Bonding modes of nitrite and nitrate in palladium(II) and platinum(II) complexes

The crystal structures of the well-known complexes, [(Me 4 en)M(II)X 2 ] (Me 4 en = N , N , N ′, N ′-tetramethylethylenediamine; M(II) = Pd(II) or Pt(II); X − = NO 2 − or NO 3 − ) have been determined. For [(Me 4 en)Pd(NO 2 ) 2 ] and [(Me 4 en)Pt(NO 2 ) 2 ], the nitrite anion acts as a monodentate N -donor ligand in the solid state. In contrast, for [(Me 4 en)Pd(ONO 2 )(O 2 NO)], the two nitrate anions act as a monodentate O -donor (ONO 2 ) and a bidentate O , O ′-donor (O 2 NO). Recrystallization of [(Me 4 en)Pt(NO 3 ) 2 ] from Me 2 SO yields the Me 2 SO adduct with a monodentate O -donor nitrate and a counteranionic nitrate, [(Me 4 en)Pt(ONO 2 )( S -Me 2 SO)](NO 3 ). The solution behavior of these complexes, including the equilibrium between coordinated and free Me 2 SO, has been investigated.