Electron spin echo studies of Cu2+ on silica surfaces: Interaction with water and ammonia adsorbates

Abstract

An electron spin echo modulation study of cupric ion exchanged into silica gel by an ammonia complex shows that Cu²⁺ is coordinated to only two NH₃ molecules. This coordination is reversible by thermal activation. Adsorption of H₂O instead of NH₃ also shows coordination to only two H₂O molecules which is thermally reversible. From these electron spin echo results and electron spin resonance spectra, it is postulated that in the presence of adsorbate the cupric ion has a distorted octahedral environment involving coordination to two adsorbate molecules and four lattice oxygens.