Complexes of ammonia and ethylenediamine with CuII on zeolite A

Abstract

Adsorption of NH₃ on a dehydrated CuA zeolite gives Cu(NH₃)²⁺₄ and a small amount of tetrahedrally coordinated Cu^II ions. These complexes are unstable and decompose by vacuum heating in the range 295–373 K to yield lattice-bonded Cu^II ions characterized by an e.p.r. signal with g‖= 2.3087, A‖= 0.015 09 cm^–1, g⊥= 2.067 and A⊥= 0.000 96 cm^–1. Above 373 K this signal transforms to g‖= 2.3715, A‖= 0.013 63 cm^–1, g⊥= 2.062 and A⊥= 0.001 92 cm^–1. Adsorption of ethylenediamine on a dehydrated CuA zeolite gives only Cu(en)²⁺, stable up to 473 K. However, in the presence of water, Cu(en)²⁺₂ and Cu(en)²⁺₃ can also be synthesized on the surface. The latter two complexes are unstable and decompose by vacuum heating to the mono-complex. Cu(en)²⁺ can also be loaded on NaA by ion-exchange from aqueous solution, but Cu(en)²⁺₂ cannot, due to space requirements and the instability of the bis-complex in the supercages of zeolite A. First it is necessary to exchange the mono-complex and to synthesize the bis-complex in situ by adding large excesses of ethylenediamine to the aqueous suspension. The e.p.r. and reflectance spectra of the various complexes depend slightly but consistently on the environment in the supercages of zeolite A. Their analysis, however, shows that this does not induce major changes in the Cu^II—N bonding characteristics.