Quadridentate versus quinquedentate co-ordination of some N₅and N₃O₂macrocyclic ligands and an unusual thermally controlled quintet ⇌ singlet spin transition in an iron(II) complex

Photoswitching of the Dielectric Constant of the Spin‐Crossover Complex [Fe(L)(CN)2]⋅H2O

“…The Fe II ion is seven-coordinate in the HS state and sixcoordinate in the LS state (Figure 4). This original feature was first suggested by Nelson et al [14] and corroborated recently by Guionneau et al [18] through X-ray investigations. It is noteworthy that the same optimized six-coordinate LS geometry was successfully obtained with different basis sets by using the seven-coordinate HS structure as a starting geometry.…”

“…The real part e' represents the displacement of the bounded charges under the effect of a time-dependent electric field. We will focus only on this latter physical quantity in the following discussion.As reported previously, [13][14][15] the magnetic behavior of [Fe(L)(CN) 2 ]·H 2 O is rather unusual: if the sample is quenched (at a rate of 20 K min À1 ) from 300 to 77 K, the HS state may be "frozen in" and remains stable for several days. The sample transforms into a pure LS state when it is heated up to 150 K. Irradiation with light of the LS state at 10 K leads to an increase in the magnetic susceptibility (LIESST effect) as shown in Figure 1 a.…”

“…A preliminary theoretical approach, based on density functional theory (DFT), to interpret the variation of the dielectric constant with the SCO is also presented. For this study, we selected the SCO complex [Fe(L)(CN) 2 ]·H 2 O [13,14] in which L is a Schiff base macrocyclic ligand derived from the condensation of 2,6-diacetylpyridine with 3,6-dioxaoctane-1,8-diamine (L = 2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene). This molecule was chosen because its critical temperature (T LIESST ), defined as the temperature at which the lightinduced HS information is erased, [8] is the highest (130 K) ever obtained for a SCO compound.…”

Anion, Solvent and Time Dependence of High‐Spin–Low‐Spin Interactions in a 3D Coordination Polymer

“…[18][19][20][21]30] The ability to remain in a metastable HS state when rapidly cooled has been noted in a dicyanide iron(II) complex with a macrocyclic Schiff base ligand. [31][32][33][34] These results show the important interplay between anion and solvent in the types of structural and magnetic properties observed.…”

Rapid Cooling Experiments and Use of an Anionic Nuclear Probe to Sense the Spin Transition of the 1D Coordination Polymers [Fe(NH2trz)3]SnF6⋅n H2O (NH2trz=4‐amino‐1,2,4‐triazole)

“…These effects were probed by trapping, partially or totally, the metastable HS state by RC for numerous Fe II SCO complexes [48][49][50][51][52][53][54][55][56][57] and a few Fe III compounds. [58] Such thermal trapping experiments were attempted to sense cooperative effects of the SCO by looking at the shape of the time dependency of the g HS relaxation curves at selected temperatures.…”