Transition Ion Strikes Back: Large Magnetic Susceptibility Anisotropy in Cobalt(II) Clathrochelates

• Published in: The journal of physical chemistry letters Vol. 5; no. 21; pp. 3799 - 3803
• Main Authors: Novikov, Valentin V, Pavlov, Alexander A, Belov, Alexander S, Vologzhanina, Anna V, Savitsky, Anton, Voloshin, Yan Z
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.11.2014
• Subjects: Molecular Structure, Quantum Chemistry, and General Theory; clathrochelates; magnetic anisotropy; transition metal complexes; paramagnetic tags; EPR
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/jz502011z

Transition-metal complexes are rarely considered as paramagnetic tags for NMR spectroscopy due to them generally having relatively low magnetic anisotropy. Here we report cobalt­(II) cage complexes with the largest (among the transition-metal complexes) axial anisotropy of magnetic susceptibility, reaching as high as 12.6 × 10–32 m3 at room temperature. This remarkable anisotropy, which results from an unusual trigonal prismatic geometry of the complexes and translates into large negative value of the zero-field splitting energy, is high enough to promote reliable paramagnetic pseudocontact shifts at the distance beyond 2 nm. Our finding paves the way toward the applications of cobalt­(II) clathrochelates as future paramagnetic tags. Given the incredible stability and functionalization versatility of clathrochelates, the fine-tuning of the caging ligand may lead to new chemically stable mononuclear single-molecule magnets, for which magnetic anisotropy is of importance.