We report an in situ IR, EPR, and high resolution XANES study on the Cu+(NO) and Cu+(NO)(2) complexes formed at 80 K in Cu+-ZSM-5. Bare Cu2+ ions (<1%) exhibit an axial EPR spectrum, while bare Cu+ ions exhibit well resolved 1s --> 4p(xy) and 1s --> 4p(z) transitions (p(xy)/p(z) splitting of 3.1 eV), reflecting the same local symmetry. Cu+(NO) complex exhibits an anisotropic EPR signal, while XANES spectrum of dinitrosyl adducts presents three resolved components ascribed to the 1s --> 4p(x), 1s --> 4p(y), and 1s --> 4p(z) transitions (p(x)/p(y) and p(y)/p(z) splitting of 3.8 and 2.6 eV, respectively) testifying the rupture of the axial symmetry of Cu+ bare cations upon NO adsorption. Upon increasing the temperature to 300 K, NO oxidizes a fraction of 75-85% of the cuprous ions. (C) 2002 Elsevier Science B.V. All rights reserved..