Acta Chim. Slov. 2004, 51, 95-106. 95 Scientific Paper UV-VISIBLE AND IR SPECTROSCOPIC STUDIES OF RUTHENIUM(II)-XYLENOL ORANGE COMPLEX Olga Solovey-Vandersteen,a Teodoziya Vrublevska,a and Heinrich Lang Ivan branko Lviv National University, Kyryta & Mejodiya Str. o, /9UUj Lviv, U krame Cnemnitz, University oj lecnnology, Strape eter Nationen 62, U91U/ Cnemnitz, uermany Received 15-10-2003 Abstract The formation of a Run-xylenol orange (XO) complex has been investigated. The respeetive complex was formed within the pH range of 2.5 to 5.0 during 90 min of heating and has an absorbance maximum at 583 nm. The molar extinction coefficient is 28800 L mol"1 cm"1. The composition of the Run-XO complex was determined by the mole ratio and continuous variations methods. The strueture of Run-XO was proposed aceording to IR spectroseopic data. Key words: ruthenium, xylenol orange, complex, UV-VIS, IR spectroscopy, determination Introduction Xylenol orange (XO) can successfully be used for the determination of many transition metals, including noble metal ions, sueh as palladium(II), " rhodium(III), ' and ruthenium(III). ' We here report on UV-VIS and IR spectroseopic studies of a novel Ru -XO complex. Based on these studies, a straightfonvard method for the determination of ruthenium(II) ions in solution is developed and tested on synthetic and real samples. Experimental Reagents and Apparatus. Ali ruthenium(II) solutions were prepared by the reduetion of an aliquot of a ruthenium(III) chloride solution with hydroxylamine aceording to Ref 7 and 8. A ruthenium(III) stock solution was prepared by dissolving RuCl3×3H20 in 3 mol L" HC1. A standard working solution was prepared by taking an aliquot of the ruthenium(III) stock solution and diluting it with 1 mol L" HC1. O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroseopic Studies... 96 Acta Chim. Slov. 2004, 51, 95-106. Freshly prepared aqueous xylenol orange solutions (cxo~10~ mol L" ) from commercially available XO (content 90%, Aldrich Chemicals Inc.) were used. Freshly prepared 0.15 mol L" solutions of hydroxylamine were utilised. The ion strength of respective solutions was kept constant by using 0.1 mol L" NaCl solutions. UV-VIS measurements were performed with an UV-VIS spectrophotometer (Lambda 40, Perkin Elmer) using 1 cm cuvettes against reference solutions. Ali absorbance measurements were performed at ca. 20 °C. The IR spectroscopic measurements were performed with an FT-IR spectrometer (Spectrum 1000, Perkin Elmer). The pH measurements were carried out with a Schott CG model 840 glass electrode pH-meter. For pH-meter calibration purpose standard buffer solutions with pH = 4.00 and pH = 10.00 were applied. The pH value of each solution was adjusted by using diluted HC1 and NaOH solutions. Procedure of ruthenium(II) Determination. A sample of a solution containing (0.1-4.9)×l0" mol L" of Ru , Ru or Ru ions (or a mixture of ruthenium ions in different oxidation states) was placed in a 25 mL volumetric flask. To this solution 5 mL of 0.15 mol L" NH2OH, 2.5 mL of 2.5×10" mol L" XO and 2.5 mL of 0.1 mol L" NaCl were added. The pH was adjusted in the acceptable range of 2.7 to 4.0 and distilled water was added. The obtained solutions were boiled for 90 min at 100 °C. Then the absorbance at Xmax = 583 nm against the reference solution was measured. Results and discussion Ruthenium(II) solutions. The reduction of Ru or Ru to Ru could be performed by using a hydroxylamine solution as described in Ref 7 and 8. The reduction process lasts 7-10 min (Figure 1). The absorption spectra of the appropriate ruthenium(II) solutions correspond to the data of Ref. 9. O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... Acta Chim. Slov. 2004, 51, 95-106. 97 0,6 0,4 - 0,2 350 400 450 500 550 600 650 vvavelength, (nm) Figure 1. Absorption spectra of the RuIII - RuII reduction process, c(RuII) = 1.00×10-4 mol L-1, c(NH2OH) = 1.51×10-1 mol L-1, pH = 1.0: 1 – RuIII, tred = 0 min; 2 – RuII,III, tred = 5 min; 3 – RuII, tred = 7.5 min. Absorption Spectra. The absorption spectra of xylenol orange and the corresponding violet coloured Ru -XO complex are shown in Figure 2. While XO has a maximum absorption at 435 nm, at the same conditions the respective RuII-XO complex absorbs at 583 nm. The shift of the absorption maximum of the Ru -XO complex is 150 nm in comparison to the maximum of the XO solution. This shifting is typical upon complex formation of XO with transition metal ions . 0,3 0,2 0,1 450 500 550 vvavelength, (nm) Figure 2. Absorption spectra of xylenol orange and Run-XO complex, pH = 4.0, theat = 90 min, c(NH2OH) = 2.0×l0~2 mol L-1, I = 0.05. (1) absorption spectrum of XO, c(XO) = 1.02×l0~5 mol L-1, (2) absorption spectrum of Run-XO, c(Run) = 1.60×10"5 mol L-1, c(XO) = 1.02×l0"5 mol L"1. 0,8 - 0 0 350 400 600 650 O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... 98 Acta Chim. Slov. 2004, 51, 95-106. The Effect of pH. Between pH of 2.5 to 5.0 ruthenium(II) ions form a complex with XO (Figure 3). The best result and hence most stable complex formation is obtained by the optimal pH of 2.7 to 4.0. In this pH range a maximum and constant absorbance is obtained (Figure 3). Ali consequent investigations were carried out within the pH range of 2.7 to 4.0. 0,2 0,1 1 234 56 pH Figure 3. Influence of pH on absorbance of ruthenium(II)-xylenol orange complex, c(Run) = 1.60×l0"5 mol L"1, c(XO) = 1.02×l0"5 mol L"1, c(NH2OH) = 2.0×l0"2 mol L"1, theat = 90 min, I = 0.05, X = 583 nm. Influence of Hydroxylamine Concentration. The influence of the hydroxylamine concentration on the complex formation of ruthenium(II)-XO was studied (Figure 4). 0,3 0,2 - 0,1 - 10 12 14 c(NH2OH)-10~ mol L" Figure 4. Influence of hydroxylamine concentration on absorbance of ruthenium(II)-xylenol orange complex, c(Run) = 1.60×l0"5 mol L"1, c(XO) = 1.02×l0"5 mol L"1, pH = 3-4, theat = 90 min, X = 583 nm. 0 0 0 2 4 6 8 O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... Acta Chim. Slov. 2004, 51, 95-106. 99 The maximal absorbance of the ruthenium(II)-XO complex is obtained at the concentration of NH2OH 1.5×10" -3.5×10" mol L" ; that values correspond to 1000-2000 surplus of c(NH20H) to c(Ru ). Lower concentrations of hydroxylamine (Figure 4) are not sufficient to reduce ali Ru to Ru . However, at higher then optimal hydroxylamine concentrations, the maximal absorbance of the Ru -XO complex is not obtained because of increasing of ion strength. The optimal ion strength for Ru -XO complex formation is 1 = 0.04-0.08. Influence of Temperature. Heating of the solutions is necessary for Ru -XO complex formation, which can clearly be seen by the colour change from yellow to violet. Colour of the Ru -XO complex develops during 90 min of heating on a water bath at 100 °C. After the heating period (0 min to 150 min), the solutions were allowed to cool (to the temperature 18-22 °C), diluted to the mark with distilled water in a volumetric flask and mixed. The influence of heating tirne on Ru -XO complex formation is shown in the Figure 5. The obtained Ru -XO complex is stable at least for 72 h. 0,5 0,4 - 0,3 0,2 0,1 - 0 -*- 30 60 90 120 time of heating, (min) 150 180 Figure 5. Influence of heating time on Run-XO complex formation, c(Run) = 3.20×l0"5 mol L" c(XO) = 2.04×l0"5 mol L"1, c(NH2OH) = 2.0×l0"2 mol L"1, pH = 3-4,1 = 0.05, X = 583 nm, T = 100 °C. Effect of the Reagent Concentration. In order to study the effect of the xylenol orange concentration on the Ru -XO complex formation, a series of absorbances were measured at various concentrations of XO against reagent blanks of the same concentration (Figure 6). The absorbance of the 0 O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... 100 Acta Chim. Slov. 2004, 51, 95-106. ruthenium(II)-XO complex increases with increasing XO concentration (Figure 6). Higher XO concentrations then ratio c(XO) / c(Ru ) = 0.6-0.65 decrease the absorbance. 0,6 0,5 - 0,4 0,3 0,2 0,1 0,5 1,5 c(XO) / c(Run) Figure 6. Variation of the absorbance of Run-XO complex versus XO concentration, c(Run) = 3.20×l0"5 mol L"1 = constant, c(NH2OH) = 3.0×l0"2 mol L"1, pH = 2.7-4.0, theat = 90 min, I = 0.07, X = 583 nm. Composition of Complex. The composition of the respective Ru -XO complex was determined by the mole ratio and Job’s method of continuous variations (Figures 6 and 7). From Figures 6 and 7 it is evident that only one distinctive Ru -XO complex is formed. The molar ratio of xylenol orange to ruthenium(II) in this complex is 1 : 2. The formation of a homobinuclear ruthenium(II) complex with xylenol orange explains why only 0.6-0.65 ratio of XO to Ru is necessary. 0.4 0.3 0.2 - 0.1 0.2 0.4 0.6 X = c(XO) / [c(Ru) + c(XO)] 0.8 Figure 7. The continuous variations curve for ruthenium(II)-XO complex, pH = 2.7-4.0, c(NH2OH) = 3.0×10-2 mol L-1, theat = 90 min, I = 0.07, ? = 583 nm. 0 0 0 O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... Acta Chim. Slov. 2004, 51, 95-106. 101 0.438 0.46 0.439 0.51 0.436 0.57 0.441 0.63 0.366 0.49 0.390 0.74 0.376 0.68 Effect of the Order of Reagent Adding. The varying orders in which the reagents were added are presented in Table 1. Table 1. Influence of order of reagent adding on the absorption of Run-XO complex at 583 nm, c(Run) = 3.21><10"5 mol L"1, c(XO) = 2.05><10~5 mol L"1, c(NH2OH) = 2.0xl0~2 mol L"1, pH = 3-4, theat = 90 min, I = 0.05, n = 6, P= 0.95. N° Order of reagent adding AA583 RSD % 1 (Rusoi + XOsoi + NH2OHsoi + NaClsoi)PH<2 adjust pH = 3-4 2 (Rusoi + XOsoi + NH2OHsoi + NaClsoi)PH<2 wait 5 min, adjust pH = 3-4 3 (Rusoi + NH2OHsoi)ph<2 wait 5 min + XOsoi + NaClsoi adjust pH = 3-4 4 (Rusoi + NH2OHsoi)ph<2 adjust pH = 3-4 + XOsoi + NaClsoi, adjust pH = 3-4 5 (Rusoi + XOsoi)pH<2 adjust pH = 3-4 + NH2OHsoi + NaClsoi, adjust pH = 3-4 6 (Rusoi + NaClsoi)PH<2 adjust pH = 3-4 + XOsoi + NH2OHsoi, adjust pH = 3-4 7 (Rusoi adjust pH = 3-4) + XOsoi + NH2OHsoi + NaClsoi, adjust pH = 3-4 where Rim, XOsoi, NH2OHsoi and NaClsoi - aliquots of Ru, XO, NH2OH and NaCl solutions; AA585 - the difference of absorbances of complex and reference solutions. The tirne necessary to reduce Ru to Ru has no influence on the absorption of the ruthenium(II)-XO complex (entries 1 and 2, Table 1) at strong acidic pH in presence of XOsoi, NaClSoi. Order of adding aliquot of NaCl or XO at strong acidic pH conditions as described in the experiments 1 to 3 seems to have no influence on the absorption of the Ru -XO complex, as long as aliquot of NH2OH is mixed with aliquot of ruthenium(III) solution. These experiments return that pH condition (pH<2 or pH = 3-4) has no influence on the reduction process of Ru to Ru when only aliquot of NH2OH is mixed with aliquot of ruthenium(III) solution (entries 3 and 4). At pH of 3 to 4 the state of ruthenium ions in the solutions changes. As a result of this, the process of reduction of Ru to Ru becomes complicated in the presence of reagents XO or NaCl (entries 5 or 6), or their mixture (entry 7) and a lower absorption has been measured. Since by the method 1 (Table 1) a maximum of absorption of the Ru -XO complex was obtained, this way of adding the reagents was used in the consequent investigations. Influence of Interfering Ions. The determination of ruthenium in different samples is generally complicated due to the presence of other noble metals in the sample, which can interfere with the ruthenium determination by other spectrophotometric methods. " ' " The separation of O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... 102 Acta Chim. Slov. 2004, 51, 95-106. Pt, Pd, Ir, Rh and Os ions is necessary in this čase, which takes additional tirne for analysis. For this reason, the influence of other noble metals on the Ru -XO complex formation was studied as well (Table 2). Complex formation of palladium(II) ions with XO is observed in a strong acidic environment' and at pH 5.8-6.2. The results of our studies show that Pd ions do not interfere the Ru with XO determination until the ratio 1 : 1 at pH = 3-4 (Table 2). Rhodium(in) ions form a complex with XO within the pH range of 2.7 to 3.3. As results of our investigation show (Table 2), rhodium(III) ions do not interfere with the ruthenium(II) determination until the ratio 1 : 1 at pH = 3.5-4 which could be explained by lower stability of Rh -XO complex in comparison with Ru -XO. Iridium(IV) ions do not interfere with the ruthenium(II)-xylenol orange complex formation till ratio 1 : 5. Higher ratio of Ir decreases the absorbance of Ru -XO. Osmium(IV) and platinum(IV) ions obstruct the determination of Ru at the higher ratio then Ru : Os = 1 : 7 and Ru : Pt = 1 : 15. Table 2. Selectivity of complex formation of ruthenium(II) with XO at pH = 3-4. Ion Ru11: Ion Ion Ru11: Ion Pdn 1 : 1 Sr11 1 : 40 IrIV 1 : 5 F- 1 : 40 Ptiv 1 : 15 Br 1 : 200 OsIV 1 : 7 J- 1 : 60 Rhm 1 : 1 NO3" 1 : 20 AlIII (masking agent) 1 : 2 S042~ 1 : 50 Ca11 1 : 40 CO32" 1 : 35 Mg11 1 : 30 CH3COO" 1 : 5 Such ions as Ca +, Mg +, and Sr + form with XO complex at the pH = 10.5. ' The results of our studies show: these ions have no influence on Ru -XO complex until ratio 1 : 40, 1 : 30 and 1 : 40, respectively. The presence of fluoride ions do not interfere ruthenium(II)-XO complex formation till ratio Ru : F" = 1 : 40 (Table 2), the absorption of the corresponding complex decreases at higher surplus of F" ions. Aluminium ions clearly interfere with the Ru -XO complex formation, however, F" ions were used as masking agent for Al + in the ratio Ru + : Al + : F" = 1 : 2 : 40. Cations, such as Cd +, Ni +, Be +, Cu +, Zr +, Fe +, Zn +, Hg + prevent the formation of Ru -XO. Small amounts of Be + and Zr + could be masked by fluoride ions. O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... Acta Chim. Slov. 2004, 51, 95-106. 103 The acetic ions form weak complex with ruthenium ions ' and may be presented in the solutions of ruthenium(II)-xylenol orange complex until ratio 1 : 5. Oxalic, tartaric, citric acids and EDTA form complex with ruthenium ions. ' ' According to results of our investigation, oxalic, tartaric, citric ions and EDTA obstruct the formation of Ru -XO complex. Calibration Curve and Sensitivity. A linear dependence was obtained for following concentrations of ruthenium(II): (0.5-12)xl0" mol L" and (1.6-49.2)xl0" mol L" at concentrations of XO which correspond to the ratio Ru : XO = 1 : 0.5-0.65. The existence of two partially overlapping linear ranges is explained by necessity to increase the XO concentration for the second linear range. The molar absorptivity of the Ru -XO complex at 583 nm was determined to be 2.88(±0.05)×l0 L mol" cm" (RSD = 1.5 %). The limit of determination of ruthenium(II) with XO had been calculated according to Ref 19 and determined to be Cmin, k=io = 6.5(±0.6)x 10" mol L" , RSD = 7% (for the first linear range). The sensitivity of the reaction, as expressed by Sandell’s notation, is 7.0 ng/cm . IR-spectroscopic Studies. The Ru -XO complex described above could be isolated by evaporation of the solvent. IR-spectra were recorded for the sodium salt of xylenol orange (for comparison) and for the Ru -XO complex (Table 3). The absorption bands at 1632 and 1400 cm" correspond to the asymmetric and symmetric v(COO") frequencies of the appropriate pentasodium xylenol orange salt. The difference Av is indicative for a monodentate structure, " which corresponds to the structure of xylenol orange in Ref. 1. Table 3. Characteristic IR absorption bands for Na5XO and Run2-XO. Na5XO Run2-XO Assignment v [cm1] v [cm1] - 1874 C=0 1632 1570 (-COO)as 1400 1460 (-COO)s - 995 Ru - O - 554 Ru - N O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... 104 Acta Chim. Slov. 2004, 51, 95-106. The absorption band at 1874 cm" can be assigned to the v(C=0) frequency of the CeH2(0) moiety, whereas the absorptions at 1570 and 1460 cm" correspond to the asymmetric and symmetric v(COO") frequencies. " Also a vibration at 554 cm" is found, which corresponds to the formation of a donor N —> Ru bond. Based on these data, following structure for the Ru 2-XO complex can be proposed: HoO O \ / H20—Ru-*-/ \ H20 O. O OHo \ / N------>-Ru—OH2 / \ O OH2 The coordination number at the ruthenium(II) ions is six with three aqua ligands and a tripodal-bound N(CH2COO)2 moiety. This structural arrangement affords a octahedral surrounding at Ru . Application to samples A powerful method of ruthenium(II) determination with xylenol orange was developed. This method was tested on synthetic solutions in presence of different noble metal ions and on real samples (Tables 4 and 5). Table 4. The results of ruthenium determination in synthetic solutions in the presence of different noble metal ions, n = 5, P = 0.95. Ruadded 10-5 mol L-1 Rudet 10"5 mol L"1 x + Ax Ru : Rh Ru : Pd Ru : Pt 1 : 15 Ru : Ir 1 : 2 Ru : Os — RSD % 3.21 3.16 + 0.05 1 : 1 1.29 3.21 3.20 + 0.03 — 1 : 1 1 : 10 1 : 2 1 : 5 0.78 4.01 3.94 + 0.06 1 : 1 — 1 : 15 — — 1.35 4.01 4.09 + 0.08 — 1 : 1 — — 1 : 5 1.64 4.01 4.01 + 0.05 — 1 : 1 1 : 10 — — 1.05 4.82 4.88 + 0.07 1 : 1 — — 1 : 2 1 : 2 1.23 where Ax = t (P,/) x S x nj"' ,/= n - 1. The results for the samples (Table 5) obtained by the determination of ruthenium(II) with xylenol orange are in agreement with the values determined by using method of ruthenium determination with o-phenantroline (o-phen). O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... Acta Chim. Slov. 2004, 51, 95-106. 105 Table 5. The results of ruthenium determination in samples, n = 5, P = 0.95. OallipiC VVtheorRu ** practRu ^theorRu 1U ^practRu ^U II101 J_/ % % mol L o-phen XO (x + Ax) RSD % (NH4)2 [RuNOCIs] 29.3 29.7 2.01 K4[Ru20Clio] XH20 27.0 26.9 1.35 Yb2Pt2SnRu 10.6 10.7 1.64 2.03 2.04 + 0.05 2.16 1.32 1.33 + 0.04 2.20 1.61 1.59 + 0.04 2.01 where Ax = t (P, J) x S x rij"' ,/= n - 1. Conclusions 11 Optimal conditions for the formation of Ru -XO have been investigated. The structure of the complex was additionally confirmed by IR spectroscopic studies. A new method was developed, which allows determination of ruthenium(II) from solutions which contain ruthenium in different oxidation states, such as Ru , Ru and Ru . The proposed method is more sensitive then other spectrophotometric procedures for ruthenium determination (Cmin,Ru-xo = 6.5x10" mol L" , Cmin,Ru-o-phen = 5x10" mol L" , ' Cmin,Ru-chromeazurois = 4x10" mol L" , ) and is recommended for ruthenium determination in different samples. References 1. B. Budesinsky, Chelates Anah Chem. 1967, 1, 15-47. 2. M. Otomo, Buli. Chem. Soc. Japan 1963, 36, 889-892. 3. V. N. Tikhonov, Russian J. Coord. Chem. 1986, 18, 1122-1126; (B. H. Thxohob, Koopd. Xumu% 1986, 18, 1122-1126). 4. C. M. Smirnov, Analysis and technology of noble metals, Metallurgy, Moscow, 1971, 164-167; (Cmhphob C. M., AHajni3 h TexHOJiorna 6jiaropoflm>ix MeTajuiOB, MeTajuiypriM, M., 1971, 164-167). 5. M. Otomo, Bunseki Kagaku 1968, 17, 125-129. 6. S. C. Srivastava, A. K. Dey, Chim. Anal. Pariš, 1969, 51, 131-135. 7. T. Ya. Vrublevskaya, L. V. Vronskaya, Zav. Lab. 1995, 61, 4-5; (T. K Bpy6neBCicaa, JI. B. BpoHCKaa, 3ae. m6. 1995, 61, 4-5). 8. T. Ya. Vrublevskaya, G. S. MaFtseva, I. N. Doroshenko, Zav. Lab. 1991, 57, 9-10; (T. K Bpy6jieBCKaa, T. C. MajibueBa, H. H. ^opomeHKO, 3ae. JIa6. 1991, 57, 9-10). 9. E. E. Mercer, R. R. Buckley, Inorg. Chem. 1965, 4, 1692-1695. 10. E. A. Seddon, R. R. Seddon, The Chemistry of Ruthenium, Elsevier, Amsterdam, 1984, 1373. 11. P. Job, Annali cli Chimica Applicata 1928, 9, 113-203. 12. G. Roebisch, W. Hofmann, Z. Chem. 1979, 19, <\20-<\2\. 13. E. Zvyagintsev, The Chemistry of Ruthenium, Nauka, Moscow, 1965, 300; (3BarHHijeB E., Xhmhh pyTeHiw, Hayica, M., 1965, 300). 14. T. D. Avtokratova, Analytical Chemistry of Ruthenium, USSR, Moscow, 1962, 264; (T. J\. ABTOKpaTOBa, AHajiHTHHecKaa xhmjw pyTeHJw, H3a-bo AH CCCP, M., 1962, 264). 15. A. Majeed, R. N. Asma, N. Firdos, F. H. Našim, M. Athar, J. Chem. Soc. Pak, 1997, 19, 218-221. 16. T. M. Buslaeva, S. N. Red’kina, I. N. Kiseliova, O. V. Rudnitskaya, N. A. Ezerskaya, Russian J. Coord. Chem. 1995, 21, 42-46; (T. M. BycjiaeBa, C. H. PeflbKHHa, H. H. KncejieBa, O. B. PyAHHTIKaa, H. A. EsepcKaa, Koopd. Xumux 1995, 21, 42-46). O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies... 106 Acta Chim. Slov. 2004, 51, 95-106. 17. E. A. Bernhard, I. N. Marov, V. K. Belyaeva, Zhurnal Neorganicheskoi Khimii 1995, 40, 1510-1519; (3. A. BepHrapAT, H. H. MapoB, B. K. EejiaeBa, )Kypn. Heopzcm. Xumuu 1995, 40, 1510-1519). 18. K. Shimizu, Buli. Chem. Soc. Japan 1977, 11, 2921-2926. 19. M. I. Bulatov, I. P. Kalinkin, Practical Handbook of Photometric Methods of Analysis, Khimiya, Leningrad, 1986, 432; (M. H. ByjiaTOB, H. n. KajniHKHH, IIpaKTiraecKoe pyKOBOflCTBO no (JiOTOMeTpnHecKHM MeTO^aM aHajra3a, Xhmhh, JI., 1986, 432). 20. E. B. Sandell, O. Hiroshi, Photometric Determination of Trace of Metals, John Wiley, N.Y., 1978, 1085. 21. D. A. Edwards, R. Richards, J. Chem. Soc, Dalton Trans. 1975, 637-643. 22. E. Szlyk, I. Lakomska, A. Grodzicki, Thermochim. Acta 1993, 223, 207-212. 23. D. J. Darensbourg, M. W. Holtcamp, B. Khandefvval, J. H. Reibenspies, Inorg. Chem. 1994, 33, 531-537. 24. K. Nakanishi, Infrared Absorption Spectroscopy, San Francisco, Holden-Day, 1962, 245. 25. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B: Application in Coordination, organometallic, and Bioinorganic Chemistry, Fifth Edition, John Wiley, Inc., USA, 1997, 384. Povzetek Raziskovali smo nastanek “Run-xylenol orange” (XO) kompleksa. Ta se je tvoril pri pH 2,5 do 5,0 med 90 minutnim segrevanjem in ima absorbcijski vrh pri 583 nm. Molarni ekstinkcijski koeficient je 28800 L mol"1 cm"1. Sestava Run-XO kompleksa je bila določena na osnovi molskega razmerja in drugih metod. Struktura Run-XO je bila predpostavljena na osnovi IR spektroskopskih podatkov. O. Solovey-Vandersteen, T. Vrublevska, H. Lang: UV-Visible and IR Spectroscopic Studies...