612820-39-0Relevant articles and documents
The spin-states and spin-crossover behaviour of iron(II) complexes of 2,6-dipyrazol-1-ylpyrazine derivatives
Elhaik, Jerome,Money, Victoria A.,Barrett, Simon A.,Kilner, Colin A.,Evans, Ivana Radosavljevic,Halcrow, Malcolm A.
, p. 2053 - 2060 (2007/10/03)
The syntheses of [FeL2]X2 (L = 2,6-dipyrazol-1- ylpyrazine [L2H], 2,6-bis{3-methylpyrazol-1-yl}pyrazine [L 2Me], 2,6-bis{3,5-dimethylpyrazol-1-yl}pyrazine [L2Me 2] or 2,6-bis{3-[2,4,6-trimethylphenyl]pyrazol-1-yl}pyrazine [L 2Mes]; X- = BF4- or ClO 4-) 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(L 2H)2][ClO4]2 is isomorphous with [Fe(L1H)2][BF4]2 (L1H = 2,6-dipyrazol-1-ylpyridine). The single crystalline solvate [Fe(L 2H)2][BF4]2·3CH 3NO2 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(L 2Mes)2]2+ are fully low-spin at 295 K. Single crystal structures of [Fe(L2Me2)2][BF 4]2·0.5{CH3}2CO·0.1H2O and [Fe(L2Mes)2][BF4]2·5CH 3NO2 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. The Royal Society of Chemistry 2003.
