Syntheses and crystal structures of two isomers of CuL²(NO³)²• 2H²O (L = N¹-isopropyl-2-methyl-1,2-propanediamine) and their thermochromism in the solid state

Abstract

Two isomeric complexes, [CuL₂](NO₃)₂ • 2H₂O, (1, red) and [CuL₂](H₂O)](NO₃)₂ • H₂O, (2, blue) (L=N¹-isopropyl-2-methyl-1,2-propanediamine) have been synthesised and their X-ray crystal structures have been determined. Both the isomers possess the same space group, P2₁\n. However, 1 is square planar and 2 is square pyramid having N₄ and N₄O chromophore, respectively around copper (II). The red isomer (1) upon heating loses water molecules yielding a violet dehydrated species, 1a which on further heating undergoes an exothermic phase transition accompanied by thermochromism, violet (1a) to blue-violet (1b) in the solid state. (1a) and (1b) are probably conformational isomers and they revert to 1 in humid atmosphere. The blue isomer (2) upon heating transforms to blue-violet species on dehydration, which reverts immediately after cooling in open atmosphere.