Towards the Molecular Design of Spin‐Crossover Complexes of 2,6‐Bis(pyrazol‐3‐yl)pyridines

Abstract The molecular design of spin‐crossover complexes relies on controlling the spin state of a transition metal ion by proper chemical modifications of the ligands. Herein, the first N,N’‐disubstituted 2,6‐bis(pyrazol‐3‐yl)pyridines (3‐bpp) are reported that, against the common wisdom, induce a spin‐crossover in otherwise high‐spin iron(II) complexes by increasing the steric demand of a bulky substituent, an ortho ‐functionalized phenyl group. As N,N’‐disubstituted 3‐bpp complexes have no pendant NH groups that make their spin state extremely sensitive to the environment, the proposed ligand design, which may be applicable to isomeric 1‐bpp or other families of popular bi‐, tri‐ and higher denticity ligands, opens the way for their molecular design as spin‐crossover compounds for future breakthrough applications.