REACTION OF NITROGEN-OXIDES WITH SALTS OF METAL-SUBSTITUTED HETEROPOLYANIONS

We have used IR spectroscopy to study the reaction with NO and NO2 of solid tetramethylammonium and cesium salts of heteropolyanions (HPA) P W11M(L)0.39 n - [M = V(V), Cr(III), Mn (II), Fe (II, III), Co (II), Ni (II), Cu(II); L = H2O, OH- or O2-], preevacuated at 110-degrees-C or 300-degrees-C Only in the case of Fe(II)-substituted heteropolyanions are nitrosyl complexes formed: PW11Fe(NO)O395- (nuNO = 1730 cm-1), whi ch leads to stabilization of the NO molecules with respect to oxidatio n by oxygen. We observed reversible reaction with NO2 by the listed he teropoly complexes. The vibrational frequencies of adsorbed NO2 are vi rtually independent of the metal M and its coordination environment in the heteropolyanion (nu1 = 1335-1360) and nu3 = 1620-1640 cm-1). This provides a basis for assuming that the NO2 groups are bonded to the o xygen atoms in the heteropoly anion with formation of the fragments O( HPA) ... NO2.