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Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes

School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
Author to whom correspondence should be addressed.
Magnetochemistry 2019, 5(1), 9;
Received: 20 December 2018 / Revised: 18 January 2019 / Accepted: 22 January 2019 / Published: 1 February 2019
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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Two phenyl ester and three benzyl ester derivatives have been synthesized from 2,6-di(pyrazol-1-yl)pyridine-4-carboxylic acid and the appropriate phenyl or benzyl alcohol using N,N′-dicyclohexylcarbodiimide as the coupling reagent. Complexation of the ligands with Fe[BF4]2·6H2O in acetone yielded the corresponding [FeL2][BF4]2 complex salts. Four of the new ligands and four of the complexes have been crystallographically characterised. Particularly noteworthy are two polymorphs of [Fe(L3)2][BF4]2·2MeNO2 (L3 = 3,4-dimethoxyphenyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), one of which is crystallographically characterised as high-spin while the other exhibits the onset of spin-crossover above room temperature. The other complexes are similarly low-spin at low temperature but exhibit gradual spin-crossover on heating, except for an acetone solvate of [Fe(L5)2][BF4]2 (L5 = benzyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), which exhibits a more abrupt spin-transition at T½ = 273 K with 9 K thermal hysteresis. View Full-Text
Keywords: iron; N-donor ligand; spin-crossover; crystal structure; magnetic measurements iron; N-donor ligand; spin-crossover; crystal structure; magnetic measurements

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Galadzhun, I.; Kulmaczewski, R.; Halcrow, M.A. Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes. Magnetochemistry 2019, 5, 9.

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