Solid-State Redox Switching of Magnetic Exchange and Electronic Conductivity in a Benzoquinoid-Bridged Mn~Ⅱ Chain Compound

摘要

We demonstrate that incorporation of a redox- active benzoquinoid ligand into a one-dimensional chain compound can give rise to a material that exhibits simultaneous solid-state redox switching of optical, magnetic, and electronic properties. Metalation of the ligand 4,5- bis(pyridine-2-carboxamido)-1,2-catechol (~(N,O)LH_4) with Mn~Ⅲ affords the chain compound Mn(~(N,O)L)(DMSO). Structural and spectroscopic analysis of this compound show the presence of Mn~Ⅱ centers bridged by ~(N,O)L~(2-) ligands, resulting partially from a spontaneous ligand-to-metal electron transfer. Upon soaking in a solution of the reductant Cp_2Co, Mn(~(N,O)L)(DMSO) undergoes a ligand-centered solid-state reduction to [Mn(~(N,O)L)]~-, as revealed by a suite of techniques, including Raman and X-ray absorption spectroscopy. The ligand-based reduction engenders a dramatic modulation of the physical properties of the chain compound. An electrochromic response, evidenced by a color change from dark green to dark purple is accompanied by a nearly 40-fold increase in magnetic coupling strength, from J= - 0.38(1) to -15.6(2) cm~(-1), and a 10,000-fold increase in electronic conductivity, from σ = 2.33(1) × 10~(-12) S/cm (E_a = 0.64(1) eV) to 8.61(1) × 10~(-8) S/cm (E_a = 0.39(1) eV). Importantly, the chemical reduction is reversible: treatment of the reduced compound with [Cp_2Fe]~+ regenerates the oxidized chain. Taken together, these results highlight the ability of benzoquinoid ligands to facilitate solid-state ligand-based redox reactions in nonporous coordination solids, giving rise to reversible switching of optical properties, magnetic exchange interactions, and electronic conductivity.