Swelling of montmorillonite containing coordination complexes of amines with transition metal cations

Swelling of montmorillonite is inhibited by interlayer organic ammonium ions. The effect of interlayer coordination complexes of ethylene diamine (En) with transition metals depends on the nature of the cations. When a fraction of interlayer Cu²⁺ or Hg²⁺ ions is chelated by two En ligands, swelling is inhibited. Zn²⁺, which forms [ZnEn₃]²⁺ complexes in aqueous solution, coordinates a maximum of two En ligands in interlayer space and permits swelling of the clay up to 1.53 nm. The effect of [NiEn₂]²⁺ and [CdEn₂]²⁺ is similar, whereas [NiEn₃]²⁺ and [CdEn₃]²⁺ ions restrict expansion to about 1.42 nm. Other chelating amines behave similarly, while nonchelating amines sorbed by montmorillonites saturated with complexing cations are hydrolyzed and swelling of the clay is prevented by the formation of ammonium ions.