Protonation-induced ligand distortion of spin-crossover complexes.

Abstract A new complex [Fe(CN) 2 (bipy-NH 2) 2 ] (2 , bipy-NH 2 = 4, 4′-diamino-2, 2′-bipyridine), which was designed through ligand exchange strategy, has been prepared and characterized. The magnetism properties of 2 have been tuned through protonate the amino groups on bipy-NH 2 ligand with HCl in stoichiometric ratio 2 :HCl below 1:1. Further increase the ratio exceed 1:1 has induced the distortion of the bipy-ammonium moieties in bipy-NH 3 2+ cation, with the dihedral angle involving the mean plane change from 0° to 37°. This distortion, on the one hand, responsible for the decomposition of 2 , on the other hand, take charge the break of the precursor complex 1 ([Fe(H 2 Bpz 2) 2 (bipy-NH 2)]) (pz = pyrazolyl) upon protonation. Graphical abstract Tuning the magnetism properties of a new complex [Fe(CN) 2 (bipy-NH 2) 2 ] (2) through protonation of the ligand bipy-NH 2 with HCl have been investigated with stoichiometric ratio of 2 :HCl below 1:1. While once the ratio larger than 1:1, ligand bipy-NH 2 has distorted with the mean plane of bipy-ammonium moieties to form a dihedral angle large to be 37°. Unlabelled Image Highlights • The protonation of a Fe(II) complex has been investigated. • The mechanism of protonation induced decomposition of Fe(II) complex has been proposed. • The mean plane of bipy-ammonium moieties has been distorted with dihedral angle large to be 37°. [ABSTRACT FROM AUTHOR]