Proton‐Induced Spin State Switching in an Fe<sup>III</sup> Complex
Conor T. Kelly, Sean Dunne, Irina A. Kühne, A. S. Barker, Kane Esien, Solveig Felton, Helge Müller‐Bunz, Y. Ortin, Grace G. Morgan
Abstract
Abstract Reversible proton‐induced spin state switching of an Fe III complex in solution is observed at room temperature. A reversible magnetic response was detected in the complex, [Fe III (sal 2 323)]ClO 4 ( 1 ), using Evans’ method 1 H NMR spectroscopy which indicated cumulative switching from low‐spin to high‐spin upon addition of one and two equivalents of acid. Infrared spectroscopy suggests a coordination‐induced spin state switching (CISSS) effect, whereby protonation displaces the metal‐phenoxo donors. The analogous complex, [Fe III (4‐NEt 2 ‐sal 2 323)]ClO 4 ( 2 ), with a diethylamino group on the ligand, was used to combine the magnetic change with a colorimetric response. Comparison of the protonation responses of 1 and 2 reveals that the magnetic switching is caused by perturbation of the immediate coordination sphere of the complex. These complexes constitute a new class of analyte sensor which operate by magneto‐modulation , and in the case of 2 , also yield a colorimetric response.