Structural, Magnetic and Mssbauer Studies of Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) Triflate and its Hydrates

The electronic properties of bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) triflate depend markedly on the extent of hydration. The trihydrate is low spin while the monohydrate is high spin at room temperature but undergoes a discontinuous transition to low spin at low temperatures. In the anhydrous complex magnetic and Mössbauer spectral data indicate that there is a minor fraction of low-spin species at room temperature and this fraction increases at low temperatures. The spin transition in the anhydrous salt is continuous and incomplete at 80 K. The structure of the trihydrate reveals an extensive hydrogen-bonding network which involves the uncoordinated NH groups of the pyrazolyl groups in the ligands, the water molecules and the anions. The disruption of this network on loss of water is believed to be responsible for the change in electronic properties. Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) triflate trihydrate: triclinic, space group P -1, a 11·490(5), b 12·218(6), c 13·666(6) Å, a 104 ·67(2), ß 104·58(2), ? 104·35(2)°, Z 2.