Synthesis of cis and trans isomers of N,N′-dimethyl-1,2-ethanediamine complexes of nickel(II) nitrate and solid-phase thermal cis-to-trans isomeric transformation

Abstract

The octahedral cis and trans isomers of [NiL₂(NO₃)₂]·nH₂O (L =N,N′-dimethyl-1,2-ethanediamine; n= 0, 2, or 4) have been synthesised. On heating in the solid state the deaquated cis-[NiL₂(NO₃)]NO₃ isomerises exothermally to trans-[NiL₂(NO₃)₂] accompanied by an irreversible thermochromic colour change from deep blue to pink. This transformation can also be brought about at room temperature in the presence of a humid atmosphere (ca. 60%) as catalyst. The effect of humidity on the composition and geometry of the complexes has been investigated.