ESR STUDY OF COPPER-AMMONIA COMPLEXES IN SOLUTION ADSORBED ON SILICA-GELS .1. WIDE-PORE SILICA-GELS

The behavior of water-ammonia solution filling the pores of silica gels with pore diameters ≥20 nm was studied by differential scanning calorimetry and electron spin resonance of Cu(II) paramagnetic probes. The copper-ammonia complexes are only in part chemisorbed on surface sites by bonding with deprotonated silanol groups. The remainder are dissolved into the intracrystalline liquid as a pentaammine complex. Upon freezing, this part segregates out as solid crystals dispersed in the frozen water-ammonia mixture. The freezing points of water-ammonia mixtures of different concentration do not correspond to those predicted by the phase diagram for bulk unadsorbed mixtures. This fact was discussed in terms of long-range solid-to-liquid interactions and of preferential adsorption of ammonia molecules on the solid surface. © 1979 American Chemical Society.