Synthesis, crystal structures and properties of iron(III) complexes exhibited both high-spin and low-spin states within the crystal lattice

The reaction of FeCl3 · 6H2O, potassium hydrotris(pyrazolyl)borate (KTp) and KSCN gives [FeTp2][TpFe(NCS)3] (1) and [FeTp2]3[Fe(NCS)6] (2), respectively. The bond lengths and angles indicate that both complexes have [FeTp2]+ cations where Fe(III) ions are in typical low-spin state, and in counter ions, [TpFe(NCS)3]− for 1 and [Fe(NCS)6]3− for 2 are both in high-spin state. Variable temperature magnetic susceptibility and ESR results also show that there are double spin states of iron(III) ions within the crystal lattice of both compounds.