Selective Pathway toward Heteroleptic Spin-Crossover Iron(II) Complexes with Pyridine-Based <i>N</i>-Donor Ligands
Igor A. Nikovskiy, Dmitry Yu. Aleshin, Valentin V. Novikov, Alexander V. Polezhaev, Ekaterina A. Khakina, Elizaveta K. Melnikova, Yulia V. Nelyubina
Abstract
A new synthetic pathway is devised to selectively produce previously elusive heteroleptic iron(II) complexes of terpyridine and N,N′-disubstituted bis(pyrazol-3-yl)pyridines that stabilize the opposite spin states of the metal ion. Such a combination of the ligands in a series of the heteroleptic complexes induces the spin-crossover (SCO) not experienced by the homoleptic complexes of these ligands or shifts it to lower/higher temperatures respective to the SCO-active homoleptic complex. The midpoint temperatures of the resulting SCO span from ca. 200 K to the ambient temperature and beyond the highest temperature accessible by NMR spectroscopy and SQUID magnetometry. The proposed “one-pot” approach is applicable to other N-donor ligands to selectively produce heteroleptic complexes─including those inaccessible by alternative synthetic pathways─with highly tunable SCO behaviors for practical applications in sensing, switching, and multifunctional devices.