complex formation of nickel(ii) and copper(ii) with...

Research ArticleComplex Formation of Nickel(II) and Copper(II) withBarbituric Acid

Naciye Tuumlrkel and M Suat Aksoy

Department of Chemistry Faculty of Arts and Sciences Uludag University 16059 Bursa Turkey

Correspondence should be addressed to Naciye Turkel nturkeluludagedutr

Received 17 December 2013 Accepted 6 January 2014 Published 12 February 2014

Academic Editors Z Aydogmus and I Zhukov

Copyright copy 2014 N Turkel and M S Aksoy This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Equilibrium studies have been carried out on complex formation of M2+ ions (M=Ni and Cu) with L = barbituric acid (BA) inaqueous solution at 250 plusmn 01∘C and with an ionic strength of 119868 = 010M (KNO

3) in aqueous medium The basicity of the ligand

was also assessed by the determination of the dissociation constants of the ligandThe experimental pH titration data were analyzedwith the help of the BEST computer program in order to evaluate the stability constants of the various species formedThe stabilityconstants of the binary systems decrease in the order of Cu(II)gtNi(II) Distribution diagrams for the species were drawn showingthe concentrations of individual species as a function of pH by the SPE software program

1 Introduction

Organotransition-metal complexes formed with biologicallyactive ligands have attracted great attention in recent yearsStudies of such complexes in biological systems can leadto a better understanding of the roles of these ligandsand can also contribute to the development of metal-basedchemotherapeutic agents Pyrimidine ring-containing com-pounds can be found in nucleic acids various vitaminsand coenzymes and they play an important role in manybiological systems [1 2] In nucleic acids they are related toanticancer chemotherapeutic antimetabolites [3] Pyrimidinemetal complexes have been studied in recent years because oftheir great variety of biological activities such as antimalarialantibacterial antitumoral antiviral activities and so forth[4ndash10] Despite the multitude of coordination complexes ofpyrimidines the organometallic chemistry of these ligandsreceived little attention mostly from Beck and coworkers[11 12]

Barbiturates are the derivatives of barbituric acid (246-trioxypyrimidine) (Scheme 1)These drugs are used formanyreasons such as hypnotics sedatives or anesthetics [13 14]They also affect the motor and sensory functions and they

are used as cures for anxiety epilepsy and other psychi-atric disorders [15 16] The production process of plasticsand pharmaceuticals requires the uses of barbituric acidIntroduced as one of the first medical use of barbituratesbarbital diethylbarbituric acid is known as veronal or diemal[17] The first psychologically active drug barbital or veronalwas introduced in 1903 by E Fischer [18] Only a fewbarbiturates have anticonvulsant properties although manyof them have sedative-hypnotic attributes However mostbarbiturates cause convulsions at large doses Phenobarbital(5 ethyl-5 phenyl barbituric acid) is used for the treat-ment of convulsive disorders [19] 55-Diethylbarbituric acid(H2debarb) is a sedative-hypnotic and even as a discontinued

chemical its low oil water partition coefficient as a result ofbiological processes makes it interesting [18] Because of theirability to coordinate with transition metals through carbonyloxygen and one or both deprotonated oxygen atoms and alsobecause of their wide use in medicine the synthesis of theirmetal complexes has received great interest

Furthermore it has been suggested that the presence ofthe metal ions in biological fluids could have a significanteffect on the therapeutic action of drugs Many diverseapplications of metal species are aimed at understanding the

Hindawi Publishing CorporationISRN Analytical ChemistryVolume 2014 Article ID 243175 5 pageshttpdxdoiorg1011552014243175

2 ISRN Analytical Chemistry

O

O NH

O

NH

Scheme 1 Structure of the barbituric acid (BA)

natural roles ofmetal ions or exploiting the unique propertiesof metal centers in the study of the biology or biochemistryof nucleic acid and nucleic acid constitutes [2]

The literature review indicated that no work has beendone on complex formation equilibria of this ligand inaqueous medium There is only one study [20] of thisligand with Cu(II) and no work on the barbituric acid withNi(II) They studied Cu(II) and Fe(II) complexation withthe barbiturate ion by the solubility method potentiometrictitration spectroscopy and photometry But they decidedthat the barbiturate anion was a monodentate ligand andcalculated that Cubar+ stability constants was log120573

1= 307plusmn

001 by potentiometry [20] So the objective of this workwas to determine the stability constants of barbituric acidcomplexes with Ni(II) and Cu(II) metallic ions

2 Experimental

21 Chemicals Barbituric acid (BA) was obtained fromMerck Chem Co Ni(NO

3)2sdot6H2O was provided by Aldrich

Chem Co and Cu(NO3)2sdot3H2O was provided by Merck

Chem Co All reagents were of analytical quality and wereusedwithout further purification For the solutions CO

2-free

double-distilled deionized water was obtained through theultrawater purification system

22 Titration Procedure Solutions of metal ions (001M)were prepared from Ni(NO

3)2sdot6H2O and Cu(NO

3)2sdot3H2O

received and standardized with ethylenediaminetetraaceticacid (EDTA) [21] HCl stock solution was prepared fromconcentrated HCl and their concentration was determinedwith standardized NaOH All potentiometric titrations werecarried out on solutions in a 100mL double-walled glass ves-sel using titroline automatic titration systemwhich interfacesto a PC with a 10mL syringe a Schott pH combinationelectrode the temperature was controlled at 250 plusmn 01∘C bycirculating water from a constant-temperature bath The cellwas equipped with a magnetic stirrer and a tightly fittingcap which contained three holes for the combined electrodenitrogen gas and automatic burette The emf was measuredunder nitrogen atmosphereThe ligand concentrations variedin 2 times 10minus3ndash6 times 10minus3M The cell was standardized with twoprimary buffers The buffer solutions were pH = 40 andpH = 70 The electrode was calibrated on the minuslog

10[H+]

scale by titration of a 001M HCl solution (adjusted to 119868 =01M by adding KNO

3) with carbonate free 01M NaOH at

25 plusmn 01∘C The electrode slope calculated from the formula

119870 = (119864pH1 minus 119864pH2)(pH2 minus pH1) was close to the Nernstianvalue 5916mV (pHunit)minus1 within gt99 The emf readingswere converted into hydrogen concentration The p119870w ofwater was calculated at ionic strength of 01M to be 1397

The acid dissociation constants of the ligands weredetermined potentiometrically by titrating the ligand (50mL)solution (2 times 10minus3ndash6 times 10minus3M) of constant ionic strength01M adjusted with KNO

3 The stability constants of the

binary complexes were determined by titrating 50mL of asolution mixture of metal(II) (Ni(II) or Cu(II)) (2 times 10minus3M)the ligand (2 times 10minus3ndash6 times 10minus3M) and 01M KNO

3 One

hundred titration points were collected at one titration Alltitrations were performed in a purified N

2atmosphere using

aqueous 01M NaOH as titrantTheoverall stability constants (120573

119901119902119903) are defined as follows

(charges are omitted for simplicity)

119901M + 119902L + 119903H 999445999468 [M119901L119902H119903] (1)

120573119901119902119903=

[M119901L119902H119903]

[M]119901[L]119902[H]119903 (2)

where M is a metal ion L is the ligand H is the protonand 119903 is the respective stoichiometric coefficient Calculationswere performed using the computer program BEST [22] on apersonal computer

The stoichiometries and the stability constants of thecomplexes formed were determined by trying various pos-sible composition models for the system studied The con-centration distribution diagrams were obtained using theprogram SPE [22]

3 Result and Discussion

Although the dissociation constants of barbituric acid havealready been reported we determined them under ourexperimental conditions by potentiometric titration in thepH range 18ndash120 The BEST computer program was usedfor calculations [22] The obtained values are listed in Table 1together with the literature data for comparison A goodagreement with earlier published data for BA is obtained [23]considering the differences in an ionic strengthTheBA formsthree species in aqueous solution denoted by H

2L HL and

L Consider

H2L 999445999468 HLminus +H+ 119870a1 =

[HLminus] [H+][H2L]

(3)

HLminus 999445999468 Lminus +H+ 119870a2 =[Lminus] [H+][HLminus]

(4)

31 Stability Constants of Ni(II)-BA Complexes Potentiomet-ric pH titrations of Ni(II) were performed at 1 1 1 2 and1 3 metalligand molar ratios at 250 plusmn 01∘C in an 010MKNO3ionic medium BA acid (solid) was added to the Ni(II)

solutions with a metalligandmolar ratio of 1 1 1 2 and 1 3Representative potentiometric titration curves for the Ni(II)-BA complexes with 1 1 1 2 and 1 3 stoichiometry are shown

ISRN Analytical Chemistry 3

Table 1 Acid dissociation constants of Barbituric acid (BA) and the stability constants of the Ni(II) Cu(II)-BA complexes (250 plusmn 01∘C119868 = 01MKNO3)

Equilibrium Constant BA Ni(II) Cu(II)

H2L 999445999468HLminus + H+ log119870H2L389 plusmn 004

(378) [23]

HLminus 999445999468 Lminus2 + H+ log119870HL1190 plusmn 004

(1230) [23]

119901M + 119902L + 119903Hminus 999445999468 [M119901L119902H119903]

log120573110

662 plusmn 009 839 plusmn 005

log120573120

1165 plusmn 003 1416 plusmn 006

log120573131

1794 plusmn 004 1920 plusmn 004

02468101214

0 1 2 3 4 5 6 7 8 9 10m

pH

III III IV

Figure 1 Potentiometric pHprofiles for solutions containing (I) BA119879BA = 20 times 10

minus3M and Ni(II) and BA in the ratios (II) 1 1 (119879Ni =20 times 10

minus3M and 119879BA = 20 times 10minus3M) (III) 1 2 (119879Ni = 20 times 10

minus3Mand 119879BA = 40 times 10

minus3M) and (IV) 1 3 (119879Ni = 20 times 10minus3M and

119879Ni = 60 times 10minus3M) respectively 119879 = 250 plusmn 01∘C and 119868 = 01

MKNO3

in Figure 1 for BA systems togetherwith the titration curve forthe free ligand (BA) Analysis of the complexed ligand curves(Figure 1) indicates that the addition of metal ion to thefree ligand solutions shifts region of the ligand to lower pHvaluesThis shows that complex formation reactions proceedby releasing protons from BA Two inflection points wereobserved at 119898 = 10 and 119898 sim 22 on the titration curves ofthe 1 1 Ni(II)-BA systems (Curve 2 in Figure 1) where 119898 isthe number of moles of base added per mole of the metal(Figure 1) Experimental data has shown that in the 119898 = 0to sim22 the NiL complex forms between pH = 60ndash110 BAligand acts as a bidentate chelating ligand via the negativelycharged imino N atom and one of the carbonyl O atomsadjacent to the imino N atom

The potentiometric titrations of the 1 2 Ni(II)-BA sys-tems were carried out under the same experimental condi-tions In these curves two inflection points were observedat 119898 = 18 and 119898 = 38 The titration of these protons ineach of these systems indicates that the NiL

2complex forms

graduallyThe second BAwas bound as the same the first BAThe potentiometric titrations of the 1 3 Ni(II)-BA sys-

tems were carried out under the same experimental condi-tions The titration of these protons in each of these systemsindicates that the NiL

3H complex forms gradually But in the

third BA molecule it was bound only once via the negativelycharged imino N atom or one of the carbonyl O atoms In

the 1 3 molar ratio potentiometric titrations the stabilityconstants of the complexes NiL NiL

2 and NiL

3H were

calculated by the BEST computer program [22] The stabilityconstants of their complexes are given in Table 1

The distribution diagrams were drawn in the titrationwhere the metal to ligand mole ratio was 1 3 They wereobtained with the aid of SPE program [22] and the concen-tration of total metal ion present sim2 times 10minus3 M set at 100 InFigure 3 the species NiL

3H for the system BA and metal ion

Ni(II) reaches a maximum of 100 at pH 100 The secondspecies NiL

2reaches a maximum of 10 at pH 70minus120 and

NiL complex species in the mole ratio of 1 moles of ligand toone mole metal presents a maximum of 70 near pH 60

32 Stability Constants of Cu(II)-BA Complexes The poten-tiometric titrations of the Cu(II)BA systems were performedat 250plusmn01∘C in an 010MKNO

3ionicmedium BA acid was

added to the Cu(II) solutions with a molar ratio of 1 1 1 2and 1 3 Two inflection points were observed at 119898 = 10 and119898 sim 22 on the titration curves of the 1 1 Cu(II)-BA systems(Curve 2 in Figure 2) where 119898 is the number of moles ofbase added per mole of the metal (Figure 2) In addition thetitration curve of the Cu(II) complex is different from that ofthe free BA curve Experimental data has shown that in the119898 = 0 to sim22 buffer zone the CuL complex forms betweenpH = 60ndash110

The potentiometric titrations of the 1 2 Cu(II)-BA sys-tems were carried out under the same experimental condi-tions In these curves two inflection points were observedat 119898 = 30 and 119898 = 50 The titration of these protons ineach of these systems indicates that the CuL

2complex forms

graduallyThe potentiometric titrations of the 1 3 Cu(II)-BA sys-

tems were carried out under the same experimental condi-tions In these curves two inflection points were observed at119898 = 40 and 119898 = 50 The titration of these protons in eachof these systems indicates that the CuL

3H complex forms

gradually In the 1 3molar ratio potentiometric titrations thestability constants of the complexes CuL CuL

2 and CuL

3H

were calculated by the BEST computer program [22] Thestability constants of their complexes are given in Table 1

The distribution diagrams were drawn in the titrationwhere the metal to ligand mole ratio was 1 3 They wereobtained with the aid of SPE program [22] and the concen-tration of total metal ion presents sim2 times 10minus3M set at 100


0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8m

pH

I III

II IV

Figure 2 Potentiometric pH profiles for solutions containing (I)BA 119879BA = 20 times 10

minus3M and Cu(II) and BA in the ratios (II) 1 1(119879Cu = 20 times 10

minus3M and 119879BA = 20 times 10minus3M) (III) 1 2 (119879Cu = 20 times

10minus3M and 119879BA = 40 times 10

minus3M) and (IV) 1 3 (119879Cu = 20 times 10minus3M

and 119879BA = 60 times 10minus3M) respectively 119879 = 250 plusmn 01∘C and 119868 = 01

MKNO3

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

Ni

NiL

NiL3H

NiL2

a(

)

Figure 3 Species distribution curves of the metal ion Ni(II) andthe BA as a function of pH for a solution initially containing 119879Ni =20 times 10

minus3Mmetal ion and 119879BA = 60 times 10minus3MBA 119879 = 250 plusmn 01∘C

and 119868 = 01MKNO3 a is the percentage of a species present with

the concentration of themetal set at 100 NiL NiL2 and NiL

3H are

the complexed species with one two and three ligand molecules

In Figure 4 the species CuL3H for the system BA and metal

ion Cu(II) reaches a maximum of 90 at pH 120The secondspecies CuL


the CuL complex species in the ratio of 1 moles of ligand toone mole metal presents a maximum of 90 near pH 40ndash100

It can be observed that the stability constants of theNi(II)-BA complexes are lower than Cu(II)-BA complexes

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

CuCuL

CuL3H

CuL2a(

)

Figure 4 Species distribution curves of the metal ion Cu(II) andthe BA as a function of pH for a solution initially containing 119879Cu =20 times 10



the concentration of the metal set at 100 CuL and CuL2 CuL

3H

are the complexed species with one two and three ligandmolecules

Acknowledgment

The authors thank the Research Fund of Uludag Universityfor the financial support given to the research projects(Project no UAP(F)-201170)

References

[1] F Hueso-Urena N A Illan-Cabeza M N Moreno-CarreteroJ M Martınez-Martos and M J Ramırez-Exposito ldquoSynthesisand spectroscopic studies on the new Schiff base derived fromthe 1 2 condensation of 26-diformyl-4-methylphenol with 5-aminouracil (BDF5AU) and its transition metal complexesinfluence on biologically active peptides-regulating aminopep-tidasesrdquo Journal of Inorganic Biochemistry vol 94 no 4 pp326ndash334 2003

[2] M S Refat S A El-Korashy and A S Ahmed ldquoA convenientmethod for the preparation of barbituric and thiobarbituric acidtransition metal complexesrdquo Spectrochimica Acta A vol 71 no3 pp 1084ndash1094 2008

[3] A Tsunoda M Shibusawa Y Tsunoda N Yasuda K Nakaoand M Kusano ldquoA model for sensitivity determination ofanticancer agents against chemically-induced colon cancer inratsrdquo Anticancer Research vol 14 no 6B pp 2637ndash2642 1994

[4] E S Raper ldquoComplexes of heterocyclic thione donorsrdquo Coordi-nation Chemistry Reviews vol 61 pp 115ndash184 1985

[5] J S Casas E E Castellano M D Couce et al ldquoA gold(I)complex with a vitamin K

3derivative characterization and

antitumoral activityrdquo Journal of Inorganic Biochemistry vol 100no 11 pp 1858ndash1860 2006

[6] M J M Campbell ldquoTransition metal complexes of thiosemi-carbazide and thiosemicarbazonesrdquo Coordination ChemistryReviews vol 15 no 2-3 pp 279ndash319 1975

[7] M C Rodriguez-Arguelles M B Ferrari G G Fava et alldquo26-Diacetylpyridine bis(thiosemicarbazones) zinc complexessynthesis structure and biological activityrdquo Journal of InorganicBiochemistry vol 58 no 3 pp 157ndash175 1995

[8] J S Casas M S Garcıa-Tasende C Maichle-Mossmer et alldquoSynthesis structure and spectroscopic properties of acetato(dimethyl) (pyridine-2-carbaldehydethiosemicarbazonato)-tin(IV) acetic acid solvate [SnMe

2(PyTSC)(OAc)]HOAc

Comparison of its biological activity with that of some struc-


turally related diorganotin(IV) bis (thiosemicarbazonates)rdquoJournal of Inorganic Biochemistry vol 62 no 1 pp 41ndash55 1996

[9] M B Ferrari G G Fava P Tarasconi R Albertini S Pinelliand R Starcich ldquoSynthesis spectroscopic and structural char-acterization and biological activity of aquachloro(pyridoxalthiosemicarbazone) copper(II) chloriderdquo Journal of InorganicBiochemistry vol 53 no 1 pp 13ndash25 1994

[10] U Koch B Attenni S Malancona et al ldquo2-(2-Thienyl)-56-dihydroxy-4-carboxypyrimidines as inhibitors of the hepatitisC virus NS5B polymerase discovery SAR modeling andmutagenesisrdquo Journal of Medicinal Chemistry vol 49 no 5 pp1693ndash1705 2006

[11] W Beck andN Kottmair ldquoNeue UbergangsmetallkomplexemitNuclein-Basen und Nucleosidenrdquo Chemische Berichte vol 109no 3 pp 970ndash993 1976

[12] N Kottmair and W Beck ldquoTungsten carbonyl complexes of2101584031015840-O-isopropylideneguanosine and 6-mercaptopurinerdquo Inor-ganica Chimica Acta vol 34 pp 137ndash144 1979

[13] A Ashnagar N G Naseri and B Sheeri ldquoNovel synthesis ofbarbituratesrdquo Chinese Journal of Chemistry vol 25 no 3 pp382ndash384 2007

[14] J N Delgado W A Remers and J B Lippincott Eds Wilsonand Gisvoldrsquos Textbook of Organic Medicinal PharmaceuticalChemistry Williams amp Wilkins Philadelphia Pa USA 9thedition 1991

[15] J-L Fillaut I de Los Rios D Masi A Romerosa F Zanobiniand M Peruzzini ldquoSynthesis and structural characterizationof (carbene)ruthenium complexes binding nucleobasesrdquo Euro-pean Journal of Inorganic Chemistry vol 2002 no 4 pp 935ndash942 2002

[16] O Temiz-Arpaci A Ozdemir I Yalcin I Yildiz E Aki-Sener and N Altanlar ldquoSynthesis and antimicrobial activityof some 5-[2-(morpholin-4-yl) acetamido] andor 5-[2-(4-substituted piperazin-1-yl)acetamido]-2-(p-substitutedphenyl)benzoxazolesrdquo Archiv der Pharmazie vol 338 no 2-3pp 105ndash111 2005

[17] T W G Solomons and C B Fryhle Organic Chemistry JohnWiley amp Sons Hoboken NJ USA 9th edition 2008

[18] J H Block and J M Beale Wilson and Gisvoldrsquos Textbook ofOrganic Medicinal and Pharmaceutical Chemistry LippincottWilliams ampWilkins Philadelphia Pa USA 11th edition 2004

[19] W O Foye T L Lemke and D A Williams Principles ofMedicinal Chemistry Williams amp Wilkins Philadelphia PaUSA 4th edition 1995

[20] N M Korotchenko and N A Skorik ldquoInteraction of copper(II)and iron(III) with barbituric acidrdquo Russian Journal of InorganicChemistry vol 45 no 12 pp 1945ndash1948 2000

[21] G Schwarzenbach and H Flaschka Complexometric TitrationsInterscience New York NY USA 1969

[22] A E Martell and R J Motekaitis Determination and Use ofStability Constants Wiley-VCH New York NY USA 1989

[23] M-J Blais O Enea and G Berthon ldquoRelations structure-reactivite grandeurs thermodynamiques de protonationdrsquohrsquoetrsquoerocycles satures et non saturesrdquo Thermochimica Actavol 20 no 3 pp 335ndash345 1977

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International


CatalystsJournal of

ElectrochemistryInternational Journal of



O

O NH

O

NH

Scheme 1 Structure of the barbituric acid (BA)

natural roles ofmetal ions or exploiting the unique propertiesof metal centers in the study of the biology or biochemistryof nucleic acid and nucleic acid constitutes [2]

The literature review indicated that no work has beendone on complex formation equilibria of this ligand inaqueous medium There is only one study [20] of thisligand with Cu(II) and no work on the barbituric acid withNi(II) They studied Cu(II) and Fe(II) complexation withthe barbiturate ion by the solubility method potentiometrictitration spectroscopy and photometry But they decidedthat the barbiturate anion was a monodentate ligand andcalculated that Cubar+ stability constants was log120573

1= 307plusmn

001 by potentiometry [20] So the objective of this workwas to determine the stability constants of barbituric acidcomplexes with Ni(II) and Cu(II) metallic ions

2 Experimental

21 Chemicals Barbituric acid (BA) was obtained fromMerck Chem Co Ni(NO

3)2sdot6H2O was provided by Aldrich

Chem Co and Cu(NO3)2sdot3H2O was provided by Merck

Chem Co All reagents were of analytical quality and wereusedwithout further purification For the solutions CO

2-free

double-distilled deionized water was obtained through theultrawater purification system

22 Titration Procedure Solutions of metal ions (001M)were prepared from Ni(NO

3)2sdot6H2O and Cu(NO

3)2sdot3H2O

received and standardized with ethylenediaminetetraaceticacid (EDTA) [21] HCl stock solution was prepared fromconcentrated HCl and their concentration was determinedwith standardized NaOH All potentiometric titrations werecarried out on solutions in a 100mL double-walled glass ves-sel using titroline automatic titration systemwhich interfacesto a PC with a 10mL syringe a Schott pH combinationelectrode the temperature was controlled at 250 plusmn 01∘C bycirculating water from a constant-temperature bath The cellwas equipped with a magnetic stirrer and a tightly fittingcap which contained three holes for the combined electrodenitrogen gas and automatic burette The emf was measuredunder nitrogen atmosphereThe ligand concentrations variedin 2 times 10minus3ndash6 times 10minus3M The cell was standardized with twoprimary buffers The buffer solutions were pH = 40 andpH = 70 The electrode was calibrated on the minuslog

10[H+]

scale by titration of a 001M HCl solution (adjusted to 119868 =01M by adding KNO

3) with carbonate free 01M NaOH at

25 plusmn 01∘C The electrode slope calculated from the formula

119870 = (119864pH1 minus 119864pH2)(pH2 minus pH1) was close to the Nernstianvalue 5916mV (pHunit)minus1 within gt99 The emf readingswere converted into hydrogen concentration The p119870w ofwater was calculated at ionic strength of 01M to be 1397

The acid dissociation constants of the ligands weredetermined potentiometrically by titrating the ligand (50mL)solution (2 times 10minus3ndash6 times 10minus3M) of constant ionic strength01M adjusted with KNO

3 The stability constants of the

binary complexes were determined by titrating 50mL of asolution mixture of metal(II) (Ni(II) or Cu(II)) (2 times 10minus3M)the ligand (2 times 10minus3ndash6 times 10minus3M) and 01M KNO

3 One

hundred titration points were collected at one titration Alltitrations were performed in a purified N

2atmosphere using

aqueous 01M NaOH as titrantTheoverall stability constants (120573

119901119902119903) are defined as follows

(charges are omitted for simplicity)

119901M + 119902L + 119903H 999445999468 [M119901L119902H119903] (1)

120573119901119902119903=

[M119901L119902H119903]

[M]119901[L]119902[H]119903 (2)

where M is a metal ion L is the ligand H is the protonand 119903 is the respective stoichiometric coefficient Calculationswere performed using the computer program BEST [22] on apersonal computer

The stoichiometries and the stability constants of thecomplexes formed were determined by trying various pos-sible composition models for the system studied The con-centration distribution diagrams were obtained using theprogram SPE [22]

3 Result and Discussion

Although the dissociation constants of barbituric acid havealready been reported we determined them under ourexperimental conditions by potentiometric titration in thepH range 18ndash120 The BEST computer program was usedfor calculations [22] The obtained values are listed in Table 1together with the literature data for comparison A goodagreement with earlier published data for BA is obtained [23]considering the differences in an ionic strengthTheBA formsthree species in aqueous solution denoted by H

2L HL and

L Consider

H2L 999445999468 HLminus +H+ 119870a1 =

[HLminus] [H+][H2L]

(3)

HLminus 999445999468 Lminus +H+ 119870a2 =[Lminus] [H+][HLminus]

(4)

31 Stability Constants of Ni(II)-BA Complexes Potentiomet-ric pH titrations of Ni(II) were performed at 1 1 1 2 and1 3 metalligand molar ratios at 250 plusmn 01∘C in an 010MKNO3ionic medium BA acid (solid) was added to the Ni(II)

solutions with a metalligandmolar ratio of 1 1 1 2 and 1 3Representative potentiometric titration curves for the Ni(II)-BA complexes with 1 1 1 2 and 1 3 stoichiometry are shown





(378) [23]


(1230) [23]

119901M + 119902L + 119903Hminus 999445999468 [M119901L119902H119903]

log120573110


log120573120

1165 plusmn 003 1416 plusmn 006

log120573131

1794 plusmn 004 1920 plusmn 004

02468101214

0 1 2 3 4 5 6 7 8 9 10m

pH

III III IV







MKNO3



2complex forms






2 and NiL

3H were











2complex forms



3H complex forms


2 and CuL

3H




0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8m

pH

I III

II IV







MKNO3

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

Ni

NiL

NiL3H

NiL2

a(

)





3H are









0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

CuCuL

CuL3H

CuL2a(

)





3H


Acknowledgment


References











2(PyTSC)(OAc)]HOAc




























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry




CatalystsJournal of







(378) [23]


(1230) [23]

119901M + 119902L + 119903Hminus 999445999468 [M119901L119902H119903]

log120573110


log120573120

1165 plusmn 003 1416 plusmn 006

log120573131

1794 plusmn 004 1920 plusmn 004

02468101214

0 1 2 3 4 5 6 7 8 9 10m

pH

III III IV







MKNO3



2complex forms






2 and NiL

3H were











2complex forms



3H complex forms


2 and CuL

3H




0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8m

pH

I III

II IV







MKNO3

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

Ni

NiL

NiL3H

NiL2

a(

)





3H are









0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

CuCuL

CuL3H

CuL2a(

)





3H


Acknowledgment


References











2(PyTSC)(OAc)]HOAc




























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry




CatalystsJournal of




0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8m

pH

I III

II IV







MKNO3

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

Ni

NiL

NiL3H

NiL2

a(

)





3H are









0

20

40

60

80

100

120

0 2 4 6 8 10 12 14pH

CuCuL

CuL3H

CuL2a(

)





3H


Acknowledgment


References











2(PyTSC)(OAc)]HOAc




























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry




CatalystsJournal of





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry




CatalystsJournal of



complex formation of nickel(ii) and copper(ii) with...

Documents