ABSTRACT
Water soluble spin-crossover (SCO) iron(II) nanoparticles (NPs) were synthesized by the polyethylene glycol (PEG) coating of [Fe(Htrz)3-3×(NH2trz)3×](BF4)2 (x = 0, 0.1, 0.5 and 1). The NPs with x = 0.1 show gradual SCO behavior over 280-330 K in water. The relaxation times, T1 and T2, were determined and the thermally-responsive T2 values making these NPs a candidate for use as a MRI contrast agent.
ABSTRACT
Iron(III) spin-crossover (SCO) complexes [Fe(qsal)2]BS·MeOH·H2O (1), [Fe(qsal)2](NS)·MeOH (2), [Fe(qnal)2](NS) (3), and [Fe(qnal)2]PS·MeOH·CH2Cl2 (4) (Hqsal, N-(8-quinolinyl)salicylaldimine; Hqnal, N-(8-quinolinyl)-2-hydroxy-1-naphthaldimine; BS, benzenesulfonate; NS, 1-naphthalenesulfonate; PS, 1-pyrenesulfonate) have been synthesized and characterized by X-ray structure determinations and temperature-dependent magnetic susceptibility measurements. The aromatic counteranions BS, NS, and PS can be used for the tuning of intermolecular coupling through a variety of weak interactions. All of the complexes show temperature-dependent SCO behavior. but the light-induced excited spin-state trapping (LIESST) effect was observed only for 1, 3, and 4 when the samples were illuminated (λ 808 nm) for 1 h at 5 K. In particular, 59% of the LS form of 1 was converted to the metastable HS state by illumination, equal to the highest degree of conversion yet known for LIESST in [Fe(qsal)2]+ derivatives. The lack of a LIESST effect for 2 may be due to the relatively limited degree of interaction between the cations and anions in the lattice, reflected in a much longer minimum Fe···Fe separation in this complex in comparison to the others.
ABSTRACT
A dinuclear helical iron(ii) complex of a new ditopic thiazolylimine ligand (L) has been synthesised via supramolecular assembly. The resulting dinuclear helical cylinder [Fe2L3]·4BF4 was investigated by variable temperature X-ray crystallography, ESI high resolution mass spectrometry, CHN analysis, FT-IR and UV-Vis spectroscopy. The nature of the spin transition was investigated by magnetic susceptibility measurements, and confirmed by VT-SCXRD and X-ray photoelectron spectroscopy. [Fe2L3]·4BF4 displays a complete spin transition with a gradual-abrupt character at T1/2 = 348 K and represents a new example of a dinuclear iron(ii) complex exhibiting a spin transition at high temperature. Both VT-SCXRD and XPS measurements show excellent correlation with the magnetic susceptibility experiments, demonstrating the power of XPS not just to confirm, but also to clearly follow the spin-state transition in Fe(ii) SCO complexes.
