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)₂]_∞ (<b>4</b>; 3,6-DBSQ-4,5-PDO^•– = 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)₂]_∞ (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)^•– = 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)₂)­(CO)₂]_∞ (<b>3</b>; 3,6-DBSQ-4,5-(MeO)₂^•– = 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>_trs = 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>_N = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (<i>E</i>_a = 31 meV) in the RT phase to a semiconductor with a large activation energy (<i>E</i>_a = 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 × 10⁷ 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)₂]_∞ (<b>4</b>; 3,6-DBSQ-4,5-PDO^•– = 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)₂]_∞ (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)^•– = 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)₂)­(CO)₂]_∞ (<b>3</b>; 3,6-DBSQ-4,5-(MeO)₂^•– = 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>_trs = 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>_N = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (<i>E</i>_a = 31 meV) in the RT phase to a semiconductor with a large activation energy (<i>E</i>_a = 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 × 10⁷ 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)₂)­(CO)₂]_∞ (<b>3</b>), where 3,6-DBSQ-4,5-(MeO)₂^•– 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>_N of 14.2 K. The electrical conductivity of <b>3</b> at 300 K is 4.8 × 10^–4 S cm^–1, 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