title: The advantage of spectrophotometric measurement for size-selective complexing of Cu(II) with O₂N₂-azacrown ligands.
abstract: A comparative investigation of the interaction of Cu(II) with a series of 15- to 19-membered mixed-donor dibenzo-substituted macrocyclic ligands, each incorporating an O2N2-donor set, has been carried out using UV-Visible studies in methanol. Although a ring size effect has been reported for a related series of Ni(II) complexes, no such metal ion discrimination has been reported for Cu(II) in terms of its binding constants with 14- to 17-membered macrocycles. Employing Job's method of continuous variation established 1:1 stoichiometry for the interaction between Cu(II) and 1-5. From UV-Visible studies applying the Benesi-Hildebrand equation, the binding constants (K) of Cu(II) with 1-5 were determined to be Cu(II)/1=3330 (±321) dm(3) mol(-1), Cu(II)/2=33,700 (±71) dm(3) mol(-1), Cu(II)/3=7260 (±151) dm(3) mol(-1), Cu(II)/4=57,000 (±257) dm(3) mol(-1) and Cu(II)/5=13,900 (±398) dm(3) mol(-1) in methanol at 25°C, respectively. The calculated binding constants showed a saw-tooth pattern in which 4 (18-membered ring) gives the highest K value for these complexes. The thermodynamic parameters (ΔG, ΔH, and TΔS) of the respective complexes have also been determined.
authors.affiliation: Department of Chemistry, Sharif University of Technology, PO Box 11155-3516, Tehran, Iran. Electronic address: Ghanbari@sharif.edu.
authors.forename: Bahram
authors.initials: B
authors.lastname: Ghanbari
authors.affiliation: Department of Chemistry, Sharif University of Technology, PO Box 11155-3516, Tehran, Iran.
authors.forename: Parisa
authors.initials: P
authors.lastname: Gholamnezhad
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D009584:Nitrogen / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods*; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
chemical_list: D001372:Aza Compounds; D008024:Ligands; D003300:Copper; D009584:Nitrogen; D010100:Oxygen
keywords: Azacrown; Benesi–Hildebrand; Binding constant; Copper (II)