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

A cobalt(II)‐based spin triangle shows a significant spin–electric coupling. [Co(3)(pytag)(py)(6)Cl(3)]ClO(4)⋅3 py crystallizes in the acentric monoclinic space group P2(1). 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 Co(3) 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 Co(3) 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 Cu(3) triangle despite the antiferromagnetic interaction being 20 times larger for the latter.