--~.---.- -
- - - - - --
-
--
1397
The Complexes of 1-(5-Tetrazolylazo)-2-naphthol
M2+
+
H2L
M 2+
+
Hl -
Ml
+
H2l
Ml
+
Hl -
Ml
+ 2 H+
~-
Ml
+
~--
Ml ~ -
~- -
Ml~ -
+
~
--
;
Ki(211)
(8)
Ki( ~1)
(C)
+ 2 H+ ;
Ki(H1)
(D)
H+ :
Ki(H) ·
(E)
H+ ;
or
Because the values of the dissociation constant of the reagent (pK" I = 2·97 ; pKa2 =
= 9 ·85, see 2), reaction schemes (8) and (D) are valid at pH* ;;:;; 2, where the form
H2L is primarily present, and schemes (C) and (D) hold for pH* ~ 4. In the pH'"
region 2 to 4 it can be assumed that the two reactions occur simultaneously - see, for
example, the composition of a solution of nickel(I1) complexes depicted in Fig. 4.
Reaction (D) practically does not occur because of the stability of complex Ml2
and complex ML2 is formed at pH* > 3 primarily through reaction (E) (Fig. 4).
Equi librium constants K:(qH) are related to stability constants [3" by the expressions
[31
= Ki(2H)K;;/K;:2
/32 = [3I K iIH)K;:2
1
= Ki(H)K;2
1
1
pH"
FIG. 4
A- pH- Curves for the H2L Solution in the Presence of Ni 2 + and Changes in the Concentrations of Individual Species
cNi = 2·534. 10- SM, c L = 2·526. 1O-4M , 530 nm, 1 cm 10·1, 10% ethanol; curve 1 calculated shape of the A = [(pH-) dependence (left-hand scale); curves M, ML, ML (right-hand scale).
Collection Czechoslov. Chern . Commun. [Vol. 43J [1978J
1398
Suchanek, Siicha :
K:
The calculated values of constants (1" and
and their confidence limits, calculated
from the average values determined at various metal - to - ligand ratios are given
in Table II.
Comparison of the complexing properties of the studied reagent H2L with the
properties of similar heterocyclic azoderivatives, i.e. pyridylazonaphthol (PAN)
or thiazolylazonaphthol (TAN), which can be carried out, for example, for copper
complexes, indicates the direct correlation between the basicity of the ligand (and the
corresponding heterocycles 2) and the stability of the complexes. The ligand basicity
and the stability of the copper(ll) complexes increases in the order TAN < L 2- <
< PAN (Table III). It follows from comparison of the spectral properties, characterized by the Am •• and emax values of the copper complexes and the corresponding
values of the molar absorption coefficients e if the H 2L and PAN reagents, that
1-( 5-tetrazolylazo )-2-naphthol has certain advantages for use as a metallochromic
indicator4. The smaller effect of the pH on the stability of the complexes of the H2L
TABLE II
The Equilibrium Constants and Spectral Characteristics of the Studied Complexes of 1-(5-Tetrazolyl)azo-2-naphthol (H 2 L)
10% wt. Ethanol, 20°C, 10·1.
P2
)'j4
)'max
smax
nm
1 mol- 1 cm- 1
. 0·9 b
3'9c
530
13 300 ::t.
0·06
b
-2'3
0'6c
-O'l d
492
520
15300 ± 750
17100 ± 1200
28500 ± 400'
455-457
Zn
8·20 ± 0·06 15·10 ± 0·1 8
-1 ·6c
- 2.94
510
18200±2800
22 800:!:: 1 20o!
463-465
Cd
7·50
-2·3 c
-3'1 4
510
100
18300 ±
17700 ± 1800f
465
Mn
5·96 ± 0·18
-3'8c
510
16900± 1200
470
Pb
8·37 ± 0·15
-1 ' 5c
510
14600 ± 1800
470
Bi e
14·13 ± 0·12
1'3 b
525
100
465
Metal
Cu
Ni
log
13·70
±
10·48
±
±
PI
log
0·07
0·06 20·17
±
0·14 14·20 ± 0' 36
log
KII(qH)
9900±
800
nm
470- 485
1 wavelength of the isosbestic point, b equilibrium constant of the reaction according to (B),
equilibrium constant for reaction (C); d equilibrium constant for reaction (E), e values of the
equilibrium constants and molar absorption coefficients are valid for I 1, f valid for the 1 : 2
complex at 530 nm.
a
C
Coliection Czechoslov. Chern. Commun. [Vol. 43] [19781
--------------------------------------------------- -----------
1399
The Complexes of 1-(5-Tetrazolylazo)-2-naphthol
reagent (because of its greater acidity) and the greater solubility (in water) of the
tetrazolyl derivative and its complexes compared with the pyridyl derivative and its
complexes also have a favourable effect. These properties were employed in developing method for determining Bi 3 +, Cu 2 +, Zn 2 + and Nj2 + by direct chelometric titration with visual or photometric indication , and displacement titrations of Pb 2 +,
Co 2 +, Cd2+, Fe3+ , AI3+ a nd Sc3+ employing the copper complex of the H2L
reagent J 3, resp.
TABLE
III
Comparison of the Properties of the Copper Complexes of Some Heterocyclic Azo Derivatives
.- --- -----
--.- - -----
Reagent
10g PI
)'1110'
nm
em" .10- 4
I mol'- I .
. cm - I
_._--_.-------_ ..
.- _
PAN a
/7·0
550
:M8
TAN b
I 1· 8
578
580
3"-2
530
1·33
H 2 Lc
13·7
t;.)..d
Comments
nm
_--
..
--.
---
125 (H 2 L+)
80 (HL)
60 (L -)
ref. 14
reL I5
ref. 1 6
130 (H 2 L)
70 (HL-)
40 (L 2 -)
this work
-- log (K. ,K. 2 ): a 14' 1, b 10·8. c 12'8, d the difference in the wavelengths of the maximum of the
copper complex and that of the given acid-base form of the reagent.
REFERENCES
I. Sucha L., Suchanek M ., Cinatlova H.: Proc. XVth Int. Conf. Coord. Chem., p. 531, Moscow
1973.
2. Suchanek M., Sucha L.: Sb. Vys. Sk. Chemicko-TechnoL Praze H10, 39 (1974).
3. Cinatlova H., Sucha L., Suchanek M .: Sb. Vys. Sk. Chemicko-TechnoL Praze HlO, 75 (1974).
4. Cinatlova H ., Sucha L.: Sb. Vys. Sk. Chemicko-Technol. Praze H12, 105 (1977) .
5. Suchanek M., Cinatlova H., Sucha L.: Sb. Vys. Sk. Chemicko-Technol. Praze HI 2, 119 (1977).
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II. Suchanek M., Sucha L.: Sb. Vys. Sk. Chernicko-Technol. Praze HJ3, in press.
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1400
Suchanek, Sucha
12. Sommer L., Kuban V., Havel J. : Folia Fac. Sci. Nat. Univ. Purkynianae Brunensis, Chemia 7,
Vol. XI, Op. 1, 3 (1970).
13. Suchanek M., Cinatlova H. , Sucha L.: Sb. Vys. Sk. Chemicko-Techno!. Praze H 12. 119 (1977).
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16. Wada H., Nakagawa G .: Nippon Kagaku Zasshi 83, 1185 (1962).
Translated by M. Stullkovoi.
Collection Czechosloy. Chern. Commun. [Vol. 431 [19781
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