Spin transition in a ferrous chloride complex supported by a pentapyridine ligand

Abstract

Apparent high-spin complex with FeN5Cl coordination sphere exhibits a complete transition to the low-spin state on cooling.

Electronic and geometric structure effects on one-electron oxidation of first-row transition metals in the same ligand framework

“…4. This value was 2.2 kcal mol −1 higher than what can be expected from the determined spin-transition temperature of the powder sample at 80 K. 15 As the solvated chloride-coordinated sample had remaining HS species down to 20 K, the B3LYP* calculations with 15% HF exchange should thus represent the complex in solution with relatively high accuracy. Calculations of the other complexes showed that they all favour high-spin states, even more so than iron, see Fig.…”

“…As we reported recently, this is due to a spin-state change (spin-crossover, SCO) from quintet 5 [Fe II -Cl] to singlet 1 [Fe II -Cl] that occurs at a temperature below 80 K in the microcrystalline powder sample. 15 To get closer to the conditions of the CV experiments, the XAS parameters were also obtained after dissolving the four samples in acetonitrile with electrolyte. The XAS spectra of the [Mn II -Cl], [Co II -Cl] and [Ni II -Cl] complexes remained unchanged as compared to the spectra recorded for the powder samples (see Fig.…”

“…29 To address this challenge, we used the SCO in [Fe II -Cl] as a reference point for selecting the functional. 15 For [Fe II -Cl] the B3LYP* functional (15% HF exchange) gave good results. It favoured the quintet over the singlet by 5.3 kcal mol −1 at room temperature, see Fig.…”

“…4 During the following two decades, Py5 complexes have also been applied as anti-tumour agents, 10,11 redox mediators for dye-sensitized solar cells, 12,13 and materials with tunable magnetic properties. [14][15][16] In the field of the artificial photosynthesis, Py5-type ligands have been reported to be a suitable scaffold for synthesizing both proton reduction [17][18][19][20] and water oxidation catalysts. [21][22][23][24] With the idea of creating a starting point for further functionalization, our group introduced the Py5OH ligand and employed it in homogeneous water oxidation catalysis using either Co II or Fe II as the metal centre.…”

“…25,26 Our recent study on the [Fe II (Py5OH)Cl] + complex showed that, unlike [Fe II (Py5OMe)Cl] + , it undergoes a spin-crossover from a high spin (HS) to low spin (LS) configuration, even in the presence of a weak-field ligand like Cl. 15 This infers that the peripheral R-groups of the ligand can affect the electronic structure of the metal centre.…”