REACTIONS OF SMECTITES WITH BINUCLEAR OXO-BRIDGED IRON COMPLEXES OF N-ALKYL-N,N-BIS(2-PYRIDYLMETHYL)AMINES

Cationic binuclear ore-and carboxylate bridged Fe(III) complexes of N- alkyl-N,N-bis(2-pyridylmethyl)amines are introduced into the interlaye r region of smectites by cation exchange reactions. The reaction can b e divided into three steps. After a predominant loading of external su rfaces, cation exchange sites at internal surfaces react, accompanied by considerable structural expansion. Both reaction stages belong to t he steep section of the exchange isotherms. At a certain loading, whic h depends on the complex substituents and the layer charge of the smec tite, the isotherms become flat. With bulky shaped complex cations and highly charged smectites, exchange is not quantitative; vermiculite-t ype minerals show a very small complex uptake. For this behaviour, bot h thermodynamic and kinetic reasons must be considered. From these res ults the number of cation exchange positions at external surfaces of s mectite crystals may be estimated.