Synthesis, characterization and thermodynamic study of copper(II) complexes with unsymmetric tetradentate Schiff base ligands and X-ray structure of {methyl-2-[N-[2-(5-chloro-2-phenolate)methylidynenitrilo]ethyl}aminato(-1)-1-cyclopentenedithiocarboxylate

A set of two Cu(II) complexes, [Cu(cdXsalen)] and [Cu(cdXsalMeen)] derived from Schiff base ligands (H2cdXsalen: methyl-2-{[2-(2-X-phenyl)methylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate and H2cdXsalMeen: methyl-2-{[1-methyl-2-(2-X-phenyl)methylidynenitrilo]ethyl}amino-1-cyclopenteneithiocarb-oxylate where X = hydroxyl, methoxy, nitro, sodiumsulfite, chloro, bromo and H2cdMesalen: methyl-2-{[2-(2-hydroxyphenyl)ethylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate; H2cdPhsalen: methyl-2-{[2-(2-hydroxyphenyl)phenylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate; H2cdMesalMeen: methyl-2-{[1-methyl-2-(2-hydroxyphenyl)ethylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate; H2cdPhsalMeen: methyl-2-{[1-methyl-2-(2-hydroxyphenyl)phenylidynenitrilo]ethyl}amino-1-cyclopentenedi-thiocarboxylate) with an unsymmetric NNOS coordination sphere have been synthesized and characterized by elemental analysis, IR, UV–Vis and mass spectrometry. The thermodynamic formation constants of the complexes were measured spectrophotometrically, at constant ionic strength 0.1 M (NaClO4), at 25 °C in DMF solvent. The trend of the complex formation for copper is as follow: