Asymmetric spin crossover behaviour and evidence of light-induced excited spin state trapping in a dinuclear iron(ii) helicate

Abstract

Reported herein are the synthesis, structural and magnetic characterisation of a dinuclear FeII triple helicate that displays an unprecedented reversible asymmetric high spin to low spin crossover characterised by a thermal hysteresis: indeed the high spin state can be recovered by white light irradiation at 10 K.

Effects of Internal and External Pressure on the [Fe(PM-PEA)2(NCS)2] Spin-Crossover Compound (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline)

“…This is probably due to the experiment that is only a fast cooling from 300 K to 10 K and not an instant quench, which strongly differs from the thermal-quenching previously performed on an X-Ray diffractometer, showing similar structures between the high temperature and the metastable HS phases [55]. Note that the discrepancy between magnetic and diffraction experiments in term of quenching effect investigation were discussed elsewhere on a similar material [56]. This effect remains however quite surprising since the efficiency of thermal quenching is expected to increase with the decrease of T 1/2 .…”

“…One similar shape of T(LIESST) was however described in 2009 on a binuclear compound. This behavior has been explained by a competition between the different states of the binuclear that are HS-HS, HS-LS and LS-LS [56]. Analogy with such conclusions might be performed here due to the presence of two different metallic sites within the materials, those of Fe that can undergo a SCO and those of Mn that do not.…”

Investigation of the Spin Crossover Properties of Three Dinulear Fe(II) Triple Helicates by Variation of the Steric Nature of the Ligand Type

“…Two years later, the Mössbauer and magnetic properties of such complexes with the ClO 4 − counter ion were examined by Garcia and Gütlich [28]. More recently, further studies of such helicates were conducted by Kruger [29,30], employing an oxygen central atom (-O-), identifying the importance of the degree of solvation on the spin transition of these compounds, as well as investigating the light-induced trapping of the excited state. Alternatively, the design and synthesis of coordination cages reported by Fujita [33], showed that the steric nature of the central atom of the ligand (C, S or O) could be manipulated to give subtly different ligand angles, which produced profound changes in the overall supramolecular architecture.…”

“…To the best of our knowledge, there are only a few examples of Fe(II) dinuclear triple helicates that are capable of undergoing a reversible spin transition [25,[28][29][30][31][32], all of which utilise the imidazole-imine moiety. Such compounds are composed of three ligands bridging two metal ion centres in a helical architecture.…”

Structures and spin states of mono- and dinuclear iron(II) complexes of imidazole-4-carbaldehyde azine and its derivatives

“…The SCO of this system was reinterpreted by Gütlich and co-workers [15]. Very recently, Pelleteret et al reported LIESST (light-induced excited spin state trapping) in a dinuclear Fe II helicate with ligands containing imidazolimine groups [16].…”