Surface layer-by-layer chemical deposition reaction for thin film formation of nano-sized metal 8-hydroxyquinolate complexes

Article abstract of DOI:10.1016/j.poly.2008.09.030

The feasibility of a novel and simple layer-by-layer chemical deposition method for the preparation of nano-sized metal 8-hydroxyquinolate complexes has been investigated and reported. Uniform nanocrystalline films have been synthesized via dipping a subs

Full text of DOI:10.1016/j.poly.2008.09.030

Polyhedron 28 (2009) 181–187
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Surface layer-by-layer chemical deposition reaction for thin film formation
of nano-sized metal 8-hydroxyquinolate complexes q
b
c
Mohamed E. Mahmoud a, , Sawsan S. Haggag , Tarek M. Abdel-Fattah
*
a Faculty of Sciences, Chemistry Department, University of Malaya, Kuala Lumpur 50603, Malaysia
b Faculty of Sciences, Chemistry Department, Alexandria University, P.O. Box 426, Alexandria 21321, Egypt
c Department of Biology, Chemistry and Environmental Science, Christopher Newport University, Newport News, VA 23606, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 May 2008
Accepted 29 September 2008
Available online 17 November 2008
The feasibility of a novel and simple layer-by-layer chemical deposition method for the preparation of
nano-sized metal 8-hydroxyquinolate complexes has been investigated and reported. Uniform nanocrys-
talline films have been synthesized via dipping a substrate alternately in metal ion solution followed by
ligand solution. The stoichiometry of the as-grown anhydrous Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) com-
plex crystals were confirmed from the metal analysis and molar stoichiometric ratio of metal ion to 8-
hydroxyquinoline. This was characterized as 1:2 for the Co(II), Ni(II), Cu(II) and Zn(II)–quinolate com-
plexes. The Fe(III)–quinolate thin film was found to exhibit a 1:3 ratio. Electron impact-mass spectra
(EI-MS) of all the synthesized thin film metal quinolate complexes were recorded and the results refer
to the existence of the molecular ion peak at the corresponding m/z values. Confirmation of such stoichi-
ometric 1:2 and 1:3 ratios were also evident from the (EI-MS) study. The deposited thin films were also
subjected to analysis by a scanning electron microscope (SEM) and a particle size P50 nm was detected.
FT-IR and UV–Vis spectroscopy were further used to confirm the structure of the metal 8-hydroxyquin-
olate complexes. Thermal gravimetric analysis (TGA) was also used to follow up the possible thermal
decomposition steps and to calculate the thermodynamic parameters of the nano-sized metal complexes.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Nano-sized
8-Hydroxyquinoline
Metal complexes
Layer-by-layer
Chemical deposition
Thin film
1. Introduction
8-Hydroxyquinoline, 8HQ, also known as oxine, its derivatives
as well as related metal complexes, are playing a uniquely impor-
Recently, more research efforts have been focused on the bene-
ficial applications of the layer-by-layer deposition technique. This
methodology has emerged and been found a more economic alter-
native for the direct preparation of thin films [1–3]. The highly
sophisticated gas-phase layer deposition method can be easily re-
placed by this simple and direct liquid-phase solution-based layer-
by-layer technique for thin film formation [4,5]. The formation of a
variety of important compounds was successfully synthesized via
the layer-by-layer thin film deposition approach. Polyelectrolyte
thin films were prepared via alternately dipping the substrate into
polycation and polyanion solutions to form polyelectrolyte multi-
layer films [6] as well as polymer-nanoclay multilayers [7]. The
application of the layer-by-layer deposition method for the forma-
tion of various metal oxide [8–10] and metal sulfide thin films [11–
13] have been reported and their optical properties investigated.
tant role in different disciplines of chemical research and applica-
tions. 8HQ, as a complexone or sequestering reagent, is considered
second to EDTA and its analogues in binding with metal ions [14].
8HQ was mainly applied for analytical purposes and separation
techniques as an excellent reagent for the extraction of metal ions
due to its extraordinary coordinating capabilities [15–20]. How-
ever, in coordination chemistry, versatile synthetic approaches
for the formation of metal complexes of 8HQ and its derivatives
were extensively used to open a wide range of di and tri-valent
metal complexes that can be used as an arsenal for various impacts
and applications in different fields. Among these applications are
the utilization of 8-hydroxyquinoline as an interesting chelating
agent for the formation of luminescent coordination compounds
as light emitting devices. A review covering the applications of me-
tal complexes of 8-hydroxyquinoline derivatives to obtain new
supramolecular sensors, emitting devices or self-assembled aggre-
gates was recently published [21]. Moreover, tris(8-hydroxyquino-
line) aluminum (Alq3) is widely used in modern organic light
emitting diodes (OLEDs) due to its excellent stability and electrolu-
minescent properties via the high dependence on the injection
behavior of the metallic contacts [22–24]. Most recent research
efforts have also been focused on the synthesis of quinolate metal
q
This work was partially presented in The 235th ACS National Meeting, New
Orleans, USA April 6–10, 2008.
* Corresponding author.
E-mail addresses: memahmoud10@yahoo.com (M.E. Mahmoud), fattah@cnu.edu
(T.M. Abdel-Fattah).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.09.030

182
M.E. Mahmoud et al. / Polyhedron 28 (2009) 181–187
complex nanomaterials by physical vapor deposition [25,26] and
adsorbent assisted physical vapor deposition [27] techniques, with
positive results at the end.
The metal contents of the quinolate complexes were determined
on a Shimadzu (AA-6650) atomic absorption spectrophotometer
after acid decomposition and suitable dilution. UV–Vis spectra of
the metal quinolate complexes were measured on a Perkin–Elmer
UV–Vis Spectrometer Lambda EZ210.
The strong necessity to fabricate thin films of various metal
derivatives in the form of oxides, sulfides and complexes to desired
shapes and sizes by an easy and simple technique has been previ-
ously reported [28]. Therefore, we present and describe in this
work a simple and rapid method for the synthesis of nanomaterials
derived from quinolate complexes of Fe(III), Co(II), Ni(II), Cu(II) and
Zn(II) based on the application of a layer-by-layer technique via
successive and alternative deposition of metal ions and ligand mol-
ecules from their aqueous and methanolic solutions, respectively,
for the formation of a thin film loaded on a glass substrate. The
structures of the thin film synthesized metal quinolate complexes
were confirmed on the basis of scanning electron microscopy
(SEM), electron impact-mass spectrometry (EI-MS) UV–Vis spec-
troscopy, Fourier Transform infrared spectroscopy (FT-IR) and
thermal gravimetric analysis (TGA).
2.3. Chemical and materials
The metal salts were all of analytical grade and were purchased
from Aldrich Chemical Company, USA and BDH limited, Poole, Eng-
land. The acetate salts were cobalt acetate, Co(OAc)2 Á 4H2O, nickel
acetate, Ni(OAc)2 Á 4H2O, copper acetate, Cu(OAc)2 Á H2O and zinc
acetate, Zn(OAc)2 Á 2H2O. Only iron was in the chloride form, FeCl3.
8-Hydroxyquinoline (8HQ) and methanol were obtained from BDH
limited, Poole, England and were used as received. The metal ion
solutions (0.1 M) were prepared from doubly distilled water by
dissolving the appropriate mass of the metal salt in a 500 ml flask.
A 0.1 M methanolic solution of 8HQ was also prepared and used.
The glass micro-slide glass substrate, of the size 76.2 mm by
25.4 mm by 1 mm, was cleaned as previously reported [10].
2. Experimental
3. Results and discussion
2.1. Layer-by-layer thin film formation of 8HQ metal complexes
3.1. SEM of the metal 8HQ complexes
The formation of the 8HQ metal complexes was carried out by a
chemical dipping method according to the following procedure. In
this method, a clean glass micro-slide of the size 76.2 mm by
25.4 mm by 1 mm was used as the solid substrate. A solution of
0.1 M metal acetate or chloride was prepared in double distilled
water and the 8HQ solution was also prepared (0.1 M) in methanol.
The clean substrate was vertically immersed into the metal ion
solution for a 30 s period to deposit the corresponding metal ion
on the substrate surface. The substrate was then immersed in the
ligand solution for another 30 s, where the pre-adsorbed metal
ion on the glass substrate was allowed to react with the ligand. A
colored and uniform thin film of the metal complex was formed
after a few dipping cycles. The reaction substrate was rinsed with
distilled water after each reaction cycle. This procedure was re-
peated several times (15–50 times) to increase the film thickness
and homogeneity.
Fig. 1 shows the SEM images of an 8HQ deposited thin film on a
glass substrate for simple comparison with the thin film metal 8-
quinolate complexes. It is evident that the 8HQ molecules are dis-
tributed into nano-sized tubes upon direct deposition on the glass
substrate and the SEM images of 8HQ are somewhat similar to the
SEM image of a carbon nanotube structure [29,30]. The diameter of
the 8HQ-nanotube was found to be in the range 33–43 nm, as mea-
sured from the SEM images.
The detected SEM images of the various metal complexes were
found to be completely different from that of 8HQ. Fig. 2(i)–(iii)
shows the SEM images of the Co(8HQ)2 complex deposited thin
film on a glass substrate after 50 times of alternate dipping in me-
tal ion solution and 8HQ ligand counter part solution. The
Co(8HQ)2 complex was observed to start forming uniform complex
particles after only a few dipping cycles, indicating that a fast com-
plex reaction is taking place for the formation of the desired thin
films. Fig. 2(i) is a 30,000-times magnified image of the Co(8HQ)2
complex particle, showing a number of deposited molecules under
one particle aggregate. Fig. 2(ii) is a 7500 times magnified image of
the Co(8HQ)2 complex and clearly refers to the existence of several
particles with different contributions of nano-sized aggregates.
2.2. Instrumentation
A Shimadzu gas chromatography–mass spectrometer (GCMS-
QP2010S) interfaced with a direct insertion probe (DIP) was used
to acquire the electron impact-mass spectra (EI-MS) of the metal
quinolate complexes, viz. Fe(III), Co(II), Ni(II), Cu(II) and Zn(II), by
the application of 70-eV as the ionization energy. The heating tem-
perature programming of the DIP was performed at 20 °C minÀ1 for
all the metal quinolate complexes. The maximum temperature was
set to 350 °C and the run time was completed in 20.0 min. The col-
lected mass spectrum of each metal quinolate complex was library
searched to obtain the best possible match.
Scanning electron microscopes (JSM-6360LA, JEOL Ltd.), (JSM-
5300, JEOL Ltd.) and an ion sputtering coating device (JEOL-JFC-
1100E) were used to examine the deposited thin film of the metal
quinolate complexes. SEM specimens were coated with gold to in-
crease the conductivity. The thermal gravimetric analysis (TGA)
and thermoanalytical curves were obtained using a Perkin–Elmer
TGA7 Thermobalance at Moubarak City, Egypt. The operating con-
ditions were as follows: a temperature heating range of 20–
1000 °C with
a , a flow rate of
heating rate of 10 °C minÀ1
20 ml minÀ1 in a pure nitrogen atmosphere and a sample mass in
the range 5–12 mg. The FT-IR spectra of the metal quinolate com-
plexes were measured on a Shimadzu Fourier Transform infrared
spectrophotometer (FTIR-8400S) in the range 4000–200 cmÀ1
.
Fig. 1. SEM image of the 8HQ deposited thin film.

M.E. Mahmoud et al. / Polyhedron 28 (2009) 181–187
183
Fig. 3. SEM image of thin film Fe(8HQ)3 complex on glass substrate based on 50-
dipping cycles.
distribution of Fe(8HQ)3 crystal growth based on layer-by-layer
complex formation. The SEM images of the other metal complexes
synthesized based on layer-by-layer thin film formation are shown
in Figs. 4–6 for the Ni(8HQ)2, Cu(8HQ)2 and Zn(8HQ)2 complexes,
respectively. The numbers of dipping cycles are 30, 15 and 15 for
the three tested complexes, respectively.
It is evident from the SEM study that all the synthesized metal
quinolate complex crystals were found to grow up from just a sin-
gle molecule to several molecules in an aggregate distribution with
particle sizes starting from a few nanometers to several hundred
nanometers. In addition, various characteristic shapes of metal
Fig. 2. SEM images of the thin film Co(8HQ)2 complex on glass substrate based on
50-dipping cycles.
Finally, Fig. 2(iii) represents a 1500-times magnified SEM image of
the Co(8HQ)2 complex deposited thin film and refers to the high
homogeneity and similarity in the Co(8HQ)2 crystal growth based
on layer-by- layer complex formation.
Fig. 3(i) and (ii) shows the SEM images of the deposited thin
film of the Fe(8HQ)3 complex after 50-dipping cycles in metal
ion and 8HQ ligand solutions. Fig. 3(i) shows a homogeneous par-
ticle size distribution of the formed Fe(8HQ)3 complex with
10,000-times magnification. Most of the Fe(8HQ)3 complex particle
sizes were identified as being under 200 nm. In a similar fashion to
the thin film formation of the Co(8HQ)2 complex, a fast complex
formation reaction of Fe(8HQ)3 thin film was characterized after
only a few dipping cycles. Fig. 3(ii) represents a SEM image of
the Fe(8HQ)3 complex deposited thin film with a homogeneous
Fig. 4. SEM image of the thin film Ni(8HQ)2 complex on glass substrate based on
30-dipping cycles.

184
M.E. Mahmoud et al. / Polyhedron 28 (2009) 181–187
%
207
100.0
351
75.0
50.0
63
145
25.0
0.0
89
117
179
181
58
347
333
222
242
250
44
103
100
153
150
271
50
200
300
350
(i). EI-MS of Cu-(8HQ) 2
%
145
100.0
75.0
50.0
25.0
0.0
117
Fig. 5. SEM image of the thin film Cu(8HQ)2 complex on glass substrate based on
15-dipping cycles.
44
89
58
63
347
quinolate complexes were identified and these SEM images are
quite different from that of 8HQ alone. The shape difference of
the metal quinolate complex crystal aggregates deposited on the
thin films is mainly dependent on the reacted metal ions.
203
218
173
187
149
242
250
329
99
100
301
300
50
150
200
350
(ii). EI-MS of Co(8HQ)
2
%
3.2. Stoichiometry based on metal analysis and EI-MS of the metal
quinolate complexes
346
100.0
75.0
50.0
25.0
0.0
The molar stoichiometric ratios of the synthesized metal com-
plexes, determined on the basis of the metal analysis, are listed
in Table 1. The metal analysis of the characterized layer-by-layer
thin film formation of the Co(II), Ni(II), Cu(II) and Zn(II) complexes
proved a good similarity to the reactions with 8HQ providing a 1:2
stiochiometric ratio. It is important to report here that the two
reaction species, metal ion and 8HQ, were prepared as 0.1 M and
174
202
58
217
145
89
44
117
318
64
118
300
300
352
350
161
150
(iii). EI-MS of Ni(8HQ)2
242
50
100
200
250
%
116
100.0
75.0
50.0
25.0
0.0
352
89
144
176
208
203
200
63
64
351
44
50
242
250
271
128
287
300
324
162
150
100
350
(iv). EI-MS of Zn(8HQ) 2
%
Fig. 6. SEM image of the thin film Zn(8HQ)2 complex on glass substrate based on
344
100.0
75.0
50.0
25.0
0.0
15-dipping cycles.
145
Table 1
Some characteristic data of thin film metal quinolate complexes.
117
200
Structure FW
Color
% Theoretical % Experimental Film
Dipping
cycles
89
(mg/
cm2)
488
63
51
172
244
326
Co(8HQ)2 346.93 Orange
Ni(8HQ)2 347.01 Yellowish % Ni = 16.91
green
Cu(8HQ)2 351.87 Olive
green
Zn(8HQ)2 353.39 Yellowish % Zn = 18.50
green
% Co = 16.99
% Co = 16.79
% Ni = 16.87
4.569
4.194
50Â
30Â
171
100
200
300
400
500
(v). EI-MS of Fe(8HQ)3
% Cu = 18.07
% Cu = 18.06
% Zn = 18.66
% Fe = 11.35
4.869
4.469
4.328
15Â
15Â
50Â
Fig. 7. EI-MS of layer-by-layer thin films of metal quinolate complexes.
Fe(8HQ)3 488.33 Black
% Fe = 11.44

M.E. Mahmoud et al. / Polyhedron 28 (2009) 181–187
185
Table 2
when the glass substrate was first dipped in metal ion solution fol-
FT-IR assignments of major peaks.
lowed by the ligand solution, a rapid complexation reaction took
place between the metal ion and 8HQ in a 1:2 ratio, respectively.
Thus, the relative concentration of the two reacting species is con-
sidered of less importance when layer-by-layer thin film metal
quinolate complexes are formed. In the same manner, the Fe(III)
ion was characterized by its reaction with 8HQ in a 1:3 ratio based
on the metal analysis of Fe(III) in the layer-by-layer thin film
Fe(8HQ)3 complex. The same observation of concentration inde-
pendence can be also assigned in this case.
Electron impact-mass spectra (EI-MS) were also acquired to
confirm the molecular masses of all the metal quinolate com-
plexes. The collected spectra of the metal complexes were library
searched for the best possible fit. The EI-MS of the Cu(8HQ)2 com-
plex, shown in Fig. 7(i), was found to exhibit a few characteristic
ion peaks. A molecular ion peak at m/z 351 (rel. int. = 75%) was de-
tected assuming 63Cu as the most abundant copper isotope. The
base peak in the EI-MS of the Cu(8HQ)2 complex, m/z 207, is re-
lated to a loss of 144 amu as the deprotonated 8HQ ligand from
the molecular ion peak. Some other fragment ion peaks were char-
acterized in the EI-MS of the Cu(8HQ)2 complex and these are di-
rectly related to direct and possible successive losses from the
ligand ion. These ion peaks were identified at m/z 145, 117, 89
and 63, with relative abundances of 35%, 20%, 23% and 40%, respec-
tively. The library search for the acquired EI-MS of the Cu(8HQ)2
complex was found to strongly fit with the stored mass spectra
of the copper 8-hydroxyquinoline complex.
Compound
8HQ [18]
Peak (cmÀ1
)
Assignment
3410
3090
1570
1380
1223
mOH
mCH
mCO
mring
mCN
Co(8HQ)2
Ni(8HQ)2
Zn(8HQ)2
Cu(8HQ)2
Fe (8HQ)3
mOH
mCH
mCO
mring
mCN
3057
1574
1338
1277
mOH
mCH
mCO
mring
mCN
3058
1577
1340
1284
mOH
mCH
mCO
mring
mCN
3053
1569
1348
1278
mOH
mCH
mCO
mring
mCN
3053
1570
1339
1279
mOH
mCH
mCO
mring
mCN
3055
1570
1378
1271
Similar EI-MS of Co(8HQ)2, Ni(8HQ)2 and Zn(8HQ)2 to that of
Cu(8HQ)2 were characterized. The molecular ion peaks of these
metal quinolate complexes were characterized at m/z 347 (rel.
int. = 100%), 346 (rel. int. = 35%) and 352 (rel. int. = 95%) assuming
59Co, 58Ni, 64Zn as the most abundant isotopes of cobalt, nickel and
zinc, respectively. These metal quinolate complexes were found to
exhibit a loss of 144 amu, for the deprotonated 8HQ ligand, from
the molecular ion peak, similar to Cu(8HQ)2. In addition, the same
characteristic ion peaks that are derived from 8HQ at m/z 145, 117,
89 and 63 are evident in the EI-MS of these metal complexes, as
represented in Fig. 7(ii)–(iv).
of 8HQ as described above for Cu(8HQ)2, Co(8HQ)2, Ni(8HQ)2 and
Zn(8HQ)2. The EI-MS of the Fe(8HQ)3 complex is shown in Fig. 7(v).
3.3. FT-IR and UV–Vis spectrophotometric analysis of thin film metal
8HQ complexes
The EI-MS of Fe(8HQ)3 exhibited a molecular ion peak at m/z
488 (rel. int. = 20%). Two successive losses of 144 amu were identi-
fied and characterized in the mass spectrum of Fe(8HQ)3 due to
elimination of two deprotonated 8HQ ligand molecules from the
molecular ion peak. These two fragment ion peaks are recorded
at m/z 344 (rel. int. = 100%) and 200 (rel. int. = 40%). Fragment
ion peaks at m/z 145, 117, 89 and 63 were also characterized in
the EI-MS of the Fe(8HQ)3 complex based on fragmentation parts
The FT-IR spectrum of 8HQ exhibited characteristic absorption
peaks for
film complexes, the absorption peak
deprotonation of the H-atom of C8-OH while the
m
(C@N) and
m
(OH). In the FT-IR spectra of the five thin
(OH) disappeared with
(C@N) was
m
m
shifted, indicating that coordination of 8HQ to the various metal
ions has taken place via the nitrogen atom of the imine group
and oxygen atom of the C8-OH group, consistent with the results
outlined in Section 3.2. A comparison of the FT-IR spectra with
Fig. 8. FT-IR of Cu(II)–quinolate complex.

186
M.E. Mahmoud et al. / Polyhedron 28 (2009) 181–187
mal parameters are compiled in Table 3. Several thermal degrada-
tion steps were identified and are mainly due to the direct
decomposition of 8HQ from the metal complexes. The Co(8HQ)2
and Zn(8HQ)2 complexes showed three possible degradation steps,
with the final stable product expected to be the metal oxide at
P985 K and P965 K, respectively. Cu(8HQ)2 was found to decom-
pose via two degradation steps in the temperature ranges 586–
701 K and 765–977 K, due to the possible loss of 8HQ from the
complex. The final product formed from the Cu(8HQ)2 complex is
also expected to be the metal oxide species at a temperature
P977 K. On the other hand, Ni(8HQ)2 and Fe(8HQ)2 were charac-
terized by their thermal gravimetric decomposition via four vari-
ous degradation steps. These steps also refer to the direct
decomposition of the bound 8HQ molecule from these two metal
quinolate complexes, leaving the corresponding metal oxide at
temperatures P919 K and P1018 K for the Ni(8HQ)2 and Fe(8HQ)2
complexes, respectively. The assigned temperature range of the
metal oxide formations is very important if the study of the optical
or electric applications of these layer-by-layer thin films of nano-
sized particles is targeted, as previously reported for similar oxides
[8–10].
Fig. 9. UV–Vis of Cu(II)–quinolate complex in ethanol.
the molar stoichiometric ratio, metal analysis data and the EI-MS
of the metal complexes revealed that 8HQ is behaving as a mono-
basic bidentate ligand in the process of layer-by-layer thin film for-
mation of all the tested complexes. The metal ions are coordinated
through two N,O metal-chelate rings in the case of Co(II), Ni(II),
Cu(II) and Zn(II), indicating that these complexes have similar
structures, and three N,O metal-chelate rings in Fe(8HQ)3, proving
the structure assigned for these thin film complexes by the stoichi-
ometric metal analysis and the EI-MS. Fig. 8 is given as a represen-
tative FT-IR spectrum of the Cu(II)-8-hydroxyquinolate complex
and the FT-IR assignments of the major peaks are given in Table 2.
The UV–Vis electronic spectra of the layer-by-layer thin film of
metal quinolate complexes were also studied and proved to exhibit
characteristic d–d transition bands. This band was centered at a
wavelength of ꢀ381 nm, with a shoulder band at ꢀ433 nm, for
the Co(8HQ)2 complex. The Zn(8HQ)2 complex showed a d–d tran-
sition band centered at a wavelength of ꢀ371 nm with a shoulder
band at ꢀ427 nm. The d–d transition bands of the Ni(8HQ)2 com-
plex were centered at a wavelength of ꢀ386 nm with a shoulder
band at ꢀ427 nm. The Cu(8HQ)2 complex showed d-d transition
bands at a wavelength of ꢀ391 nm and two shoulder bands at
ꢀ235 and 427 nm. Finally, the Fe(8HQ)3 complex exhibited three
d–d transition bands centered at ꢀ363, 461 and 578 nm. Fig. 9
shows a representative UV–Vis spectrum for the Cu(II)–8-hydroxy-
quinolate complex.
4. Conclusion
The outlined results in this work directly refer to the suitability
and applicability of the layer-by-layer chemical dipping method as
a simple, efficient, low cost and rapid technique for the formation
of nano-sized metal 8-hydroxyquinolinate complexes based on
crystal growth and thin film formation. The reaction between the
metal ion and 8HQ is very fast and a uniform thin film can be ob-
served after only a few dipping cycles. The stoichiometry of the
metal quinolate thin film is complete regardless of the concentra-
tion of these two interacting species. In addition, the assigned tem-
perature for metal oxide formation is another dimension in this
work owing to the possible extension of the presented method
for such thin film oxide formation by simply annealing the metal
complexes.
Several factors are considered to be of great importance upon
application of the layer-by-layer thin film formation of metal com-
plexes that must be explored in order to identify the optimum con-
ditions and generalize the presented method for the formation of
nano-sized metal complexes. These include the effect of (i) metal
and ligand concentration on the stoichiometry of the metal com-
plex and the particle size, (ii) number of dipping cycles on the par-
ticle size, (iii) immersion time on the particle size, (iv) pH of the
metal and ligand solutions on the complex formation and (v) sol-
3.4. Thermal gravimetric analysis of the metal 8HQ complexes
Thermal gravimetric analysis of the layer-by-layer synthesized
thin film metal quinolate complexes was performed and the ther-
Table 3
Thermal gravimetric data of the layer-by-layer metal quinolate complexes.
Compound
Co(8HQ)2
Step
Temperature range (K)
DTGmax (K)
Wt. loss (% calculated)
n
Ea (J molÀ1
)
D
S (J molÀ1 KÀ1
)
R
Ln(A)
1
2
3
394–455
685–743
959–985
433
725
893
8.40
11.45
34.40
1
1
1
69.66
186.47
208.26
À91.69
0.53
À35.62
0.97753
0.98484
0.98775
18.80
30.41
26.27
Ni(8HQ)2
1
2
3
4
381–437
621–719
719–832
832–919
413
701
739
881
10.38
42.39
18.36
16.16
1
1
1
zero
76.29
À68.87
À3.52
0.98504
0.99419
0.96222
0.47928
21.50
29.89
14.73
0.54
176.67
103.05
28.76
À129.9
À249.4
Cu(8HQ)2
Zn(8HQ)2
1
2
586–701
765–977
636
863
45.65
31.70
1
1
107.08
98.99
À95.39
À155.8
À110.3
À11.33
À108.3
0.95730
0.97669
18.74
11.78
1
2
3
387–429
629–731
765–965
413
708
843
8.19
23.84
45.21
1
zero
1
58.03
173.73
139.51
0.95632
0.94297
0.99169
16.51
28.96
17.48
Fe(8HQ)2
1
2
3
4
622–650
652–677
768–868
967–1018
643
663
824
983
5.33
6.66
22.20
10.65
0.5
0.5
1
283.81
140.75
178.75
274.36
188.87
À43.46
À45.74
19.95
0.92750
0.94548
0.97676
0.93071
52.94
25.03
24.97
33.05
1

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