Study of the coordination of Cu2+ in zeolite Y: Interaction with water andammonia

The ligand field spectrum of Cu(II) exchanged zeolite Y, obtained after sat uration with H2O and NH3 and during the gradual desorption of these ligands , was measured by diffuse reflectance spectroscopy (DRS). DFT and ab-initio calculations on several model clusters were performed to interpret the spe ctra. The structure of the model clusters was optimized by means of density functional theory (DFT), using the B3LYP functional. The electronic spectr a of the models were calculated using multiconfigurational perturbation the ory based on a CASSCF wavefunction (CASPT2) and compared with the DRS spect ra. Firstly, several [Cu(NH3)(y)(H2O)(x)](2+) complexes were studied. It wa s shown that in fully hydrated Cu(II)Y, a [Cu(H2O)(6)](2+) complex can be p resent in the cages of the zeolite. In Cu(II)Y, saturated with NH3, the [Cu (NH3)(4)](2+) complex is present, but the Cu2+ center in this complex must still be coordinated to one or two lattice oxygens in the zeolite. Secondly , calculations were performed on large cluster models, representing the ads orption complexes of one H2O or one NH3 ligand on Cu2+ in the six-ring site s in zeolite Y. The ligand field spectrum of partially dehydrated and deamm oniated Cu(II)Y shows d-d transitions at a lower energy than the spectrum o f fully dehydrated Cu(II)Y, which is confirmed by the CASPT2 results of the six-ring clusters. (C) 2000 Elsevier Science B.V. All rights reserved.