From dinuclear to tetranuclear zinc complexes through carboxylate donors: structural and luminescence studies

Abstract

Carboxylate zinc complexes of general formula [Zn₂L^x(p-OOC–C₆H₄–CHO)], [Zn₂L^x(o-OOC–C₆H₄–COOH)], [(Zn₂L^x)₂(OOC–CH₂–COO)], [(Zn₂L^x)₂(OOC–CH₂CH₂–COO)] and [(Zn₂L^x)₂(p-OOC–C₆H₄–COO)] (x = 1, 2; H₃L¹ = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H₃L² = 2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were isolated with different solvates. The crystal structures of [Zn₂L¹(p-OOC–C₆H₄–CHO)]·2.5DMSO·2H₂O, [(Zn₂L¹)₂(OOC–CH₂CH₂–COO)]·4.25H₂O·0.75MeOH·0.5MeCN, [(Zn₂L²)₂(OOC–CH₂CH₂–COO)]·7H₂O·0.25MeOH and [(Zn₂L¹)₂(p-OOC–C₆H₄–COO)]·2.5H₂O·MeOH·6EtOH demonstrate that their different nuclearities are a function of the carboxylate donor, with the aldehyde residue remaining uncoordinated in [Zn₂L¹(p-OOC–C₆H₄–CHO)]·2.5DMSO·2H₂O. The solution studies further support the dissimilar nuclearity of the complexes and agree with a dinuclear nature for those complexes containing ortho-phthalate or 4-formylbenzenecarboxylate, and a tetranuclear arrangement when malonate, succinate or terephthalate are used as co-ligands. The ability of both Schiff base ligands to recognize Zn(II) in solution was studied by UV-vis and emission spectroscopies. The luminescent properties of the ligands and their isolated complexes are also discussed in detail.