- About this Journal ·
- Aims and Scope ·
- Article Processing Charges ·
- Articles in Press ·
- Author Guidelines ·
- Bibliographic Information ·
- Citations to this Journal ·
- Contact Information ·
- Editorial Board ·
- Editorial Workflow ·
- Free eTOC Alerts ·
- Publication Ethics ·
- Reviewers Acknowledgment ·
- Submit a Manuscript ·
- Subscription Information ·
- Table of Contents
ISRN Analytical Chemistry
Volume 2012 (2012), Article ID 345684, 5 pages
Study of Metal-1,10-Phenanthroline Complex Equilibria by Potentiometric Measurements
Department of Chemistry, Faculty of Arts and Sciences, Uludağ University, 16059 Bursa, Turkey
Received 30 August 2012; Accepted 9 October 2012
Academic Editors: B. K. Jena and S. Sforza
Copyright © 2012 Naciye Türkel. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The interaction of Sc(III), Y(III), and La(III) ions with 1,10-phenanthroline (Phen) has been investigated, using the potentiometric method at 25 and M KNO3. Collected potentiometric data were processed by the “BEST” software program to establish the complexation model for each system. SPE software program was used to evaluate the concentration distributions of the species formed in solution. The stability constants for the binary complexes increased as the ionic radii of the metal cations decreased.
Scandium (Sc(III)) and Yttrium (Y(III)) are the transition elements that have been known for hundreds of years. Y(III) is generally present with rare-earth elements in the nature. Hence, the chemistry of Y(III) was developed in conjunction with the chemistry of rare-earths chemistry . The element above Y(III) on the periodical table is Sc(III). Like Y(III) and Lanthanum(La(III)), Sc(III) is also present as +3 state. Ionic radii of La(III), Y(III), and Sc(IIII) are 1.17 Å, 0.89 Å, and 0.83 Å, respectively. The thermodynamic stabilities of the various complexes of La(III), Y(III), and Sc(III) are inversely correlated to their ionic radii (e.g., increase in the thermodynamic stability results from the decreased ionic radii of these elements). The coordination compounds of Sc(III) has attracted increasing interest in recent years. Previous developments in the field of the coordination chemistry of Sc(III), Y(III), and La(III) have been reviewed [2, 3].
Previously, complexes formed between oxygen and nitrogen donating ligands and metal ions of Sc(III), Y(III), and La(III) have been investigated using potentiometric methods by several authors. The results of those previous studies suggested that Sc(III) ion forms the most stable complexes in binary ligand system in aqueous solution. The complexes of Sc(III), Y(III), and La(III) formed in different ionic mediums have been the most adequate complexes to identify the coordination number and the structure of these complexes [4–10].
1,10-Phenantroline (Phen) (Scheme 1) and its various derivatives are widely used ligands in the different fields of chemical industry . Heteroaromatic group on the Phen provides a binding site for different metal ions. Phen has a rigid structure and has two aromatic nitrogens which contains unshared electron pairs, that can bind metal ions [12, 13]. Due to its ¶-electron deficiency, Phen becomes an excellent ¶-electron acceptor. Certain derivatives of Phen contain amine groups. Due to this chemical feature, Phen is used as ligand for soft and hard sites. Most of the research on the Phen derivates focuses on their catalytic, redox, photoredox, biological activities, and their supramolecular chemistry [13–18]. Phen and its derivatives have very significant roles in the development of supramolecular chemistry [19–21]. In addition, due to their certain chemical features (e.g., luminescence emission, redox, stabilities, etc.), Phen and its derivatives play a significant function in the development of polypyridyl metal complexes of Ru(II) . Being luminescent compounds, Ru-Phen derivates are also important compounds for the analysis of certain biochemical and biophysical features of biological molecules such as DNA [23–27].
The purpose of this study is to gain further information on Phen’s ability to form ML and ML2 complexes with Sc(III), Y(III), and La(III), and to use potentiometric titration techniques to identify and characterize the structures of any binary complexes that were formed in the aqueous solution. The results on the stabilities and the structures of metal-Phen complexes analyzed in this study are presented in this article.
2. Experimental Section
The Phen (Merck, 99.5% purity) was used without further purification. Its purity and concentration was confirmed by titration 0.1 M NaOH. (Aldrich, 99.9% purity), (Sigma, 99.9% purity), and (Fluka, 99.9% purity) were standardized by EDTA titrations . To adjust the ionic strength of the metal cation solutions (Merck, 99% purity) was used. A NaOH (Merck, 97% purity) solution was prepared from concentrated stock solution (1 M NaOH) by dilution. All of the experiments were conducted with Grade a glassware and doubly distilled water.
2.2. Potentiometric Measurements
The potentiometric titration reactions were measured with a personal computer (PC) system, as described previously . The solutions were adjusted to an ionic strength of 0.1 M with KNO3 in a 100 mL jacketed glass cell equipped with a magnetic stirrer, and a water bath was used to control the temperature to °C. A slight positive pressure of purified nitrogen was maintained in the titration cell in order to exclude oxygen and carbon dioxide from the reaction solutions.
The combined electrode calibration, in terms of hydrogen ion concentration, was accomplished by adding a standardized solution of NaOH to a standardized solution of HCl (both solutions were adjusted to an ionic strength of 0.1 M). The values of and the response slopes from the potentiometric titrations were measured by fitting a straight line through the experimental points collected from pH 1.5 to 12. A value of 13.75 was determined in the present study.
The metal stability constants of Phen with Sc(III), Y(III), and La(III) were determined directly by potentiometric titrations. Uniform volumetric additions of standardized NaOH (titrant) were made to all systems, and the potential was recorded as a function of the added volume. The pH-potentiometric titrations were performed using constant amount of metal ion to variable amount of ligand concentration ([M]/[L], ratios) for all of the metal-Phen systems studied. For the Sc(III) : Phen system, the stability constants were quantified using [M]/[L] ratios of 1 : 1, 1 : 2, 1 : 3 and 1 : 10 and a metal concentration of 9.668 × 10−2 M. The experimental points were collected from pH 2 to 12. Complexation studies of the Y(III) : Phen and La(III) : Phen systems were performed using [M]/[L] ratios of 1 : 1 to 1 : 10 with metal concentrations of 1.04 × 10−1 M and 9.180 × 10−2 M, respectively. The experimental points were collected between pH ranges 2–8 (for Y(III) : Phen) and 2–8 (for La(III) : Phen). BEST software program was used to analyze the potentiometric data collected from the titrations studies, as described previously . The water and Phen acid dissociation constants, as well as all known stability constants were held constant during the refinement operations of the different metal-Phen systems studied (as defined for these equilibria.)
3. Results and Discussion
3.1. Acid Dissociation Constants of 1,10-Phenanthroline
The acid dissociation constants of Phen were determined potentiometrically in I = 0.1 M KNO3 ionic medium at 25°C. A titration curve of Phen, prepared in the absence of metal cations, is shown as curve I in Figure 1. Proton ionization sites of Phen are assigned to the two ring nitrogen atoms in Phen. Previously published data supported the corresponding acid dissociation constants presented in Table 1 . The results given in Table 1 can be described as in the following equations (1) and (2)
3.2. Stability Constants of Sc(III)-Phen Complexes
Titration of solutions containing 1 : 1, 1 : 2, 1 : 3, and 1 : 10 ratios of metal ion to ligand (Figure 1, curve II, III and IV) results in marked inflection point at m = 4.0 which corresponds to the formation of chelates that have the compositions of and , respectively. In the buffer region near the inflection point, four protons were titrated per metal ion. The following equations (3) and (4) can describe the equilibria involved in this region:
For the potentiometric titrations performed with various molar ratios, the presence of complexes such as , , , , , , , , which might occur in the ionic medium, were examined using the BEST  software. The software was also used to calculate the stability constants of the and for various metal/ligand molar ratios ranging from [M]/[L] of 1 : 1 to 1 : 10. However, the software calculations rejected all species except and . The probable structures of the corresponding , species in aqueous solution were proposed as follows. For the , species, Sc(III) ion coordinates with both N atoms in phenanthroline ring. The analyzed results showed that the stability constant values obtained for and were the same at all molar ratios. Sigma fit () was found to be lower than 0.02 in all of the stability constant calculations. Stability constants obtained in the present study for and are given in Table 1.
The distribution diagram, computed by the SPE  software for a solution containing 9.668 × 10−2 M Sc(III) and 1.934 × 10−1 M Phen, is shown in Figure 3. The free metal ion predominates only at acidic pH values, that is, below 3.9, whereas upon increasing the pH the sequential formation of , is observed. An analysis of the distribution diagram explains that at pH values close to 3.9 nearly 100% of the solution contains the species. is not formed at detectible amount up to pH 3.9.
3.3. Stability Constants of Y(III)-Phen Complexes
Potentiometric titrations of the Y(III) : Phen system were studied at various molar ratios ranging from 1 : 1 to 1 : 10 in I = 0.1 M ionic medium at 25°C. Addition of base to a solution containing equimolar amounts of Y(III) ion and ligand results in a pronounced inflection at m = 2.0 and m = 4.0 (Figure 2).
For the potentiometric titrations performed with various molar ratios, the BEST software was used to examine complexes such as , , , , , , , , and which might occur in the medium. The stability constants of the complex were also calculated with the BEST software for various metal/ligand molar ratios ranging from [M]/[L] of 1 : 1 to 1 : 10. However, the software calculations rejected all species except . The probable structure of the corresponding species in aqueous solution was proposed as follows. For the , species, Y(III) ion coordinates with both N atoms in phenanthroline ring of one of Phen. The analyzed results showed that the stability constant values obtained for species same at all molar ratios. The following equation (5) can describe the equilibria involved in this region:
For all of the stability constant calculations, sigma fit () was found to be lower than 0.04. The stability constants calculated for the Y(III) : Phen system at varying molar ratios and concentrations were given in Table 1.
Based on the distribution diagram, the speciation of the major metal-ligand species was determined within the defined pH ranges by the SPE software. As shown in Figure 4, the species is the primary species prevalent in an aqueous solution at pH 5.0. constitutes ~93% of the solution’s content. The major species is (Figure 4).
3.4. Stability Constants of La(III)-Phen Complexes
Potentiometric titrations of the La(III) : Phen system were studied at various molar ratios ranging from 1 : 1 to 1 : 10 in I = 0.1 M ionic medium at 25°C. The potentiometric titration curves of a 1 : 1 mole ratio of La(III) to Phen exhibit inflection points at m = 2.0, 4.0 and 5.0 (Figure 2).
For the potentiometric titrations done at various molar ratios, the BEST software was used to examine complexes such as , , , , , , , , and which might occur in the medium. The stability constants of the LaL+3 species were calculated with the BEST software for various metal/ligand molar ratios changing from 1 : 1 to 1 : 10. However, the software rejected all other species except . The probable structure of the corresponding species in aqueous solution was proposed as follows. For the , species, La(III) ion coordinates with both N atoms in phenanthroline ring of one of Phen. The following equation (6) can describe the equilibria involved in this region:
For all of the stability constant calculations, sigma fit () was found to be lower than 0.04. The stability constants calculated for the La(III) : Phen system at varying molar ratios and concentrations were given in Table 1.
Figure 5 displays the distribution diagram for the La(III) : Phen system as a function of pH by the SPE software. As shown in Figure 5, the species is major species found in an aqueous solution at pH 4.5. The species constitutes ~97% of the solution’s content.
In conclusion, the study of Sc(III), Y(III), and La(III)/Phen in aqueous solutions by potentiometric titrations gave the following results.(a)Two metal/ligand complexes , form at equilibrium and the relevant stability constants were determined(b) is the predominant metal species in a wide pH range (c)One metal/ligand complex forms at equilibrium and the relevant stability constants were determined(d)One metal/ligand complex forms at equilibrium and the relevant stability constants were determined(e)The order of stability is scandium(III) > yttrium(III) > lanthanum(III).This pattern demonstrates that complex stability decreases as the size of the cation increases.
- U. Özer, “Mixed ligand chelates of scandium(III) and yttrium(III) in aqueous solution,” Chimica Acta Turcica, vol. 13, pp. 253–270, 1985.
- G. A. Melson and R. W. Stotz, “The coordination chemistry of scandium,” Coordination Chemistry Reviews, vol. 7, no. 2, pp. 133–160, 1971.
- J. A. A. Mc Cleverty, Specialist Periodical Reports Inorganic Chemistry of Transition Elements, vol. 4, Library of Congress Catalog no.72-83458, The marketing officer, The Chemical Society Burlington House, London, UK, 1976.
- N. Türkel, “Stability of metal chelates of some hydroxamic acid ligands,” Journal of Chemical and Engineering Data, vol. 56, no. 5, pp. 2337–2342, 2011.
- N. Türkel, “Stability constants of lanthanide(III) chelates of 8-quinolinol-5-sulfonate,” Asian Journal of Chemistry, vol. 18, no. 3, pp. 1978–1986, 2006.
- N. Türkel and U. Özer, “Potentiometric investigations of some catechol derivatives of scandium,” Russian Journal of Coordination Chemistry/Koordinatsionnaya Khimiya, vol. 31, no. 3, pp. 213–217, 2005.
- N. Türkel and U. Özer, “Salicylic acid derivatives form stable complexes with scandium(Ill) ion in aqueous solution,” Chemical and Pharmaceutical Bulletin, vol. 48, no. 6, pp. 870–872, 2000.
- Z. M. Wang, H. K. Lin, S. R. Zhu, T. F. Liu, and Y. T. Chen, “Spectroscopy, cytotoxicity and DNA-binding of the lanthanum(III) complex of an L-valine derivative of 1,10-phenanthroline,” Journal of Inorganic Biochemistry, vol. 89, no. 1-2, pp. 97–106, 2002.
- K. Arora and K. Burman, “Lanthanide (III) metal complexes with nitrogen donor ligands—a review,” Reviews in Inorganic Chemistry, vol. 29, no. 2, pp. 83–101, 2009.
- R. N. Marques, C. B. Melios, N. C. S. Pereira et al., “Complexation of some trivalent lanthanides, scandium(III) and thorium(IV) by benzylidenepyruvates in aqueous solution,” Journal of Alloys and Compounds, vol. 249, no. 1, pp. 102–105, 1997.
- G. Wilkinson, R. D. Gillard, and J. A. M. Cleverty, Comprehensive Coordination Chemistry, vol. 2, Pergamon, Oxford, UK, 1987.
- C. Bazzicalupi, A. Bencini, V. Fusi, C. Giorgi, P. Paoletti, and B. Valtancoli, “Lead complexation by novel phenanthroline-containing macrocycles,” Journal of the Chemical Society—Dalton Transactions, no. 3, pp. 393–399, 1999.
- P. G. Sammes and G. Yahioglu, “1,10-Phenanthroline: a versatile ligand,” Chemical Society Reviews, vol. 23, no. 5, pp. 327–334, 1994.
- C. E. A. Palmer, D. R. McMillin, C. Kirmaier, and D. Holten, “Flash photolysis and quenching studies of copper(I) systems in the presence of Lewis bases: inorganic exciplexes?” Inorganic Chemistry, vol. 26, no. 19, pp. 3167–3170, 1987.
- S. Sakaki, G. Koga, and K. Ohkubo, “Successful photocatalytic reduction of MV2+ with [Cu(NN) (PPh3)2]+ (NN = 2,9-dimethyl-1,10-phenanthroline or 4,4′,6,6′-tetramethyl-2,2′-bipyridine) upon near-UV-light irradiation and a novel solvent effect on its catalytic activity,” Inorganic Chemistry, vol. 25, no. 14, pp. 2330–2333, 1986.
- D. M. Walba, Q. Y. Zheng, and K. Schilling, “Experimental studies on the hook and ladder approach to molecular knots: synthesis of a topologically chiral cyclized hook and ladder,” Journal of American Chemical Society, vol. 114, pp. 6259–6260, 1992.
- S. S. Zhu and T. M. Swager, “Conducting polymetallorotaxanes: metal ion mediated enhancements in conductivity and charge localization,” Journal of the American Chemical Society, vol. 119, no. 51, pp. 12568–12577, 1997.
- D. J. Cárdenas, P. Gaviña, and J. P. Sauvage, “Construction of interlocking and threaded rings using two different transition metals as a templating and connecting centers: catenanes and rotaxanes incorporating Ru(terpy)2-units in their framework,” Journal of the American Chemical Society, vol. 119, no. 11, pp. 2656–2664, 1997.
- R. Ziessel, A. Harriman, J. Suffert, M. T. Youinou, A. De Cian, and J. Fischer, “Copper(I) helicates containing bridging but nonchelating polypyridine fragments,” Angewandte Chemie, vol. 36, no. 22, pp. 2509–2511, 1997.
- C. O. Dietrich-Buchecker and J. P. Sauvage, “A Synthetic molecular trefoil knot,” Angewandte Chemie, vol. 28, pp. 189–192, 1989.
- F. Sallas, A. Marsura, V. Petot, I. Pintér, J. Kovács, and L. Jicsinszky, “Synthesis and study of new ß-Cyclodextrin ‘Dimers’having a metal coordination center and carboxamide or urea linkers,” Helvetica Chimica Acta, vol. 81, no. 4, pp. 632–645, 1998.
- A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, and A. von Zelewsky, “Ru(II) polypyridine complexes: photophysics, photochemistry, eletrochemistry, and chemiluminescence,” Coordination Chemistry Reviews, vol. 84, pp. 85–277, 1988.
- R. E. Holmlin, E. D. A. Stemp, and J. K. Barton, “Ru(phen)2dppz2+ luminescence: dependence on DNA sequences and groove-binding agents,” Inorganic Chemistry, vol. 37, no. 1, pp. 29–34, 1998.
- R. B. Nair, E. S. Teng, S. L. Kirkland, and C. J. Murphy, “Synthesis and DNA-binding properties of [Ru(NH3)4dppz]2+,” Inorganic Chemistry, vol. 37, pp. 139–141, 1998.
- W. Jian-Zhong, L. Li, T. X. Zeng et al., “Synthesis, characterization and luminiscent DNA-binding study of a series of ruthenium complexes containing 2-arylimidazo[f]1,10-phenanthroline,” Polyhedron, vol. 16, no. 1, pp. 103–107, 1997.
- C. Hiort, P. Lincoln, and B. Nordén, “DNA binding of Δ- and Λ-[Ru(phen)2DPPZ]2+,” Journal of the American Chemical Society, vol. 115, no. 9, pp. 3448–3454, 1993.
- G. Zhao, H. Sun, H. Lin, S. Zhu, X. Su, and Y. Chen, “Palladium(II) complexes with N,N'-dialkyl-1,10-phenanthroline-2,9- dimathanamine: synthesis, characterization and cytotoxic activity,” Journal of Inorganic Biochemistry, vol. 72, no. 3-4, pp. 173–177, 1998.
- G. Schwarzenbach and H. Flaschka, Complexometric Titrations, Interscience, New York, NY, USA, 1969.
- A. E. Martell and R. J. Motekaitis, Determination and Use of Stability Constants, VCH, New York, NY, USA, 1989.
- C. R. Krishnamoorthy, S. Sunil, and K. Ramalingam, “The effect of ligand donor atoms on ternary complex stability,” Polyhedron, vol. 4, no. 8, pp. 1451–1456, 1985.