We report the magnetism and conductivity for a redox pair of iron-quinoid metal-organic frameworks (MOFs). The oxidized compound, (MeNH)[FeL]·2HO·6DMF (LH = 2,5-dichloro-3,6-dihydroxo-1,4-benzoquinone) was previously shown to magnetically order below 80 K in its solvated form, with the ordering temperature decreasing to 26 K upon desolvation. Here, we demonstrate this compound to exhibit electrical conductivity values up to σ = 1.4(7) × 10 S/cm (E = 0.26(1) cm) and 1.0(3) × 10 S/cm (E = 0.19(1) cm) in its solvated and desolvated forms, respectively. Upon soaking in a DMF solution of CpCo, the compound undergoes a single-crystal-to-single-crystal one-electron reduction to give (CpCo)(MeNH)[FeL]·4.9DMF. Structural and spectroscopic analysis confirms this reduction to be ligand-based, and as such the trianionic framework is formulated as [Fe(L)]. Magnetic measurements for this reduced compound reveal the presence of dominant intralayer metal-organic radical coupling to give a magnetically ordered phase below T = 105 K, one of the highest reported ordering temperatures for a MOF. This high ordering temperature is significantly increased relative to the oxidized compound, and stems from the overall increase in coupling strength afforded by an additional organic radical. In line with the high critical temperature, the new MOF exhibits magnetic hysteresis up to 100 K, as revealed by variable-field measurements. Finally, this compound is electrically conductive, with values up to σ = 5.1(3) × 10 S/cm with E = 0.34(1) eV. Taken together, these results demonstrate the unique ability of metal-quinoid MOFs to simultaneously exhibit both high magnetic ordering temperatures and high electrical conductivity.

Partial oxidation of an iron-tetrazolate metal-organic framework (MOF) upon exposure to ambient atmosphere yields a mixed-valence material with single-crystal conductivities tunable over 5 orders of magnitude and exceeding 1 S/cm, the highest for a three-dimensionally connected MOF. Variable-temperature conductivity measurements reveal a small activation energy of 160 meV. Electronic spectroscopy indicates the population of midgap states upon air exposure and corroborates intervalence charge transfer between Fe and Fe centers. These findings are consistent with low-lying Fe defect states predicted by electronic band structure calculations and demonstrate that inducing metal-based mixed valency is a powerful strategy toward realizing high and systematically tunable electrical conductivity in MOFs.

We report a 2D manganese benzoquinoid network that undergoes simultaneous redox switching of magnetic order and electrical conductivity.

We report the synthesis of a semiquinoid-bridged single-chain magnet, as generated through a thermally induced metal-ligand electron transfer. Reaction of FeCl with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (LH) in the presence of (NMe)Cl gave the compound (NMe)[LFeCl]. Together, variable-temperature X-ray diffraction, Mössbauer spectra, Raman spectra, and dc magnetic susceptibility reveal a transition from a chain containing (L)Fe units to one with (L)Fe upon decreasing temperature, with a transition temperature of T = 213 K. The dc magnetic susceptibility measurements show strong metal-radical coupling within the chain, with a coupling constant of J = -81 cm, and ac susceptibility data reveal slow magnetic relaxation, with a relaxation barrier of Δ = 55(1) cm. To our knowledge, this compound provides the first example of a semiquinoid-bridged single-chain magnet.

The ability of tetraazalene radical bridging ligands to mediate exceptionally strong magnetic exchange coupling across a range of transition metal complexes is demonstrated.