Tris(pyrazolyl)ethane Ligands Methylated at the 3–, 4–, and 5–positions and their Fe (II) Complexes

The 2:1 Fe(II) complexes of new tris(pyrazolyl)ethane (tpe) ligands, methylated at either the 3-, 4-, or 5-position of the pyrazoles, were prepared. Structural studies of the three new complexes will be presented. Crystal structures of the new tpe complexes indicate that the Fe—N bond lengths range from 1.93 Å to 1.98 Å, suggestive of mainly low-spin complexes. However, NMR and X-ray results show that the complex with tris(3-methylpyrazolyl)ethane is exhibiting the onset of spin crossover behavior near room temperature.