Proton‐Induced Spin State Switching in an Fe^III Complex

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.

Anomalous Hydroboration at a Four-Coordinate Ni(II) Diphenylvinylphosphine Complex: Geometric Impacts on Solution Equilibria

“…1 H NMR spectra are reported in parts per million (ppm) and are referenced to residual solvent e.g., 1 H(C 6 D 6 ): δ 7.16; 13 C(C 6 D 6 ): 128.06; coupling constants are reported in Hz. 13 C, 11 B, and 31 P NMR spectra were performed as proton-decoupled experiments and are reported in ppm. All data were acquired at 298 K. Magnetic moment calculations were performed using the Evans method where HMDSO was used as an internal standard in C 6 D 6 .…”

“…3−5 Recent work has explored metal-based spin-changes as a consequence of ligand hemilability, 6 solvent coordination, 7,8 chirality, 9 and secondary coordination sphere protonation effects. 10,11 For example, Holland and co-workers described a Co(I) βdiketiminate complex with a single carbonyl ligand. In the solid state, this compound is formally four-coordinate, engaging a flanking 2,6-diisopropylphenyl ring via an η 2 -C� C interaction, giving an S = 0 system.…”

“…Alterations to metal complex geometries and spin states can have a profound impact on downstream reactivity. , A reliable understanding of the effects of ligand substitution pattern on corresponding metal complex geometry and electronic properties is of importance to predict later chemical reactivity. In this space, metal-containing complexes featuring first-row elements have been leveraged to explore these phenomena, in part owing to their ability to support unpaired electrons. − Recent work has explored metal-based spin-changes as a consequence of ligand hemilability, solvent coordination, , chirality, and secondary coordination sphere protonation effects. , For example, Holland and co-workers described a Co­(I) β-diketiminate complex with a single carbonyl ligand. In the solid state, this compound is formally four-coordinate, engaging a flanking 2,6-diisopropylphenyl ring via an η 2 -CC interaction, giving an S = 0 system.…”