Synthesis and Characterisation of Two New Iron(II) Spin‐Crossover Complexes with N4O2 Coordination Spheres – Optimizing Preconditions for Cooperative Interactions

• Published in: European Journal of Inorganic Chemistry Vol. 2008; no. 31; pp. 4891 - 4898
• Main Authors: Weber, Birgit, Kaps, Eike S., Desplanches, Cedric, Létard, Jean‐François, Achterhold, Klaus, Parak, Fritz G.
• Format: Book Review Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 01.11.2008; Wiley-VCH Verlag
• Subjects: Chemical Sciences; Iron; Magnetism; Material chemistry; N,O ligands; Iron; Magnetism; O ligands
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200800420

Two new spin‐crossover complexes, [FeL1(phpy)2] (1) and [FeL2(phpy)2](phpy) (2), with L1 and L2 being tetradentate N2O22–‐coordinating Schiff‐base‐like ligands {L1 = (E,E)‐[diethyl 2,2′‐[1,2‐phenylenebis(iminomethylidyne)]bis(3‐oxobutanoato)(2–)‐N,N′,O3,O3′], L2 = [(3,3′)‐[1,2‐phenylenebis(iminomethylidyne)]bis(2,4‐pentanedionato)(2–)‐N,N′,O2,O2′]and phpy = 4‐phenylpyridine} have been investigated using temperature‐dependent susceptibility and photomagnetic measurements, as well as Mössbauer spectroscopy and X‐ray structure analysis. Compound 1 shows a cooperative spin transition with a thermal hysteresis loop approximately 4 K wide (T1/2↓ = 232 K and T1/2↑ = 236 K). The spin transition of 2 is gradual with T1/2 ≈ 290 K. Results from X‐ray structure analysis indicate that the cooperative interactions are due to elastic interactions with several intense C–C contacts in the case of 1. The change of the spin state at the iron centre is accompanied by a change of the O–Fe–O angle, the so‐called bite of the equatorial ligand, from 107° in the high‐spin state to 89° in the low‐spin state. Reflectivity measurements of 1 indicate that the Light‐Induced Excited Spin State Trapping (LIESST) effect occurs at the sample surface at low temperatures. In the bulk solid, photomagnetic properties with a photoexcitation level of 30 % and a T(LIESST) value of 41 K are observed using a SQUID magnetometer. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) The magnetic and photomagnetic properties of two new spin‐crossover complexes with N4O2 coordination are presented. From the data for six spin‐crossover complexes, an initial explanation was given with regard to which parameters are responsible for the extent of intermolecular interactions in this type of complex.