A reversible metal–ligand bond break associated to a spin-crossover

Abstract

The [Fe(II)L(CN)(2)].H(2)O complex, dicyano[2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene]iron(II) monohydrate, exhibits a thermal induced metal-ligand bond break reversible in the solid state and associated to a spin crossover that corresponds to an unprecedented structurally characterized modification of the coordination metal environment from a hepta-coordinate high spin state to a hexa-coordinate low spin state.

A critical review of the T(LIESST) temperature in spin crossover materials − What it is and what it is not

“…It was then evidenced that the highest T(LIESST) should be obtained for the largest modification of the trigonal distortion from HS to LS [24,26,28]. This empirical observation has been confirmed so far, and the highest T(LIESST) for an iron(II) molecular complex corresponds indeed to the largest observed polyhedron distortion [37]. Interestingly, since T 1/2 was also evidenced as depending on the trigonal distortion, a linear dependence of T(LIESST) and T 1/2 was confirmed on the basis of structural data and a comparison of the relationships allow one to envisage the temperature range for a given family of SCO compounds (Figure 3).…”

Photothermal studies of the room temperature photo-induced spin state change in the Fe(III)(salten)(mepepy) complex

“…Such a spin state induced bond cleavage has been observed previously for a dicyano [2,13-dimethyl-6,9- [23]. This complex undergoes both an optically and thermally induced spin state change in the solid state over the temperature range from $125 to 150 K. In the high-spin state [Fe(II)L(CN) 2 )]ÁH 2 O exhibits pentagonal bipyramidal geometry with a hepta-coordinate ligation around the central iron.…”

“…Distances: a = 2.035 Å, b = 1.977 Å, c = 1.965 Å, d = 1.888 Å, e = 1.892 Å and f = 2.022 Å AB (from[23]). Bottom: structure of the trans and cis isomers of mepepy.…”

Ligand Association/Dissociation Paths and Ill‐Defined Coordination Numbers

“…[20,60] All those complexes appear as well-defined seven-coordinated pentagonal bipyramids (PBPY-7), with corresponding shape measures smaller than 0.3 (Scheme 4). The only exception is an Fe II compound at low temperature, [19] at which one of the ether groups partially dissociates from the ligand, simultaneously to a spin-crossover transition. In that case, the increase of the pentagonal bipyramidal measure and the decrease in the octahedral measure both indicate that the structure is practi- Figure 7.…”

“…Hypocoordination of multidentate ligands has also been shown to be important in some spin-crossover systems because a change in coordination number is associated with the change in spin state with temperature. [19,20] To exemplify how the comparison of structural data for related compounds can provide still images of ligand association/dissociation processes, let us focus on a prototypical solid-state compound, TiO 2 in its anatase polymorphic form. In that structure, [21] the coordination sphere of the Ti ions is significantly distorted from the perfect octahedron (Figure 1, center).…”