Multifunctional
One-Dimensional Rhodium(I)–Semiquinonato
Complex: Substituent
Effects on Crystal Structures and Solid-State Properties
- Publication date
- Publisher
Abstract
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
