Halogen Substitution Effects on N2O Schiff Base Ligands in Unprecedented Abrupt FeII Spin Crossover Complexes

• Published in: Chemistry : a European journal 2017-05, Vol.23 (29), p.7052-7065
• Main Authors: Phonsri, Wasinee, Macedo, David S., Vignesh, Kuduva R., Rajaraman, Gopalan, Davies, Casey G., Jameson, Guy N. L., Moubaraki, Boujemaa, Ward, Jas S., Kruger, Paul E., Chastanet, Guillaume, Murray, Keith S.
• Format: Article
• Language: English
• Subjects: Ambient temperature; Broken symmetry; Chemistry; Coordination compounds; halogen bonding; Imines; intermolecular interactions; Iron; iron complexes; Low temperature; Magnetic properties; Nitrous oxide; Room temperature; Schiff base ligands; spin crossover; Spin transition; Spin transitions; Substitutes
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201700232

A family of halogen‐substituted Schiff base iron(II) complexes, [FeII(qsal‐X)2], (qsal‐X=5‐X‐N‐(8‐quinolyl)salicylaldimines)) in which X=F (1), Cl (2), Br (3) or I (4) has been investigated in detail. Compound 1 shows a temperature invariant high spin state, whereas the others all show abrupt spin transitions, at or above room temperature, namely, 295 K (X=I) up to 342 K (X=Br), these being some of the highest T1/2 values obtained, to date, for FeII N/O species. We have recently reported subtle symmetry breaking in [FeII(qsal‐Cl)2] 2 with two spin transition steps occurring at 308 and 316 K. A photomagnetic study reveals almost full HS conversion of [FeII(qsal‐I)2] 4 at low temperature (T(LIESST)=54 °K). The halogen substitution effects on the magnetic properties, as well as the crystal packing of the [FeII(qsal‐X)2] compounds and theoretical calculations, are discussed in depth, giving important knowledge for the design of new spin crossover materials. In comparison to the well known iron(III) analogues, [FeIII(qsal‐X)2]+, the two extra π–π and P4AE interactions found in [FeII(qsal‐X)2] compounds, are believed to be accountable for the spin transitions occurring at ambient temperatures. All about the spin! A family of FeII spin crossover complexes containing N2O Schiff base ligands, [FeII(qsal‐X)2] in which X=F (1), Cl (2), Br (3) or I (4), has been investigated in detail (see figure). Most of the compounds show abrupt spin transitions, at or above room temperature. Important knowledge for the design of new spin crossover materials is discussed.