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 (-) = NO2 (-) or NO3 (-)) have been determined. For [(Me(4)en)Pd(NO2)(2)] and [(Me(4)en)Pt(NO2)(2)], the nitrite anion acts as a monodentate N-donor ligand in the solid state. In contrast, for [(Me(4)en)Pd(ONO2)(O2NO)], the two nitrate anions act as a monodentate O-donor (ONO2) and a bidentate O,O'-donor (O2NO). Recrystallization of [(Me(4)en)Pt(NO3)(2)] from Me2SO yields the Me2SO adduct with a monodentate O-donor nitrate and a counteranionic nitrate, [(Me(4)en)Pt(ONO2)(S-Me2SO)](NO3). The solution behavior of these complexes, including the equilibrium between coordinated and free Me2SO, has been investigated.