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Santoro A, Kershaw Cook LJ, Kulmaczewski R, et al. Iron(II) complexes of tridentate indazolylpyridine ligands: enhanced spin-crossover hysteresis and ligand-based fluorescence. Inorg Chem. 2015;54(2):682-93doi: 10.1021/ic502726q.
Santoro, A., Kershaw Cook, L. J., Kulmaczewski, R., Barrett, S. A., Cespedes, O., & Halcrow, M. A. (2015). Iron(II) complexes of tridentate indazolylpyridine ligands: enhanced spin-crossover hysteresis and ligand-based fluorescence. Inorganic chemistry, 54(2), 682-93. https://doi.org/10.1021/ic502726q
Santoro, Amedeo, et al. "Iron(II) complexes of tridentate indazolylpyridine ligands: enhanced spin-crossover hysteresis and ligand-based fluorescence." Inorganic chemistry vol. 54,2 (2015): 682-93. doi: https://doi.org/10.1021/ic502726q
Santoro A, Kershaw Cook LJ, Kulmaczewski R, Barrett SA, Cespedes O, Halcrow MA. Iron(II) complexes of tridentate indazolylpyridine ligands: enhanced spin-crossover hysteresis and ligand-based fluorescence. Inorg Chem. 2015 Jan 20;54(2):682-93. doi: 10.1021/ic502726q. Epub 2015 Jan 07. PMID: 25563430.
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Inorg Chem. 2015 Jan 20;54(2):682-93. doi: 10.1021/ic502726q. Epub 2015 Jan 07.

Iron(II) complexes of tridentate indazolylpyridine ligands: enhanced spin-crossover hysteresis and ligand-based fluorescence.

Inorganic chemistry

Amedeo Santoro, Laurence J Kershaw Cook, Rafal Kulmaczewski, Simon A Barrett, Oscar Cespedes, Malcolm A Halcrow

Affiliations

  1. School of Chemistry, University of Leeds , Woodhouse Lane, Leeds LS2 9JT, United Kingdom.

PMID: 25563430 DOI: 10.1021/ic502726q

Abstract

Reaction of 2,6-difluoropyridine with 2 equiv of indazole and NaH at room temperature affords a mixture of 2,6-bis(indazol-1-yl)pyridine (1-bip), 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine (1,2-bip), and 2,6-bis(indazol-2-yl)pyridine (2-bip), which can be separated by solvent extraction. A two-step procedure using the same conditions also affords both 2-(indazol-1-yl)-6-(pyrazol-1-yl)pyridine (1-ipp) and 2-(indazol-2-yl)-6-(pyrazol-1-yl)pyridine (2-ipp). These are all annelated analogues of 2,6-di(pyrazol-1-yl)pyridine, an important ligand for spin-crossover complexes. Iron(II) complexes [Fe(1-bip)2](2+), [Fe(1,2-bip)2](2+), and [Fe(1-ipp)2](2+) are low-spin at room temperature, reflecting sterically imposed conformational rigidity of the 1-indazolyl ligands. In contrast, the 2-indazolyl complexes [Fe(2-bip)2](2+) and [Fe(2-ipp)2](2+) are high-spin in solution at room temperature, whereas salts of [Fe(2-bip)2](2+) exhibit thermal spin transitions in the solid state. Notably, [Fe(2-bip)2][BF4]2·2MeNO2 adopts a terpyridine embrace lattice structure and undergoes a spin transition near room temperature after annealing, resulting in thermal hysteresis that is wider than previously observed for this structure type (T1/2 = 266 K, ΔT = 16-20 K). This reflects enhanced mechanical coupling between the cations in the lattice through interdigitation of their ligand arms, which supports a previously proposed structure/function relationship for spin-crossover materials with this form of crystal packing. All of the compounds in this work exhibit blue fluorescence in solution under ambient conditions. In most cases, the ligand-based emission maxima are slightly red shifted upon complexation, but there is no detectable correlation between the emission maximum and the spin state of the iron centers.

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