Spin State Chemistry: Modulation of Ligand pK_a by Spin State Switching in a [2×2] Iron(II) Grid-Type Complex

Abstract

The iron(II) [2×2] grid complex Fe-8H has been synthesized and characterized. It undergoes spin-crossover (SCO) upon deprotonation of the hydrazine-based terpyridine-like ligand. The deprotonation patterns have been determined by X-ray crystallography and H NMR spectroscopy and discussed in relation to the spin state of the iron(II) centers, which influences greatly the p K of the ligand. The synthesis of the magnetically silent zinc(II) analogue is also reported, and its (de)protonation behavior has been characterized to serve as a reference for the study of the Fe grid complexes. DFT computations have also been performed in order to investigate how the successive deprotonation of the bridging ligands affects the SCO behavior within the grid.

Revealing Hot and Long-Lived Metastable Spin States in the Photoinduced Switching of Solvated Metallogrid Complexes with Femtosecond Optical and X-ray Spectroscopies

“…When triggered by ultrafast laser-excitation, which is inherently wavelength-selective, photoinduced spin-state switching (PSS) and light-induced excited spin-state trapping (LIESST) in organized arrays of TM ions constitute some of the most promising approaches for realizing the long-standing goal of initiating chemical reactions through prompt changes of spin [13][14][15][16][17] .…”

A Brønsted‐Ligand‐Based Iron Complex as a Molecular Switch with Five Accessible States

“…To date, very few examples of protonation‐controlled state‐switching in molecular species are known. Most recently, Lehn and co‐workers showed that the SCO behavior of a polynuclear {Fe 4 } grid‐type complex can be modified in response to pH by using protic ditopic ligands . And while mononuclear Fe II ‐complexes which reversibly respond to protonation/deprotonation are known, these systems can be switched between just two discrete states .…”

Acidity-Driven Bidirectional Room-Temperature Spin-State Switch and Fluorescence Modulation of a Mononuclear Fe(II) Complex

“…Only a few pH responsive SCO examples reported, and the modulation of magnetic properties is due to the change of the overall ligand-field strength upon ligand protonation/deprotonation. [32][33][34][35][36] Nowak et al 37 reported proton-driven coordination-induced spin-state switching (PD-CISSS) of iron(II) complexes in solution and as composite materials. Recently, we also reported successful switching of the spin state of an Fe(II) complex in solution as a result of reversible dissociation-association of the coordination sphere driven by protonation and deprotonation.…”