Azo complexes of Cu(II), Co(II), Ni(II), Cd(II), Th(IV), and UO 2(VI) ions. Mixed-ligand complexes, pyrolysis products and biological activity

Article abstract of DOI:10.1081/SIM-200026204

The reactions of azo ligand, 2-[2′-carboxyphenylazo]-5,5-dimethyl-1, 3-cyclohexane-dione, (H₂L), with the metal ion Cd(II), Cu(II), Ni(II), Co(II), Th(IV), or UO₂(VI) in the presence of LiOH as a deprotonating agent, yielded binary m

Full text of DOI:10.1081/SIM-200026204

SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 8, pp. 1349–1378, 2004
Azo Complexes of Cu(II), Co(II), Ni(II),
Cd(II), Th(IV), and UO2(VI) Ions.
Mixed-Ligand Complexes, Pyrolysis
Products and Biological Activity
*
Mahmoud M. Mashaly, Atef T. Ramadan,
Basheir A. El-Shetary, and Areej K. Dawoud
Department of Chemistry, Faculty of Education,
Ain Shams University, Roxy, Cairo, Egypt
ABSTRACT
The reactions of azo ligand, 2-[20-carboxyphenylazo]-5,5-dimethyl-1,3-
cyclohexane-dione, (H2L), with the metal ion Cd(II), Cu(II), Ni(II),
Co(II), Th(IV), or UO2(VI) in the presence of LiOH as a deprotonating
agent, yielded binary mononuclear complexes. The binary Cu(II)
complex reacts with the ligands 1,10-phenanthroline or 2-aminopyridine
to form mixed-ligand complexes. All the binary complexes of Cd(II),
Cu(II), and Ni(II) have octahedral configurations, while the Co(II)
complex is square-planar. The binary complexes of Th(IV) and
*
Correspondence: Mahmoud M. Mashaly, Department of Chemistry, Faculty of
Education, Ain Shams University, Roxy, Cairo, Egypt; E-mail: mashalym@hotmail.
com.
1349
DOI: 10.1081/SIM-200026204
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Mashaly et al.
UO2(VI) have distorted dodecahedral geometries. The mixed-ligand
complexes have octahedral configurations. Thermal studies on these com-
plexes showed the possibility of obtaining new complexes pyrolytically,
where the complexes decompose through several isolable as well as non-
isolable intermediates during heating. The structures of all complexes and
the corresponding thermal products were elucidated by elemental ana-
lyses, conductance, IR and electronic absorption spectra, magnetic
moments, 1H NMR and TG–DSC measurements as well as by mass spec-
troscopy. The ligand and some of the complexes were found to activate
the enzyme pectinlyase.
Key Words: Azo complexes; Mixed-ligand; Pyrolysis; Biological
activity.
INTRODUCTION
The widespread application of azo compounds and their metal chelates as
dyes, acid–base redox indicators, metallochrome, and histological stains have
attracted the interest of many investigators.[1–5] The sulfonated dye congo red
(CR) is clinically useful as a histological stain for amyoid, as well as an HIV
protease and reverse transcriptase inhibitor. CR has been shown to inhibit the
conversion of the “good” form of scrapie prion protein to the “bad”. The CR
crystal structure as well as a model far its complex with HIV protease have
been described.[6]
Azo dyes exhibit strong pharmacological activities and are also used for
dyeing food stuff and preserving food grains.[7,8] Pectinlyase is one of the pec-
tinases which is a group of enzymes used in fruit and textile industries.[9]
These enzymes break down complex polysaccharides of plant tissues into
simpler molecules like galacturonic acid. The role of acidic pectinases
in bringing down the cloudiness and bitterness of fruit juices is well
established.[10] Recently, there has been a good number of reports on the appli-
cation of alkaline pectinases in the textile industry for the retting and degum-
ming of fiber crops, production of good quality paper, fermentation of coffee
and tea, oil extractions, and treatment of pectic waste water.[10]
In this paper, we report the synthesis and characterization of binary
complexes of 2-[20-carboxyphenylazo]-5,5-dimethyl-1,3-cyclohexanedione
(H2L) Fig. 1, with the transition metal ions Cd(II), Cu(II), Co(II), and
Ni(II) and the actinide metal ions Th(IV) and UO2(VI). Also described
are mixed ligand complexes of Cu(II) ion with H2L and 2-aminopyridine
(2-ampy) or 1,10-phenanthroline (1,10-phen). Thermal studies explored
the possibility of obtaining new complexes which cannot be prepared
from solutions.

Azo Complexes
1351
Figure 1. Structures of 2-[20-carboxyphenylazo]-5,5-dimethyl-1,3-cyclohexanedione
(H2L), 2-aminopyridine (2-ampy), and 1,10-phenanthroline (1,10-phen).
EXPERIMENTAL
Materials
All chemicals used in the present investigation were from BDH, Analar or
.
Merck and included Cd(NO3)2 4H2O, Cu(NO3)2 H2O, Ni(NO3)2 6H2O,
.
.
.
Co(NO3)2 6H2O, Th(NO3)4 5H2O, and UO2(NO3)2 5H2O, 2-aminopyridine,
.
.
.
1,10-phenanthroline, LiOH H2O, nitric acid, hydrochloric acid, ammonia,
murexide, eriochrome black T and xylenol orange indicators, hexamethylene-
triamine, and ethylenediaminetetraacetic acid disodium salt. The solvents
used were methanol, ethanol, dimethyl formamide (DMF), and dimethyl sulf-
oxide (DMSO). These solvents were reagent grade. The organic ligand (H2L)
was prepared by literature methods[11,12] through coupling the diazonium salt
2-aminobenzoic acid with 5,5-dimethyl-1,3-cyclohexanedione. The coupling
occurs in sodium acetate medium. The purity of the ligand was checked by
elemental analyses, 1H NMR, and TLC.
Analyses and Physical Measurements
Electronic spectra of solutions of the organic ligand (H2L) and their
complexes in DMF were recorded on a Jasco model V-550 UV-Vis spectro-
photometer. IR spectra were recorded on a Perkin–Elmer 437 ER spectrometer
using KBr discs; polyethylene was used as a calibrant. Magnetic suscepti-
bilities of the complexes were measured by the Gouy method at room temp-
erature using a Johnson Matthey, Alfa Products, model MKI magnetic
susceptibility balance. The effective magnetic moments were calculated

1352
Mashaly et al.
using the relation meff ¼ 2.828(xm T)1/2 B.M., where xm is the molar suscep-
tibility corrected using Pascal’s constants for diamagnetism of all atoms in the
compounds. 1H NMR spectra (DMSO-d6) were recorded at room temperature
on a Varian FT-290.90 MHz spectrometer, using TMS as an internal standard.
TG-DSC measurements were carried out on a Shimadzu thermogravimetric
analyzer using the TA-50 WSI program. Mass spectra were recorded at
70 eV and 300 8C on a MS 5988 Hewlett–Packard mass spectrometer.
Melting or decomposition points were determined on a Gallenkamp, melting
point apparatus, England. Conductivities were measured in solutions of the
complexes in DMF (1023 M) using a model LBR WTWD-812 Weilheim
conductivity meter, fitted with a model LTA 100 cell. Analyses of the
metals followed decomposition of their complexes with concentrated nitric
acid. The resultant solutions were diluted with water and filtered to remove
the precipitated ligand. The solutions were then neutralized with aqueous
ammonia solution and the metal ions titrated with EDTA. Microanalyses of
carbon, hydrogen, nitrogen, and sulfur were carried out at the Microanalytical
Center, Cairo University, Giza, Egypt.
.
Preparation of the Metal Complexes
The binary complexes as well as the mixed-ligand complexes were pre-
.
pared in the presence of LiOH H2O as a deprotonating agent.
Preparation of the Binary Complexes
.
Molar Ratio M : H2L : LiOH ¼ 1 : 1 : 1. A mixture of LiOH H2O (0.17 g,
4 mmol) and H2L (1.15 g, 4 mmol) in 50 mL of methanol was added to the
metal salt (4 mmol) dissolved in the least amount of water, namely
.
.
.
.
Cd(NO3)2 4H2O, Cu(NO3)2 3H2O, Ni(NO3)2 6H2O, Co(NO3)2 6H2O,
.
.
Th(NO3)4 5H2O, or UO2(NO3)2 5H2O. The reaction mixture was refluxed
for 3 hr with constant stirring and was left to cool at room temperature to
ensure the complete formation of metal complexes. The precipitated solid
complexes were filtered, washed several times with 50% (v/v) methanol–
water to remove any traces of the unreacted starting materials. Finally, the
complexes were washed with diethyl ether and dried in a vacuum desiccator
over anhydrous CaCl2.
Preparation of the Mixed-Ligand Complexes
Molar Ratio Cu(II) : H2L : 2-ampy or 1,10-phen : LiOH ¼ 1 : 1 : 1 : 1. A
.
mixture of LiOH H2O (0.17 g, 4 mmol) and H2L (1.15 g, 4 mmol), and

Azo Complexes
1353
2-aminopyridine (0.376 g, 4 mmol) or 1,10-phenanthroline (0.79 g, 4 mmol) in
.
60 mL of methanol was added to Cu(NO3)2 3H2O (0.97 g, 4 mmol) dissolved
in the least amount of water. The reaction mixture was refluxed for 4 hr with
constant stirring and was left to cool at room temperature to ensure the com-
plete formation of the metal complexes. The precipitated solid complexes
were filtered, washed several times with 50% (v/v) methanol–water to
remove any traces of the unreacted starting materials. Finally, the mixed-
ligand complexes were washed with diethyl ether and dried in a vacuum
desiccator over anhydrous CaCl2.
Pyrolytic Preparation of Some Metal Complexes
New solid metal complexes (9)–(11), Table 1, were prepared pyro-
lytically by heating the corresponding mother complexes (4), (6), and (7),
respectively, to the temperatures at which the exothermic or the endothermic
peak is observed. The complex under investigation was placed in a porcelain
crucible and heated slowly in an oven to the maximum temperature of 350 8C.
The heating rate did not exceed 5 8C min21. The heating was continue until it
reached the temperature at which the exothermic or endothermic peak was
observed in the DSC curve of the original complex. The complex was kept
at this temperature for a further 1/2 hr, to ensure the removal of all of the
liberated species and to avoid the occurrence of a backward reaction to the
original complex. The new product was allowed to cool to room temperature
and then was characterized.
Pyrolytic Preparation of [Cu(L)(2-ampy)2] (9)
This compound was prepared by heating complex (4) to 170 8C till
constant weight. The color of the complex is olive green, which differed
from the color of the mother complex.
Pyrolytic Preparation of [Ni(HL)(NO3)(OH2)] (10)
This compound was prepared by heating complex (6) at 160 8C to a
constant weight. The color of the complex is deep brown which differed
from the color of the mother complex.
Pyrolytic Preparation of [Th(HL)(L)]NO3 (11)
This compound was prepared by heating complex (7) at 196 8C to a
constant weight; the color changed from yellow to brown.

1354
Mashaly et al.

Azo Complexes
1355
Pectinlyase Enzyme Testing
The compounds were tested according to the method of Collmer et al. as
follows:
1. A 100 ml DMF solution of each compound was added to a reaction
mixture consisting of 1.0 mL of pectinlyase enzyme (100 unit/mL),
1.0 mL of citrus pectin (0.5%), 0.5 mL of CaCl2, and 100 mL of
tris buffer (pH 9.0).
2. The reaction mixture was incubated at 25 8C for 60 min.
3. The reaction was stopped by adding 3.5 mL of 0.5 HCl.
4. The UV–vis spectrum of the reaction mixture in each case was
measured at 235 nm using a UV–visible spectrophotometer.
5. The results were recorded in Table 6 as percentage of the control,
i.e. without any compound.
6. The action of enzyme without tested compounds (control) was con-
sidered to be 100%.
7. The action of the ligand and metal complexes on the enzyme were
compared with the control. Percentages over 100% were considered
as activation, while those less than 100% were considered as
inactivation.
RESULTS AND DISCUSSION
The reactions of the rigid-structure azo ligand, (H2L), with the metal ions
Cd(II), Cu(II), Ni(II), Co(II), Th(IV), or UO2(VI) in the presence of LiOH as
deprotonating agent, yielded the binary mononuclear complexes, Figs. 3 and
5–8, structures (1), (2), (5)–(8). The binary Cu(II) complex of H2L reacts with
the ligand 1,10-phen or 2-ampy to form the mixed-ligand complexes, Fig. 4,
structures (3) and (4). The isolated binary and mixed-ligand complexes were
amorphous uponremovalofthe solvent. Tables 1, 3–6 show the results obtained.
The following representative equations illustrate the formation of some of
the complexes obtained:
Metal nitrate : H2L : LiOH ¼ 1 : 1 : 1
2H2L þ CdðNO3Þ ꢀ 4H2O þ LiOH
! ½Cd(HL) ꢁ ꢀ2H2O þ LiNO3 þ HNO3 þ 4H2O
ð1Þ
ð2Þ
2
ð1Þ
2H2L þ CuðNO3Þ2 ꢀ 3H2O þ LiOH
! ½Cu(HL)2ꢁ þLiNO3 þ HNO3 þ 4H2O
ð2Þ

1356
Mashaly et al.
2H2L þ CoðNO3Þ ꢀ 6H2O þ LiOH
! ½Co(HL) ꢁ ꢀ2H2O þ LiNO3 þ HNO3 þ 6H2O
ð3Þ
ð4Þ
2
ð5Þ
H2L þ NiðNO3Þ2 ꢀ 6H2O þ LiOH
! ½Ni(HL)NO3ðOH2Þ2ꢁ ꢀ3H2O þ LiNO3 þ 2H2O
ð6Þ
2H2L þ ThðNO3Þ4 ꢀ 5H2O þ LiOH
! ½Th(HL)2NO3ðOH2Þꢁ NO3 þ LiNO3 þ HNO3 þ 5H2O
ð5Þ
ð6Þ
ð7Þ
2H2L þ UO2ðNO3Þ2 ꢀ 5H2O þ LiOH
! ½UO2ðHLÞ2ðOH2Þ2ꢁ ꢀ1 12 H2O þ LiNO3 þ HNO3 þ 2 12 H2O
ð8Þ
Copper nitrate : H2L : 1,10-phen or 2-ampy : LiOH ¼ 1 : 1 : 1 : 1
2H2L þ 1; 10-phen þ CuðNO3Þ ꢀ 3H2O þ LiOH
! ½Cu(HL) ð1; 10-phenÞꢁ þ2LiNO3 þ HNO3 þ 4H2O
2 ð3Þ
ð7Þ
ð8Þ
H2L þ 2ð2-ampyÞ þ CuðNO3Þ2 ꢀ 3H2O þ LiOH þ CH3OH
! ½Cu(HL)ð2-ampyÞ2NO3ꢁ ꢀ CH3OH þ LiNO3 þ 4H2O
ð4Þ
IR SPECTRA
The IR spectra of the free ligand (H2L) and its metal complexes are listed
in Table 2. The organic ligand (H2L) which has a rigid structure, forms the
following tautomers:
The IR spectrum of the free ligand (H2L) provides evidence for the azo
form in the solid state, where the band observed at 1479 cm21 is characteristic
of v(N55N).[14–18] The bands due to v(NH) or v(OH) of the enolic hydroxyl
group which would appear at ꢀ3200 cm21 were not observed. This indicates
that the tautomer (a) in Fig. 2 is the predominant structure for the azo ligand
H2L. The broad band observed at 3364 cm21 in the spectrum of the free ligand
(H2L) is assigned to v(OH) of the carboxylic group which is also hydrogen
bonded. The carbonyl group of the COOH group was observed at
1703 cm21. In all complexes the band due to v(OH) of the carboxylic group
is absent, indicating its deprotonation on complexation. The participation
of the carboxylate group in complex formation is also confirmed by the

Azo Complexes
1357

1358
Mashaly et al.

Azo Complexes
1359
Figure 2. The possible tautomers for the ligand 2-[20-carboxyphenylazo]-5,5-
dimethyl-1,3-cyclohexanedione (H2L) in solution.
disappearance of the bands due to v(C55O) of the COOH group and appear-
ance of two new bands at 1478–1533 and 1312–1389 cm21 assigned to
vas(COO2) and vs(COO2), respectively. This indicates that the carboxylate
group behaves as a monoanionic, monodentate group.[19–22] The stretching
vibrations of carbonyl groups of the b-diketone moiety of the ligand (H2L)
were observed at 1676 and 1646 cm21. The first band is slightly affected in
all complexes of (H2L), while the second band was shifted to lower frequen-
cies (20–35 cm21) except for the complexes (3), (5), and (8). The azo group in
the free ligand (H2L) was observed at 1479 cm21 and shifted to lower frequen-
cies (30–73 cm21) in all of the metal complexes. From the above results it can
be concluded that the free ligand (H2L) behaves either as a monoanionic,
bidentate ligand, via one of the oxygens of the carboxylate group and the
neighboring nitrogen atom of the azo group or as a monoanionic, tridentate
ligand via one of the oxygen atoms of the carboxylate group, the neighbouring
nitrogen atom of the azo group and the oxygen atom of one of the carbonyl
groups of the b-diketone moiety. The IR spectrum of the uranyl complex
showed a strong band at 928 cm21 assigned to the antisymmetric
v3(O55U55O) vibration.
The mixed-ligand 1,10-phenanthroline complex (3), showed a new band
at 1576 cm21, which would be due to the coordinated C55N group of 1,10-
phenanthroline.[23–26] The mixed 2-aminopyridine complex (4), showed two

1360
Mashaly et al.
new bands at 3163 cm21 and 978 cm21. The second band is assigned to the
skeletal vibration of the pyridine ring,[27] breathing mode, while the first
band is due to the coordinated NH2 group.
The coordinated NO3 group in complexes (6) and (7) showed two bands at
1033–1054 and 1304–1369 cm21 and may be assigned to the asymmetric and
symmetric stretches v1 and v2 of the nitrate group. We can conclude that the
NO3 group is coordinated in a unidentate manner.[28] The nitrate anion[29]
in complex (7) also showed a band at 1385 cm21. The IR spectra of the
complexes showed new bands at 576–699 and 456–571 cm21, assigned to
v(M–O) and v(M–N), respectively. The v(OH) frequencies of lattice water
molecules or solvated CH3OH were observed at 3398–3414 and
3429 cm21, respectively,[23] while the IR spectra of the complexes display
the absorption peaks of coordinated water molecules at 3484–3522 cm21
.
Nuclear Magnetic Resonance Spectral Studies
1
The assignments of the main signals in the H NMR spectra of the free
ligand (H2L) and its diamagnetic cadmium complex are listed in Table 3.
The free ligand showed a signal at d 15.73 ppm (s, 1H) due to the carboxylic
.
group proton. This signal is absent in the complex [Cd(HL)2] H2O (1). This
indicates the deprotonation of the carboxylic group during the formation of the
metal complexes. The free ligand also showed signal due to the aromatic
protons at d 7.27–8.05 ppm (m, 4H) which was slightly shifted downfield
Table 3. 1H NMR Data (d, ppm) for organic ligand, H2L, and its diamagnetic
cadmium complex.
(CH)
aromatic
(CH)
aliphatic
Compound
(COOH)a
Additional signals
H2L (Free
ligand)
15.73
(s, 1H)
7.27–8.05
(m, 4H)
1.05
(s, 6H)
5.24 (s, 1H) proton of
active methylene, 2.5–
2.66 (d, J ¼ 5.2 Hz, 4H)
protone of CH2 group.
5.27 (s, 1H) proton of
active methylene, 2.51–
2.58 (d, J ¼ 4.7 Hz, 4H)
proton of CH2 groups,
3.04 (s, 2H) lattice water.
(1)
—
7.29–8.15
(m, 4H)
1.03
(s, 6H)
Note: s, singlet; d, doublet; and m, multiplet.
aChemical shifts with reference to TMS.

Azo Complexes
1361
in the complex. The signal due to the aliphatic protons was observed at
d 1.05 ppm (s, 6H) due to the CH3 groups of the ligand (H2L) and was slightly
shifted upfield in the complex (1). The lattice water molecule was observed at
d 3.04 ppm (s, 2H) for complex (1).
Conductivity Measurements
The conductance of solutions of the complexes in DMF (1023 M) are
shown in Table 4. Complex (7) is a 1 : 1 electrolyte while the other complexes
are non-electrolytes.
Magnetic Moments and Electronic Spectra
The UV-Visible spectra of the free ligand H2L and its metal complexes
were carried out as DMF (1023 M) solutions. The values of band positions
(cm21) and molar absorptivities (1max L cm21 mol21) together with the mag-
netic moment values are listed in Table 4. The UV–visible spectra of the
ligand showed bands at 35,088, 28,409, and 23,981 cm21 assigned to
p ! pꢂ, n ! pꢂ, and charge transfer transitions within the molecule,
respectively. The bands of the free ligand were slightly shifted to blue or
red regions in all complexes, while new bands were observed in the visible
region for the Cu(II), Co(II), and Ni(II) complexes due to d ! d transitions.
The magnetic moment of the binary complex of Cu(II), (2) is 1.95 BM.
The visible bands of this complex exhibit two transition bands at 19,231
2
2
and 15,221 cm21 which unambigously may be assigned to the B1g ! Eg
2
2
and B1g ! B2g transitions, respectively, corresponding to a distorted octa-
hedral geometry around the copper ion.[28] The proposed structure of the
binary complex (2) is shown in Fig. 3. The actual geometry of the complex
whether the fac or mer is not known.
The mixed-ligand complexes of Cu(II) with 1,10-phenanthroline, (3) and
2-aminopyridine, (4), showed magnetic moment values, meff, in the range
1.87–1.89 BM. These values correspond to one unpaired electron and offer
evidence for the mononuclear structures of the complexes. The mixed-
ligand complexes of Cu(II) exhibited two transitions bands in the regions
19,084–19,231 and 15,083–15,221 cm21. The transitions including the
mixed-ligand complexes are similar in energies to those of the binary
complex (2). This indicates that the geometry of the copper ion in the
mixed-ligand complexes is distorted octahedral. The proposed structures of
the mixed-ligand-1,10-phenanthroline complex (3) and that of the mixed-
ligand-2-aminopyridine complex (4) are shown in Fig. 4.

1362
Mashaly et al.
p
p
p
m

Azo Complexes
1363
Figure 3. Suggested structure of the binary Cu(II) complex, [Cu(HL)2] (2).
The binary Co(II) chelate, (5) has the room temperature magnetic
moment of 2.71 BM, as expected for a square-planar Co(II) complex.[30,31]
The visible spectra exhibit peaks at 22,321 and 18,975 cm21, assignable to
2
2
2
2A1g ! Eg and A1g ! E2g transitions, respectively, and are compatible
Figure 4. Suggested structures of the mixed-ligand 1,10-phenanthroline and 2-amino-
.
pyridine Cu(II) complexes, [Cu(HL)2(1,10-phen)] (3) and [Cu(HL)(2-ampy)2NO3]
CH3OH (4).

1364
Mashaly et al.
with a square-planar geometry. The proposed structure of the binary cobalt(II)
complex is shown in Fig. 5.
The magnetic moment of the binary Ni(II) complex (6) is 2.89 BM,
suggesting its octahedral structure.[31]
The bands in the region 20,121 and 14,663 cm21 are assignable to the
3
3
3
3
electronic transitions A2g ! T1g(F) and A2g ! T1g(P), respectively.
The proposed structure of the binary Ni(II) complex is shown in Fig. 6.
The binary complexes of Cd(II), Th(IV), and UO2(VI) are diamagnetic
and the electronic spectra of the complexes are dominated only by the
1
ligand bands. The elemental analyses and H NMR spectrum showed that
the Cd(II) complex (1) has an octahedral configuration, Fig. 7.
The complexes of Th(IV), (7), and the UO2(VI) complexes (8) have the
coordination number 8 and are in distorted dodecahedral geometry. The pro-
posed structures of Th(IV) and the UO2(VI) complexes are shown in Fig. 8.
Thermal Analyses
The results of TG-DSC analyses of the binary and mixed-ligand
complexes are shown in Table 5. The results show good agreement with the
.
Figure 5. Suggested structure of the binary cobalt(II) complex, [Co(HL)2] H2O (5).

Azo Complexes
1365
.
Figure 6. Suggested structure of the binary Ni(II) complex, [Ni(HL)NO3(OH2)2]
3H2O (6).
theoretical formulae as suggested from the analytical data. The complexes (1),
(5), (6), and (8) become anhydrous at 76–110 8C. The loss of hydrated water
molecules was accompanied by an endothermic peak with DH, 33.67–
71.50 J/g. The molecule of CH3OH in the outer sphere of the complex (4)
.
Figure 7. Suggested structure of the binary Cd(II) complex, [Cd(HL)2] H2O (1).

1366
Mashaly et al.

Azo Complexes
1367

1368
Mashaly et al.
Figure 8. Suggested structures of the binary Th(IV) and UO2(VI) complexes,
1
.
[Th(HL)2NO3(OH2)]NO3 (7) and [UO2(HL)2(OH2)2] 12H2O (8).
was eliminated at 108 8C. The loss of the methanol molecule from the previous
complex was accompanied by an endothermic peak at DH, 62.93 J/g. The
coordinated water or CH3OH molecules were eliminated from the complexes
at relatively higher temperatures than the lattice water[32] or outer sphere
Table 6. Percentage activation or inactivation of the tested compounds.
% of the activation or
inactivation of the
enzyme pectinlyase
Compound
H2L (Free ligand)
.
(1) [Cd(HL)2] H2O
149.13
111.67
81.31
(2) [Cu(HL)2]
(4) [Cu(HL)(2-ampy)2NO3] CH3OH
.
94.11
.
(5) [Co(HL)2] H2O
.
(6) [Ni(HL)NO3 (OH2)2] 3H2O
157.78
151.55
153.28
142.56
(7) [Th(HL)2NO3 (OH2)]NO3
1
.
(8) [UO2(HL)2(OH2)2] 12H2O
Note: The control (the reaction mixture including the enzyme without
any additives) was considered to be 100%, values above 100% are
considered as activation while values less than 100% are considered as
inactivation.

Azo Complexes
1369
CH3OH molecules. There are three routes for the removal of coordinated
water molecules from the complexes which are described below:
1. The coordinated water molecules are eliminated in a separate step, as
in complex (8). The elimination of coordinated water molecules in
this step (196 8C) is accompanied by an endothermic peak and
leads to a non-isolable complex.
2. Partial elimination of coordinated water molecules from the complex.
This is observed in complex (6) which loses one molecule of coordi-
nated water at 160 8C (DH ¼ 26.51 J/g) which leads to an isolable
complex [Ni(HL)(OH2)(NO3)].
3. Elimination of coordinated water molecule(s) accompanied by loss of
HNO3, as in complex (7) at 196 8C (DH ¼ 232.10 J/g) and leads to
an isolable complex, [Th(HL)(L)(NO3)].
The elimination of the HNO3 molecule from complex (4) at 170 8C
(DH ¼ 126.22 J/g) occurred in a separate step and leads to the isolable
complex [CuL(2-ampy)2]. The removal of HNO3 from the complex involves
a NO23 ion and a proton from the organic ligand.
The mixed-ligand complexes are thermally stable to .200 8C. The com-
plexes start to decompose at a relatively higher temperatures, .260 8C, and
;;
the organic ligand loses gaseous compounds CO2, CO, (CN)2, HC CH,
CH3–CH3, etc.
Pyrolysis Studies
The structures of the obtained new products were elucidated on the basis
of elemental analyses, IR and electronic absorption spectra, magnetic
moments, and 1H NMR measurements as well as by mass spectroscopy
(Tables 1, 3, and 5). The UV-Visible spectra of the heated products (9)–
(11) showed the ligand bands as in the original complexes, but slightly
shifted to longer or shorter wave numbers (cm21). The IR spectra of the pyro-
lytic products showed the disappearance of v(C55O) of the COOH group and
the appearance of two new strong bands at 1494–1534 and 1445–1466 cm21
due to vas(COO) and vs(COO), respectively. This indicates that the carboxylic
group behaves as a monoanionic bidentate group.[20,23,33,34] All of the pyro-
lysis products showed the bands due to v(M–O) and v(M–N) at 567–699
and 486–542 cm21, respectively.

1370
Mashaly et al.
[Cu(L)(2-ampy)2] (9)
The IR spectrum showed the disappearance of bands corresponding to
the coordinated carbonyl groups of COOH and the b-diketone moiety. The dis-
appearance of the latter bands may be due to tautomerism (keto $ enol) in the
b-diketone ring. The enolic OH group loses its proton, which combines with the
NO3 ion to form the eliminated HNO3 molecule. This was confirmed by the dis-
appearance of v(NO3) from the IR spectrum of the heated product. The v(N55N)
band was observed at 1412cm21, indicating that this group is still coordinated to
thecopperion. Theremaining IRbands ofthe heatedproduct are asinthe original
complex (4) except for the disappearance of the band at 3529cm21 due to v(OH)
of CH3OH. Conductivity measurements of the thermal product in DMF solution
revealed the non-electrolytic nature of the complex. The magnetic moment, meff,
of the heated product was 1.94 BM, which reveals the presence of one unpaired
electron and shows no copper–copper interaction. The absorption bands
observed in the visible region at 19,493 and 14,936cm21 are due to d ! d tran-
2
2
sitions and are assigned to the 2B1g ! Eg and 2B1g ! B2g transitions, respect-
ively, corresponding to a distorted octahedral geometry of the copper ion.[28]
From theaboveresultsand theelemental analysesinTable1the product obtained
on heating may be represented as [Cu(L)(2-ampy)2] as indicated in Eq. (9) and its
proposedstructure isshown inFig. 9. The actualgeometriesofthe aminopyridine
rings whether cis or trans is not known.
½CuðHLÞð2-ampyÞ2ðNOÞ3ꢁ ꢀ CH3OH
170 C
W
ꢃꢃꢃꢃꢃ! ½CuðLÞð2-ampyÞ2ꢁ þHNO3 þ CH3OH
ð9Þ
ð9Þ
Figure 9. Structure of [Cu(L)(2-ampy)2] (9) obtained by heating complex (4) to 1708C.

Azo Complexes
1371
Ni(HL)(NO3)(OH2)] (10)
The IR spectrum of the heated product showed the disappearance of
the band due to lattice water molecules (3398 cm21), and the remaining
IR bands are as those as seen in the mother complex. The low conductance
of a DMF solution of this product proved that it is a non-electrolyte. The mag-
netic moment of the heated product was 2.93 BM, suggesting that it has an
octahedral structure.[32] The transition bands at 19,940 and 15,540 cm21 are
3
3
3
3
assignable to A2g ! T1g(F) and A2g ! T1g(P) [10] transitions, respect-
ively. From the above results and the elemental analyses in Table 1, the
product obtained on heating may be represented as [Ni(HL)(NO3)(OH2)] as
indicated in Eq. (10) and its proposed structure is shown in Fig. 10.
½NiðHLÞðNO3ÞðOH2Þ2ꢁ ꢀ 3H2O
160 C
W
ꢃꢃꢃꢃꢃ! ½NiðHLÞðNO3ÞðOH2Þꢁ þ4H2O
ð10Þ
ð10Þ
[Th(HL)(L)]NO3 (11)
The IR spectrum showed the disappearance of the band due to the coor-
dinated carbonyl group of the b-diketone moiety. This may be due to the
formation of an enolic –OH group, which is confirmed by a band observed
at 3424 cm21. The deprotonation of one –OH group and its combination
with a NO23 ion, leads to the elimination of a HNO3 molecule. This was
Figure 10. Structure of [Ni(HL)(NO3)(OH2)] (10), obtained by heating of complex
(6) at 160 8C.

1372
Mashaly et al.
also supported by the disappearance of the bands at 1304 and 1033 cm21, due
to the coordinated NO23 group. The band due to the ionic NO23 group was
observed at 1392 cm21. The IR spectrum of the heated product showed the
overlap between vs(COO2) and v(N55N) and both appear as a strong single
1
band at 1454 cm21. The H NMR spectrum showed a signal corresponding
to the coordinated enolic OH group at d 16.02 ppm (s, 1H), which confirms
the presence of the tautomers (keto $ enol) in the b-diketone moiety. The
disappearance of the signal at ꢀd 5.27 ppm, due to the proton of the active
methylene group in the b-diketone moiety also supports the presence of the
1
enol form. The H NMR spectrum of the heated product showed signals
assigned to the aromatic protons at d 7.20–8.13 ppm (m, 6H) and the aliphatic
protons at d 3.45 ppm (s, 8H) and d 1.06 ppm (s, 12H). The conductance of a
DMF solution of the heated product indicates that it is a 1 : 1 electrolyte, con-
firming the presence of the NO23 anion in the outer sphere of the complex. The
electronic spectrum of the diamagnetic thermal Th(IV) product is dominated
by the ligand bands (see Table 5).
From the above results and its elemental analyses in Table 1, the product
obtained on heating may be represented as [Th(HL)(L)]NO3 as indicated in
Eq. (11) and which has a distorted dodecahedral geometry. Its proposed struc-
ture is shown in Fig. 11.
W
196 C
½ThðHLÞ2ðNO3ÞðOH2ÞꢁNO3 ꢃꢃꢃꢃꢃ! ½ThðHLÞðLÞꢁNO3 þHNO3 þ H2O
ð11Þ
ð11Þ
Mass Spectra
Mass spectral data are consistent with the formulations [Cu(L)(2-ampy)2]
(9) and [Th(HL)(L)]NO3 (11) which give the parent ions at m/z 539 (calcu-
lated value 538.06) and 868 (calculated value 867.62), respectively.
The mass spectrum of complex (9), shows the presence of a mass frag-
ment corresponding to C20H20N4O4Cuþ, m/z 444.75 (2.18%), which loses a
CO2 molecule to give the fragment C19H20N4O2Cuþ, m/z 400.30 (8.80%),
followed by the loss of a C5H6N2 molecule to give the fragment
C14H14N2O2Cuþ, m/z 306.20 (2.32%) and finally the fragment due to CuOþ
is present at m/z 80.10 (3.81%).
Complex (11) shows the presence of a mass fragment corresponding to
C30H29N4O8Thþ, m/z 807.45 (8.60%), which loses a CO2 molecule to give
the fragment C29H29N4O6Thþ, m/z 764.0 (3.50%) then loses a C6H4N2
molecule to give the fragment C23H25N2O6Thþ, m/z 658 (8.0%), followed
by the loss of a CH3–CH3 molecule to give the fragment C21H19N2O6Thþ,

Azo Complexes
1373
Figure 11. Structure of [Th(HL)(L)]NO3 (11) obtained by heating complex (7) to
196 8C.
m/z 628.50 (8.82%) and finally the fragment due to ThOþ is present at m/z
248.15 (28.67%). The fragmentation pattern is shown in Fig. 12.
Biological Activities of Metal Complexes
The investigated compounds were tested as modulators of the enzyme
pectinlyase produced by the thermophilic fungus Thermomyces lanuginosus.
The activations of this enzyme given by our compounds may help in the
improvement of their action in many industries. The metal complexes of the
free ligand H2L gave the same activities and were comparable with those of
the free ligand, except for the binary Cu(II) complex (2) and the mixed
2-ampy complex (4), which resulted in decrease of the enzyme activity.
From the above results we can conclude that the free ligand H2L activates
the enzyme pectinlyase. All the tested metal complexes also activate the
enzyme pectinlyase except for the complexes (2) and (4). The activations of
this enzyme by our compounds may help in the improvement of their action
in many industries.

1374
Mashaly et al.
Figure 12. Fragmentation pattern of complex (11).

Azo Complexes
1375
CONCLUSIONS
The reaction of the azo ligand H2L with the metal ions Cd(II), Cu(II),
Ni(II), Co(II), Th(IV), or UO2(VI) in the presence of LiOH as a deprotonating
agent, yielded binary mononuclear complexes.
The binary Cu(II) complex of (H2L) reacts with the ligands 1,10-
phenanthroline or 2-aminopyridine to form mixed-ligand complexes.
From the results of both the 1H NMR and IR spectra, the free ligand
H2L behaves either as a monoanionic, bidentate ligand through the
oxygen atom of the carboxylate group and the nitrogen atom of the azo
group, or as a monoanionic tridentate ligand through the oxygen atom of
the carboxylate group, the nitrogen atom of the azo group and the
oxygen atom of one carbonyl group of the b-diketone moiety. The
mixed-ligand 1,10-phen behaves as a neutral bidentate ligand through the
nitrogen atoms of the rings, while 2-ampy behaves as a neutral monoden-
tate ligand via the amino group. The binary Cu(II), Ni(II), and Cd(II) com-
plexes have octahedral configurations, while the binary complex of Co(II)
has a square-planar geometry. The binary complexes of Th(IV) and
UO2(VI) have distorted dodecahedral geometries. The mixed-ligand com-
plexes have octahedral configurations.
The actual possible geometric isomers for the synthesized complexes
are not determined and would be interesting to investigate them in a
further study.
The thermal studies explored the possibility of obtaining new complexes
which cannot be prepared from solutions. The vas(COO) and vs(COO) of the
heated products indicate that the carboxylate group behaves as a monoanionic,
bidentate group. The geometries of the heated product are similar to the orig-
inal complexes. Although some of the original complexes lose two molecules
of coordinated water, the resulted complexes compensate the decrease in
coordination sites through the change in the mode of coordination of the
carboxylate group.
The free ligand (H2L) activates the enzyme pectinlyase. All the tested
metal complexes activate the enzyme pectinlyase except for the complexes
(2) and (4).
ACKNOWLEDGMENT
The authors wish to express their thanks to Dr. Usama Fahmy Ali Hamed,
Biology Department, Faculty of Education, Ain Shams University for the bio-
logical testing.

1376
Mashaly et al.
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Received January 19, 2003
Accepted March 19, 2004