Acta Chim. Slov. 2003, 50, 1-14. 1 POTENTIOMETRIC STUDY OF THE NEW SYNTHEZISED l-BENZYL-4- PIPERAZINEGLYOXIME AND l-METHYL-4-PIPERAZINEGLYOXIME AND THEIR DIVALENT METAL COMPLEXES Muzaffer Can,* Hayati Sari Gaziosmanpasa University, Art and Science Faculty, Chemistry Department, 60250, Tokat, Turkey e-mail: mcan@gop.edu.tr Mustafa Macit Ondokuzmayis University, Department of Chemistry, 55139 Samsun, Turkey Received 18-09-2002 Abstract The deprotonation constants of l-benzyl-4-piperazineglyoxime (BPGO) and l-methyl-4-piperazineglyoxime have been determined in 0.1 mol drn3 NaCl at 25 °C potentiometrically (Molspin). The pKa values have been found as 9.79, 7.04 and 3.19 for BPGO and 9.56, 7.62 and 3.01 for MPGO in acidic medium. Protonation order of nitrogen atoms in the ligands has been determined by theoretical calculation (Semi-empirical AM1 method). In various pH conditions, the different complexes, which are formulated as MHsLz, MH5L2, MH4L2, MH3L2, MH2L2, MHL2, ML2, MH.jLz and MH.2L2 have been formed by titration of the transition metal ions (Cu2+, Co2+, Ni2+ and Zn2+) and ligands mixtures with NaOH. The stabillity constants of each complex have been calculated by SUPERQUAD computer program and general mechanisms have been proposed with regard to the formation of these complexes (MH2nL2 and MH^Lz). Indroduction There has recently been a great deal of interest in coordination compounds containing vic-dioximes ligands. It is reported that vic-dioximes have three isomers, syn, anti, and amphi forms, depending on the position of -OH groups in molecule.1"5 The syn-isomer does not constitute complex with metals but anti- and amphi forms give two different colored complexes with the same metals.2"5 The transition metal complexes of anti-dioximes are essentially square-planar structures with the four nitrogen atoms of two vic-dioxime molecules coordinating to the metal ion.1'6 The stable complexes prepared with vic-dioxime ligands have been used extensively for different purposes such as analytical and medicinal chemistry, pigments and biochemistry. Schrauzer7 has found that this kind of complexes exhibits semiconductor property. Aydogdu et al M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... 2 Acta Chim. Slov. 2003, 50, 1-14. have also synthesized new Ni-glyoxime complexes and found that these complexes have inorganic semiconductor behaviors.8 In the literature, the numerous vic-dioximes and their transition metal complexes have been investigated for a long period of tirne.1'2'9'10 However, potentiometric and spectrophotometric characterizations of their protonation and stability constants have not been investigated so far. Thus, the purpose of this work is to investigate the deprotonation constants of 1-benzyl-4-piperazineglyoxime and l-methyl-4-piperazineglyoxime and the stability constants of their complexes with Cu2+, Ni2+, Co2+ and Zn2+ potentiometrically. Results and discussion Protonation Constants The structures of the ligands investigated have been shown in Scheme la and b. <{ y—CH 2—N N -C =N—OH H3C-N N -C = N -OH ^-----' ^-------' H-c=N—OH \-------' HC = N -O H 46 4 6 3 b Scheme 1 The potentiometric titration curves of the ligands, BPGO and MPGO, have been shown in Figurel. As seen in Figure 1, there are two sharp end points for BPGO. In the MPGO (Figure 1), although the first end point is sharp, the second end point is not. The deprotonation constants calculated by SUPEROUAD for the ligands have been given in Table 1. As can be seen in this Table, three pKa values for each ligand have been calculated. The pKa values of the ligands are similar to each other, because their Chemical structures consist of the same groups except for benzyl and methyl groups. As known, if the difference between two pKa values is higher, the end points of the titration curves are sharper. When pK2a and pK3a are compared for each ligand, it is seen that there are differences between two pKa (ApKa) values, which are 2.75 log unit for BPGO and 1.94 log unit for MPGO. Since this difference in the MPGO is lower than that of BPGO, the second end point belonging to MPGO is not sharp. The difference between pKa2 and pKal values of MPGO and BPGO are 4.61 log unit and 3.85 log unit respectively. Thus, the first end point for MPGO is sharper than it is for BPGO. M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... Acta Chim. Slov. 2003, 50, 1-14. 3 10- pH ml NaOH Figure 1: Potentiometric titration curves for BPGO and MPGO. Table 1. Deprotonation constants of MPGO and BPGO studied at 25 °C in aqueous NaCl (/ = 0.100 mol dm"3). Ligands MPGO BPGO Species log ß pKa LH3 20.191 ±0.032 3.007 LH2 17.184 ±0.025 7.620 LH 9.564 ±0.017 9.564 LH3 20.012 ±0.012 3.187 LH2 16.825 ±0.008 7.035 LH 9.790 ±0.006 9.790 The species distribution curves of BPGO and MPGO have been shown in Figures 2a and 2b. As can be seen from the species distribution diagram, three groups on each ligand protonate at pH 2, and their three-protonated form is LH3. When pH is increased, the ligands lose gradually the protons and convert to the other various forms, LH2, LH and L. The formation of free ligand (L) starts at pH 7.80 and reaches maximum concentration at pH 10.5 (95%). The formation rates of all other species (LH3 at pH 2, LH2 at pH 5 and LH at pH 8) are quite high (above 80%). There are four nitrogen and two hydroxyl groups in the BPGO and MPGO as seen in Scheme 1. The pKa value belonging to hydroxide group (=N-O-H) has been obtained as 2.81 by only Akay et al.11 However, in some studies,12"14 there are no 8 6 4 0 2 4 6 M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... 4 Acta Chim. Slov. 2003, 50, 1-14. definitions about pKa value for hydroxide groups of glyoximes. The pKa values calculated in this work are 3.19, 7.04 and 9.79 for BPGO and 3.01, 7.62 and 9.56 for ^—-~~~. \ \LH3 / \/ LH2 1 \/ X l A / v A / V. X=~=Lr' _^—~* "-—^^_ / ""^4 ^ X ; \ / \ r L/ w Y \/ :v /\ LH/ \ / /\ /\ . I\ / V V \ ^_ _-~- 2 4 6 8 10 2 4 6 8 10 pH pH a) b) Figure 2: Distribution curves of BPGO (a) and MPGO (b) Species MPGO and in acidic media. Ali these values defined as macro dissociation constants probably belong to nitrogen atoms in the ligands. In this čase, three nitrogen atoms in each ligand can be protonated, but one nitrogen and hydroxyl groups can not. So, three equilibrium equations can be written for deprotonation of nitrogen atoms in the ligands. (LHn and n= 3). The deprotonation equilibrium is as seen in the following equations (Ligand charges are omitted for clarity). LHn ^=^ LHn.! + H+ and the deprotonation constants (Kn n=l,2 and 3) are given as [LHnl][ H + ] Kn = iiij- Theoretical Calculation The determination of the protonation order of BPGO and MPGO are not possible with experimental methods such as NMR, IR, and UV. So, in this study, theoretical calculations have been made in order to examine the structure of the species and to determine protonation order of nitrogen atoms in the ligands. The formation heats (Hf) and the total energies (TE) of the ligands and mono-protonated species were calculated by Semi-Empirical AM1 method. In addition, the proton affinity of each nitrogen atom M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... Acta Chim. Slov. 2003, 50, 1-14. 5 (PA) in the ligands was found using formation heats in the following equation and given in Table 2. PA= 367.2 +AHf°(B) - AHf°(BH+) Where, PA is the proton affmity of B types; AHf°(B) is the formation heat of B molecule; AHf°(BH+) is the formation heat of BH+ molecule, and 367.2 is the formation heat of H+ 15. Table 2. The Calculated Hf, TE and PA Values with AM1 Method for BPGO and MPGO and Their Monoprotonated Forms. a) H f TE PA BPGO 51.25 -77879.61 - 1 N-H+ 197.57 -78048.01 220.88 2 N-H+ 206.57 -78039.20 211.88 3 N-H+ 199.35 -78046.41 219.10 4 N-H+ 221.57 -78024.20 196.89 5 0H2+ 236.81 -78008.96 181.65 6 0H2+ 251.46 -77994.30 166.99 b) MPGO 23.23 -58905.84 - 1 N-H+ 174.38 -59069.60 216.05 2 N-H+ 178.65 -59065.33 211.78 3 N-H+ 172.20 -59071.77 218.22 4 N-H+ 194.03 -59049.95 196.40 5 0H2+ 208.88 -59035.10 181.95 6 0H2+ 222.73 -59021.25 167.70 Proton affinity gives information about protonation order. Since the nitrogen atom having the highest PA is 1N in BPGO, it has more basic characters than the others. Thus, the first protonated nitrogen is 1N in this ligand. According to the calculated results (TE, Hf and PA), protonation orders of nitrogen atoms in the BPGO are 1N, 3N and 2N. Whereas, the first protonated nitrogen is 3N as seen in the calculated values for MPGO. The reason for fact that the first protonated nitrogen 1N in the BPGO and 3N in the MPGO is that the inductive effect of benzyl group is higher than that of methyl group. That is, though BPGO and MPGO have similar protonation trends in the pH range investigated, 1N atom in BPGO shows more basicity property than 1N atom in the MPGO, because benzyl group increases the electron density on 1N atom by inductive effect. Thus, as a difference from BPGO, the protonation orders of nitrogen atoms in the MPGO are 3N, 1N and 2N, according to the calculated PA. Since the most acidic nitrogen atoms in both ligands are 4N atoms in terms of PA, their protonations are not M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... 6 Acta Chim. Slov. 2003, 50, 1-14. performed. The TE and Hf values also confirm that protonation arrangement is 1, 3, 2 for BPGO and 3,1 and 2 for MPGO. In conclusion, according to the data obtained from theoretical calculation, 9.79 (pKas), 7.04 (pKa2), and 3.19 (pKai) values belong to IN, 3N and 2N in BPGO and 9.56 (pKas), 7.62 (pKa2), and 3.01 (pKal) values belong to 3N, IN and 2N in MPGO respectively (Table 2). For piperazine rings in the BPGO, the calculated pKa values for IN is approximately similar to the literature values. Frenna et al16 have found pKa values of -NI in piperazine as 9.85 and the pKa of IN value found by Astrom17 is 10.00. The pKa value belonging to 2N in the piperazine is different from in the literature values. In this work, the calculated pKa values for 2N in the piperazine ring are 3.18 for BPGO and 3.00 for MPGO. These values are more acidic than literature values16'17 because of the first performing protonation of IN (in BPGO) and 3N (in MPGO) atoms, and repulsion of two positive charges on each ligand occurring as a results of protonation of IN and 2N atoms in BPGO and 3N and 2N atoms in MPGO. Stability Constants of Metal Complexes To determine the stoichiometry and stability constants of complex, which take plače between the ligand and various metal ions (Zn, Ni, Co and Cu), the solutions including metal ions, the ligands (1:2 ratio) and certain amount acid have been titrated with standard NaOH solution. The titration curves obtained from these titrations have been given in Figure 3. As seen in Figure 3, there are two end points in ali titration curves, but their end points are different from each other because of the various degree of hydrolysis of the metal ions. The change in the end point is proportional with the hydrolysis degree. This čase has been seen in the solution including various concentrations of Cu ion clearly.18 By increasing the hydrolysis degree, the end point shifts to right. It was observed that the interactions of the ligand with metals ions (at 2:1 ratios) lead to mainly one kind of complexation (See Scheme 2). Ni-BPGO (pink), Ni-MPGO (pink), Cu-BPGO (brown), Co-BPGO (brown) insoluble complexes have been obtained in alkali media (over pH 10). Since the others complexes are soluble, their insoluble complexes have not been obtained but, the titration solutions were collared. Since crystallization of these complexes could not be performed, their structures have not been M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... Acta Chim. Slov. 2003, 50, 1-14. 7 determined by X-Ray studies. But, the UV-Vis spectra of Ni-BPGO and Ni-MPGO solutions have been obtained and given in Figure 4. ^as^^'"^ f/f/ y\1 /c" fj //^^^- M ______—-** a b Figure 3: Titration Curves for M-BPGO (a) and M-MPGO (b) As seen in Figure 4, although there are no absorption bands in the spectra of ligands and Ni ions, there are some broad absorption bands belonging to soluble Ni-BPGO and Ni-MPGO complexes at 370, 470 and 535 nm. Also, the same broad bands have been observed in the UV-spectra of the other metal-ligand complexes. VA 2 1 . M PGO \ 2. BPGO 3. Ni-B PGO \ \ 4. Ni-M PGO \K 5 . N i \ W avelength[nm ] Figure 4: The UV-spectra registered for the M-MPGO and MPGO In the literature, there are similar studies with regard to the synthesis of transition metal ion- glyoxime complexes. Dincer et al9 have synthesized a complex on form of ML2 between Ni and bis-N-2,6-dimethylphenyl-amino-glyoxime, and its structure has been characterized by X-Ray method. Aydogdu et al. and Özcan et al. have also synthesized some new complexes between Ni(II) and proposed vic-dioximes at the u u 0 2 4 6 81 m l N aOH mL NaOH Abs L- 200 400 600 B00 M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... 8 Acta Chim. Slov. 2003, 50, 1-14. same structures.8'19 Ali ligands investigated by researchers consist of the same group except for benzyl and methyl groups. Therefore, the possible structure of M-BPGO and M-MPGO are as below (Scheme 2). Hydrogen bonds form between hydroxyl groups of the ligands as proposed in the literature. /Q...ft...Q X~N N—C =IK _,N =C—N C =N- :m < H Vx X = Ph-CH2-, CH3 K>- ¦ H-cr •N =C H Scheme 2 The data obtained from Ni2+-BPGO and MPGO titrations have been evaluated using SUPERQUAD program and the species distribution curves obtained from calculations have been given in Figure 5. The ligands and the metal ions form various complexes formulated as MH5L2, MH4L2, MH3L2, MH2L2, MHL2 and MH-1L2, depending on pH. It has also been observed that the similar complexes form between Cu2+, Co2+ and Zn2+ ions and the ligands. A Ni2* 2 NlH.L, n 5l 2 3 NlH.L, 4 NlHJ , 5 NlH,L, 6 7 NlL2 8 NlH ,L7 9 NlH^Lj L2 \/8 4 6 8 10 2 4 6 8 10 a b Figure 5: Species Distribution Curves for Ni-BPGO (a) and MPGO (b) systems At the pH < 2, LH3 specie occurs. With the formation of LH2 at above pH 2, complexes in the various forms (1-9 in Figure 5) start to form. The formation of intermediate complexes such as MH5L2, MH3L2 and MHL2 (or LHnMLHn.i type complex) has also been observed because titrant volume added in these titrations is very H H uu 100 30 HO 30 dO 40 40 5/ m m 3 /\ \ P H M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... Acta Chim. Slov. 2003, 50, 1-14. 9 little (0.04 mL). If the species distribution curves in Figure 5 are examined, it has been seen that the complexes such as MH2nL2, MH2n.iL2 and MH.2L2 occur and in addition, free Ni(II) ions exist in the titration solution until pH 8. Theoretical calculations have shown that protonation of 3N atom in MPGO firstly performs. With deprotonation of 3N at pH 7, NiL2 complex starts to form and after pH 7, ali Ni ions coordinate on side of 3N and 4N atoms of the ligands. At between pH 2-8 in the titration solution, since there are only protonated ligands (1NH+, 3NH+ and 2NH+) and water molecules, metal atoms are coordinated from two ligands on 4N atoms and n mol water molecules or two ligands and hydroxyl groups belonging to ligands and MH5(L2)(n.H20) or MH5L2 complexes can occur. After pH 8, hydroxide groups added as titrant or forming by hydrolysis of metal ions bound to metal ions instead of water molecule and so, M(OH)2L2 (or MH.2L2) specie complex forms, as seen in Figure 5. For Ni(II)-BPGO and MPGO systems, the first interaction appeared at pH 2-6, and the complexes initially formed in considerable concentration are five protonated mononuclear chelates (NiH5L2). The calculated concentrations are around 80% at the same pH range. These species ratios are similar for both ligands. Other stable complex of Ni(II) ions is NiFLI^ (95% for BPGO and 85% for MPGO) at pH 2-8. At pH 5-8, the formation rate of NiH3L2 is 30% for Ni-BPGO, 60% for Ni-MPGO system. By the increasing of pH, the other species, NiH2L2, NiHL2 and NiL2, form. Intermediate complex (NiHL2) is at the lowest level (5%) among them. This specie is 20% for MPGO. As the pH is increased above 7, the unprotonated mononuclear species [ML2] starts to form, then becomes the predominant species in the solution. This čase can be explained with deprotonation of ali amino and imino groups of the ligands. For the Cu(II)-BPGO and MPGO systems, CuHL2 and CuL2 exist as major compenents in solution. At pH 8, this chelats reach maximum level (95%), then above pH 8 hydroxide group is bound to the metal ions and species of Cu(OH)L2 and Cu(OH)2L2 form. Mathematical analysis of the titration points reveals that the CuH2L2, CuH3L2 and CuH4L2 form at the same tirne and are found to be in considerable amount. The formation of protonated mononuclear complexes undergoes simple deprotonation reactions at high pH. M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... 10 Acta Chim. Slov. 2003, 50, 1-14. For the Co-Ligand system, the pentaprotonated mononuclear cobalt complex is CoH5L2 between pH 2 and 5 and reaches its highest percentage (75%) at pH 2. The main complex formed is CoH4L2 at pH 2-7 and it reaches 90% at pH 5. The other species are the same as the Cu-Ligand systems. The predominant species is tetraprotonated complexes, CoH4L2. The maximum rates of Co-BPGO system for CoH2L2, CoHL2 and CoL2 are 40%, 42% and 30% respectively between pH 4 and 9. After pH 7, the hydroxide complexes form and which are also similar to Co-MPGO system. Finally, in the Zn(II) system, the main complex forms in the type of ZnH5L2 and it reaches 95% at pH 5 and fmishes at pH 7.5. From pH 5 to 10, the other species (ZnH4L2, ZnH3L2, ZnH2L2, ZnHL2, and fully protanated ZnL2 chelate) form in the lower concentrations. Their formation percentages change from 10% (ZnH2L2) to 70%. After pH 8, as seen in the titration curve (Figure 3) for this system, Zn (II) ions start to hydrolyse and form only hydroxide complexes with hyroxide ions. Both distrubitions curves are similar to each other. Obtaining the protonation constants for BPGO and MPGO using SUPERQUAD, overall stability constants have been calculated at the same way and the logjB values obtained from these calculations for ali metal ions-ligand complexes have been given in Table 3. The stability contstants of the mononuclear complexes for M(II)-MPGO system decrease in the order Zn(II)(log KZ„L2 = 20.82)>Cu(II)>Co(II)>Ni(II) and for M(II)-BPGO system in the order Co(II)>Ni(II) >Cu(II)>Zn(II). The reason for the orders being different is that the inductive effect between benzyl and methyl groups is different as reported above. A comparison of stability constants of the Ni(II) complexes with these two ligands (log /5[ML2]), log /5[Ni-(BPGO)2]=23.22 log /5[Ni-(MPGO)2]=17.88) indicates that the imino groups (=N-OH) in the ligand plays an important factor on the stability of mononuclear complex formation. Benzyl group in BPGO causes the imino groups to gain more basic property. So, a more stable complex forms between Ni and BPGO above pH 7. M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... Acta Chim. Slov. 2003, 50, 1-14. 11 Table 3. Stability constant data for the complexation of Cu2+ Ni2+ Co2+ and Zn2+ with MPGO and BPGO at 25 °C in aqueous NaCl (/ = 0.100 mol dm"3) /3pqr = [MpLqHr]/[M]p[L]q[H]r pqr* Ni(II) Cu(II) Co(II) Zn(II) M(II)-MPGO complexes 102 17.884 +0.014 18.279 ±0.016 18.034 ±0.006 20.823±0.027 112 25.334 +0.043 25.616 ±0.009 25.811 ±0.043 28.794 ±0.070 122 33.198+0.012 32.458 ±0.006 33.488 ±0.036 36.832 ±0.110 132 40.361 ±0.027 38.231 ±0.011 40.512 ±0.081 45.540±0.019 142 46.372 ±0.027 43.808±0.012 46.390 ±0.100 52.997±0.012 152 49.687 ±0.013 - 9.508 ±0.121 59.009±0.017 162 - - - 62.156±0.031 1-12 8.946 ±0.015 8.954 ±0.027 9.286 ±0.064 11.375±0.035 1-22 -1.025±0.022 -1.638 ±0.034 -0.423 ±0.151 1.916±0.033 M(II)-BPGO complexes 102 23.218±0.014 20.885±0.046 23.716±0.014 20.757±0.019 112 29.839±0.025 30.545±0.033 31.032±0.017 28.907±0.056 122 38.219±0.025 37.237±0.025 38417±0.021 36.781±0.079 132 44.707±0.022 43.552±0.034 45.147±0.022 45.266±0.031 142 51423±0.030 49.151±0.030 51453±0.018 52.350±0.027 152 55.154±0.05 54.864±0.023 55.242±0.041 58.736±0.034 162 57.895±0.076 58.600±0.021 58.691±0.035 - 1-12 13.955±0.013 9.590±0.030 14401±0.024 11.163+0.038 *(p:number of metal, q: number of hydrogen (positive values) or hydroxide(negative values), r. number of ligand in the complex. Conclusions The deprotonation constant (pKa) values determined are 9.79 (pKa3), 7.04 (pKa2) and 3.19 (pKal) for BPGO and 9.56 (pK^), 7.62 (pKa2) and 3.01 (pKal) for MPGO in acidic medium. When the solution including the ligand and Ni2+, Cu2+' Co2+ and Zn2+ at 2:1 ratio are titrated with the alkali, various complexes (MH6L2-MH.2L2) occur. It has been seen that the first protonations of IN atom in the BPGO and 3N atom in the MPGO occur. The reason for this difference was explained as the presence of different inductive effect between benzyl and methyl groups. This effect can also have an effect in the order of stability constants. The general mechanisms given below have been proposed with regard to the formation of complexes (MH2nL2 and MH2n.!L2); for the formations of MH6L2, MH4L2 and MH2L2 complexes, LHn+1 + OH- ^^ LHn + H20 2 LHn + M ^^ MH2nL2 M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... 12 Acta Chim. Slov. 2003, 50, 1-14. and for the formation of intermediate complexes (MH5L2, MH3L2 and MHL2), LHn + LHn.i + M ^ > MH2n.iL2 n=0,1,2,3 Experimental l-Benzyl-4-piperazineglyoxime (BPGO) and l-Methyl-4-piperazineglyoxime (MPGO) have been synthesized according to the literature9 and their stock solutions (2.00xl0"3 mol dm"3) used in the titrations have been prepared. The purities and the exact concentrations of stock solutions of the ligands and titrant have pH-metrically been confirmed using the Gran method.20 Solutions of metals ions (0.001 mol dm"3) have been prepared from CuCl2, ZnCl2, NiCl2.6H20 and CoCl2.6H20 (Fluka) as recieved. Potassium hydrogen phthalate (KHP) has been prepared from Fluka reagent as buffer solution (0.05 molal) and used for the calibration of the combination pH electrode according to the method of MOLSPIN21. Carbonate-free standard NaOH solution (ca. 0.025 mol dm"3) has been used as titrant. HC1 stock solutions used for obtaining pH 3.0 have been prepared from concentrated HC1 (Merck) and its concentration has been determined by pH-metric titrations. The pH-metric and spectrophotometric measurements have been carried out at an ionic strength of 0.100 mol dm"3 (NaCl). The pH has been measured with MOLSPIN automatic titration system,21 which interfaces to a PC, with a 10 cm3 syringe, a SenTix 20 pH combination electrode (WTW, Weilheim). Ali titrations have been carried out between pH 3.0-11.0 and under nitrogen atmosphere. The ligands concentrations have varied in the range 1.00 x 10"4 - 2.00 x 10"4 mol dm"3. The pH-metric data have been used to find the stoichiometry, deprotonation and stability constants using the SUPEROUAD computer program.22 The standart deviations (o values) computed by SUPEROUAD refer to random errors. A JASCO V-530 UV/VIS spectrophotometer has been used to record the spectra in the region 200-800 nm. In the UV studies, the concentrations of the ligands and metal ions were 2.00 x 10"4 and 1.00 x 10"4 mol dm"3 respectively. The theoretical calculations have been performed by Semi-empirical (AM1) method.23"25 This method is used to study some complex structures such as polymers26 M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... Acta Chim. Slov. 2003, 50, 1-14. 13 and similar study.27 Total energy and heats of formation have been calculated and the protonation order in the ligands was determined according to the results. Summary of experimental parameters used in this work have been given in Table 4. Table 4. Summarv of the experimental parameters for the potentiometric stability constants measurements. System : MPGO or BPGO with H+ Cu2+, Ni2+, Co2+ and Zn2+ in water Solution composition : [L] range/mol dm"3 0.001-0.002 [M] range/mol dm"3 0.001 ionic strength/mol dm"3 0.1 electrolvte NaCl Experimental Method : pH-metric titration in range pH 3-11 log /Vi -13.78 T/°C : 25.0 ntota : 250 3 SUPERQUAD MOLSPIN ntItb Method of calculation Titration svstem a Number of titration points per titration b Number of titrations per metal ligand system M: Metal ion, L: ligand, ß: overall stability constant Acknowledgements The authors wish to thank Riza Abbasoglu (from Karadeniz Technical University, in TURKEY) for providing Hyperchem package program and to Prof. Arthur K. Covington (from Newcastle University, in the UK) for using Molspin Titration System and SUPERQUAD. References and Notes 1. S. B. Pedersen and E. Larsen, Acta Chem. Scand. 1973, 27, 3231. 2. A. Chakravorty, Coord. Chem. 1974, 13, 1. 3. A. Nakamura, A. Konishi and S. Otsuka, J. Chem. Soc. Dalton Trans. 1979, 488. 4. Ö. Bekaroglu, S. Sanbasan, A. R. Koray, B. Nuber, K. Weidenhammer, J. Welss and M. L. Ziegler, Acta. Cryst. 1978, 34, 3591. 5. S. Sanbasan, Ö. Bekaroglu and H. Wyden, Thermochim. Acta 1978, 25, 349. 6. A. Gül and Ö. Bekaroglu, J. Chem. Soc. Dalton Trans 1983, 2537. 7. G. N. Schrauzer, J. Windgassen, J. Am. Chem. Soc. 1967, 89, 143. 8. Y. Aydogdu, F. Yakuphanoglu, A. Aydogdu, E. Tas, A. Cukurovali, Solid State Sciences 2002, 4, 879. 9. M. Macit, H. Bati and B. Bati, Synth. React. Inorg. Met-Org. Chem. 1998, 28, 833. 10. U. Dincer, F. Ercan, M. Macit and A. Gulce, Acta. Cryst. C52 1996, 2680. 11. M. A. Akay, N. Durust, Y. Durust, E. Kilic, Anal. Chim. Acta 1999, 392, 343. 12. E. Farkas, H. Csoka, S. Gama, M. A. Santos, Talanta, 2002, (In Press). 13. V. Bochkova, V. Peshkova, Zhur. Neorg. Khim. 1958, 3, 1132. 14. G. Manku, Z. Anorg. Allg. Chem. 1971, 382, 202. M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl... 14 Acta Chim. Slov. 2003, 50, 1-14. 15. M. J. S. Dewar and K. M. Dieter, J. Am. Chem. Soc. 1986, 108, 8075. 16. V. Frenna, V. Vivona, G. Consiglio J. Chem. Soc. Perkin Trans. II, 1985, 1865. 17. O. Astrom, Anal. Chim. Acta 1977, 88, 17. 18. H. Sari, PhD Thesis, (unpuplished) University of Newcastle-upon-Tyne, 1998. 19. E. Ozcan, E. Karapinar, B. Demirtas, Transition Metal Chemistry 2002, 27, 557. 20. G. Gran,v4cta Chem. Scand. 1950, 4, 559. 21. L. D. Pettit, “Molspin Software for Molspin pH Meter”, Sourby Farm, Timble, Otley, LS21 2PW, UK. 1992. 22. G. Gans, A. Sabatini and A. Vacca, J. Chem. Soc. Dalton Trans. 1985, 1195. 23. M. J. S. Dewar, E. G. Zoebisch, E. F. Healy, J. J. P. Stewart, J. Am. Chem. Soc. 1985, 107, 3902. 24. M. J. S. Dewar, K. M. Dieter, J. Am. Chem. Soc. 1986, 108, 8075. 25. J. J. P. Stewart, J. Comp. Aided Mol. Design 1990, 4, 1. 26. L. Nyulaszi, P. Varnai, T. Veszpremi, J. Molecular Structure (Theochem) 1995, 55, 358. 27. G. A. Ibanez, A. C. Olivieri and G. M. Escandar, J. Chem. Soc, Faraday Trans. 1997, 93 , 545. Povzetek Potenciometrično smo določili deprotonacijske konstante 1-benzil-4-piperazinglioksima (BPGO) in 1-metil-4-piperazinglioksima (MPGO) pri 25 °C, v 0.1 mol dm-3 NaCl. Za BPGO so bile določene pKa vrednosti 9.79, 7.04 in 3.19, za MPGO pa 9.56, 7.62 in 3.01. Vrstni red protonacije dušikovih atomov liganda je bil določen s teoretičnim izračunom (semi-empirična AM1 metoda). Pri različnih vrednostih pH, v raztopinah nastanejo različni kovinski kompleksi z ligandoma. Pri titracijah so bili uporabljeni ioni kovin prehoda (Cu2+, Co2+, Ni2+ in Zn2+), predvidoma pa nastanejo zvrsti MH6L2, MH5L2, MH4L2, MH3L2, MH2L2, MHL2, ML2, MH1L2, MH-2L2. Konstante stabilnosti komplekcov so bile izracunane z racunalniškim programom SUPERQUAD, predlagani so tudi splošni mehanizmi tvorbe kompleksov v opisanih sistemih. M. Can, H. Sari, M. Macit: Potentiometric Study Of The New Synthezised 1-Benzyl...