Iron(III) spin-crossover (SCO) complexes [Fe(qsal)]BS·MeOH·HO (1), [Fe(qsal)](NS)·MeOH (2), [Fe(qnal)](NS) (3), and [Fe(qnal)]PS·MeOH·CHCl (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)] 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.
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.
A dinuclear helical iron(ii) complex of a new ditopic thiazolylimine ligand (L) has been synthesised via supramolecular assembly. The resulting dinuclear helical cylinder [FeL]·4BF 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. [FeL]·4BF displays a complete spin transition with a gradual-abrupt character at T = 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.
Water dispersible metal complex nanoparticles were synthesized using the polyethylene glycol (PEG) coating method. The χmT values at room temperature for the NPs 1–3 were calculated using the Evans method, and the proton relaxation times, T1 and T2, were measured employing MRI. Both relaxation times were observed to decrease with increasing χmT value.
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