Towards Spin Crossover Applications

Picosecond X-ray Absorption Spectroscopy of a Photoinduced Iron(II) Spin Crossover Reaction in Solution

“…This difference spectrum probes the changes in the electron density around the Fe atom after the 1 A 1 f 1 MLCT excitation, but prior to the ground-state recovery. 37 For comparison, the difference absorption spectrum of the ground-state high-spin complex ([Fe(tren(6-Me-py) 3 )](PF 6 ) 2 ) and [Fe(tren-(py) 3 )](PF 6 ) 2 , obtained from the steady-state measurements, is plotted below the transient data in Figure 4a. The steady-state difference spectrum is scaled by a factor of 0.1 to account for the 10% photoexcitation of the ground-state species in solution by the laser pump pulse.…”

“…An advantage of this system in the present context lies in the ability to control the ground state of the molecule through synthetic means. It is known that replacement of the protons ortho to the pyridyl nitrogens with methyl groups converts the low-spin ( 1 A 1 : (t 2 ) 6 (e) 0 ) complex, [Fe(tren(py) 3 )](PF 6 ) 2 to a high-spin ( 5 T 2 : (t 2 ) 4 (e) 2 ) analogue, [Fe(tren(6-Me-py) 3 )](PF 6 ) 2 . 33 X-ray crystallographic studies have confirmed the hexadentate nature of the ligands in both complexes, resulting in a slightly distorted octahedral molecular geometry around the iron atom.…”

Bulk spin-crossover in the complex [FeL(NCS)2] of a tris(pyridyl)ethane-derived N4-ligand—a temperature-dependent crystallographic study

“…2 Iron(II) and iron(III) complexes account for the biggest share and are most intensively studied with regard to applications in information storage and spintronics. [3][4][5] In these compounds, the transition takes place between the enthalpically preferred lowspin (LS) and the entropically preferred high-spin (HS) state; for Fe 2+ /Fe 3+ , these are the states 1 A 1g / 2 T 2g (LS) and 5 T 2g / 6 A 1g (HS), respectively. As subtle changes in molecular structure or solid-state arrangement can lead to dramatic changes in the switching behaviour, 6 the synthesis 7 as well as theoretical description 8 of such SCO compounds are the subject of intense current research.…”

“…12 Beyond two-dimensional arrangements like thin films, mono-or bilayers, spin-state interconversion has recently also been detected in one-dimensional chains of oligonuclear "beads" of [Fe II (dptp) 2 ](BF 4 ) 2 (dptp: 2,6-di[1H-pyrazol-1-yl]-4-[thiocyanatomethyl]pyridine) on highly oriented pyrolytic graphite (HOPG), by current-imaging tunnelling spectroscopy (CITS). 13,14 Nanoparticles of [Fe II {(mepy) 3 tren}](PF 6 ) 2 ([mepy] 3 tren: tris[4-(6-methylpyridin-2-yl)-3-aza-3-butenyl]amine) may be considered as zero-dimensional entities. They show thermal SCO characteristics that differ from those of the bulk substance, and the crystallinity of the particles has a major influence on relaxation dynamics after light-induced excited spinstate trapping (LIESST).…”

“…The results shed light on the molecular changes associated with the spin-state transition in the crystalline state and help assess the role of intermolecular vs. molecule-substrate interactions on surfaces. (3) are readily synthesised in high yields by addition of L to iron(II)/iron(III) chloride and (for 3) subsequent ligand/anion exchange, using a tetrabutylammonium salt (see Scheme 1). While the SCO in 1 is the focus of the present work, HS-iron(II)/iron(III) complexes 2 and 3, as well as the already published LS-iron(II) photosensitiser [Fe(CN) 2 L] (4), 18 serve as structural models for comparison of spin-state dependent parameters.…”