INTRODUCTION
In recent years, with the development and expansion of industries and
industrial zones, the pollution of the water environment caused by metals has
been increasing. Metal ions such as copper, cobalt, nickel, zinc usually coexist
together in waste water.
Analytical chemistry should investigate new methods, techniques and
analytical procedures which are rapid, sensitive, accurate and highly selective.
Among them, the direction of research and development of analytical methods
in combination with statistical algorithms for simultaneous analysis of
multicomponent mixtures is increasingly taken up by many analytical chemists.
The 5-bromosalicylaldehyde thiosemicarbazone (5-BSAT) reagent is
capable of reacting with transition metal ions to form chelates which are
colored and stable by coordinating to the central ion through azomethine
nitrogen atom, sulphur atom and/or not phenolic oxygen atom, forming fiveand

six-membered

heterocycles.

Some

researches

have

studied

the

complexation of 5-BSAT reagent with Ag(I), Pt(II), Pd(II), Mn(II), Cu(II),
Ni(II), Fe(III), Ru(III) ions and their biological activities or magnetic

structure of the complex is proposed with the molecular formula of

reagent. Simultaneously, add more data of complexes of Co(II) and Ni(II) for
analytical purposes.

Ni(C8H8ON3SBr)2.
3. Spectral technique (H-point satandard addition method, HPSAM) and

2. Study the optimum conditions for complexation in solution.

statistical algorithms (principal component regression (PCR), partial

3. Research on the structures of the formed complexes.

least squares (PLS)) have been studied for application in simultaneous

4. Research on the development of methods for simultaneous

determination of mixture of metal ions with overlapping UV-VIS

determination of Ni(II) and Zn(II), Cu(II) and Co(II) mixtures by
spectrophotometry combined with spectral techniques, statistical algorithms
using 5-BSAT reagent and practical applications.

spectra of complexes.
4. Studied on the application in simultaneous determination of Ni(II) and
Zn(II), Cu(II) and Co(II) mixtures by HPSAM method and Cu(II) and

The scientific significances of the thesis:




formed after 5 minutes of reaction and stable for 30 minutes. Zn(II) ion

3. Successful application of HPSAM, PCR, PLS methods for

forms a 1:1 stoichiometric complex. The stability constant of Zn(II)-5-

simultaneous spectrophotometric determination of zinc, nickel, copper and

5

BSAT complex calculated by molar ratio method is 4.21×10 . The

cobalt mixtures.

calibration curve of the Zn(II) ion measured at different ranges is linear
in the range 2.0×10-6 – 6.0×10-5 mol.L−1 for this ion; LOD and LOQ are
-9

-8

3.26×10 M and 1.09×10 M, respectively. The molar absorptivity (ε)
4

−1

−1

for the complex is 1.08×10 L.mol .cm . Based on FT-IR, NMR, MS

in DMF, dioxane to form a yellow solution, insoluble in normal organic
solvents and quickly decomposed in acid solution.

of reaction and stable for 45 minutes. Co(II) ion forms a 1:2

The 5-BSAT reagent has absorption maxima at 290 and 340 nm in the

stoichiometric complex. The stability constant of Co(II)-5-BSAT

ultraviolet region, attributed to   * and n  * transitions. In the basic

12

complex calculated by molar ratio method is 1.28×10 . The calibration

medium, λmax moves towards the long wavelength (386 nm), due to the

curve of the Co(II) ion measured at different ranges is linear in the

protonation of the OH group, which increases the degree of conjugation in the

range

8.0×10

-6

–

molecule. The FT-IR spectrum of this reagent has the characteristic frequencies


simulated by IQmol and Q-Chem softwares, the structure of the

1.1.2. Application of complex of 5-BSAT and metal ions in analysis

complex is proposed with the molecular formula of Co(C8H7ON3SBr)2.

The 5-BSAT reagent was used for the analysis of Fe(II), Co(II),

- Ni(II)-5-BSAT complex is yellow, has maximum absorbance at

Cu(II). In 2002, the Fe(II) complex was published by G. Ramanjaneyulu et

378 nm in optimum pH of 6.5. The complex is formed after 5 minutes

al. In aqueous DMF medium, the complex showed absorption maximum at 385

of reaction and stable for 30 minutes. Ni(II) ion also forms a 1:2

nm, pH 5.0-6.0. The authors used this complex for the determination of Fe(II)

stoichiometric complex. The stability constant of Ni(II)-5-BSAT

in grape leaves, multivitamin capsules and human blood. The Co(II) complex

11

complex calculated by molar ratio method is 4.45×10 . The calibration

was published in 2003. The complex showed absorption maximum at 410 nm in


DMF medium. The greenish yellow colored complex was formed in pH 4-5,
with

the

absorption

maximum

at

390 nm. The authors have applied for the determination of copper in grape

Sample

leaves
and aluminum based alloy samples by third derivative spectrophotometry.

Cfound

C

(10-6 M)

Recovery (%)

(10-6 M)

Error (%)


N2

8

8.013

7.774

100.16

97.18

0.16

-2.83

with Ag(I), Pt(II), Pd(II), Mn(II), Cu(II), Ni(II), Fe(III), Ru(III) ions and their

N3

10

10.249

10.093

102.49 100.93

2.49

PLS

PCR

PLS

PCR

PLS

PCR

necessary, although the absorption maxima of their complexes are very close to

N1

8

7.979

8.002

99.74

100.03

-0.26

0.03


108.60

7.20

8.60

Introduction of the analytical properties of zinc, nickel, cobalt and
copper ions

The results showed that the found concentration of two ions were not

1.3.

Some methods of determination of zinc, nickel, cobalt and copper

1.4.

Some methods of simultaneous determination of multicomponent
mixtures by spectrophotometry

relative errors of the two methods were acceptable).
Conclusion: The spectrophotometric method in combination with

1.4.1. Vierordt method

multivariate regression methods such as PLS and PCR has been applied for

1.4.2. H-point standard addition method

simultaneously determinating the mixture of Cu2+ and Co2+ in 8 standard

maximum absorbance at 381 nm in optimum pH of 6.8. The complex is

1.4.3. Spectrophotometry combined with multivariate regression methods
4

25


- Determining the concentration of Cu(II) and Co(II) ions: The results of
2+

2+

calculating concentrations of the Cu

và Co

ions in 8 standard samples and

the accuracy of methods were presented in Table 3.42, Table 3.43.
2+

Table 3.42. The found concerntration of Cu in training set

Sample

Cfound

C



PCR

The content of the method is to establish the dependence of A(A) on

M1

4

3.826

3.933

95.65

98.33

-4.35

-1.68

CR when CM = const and the dependence of A(A) on CM when CR = const. The

M2

4

3.924

3.931


5.417

5.454

108.34 109.08

8.34

9.08

M5

8

7.747

7.670

96.84

95.88

-3.16

-4.13

M6

10


12

12.317

12.341

102.64 102.84

2.64

2.84

Table 3.43. The found concerntration of Co2+ in training set

Sample

C

Cfound

(10 M)

Recovery (%)

(10-6 M)

-6

when CM = const has a breakpoint

PLS

PCR

PLS

PCR

stability constant β:

M1

6

5.744

5.682

95.73

94.70

-4.27

-5.30

M2

8


6

6.733

6.717

112.22 111.95

12,22

11,95

value of εP calculated from the molar ratio method in Section 1.5.2 can be used,

M5

8

7.835

7.893

97.94

98.66

-2.06

-1.34


-5.30

-6.60

regression line is the molar absorption coefficient of the complex.

M8

3

2.894

2.908

96.47

96.93

-3.53

-3.07

1.6.

The results showed that the found concentration of Cu

2+

2+



Moreover, the calculated results proved that the proposed method was suitable
for the simultaneous determination of Cu2+ and Co2+ in complex mixtures.

peak in range 365 - 600 nm. But in the presence of some metal ions, peaks

According to TCVN 5945-2005, the content of copper in industrial waste

occur in the range 375 - 410 nm depending on the metals. Previous studies only

water is not more than 2 mg/l. This shows that this water sample has the content

analyzed individual metals and applied in analysis. These works can be

of copper exceeding the allowed standard above 50%. Therefore, a more

summarized

efficient waste water treatment process is required.

as

follows: Cu(II)-5-BSAT

complex

has

been


PCR

in

Preparation of research solution samples:

Zn(II)–5-BSAT complex. Therefore, the studies of new metal complexes and

Two sets of standard solutions were prepared. The calibration set

further information of cobalt and nickel complexes with 5-BSAT reagent are

contains 11 standard solutions. The concentration of each cation solution was in

necessary. However, their absorption spectra are very close together, so the

the linear dynamic range of the cation, for the preparation of each solution,

studies

different volumes of two cation solutions (0.01 M) were added to 1.0 ml 5-

in

simultaneous

determination

have



the wavelength increases. In appropriate conditions, in the presence of some

After 20 minutes of the solution prepared, the spectra of the solutions

2+

2+

2+

2+

transition metal ions (such as Fe , Cu , Co , Ni ), the solution will appear

were measured in the wavelength range 370-446 nm with 4 nm intervals.

the color and has a peak in the range 360-450 nm. Therefore, the main base of

Comparative solutions were prepared similarly but without metal ion. Save the

the thesis is the use of spectrophotometric method in this wavelength range. On

results in the form of a matrix (8 × 20) and (3 × 20) for training samples and

the other hand, due to the absorption maxima of the metal complexes are very

test samples, and transfer the data into software R 3.3.3 for calculations.

close together, the metals often coexist together in the analytical samples, the

Investigation of interactive signals of 5-BSAT reagent with some metal
ions is performed by investigating the absorption spectra of each system in the

- Establishing two H-point standard addition straight lines:

wavelength range 300 – 700 nm. From the absorption spectra, the absorption

The standard addition analytical samples were prepared when Cu

2+

was

maxima of the reagent and the complexes are identified. Therefore, new formed

added. The absorbances of the solutions were measured at wavelength pair λ1 =

complexes are discovered and the orientation for study in simultaneous analysis

390 nm, λ2 = 419 nm (repeat measurement 3 times).

of metal ions which form complexes with reagent is given.

- Calculating concerntration of Cu(II) and Co(II) ions: The results of

2.2.2. Study the optimum conditions of the complexes

sample analysis are shown in Table 3.38.

After the complexation signals have been found, the optimum conditions


0.987

A390 = 0.038C + 0.662

0.997

A419 =0.014C + 0.550

0.988

A390 = 0.038C + 0.663

0.997

A419 =0.014C + 0.512

0.982

-6

CCu 2 (10 M)

CCo2 (10 M)

5.02

3.46

4.67

3.04± 0.31

2.02± 0.06

2.2.4. Application of H-point standard addition method

and calculated geometrically using IQmol and Q-Chem 4.4 softwares to

In this thesis, H-point standard addition method (HPASM) is used for

This result was compares to the analytical results determined by atomic

simultaneous spectrophotometric determination of Zn(II) and Ni(II) mixtures

absorption spectrometry (AAS) and was shown in Table 3.39.
Table 3. 39. Comparison between experimental contents of Cu2+ and Co2+ in

2.2.5. Application of multivariate regression algorithms PCR, PLS

plated waste water of by HPSAM and AAS method

Ion

Results

by

HPSAM (mg/l)

Results

-5.59

2

Co2+

2.02

2.10

96.19

-3.81

The amounts of metal ions obtained by the proposed methods were in
good agreement with those obtained by AAS (SMEWW 3500-2005).
22

and Cu(II) and Co(II) mixtures in synthetic and real samples.

algorithms runs on R software with programs and packages such as e1071, pls
...
2.3.

Calculation of the results and errors

2.4.

Chemicals and Instruments
7


Recovery

CLT (106 M)

CTN (106 M)

Copper

8.00

7.99±0.11

0.063

0.79

99.90

Cobalt

8.00

7.99±0.08

0.045

0.56

99.91


0.090

1.13

99.58

Cobalt

10.00

9.98±0.13

0.070

0.70

99.83

Copper

10.00

9.98±0.17

0.095

0.95

99.77

H-point

standard

addition

method

in

stable for a long time. Absorbance decreased slightly over a period of 30

spectrophotometric determination of copper and cobalt ions in real

minutes. Therefore, in later studies, absorption measurements were performed

samples

at the range 5 - 20 min after mixing of reagents.

In this condition, the

absorbance of the reagent was also very low and varied negligibly.
* Effect of reagent concentration:
The results showed that, when the amount of reagent is twofold excess
over maximum concentration of Zn(II), the formation of complex gets
maximum. In the following experiments, a concentration ratio of 1:2 is used.

The effects of foreign species on the simultaneous determination of Cu2+
and Co2+ were investigated by measuring the absorbance of the solutions


- Sampling:

at different ranges is linear in the range 2.0×10-6 – 6.0×10-5 mol.L−1 for this ion.
The determined molar absorptivity (ε) for the complex is 1.08×104
L.mol−1.cm−1, LOD and LOQ are 3.26×10-9 M and 1.09×10-8 M, respectively.
8

Samples are taken directly from settling tank of Phuc Thinh Company
Limited, 28B, Nguyen Hien Le Street, Tan Binh District, Ho Chi Minh
21


3.1.3. The composition of complex and its structure

(mg/l)

Ni2+

2.45

2.55

96.08

-3.92

The composition of complex was determined by molar ratio method. The

2+


3.2.1. Studying the complexation of Co(II) ion with the 5-BSAT reagent

for the simultaneous determination of Ni and Zn in complex mixtures.
This shows that this water sample has the content of nickel exceeding the

The results showed that, cobalt ion forms a brown colored complex with

allowed standard many times. The content of zinc in the water is lower than the

5-BSAT reagent. In solution, the complex shows absorption maximum at 405

prescribed standards. Therefore, a more efficient waste water treatment process

nm. The complex is formed after 5 minutes of reaction and stable for 45

is required.

minutes at pH 5.0. The appropriate volume of DMF solvent is 2.5 mL. The

Conclusion: Spectrophotometric method combining the HPSAM

formed complex is a complex with a 1:2 metal:ligand stoichiometry. The

algorithm to simultaneous determination of Ni2+ và Zn2+ gives the relatively

calibration curve of the Co(II) ion measured at different ranges is linear in the

high accuracy and reliable results.



3.2.2. Studying the complexation of Ni(II) ion with the 5-BSAT reagent
The results showed that, nickel ion forms a green colored complex with

of Cu(II) were added.
* Establishing two H-point standard addition straight lines:

5-BSAT reagent. In solution, the complex shows absorption maximum at 378

The absorbances of the H1, H2, H3, H4 mixed solutions were measured at

nm. The complex is formed after 5 minutes of reaction and stable for 30

wavelength pair λ1 = 390 nm, λ2 = 419 nm (repeat measurement 3 times). From

minutes at pH 6.5. The appropriate volume of DMF solvent is 2 mL. The

these values, construct the regression line pairs A = f(CCu added) each range of

formed complex is a complex with a 1:2 metal:ligand stoichiometry. The

solutions for each measurement.

calibration curve of the Ni(II) ion measured at different ranges is linear in the

*Calculating concerntration of Cu(II) and Co(II) ions: Table 3.34

range 2.0×10-6 – 6.0×10-5 mol.L−1 for this ion; LOD and LOQ are 1.07×10-8 M

synthesizes and treats statistically the analytical results of H1, H2, H3, H4


stable for 45 minutes at pH 5.0. The appropriate volume of DMF solvent is 2.5

times. The content of zinc in the water is lower than the prescribed

mL. The formed complex is a complex with a 1:1 metal:ligand stoichiometry.

standards. Therefore, a more efficient waste water treatment process is required.

The calibration curve of the Cu(II) ion measured at different ranges is linear in
-6

-5

Analysis of plated waste water:

−1

the range 4.0×10 – 9.6×10 mol.L for this ion. The molar absorptivity (ε) for
4

−1

- Sampling:

−1

the complex is 1.09×10 L.mol .cm . The Cu(II)-5-BSAT complex is quite
5


mL at rotary vacuum evaporator and the solution was left overnight. The
resulting crystalline compound was filtered, washed with ethanol-dioxane
(V:V=1:1) mixture, and dried in vacuum. Yellow white crystalline product is

C Ni 2 (10-6 M)

C Zn 2 (10-6 M)

8.33

3.63

8.24

3.80

8.47

3.85

Average concentration (mol/l)

8.35 ± 0.29

3.76 ± 0.29

Average concentration of initial sample (mg/l)

2.45 ± 0.09


A399=0.0073C+0.1031

0.9990

A370=0.0159C+0.1362

0.9992

A399=0.0074C+0.1039

0.9991

A370=0.0157C+0.1387

0.9992

A399=0.0071C+0.1054

0.9988

This result was compares to the analytical results determined by atomic
absorption spectrometry (AAS) and was shown in Table 3.27.

coordination with metal ions are –NH2, –C=S, –CH=N, azomethine and –OH

Table 3.27. Comparison between experimental contents of Ni2+ and Zn2+ in plated

phenol. IR spectra of the complex show characteristic bands of OH, NH2 are

waste water of by HPSAM and AAS method


In 5-BSAT molecule, the O atom in OH goup has a high

added. The absorbances of the solutions were measured at wavelength pair λ1 =

electronegativity, so that the free electron pair is held, the -NH2 group has a p-

370 nm, λ2 = 399 nm (repeat measurement 3 times).

resonance effect with the adjacent C=S group, in the 5-BSAT molecule. In

- Calculating concerntration of Ni(II) and Zn(II) ions: The results of
sample analysis are shown in Table 3.22.

pairs on the N atom of the NH group with the C=S group. Thus, it can be

Table 3.22. Analytical results of Ni2+ and Zn2+ mixture in

deduced that the NH2, NH group is not involved or weakly participates in
coordination with the Zn(II) ions because the N atom lacked electrons as a

ceramic waste water
No.

1
2
3

addition, the NH group also has a p- resonance effect between free electron


0.9988

-6

C Ni 2 (10 M)

C Zn 2 (10 M)

7.41

4.32

6.96

4.48

result of the p- resonance.
5-BSAT exhibit a sharp band at 1612 cm-1 due to azomethine linkage
(C=N). In the complex, this band appears at a lower frequency (1600 cm-1) and
has a weaker intensity than that on the free ligand. This clearly indicates the
involvement of N atom in coordination due to a reduction in the electron
density in the azomethine linkage. The absorption at 1064 cm-1 of the C=S

7.40

4.24

vibration in the complex has a change in the absorption frequency, but its

Average concentration (mol/l)

HPSAM
(mg/l)

by

Results
ASS
method

absorption frequencies in both 5-BSAT and complex spectra. However, the
vibration of the O-H bond in the complex has a sharp decrease in intensity, due

by
Recovery

Error

(%)

(%)

(mg/l)

Ni2+

2.13

2.21

96.38

for the simultaneous determination of Ni2+ and Zn2+ in complex mixtures.

1H, –NH2), 8.30 (s, 1H, NH), 8.23 (s, 1H, OH), 8.21 (s, 1H, HC=N), 8.16 (s,
1H, Ar-H), 7.34 (dd, J1 = 8.5, J2 = 2.5 Hz, 1H, Ar-H), 6.83 (d, J = 8.5 Hz, 1H,
Ar-H);

18

11


13

C-NMR (125 MHz, DMSO-d6, δ (ppm): 178.3 (C=S), 156.0 (C–O),

137.7 (CH=N, azomethine), 133.8, 128.8, 123.4, 118.6, 111.6 (5 left aromatic C
atoms)

H2

Mass spectra of the Zn(II)–5-BSAT complex:
H3

[M]+ = 355.0091, [M]+calculated = 354.8969.
Therefore, in the complex, 5-BSAT behave as a tridentate ligand,
coordinating to the central ion through azomethine nitrogen atom, sulphur atom
and phenolic oxygen atom, forming two five- and six-membered heterocycles.
From FT-IR, 1H-NMR and MS spectroscopies, the structures of the
complex is proposed in Fig.3.25.
8


H

5

3

Zn
O

1

O

24

5.00

4.98 ± 0.24

0.096

1.94

99.6

Zinc

10.00


101.0

Nickel

10.00

9.97 ± 0.06

0.025

0.25

99.7

Zinc

10.00

10.05 ± 0.09

0.035

0.35

100.5

Nickel

10.00



standard

addition

method

in

spectrophotometric determination of nickel and zinc ions in real samples
The effects of foreign species on the simultaneous determination of Ni2+
and Zn2+ were investigated by measuring the absorbance of the solutions
containing 2×10-5 M of each metal ion in the presence of various amounts of
other ions. An ion was considered to interfere when its presence produced a
variation in the absorbance of the sample greater than 5%.

The molecular structure of Zn(II)–5-BSAT complex was simulated by

The results show that, Fe3+, Cr3+, Cu2+, Co2+, Cd2+ ions interfered

using IQmol program. An attempt to gain a better insight on the molecular

strongly to complexation of Zn2+ and Ni2+ ions with 5-BSAT when the

structure of the complex, geometric optimization has performed using

concerntration of these ions is less than 1.6-5.0 times of the concerntration of

DFT/B3LYP method as implemented in Q-Chem 4.4. Convergence criteria


Ho Chi Minh City. Then, the sample was safted in a 1 liter of PE bottle, then

lengths of N2-N4 and N2-C6 also indicate the coordination of the azomethine

added about 3 mL of concerntrated solution of HNO3.

nitrogen atom. The bond angles around zinc are between 87.6-113.0°. The bond

- Establishing two H-point standard addition straight lines:

angles around the Zn(II) center (~109.5°) prove that the geometry is tetrahedral.
12

17


atom of the phenolic OH-group. The experimental results show that, the Zn(II)
complex is weaker than Cu(II) and Ni(II) is weaker than Co(II). In complexes

Finally, from the interpretation of spectral data and QM calculations, it is
possible to draw up the tentative structure of the complex (shown in Fig.3.26).

with the same coordinating number of 4, the above rule is consistent with the
decrease in ionic radius from Zn(II) to Cu(II) and Ni(II) (R = 0.60, 0.57 and
0.55 Å ) and gradually increase the electronegativity ( = 1.65, 1.90 and 1.91).
The absorption spectra of the complexes overlap with each other and
cannot well resolved by the traditional procedures using simple calibrations.
This is the base for us to study statistical algorithms to simultaneous analysis of
the multi-component mixtures.
3.4.

Based on the absorption spectra of Ni(II) and Zn(II) complexes, the best

with 5-BSAT reagent. In solution, the complex shows absorption maximum at

pair of wavelengths was λ1 = 370 nm and λ2 = 399 nm when standard solution

381 nm. The complex is formed after 5 minutes of reaction and stable for 30

of Zn(II) were added.

minutes at pH 6.8. The formed complex is a complex with a 1:1 metal:ligand

* Establishing two H-point standard addition straight lines:

stoichiometry. The calibration curve of Zn(II) ion measured at different ranges

The absorbances of the H1, H2, H3, H4 mixed solutions were measured at

is linear in the range 2.0×10-6 – 6.0×10-5 mol.L−1 for this ion. The molar

wavelength pair λ1 = 370 nm, λ2 = 399 nm (repeat measurement 3 times). From

absorptivity (ε) for the complex is 1.08×104 L.mol−1.cm−1. The Zn(II)-5-BSAT

these values, construct the regression line pairs A = f(CZn added) each range of

complex is quite stable with the stability constant of 4.21×105.

solutions for each measurement.



5.00

(106

Standard
6

CTN (10 M)

deviation

CV (%)

S

4.97 ± 0.24

0.095

1.92

3.3.2. Co(II)–5-BSAT complex

Recovery
(%)

99.4

section 3.3.1

and Cu(II) complexes are summarized in Table 3.4.
Table 3.1. Summary of complex study results of 5-BSAT with
Zn(II), Co(II), Ni(II), Cu(II)
Zn(II)–5-BSAT Co(II)–5-BSAT Ni(II)–5-BSAT Cu(II)–5-BSAT

Fig. 3.3. Structure of the Co(II)-5-BSAT complex

3.3.3. Ni(II)-5-BSAT complex
Synthesis of the Ni(II)–5-BSAT complex: The procedure is similar to

λmax (nm)

381

405

378

395

pH

6.5 – 7.0

5.0 – 6.0

6.5 – 7.0

5.0 – 6.0



6.0 ×10-5 M

9.6×10-5 M

1:1

1:2

1:2

1:1

The results show that, the Ni(II)–5-BSAT complex is a complex with a

β

4.21×10

1:2 metal:ligand stoichiometry. The molecular formula of the complex is

ε

1.08×104

Ni(C8H8ON3SBr)2.

(L.mol−1.cm−1)

In the complex, the 5-BSAT reagent behaves as a bidentate ligand,

Ni(II)–5-BSAT is proposed as shown in Fig. 3.29.
Br

The results showed that, in weak acidic media, the 5-BSAT reagent
forms complexes with ion Ni(II), Zn(II), Cu(II) and Co(II) with the maximum

OH
HN
H2N

N

S

NH2

absorbances at 378 nm, 381 nm, 395mn and 405 nm, respectively. The

OH

experimental data showed the formation of a complex with a 1:1 (for Zn(II) and

Ni
S

NH
N

Cu(II) complexes) or 1:2 (for Co(II) and Ni(II) complexes) metal:ligand
Br