Preparation and Solid-phase Thermal cis-trans Isomerization of the Mixed Bis(diamine)chromium(III) Complexes of the Type [CrX2(aa)(bb)]X·nH2O

Abstract

Abstract The mixed bis(diamine)chromium(III) complexes trans- and cis-[CrX2(aa)(bb)]X·nH2O were prepared and characterized where X is chloride or bromide ion; aa and bb are different diamines selected from ethylenediamine (en), propylenediamine (pn) and trimethylenediamine (tn); and n is a number of 0 to 2. The cis-trans isomerization of the above complexes was investigated non-isothermally (derivatographically) and isothermally in the solid-phase. The isomerization was found to be one-way (trans-to-cis) and exothermic. The activation energies were estimated for dehydration or dehydration plus dehydrohalogenation (Ed) and isomerization (Ei. The intermediates mer-[CrBr3(en)(pn)]·2H2O and mer-[CrBr3(pn)(tn)]·2H2O were isolated during the isomerization of trans-[CrBr2(en)(pn)]Br·2H2O and trans-[CrBr2(pn)(tn)](H5O2)Br2, respectively. Bond rupture was proposed to be operative in the pathway of the isomerization.