New Spin‐Crossover Complexes of Substituted 2,6‐Bis(pyrazol‐3‐yl)pyridines.

Here we report two new ligands from a 2,6‐bis(pyrazol‐3‐yl)pyridine family often used in spin‐crossover research and their iron(II) and cobalt(II) complexes with the metal ion trapped in the high‐spin state in solids (according to magnetometry and X‐ray diffraction data). The iron(II) complexes, however, show a gradual spin‐crossover in acetonitrile solution, as probed by the popular Evans method and an analysis of temperature dependent chemical shifts, both rooted in variable‐temperature NMR spectroscopy. The observed stabilization of the high‐spin state by the electron‐withdrawing substituents mirrors the trend previously reported for spin‐crossover iron(II) complexes of isomeric 2,6‐bis(pyrazol‐1‐yl)pyridines. [ABSTRACT FROM AUTHOR]