Abstract
Treatment of 4-hydroxy-2,6-dibromopyridine with four equivalent of deprotonated pyrazole in hot diglyme affords 4-hydroxy-2,6-di(pyrazol-1-yl)pyridine (L) in low yield. The three complex salts [FeL2]X2 (X− = BF4−, 1; X− = ClO4−, 2; X− = PF6−, 3) have been prepared, and crystallographically characterised as their methanol solvates. The solvate structures contain complexes that are fully high-spin (1 and 3), or in a mixed high:low spin state population at 150 K (2). Bulk samples of 1 and 2 obtained from methanol/diethyl ether contain a second, minor crystal phase that exhibits an abrupt spin-transition near 200 K. Recrystallisation of 1 and 2 from nitromethane/diethyl ether affords powder samples that are highly enriched in this spin-transition phase.
Highlights
The [Fe(bpp)2]2+ family of complexes [1,2,3] is widely used in the field of spin-crossover research (Scheme 1) [4,5]
We report here the corresponding ligand from the bpp series, 4-hydroxy-2,6-di(pyrazol-1-yl)pyridine (L), and its iron complex salts
Of the appropriate iron(II) salt by L in nitromethane, which yielded the products as yellow microcrystals after the usual work-up
Summary
The [Fe(bpp)2]2+ (bpp = 2,6-di{pyrazol-1-yl}pyridine) family of complexes [1,2,3] is widely used in the field of spin-crossover research (Scheme 1) [4,5]. While they often undergo spin-crossover near room-temperature [1], the particular advantage of this class of compounds is that synthetic methods are available to functionalise every position of the bpp ligand framework [6]. In Scheme 1) are of particular use, since they allow functionality to be introduced onto the complex without exerting a steric influence on the metal coordination sphere. Since complexes related to [Co(bpp)2]2+ are high-spin [19], [CoL2]2+ was not investigated in this study because the L ligand was only available in small quantities
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