Spectral and magnetic properties of phenylazo-6-aminouracil complexes.

Article abstract of DOI:10.1016/S1386-1425(03)00226-9

Complexes of Co(II), Ni(II) and Cu(II) with substituted phenylazo-6-aminouracils containing (-H, p-OH, p-CH(3), p-OCH(3) p-COOH) have been synthesized and characterized by elemental analysis, magnetic measurements and spectral measurements (IR, UV-Vis, ES

Full text of DOI:10.1016/S1386-1425(03)00226-9

Spectrochimica Acta Part A 60 (2004) 77–87
Spectral and magnetic properties of phenylazo-6-aminouracil complexes
Mamdouh S. Masouda,∗, Saeda A. Abou El-Eneinb, Mohamed E. Ayadb, Ahmed S. Goherb
a
Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt
b
Chemistry Department, Faculty of Science, Minufiya University, Shebin El-Kome, Egypt
Received 6 January 2003; accepted 17 March 2003
Abstract
Complexes of CoII, NiII and CuII with substituted phenylazo-6-aminouracils containing (-H, p-OH, p-CH3, p-OCH3 p-COOH)have been syn-
thesized and characterized by elemental analysis, magnetic measurements and spectral measurements (IR, UV–Vis, ESR). Infrared spectra as-
signed the fundamental bands of the major groups, O–H, N–H, C–H, C=O, C=N, N=N, C–N and C–O (␯, ␦and ␥modes of vibrations). The ab-
senceof␯OH andtheappearanceof␯C=O intheinfraredspectraofthefreeligandsof5-(p-tolylandp-anisylazo)-6-aminouracil, assignedtheketo
structure, whereas in cases of 5-(phenyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracil ligands, the data showed strong ␯ and
OH
␯
C=O bands to assign keto–enol tautomerisms. The modes of interactions between the ligands and the metals were discussed, where oxygen and
nitrogen atoms (of amino–amide groups) are involved in chelation. The azo group was not involved in chelation for all the prepared complexes
except those of copper complexes derived from 5-(phenyl, p-tolyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracils. The room tem-
perature effective magnetic moment values, the Nujol mull spectra and ESR provedthat all the prepared complexes were ofoctahedral geometry,
exceptthenickelcomplexderivedfrom5-(phenylazo)-6-aminouracilandcobaltcomplexderivedfrom5-(p-carboxy-phenylazo)-6-aminouracil
were square planar.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Spectra; Magnetism; Structures; Complexes; Azouracil
1. Introduction
Barbiturates display a wide variety of responses in the
body depending on the nature of substituted groups [1–4].
The properties vary from simple sedation to hypnosis, prob-
ably due to the susceptibility of the acidic hydrogen to rapid
metabolic attack and subsequent degradation of the com-
pounds within the body [5–8]. In our laboratory [9–43],
much work has been carried out on the chemistry of such
important biological pyrimidine compounds. In this paper,
the interest is focused to study the chelating properties of
6-aminouracils and their azo compounds based on elemen-
tal analysis, magnetic moments, spectral methods (UV–Vis,
IR) and ESR for copper complexes.
The amines used were aniline, p-aminophenol, p-touldine,
p-anisidine and p-carboxy aniline. The following abbre-
viations are given for the compounds under investigation:
5-(phenylazo)-6-aminouracil (H2L1), 5-(p-hydroxyphenyl-
azo)-6-aminouracil (H2L2), 5-(p-tolylazo)-6-aminouracil
(H2L3), 5-(p-anisylazo)-6-aminouracil (H2L4), 5-(p-carboxy
phenylazo)-6-aminouracil (H2L5).
Eighteen transition metal (CoII, NiII and CuII) complexes
of the stoichiometries 1:1, 1:2, 1:3 and 2:3 (M:L ratio)
were prepared and analyzed. All the complexes were pre-
pared in a similar way as follows: 0.01 mol of the metal
chloride salt in 50 ml ethanol was added to 0.02 mol of
the ligand in presence of 50 ml ethanol. The reaction mix-
ture was refluxed for 2 h. The complex was filtered off,
washed several times with water–ethanol and dried in a
vacuum desiccator over CaCl2 for 1 day. The preparation of
2. Experimental
The azo compounds (I) were prepared by the usual dia-
zotization process [44] of 6-aminouracil.
∗
Corresponding author.
E-mail address: drmsmasoud@yahoo.com (M.S. Masoud).
1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S1386-1425(03)00226-9

78
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
Table 1
Color, elemental analysis, Nujol mull electronic absorption spectra (␭max, nm) and the room temperature effective magnetic moment values (␮eff , 298 K)
Compound
Color
% Calculated (% found)
␮
298 K
␭
max
(nm)
eff
C
H
N
M
Cl
H2L1
Yellow
Brown
Orange
Brown
Brown
Brown
Brown
Brown
Yellow
Yellowish–green
Yellow
Grey
Brown
Brown
Orange
Brown
Yellow
Orange
Orange
Brown
52.0 (51.9)
39.5 (39.4)
44.8 (44.5)
42.4 (42.6)
48.6 (48.5)
38.1 (38.0)
41.1 (41.2)
34.2 (34.0)
53.9 (53.8)
43.1 (43.2)
48.9 (48.8)
40.5 (40.4)
50.6 (50.4)
41.6 (41.5)
38.3 (38.3)
42.6 (42.8)
48.0 (47.9)
36.8 (36.8)
37.7 (37.7)
39.8 (39.5)
3.9 (3.9)
3.9 (4.1)
3.6 (3.4)
3.9 (4.1)
3.7 (3.6)
3.5 (3.4)
3.1 (3.2)
4.7 (4.5)
4.5 (4.3)
4.9 (4.9)
4.1 (3.9)
5.2 (5.5)
4.2 (4.2)
3.7 (3.5)
4.2 (4.2)
5.3 (5.1)
3.3 (3.2)
3.6 (3.6)
4.1 (4.0)
4.2 (4.2)
30.3 (30.2)
22.7 (22.7)
25.5 (25.4)
24.1 (24.0)
28.3 (28.1)
22.2 (22.4)
24.0 (24.0)
14.2 (13.8)
28.6 (28.5)
22.9 (22.7)
25.9 (26.0)
21.5 (21.5)
26.8 (26.7)
22.1 (22.2)
20.4 (20.4)
17.1 (17.0)
25.4 (25.3)
17.9 (17.8)
16.9 (16.9)
18.6 (18.5)
–
–
–
–
–
–
–
–
–
4.9
–
Co–H2L1
Ni–H2L1
Cu–H2L1
H2L2
12.7 (12.6)
10.7 (10.6)
10.9 (10.9)
–
12.5 (12.3)
13.4 (13.5)
12.9 (12.7)
–
6.4 (6.5)
7.2 (7.3)
6.5 (6.3)
–
12.4 (12.3)
8.5 (8.4)
7.8 (7.8)
–
407, 357, 318
586, 435, 316
Diamagnetic
2.52
–
864, 545, 415, 390
–
423, 323, 276, 231
583, 841, 413, 393, 316, 270
583, 503, 432, 318
–
652, 484, 416, 279, 237
469, 412, 287, 600
435, 409, 401, 312
–
401, 296, 279, 244
517, 440, 401, 310, 280, 245
507, 403, 309, 274, 238
–
Co–H2L2
Ni–H2L2
Cu–H2L2
H2L3
Co–H2L3
Ni–H2L3
Cu–H2L3
H2L4
Co–H2L4
Ni–H2L4
Cu–H2L4
H2L5
Co–H2L5
Ni–H2L5
Cu–H2L5
5.2
3.12
2.82
–
5.5
3.15
2.8
–
4.6
3.21
1.54
–
2.5
3.22
0.5
14.4 (14.2)
–
–
–
–
–
–
5.2 (5.0)
8.5 (8.6)
–
–
–
–
15.1 (15.2)
14.2 (14.1)
8.4 (8.3)
468, 410, 354, 322, 276
517, 413, 257, 283
436, 315, 286, 253, 218
All the complexes are with m.p. > 300 ◦C.
5-(phenylazo)-6-aminouracil complexes were prepared in
an ammoniacal-ethanolic medium. The C, H and N analyti-
cal data of the compounds, (Table 1) were carried out at the
central microanalytical laboratory, Chemistry Departments,
Faculties of Sciences, Cairo and Alexandria Universities.
The metal contents were determined by EDTA complex-
ometric titration [45] and atomic absorption technique.
Spectrophotometric measurements were recorded on a
UV–Vis double beam spectrophotometric—ratio recording
Microcomputer Control, Model Lambda 4B, Perkin Elmer
covering the wavelength range 190–850 nm. The spectra of
the ligands solutions at different pHs (2–12) were carried
out. The electronic absorption spectra of the solid com-
plexes were measured in Nujol mull following the method
described by Lee et al. [46]. The KBr infrared spectra of
the ligands and their metal complexes were recorded us-
ing Infrared Spectrophotometer Model 1430 Perkin Elmer,
revealed that the complexes of phenyl, anisyl, tolyl and hy-
droxy ligands have maximum electronic spectral bands at
407, 401, 484 and 423 nm with magnetic moment values 4.9,
4.6, 5.5 and 5.2 B.M., respectively, consistent with the octa-
hedral and pseudo octahedral structures [47]. However, the
5-(p-carboxyphenylazo)-6-aminouracil cobalt complex has
Nujol mull spectral bands at 468 (w.b) and 410 (s) nm with
␮
of 2.52 B.M., to assign square planar structure [48].
eff
3.1.2. Nickel complexes
The analytical data, (Table 1) revealed that these com-
plexes are with the mole ratios 1:1, 1:1, 1:2, 1:3 and 2:3
from 5-(p-carboxyphenyl, phenyl, p-anisyl, p-tolyl and
p-hydroxyphenylazo)-6-aminouracil, respectively. The Nu-
jol mull electronic spectral features gave doublet bands
in the wavelength range 401–496 and 517–583 nm due
3
3
3
3
to A2g→ T1g(p) and A2g→ T1g transitions, respec-
tively, gathered with magnetic moment values (3.15–3.22
B.M.) to assign a high spin octahedral structure [49]. The
covering the range 4000–200 cm−1
.
slightly higher ␮ values above that for the spin-orbit
eff
only arises from slight mixing of multiplet excited state
in which spin-orbit coupling is appreciable [50]. However,
the Nujol mull electronic spectra of the diamagnetic nickel
5-(phenylazo)-6-amino-uracil complex showed bands at
3. Results and discussion
3.1. Stereochemistry of the metal complexes
3
3
435 (w.b) and 586 (b) nm due to A2g→ T1g(p) and
3.1.1. Cobalt complexes
3A2g→ T1g transitions in a square planar geometry [51],
3
The analytical data, (Table 1) gave that the cobalt com-
plexes separated from—(phenyl, p-anisyl and p-hydroxy-
phenylazo)-6-aminouracils are with mol ratio 2Co:3L to give
Co2(HL)2L·nH2O·mC2H5OH, where n=6, 3, 5, m=0.25, 0
and 0, respectively. However, the complexes of (p-tolyl and
p-carboxyphenylazo)-6-aminouracils are with the formula
Co(HL)2H2L·7H2O (1:3) and CoL·2H2O·0.5C2H5OH (1:1),
respectively. The Nujol mull electronic absorption spectra
respectively. The strong band at 316 nm is due to n–␲*
transition.
3.1.3. Copper complexes
The analytical data, (Table 1) gave 1Cu:2L mol ra-
tio for the complexes separated from 5-(phenyl, p-anisyl
and p-carboxyphenylazo)-6-aminouracil compounds with

M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
79
formula: Cu(HL)2·0.5H2O·0.25C2H5OH, Cu(H2L)2·2Cl·
3.5C2H5OH and Cu(HL)2·4H2O·1.5C2H5OH, respectively.
However, the copper(II) complex of the p-hydroxyphenyl-
compound in the 1Cu:1L mol ratio, (Table 1) of the formula:
Cu(H2L)·H2O·2C2H5OH·2Cl. In a similar way, the cop-
per(II) of 5-(p-tolylazo) 6-aminouracil compound having the
formula Cu(HL)2·H2L·10H2O. The Nujol mull electronic
absorption spectra of copper complexes; display the spectral
bands at 309–390, 409–451, 503–583, 683 and 864 nm. The
first band assigned to intraligand charge transfer transition
[50]. The latter four bands are due to complex formation.
The fourth and fifth spectral bands appeared only in the
5-(phenylazo)-6-aminouracil copper complexes, of a square
pyramidal or distorted octahedral configuration of the transi-
derived from p-anisyl- and p-hydroxyphenyl-compounds
gave weak bands centered at 507, 583 and 503 nm with the
presence of strong bands at 403 and 432 nm referring to
the d–d transition of CuII in a tetragonal field [51,52]. The
p-tolyl- and p-carboxyphenyl–copper complexes showed
very weak bands at 401, 409, 435 and broad band at 436
nm, respectively, to typify d–d transition of copper com-
plex in a tetragonal distorted octahedral geometry about
CuII ion. The magnetic moment values of all the prepared
copper complexes are in the range 2.3–2.86 B.M., while
those of p-anisyl and p-carboxy-compounds are with ␮
eff
1.54 and 0.5 B.M., respectively. The higher value is prob-
ably assigned to the absence Cu–Cu interaction and due to
the creation of highly positive centers, e.g. in the form of
alloyed structures. The lower values less than the spin only
2
tion 2Eg→ T2g(D) [51,52]. The prepared copper complexes
Table 2
Fundamental infrared bands (cm−1) of 5-(phenylazo)-6-aminouracil and its complexes
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3420 (b)
3430 (b)
3320 (v.w)
3200 (v.w)
–
3440 (b)
3300 (w)
–
3150 (v.w, b)
3110 (w.b)
3000
2920 (v.w)
2800 (sh)
–
1735 (s.sh)
1695 (v.w)
1630 ( m)
–
1600 (m)
1545, 1535, 1525
1510 (w), 1495, 1475
1450 (w)
1415 (w), 1390
1390
3420 (b)
3300 (m)
–
3160 (sh.w)
3100 (b)
3000
2920 (w.sh)
2840 (b.w)
–
1735 (s.sh)
–
␯
␯
␯
␯
␯
OH
NH
NH
NH
NH
3350 (w)
3280 (w)
3190 (w)
3100 (w)
3040 (sh.w)
2960 (v.w)
2780 (v.w)
1785 (w)
1735 (s.sh)
1720 (w)
1650 (v.s)
–
1585 (m)
1540 (v.w)
1505–1495 (m)
1450 (s) (b)
1420 (s) (b)
1370 (m.sh)
1330 (sh), 1320 (w)
1300 (sh.s)
1260 (sh.s)
–
of amino
of amino
of amide
of amide
–
3060 (w)
2910 (v.w.sh)
–
NH in H.b amide, CH of aryl
NH in H.b amide, CH of aryl
–
1720 (w)
1710 (w)
1665 (w)
1620
1590 (w)
1540, 1530 (w.sp)
1485 (s), 1500 (sh.w)
1450 (w)
1415 (m.b)
1360 (v.w)
–
1280 (v.s)
1280 (sh.w)
1240 (sh.w)
1210 (sh.w)
1160 (sp)
1150, 1135 (sp)
1070 (v.w)
–
1020 (v.w)
1000
900 (v.w)
–
830 (v.w)
–
755 (s.sh)
–
␯
C=O
␯
C=O
1640 (s)
–
␦
␯
␯
␦
␦
␯
␯
of amino
NH
C=N
C=N
1595 (s)
1545, 1550 (sp.w)
1490, 1475 (v.w.sp)
1420 (w)
1415 (v.w)
1380 (sh)
–
1300 (m.sh)
1270 (sp.s)
1240 (sp.s)
1205 (sp.s)
1165 (w)
1140 (w)
1070 (v.w)
1040 (w.sh)
1020
amide
amide
NH
NH
N=N
N=N
C–N amide
–
␦
␦
OH
OH
1300 (m)
1270 (d)
1250 (d)
1205 (d)
1160 (sp.w)
1120 (sp.w)
1070 (v.w)
1040–1020 (sp)
–
995 (w)
950 (w)
880 (v.w)
–
C–N of amino
C–N of amino
C–N of amino
–
1175 (v.w)
1150 (w)
1080 (s)
␯
␯
␯
␯
C–OH
C–OH
C–OH
C–OH
–
1010 (v.w)
990 (v.w)
910 (m.sh)
875 (w.sh)
850 (w.sh)
810 (s)
755 (s.sh)
710 (w)
680 (s)
650 (w)
630 (w)
610 (v.w)
515 (m) (sp)
495 (m) (sp)
410 (s)
Ring vibration
Ring vibration
995 (w)
950 (w.sh)
–
␥
␥
␥
␥
␥
␥
–OH
–OH
N–H
N–H
N–C=O
N–C=O
–
825 (b)
825 (b)-
765 (s.sh)
700 (s)
680 (v.w)
640 (sh)
–
(amino)
(amino)
755 (s.sh)
705 (w)
680 (v.w)
660 (v.w)
–
560 (v.w)
520 (sp)
500 (sp)
440 (b)
690 (s.sh)
670 (w.sh)
655 (w.sh)
570 (v.w)
500 (m.sh)
␥
␥
␳
C–OH
C–OH
570 (s)
510 (sp)
493 (sp)
435 (sh)
(amino)
(amino)
of amide
NH
NH
NH
␳
␳
430 (w.b)
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder; (h.b) hydrogen bonded.

80
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
value (1.73 B.M) indicate magnetic exchange interaction
between adjacent CuII.
ation. More support for the contribution of the nitrogen atom
of the amide group of the ligand on chelation, where strong
␥
(N–C=O) [56] and ␳NH band appeared at {710 (w), 680 (s)}
3.2. Infrared spectra of the metal complexes
and 410 (s) cm−1, respectively. The latter band is shifted
to higher frequency in all complexes. The ␥(N–C=O) bands
changed only in their positions in nickel(II) complex. In the
copper complex, the first band is shifted to lower frequency
by 10 cm−1 and the second band is unaffected. In the cobalt
complex, the first band is absent and the second one is shifted
to higher frequency. The strong ligand azo group bands at
1450 and 1420 cm−1 are shifted from their positions by (30
and 5 cm−1) accompanied with a weak appearance, in cop-
per complex and unaffected in both cobalt(II) and nickel(II)
complexes. So, the azo group is involved in the structural
configuration with CuII rather than NiII and CoII. The 2:3
cobalt complex derived from 5-(phenylazo)-6-aminouracil
exists as octahedral geometry, where two ligands of these
are of tridentate, while the third is tetradentate attachment.
The mainly groups used for chelation with cobalt(II) are
OH, NH of (amino and amide groups). The square planar
and distorted octahedral 1:2 nickel and copper complexes,
respectively, are assigned. The ligand bounds to the metal
via bidentate attachment OH and NH (amide). The infrared
spectra showed that the azo group takes place in chelation
with CuII. The following structures are given as follows:
The infrared spectra of the free 5-(phenylazo)-6-amino-
uracil ligand and its complexes, Table 2, gave that the lig-
and gave strong and weak carbonyl bands at 1735 and 1720
cm−1. The first one is unaffected on complexation with NiII
and CuII and is shifted to 1720 cm−1 with CoII. The sec-
ond one disappeared in copper complex and shifted to lower
frequency (1710 and 1695 cm−1) in presence of CoII and
NiII, respectively. The ligand bands at {1330 (sh), 1320 (w),
1300 (s)} and {910 (m), 875 (w), 850 (w) cm−1} assigned to
␦
OH
and ␥OH, respectively [53]. These bands are absent and
shifted to lower frequencies, respectively, on complexation
with CoII. However, the first and second ␦OH ligand bands
are disappeared, while the third one still remains at the same
positions in NiII and CuII complexes. The ␥OH ligand at 910
cm−1 shifted to 950 cm−1 in CuII and NiII complexes, while
the ligand bands at 875 and 850 cm−1 are absent in the CuII
complex and the second one is absent in NiII complex. The
␯ and ␥ C–OH bands of free ligand at {1150 (w), 1080 (s)}
and {650 (w), 630 (w)} cm−1 are strongly affected on com-
plexation in their shapes and positions [53,54]. The weakly
broad ␯
ligand band at 3420 cm−1 is shifted to lower
OH
frequency by chelation. However, the free ligand exhibits
bands at 3350 (w), 3280 (w); 1650 (s); 810 (s), 515 (m) and
495 (m) cm−1 [55], due to different modes of vibrations of
NH2 group, namely ␯, ␦, ␥ and ␳. On complexation, these
bands show the following remarks: (i) the first ␯ (amino)
NH
band becomes more distinctive and shifted to 3300 cm−1 in
CuII and NiII complexes. The second ␯ (amino) is absent
NH
in copper(II) and nickel(II) complexes. Meanwhile, such re-
gion in cobalt(II) complex appeared at lower frequency with
a very weak feature overlapped with ␯
band in a broad
OH
feature. The presence of six water molecules explained such
broadness; (ii) the ␦NH (amino) ligand band is shifted from
its position and changed in appearance by complexation; (iii)
the ␥NH (amino) of ligand is shifted by 15 cm−1 with some
broadening in case of copper and nickel complexes. In case
of the cobalt complex, this band is absent. So, the NH2 group
is of great importance on chelation with CoII rather than
NiII and CuII. The appearance of broad bands, at 2840 and
2800 cm−1 in copper(II) and nickel(II) complexes are due
to strongly associated hydrogen bonded complexes. The two
weak ␯NH (amide) ligand bands are at 3190 and 3100 cm−1
.
The first one is shifted to lower frequency with very weak
feature in nickel(II) and copper(II) complexes. The second
one is unaffected and shifted to 3110 cm−1 in copper(II)
and nickel(II) complexes, respectively, and becomes more
sharp. However, the ␯ (amide) ligand bands disappeared
NH
in cobalt complexes due to its existence in the enol form.
This is established by the presence of the broad band at 1620
The absence of ␯ and the appearance of ␯
(1805,
OH
C=O
cm−1 due to ␯
in cobalt spectrum. The ␦NH (amide) lig-
1750 cm−1) and ␯
(1170, 1145 cm−1) in the infrared
C=N
C–OH
and bands changed in their positions and shapes by complex-
spectra of 5-( p-tolylazo)-6-aminouracil, (Table 3) assigned

M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
81
Table 3
Fundamental infrared bands (cm−1) of 5-(p-tolylazo)-6-aminouracil and its complexes
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3430 (b)
3180 (b)
3020 (v.w)
2920 (w.sh)
2850 (w.sh)
2800 (w.sh)
1805 (w)
1750 (s)
1625 (s)
1535 (s)
1490 (sh)
1455 (m)
1410 (s)
1395 (v.w.sh)
1300 (w.b)
1260–1275 (b)
1215 (s)
1170 (v.w) (sp)
1145 (v.w) (sp)
1105 (mb)
–
3440–3330 (b.sh)
3210 (s)
3460–3320 (b.sh)
–
–
–
–
3400 (m)
–
␯
␯
␯
␯
␯
(amino)
(amide)
(amide)
NH
NH
3020 (sh)
2920 (sh)
2850 (sh)
2780 (w)
1805 (w)
1740 (s)
1625 (s)
1530 (s)
1495 (sh.w)
1450 (s)
1410 (sp.s)
1390 (sp.s)
1315 (w) 1305 (w)
1260–1270 (w.b)
1210 (m)
1165 (sp) (w)
1145 (sp) (w)
1100 (m)
–
1020 (m)
815 (s)
760 (m)
680 (m)
625 (b)
3010 (sh)
2950, 2900
2830 (w)
2750 (sh.w)
–
1705 (m)
1625 (m), 1570 (w)
1525 (w)
1500 (v.w.sh)
1465 (w.b)
–
1390 (s)
–
1285 (s)
1230 (s)
–
NH
C–H
C–H
–
1805 (w)
–
–
␯
␯
␦
␦
C=O
C=O
(amino), ␯
C=C
(amide)
NH
1530 (s)
1495 (sh.w)
1450 (s)
1415 (sp.s)
1390 (sp.s)
1305 (w)
1260–1270 (b.s)
1215 (s)
1165 (w.sp)
1145 (w.sp)
1100 (m)
–
1020 (m)
820 (s)
760 (m)
680 (m)
625 (b)
530 (s)
475 (m)
415
NH
␯
␯
␦
␦
N=N
N=N
OH
(amide)
C–N
C–N (amino)
C–N (amino)
␯
␯
␯
␯
C–OH
C–OH
C–OH
C–OH
–
110 (s)
1050 (m)
1020 (m)
810 (sh)
775 (m)
670 (m)
625 (s)
545, 515 (sp.m)
–
1020 (m)
825 (s)
760 (s)
675 (w)
635 (b)
535 (s)
470 (m)
–
Ring vibration
␥
␥
Ring bend and C–OH twist (broad)
␥
+ CH out of plane bend
NH
22 + CH out of plane bend
NH
N–C=O
530 (s)
475 (m)
410
␥
C=O
␳
(NH2)
NH
425
–
–
–
355 (w.b)
␳
NH
(amide)
Abbreviations, (s) strong; (m) medium; (w) weak; (v.w) very weak; (b) broad; (sp) splitted; (sh) shoulder.
drogen bonding. In the CuII complex, the ␯
and ␥NH
2
the keto structure. The compared data of the free ligand
and its complexes showed that: (i) the azo group bands of
the ligand (1455, 1410 cm−1) are unaffected in presence of
CoII and NiII. In the case of the CuII complex, the first one
shifted to 1465 cm−1 in a weak broad feature, and the sec-
ond one is absent. So, the azo group is involved in chelation
NH2
and ␯
(amino) bands showed change in the shape and
C–N
the position on complexation (Table 3).
The infrared spectra of complexes deduced that the ligand
is of bidentate attachment through nitrogen atom of amide
and the adjacent oxygen atom in case of NiII and CoII. The
azo group and the oxygen atom in position [4] are involved
in coordination with CuII. So, the NH of amide groups of the
ligand is changed on chelation, i.e. both groups are involved
on chelation, probably due to some intermolecular hydrogen
bond with some water molecules.
with CuII and not in CoII and NiII; (ii) the first ␯
ligand
C=O
band (1805 cm−1) appeared at the same position in presence
of CoII and NiII, and is absent in case of CuII, while the
second ␯
through complexation. The ␯
(1750 cm−1) ligand band showed blue shift
C=O
(1170, 1145 cm−1) and
C–OH
␥
(535 cm−1) ligand bands are unaffected on chelation
C=O
All the measurements suggested the following structures:
to CoII and NiII, but are affected on complexation to CuII.
The data typified that the enolic oxygen is involved in the
structure of the CuII complex. This is confirmed with the
strong band at 1390 cm−1 and the appearance of the new
band at 1050 cm−1, due to ␯C–OH, while the keto form is
more predominant in the NiII and CuII complexes; (iii) the
␯
NH, ␯C–N, ␥N–C=O, ␳ modes of the vibration of ligand
NH
NH amide bands at 3180, 3100, 1300, 635 cm−1, respec-
tively, are affected on complexation with different degrees
in the shape and the position, i.e. the nitrogen atom of the
amide takes place on complexation; (iv) the different modes
of vibrations of NH (amino) ligand bands of free ligand are
unaffected on complexation with CoII and NiII, except the
␯
NH
appeared in a broad shoulder, possibly due to the hy-

82
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
(s) cm−1}, respectively, are blue-shifted on complexation
except the 1480 cm−1 band is red-shifted. The ␯
lig-
C–N
and amide band (1370 cm−1) is blue-shifted by 20 cm−1
in a very weak feature. In general, all data pointed that
both nitrogen (amino and amide) and oxygen atoms are
active sites for complexation. The weak splitted bands at
1435, 1415 cm−1 assigned the azo group in the free lig-
and not involved in chelation. The presence of a band at
1395 cm−1 assigned to ␦OH through hydrogen bond with
azo group. So, the following structures could be deduced
as follows:
The infrared spectra of the 5-( p-anisyl-azo)-6-aminouracil
acid complexes, (Table 4) gave the keto tautomer is pre-
dominant for this ligand assigned by the absence of ␯
OH
and the presence of keto bands at (1870, 1740 and 1680
cm−1). The 1870 cm−1 ligand band is absent in all com-
plexes. The strong ␯ and ␥ C=O ligand bands at 1740,
1680 and 515 cm−1, respectively, are affected with dif-
ferent degrees on complexation (Table 4). Similarly, the
␦
OH
(1325, 1300 cm−1), ␥OH (885 cm−1) and ␥C–OH (635
cm−1) ligand bands revealed the change in their positions
and shapes on chelation. The infrared spectrum of lig-
and reveals the ␯, ␦, ␥ and ␳ NH (amino) at 3440 (w),
{1635 (s) and 1590 (w)}, 855 (w) and 440 (m) cm−1. The
first band is absent in nickel complex and blue-shifted by
40 cm−1 in CuII and still remained at the same position
in CoII with change in feature. The second and fourth
bands are blue-shifted in all complexes. The third band
is absent on chelation. The broad ␯
and ␦NH (amide)
NH
ligand bands at (3210–3250 cm−1) and {1535 (m), 1480
Table 4
Fundamental infrared bands (cm−1) of 5-(p-anisylazo)-6-aminouracil and its complexes
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3440 (w)
3210–3250 (sp)
3070 (w)
2930 (w)
2840 (w)
2790 (w)
1870 (m.b)
1740 (s)
3440 (sh.w)
3180 (b)
3020 (sh.w)
2950 (sh.w)
2825 (w)
2780 (sh.w)
–
1730 (sh)
1710
1620 (s)
1580 (sh.w)
1525 (b.m)
1495 (m)
1445 (w)
1415 (w)
–
3400 (v.w.b)
3180 (b)
␯
␯
of amino
of amide
NH
NH
3200 (s)
3010 (sh.w)
2950 (sh.w)
2850 (w)
2770 (w)
–
3020 (sh.w)
2910 (sh.w)
2825 (w)
2780 (sh.w)
–
1740 (v.w.sh)
1710 (w)
1620 (s)
1585 (sh.w)
1525 (b.m)
1495 (m)
1450 (w)
1415 (w.b)
NH in hydrogen bond
CH of aryl
CH of OCH3
CH of OCH3
Diketone
1755 (s.w.b)
–
␯
C=O
1680 (s)
1635 (s)
␯
C=O
1620 (s)
1585 (sh.w)
1525 (m)
1495 (s)
1445 (w)
1415 (w)
␦
␳
␦
␦
␯
␯
of NH2
NH
NH
NH
NH
1590 (w)
1535 (m)
1480 (s.b)
1435 (sp.w)
1415 (sp.w)
of amino + C=C
of amide
of amide
N=N
N=N

M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
83
Table 4 (Continued )
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
–
1395 (w)
1350 (sh.w)
1345 (v.w.sh)
1305 (sh.w)
1285 (v.w)
1240 (s)
1210 (m)
1170 (m)
1145 (m)
1100 (m)
1020 (s)
930 (sh.w)
–
1395 (w)
1350 (sh.w)
1345 (v.v.w.sh)
1305 (w.sh)
1285
1240 (s)
1210 (m)
1170 (m)
1145 (m)
1100 (s)
1020 (s)
930 (sh.w)
–
1395 (w)
1350 (sh.w)
–
1305 (w.sh)
1285
1245 (s)
1210 (m)
1175 (m)
1145 (m)
–
1020 (s)
930 (sh.w)
–
␦
␯
␦
␦
␯
␯
␯
␯
␯
␯
OH
1370
of amide
C–N
OH
1325 (w)
1300 (s)
1260 (v.w.sh)
1240 (s)
1200 (w.sh)
1175 (v.s)
1115 (w)
1100 (s)
1020 (s)
985 (sh.w)
885 (s)
855 (w)
825 (s)
775 (v.w)
765 (s)
680 (sp.w)
670 (sp.w)
635 (v.w.sh)
515 (v.s)
480 (w)
440 (m)
415 (w)
390 (sh.w)
–
OH
of amino
of amino
of amino
C–N
C–N
C–N
C–OH
C–OH
C–OH
␥
␥
␥
␥
␥
OH
OH
NH
NH
NH
–
–
–
of NH2
of NH2
of NH2
825 (s)
780 (w)
755 (s.b)
–
670 (m)
615 (s.b)
530 (v.s)
475 (m)
430 (w)
405 (w)
–
825 (s)
830 (s)
–
755 (s.b)
–
670 (w)
615 (b)
530 (m)
475 (w)
430
410, 405 (sh)
395 (v.w)
350, 340 (sp.w)
780 (w)
755 (s.b)
–
670 (m)
610 (s.b)
530 (v.s)
470 (m)
430 (w)
405 (w)
–
C–H out of plane
␥
␥
␥
␥
␥
C–OH
C–OH
C–OH
C=O
C=O
␳
␳
amino
amino
NH
NH
–
350 (sh.w)
M–Cl
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
However, the ␯
of 5-(p-hydroxyphenylazo)-6-amino-
are tautomerised to the enol skeleton where one of them is
utilized for chelation. This is supported by the presence of
C=O
uracil ligand bands at 1750 (w), 1720 (w), 1705 (s) and 1690
(m) cm−1 are affected on chelation with different degrees.
Only one carbonyl group is affected on chelation with CuII,
while in presence of CoII and NiII, the two carbonyl groups
␯
at 3500 cm−1 in cobalt and nickel complexes. The data
OH
for the ␥C=O, ␦OH, ␥OH and ␯
typified that the oxygen
atom is a center for complexation (Table 5).
C–OH
Table 5
Fundamental infrared bands (cm−1) of 5-(p-hydroxyphenylazo)-6-aminouracil and its complexes
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
–
3500 (w)
3420 (m)
3280 (sh)
3190 (sh), 3110 (w)
3000 (w)
2910 (sh.w)
2880 (sh w)
2840 (sh)
2770 (w)
–
3500 (w)
3420 (m)
–
3120–3180 (b)
3000 (w)
2910 (sh)
2880 (sh w)
2840 (sh)
2760 (w)
–
–
␯
␯
␯
␯
OH
3400 (s)
3400 (s)
3330 (sh)
3120–3180 (b)
3050 (sh)
2960 (sh)
2900 (sh)
2830 (sh)
2760 (sh.w)
–
(amino), ␯
phenol
OH
NH
3310 (sh)
3120–3180 (b)
3050 (sh.w)
2960 (sh)
2900 (sh)
2830 (w)
2760 (w)
1750 (w)
1720 (sh.w)
1705 (m)
1690 (sh.w)
1670 (v.w)
1630 (m)
1590 (w)
1510 (m)
1460 (m)
1430 (w)
1395 (s)
NH=amino
NH
amide
CH-aryl
CH-aryl
␯
C=O
C=O
C=O
C=O
–
–
–
␯
1705 (sh.w)
1690, 1675 (sp.w)
–
1620 (m.b)
1580 (v.w)
–
1460 (w)
1400 (w)
1375 (s)
–
1705 (v.w.sh)
1690, 1670 (w.sp)
–
1620 (m)
1580 (v.w)
–
1460 (w)
1400 (w)
1375 (s)
–
1705 (m)
1690 (v.w)
–
1625 (m)
1580 (sh.w)
1510 (w)
1465 (m)
–
␯
␯
␯
C=C
␯
␯
␦
␦
␯
␦
␦
(NH2)
(NH2)
amide
amide
NH
NH
NH
NH
N=N
OH
1395 (s)
–
1290 (s)
(enol, phenol)
1310 (w)
1280 (v.s)
OH
1290 (s)
1290 (s)
C–N amine and ␦OH of phenol

84
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
Table 5 (Continued )
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
1235 (s)
1230 (b.m)
1120 (m)
–
1060 (w)
1015
1230 (b.m)
–
1115 (m.b)
1060 (w)
1015 (w)
–
1235 (s)
C–N amine and ␦OH of phenol
1140 (sp.m)
1110 (sp.m)
1050 (m)
1015 (v.w)
985 (v.w)
825 (w)
770 (s)
760 (v.w.sh)
715 (w)
680 (v.w), 665 (v.w.sp)
650 (w.sh)
625 (m)
545 (sp.s)
515 (sp.s)
425 (w)
1165 (w.b)
1115 (m)
1055 (m)
1020 (w)
985 (w)
␯
␯
␯
C–OH
C–OH
C–OH
Ring vibration
Ring vibration
–
850 (sh)
780 (sp.s)
765 (sp.s)
725 (w.b)
675 (s)
–
625 (s)
550 (w) (s) (sp)
515 (w) (s) (sp)
450 (b)
–
850 (s)
845 (b)
␥
␥
␥
␯
OH
NH
NH
780 (sp.s)
765 (sp.s)
725 (w.b)
675 (s)
775 (sp.w)
765 (sp.w)
715 (w)
675, 685 (sp.w)
–
(NH2)
(NH2)
amide
NH
␦
␦
␯
–C–OH
–C–OH
N–C=O
–
625 (s)
625 (s)
550 (w) (s) (sp)
515 (w) (s) (sp)
450 (b)
–
545 (sp.s)
515 (sp.s)
470 (sh.w), 430 (sh.w)
350 (s)
␥
␥
C=O
C=O
␳
amino
NH
–
M–Cl
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
The ␯, ␦, ␥ and ␳ and NH (amino) ligand bands are
affected in position and shape on complexation with CoII
and NiII. However, these bands are unaffected in presence
of CuII. So, according to these data the nitrogen atom is
involved for structural configuration in both cobalt and
nickel complexes. Such conclusion is not valid in the cop-
per complex (Table 5). The ligand broad ␯
(amide)
NH
bands at 3120–3180 cm−1 are shifted from its position in
the cobalt complex. However, this band still remains at
the same position in the nickel and copper complexes. The
␦
NH
(amide) bands at 1510 (m) and 1460 (m) cm−1 are
affected by complexation in CoII, NiII and not changed in
CuII. The ␥NH (amide) of ligand at 715 cm−1 is red-shifted
by 10 cm−1 with a broad nature in cobalt and nickel com-
plexes and not affected in copper complex. So, the nitrogen
atom (amide) is involved on chelation with CoII and NiII
only. The ␯
at 1430 cm−1, is absent in presence of
N=N
CuII and blue-shifted by 30 cm−1 in the cases of NiII and
CoII. The ␦OH (1395) cm−1 is shifted to 1375 cm−1 in
CoII and NiII assigned to hydrogen bond with azo group
[54]. The 2:3 cobalt and nickel complexes are in an oc-
tahedral geometry, where two ligands of the three are of
tridentate attachment, while the third is pentadentate attach-
ment. For the 1:1 octahedral copper complex, the ligand
is of bidentate geometry using azo and one of carbonyl
groups.
The 5-(p-carboxyphenylazo)-6-aminouracil, (Table 6)
gave strong bands at 3480 and 1720 cm−1 for ␯
and
OH
␯
[55], respectively, i.e. keto–enol structure. The ␯
,
C=O
OH
␯C=O, ␥OH, ␥C=O and ␯
ligand bands are affected with
C–OH
different degrees on complexation. So, the oxygen atom is
considered for complexation. The ligand ␯ (amino) at
NH
3230 cm−1 remains at the same position in the copper com-
plex and red-shifted by 10 cm−1 with weak nature in the
nickel complex and is absent in cobalt complex. Meanwhile,
the strong ␦NH (amino) ligand band is absent in presence of
CoII and not changed in the NiII and CuII cases. The strong
␥
(amino) Bands of the ligand at 795 and 770 cm−1 are
NH
of weak splitted nature became at 775 and 760 cm−1 in
cobalt complex. The first band is only affected in nickel and
copper complexes. The data depicted that the amino group

M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
85
Table 6
Fundamental infrared bands (cm−1) of 5-(p-carboxyphenylazo)-6-amino-uracil and its complexes
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3480 (b.s)
3230 (b.m)
3140 (sh.w)
3100 (sh.v.w)
3030 (w)
2920 (sh.v.w)
2810 (w)
1720 (sharp)
–
1645 (sp)
1630 (sp)
1590 (m.sharp)
1545 (s.p)
1485 (v.w), 1465 (m)
1415 (sharp)
1385 (sharp)
–
1265 (b.m)
1215 (w)
1160 (w)
1105 (w)
1095 (w)
1025 (v.w)
1000 (v.w)
–
3440 (b)
–
3160
3380, 3440 (w.b.sp)
3240 (sp.b)
3180
–
–
3420 (w.b)
3230 (m)
–
␯
␯
␯
␯
OH
NH
NH
NH
(amino)
(amide)
(amide)
–
–
3020 (sh)
2920 (sh)
2840 (sh)
1730
1710 (sh.w)
1670 (v.w.sh)
1625 (s)
–
1545 (s)
1480 (w), –
1410 (w)
1380 (m.b)
1290 (sh)
1255
1210 (w)
1165 (s)
1100
3020 (sh.w)
2920 (v.w)
2840 (v.w)
1720–1735
–
1660–1690 (b)
1625 (sh.v.w)
1590 (v.s)
1545
1495 (s),–
1430, 1410 (w.sp)
1390 (w)
1300 (s)
1260
1225 (s)
1155 (sharp)
1125 (m)
1100 (w)
1040 (v.w)
1000 (v.w)
960, 920 (v.w)
840–820 (b)
–
Aryl
Aryl
␯
␯
2920
2840
of COOH
OH
1740 (m)
1705 (sh.w)
1665 (m)
1610 (sh.w)
1590 (m)
1545 (s)
1500 (sh.w), –
1410 (w)
1395 (m.b)
1290 (sh.w)
1265
C=O
␯
␯
C=O–COOH
C=C
␥
of NH2
NH
␯as COO
␥
␯
(amide)
NH
N=N
␯
␦
␦
COOH, C-N
SY
OH
OH
–
C–N (NH2)
C–N (amide)
␯
␯
␯
1155 (b)
1100
–
C–OH
C–OH
C–OH
–
–
–
1005 (w)
–
1010 (w)
–
840–815 (b)
–
780 (sh.v.w)
770 (m)
705 (w)
–
660 (sh.w)
605 (m)
–
Ring vibration
850 (s)
825 (v.w)
795 (m)
770 (s)
705 (w)
845 (w)
815 (w)
775 (sp.w)
760 (sp.w)
700 (m)
–
650 (w.b)
605 (sh.b)
550 (sh.w) 520 (m)
550 (sh.w) 520 (m)
475 (w)
430 (s)
␥
␥
␥
␥
␥
␥
␥
␥
OH
OH
–
NH
765 (m)
NH
720 (w) (sp)
695 (w) (sp)
650 (m)
580 (s)
550 (w)
520 (w)
490 (s)
420 (s)
C–OH
C–OH
O–C=O
N-C=O
680 (w)
655 (v.w.sh)
615 (b.m)
555 (w)
520 (w)
480 (w)
520 (m)
475 (w)
430 (s)
␥
␳
C=O
430 (w)
(amide)
NH
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
is strongly contributed with CoII and not with CuII and NiII
complexes. The ␯
and ␦NH (amide) ligand bands are at
NH
{3140, 3100} and 1485 cm−1, respectively [56].
The data pointed to the following structure:
3.2.1. Electron spin resonance of copper complexes
The ESR spectral pattern of (p-tolyl, p-anisyl and
p-carboxyphenylazo)-6-aminouracil copper complexes,
(Table 7), gave anisotropy natural with axial compressed
and 2.11, respectively, g =2.05, 2.05 and 2.03, respec-
⊥
symmetry, where g > g > ge (free-electron spin 2.003)
tively. The calculated ꢁgꢂ=(g + 2g )/3 are 2.11, 2.12 and
ꢀ ⊥
ꢀ
⊥
indicating a dx2−y2 ground state in an octahedral geometry
[57]. These complexes gave two g-values: g =2.23, 2.26
2.06, respectively. Deviation of ꢁgꢂ from that of free electron
(2.0023) suggests the high covalence property of these
ꢀ

86
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 77–87
Table 7
ESR parameters for copper(II) 5-(p-substituted phenylazo)-6-aminouracil complexes
2
Substituents
ESR parameters
A
–
A
–
␣
f2
ꢀ
⊥
g
g
gs
ꢁgꢂ
G
ꢀ
⊥
5-(Phenylazo)-6-aminouracil
–
–
2.05
–
–
–
–
5-(p-Tolylazo)-6-aminouracil
5-(p-Anisylazo)-6-aminouracil
5-(p-Carboxyphenylazo)-6-aminouracil
2.23
2.26
2.11
2.05
2.05
2.03
–
–
–
2.11
2.12
2.06
4.60
5.20
3.66
225.0
225.0
185.00
20.00
25.00
18.50
0.91
0.94
0.67
1.00
1.44
0.98
complexes with distorted symmetry [58].
decrease the contact hyperfine interaction. Therefore, if the
4s-character in the ground state is known, it is possible to
know the axial field strength. In the presence of a small
percentage of 4s-character in the ground state, the fraction
of the 3d-character in the CuII 3d–4s ground state, f, can be
determined from the following equation [63]:
The g and hyperfine coupling constant (A) components
indicate dynamic tetragonal distortion for (dx2−y2 ground
state) [59].
The g value in copper(II) complexes can be used as a
ꢀ
measure of the covalent character of metal–ligand bond [60].
If this value is more than 2.3, the environment is essentially
ionic, but if it is less than this limit, assigned the covalent
ꢀ
ꢁ
7
4
A
A
2
3
5
6
7
||
␣2f2 =
−
+
g −
||
g −
⊥
0.036 0.036
21
environment. The g values of these complexes show con-
ꢀ
siderable mixed ionic–covalent character.
The f2 values for the previous complexes are 1.0, 1.44
and 0.98, respectively.
The g-values are taken to calculate the exchange inter-
g −2
||
action [61]: G=g
. If G > 4, the local tetragonal axes
The corresponding equation for obtaining ␣2 from the
isotropic A value is:
⊥−2
are aligned parallel, or only slightly misaligned, i.e. the
exchange coupling is negligible, and if G < 4 significant
exchange coupling is present, (considerable interaction in
the solid complexes occurs). The G value of 3.66 for the
p-carboxy–copper complexes leads to spin exchange inter-
action between CuII ions in the solid state. The p-tolyl
and p-anisyl, complexes are with G=4.6 and 5.2, respec-
tively, to assign tetragonal distortion geometry [61]. The
ESR spectrum of the p-anisyl complex showed some broad-
ness, due to the presence of some polymeric nature. This
|A|
g − 2.0023
␣2 =
+
PK
K
where P is the free-ion dipole term proportional to 1/r3 and
is given a value of 0.036 cm−1, K is the Fermi constant term
and is usually given a value of 0.43 [63].
The ␣2 value for 5-(phenylazo)-6-aminouracil copper
complex is 0.918. The values of ␣2 of the mentioned cop-
per complexes prove that these complexes are in tetragonal
distorted structures and the ligands behave as nitrogen and
oxygen donors [65,66] through chelation.
is convenient with ␮ 1.6 B.M. The ESR spectrum of
eff
the 5-(phenylazo)-6-aminouracil copper complex shows an
isotropic behavior with g=2.05. The spectrum is character-
istic of dx2−y2 octahedral geometry around CuII ion with
covalent bond [55].
It is possible to measure the ␴-bond parameter, ␣2, where
␣ is the coefficient of the ground state dx2−y2 orbital, from
the approximate expression [62–64]:
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