Issue 10, 2003
From the journal:

Dalton Transactions

The spin-states and spin-crossover behaviour of iron(ii) complexes of 2,6-dipyrazol-1-ylpyrazine derivatives†

Jérôme Elhaïk,a   Victoria A. Money,b   Simon A. Barrett,a   Colin A. Kilner,a   Ivana Radosavljevic Evansb  and  Malcolm A. Halcrow*a  

* Corresponding authors

a Department of Chemistry, University of Leeds, Woodhouse Lane, Leeds, UK
E-mail: M.A.Halcrow@chem.leeds.ac.uk

b Department of Chemistry, University of Durham, South Road, Durham, UK

Abstract

The syntheses of [FeL2]X2 (L = 2,6-dipyrazol-1-ylpyrazine [L2H], 2,6-bis{3-methylpyrazol-1-yl}pyrazine [L2Me], 2,6-bis{3,5-dimethylpyrazol-1-yl}pyrazine [L2Me2] or 2,6-bis{3-[2,4,6-trimethylphenyl]pyrazol-1-yl}pyrazine [L2Mes]; X− = BF4− or ClO4−) are described. Solvent-free [Fe(L2H)2][BF4]2 and [Fe(L2H)2][ClO4]2 exhibit very similar abrupt spin-state transitions at 223 K and 208 K respectively, which show hysteresis loops of 3–5 K. Powder diffraction measurements afforded related, but not identical, unit cells for these two compounds, and imply that [Fe(L2H)2][ClO4]2 is isomorphous with [Fe(L1H)2][BF4]2 (L1H = 2,6-dipyrazol-1-ylpyridine). The single crystalline solvate [Fe(L2H)2][BF4]2·3CH3NO2 undergoes a similarly abrupt spin-state transition at 198 K. Polycrystalline [Fe(L2Me)2][BF4]2 and [Fe(L2Me)2][ClO4]2 are isomorphous with each other and also exhibit spin-state transitions at low temperature, although these are very different in form. In contrast, both salts of [Fe(L2Me2)2]2+ and [Fe(L2Mes)2]2+ are fully low-spin at 295 K. Single crystal structures of [Fe(L2Me2)2][BF4]2·0.5{CH3}2CO·0.1H2O and [Fe(L2Mes)2][BF4]2·5CH3NO2 show low-spin complex dications, and imply that [Fe(L2Me2)2][BF4]2 is low-spin as a result of intra-ligand steric repulsions involving the pyrazole 5-methyl substituents. NMR and UV/vis data in MeCN and MeNO2 show that the spin states of all four complex dications are similar in solution and the solid state except for [Fe(L2Me2)2]2+, which exists as a mixture of high- and low-spin species in these solvents.

Graphical abstract: The spin-states and spin-crossover behaviour of iron(ii) complexes of 2,6-dipyrazol-1-ylpyrazine derivatives

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Article information

DOI
https://doi.org/10.1039/B210368K
Article type
Paper
Submitted
22 Oct 2002
Accepted
06 Jan 2003
First published
23 Apr 2003

Dalton Trans., 2003, 2053-2060

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The spin-states and spin-crossover behaviour of iron(II) complexes of 2,6-dipyrazol-1-ylpyrazine derivatives

J. Elhaïk, V. A. Money, S. A. Barrett, C. A. Kilner, I. R. Evans and M. A. Halcrow, Dalton Trans., 2003, 2053 DOI: 10.1039/B210368K

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