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) PW11M(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°C or 300°C. Only in the case of Fe(II)-substituted heteropolyanions are nitrosyl complexes formed: PW11Fe(NO)O 39 5− (vNO=1730 cm−1), which leads to stabilization of the NO molecules with respect to oxidation by oxygen. We observed reversible reaction with NO2 by the listed heteropoly complexes. The vibrational frequencies of adsorbed NO2 are virtually independent of the metal M and its coordination environment in the heteropolyanion (v1=1335−1360) and v3=1620−1640 cm−1). This provides a basis for assuming that the NO2 groups are bonded to the oxygen atoms in the heteropoly anion with formation of the fragments OHPA...NO2.