N. Sarı – P. Gu¨rkan · Some Novel Amino Acid-Schiff Bases
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water (10 ml) was added dropwise to the reaction mixture complexes; respectively, from potentiometric data [35]. The
and it was then stirred and heated again for three hours at average values and standard deviations are given in Table 4.
50 ◦C. The mixture was kept for two days at room tempera-
ture. The solid product was filtered, washed with water and
acetone-water (1:1) solutions and dried in vacuo at 50 C.
Solid state conductivity measurements
◦
Solid state electrical conductivities (σ) were measured
with a Nippon NP-900 multimeter using the four-probe tech-
nique. Solid state electrical conductivitiy may be defined
as the ratio J/E of net charge motion, J (current density),
brought about by an electric field E.
Yields are between 83 – 72%.
Potentiometric reagents and solutions
Triply distilled water was used as solvent. All metal ion
solutions were prepared from their analytical grade chlo-
rides and standardized by the atomic absorption spectro-
scopic method. A standard 0.051 M KOH solution (Merck)
was used for titrations. KCl (Merck, extra pure) and concen-
trated HCl (Merck, extra pure) were used for preparation of
1.0 M KCl and 0.056 M HCl solutions. HCl solution was
standardized against standard KOH solutions. Alkali solu-
tions were stored under nitrogen atmosphere.
σ = J/E
The four-probe technique used for measuring the solid-state
conductivity of pressed pellets was developed by van der
Pauw [20]. Here, four points of contact, almost equally
spaced on the periphery of the sample, were made with a con-
ductive paste such as electrodag. The current (i) was passed
through two adjacent contacts while the voltage drop (V) was
measured across the other two as shown in Figure 4.
Potentiometric measurements
Measurements were carried out using a Janway pH-meter
equipped with a Janway combined glass electrode. The sys-
tem was calibrated to read hydrogen ion concentration by
Fig. 4. Van der Pauw technique for the
measurement of the conductivity.
◦
titration of a hydrochloric acid solution at 25 0.1 C and
0.1 M KCl ionic strength with KOH solution according
to Gran’s method [34]. Small amounts (∆ν = 0.05 ml) of
titrant KOH solution were added with a microburette. Sam-
ple solutions were titrated in a double walled glass cell
maintaned at 25 0.1 ◦C in nitrogen atmosphere. Titrations
were performed over the pH ranges 2.0 – 11.0 for the lig-
ands and 2.0 – 9.0 for the complexes using 25 0.01 cm3
samples. There was no precipitation within the pH range
for the titrations performed. The concentration of the lig-
ands was 4.0.10−3 M and metal-to-ligand molar ratio was
1:4. The following solutions were titrated potentiometrically
against 0.051 M KOH: i) HCl+KCl, ii) HCl+KCl+ligand and
The van der Pauw technique takes into account the sam-
ple thickness (d) and thus it must be measured along with the
current-voltage characteristics of the samples. The formula
employed for the measurement of conductivity is
σ = ln2/πd ·I/V.
The pellets of the Schiff bases and the complexes were pre-
pared at a loading of ca. 7 tons and thickness of ca. 0.05 cm.
Acknowledgements
The authors are grateful to the Research Foundation of
iii) HCl+KCl+ligand+metal ion. PKAS and BEST computer Gazi University, for supporting this study. We are thankful to
programs were used for determination of the protonation the Dr. B. Sarı for providing laboratory facilities for conduc-
constans of the ligands and stability constants of the ML type tivity measurements.
¨
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