Iron(II) complexes of 2,6-di(1H-pyrazol-3-yl)-pyridine derivatives with hydrogen bonding and sterically bulky substituents

Syntheses of 2,6-di(5-aminopyrazol-3-yl)pyridine (L(1)), 2,6-di(5-tertbutylcarboxamidopyrazol-3-yl)pyridine (L(2)), 2,6-di(5-tertbutylpyrazol-3-yl)pyridine (L(3)), 2-(5-tertbutylpyrazol-3-yl)-6-(5-methylpyrazol-3-yl)pyridine (L(4)) and 2-(5-tertbutylpyrazol-3-yl)-6-(5-aminopyrazol-3-yl)pyridine (L(5)) are reported. Iron complex salts of the first four ligands were crystallographically characterised. The structures exhibit intermolecular hydrogen bonding between the cations and the anions and/or solvent, leading to a fluorite (flu) net, a 1D ladder structure, and a homochiral self-penetrating helical network related to the (10,3)-a (srs) topology. All the complexes are high-spin in the crystal, and bulk samples are also fully or predominantly high-spin at room temperature and below although two of the dried materials exhibit partial spin-state transitions on cooling.