Unusual nitrite complexes of iron(III) and iron(II) stabilized by the tris(3,5-dimethylpyrazolyl)borate ligand

Halide metathesis with silver nitrite allows for either stepwise or complete substitution of all three chloride ligands in the iron(III) compound [NEt4][HB(3,5-Me(2)pz)(3)FeCl3] (ii to give the complexes [NEt4][HB(3,5-Me(2)pz)3(F)e(ONO)(x)Cl3-x], x = 1-3 (2-4), and [NEt4][HB(3,5-Me(2)pz)(3)Fe(eta(2)-ONO)Cl] (5), which were characterized by elemental analyses, electrochemistry and IR, EPRI and UV-vis spectroscopy. Single-crystal X-ray diffraction was used to characterize the ferric complexes 2 and 3 and the ferrous chelating nitrito complex, 5. The crystal structures of the ferric complexes exhibit monodentate, O-bound nitrito ligands, while the change in metal oxidation state from +3 to +2 leads to a chelating nitrito ligand in 5.