Characterization of N-hexadecyl-5-iminomethyl-8-hydroxyquinoline and oriented crystallization of CuSO4?5H2O under its monolayer

Article abstract of DOI:10.1039/a704267a

A new amphiphilic ligand, N-hexadecyl-5-iminomethyl-8-hydroxyquinoline (HIHQ), has been synthesized in a convenient method and the characteristics of its monolayer on pure water and on a subphase containing copper ions investigated. LB films of HIHQ were studied by small angle X-ray scattering, UV-VIS and XPS spectra. An oriented crystallization was examined at the monolayer/water interface. A good selection of the (110) crystal face of CuSO₄?SH₂O occurred at the solid state of the monolayer due to the perfect match between this crystal face and the definite lattice structure of the monolayer.

Full text of DOI:10.1039/a704267a

J O U R N A L O F
Characterization of N-hexadecyl-5-iminomethyl-8-hydroxyquinoline
and oriented crystallization of CuSO ·5H O under its monolayer
4
2
Chaoyang Jiang, Ruikang Tang and Zihou Tai*
State Key L aboratory of Coordination Chemistry, Coordination Chemistry Institute,
Nanjing University, Nanjing, 210093, P.R. China
C H E M I S T R Y
A new amphiphilic ligand, N-hexadecyl-5-iminomethyl-8-hydroxyquinoline (HIHQ), has been synthesized in a convenient method
and the characteristics of its monolayer on pure water and on a subphase containing copper ions investigated. LB films of HIHQ
were studied by small angle X-ray scattering, UV–VIS and XPS spectra. An oriented crystallization was examined at the
monolayer/water interface. A good selection of the (110) crystal face of CuSO ·5H O occurred at the solid state of the monolayer
4
2
due to the perfect match between this crystal face and the definite lattice structure of the monolayer.
Inspired by investigation of biomineralization, crystallization
of minerals in biological systems, the study of oriented crys-
tallization of inorganic compounds at inorganic/organic
interfaces has received considerable attention and developed
rapidly in recent years.1–5 Various organized molecular films
were used as templates, but monolayers, tailored by specific
chemical modification, were always used as good organic
substrates for controlled oriented inorganic crystallization.6–9
Up to now, many papers about the nucleation and growth of
inorganic crystals under monolayers have been published and
the influences of some factors such as chemical binding, lattice
matching and structural complementarity between crystals and
monolayers have been discussed.10–15
Apparatus
C,H,N analyses of HIHQ were performed using a Perkin-
Elmer Model 240C elemental analyzer. UV–VIS spectra were
measured with a Shimadzu Model 240 UV–VIS recording
spectrophotometer. XPS spectra of the films were obtained on
an X-ray photoelectron spectrometer (Escalab MK-II), which
was operated at 15 kV–20 mA (300 W) using Al-Ka radiation.
A Langmuir KSV5000 trough system was used in LB film
preparation. The formed crystals were studied by optical
microscopy and crystal faces examined by a rotating-anode
X-ray diffractometer (D/Max-RA, Rigaku, Japan).
Isotherm measurement and fabrication of LB films
8
-Hydroxyquinoline and its derivatives readily form insol-
uble precipitates with many metal ions, and are available in
the laboratory as analytical reagents and for the extraction of
many metal ions,16 incorporating 8-hydroxyquinoline or
its derivatives in LB films; such films may have potential
applications in biomineralization.17,18 Here, a new amphi-
philic ligand, N-hexadecyl-5-iminomethyl-8-hydroxyquinoline
The surface pressure–area (p–A) isotherms were measured in
the usual manner as reported elsewhere.20 After the monolayer
had self-organized for ca. 30 min, the LB films were fabricated
at a surface pressure of ca. 30 mN m−1 by lifting–dipping
cycling of the substrate. The speed of the slide for the first
layer was 1 mm min−1, then raised to 3 mm min−1. All work
was carried out in a dust-free box at 20 °C.
(
HIHQ), was synthesized using a convenient method and
characterized by elemental analysis, IR, and UV–VIS spectral
studies. The coordination of HIHQ with copper ions at the
air/water interface and the oriented crystallization of
CuSO ·5H O at a HIHQ monolayer were also investigated.
Crystal growth of CuSO ·5H O at an HIHQ monolayer
4
2
CuSO (20 g) was added to water (50 g) at 40 °C and the
4
4
2
solution was filtered at 20 °C. The filtrate was heated to 30 °C
and transferred into the KSV5000 minitrough. When the
temperature was lowered to 22 °C, on the surface of the filtrate,
the monolayer of HIHQ was carefully and slowly spread from
a 1.0×10−3 mol dm−3 solution in chloroform. After the
chloroform had been evaporated off, a stable monolayer was
compressed into solid or other phases according to its p–A
curve, meanwhile, the temperature was reduced to 20 °C and
CuSO ·5H O crystals were induced to form at the monolayer.
Experimental
Materials
8
-Hydroxyquinoline (Shanghai Chemical Reagents Co.) and
hexadecylamine (Fluka Chemical Co.) were used without any
further purification. All solvents were purified by standard
procedures. CuSO was of A.R. grade, purchased from
Shanghai Chemical Reagents Co. Water used in the experi-
ments was doubly distilled and purified by ion exchange.
4
4
2
Results and Discussion
Synthesis
Formation of monolayers of HIHQ on aqueous subphase
The synthesis procedure for the amphiphilic ligand, N-hexa-
decyl-5-iminomethyl-8-hydroxyquinoline (HIHQ) is illustrated
in Scheme 1. This route involves the preparation of 5-formyl-
Fig. 1 shows the surface pressure–area (p–A) isotherm of HIHQ
monolayer on pure water and displays expanded, coexistent
and condensed regions at different surface pressures. The
plateau might indicate that a phase change or a change in
orientation of the headgroup fragment of HIHQ, which occurs
when the surface pressure is increased to 20 mN m−1. A
8
-hydroxyquinoline,19 and its condensation reaction with a
long chain alkylamine. This method is more convenient than
that of N-hexadecyl-8-hydroxyquinolinecarboxamide (HHQ),
which we have studied previously.17 The product HIHQ is a
yellow-green powder, Anal. Calc. for C H N O: C, 78.70; H,
˚
limiting area A of ca. 60 A2 per molecule is obtained in the
0
expansion region. However, with increase of surface pressure,
˚
26 40 2
10.11; N, 7.03. Found: C, 78.71; H, 10.11; N, 7.03%. The
synthesis of HIHQ will be detailed elsewhere.
two other values of A , 40 and 29 A2, were obtained in the
compression region.
0
J. Mater. Chem., 1998, 8(1), 81–84
81

CHO
OH
HC NC16H
33
CHCl
3
, NaOH
H
2
NC16
H
33
2
C H
5
OH
C
2 5
H OH
N
N
N
OH
OH
Scheme 1 Synthesis of the amphiphilic molecule HIHQ
Fig. 1 Surface pressure–area isotherms of HIHQ on pure water (solid
line), and a subphase containing 10−3 mol dm−3 CuSO (dashed line)
4
The small-angle X-ray scattering profile of 13-layer LB films
of HIHQ deposited from pure water is shown in Fig. 2. Only
one broad Bragg peak (2h=2.282°) is observed. The derived
Fig. 3 Stacking modes of HIHQ molecules at the air/water interface.
The dashed circle represents a copper ion.
˚
bilayer spacing (38.711 A) is much smaller than twice the
˚
thickness of the length of molecule (2×23.4 A). As Y-type
bilayer structure was formed, the incline mode is proposed
increase of surface pressure, the orientation of the quinoline
ring in the monolayer changes from a ‘flat’ to an ‘edge on’
structure, and when the surface pressure is >50 mN m−1, a
‘stand up’ structure is adopted. This molecular orientation of
HIHQ in the monolayer can be ascribed to the hydrophilicity
of the head group: phenolic hydroxy and tertiary amine. More
evidence on these oriented structures will be collected by
Brewster angle microscopy in the future.
[
Fig. 3(b)].
˚
The area per molecule (60 A2) corresponds to a cross-
sectional area of 8-hydroxyquinoline approximated by a rec-
tangular block with dimensions 8.4×7.4×3.6 A3 according to
˚
a space-filling molecular (CPK) model. The values, 40 and
˚
2
9 A2, per molecule might correspond to the incline side
˚
area [(8.42+7.42)1/2×3.6 A2] and the vertical side area
˚
(
8.4×3.6 A2) of the 8-quinolinol ring of HIHQ. The thickness
˚
of a single monolayer of HIHQ estimated by SAXS is 19.50 A
corresponding to the structure in Fig. 3(b); we can deduce that
the Y-type bilayer was formed during the deposition process
of HIHQ and the molecular orientation in the LB film is of
the structure shown in Fig. 3(b) rather than in Fig. 3(a) or (c).
Obviously, the HIHQ molecule has different oriented struc-
tures under various surface pressures. At lower surface pressure,
the 8-quinoline ring lies on the surface [Fig. 3(a)]. With
Formation of monolayers of HIHQ on a subphase containing
copper ions
In general, the p–A isotherm and the organization of the
monolayer depend strongly on the composition of the sub-
phase. The presence of metal ions in a subphase has a marked
effect on the behavior of the monolayer, especially for mono-
layers of amphiphilic molecules with coordinating head groups.
When Cu2+ ions were added to the subphase, the character-
istics of the HIHQ monolayer were changed remarkably. Fig. 1
also shows the surface pressure–area per molecule of a mono-
layer of HIHQ on a subphase containing Cu2+. The isotherm
displays a typical condensed region. The limiting area per
˚
molecule on the Cu2+-containing subphase is 20 A2 at a surface
pressure of 30 mN m−1 (A ).
3
0
Fig. 2 shows the SAXS profile of 13-layer LB films of HIHQ
deposited from a subphase containing Cu2+ ions (dashed line).
One broad Bragg peak at 2.388° is observed and the derived
˚
bilayer spacing is 37.008 A. The slight change from 38.711 to
˚
7.008 A is evidence of an altered stacking mode of the HIHQ
3
monolayer on different subphases. As the thickness of a single
˚
monolayer of HIHQ estimated by the CPK model is 18.67 A
in Fig. 3(d), we can deduce that this orientation is adopted.
UV–VIS spectra and XPS studies of monolayers
Fig. 2 Small X-ray scattering patterns of a 13-layer LB film of HIHQ
obtained from pure water (solid line) and from a subphase containing
copper ions (dashed line)
To confirm the interaction between the amphiphilic HIHQ
monolayer and copper ions contained in the subphase, UV–VIS
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J. Mater. Chem., 1998, 8(1), 81–84

spectra and XPS studies of the LB films of HIHQ deposited
in pure water and in a copper containing subphase were
investigated.
revealed that the favoured crystal face was (110). Just as the
Cu ions induce HIHQ formation in the deposition of LB films
in the presence of Cu2+, so the HIHQ monolayer induces
formation of CuSO ·5H O crystals at the monolayer in the
Fig. 4 shows UV–VIS spectra of HIHQ in ethanol, a 13-
layer LB film on a quartz substrate deposited from pure water
and from a subphase containing Cu2+ ions, respectively.
4
2
crystallization process.
As already known, the influence of an inorganic–organic
interface is important in the regulation of inorganic crystal
growth and in the resulting specificity of crystal morphology
and particle aggregation.23–25 It is postulated that the localized
chemical control, spatial localization and constraints, and
molecular complementarity can influence the matching
between the potential fields surrounding the inorganic and
organic surfaces.
Compared with the absorption of HIHQ in ethanol, the 1L
band of an HIHQ LB film deposited from pure water is
bathochromically shifted from 400 to 410 nm, and that of the
a
1
B band in LB film is shifted from 240 to 245 nm. These red
b
shifts might be attributed to a strong interaction between the
molecules of HIHQ in the LB film. Similarly, different absorp-
tion spectra were obtained by constructing LB films on different
subphases. Red shifts of 1L (from 410 to 420 nm) and 1B
HIHQ is an amphiphilic ligand. According to the principle
of coordination and HSAB (theory of hard and soft acids and
bases), it coordinates preferably to soft acids such as Cu2+.
HIHQ is also a typical surface active agent and can increase
the concentration of the solute in domains located under the
monolayer. When the monolayer HIHQ is formed, the local
concentration of CuSO ·5H O, Cu2+ ions and the value of
a
b
(
from 245 to 257 nm) bands were observed in the LB film
deposited from a subphase containing copper ions. In particu-
lar, a band at 203 nm, which is assigned to the np* transition
of the long alkyl chain, was also red shifted and observable in
the UV. All these indicated that interfacial coordination occurs
immediately after spreading the HIHQ molecules on a sub-
phase containing Cu2+ ions.
4
2
supersaturation ratio (S) at the interface are increased. On the
other hand, the surface energy is decreased upon formation of
the monolayer. The monolayer can be also considered as a
different phase formed on the surface of the solution and can
act as a site for heterogeneous nucleation; the Gibbs energy
(G ) of heterogeneous nucleation is much lower than G for
XPS is a technique which provides elemental and chemical
information about a solid surface, and generally, the shift of
binding energy usually provides a measurement of the electron
density about the atom with the shift increasing with decrease
in electron density.21,22 In our experiment, two nitrogen atom
signals (399.1, 400.1 eV) were observed for the HIHQ film
deposited from pure water. A similar result (399.5, 400.1) was
obtained for the HIHQ film deposited from a subphase con-
taining copper ions. The 400.1 eV signal can be assigned to N
I
I
homogeneous nucleation. Thus, nucleation of CuSO ·5H O
occurs initially at the interface between the monolayer and
the solution.
4
2
In the period of crystal growth, since the crystals are attached
to the monolayer, they are restricted in growing towards the
monolayer. Some directions of crystal expansion are inhibited
and a remarkable growth distortion along (110) at the mono-
layer is observed. Since the monolayer cannot bear too heavy
masses when the crystal expands to a certain size its mass will
overcome the support force of the monolayer and the crystal
will separate from the monolayer and drop down to the bottom
of the solution.
1
s of nitrogen atoms near the alkyl chain. The shift of the
binding energy of the nitrogen atom of the quinoline ring
from 399.1 to 399.5 eV) and that of oxygen (from 532.1 to
32.4 eV) show that the coordination bonds were formed in
(
5
conjunction with electron transfer from N and O atoms of the
monolayer to copper ions. The surface composition of the LB
films constructed from the Cu2+ aqueous subphase was also
determined by XPS. It is found that the Cu5N5C atomic ratio
was ca. about 154552; two HIHQ molecules appear to interact
with one copper ion as shown in Fig. 3(d).
The most important aspect of the crystal growth under the
monolayer is the oriented crystallization and the CuSO ·5H O
4
2
crystal has a given face (110) attached to the monolayer
corresponding to the interaction between the crystal and the
monolayer. The key to specificity in nucleation is the presence
of some forms of molecular complementarity between func-
tional groups on the HIHQ monolayer and copper ions, which
determines the specificity in nucleation and orientation of the
crystals. In fact, the monolayer is an organized aggregation
and has a definite lattice structure. If the lattice of the mono-
layer is similar to a certain crystal face of CuSO ·5H O, then
Oriented crystallization of CuSO ·5H O under HIHQ
monolayers
4
2
In the absence of the monolayer, the crystallization of
CuSO ·5H O in the supercooled solution is uncontrolled.
4
2
Nucleation occurred both at the air–water interface and at the
bottom of the trough. These crystals were randomly aggregated
and had a heterogeneous size distribution. However, nucleation
of CuSO ·5H O was induced by the compressed HIHQ mono-
4
2
4
2
this crystal face will readily form under the monolayer.
We studied the lattice structure of the HIHQ monolayer on
the subphase of Cu2+ by computer simulation26,27 and results
are shown in Fig. 6; the structural parameters of the monolayer
are: a=7.0, b=6.0, h=72.5°, with the area per molecule of
layer and was found to be oriented. X-Ray diffraction patterns
˚
Cu2+(HIHQ) on the monolayer being 40.0 A2. The corre-
2
sponding lattice parameters of the (110) crystal face of
Fig. 4 UV–VIS absorption spectra of HIHQ in ethanol solution (a),
HIHQ LB film deposited from pure water (b) and from a subphase
containing Cu2+ ions (c)
Fig. 5 Topographies of the CuSO ·5H O crystals. A CuSO ·5H O
crystal removed from the monolayer (a) is different from one grown
without the monolayer (b).
4
2
4
2
J. Mater. Chem., 1998, 8(1), 81–84
83

K. Kendall, G. L. Messing, J. Blackwell, P. C. Rieke,
D. H. Thompson, A. P. Wheeler, A. Veis and A. I. Caplan, Science,
1
992, 255, 1098.
L. Addadi and S. Weiner, Angew. Chem., Int. Ed, Engl., 1992, 31,
53.
5
1
6
7
8
S. Mann, J. Chem. Soc., Dalton T rans., 1993, 1.
S. Mann, Nature (L ondon), 1993, 365, 499.
X. K. Zhao, S. Baral, R. Rolandi and J. H. Fendler, J. Am. Chem.
Soc., 1988, 110, 1012.
9
R. F. Ziolo, E. P. Giannelies, B. A. Weinstein, M. P. O’Horo,
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Fig. 6 The matching between Cu2+(HIHQ) and the (110) face of
2
CuSO ·5H O. Each Cu2+ ion is coordinated by two HIHQ molecules
4
2
and the arrangement of the Cu2+ under the monolayer is a=7.0,
˚
10 E. M. Landau, S. G. Wolf, M. Levanon, L. Leiserowitz, M. Lahav
and J. Sagiv, J. Am. Chem. Soc., 1989, 111, 1436.
1
2
b=6.0 A and h=72.5°, which is similar to those on the (110) face
˚
of a CuSO ·5H O crystal (6.97, 5.96 A and 72.8°).
4
2
1
I. Weissbuch, F. Frolow, L. Addadi, M. Lahav and L. Leiserowitz,
J. Am. Chem. Soc., 1990, 112, 7718.
S. Rajam, B. R. Heywood, J. B. A. Walker, S. Mann, R. J. Davey
and J. D. Birchall, J. Chem. Soc., Faraday T rans., 1991, 87, 727.
CuSO ·5H O are: 6.97, 5.96 and 72.8° and the area per Cu2+
monolayer.
1
4
2
˚
ion on the face is 39.68 A2 in good accord with the HIHQ
13 X. K. Zhao, J. Yang, L. D. McCormick and J. H. Fendler, J. Phys.
Chem., 1992, 96, 9933.
1
4
A. Berman, D. J. Ahn, A. Lio, M. Salmerson, A. Reichert and
D. Charych, Science, 1995, 269, 515.
Conclusions
1
5
S. Mann, D. D. Archibald, J. M. Didymus, T. Douglas,
B. R. Heywood, F. C. Meldrum and N. J. Reeves, Science, 1993,
261, 1286.
N. Zakareia, S. M. Khalifa, M. Fofal and H. F. Aly, Radiochim.
Acta, 1989, 47, 229.
J. Ouyang, Z. Tai, C. Jiang and W. Tang, Spectrosc. L ett., 1996,
Here, we have reported the synthesis and characterisation of
a novel amphiphilic ligand HIHQ. The characterization of
HIHQ monolayers shows that in a monolayer, HIHQ can
coordinate with copper ions contained in the subphase. As a
new kind of template, the HIHQ monolayer can induce
oriented crystallization of CuSO ·5H O and a good selection
1
1
1
6
7
8
29, 763.
J. Ouyang, Z. Tai and W. Tang, J. Mater. Chem., 1996, 6, 963.
4
2
of the (110) crystal face occurs at the solid state of the
monolayer.
19 G. R. Clemo and R. Howe, J. Am. Chem. Soc., 1955, 3352.
20 J. Ouyang, Z. Tai and W. Tang, T hin Solid Films, 1996, 289, 199.
2
1
K. Kurihara, T. Kawahara, D. Y. Sasaki, K. Ohto and
T. Kunitake, L angmuir, 1995, 11, 1408.
This research work was funded by a grant from the National
Natural Science Foundation of China.
22 Y. Ikeura, K. Kurihara and T. Kunitake, J. Am. Chem. Soc., 1991,
13, 7342.
1
2
3
R. Tang, Z. Tai and Y. Chao, J. Chem. Soc., Dalton T rans., 1996,
4439.
S. Mann, Struct. Bonding (Berlin), 1983, 54, 127.
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J. Mater. Chem., 1998, 8(1), 81–84