Spin–Electric Coupling in a Cobalt(II)‐Based Spin Triangle Revealed by Electric‐Field‐Modulated Electron Spin Resonance Spectroscopy

Abstract

A cobalt(II)-based spin triangle shows a significant spin-electric coupling. [Co₃ (pytag)(py)₆ Cl₃ ]ClO₄ ⋅3 py crystallizes in the acentric monoclinic space group P2₁ . The intra-triangle antiferromagnetic interaction, of the order of ca. -15 cm^-1 (H=-JS_a S_b ), leads to spin frustration. The two expected energy-degenerate ground doublets are, however, separated by a few wavenumbers, as a consequence of magnetic anisotropy and deviations from threefold symmetry. The Co₃ planes of symmetry-related molecules are almost parallel, allowing for the determination of the spin-electric properties of single crystals by EFM-ESR spectroscopy. The spin-electric effect detected when the electric field is applied in the Co₃ plane was revealed by a shift in the resonance field. It was quantified as Δg_E /E=0.11×10^-9 m V^-1 , which in terms of frequency corresponds to approximately 0.3 Hz m V^-1 . This value is comparable to what was determined for a Cu₃ triangle despite the antiferromagnetic interaction being 20 times larger for the latter.