spins between the ferromagnetic 1D
chains at <i>T</i><sub>N</sub> = 10.9 K. Furthermore, this
compound exhibits an interesting crossover from a semiconductor with
a small activation energy (<i>E</i><sub>a</sub> = 31 meV)
in the RT phase to a semiconductor with a large activation energy
(<i>E</i><sub>a</sub> = 199 meV) in the LT phase. These
behaviors are commonly observed for <b>3</b>. Alternating current
susceptibility measurements of <b>4</b>, however, revealed a
frequency-dependent phenomenon below 5.2 K, which was not observed
for <b>3</b>, thus indicating a slow spin relaxation process
that possibly arises from the movements of domain walls. In contrast,
compound <b>5</b>, which possesses a strongly dimerized structure
in its 1D chain, shows no sign of strong ferromagnetic interactions
and is an insulator, with a resistivity greater than 7 × 10<sup>7</sup> Ω cm
Bistable Multifunctionality and Switchable Strong Ferromagnetic-to-Antiferromagnetic Coupling in a One-Dimensional Rhodium(I)–Semiquinonato Complex
We
present a comprehensive study of the synthesis, heat capacity,
crystal structures, UV–vis−NIR and mid-IR spectra, DFT
calculations, and magnetic and electrical properties of a one-dimensional
(1D) rhodium(I)–semiquinonato complex, [Rh(3,6-DBSQ-4,5-(MeO)<sub>2</sub>)(CO)<sub>2</sub>]<sub>∞</sub> (<b>3</b>), where
3,6-DBSQ-4,5-(MeO)<sub>2</sub><sup>•–</sup> represents
3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato
radical anion. The compound <b>3</b> comprises neutral 1D chains
of complex molecules stacked in a staggered arrangement with short
Rh–Rh distances of 3.0796(4) and 3.1045(4) Å at 226 K
and exhibits unprecedented bistable multifunctionality with respect
to its magnetic and conductive properties in the temperature range
of 228–207 K. The observed bistability results from the thermal
hysteresis across a first-order phase transition, and the transition
accompanies the exchange of the interchain C–H···O
hydrogen-bond partners between the semiquinonato ligands. The strong
overlaps of the complex molecules lead to unusually strong ferromagnetic
interactions in the low-temperature (LT) phase. Furthermore, the magnetic
interactions in the 1D chain drastically change from strongly ferromagnetic
in the LT phase to antiferromagnetic in the room-temperature (RT)
phase with hysteresis. In addition, the compound <b>3</b> exhibits
long-range antiferromagnetic ordering between the ferromagnetic chains
and spontaneous magnetization because of spin canting (canted antiferromagnetism)
at a transition temperature <i>T</i><sub>N</sub> of 14.2
K. The electrical conductivity of <b>3</b> at 300 K is 4.8 ×
10<sup>–4</sup> S cm<sup>–1</sup>, which is relatively
high despite Rh not being in a mixed-valence state. The temperature
dependence of electrical resistivity also exhibits a clear hysteresis
across the first-order phase transition. Furthermore, the ferromagnetic
LT phase can be easily stabilized up to RT by the application of a
relatively weak applied pressure of 1.4 kbar, which reflects the bistable
characteristics and demonstrates the simultaneous control of multifunctionality
through external perturbation