Study on the Equilibria of the Complex Formation of the Ion-pair of Germanium(IV) with 4-Nitrocatechol and 1,4-Diphenyl-3-(phenylamino)-1H-1,2,4-triazole

The complex formation of the ion-pair formed between the anionic chelate of Ge(IV)–4-nitrocatechol (4-NC) and the cation of 1,4-diphenyl-3-(phenylamino)-1H-1,2,4-triazole (Nitron, Nt) in the liquid-liquid extraction system Ge(IV)–4NC–Nt–H2O–CHCl3 was studied by spectrophotometry. The optimum extraction-spectrophotometric conditions for the complex formation were established. The validity of Beer’s law was checked and some analytical characteristics of the system were calculated. The effect of co-existing ions and reagents on the process of complex formation was investigated. The association process in aqueous phase and the extraction equilibria were studied and quantitatively characterized. The following key constants of the processes were calculated: association constant, distribution constant, extraction constant and recovery factor. The molar ratio of the reagents was determined by independent methods. A reaction scheme and a general formula of the complex were suggested.


Introduction
The germanium and its compounds are widely used in various important areas of technology, science, and medicine.Germanium is present in all living plant and animal matter in micro-trace quantities and it is essential from a biochemical point of view.The germanium is relatively less toxic compared to many other metals.The accumulation of relatively high doses of germanium (milligram order of germanium per 1 g tissue) causes severe poisoning, including impairments in kidney, nerves, muscles.On the other hand, germanium deficiency can lead to seriously hematologic disorders and tumor formation.][3][4][5][6][7][8] The germanium is a third row post-transition metal and its chemistry has developed considerably in the recent years, indicated by the large number of publications in the scientific literature.Germanium(IV) forms complexes with various natural organic ligands containing O, N and S donor atoms such as polyphenols and their functional derivatives, polyhydroxycarboxylic acids, aminopolyhydroxycarboxylic acids, thiopolycarboxylic acids, 8hydroxyquinoline and its derivatives, aromatic derivates of hydroxyaldehydes and hydroxyketones, hydroxyazodyes.0][11][12][13][14][15][16][17] Germanium(IV) gives colored chelates with aromatic compounds, containing two or more hydroxyl groups in o-position relative to each other.The colored anionic chelates of Ge(IV) form ion-associated complexes with bulky organic cations, like tetradecyl(trihexyl)phosphonium, methyltrioctylammonium, tetrazolium, cetylpyridinium, cetyltrimethylammonium, tetraphenylammonium, tetraphenylarsonium. [18][19][20][21][22][23][24][25] Racheva et al.: Study on the Equilibria of the Complex Formation ...
) is an organic compound containing a quaternary nitrogen atom included in a five-membered ring. 26The structure and properties of the nitron determine its ability to form ion-associated complexes with anionic chelates of metals.The bulky hydrophobic organic substituents in the molecule of the nitron increase the extractability of the ionassociated complexes.][33][34] The liquid-liquid extraction is a part of the chemistry of the solutions and the coordination compounds.It is applied to study the processes of complex formation and the extraction equilibria.][37][38] The aim of this research was to study spectrophotometrically the extraction equilibria of the complex formation of the ion-pair formed between the anionic chelate of Ge(IV)-4-nitrocatechol (4-NC) and the cation of 1,4-diphenyl-3-(phenylamino)-1H-1,2,4-triazole (Nitron, Nt) in the liquid-liquid system Ge(IV)-4-NC-Nt-H 2 O-CHCl 3 as well as to evaluate the possible applications of the system for determination of traces of germanium(IV) in alloys, biological, medical and pharmaceutical samples.

Procedure for Establishment of the Optimum Extraction-Spectrophotometric Conditions
The required aliquots of the solutions of Ge(IV), 4-NC and buffer needed to adjust the pH of the aqueous phase were introduced into 250 cm 3 separatory funnels.The resulting solutions were diluted with distilled water to a total volume of 10 cm 3 .A required aliquot of a chloroform solution of Nitron was added and then the organic phase was brought up to 10 cm 3 with chloroform.The funnels were shaken for a defined time.A portion of the organic extract was filtered through a filter paper into a 1 cm cell and its absorbance was measured against a blank run in parallel.

3. Procedure for Determination of the Distribution Constant
The distribution constant (K D ) was determined from the ratio , where A 1 and A 3 are the absorbance (measured against blanks) obtained after a single and triple extraction, respectively.The single extraction and the first stage of the triple extraction were performed under the optimum conditions for complex formation (Table 1, column 1).The organic layers were transferred into 25 cm 3 calibrated flasks and the flask from the single extraction was brought to volume with chloroform.The second stage of the triple extraction was performed by adding 7 cm 3 of chloroform to the aqueous phase that remained after the first stage.After extraction, the obtained extract was added to this first stage of the triple extraction.The third stage of the triple extraction was performed in the same manner as for the second stage and the extract was added to those of the first two stages.The volume of the flask was brought to the mark with chloroform.The calibrated flasks were shaken before the spectrophotometric measurements. 30

1. Optimum Extraction-Spectrophotometric Conditions
The absorption spectrum of the extract of the studied ion-pair formed between the anionic chelate of Ge(IV) with 4-NC and nitronium cation in CHCl 3 was characterized by an absorption maximum in the visible range (λ max = 405 nm) (Figure 1).The influence of the acidity of the aqueous phase on the extraction of the anionic chelate Ge(IV)-4-NC into the organic phase in the form of an ion-pair with the nitronium cation was investigated.The maximum and constant extraction of the ion-associated complex is achieved in the pH range from 3.0 to 4.5.Acetate buffer solution with pH = 4.0 was used in all further experiments.The results showed that the extraction equilibrium is achieved for shaking time of not less than 60 s.A longer shaking time did not affect the absorbance.The experiments were performed for 2 min.The concentrations of the reagents are the most important factor inf-luencing the extraction equilibria.The chelate formation of Ge(IV)-4-NC requires 15.0-fold excess of 4-NC (C 4-NC ≥ 3.0 × 10 -4 mol L -1 ) and 5.1-fold excess of Nitron (C Nt ≥ 1.0 × 10 -4 mol L -1 ) for maximum association and extraction.The optimum experimental conditions for the extraction of the ion-associated complex are summarized in Table 1, column 1.

2. Beer's Law, Apparent Molar Absorptivity and Other Analytical Characteristics
The range of obedience to Beer's law, i.e. the linear relationship between the germanium(IV) concentration in the aqueous phase (C Ge(IV) , μg mL -1 ) and the absorbance of the ion-association complex in the organic phase after extraction was studied using regression analysis under the optimum conditions for complex formation.The equation of a straight line was found to be Y = 0.3807 X + 0.0483 with a correlation coefficient squared 0.9982.Under the optimum conditions for complex formation, the linearity is observed for concentrations up to 5.81 μg cm -3 Ge(IV).Further analytical characteristics, such as apparent molar absorptivity ε ', adherence to Beer's law, Sandell's sensitivity, limit of detection and limit of quantification, are shown in Table 1, column 2.

Effect of Co-existing Ions and Reagents on the Complex Formation
The effect of various co-existing ions and reagents on the process of complex formation of the ion-pair formed between the anionic chelate Ge(IV)-4-NC and nitronium cation was studied under optimum extraction conditions (Table 1, column 1).The concentration of Ge(IV) in the presence of the co-existing ions and reagents was determined from the sequence of Beer's law.A deviation of ±3% from the absorbance of the ion-associate in the absence of co-existing ions was accepted as an interfering effect.The results are presented in Table 2. From them, it can be concluded that most of the ions studied do not interfere, but some of them, like Br -, F -, I -, C 6 H 5 O 7 2-in concentrations lower than the indicated. 39Vanadium(V) can be co-precipitated with Fe(III) in alkali medium. 40

4. Molar Ratios of the Complex, Reaction Scheme and Suggested General Formula
The molar ratios of the complex were determined by three independent methods.The straight-line method of
Asmus and the mobile equilibrium method were applied to prove the molar ratios Ge(IV):4-NC and Ge(IV):Nt. 41he results from the application of these methods are shown in Figures 2÷4, respectively.On the basis of the results it can be concluded that Ge(IV), 4-NC and Nitron in-teract in molar ratio 1:3:2.The application of the method of continuous variations confirmed the molar ratio Ge(IV):Nt = 1:2 (Figure 5). 41 hed by the independent methods mentioned above was is Ge(IV):4-NC:Nt = 1:3:2.Therefore, the complex formation of anionic chelate Ge(IV)-4-NC can be given by equation ( 1): Having in mind the reaction of chelate formation of Ge(IV)-4-NC and molar ratio indicated above, it can be suggested that the formation of the ion-associate in the aqueous phase, its distribution between the aqueous and the organic phases and its extraction in chloroform can be given by the following equations (2-4).
Hence, the ion-pair formed between the anionic chelate of Ge(IV)-4-NC and the nitronium cation can be represented by the general formula (Nt) 2 {Ge[O 2 C 6 H 3 (NO 2 )] 3 }.

5. Extraction Equilibria, True Molar Absorptivity and Recovery Factor
The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized with respect to the following key constants: association constant, distribution constant, extraction constant and recovery factor.
The association constant β was determined by the method of Komar-Tolmachev from equation (5). 41 where l is the cuvette thickness (l = 1 cm); n is the molar ratio between the components independently determined (e.g. by the mobile equilibrium method, the straight-line method of Asmus or the method of continuous variations) (n = 2), ε is the true molar absorptivity.
The true molar absorptivity ε was determined by the method of Komar-Tolmachev (Figure 6) from the equation of a straight line Y = 2.1644 X + 3.2386 (ε = 1 / (b × 10 -5 ) and its value is given in Table 1, column 2. 41 The distribution constant (K D ) was determined by equation (6), where A 1 and A 3 are the absorbance (measured against blanks) obtained after a single and triple extraction, respectively.
The recovery factor was determined from the equation (7): The extraction constant K ex was calculated by two independent methods: where β was determined by the method of Komar-Tolmachev.
The values of the equilibrium constants and the recovery factor are presented in Table 3.The results obtained by independent methods are statistically dissimilar and confirm the proposed scheme of the process of complex formation of the ion-pair in the aqueous phase, its distribution between the aqueous and the organic phases and its extraction in chloroform.

Conclusion
The extraction equilibria for complex formation of the ion-pair formed between the anionic chelate of Ge(IV)-4-nitrocatechol (4-NC) and the cation of 1,4-diphenyl-3-(phenylamino)-1H-1,2,4-triazole (Nitron, Nt) was studied by spectrophotometry.The processes of the chelate formation and extraction of the ion-associated complex Ge(IV)-4-NC-Nt into chloroform were investigated.The optimum conditions for the association in aqueous phase and extraction of the ion-associated complex were established.The validity of Beer's law was checked and a linear relationship between the germanium(IV) concentration in the aqueous phase and the absorbance of the ion-association complex in the organic phase extraction was observed for concentrations up to 5.81 μg mL -1 Ge(IV).The presence of hydrophobic substituents, phenyl groups in the molecule of the triazole, increased the solu-  8), where β is determined by the Komar-Tolmachev method; e Calculated by Likussar-Boltz method (equation ( 9)); f Calculated by equation (7).
bility of the ion-associated complex in the organic solvent.The molar ratio of the components, determined by independent methods, shows that the ion-associated complex could be represented with the general formula (Nt) 2 {Ge[O 2 C 6 H 3 (NO 2 )] 3 }.A corresponding reaction scheme of the complex was also suggested.The equilibrium constants and analytical characteristics needed for the quantitative assessment of the extraction equilibrium were calculated, i.e. the association constant (β), the distribution constant (K D ), the extraction constant (K ex ), the recovery factor (R), the apparent molar absorptivity (ε'), the true molar absorptivity (ε), the limit of detection (LOD), the limit of quantification (LOQ) and the Sandell's sensitivity (SS).From the analytical characteristics of the extraction system Ge(IV)-4-NC-Nt-H 2 O-CHCl 3 , it can be concluded that the ion-pair formed between the anionic chelate of Ge(IV)-4-NC and the nitronium cation allows determinations of Ge(IV) with a high sensitivity.
complexone III in concentrations higher than the indicated ones, hinder the extraction of Ge(IV) as an associated complex with 4-NC and Nitron.The extraction equilibrium is hindered by Al(III), Cr(III), Cr(VI), Fe(III), Mo(VI), W(VI) and V(V).The interfering ions can be masked or removed from the extraction system to avoid this.Our investigations as well as the studies published in the literature show that the some of the co-existing ions, like Al(III), Cr(III) and Fe(III) can be removed by their preprecipitation with OH at pH = 11.The co-existing ions, like Mo(VI) and W(VI) can be masked with added L-ascorbic acid, Complexone III, C 6 H 5 O 7 2-or C 2 O 4

Table 2 .
Effect of co-existing ions and reagents on the complex formation of the ion-associate Ge(IV)-4-NC-Nt for extraction in the presence of 14 μg Ge(IV)