Anion dependence in the spin-crossover properties of a Fe(ii) podand complex

Abstract

We report the syntheses, characterisations, and spin state behaviours of salts of the tripodal-ligated Fe(II) complex [FeL(6-OH)]X(2) (L(6-OH) = tris{4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl}amine, X = OTf(-) (1), Br(-) (2), I(-) (3), BPh(4)(-) (4)). Covalent linking of the ligand arms is imperative as a high-spin bis(tridentate) complex (5) is formed when a non-tethered ethyl iminopyridine ligand (L(2) = 4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl) is used. For salts 1-4, thermally-induced spin-crossover (SCO) is observed in the solid state, with dependence on anion and solvate molecules. Salts with larger anions show more complete SCO centred at higher temperatures (1 > 3 > 2); the triflate salt 1 (T(1/2) = 173 K) also shows the strongest cooperativity of the compounds examined. Hydrogen bonding appears to be critical to SCO in this family of salts: limiting interactions by use of tetraphenylborate produces a high-spin complex down to 5 K. In protic solvents such as methanol, spectra of [FeL(6-OH)](2+) are largely unchanged over a period of three days, but dissociate when interrogated with strong field bidentate ligands. Compounds 1-3, and 5 remain high spin in solution down to 180 K, consistent with the data obtained in the solid state.

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

“…[g] 532 nm light irradiation. [h] 650 nm light irradiation, [i] 640 nm light irradiation, L=4‐hydroxy‐ N ′‐[(pyridin‐2‐yl)methylene]benzohydrazide Hqnal‐12= N ‐(8′‐quinolyl)‐1‐hydroxy‐2‐naphthaldimine, H 2 qsalc=4‐hydroxy‐3‐[(8‐quinolinylimino)methyl]benzoic acid, L 2 =4‐[(6‐methanol)‐2‐pyridyl]‐3‐aza‐3‐butenyl), HL 1 = N ′‐[(pyridin‐2‐yl)methylene]benzohydrazide. HL 2 = N ′‐[1‐(pyridin‐2‐yl)ethylidene]benzohydrazide, HL 3 = N ′‐[phenyl(pyridin‐2‐yl)methylene]benzohydrazide, HL 4 =2‐hydroxy‐ N ′‐[(pyridin‐2‐yl)methylene]benzohydrazide, HL 5 =2‐hydroxy‐ N ′‐[1‐(pyridin‐2‐yl)ethylidene]benzohydrazide, HL 6 =2‐hydroxy‐ N ′‐[phenyl(pyridin‐2‐yl)methylene]benzohydrazide,HL1=2‐hydroxy‐3‐methyl‐ N ′‐[1‐(pyridine‐2‐yl)‐butylidene]benzohydrazide, HL2=2‐hydroxy‐ N ′‐[1‐(pyridine‐2‐yl)butylidene]benzohydrazide.…”

“…On the other hand, there is at rend in the P4AE interactions among compound 2, 3 and 4.I ti si nteresting to note that P4AE interactions are weaker from X = I < Cl < Br as the T 1/2 increases. This observation does not seem plausi- [15] Hqnal-12 = N-(8'-quinolyl)-1-hydroxy-2-naphthaldimine,H 2 qsalc = 4-hydroxy-3-[(8-quinolinylimino)methyl]benzoic acid, [28] L 2 = 4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl), [ [11] = [Fe III (qsal-Br) 2 ]NO 3 ·2MeOH, Ref. [10] = [Fe III (qsal-I) 2 ]CF 3 SO 3 ·MeOH.…”

Guest Binding Subtly Influences Spin Crossover in an FeII4L4 Capsule

“…[1] Many such capsules have been constructed through subcomponent self-assembly-the formation of complex structures through the metal-templated reaction of simple aldehyde and amine building blocksusing iron(II) as a structural template; [2] to date mostly capsules with low-spin state iron(II) have been reported. Spin crossover (SCO) within iron(II) complexes is a phenomenon of interest from both fundamental [3] and functional [4] points of view. [5] Due to its applications in molecular switching, memory and display devices, SCO in supramolecular structures has been explored in molecular frameworks, [6] polymeric materials, [5a, 7] and discrete multinuclear complexes.…”

Magnetogenese in Wasser, ausgelöst durch einen chemischen Analyten

“…Vielzähnige Liganden, die zu binären LS-Komplexen führen, das Eisenzentrum nicht dazu bringen, einen LS-Zustand einzunehmen, wenn "nur" drei Stickstoffatome sp 2 -konfiguriert sind. [60] Nur Liganden, die ganze sechs iminartige Stickstoffatome enthalten, haben bisher LS-Komplexe ergeben: Während der Py3tame-Komplex [59] gespannt ist (sein LS-Zustand muss daher als schwach eingeschätzt werden), zeigt derjenige von Py3tren [61] die Tendenz zur Dekoordinierung eines Arms; [70] obwohl sechs Zähne vorliegen, die eine hohe Ligandenfeldaufspaltung bewirken, eignen sie sich daher nur bedingt für den Entwurf einer magnetogenen Einheit.…”