Tuning spin-crossover transition temperatures in non-symmetrical homoleptic meridional/facial [Fe(didentate)₃]²⁺complexes: what for and who cares about it?

Abstract

The spin transition temperatures of [Fe(didentate)3]2+ in acetonitrile (didentate = 2-X-benzimidazole) can be stepwise decreased by 40 K along the series X = pyrazine > pyridine > pyrimidine.

Peculiar Spin-Crossover Behavior in the 2D Polymer K[FeIII(5Cl-thsa)2]

“…Best-fit local structure parameters around Fe atoms in 1 are summarized in Table . The best-fit lengths of Fe–N­(O) and Fe–S bonds are similar to those in other closely related iron coordination compounds with thiosemicarbazone ligands according to available literature . It is interesting to note that the EXAFS results on the local structure parameters of the iron­(III) coordination octahedron for the K­[Fe­(5Cl-thsa) 2 ] powder sample of the main polymorph at 300 K demonstrate an excellent convergence with X-ray crystallographic data obtained on the single crystal of the minor polymorph of 1 .…”

“…Zelentsov and co-workers first characterized their anomalous magnetic behavior in early 1970s . It should be noted that the synthesis conditions exert a noticeable effect on the SCO parameters of the compound under study. ,− Depending on the pH of the solution, these ligands can form cationic, , neutral, and anionic iron­(III)-coordinated complexes. This gives rise to essentially different SCO parameters of the resultant compound .…”

“…These properties of iron­(III) thsa-complexes could be potentially applied in modern electronic devices such as switches, data storages elements or optical components. − It should be noted that spin-crossover iron­(II) compounds with a 2D polymer structure are thoroughly studied and characterized enabling their use in the design of innovative devices . In contrast, the vast majority of studies devoted to SCO [Fe III (R-thsa) 2 ] − complexes are strongly hindered by the lack of high-quality single crystals suitable for X-ray diffraction studies. ,, This problem seriously complicates the establishment of magneto-structural correlations for the whole class of thsa-complexes which hinders their practical application. − In turn, X-ray structures of [Fe­(5Br-thsa) 2 ] − salts were solved for Li + , K + , Cs + , and NH 4 + cations, while the only structure of the [Fe­(5Cl-thsa) 2 ] − -based salt with a NH 4 + cation was obtained . The NH 4 [Fe­(5Cl-thsa) 2 ] salt shows an incomplete SCO transition (γ HS = 4 → 37%) in a 80–300 K temperature range, whereas the structures obtained at 135 and 298 K do not demonstrate significant changes in the coordination FeS 2 N 2 O 2 octahedron.…”

Stereoisomeric coordination polymers based on facial and meridional six-coordinate dysprosium(iii )

“…1 The physical properties of the two stereoisomers could be different, such as the light-emitting properties of Ir(III) complexes 2,3 and the spin-crossover transition of Fe(II) complexes. 4 Because of the small differences in their chemical properties, it is challenging to selectively synthesise one of the isolated isomers. 5 Moreover, only a handful of fac/mer isomers of lanthanide complexes have been reported, [6][7][8][9] due to the predominant ionic bonding regimes of the 4f-elements.…”

Spin-Crossover in Supramolecular Iron(II)–2,6-bis(1H-Pyrazol-1-yl)pyridine Complexes: Toward Spin-State Switchable Single-Molecule Junctions

“…Ever since its genesis dating back to the 1930s, 1 the spin-crossover (SCO) phenomenon 2 − 7 continually attracted the interest of chemists and physicists alike, and the device suitable characteristics of the SCO systems have been elucidated. 8 − 11 First-row transition metal complexes featuring a d 4 –d 7 electronic configuration undergo SCO 12 − 19 upon application of an external stimulus, for example, temperature, light, or electrical field.…”