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

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 [(Zn ₂L^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-C₆H ₄-CHO)]·2.5DMSO·2H₂O, [(Zn₂L ¹)₂(OOC-CH₂CH₂-COO)]·4. 25H₂O·0.75MeOH·0.5MeCN, [(Zn₂L ²)₂(OOC-CH₂CH₂-COO)]·7H ₂O·0.25MeOH and [(Zn₂L¹) ₂(p-OOC-C₆H₄-COO)]·2.5H ₂O·MeOH·6EtOH demonstrate that their different nuclearities are a function of the carboxylate donor, with the aldehyde residue remaining uncoordinated in [Zn₂L¹(p-OOC-C ₆H₄-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.