Determining the site of reduction of 4-NO2-2,2'-bipyridine and [Pt(4-NO2-2,2'-bipyridine)Cl2].

In situ UV/Vis and EPR spectroelectrochemistry experiments show that the unpaired electron in [4-NO(2)-bpy](1-) sits in an orbital which is based on the 4-NO(2)-py moiety and not spread over both py rings. The unpaired electron in [Pt(4-NO(2)-bpy)Cl(2)](1-) is based on the 4-NO(2)-bpy ligand with some [bpy](1-) character. Labelling the NO(2) group of 4-NO(2)-bpy with (15)N revealed that the larger coupling constant in the EPR spectrum of [4-NO(2)-bpy](1-) can be assigned to the N atom of the NO(2) group. This coupling constant is significantly smaller in the EPR spectrum of [Pt(4-NO(2)-bpy)Cl(2)](1-).