On the nature of the spin ground state of iron(II) in Fe(2,9-di-CH3-phenanthroline)2(NCS)2

The temperature dependence of the zero field Mossbauer spectrum and magnetic susceptibility of Fe(2,9-di-CH3-phenanthroline)2(NCS)2 over the range 1.8 to 300 K shows that the complex contains spin quintet iron(II) at all temperatures. The ligand is apparently to the weak field side of the ‘crossover point’ and contrary to the results of a previous study there is no evidence of a transition to a lower multiplicity (triplet or singlet) ground state. The observed decrease of the magnetic moment (4.81 μβ at 302 K to 3.48 μβ at 1.82 K) is consistent with zero field splitting (|D|≈ 5 cm−1) of the ground spin manifold.