Two New Iron(II) Spin‐Crossover Complexes with N₄O₂ Coordination Sphere and Spin Transition around Room Temperature

Abstract

Both complexes are spin-crossover compounds that were characterised by using magnetic measurements, X-ray crystallography and temperature-dependent 1 H NMR spectroscopy. Special attention was given to the role of the two

Influence of Hydrogen Bonding on the Hysteresis Width in Iron(II) Spin‐Crossover Complexes

“…[15] Significant differences in the transition temperature of [FeH 2 L5(py) 2 ]·py in the solid state (T 1/2 Ͼ 350 K) and in solution (T 1/2 ≈ 200 K, both gradual spin transitions) were also associated with the hydrogen-bond network observed in the X-ray structure. [11] Such observations are not limited to monomeric complexes. For the 1D chain material [Fe(NH 2 trz) 3 ](NO 3 ) 2 , the 33 K wide thermal hysteresis loop is associated with a network of hydrogen bonds, [22,33] and for the very similar [Fe(Htrz) 2 (trz)](BF 4 ), an extended network of hydrogen bonds had been singled out to be the origin of the 40 K large hysteresis above room temperature.…”

“…[13] and H 4 L5 from ref. [11] A ST is associated with changes in the bond length between the iron centre and the donor atoms. These changes most likely influence the strength of the hydrogen bond to the donor atom, for example, in the case of 1 HT between the NH of the imidazole ligand and O1 of the equatorial ligand.…”

“…[9,[13][14][15] For some of the examples, an influence of the hydrogen bonds on the electron density of donor atoms and by this on the ligand field strength is discussed. [10][11][12][13] To date, however, no consistent model for the explanation of the different effects is available. A detailed understanding of the interplay of hydrogen bonds and wide hysteresis loops is essential for a purposeful synthesis of SCO materials for potential applications.…”

“…[9] The possibility to influence the ST behaviour by hydrogen bonds has been already introduced in the literature. Several examples demonstrate an influence of the presence or absence of hydrogen bonds on both the transition temperature [10][11][12][13] as well as on cooperative effects. [9,[13][14][15] For some of the examples, an influence of the hydrogen bonds on the electron density of donor atoms and by this on the ligand field strength is discussed.…”

Control of Exchange Interactions in Trinuclear Complexes Based on Orthogonal Magnetic Orbitals

“…finding, we designed a new ligand H 4 L based on 4,5-diaminocatechol with two additional hydroxy groups on the phenyl ring that can act as H-bond donors/acceptors. [9] First investigations on the structure and magnetic properties of its iron(II) complexes showed that thermal spin transitions are observed for the octahedral complexes [10] and the number of intermolecular H-bonds increased relative to the number in the original complexes. [9] Rosa and coworkers reported for similar Schiff base ligands the synthesis of trinuclear NiV(O)Ni complexes by deprotonation of the hydroxy groups on the phenyl ring of the monomer nickel(II) complexes.…”