1. Introduction The 2,2’-oxydiacetato [ODA = O(CH2CO2)2

2-] anion can

1[2

3,4

5

(H2 2 2O)]

Central European Journal of Chemistry

Investigations of ternary complexes of Co(II) and Ni(II) with oxydiacetate anion and 1,10-phenanthroline or 2,2’-bipyridine in solutions

* E-mail: wdaro@wp.pl

Received 9 July 2013; Accepted 17 September 2013

Abstract:

© Versita Sp. z o.o.Keywords:

1

2

Dariusz Wyrzykowski1*, Joanna Pranczk1, Dagmara Jacewicz1, Aleksandra Tesmar1 2 1

Research Article

Potentiometric (PT) and conductometric (CT) titration methods have been used to determine the stoichiometry and formation constants in water for a series of ternary complexes of Co(II) and Ni(II) involving the oxydiacetate anion (ODA) and 1,10-phenanthroline (phen) or 2,2’-bipyridine (bipy) ligands, namely [Co(ODA)(phen)(H2O)], [Co(ODA)(bpy)(H2O)], [Ni(ODA)(phen)(H2O)] and [Ni(ODA)(bpy)(H2O)]. The ternary complex formation process was found to take place in a stepwise manner in which the oxydiacetate ligand acts as a primary ligand and the phen or bipy ligands act as auxiliary ones. The stability of the ternary complexes formed is discussed in the relation to the corresponding binary ones. Furthermore, the kinetics of the substitution reactions of the aqua ligands in the coordination sphere of the

in the 288–303 K temperature range, at a constant concentration of phen or bipy and at seven different concentrations of the binary

was discussed.

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Investigations of ternary complexes of Co(II) and Ni(II) with oxydiacetate anion and 1,10-phenanthroline or 2,2’-bipyridine in solutions

2

2. Experimental procedure

2.1. Synthesis2O)3 2O, [Co(ODA)

(H2O)2 2 2 2O, [Co(ODA)2 2 2 2O

2 2

3

2.2. Potentiometric titration (PT)

[

2+ or Co2+2 4

2+ or Co2+2

4

7

titrand concentrations, etc 7-

2.3. Conductometric titration (CT)

-1

-1 -1

2+ or Co2+2

2+ or Co2+

2

2.4. Kinetics measurements

-1

i.e.

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D. Wyrzykowski et al.

11

3. Results and discussion

2

2-

+ - +

2-

Ka2 - (H2ODA = ODA2- +

H+ Ka+ + +) and

2-

K K1

1

2-

mer

3 mer-1 than its fac

1

mer3,12

2 2 2

1

1 2ODA are 2

1the H2

+ and OH-

11

2

2(s) + 2

Table 1. pKa and logK values (standard derivation values in parentheses) for the M-ODA-B interactions obtained by adapting the equilibrium model to PT data. Equlibria are written in the direction that the reactions occur.

pKa or logK Equilibrium model M2+ = Co2+ M2+ = Ni2+

B = phen B = bipy B = phen B = bipy

pKa BH = B-+H+ 4.97 (±0.03) 4.27 (±0.05) 5.01 (±0.12) 4.37 (±0.07)

pKa1 H2ODA = HODA- + H+ 1.76 (±0.19) 2.61 (±0.11) 2.26 (±0.15) 2.34 (±0.05)

pKa2 HODA- = ODA2- + H+ 3.71 (±0.03) 3.19 (±0.06) 3.74 (±0.05) 3.80 (±0.15)

MM(ODA)logK M2+ + ODA2- = M(ODA) 3.51 (±0.04) 3.50 (±0.08) 3.48 (±0.05) 3.37 (±0.06)

M(ODA)M(ODA)(B)logK MODA + B = M(ODA)(B)(H2O) 4.33 (±0.04) 3.33 (±0.06) 4.40 (±0.15) 3.50 (±0.10)

pKM(ODA)B(H2O)

M(ODA)(B)(H2O) =M(ODA)(B)(OH)- + H+ 9.27 (±0.13) 8.82 (±0.11) 9.18 (±0.05) 9.00 (±0.08)

Scheme 1. The mer and fac conformation of the oxydiacetate ligand.

109

Investigations of ternary complexes of Co(II) and Ni(II) with oxydiacetate anion and 1,10-phenanthroline or 2,2’-bipyridine in solutions

2 is

2

2 1

2

1

and

1

K13

MM(ODA)

M(ODA)M(ODA)(B) logloglog KKK

K

K

Figure 1. Conductometric titration curves of the H2ODA (1.51 mM) (1), Ni(II) (1.47 mM) + H2ODA (1.51 mM) (2) and Ni(II) (1.47 mM) - H2ODA (1.51 mM) + phen (1.48 mM) (3) systems with 25 mM NaOH.

Scheme 2. Hydrolysis of the ternary complex.

110

D. Wyrzykowski et al.

22 and 3

K ) 14 and 5

Figure 2. Concentration distributions of Ni(II) (1), Ni-ODA (2), [Ni(ODA)(phen)(H2O)] (3) and [Ni(ODA)(phen)(OH)]- (4) as a function of pH in the Ni(II) – H2ODA – phen system.

Figure 3. Concentration distributions of Ni(II) (1), Ni-ODA (2), [Ni(ODA)(bipy)(H2O)] (3) and [Ni(ODA)(bipy)(OH)]- (4) as a function of pH in the Ni(II) – H2ODA – bipy system.

111

Investigations of ternary complexes of Co(II) and Ni(II) with oxydiacetate anion and 1,10-phenanthroline or 2,2’-bipyridine in solutions

k

][M(ODA)(B)d

)]d[M(ODA)(B kt

k

2 5

Figure 4. Electronic spectra of the substrate Ni-ODA (1), the ternary complex Ni-ODA-phen (2) and the product of the substitution reaction Ni-ODA + phen (3) in an aqua solution.

Figure 5. Electronic spectra of the substrate Co-ODA (1), the ternary complex Co-ODA-phen (2) and the product of the substitution reaction Co-ODA + phen (3) in an aqua solution.

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D. Wyrzykowski et al.

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4. Conclusions

Table 2. Concentration and temperature dependences of rate constants k(s-1) (± standard derivation) of the substitution of Ni-ODA with phen. The concentration of phen is constant and equals to 2.88 mM.

Ni-ODA[mM]

Temperature [K]

288 293 298 303

4.0 11.14±0.04 12.16±0.04 14.07±0.05 17.56±0.04

4.5 15.24±0.04 17.14±0.04 18.79±0.04 24.72±0.04

5.0 23.34±0.04 25.72±0.05 26.62±0.04 33.51±0.04

5.5 28.91±0.04 35.77±0.03 36.89±0.04 43.21±0.04

6.0 32.26±0.04 43.16±0.03 47.30±0.03 52.69±0.04

6.5 37.49±0.03 49.07±0.02 55.90±0.02 67.44±0.04

7.0 44.45±0.03 58.75±0.02 69.47±0.04 77.87±0.04

Table 3. Concentration and temperature dependences of rate constants k(s-1) (± standard derivation) of the substitution of Ni-ODA with bipy. The concentration of bipy is constant and is equal to 2.88 mM.

Ni-ODA[mM]

Temperature [K]

288 293 298 303

4.0 11.28±0.01 12.23±0.01 14.87±0.01 20.11±0.01

4.5 14.30±0.01 15.37±0.01 18.55±0.01 24.88±0.01

5.0 14.30±0.01 15.37±0.01 18.55±0.01 24.88±0.01

5.5 19.44±0.03 21.84±0.09 26.09±0.01 30.21±0.01

6.0 22.29±0.01 23.83±0.01 28.67±0.01 33.17±0.01

6.5 25.62±0.01 26.40±0.01 30.76±0.02 36.20±0.01

7.0 27.50±0.02 29.22±0.02 32.93±0.02 39.37±0.01

Table 4. Concentration and temperature dependences of rate constants k(s-1) (± standard derivation) of the substitution of Co-ODA with phen. The concentration of phen is constant and equals to 2.88 mM.

Co-ODA[mM]

Temperature [K]288 293 298 303

4.0 0.121±0.001 0.127±0.001 0.152±0.001 0.197±0.001

4.5 0.216±0.001 0.191±0.001 0.245±0.003 0.276±0.001

5.0 0.241±0.001 0.278±0.001 0.315±0.001 0.367±0.001

5.5 0.271±0.001 0.322±0.001 0.379±0.001 0.444±0.001

6.0 0.341±0.001 0.369±0.001 0.430±0.002 0.489±0.001

6.5 0.406±0.001 0.425±0.020 0.483±0.002 0.555±0.002

7.0 0.490±0.001 0.517±0.020 0.574±0.001 0.622±0.001

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Investigations of ternary complexes of Co(II) and Ni(II) with oxydiacetate anion and 1,10-phenanthroline or 2,2’-bipyridine in solutions

i)

ii

2 2

i.e 2 2

Acknowledgements

Table 5. Concentration and temperature dependences of rate constants k(s-1) (± standard derivation) of the substitution of Co-ODA with bipy. The concentration of bipy is constant and is equal to 2.88 mM.

Co-ODA[mM]

Temperature [K]288 293 298 303

4.0 360.15±0.02 374.64±0.02 386.12±0.03 394.56±0.02

4.5 410.36±0.03 419.62±0.04 431.15±0.02 446.08±0.02

5.0 456.44±0.02 471.98±0.03 475.74±0.03 488.75±0.05

5.5 502.12±0.02 523.97±0.03 525.13±0.05 532.67±0.02

6.0 561.18±0.03 569.96±0.01 578.21±0.05 581.42±0.04

6.5 620.02±0.04 621.03±0.02 631.14±0.01 634.13±0.02

7.0 680.79±0.03 681.03±0.03 686.39±0.02 688.57±0.03

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