Design of chiral homodinuclear complexes based on the coordinating behaviour of some symmetric ligands

Abstract

The crystal structures determined for [Zn₂L¹(acac)]·H₂O and [Zn₂L²(acac)]·H₂O·MeCN·MeOH show that both compounds are chiral, although crystallising as racemates. This was not unexpected, as these complexes had been designed on the basis of the coordinating behaviour of acac in combination with 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine (H₃L¹) and 2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine (H₃L²). The reactivity of Zn(acac)₂·nH₂O with compartmental H₃L^x (x = 1 or 2) has been investigated under different reaction conditions. Thus, depending on the temperature, the reaction with H₃L¹ can yield [Zn₂L¹(acac)]·H₂O or [Zn₂L¹(OAc)]·H₂O, whilst the interaction of Zn(acac)₂·nH₂O with H₃L² only gives rise to crystalline [Zn₂L²(acac)]·H₂O·MeCN·MeOH. This latter species loses the most volatile solvates on drying to yield [Zn₂L²(acac)]·H₂O. Both [Zn₂L^x(acac)]·H₂O complexes have been fully characterised by analytical and spectroscopic methods.