Preparation and Solid-phase Thermal cis-α↔cis-β Isomerization of the Chromium(III) Triethylenetetramine Complexes

Abstract
Heating of a mixture of CrCl3·6H2O and triethylenetetramine (trien) produced violet products which gave cis-α-[Cr2(OH)2trien2]X4·2H2O and cis-α-[Cr(OH)(H2O)trien]X2·H2O (X=Cl, Br or I) on treatment with aqueous NaX solutions. cis-α-[CrCl2trien]Cl·2H2O were obtained in the presence of a trace amount of water. Absolutely dry conditions are necessary for the preparation of cis-β-[CrCl2trien]Cl. The thermally induced reversible cis-α↔cis-β isomerization was detected in the complexes cis-α-[Cr(OH)(H2O)trien]Cl2·H2O and cis-β-[CrCl2-trien]Cl by means of derivatography and high-temperature IR spectroscopy. The former cis-α-hydroxoaqua complex was found to be converted irreversibly into cis-β-form above 225 °C in the solid-phase. The cis-β-form obtained readily isomerized to cis-α-form in aqueous media. The dimeric cis-α-[Cr2(OH)2trien2]4+ was converted gradually into the monomeric cis-α-[Cr(OH)(H2O)trien]2+ in water.