Complexation of Ferrous and Cupric Ions by Phenanthroline and Terpyridine Langmuir Films Shlomit Kraus and Daniel Mandler* Department of Inorganic and Analytical Chemistry, The Hebrew UniVersity of Jerusalem, Jerusalem 91904, Israel ReceiVed April 29, 2006. In Final Form: July 4, 2006 The complexation of Fe II and Cu II ions by phenanthroline and terpyridine-based Langmuir films was studied by the effect the added ions in the subphase on the isotherms. We found that Cu II had a pronounced effect on the isotherm consisting of phenanthroline moieties forming a square-planar 1:2 (Cu II /phenanthroline) complex. However, Fe II affected the isotherm made of 1:1 phenanthroline/terpyridine amphiphiles as a result of forming a pentacoordinate complex. 1. Introduction The interaction between Langmuir films and metal ions has been of interest as a model for natural systems as well as a selectivity factor in designing sensing devices. 1-6 A variety of amphiphile monolayers based on mono- and multidentate ligands have been studied in the presence of metal ions in the subphase. 7-10 Surveying these studies reveals that most of the investigated Langmuir films do not exhibit high selectivity toward transition- metal ions as has been evidenced by the small effect of the ions on the isotherm. Not surprisingly, cupric ions usually showed the highest affinity toward Langmuir films, which could be attributed to the square-planar complex that is relatively easily formed at the water-air interface. 11-15 However, to the best of our knowledge, the formation of octahedral complexes that prevail among many first raw transition metals (e.g., Fe 2+ and Co 2+ ) has not been reported at the water-air interface. Here we report on the selective interaction between Langmuir films made of 7-tridecyl-4-methyl-1,10-phenanthroline (I) and a mixture of I and 4′-hexadecyloxy-2,2′/6′,2′′-terpyridine (II) with Cu 2+ and Fe 2+ , respectively. 2. Experimental Section Langmuir films and deposition experiments were carried out using a Nima Technology (Coventry, U.K.) trough (model 312DMC) with a surface area between 40 and 300 cm 2 . The surface pressure was measured by a Wilhelmy plate. Cyclic voltammetry was performed with a CH Instruments 750B potentiostat (Austin, TX) using a conventional three-electrode cell. Absorbance measurements were made by a UV3101PC spectrophotometer (Shimadu, Japan). Indium tin oxide (ITO, CG-60IN, 15-25 Ω) plates were obtained from Delta Technologies (Stillwater, MN) and used after rinsing with ethanol and water. 7-Tridecyl-4-methyl-1,10-phenanthroline (I) and 4′-hexadecyloxy-2,2′/6′,2′′-terpyridine (II), 4-heptadecylpy- ridine were synthesized by us as previously described. 16,17 Bis-1,- 10-phenanthrolinecopper(II) dinitrate, Cu(phen) 2 (NO 3 ) 2 and bis-2,2′/ 6′,2′′-terpyridineiron(II) dichloride, Fe(tpy) 2 Cl 2 were synthesized following the literature. 18,19 All aqueous solutions were prepared using deionized water (EasyPure UV, Barnstead). Glass plates were silanized using dichlorodimethylsilane following a conventional procedure. 20 Langmuir films of I, II, and a 1:1 (molar ratio) mixture of I and II were formed by spreading a chloroform solution (0.5 mg‚mL -1 of each ligand) at the water-air interface and letting the solvent evaporate for at least 10 min before compressing (25-75 cm 2 ‚min -1 ) the trough. The aqueous subphase contained 1 mM H 2 SO 4 (pH 3.0). After each compression, the trough was slowly expanded (the hysteresis in all experiments was negligible), and metal ions were injected into the subphase. A magnetic stirrer placed in the subphase was used to stir the solution prior to compressing the interface. The isotherms were recorded at 22 °C. Monolayer deposition was carried out under a constant surface pressure of 22 mN‚m -1 and 10 -5 M Cu 2+ or Fe 2+ in the subphase (Z and Y-type depositions, respectively) at 10 mm‚s -1 followed by carefully washing with water. Cyclic voltammetry (CV) was performed using an ITO electrode as the working electrode, a graphite rod as the counter electrode, and Ag/AgCl as the reference electrode. The solutions were deaerated * Corresponding author. E-mail: mandler@vms.huji.ac.il. (1) Roberts, G. G. Langmuir-Blodgett Films; Plenum Press: New York, 1990. (2) Petty, M. C. 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