Electron paramagnetic resonance and infrared studies of the tetraamminecopper (II) in a Y zeolite

Abstract

A series of copper-exchanged Y zeolites with exchange levels of 2.9, 4.3, 17, 25, 41, 55 and 75% have been examined using electron paramagnetic resonance (epr) and infrared (ir) spectroscopy. In the dehydrated CuY - 2.9, CuY - 4.3, and CuY -- 17 samples one, two and three cupric ion species, respectively, were detected by epr, with a new spectrum being superimposed upon the spectrum of the previous sample. The magnetic parameters of these three types of cupric ions differ from results published previously by other groups. A further increase in copper exchange produced an isotropic line which overlapped the anisotropic spectra of isolated cupric ions. This isotropic line, observed in the CuY -- 41 and CuY -- 55 zeolites, arises from cupric ions located in sites where they undergo spin exchange. In both samples there was evidence that isolated cupric ions were also present. Upon adsorption of ammonia the epr spectra of all samples changed. For all but the CuY -- 55 sample the spectrum of the isolated cupric ions was replaced by the characteristic spectrum of the copper(II)-ammine complex. For the CuY -- 55 zeolite the spectrum was isotropic. In the case of the CuY -- 41 sample the disappearance of the isotropic spectrum means that the cupric ion pairs were separated. This change in the epr spectrum of CuY -- 41 upon adsorption of ammonia confirms that many of the cupric ions move out of the sodalite cages, and it is postulated that most of the complexes are formed in the supercages of the zeolite. ...