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

Abstract

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-).

Functionalized pyridine in pyclen-based iron(iii) complexes: evaluation of fundamental properties

“…4). 30,47 Similar trends to the iron(III) complexes were observed for the reduction events in the ligands, where the more EWG character to the pyridine ring correlated to more positive reduction waves. It should be noted that the reduction wave of L6 (E pc ¼ À783 mV) is signicantly more positive compared to the other ligands (Table S14 †), almost overlapping with the redox window of iron complexes themselves.…”

On the electronic structure of nitro-substituted bipyridines and their platinum complexes

“…These coupling constants are similar to those for [4-NO 2 -bipy] -. 13 Hence, the SOMO of [4,4¢-( 15 NO 2 ) 2 -bipy]is largely localised on only one of the nitro-bearing rings, not delocalised over the whole molecule, consistent with the UV/Vis data (see above).…”

“…For the mono-subtituted [Pt(x-NO 2 -bipy)Cl 2 ]family, only the x = 4 species gives a well resolved spectrum. 13 Similar analysis gives Pt valence orbital admixture to the SOMO of 7%, intermediate between the mono-and un-substituted complexes.…”

“…10- 12 Recently, we have investigated the effects of strongly electron withdrawing groups on the bipyridyl, for example, in 4-NO 2 -bipy. 13 We showed that the LUMOs of 4-NO 2 -bipy and its [Pt(4-NO 2 -bipy)Cl 2 ] complex, are largely localised on the nitro-bearing half of the bipyridyl group. Moreover, for the complex there is significantly less admixture of Pt valence orbitals to the LUMO compared to the [Pt(bipy)Cl 2 ] parent complex.…”

“…We previously showed by 15 N labelling that the smaller of these couplings is to the nitro-N, in contrast to the free ligand. 13 Hence there is a significant redistribution of the spin density from the nitro group to the pyridyl ring on coordination to a metal ion. In addition, a 33.2 ¥ 10 -4 cm -1 coupling to 195 Pt (33% natural abundance, I = 1/2) is resolved.…”