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