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Updated: Jun 24, 2026
Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
Published on: June 9, 2023
Tuning the Magnetic Properties of Heterotrimetallic Co-M-Co (M = Ni and Pd) Chain Complexes via Redox Modulation and
Ming-Chuan Cheng1, I-Cheng Tu2, Yi-Hung Liu1
1Department of Chemistry, National Taiwan University, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan.
Abstract:
Spin crossover (SCO) describes the reversible interconversion between low-spin and high-spin electronic configurations in transition metal complexes, arising from a delicate balance between ligand field splitting and electron pairing energy. Cobalt-based extended metal atom chains (EMACs) and their heterometallic analogues, HEMACs, offer a versatile platform for probing spin-state energetics and switchable magnetism through variations in metal-metal and metal-ligand interactions. Here, we report the synthesis, redox chemistry, and magnetic properties of the heterometallic chains [CoPdCo(dpa)4Cl2] (1) and [CoNiCo(dpa)4Cl2] (2, dpa = 2,2'-dipyridylamido), together with their one-electron oxidized derivatives [1][SbCl6] and [2][PF6]. Variable-temperature single-crystal X-ray diffraction, SQUID magnetometry, variable-temperature 1H NMR spectroscopy, and density functional theory reveal that redox reaction and central metal substitution can modulate the spin-state equilibria of these Co-M-Co chains. The neutral complexes 1 and 2 feature antiferromagnetically coupled high-spin Co(II) termini, with 2 displaying structure-dependent spin crossover in the solid state. Upon oxidation, [1][SbCl6] adopts a robust high-spin configuration over the entire temperature range studied, whereas [2][PF6] undergoes an incomplete, temperature-driven spin crossover between low-spin and high-spin states, as evidenced by concerted structural, magnetic, and spectroscopic signatures. DFT calculations elucidate the delicate enthalpy-entropy balance governing these behaviors and highlight the role of central metal size and Co-N bond metrics in biasing the spin-state landscape. These results provide insight into the interplay between redox state, spin-state behavior, and heterometallic chain composition in cobalt-based HEMACs.
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