Electron spin resonance and electron spin echo modulation spectroscopic studies of cupric ion - Adsorbate interactions in synthetic clinoptilolite

The site locations and adsorbate interactions of Cu²⁺ in Cu²⁺-exchanged synthetic clinoptilolite have been determined by electron spin resonance and electron spin echo modulation spectroscopes. Strong effects of the H⁺, Li⁺, Na⁺, and K⁺ cocations have been found on the coordination number and on the location of the cupric ion. Cu²⁺ coordinates three molecules of water in hydrated CuH - clinoptilolite (CuH - Clino) and in CuLi - Clino, but only two molecules of water in hydrated CuNa - Clino and CuK - Clino. Two cupric ion sites are observed in many cases and are attributed to sites in ten-ring and eight-ring main channels. Activation to 400°C is sufficient to remove these water molecules and cause migration of Cu²⁺ to an eight-ring intersecting channel. Adsorption of polar molecules such as water, ammonia, alcohols, and acetonitrile causes the migration of Cu²⁺ into the main channels to coordinate with the adsorbate. Cu²⁺ forms complexes with three molecules of ethanol and four of ammonia in CuH - Clino, but only coordinates to two molecules of ethanol or methanol and three of ammonia in CuNa - Clino, and to one molecule of ethanol or methanol and three of ammonia in CuK - Clino. Cu²⁺ coordinates four molecules of acetonitrile at the center of a main channel in clinoptilolite, and this coordination number is unaffected by the alkali metal cocations.