Supramolecular compounds of azo dyes derived from 1-phenylazo-2-naphthol and their nickel and copper complexes

Article abstract of DOI:10.1080/10610278.2014.899598

In this study, experimental techniques including Raman, infrared and X-ray crystal diffraction, as well as quantum chemistry calculations, are used to investigate two new azo dyes supramolecular complexes: 1-phenylazo-2-naphthol (Sudan I) with nickel(II)

Full text of DOI:10.1080/10610278.2014.899598

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Supramolecular compounds of azo dyes derived from
1-phenylazo-2-naphthol and their nickel and copper
complexes
Gilson Rodrigues Ferreiraabc, Bruna Luana Marciald, Humberto Costa Garciaa, Fabiano R.L.
Faulstiche, Hélio F. Dos Santosb & Luiz Fernando C. de Oliveiraa
a Núcleo de Espectroscopia e Estrutura Molecular (NEEM), Departamento de Química,
Universidade Federal de Juiz de Fora, Juiz de Fora, MG 36036-330, Brazil
b Núcleo de Estudos em Química Computacional (NEQC), Departamento de Química,
Universidade Federal de Juiz de Fora, Juiz de Fora, MG 36036-330, Brazil
c Faculdade de Ciências Médicas e da Saúde de Juiz de Fora, Hospital Maternidade
Therezinha de Jesus - SUPREMA, Juiz de Fora, MG 36033-003, Brazil
d Instituto Federal Goiano, Campus Morrinhos, Rodovia BR-153, Km 633, Caixa-postal: 92,
Morrinhos, GO 75650-000, Brazil
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e Centro de Tecnologia Mineral (CETEM), Ministério da Ciência, Tecnologia e Inovação,
Cidade Universitária, Rio de Janeiro 21941-908, Brazil
Published online: 07 Apr 2014.
To cite this article: Gilson Rodrigues Ferreira, Bruna Luana Marcial, Humberto Costa Garcia, Fabiano R.L. Faulstich, Hélio
F. Dos Santos & Luiz Fernando C. de Oliveira (2014): Supramolecular compounds of azo dyes derived from 1-phenylazo-2-
naphthol and their nickel and copper complexes, Supramolecular Chemistry, DOI: 10.1080/10610278.2014.899598
To link to this article: http://dx.doi.org/10.1080/10610278.2014.899598
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Supramolecular Chemistry, 2014
http://dx.doi.org/10.1080/10610278.2014.899598
Supramolecular compounds of azo dyes derived from 1-phenylazo-2-naphthol
and their nickel and copper complexes
Gilson Rodrigues Ferreiraa,b,c, Bruna Luana Marciald, Humberto Costa Garciaa, Fabiano R.L. Faulstiche,
b
Helio F. Dos Santos and Luiz Fernando C. de Oliveira *
a
´
a
´
Nucleo de Espectroscopia e Estrutura Molecular (NEEM), Departamento de Quımica, Universidade Federal de Juiz de Fora, Juiz de
Fora, MG 36036-330, Brazil; Nucleo de Estudos em Quımica Computacional (NEQC), Departamento de Quımica, Universidade
´
b
´
´
´
c
ˆ
´
´
Federal de Juiz de Fora, Juiz de Fora, MG 36036-330, Brazil; Faculdade de Ciencias Medicas e da Saude de Juiz de Fora, Hospital
Maternidade Therezinha de Jesus - SUPREMA, Juiz de Fora, MG 36033-003, Brazil; Instituto Federal Goiano, Campus Morrinhos,
´
Rodovia BR-153, Km 633, Caixa-postal: 92, Morrinhos, GO 75650-000, Brazil; Centro de Tecnologia Mineral (CETEM), Ministerio da
ˆ ´
Ciencia, Tecnologia e Inovacꢀa˜o, Cidade Universitaria, Rio de Janeiro 21941-908, Brazil
d
e
(Received 12 February 2014; accepted 24 February 2014)
In this study, experimental techniques including Raman, infrared and X-ray crystal diffraction, as well as quantum chemistry
calculations, are used to investigate two new azo dyes supramolecular complexes: 1-phenylazo-2-naphthol (Sudan I) with
nickel(II) ion and 1-(2,4-xylylazo)-2-naphthol (Sudan II) with copper(II) ion. The crystallographic structures have been
solved for bis-1-(pheny-l-azo)-2-naphtholatenickel(II) and bis-1-(2,4-xylylazo)-2-naphtholatecopper(II) complexes,
revealing the presence of supramolecular interactions, such as the centroid–centroid p-stacking interactions and CH· · ·p
hydrogen interactions. These weak intermolecular interactions appear to play an important role on the crystal structure
stability for both compounds. Density functional theory calculations at B3LYP/6-311þþG(d,p) level were performed in
order to help understanding such molecular interactions and to assign the vibrational spectra. The experimental and
theoretical data have allowed the analysis of the packing forces, revealing charge accumulation at key molecular regions.
Keywords: azo dyes; metal complexes; supramolecular chemistry; Raman spectroscopy
Introduction
Crystallographic structures of azo dyes have been
described in the literature (12–17), but most of the work
focuses on the tautomeric equilibrium between azo and
hydrazo forms, mainly for the azo dyes derived from
1-phenylazo-2-naphtol (Scheme 1) where the structural
difference is on the substituent bonded to the phenyl or
naphthol rings. However, the discussions about supramo-
lecular interactions are rarely mentioned. The supramole-
cular packaging of this class of compounds is completely
different when the functional groups are changed, and
weak interactions of the p-stack type can be observed.
Several inorganic synthesis (3–5, 18) have been carried
out aiming to produce more intense dyes using transition
metal ions; however, no crystallographic structures of such
azo dyes derived from 1-phenylazo-2-naphthol have been
described so far.
Azo compounds belong to a very important class of
chemicals receiving attention by the scientific media, as
they are highly coloured and can be used as dyes and
pigments, even in the food industry (1). The structures of
the azo dyes are of specific interest to the dyes and
pigments industries, as many of the materials commer-
cially significant properties (solubility, habit, stability and
even colours) are dependent on or are influenced by their
solid-state structures (2). Recently, azo metal chelates have
also attracted increasing attention due to their interesting
electronic and geometrical features in connection with
their application for molecular memory storage, nonlinear
optical elements and printing systems (3–5). Another
advantage for complexes involving azo dyes and transition
metal ions is the possibility to obtain new compounds with
biological activity (6, 7). Transition metals have also been
used in the treatment of several diseases, as metal
complexes which are capable of cleaving DNA under
physiological conditions are of interest in the development
of metal-based anticancer agents (8, 9). This is an impetus
for inorganic chemists to develop innovative strategies for
the preparation of more effective, target-specific and
preferably non-covalently bound anticancer drugs (10, 11).
Supramolecular interactions of aromatic systems have
attracted the attention of many researchers in recent years
(19–23). The supramolecular arrangement of azo dyes are
based on non-covalent supramolecular interactions, which
keep packaged the whole system, and also has raised
particular interest in this chemical system. Azo dyes derived
from 1-phenylazo-2-naphthol system have two aromatic
ringswhicharegoodcandidatestogenerateinteractionssuch
*Corresponding author. Email: luiz.oliveira@ufjf.edu.br
q 2014 Taylor & Francis

2
G.R. Ferreira et al.
Scheme 1. Tautomeric equilibrium between azo and hydrazo form for Sudan I (R1 ¼ R2 ¼ H) and Sudan II (R1 ¼ R2 ¼ CH3).
as p-stacking and are responsible for different arrangements
of the crystalline system (24). However, the formation of a
metallic complex with azo dyes can provide other
arrangements presenting no crystalline analogy with the
isolated ligand; in this sense, there are few studies in
literature reporting the supramolecular arrangement of
metallic complexes involving azo dyes (2, 15, 25).
equipped with CCD detector thermoelectronically refriger-
ated (–708C), 80 £ objective having 0.75 numerical aperture,
1800 grooves/mm grating and 300 mm confocal aperture. The
samples were excited by a 785.5-nm diode laser with 60 S
exposition time and five accumulations for each spectral
window. Infrared spectra were recorded in a Bomem FTIR
MB102 spectrometer in the 1800–360 cm–1 region, of the
sample supported in a KBr pellet, with 4 cm–1 of spectral
resolution, and 128 scans. Single-crystal X-ray data were
collected using an Oxford Gemini A (Ultra Diffactometer
In the present study, we report the experimental and
theoretical investigation using Raman, infrared spec-
troscopy and X-ray diffraction of bis-1-phenylazo-2-
naphtholatenickel(II) and bis-1-(2,4-xylylazo)-2-naphtho-
latecopper(II) complexes, aiming to get insight on the
main driving forces responsible for the supramolecular
interactions in such compounds.
˚
Agilent, CA, USA) with m(Cu K) (l ¼ 3.959 A) at
temperature 150 K for Sudan I and Sudan II complexes.
Data collection, reductionandcell refinement were performed
by CrysAlis RED, Oxford diffraction Ltd (26), Version
1.171.32.38. The structures were determined and refined
using SHELXL-97 (27). The empirical isotropic extinction
parameter x was refined according to the method previously
described by Larson (28), and a Multiscan absorption
correction was applied (29). The structures were drawn by
ORTEP-3 for Windows (30) and Mercury (31) programs.
Experimental
Materials and experimental methods
All azo-compounds were purchased from Aldrich and used
without any further treatment; the solvents used were
spectroscopic grade. The synthesis of bis-1-(phenylazo)-2-
naphtholatenickel(II) was carried out by slow addition of
1 mmol of 1-phenyl-azo-2-naphthol dissolved in methanol
30mL to 1 mmol of Na2CO3 under stirring and then to
1 mmol of nickelchloride hexahydrate dissolvedindeionised
water. The reaction was refluxed at 608C for ca. 8 h, yielding
an orange solid which was filtered and washed several times
with cold deionised water; after drying it was isolated in 67%
yielding. Good crystals for X-ray analysis were obtained
from slow evaporation of a toluene solution in a test tube on
the bench at room temperature. The procedure to obtain bis-
1-(2,4-xylylazo)-2-naphtholatecopper(II) was similar:
1 mmol of 1-(2,4-xylylazo)-2-naphthol was solubilised in
30mLofmethanoland1 mmolofNa2CO3 slowlyaddedwith
stirring, followed by 1 mmol of CuCl2. The resulting solution
was refluxed for 8 h whereupon a red precipitate was isolated
by filtration and washed with cold water to yield 68% of the
desired product. The same procedure for obtaining good
crystals for X-ray analysis described above was done for the
copper complex. Themeltingpoints forboth complexeswere
above 3508C, and the molecular formulae obtained by X-ray
diffraction were C32H22NiN4O2 and C36H30CuN4O2.
Calculations
The structures for the metal complexes were fully
optimised in gas phase at B3LYP (32, 33) level using
the 6-311þþG(d,p) (34) triple-zeta basis set with
inclusion of diffuse and polarisation functions at heavy
and hydrogen atoms (the optimised structures are shown
in Figure S1 as Supplementary Material). All of the
geometries were considered as neutral species with the
multiplicities set to singlet for the nickel complex and
doublet for the copper complex. The final geometries
were characterised as minima on the potential energy
surface through harmonic frequencies calculation (all
frequencies found real). The infrared (IR) and Raman
intensities were also calculated and the band spectra
simulated by fitting a Lorentzian-type function (35), with
parameters set to 10 cm–1 for the average width of the
peaks at half height and 2 £ 10–6 mol cm–3 for sample
concentration. The spectra for all species were then
assigned according to the normal-mode analysis. Fre-
quency scaling was not needed as the predicted values and
the spectra profiles were in satisfactory agreement with
experimental ones, allowing unambiguous band assign-
Raman spectra were recorded in the solid phase using a
LabRAM, Micro-Raman Spectrometer Jobin Yvon/Horiba

Supramolecular Chemistry
3
Figure 1. (Colour online) Thermal ellipsoid representation of (a) C36H30NiN4O2 and (b) C36H30CuN4O2 showing the atom labelling
scheme. The thermal ellipsoids are scaled to the 50% probability level. Hydrogen atoms are drawn to an arbitrary scale.
ments. In order to analyse the intermolecular interactions
in the solid state, the unit cell containing four repeating
molecular units were partially optimised with only
hydrogen positions set freely for optimisation. The
molecular electrostatic potentials (MEP) (36, 37) for the
distinct complexes were generated using the CUBEGEN
utility available in the Gaussian 09 package. The MEP
was mapped onto 0.02 e/bohr3 electron density surface.
All calculations were carried out with Gaussian 09 (38)
group P 2 1 with four molecules in the unit cell. The
repeating unit of this structure occurs along its vertices and
the centre of the unit cell, clearly showing the existence of
an inversion centre. The crystallographic structure
presents a central unit of the complex pointing to other
four units, each one at the corners of a parallelogram,
which also presents the nickel atoms exactly over the axis
of the same parallelogram (Figure 2(a)), whereas the
supramolecular arrangement can be seen along the b axis,
according to Figure 2(b). The crystallographic refinements
are listed in the Table 1 and the bond lengths and bond
angles are shown in Table S1 as Supplementary Materials.
The structure described here shows bond angles of 172.828
for the dihedral C11N1N2C1 (Figure 1(a)) and 2147.378
for the C12C11N1N2. For the free ligand, these angles are
close to 1808 indicating a planar structure(35). The
centroid-Ni-centroid (ring naphthol or ring phenyl) angle
is 180.08 which affects the overall crystallographic
arrangement by creating one adjacent plane in relation to
´
program as installed in the computers of the Nucleo de
´
Estudos em Quımica Computacional.
Results and discussion
X-ray diffraction measurements for the coordination
complexes
Figure 1(a) shows the thermal ellipsoid representation of
the new structure for Sudan I nickel complex; this nickel
complex was crystallised in the triclinic system, space
Figure 2. (Colour online) (a) Bi-dimensional arrangements parallel to the ac plane for the C36H30NiN4O2 (Symmetry Code i: 1 2 x,
1 2 y, 1 2 z), (b) arrangements parallel to the ab plane and (c) electrostatic and p-stacking interaction parallel to the ab plane.

4
G.R. Ferreira et al.
Table 1. Main crystallographic parameters of the structure refinement for C36H30NiN4O2 and C36H30CuN4O2 complexes.
Compound
Complex nickel Sudan I
Complex cooper Sudan II
Formula
C32H22NiN4O2
553.23
149.95(10)
Monoclinic
P21/n
17.1357(6)
3.95810(10)
17.2578(7)
98.064(3)
1158.93(7)
2
C36H30CuN4O2
61,418
150.00(10)
Monoclinic
P21/n
10.7157(2)
11.9298(2)
11.7645(2)
105.802
1447.09(4)
2
Formula weight (g mol–1
Temperature (K)
Crystal system
Space group
)
˚
a (A)
˚
b (A)
˚
c (A)
b
V (A)
3
˚
Z
Crystal size (mm)
uPang1 ðdegÞ
0.49 £ 0.08 £ 0.04
2.58–66.33
1.585
0.76 £ 0.24 £ 0.11
1.79–29.52
1.410
dcalc ðg cm–1
Þ
mðMo KaÞ ðmm–1
Þ
0.879
0.796
Transmission factors ðmin=maxÞ
Reflections measured=unique
Rint
0.916/0.961
19132/2042
0.0742
1699
178
0.0699
0.2106
1.120
0.177
0.794/0.917
67620/4064
0.0564
3459
196
0.0346
0.0987
1.0987
0.072
Observed reflections ½F2o . 2sðFo2Þꢀ
No. of parameters refined
[Fo . 2s(Fo)]
wR [Fo2 . 2s(Fo)2]
S
RMS peak
the naphthol ring and to the phenyl rings (Figure 2(c)). The
solid-statearrangementdisplayssupramolecularinteractions
of the p-stacking type between the two adjacent rings of the
naphthol group (Figure 2(c)). The distance between the two
centroids from the naphthol groups (opposite rings) is 3.852
˚
(2)A, whereasthe centroid–centroiddistanceoftheadjacent
˚
rings is 3.958(2) A (not shown in Figure 2(c)). These
complex was crystallised in the monoclinic system, space
group P21/n with two molecules in the unit cell. The
repeating unit of this structure occurs with the metal
located in the axis b of the unit cell extending over the ac
plane (Figure 3(a)) and the supramolecular packaging
along ab plane (Figure 3(b)). Conventional interactions
such as p-stacking type were not found, although this
compound contains several centroids. However, it is
strongly suggestive that the interaction that keeps the
packaging of this supramolecular system is based on the
CH interaction present in the naphthol rings with adjacent
centroids present in the phenyl groups (CH· · ·p interaction
– Figure 3(c)). The distance between the CH b groups
from the naphthol ring to the adjacent centroid of the
distances suggest an arrangement which is maintained by
supramolecular p-stacking interactions observed between
thecentroidsofthenaphtholgroups, being notablyimportant
for the packaging of this crystalline system. Such packing in
columns of p-stacking molecules extends in the same
direction of the b-axis.
In order to probe the molecular arrangement of the unit
cell, the electrostatic potential surface was generated for
the solid-state structure including four repeating units.
Figure S2 in the Supplementary Material shows the MEP
along the packaging of this supramolecular crystal lattice,
whose colour scale ranges from red (negative MEP) to
blue (positive MEP). The nickel atom seems to experience
a purely electrostatic interaction with the oxygen atoms of
the layers above and below. The interplanar Ni–O
˚
distance was 3.188 A (Figure 2(c)) and is smaller than the
˚
one measured between adjacent rings (3.958 A, p-
stacking). It is straightforward to note that the oxygen
atoms are much more polarised than other parts of the
molecule suggesting an electrostatic interaction with the
metal atom.
˚
phenyl ring is 3.399 A, as shown in Figure 3(c). It is also
important to note that the angle between the naphthol
centroids and the CH group of the phenyl ring is 155.868,
which is significantly smaller than the optimal value of
1808, decreasing the interaction strength. The structure
described here shows bond angles of 176.508 for
C11N2N1C5 and 276.718 C12C11N1N2 dihedral. This
clearly shows that the phenyl ring is almost perpendicular
to NN bond mainly due to the steric hindrance of methyl at
ortho position. The MEP for the cooper complex
monoclinic system is shown in Figure S3 in the
Supplementary Material; the result suggests that in the
gas phase, the phenyl ring is the molecular region of
the complex presenting a higher charge density, whereas
the hydrogen from the naphthol ring has been character-
ised as positive centre, suggesting a non-classical CH· · ·p
Figure 1(b) shows the thermal ellipsoid representation
of the new structure for Sudan II copper complex; this

Supramolecular Chemistry
5
Figure 3. (Colour online) (a) Bi-dimensional arrangements parallel to the ab plane for the C36H30CuN4O2 (Symmetry Code i: 1 2 x,
1 2 y, 1 2 z), (b) arrangements parallel to the bc plane and (c) interactions of the type CH· · ·p in the bc plane.
˚
O–Cu distance, of 1.877(17) A. The nickel complex
˚
presents the N–Ni bond equal to 1.911(3) A, which is also
˚
slightly shorter than the N–Cu bond 1.918(12) A.
interaction directed to the phenyl ring centroid as the
major feature responsible for the supramolecular packa-
ging of this system.
Molecular modelling based on DFT calculation was
used to predict structural and spectroscopic properties for
the nickel and copper complexes. The B3LYP/6-31þþG
(d,p)-optimised geometries for the two complexes are
depicted in Figure S1 as Supplementary Material, with the
main structural parameters quoted in Tables S1 and S2.
Both complexes show square planar geometry around the
metal with O1NiO1i, O1CuO1i, N1NiN1i and N2CuN2i
angles equal to 1808, which is in good agreement with the
experimental data. Overall, there are no significant
differences between the experimental data from X-ray
diffraction and those calculated for isolated molecule,
which suggests that intermolecular forces are not much
pronounced. Experimentally, the Ni(II) complex presents
O1NiN1 angles equal to 90.018 and for the copper complex
the O1CuN2 angle is 89.588. Regarding the O–Ni bond, the
Spectroscopic analysis
Table 2 shows the main vibrational wavenumbers and
assignments of the IR and Raman spectra for both
compounds. The observed and calculated IR spectra can
be seen in Figures S4 and S5 in Supplementary Material.
Although having different metal centres and structural
differences on the phenyl rings, both complexes present
similar IR spectra. The IR spectra present bands at 565, 471
and 456 cm–1 for the nickel complex which are assigned
according to the normal mode analysis as ns(NiO). The
band at 502 cm–1 has been assigned to ns(NiN). In the low
wavenumber region, the copper complex presents bands at
563, 494 and 454 cm–1, due to the symmetric ns(CuO),
whereas the band at 506 cm–1 refers to the ns(CuN) mode.
Generally, such bands are difficult to attribute due to their
˚
experimental value is 1.843(3) A, slightly shorter than the

6
G.R. Ferreira et al.
Table 2. Experimental main vibrational wavenumbers (in cm–1) for bis-1-phenylazo-2-naphtholatenickel(II) and bis-1-(2,4-xylylazo)-
2-naphtholatecopper (II).
Infrared
Nickel complex Copper complex
Raman
Assignments
Nickel complex Cooper complex
Assignments
1618 m
1595 w
1548 m
1500 vs
1463 w
1614 m
1595 w
1548 m
1502 vs
1477 w
1377 w
1406 w
1359 vs
nsCC naphthol
nsCC naphthol
1588 w
1543 w
1499 w
1600 w
1550 w
1506 w
1483 w
1443 w
1357 vs
1301 w
1241 w
1205 w
nsCC þ dCH
nsCC þ dCH þ nsCN
nsCO þ dCH þ nsNN
dCH þ nsCC þ nsNN
nsCO þ dCH þ nsCN
dCH þ nsCO þ nsCC
nsCC
nsCC þ dCH naphthol
nsCC þ dCH þ nsCC þ nsCN
nsCO þ dCH þ nsCN
1463 w
nsCO þ dCH3 þ nsCN þ nsCC 1360 vs
1404 w
1369 vs
1321 m
1304 m
1257 w
1214 w
1187 m
1147 m
1103 w
1028 w
1000 m
958 w
909 w
862 w
734 vs
695 vs
565 w
nsCO þ dCH þnsCN þ nsCC
nsCC þ dCH þ nsCN
nsCC þ dCH þ nsCN
nsCO þ dCH þ nsCC
nsCC þ dCH naphthol
nsCC þ dCH
1302 w
1250 w
1199 m
1166 m
1095 w
996 w
nsCC þ dCH
nsCC þ dCH
nsCC þ dCH
nsCC þ dCH
nsCC þ dCH
vCH
vCH
dCCC
vCH/nCuN
dCCC
dCCC
vCH þ nNiN
nsCC þ nsCN þ nsCN
vCH
vCH
vCH
dNiN/dCuN
dNiO þ vCH/nsCuO
dNiO/dCuO
1307 m
1255 w
1215 w
1183 m
1149 m
1097 w
1034 w
995 m
948 w
909 w
872 w
760/719 vs
699 w
563 w
1099 w
998 w
908 w
nsCC þ dCH
906 w
738 w
nsCC þ dCH
nsCC þ dCH naphthol
580 w
556 w
533 w
dCH/dCH3
dCCC
561 w
530 w
523 vs
510 w
493 w
427 vs
389 m
297 m
263 w
228 m
200 m
dCH
nsCuN þ nsCC þ vCH
vCH
vCH naphthol
431 w
375 w
vCH naphthol
nsNiO þ nsCC/nsCuO
502 w
471 w
456 w
506 w
494 w
454 w
nsNiN/nsCuN
nsNiO/nsCuO þ nsCC
nsNiO/nsCuO
280 w
234 w
199 w
Note: vs, very strong, w, weak and m, medium.
relatively low intensities, being a combination of several
vibrational modes such as ns(CC), v(CH) and ds(CH), all of
them related to the organic skeleton. Another interesting
aspect of these spectra is the split of the vibrational modes
into two distinct moieties of the molecules, namely the
phenyl ring and the naphthol ring. Both complexes show
bands at 1500 cm–1 as the most intense ones, assigned as a
coupled mode [(ns(CN) þ ns(CC) þ n(CvO) þ ds(CH)];
the bands at 1369/1359 cm–1 are also assigned to a mixture
of vibrational mode [(ns(CN) þ ns(CC) þ ds(CH)], and the
bands at 734/760 cm–1 are assigned to the vs(CH) from the
naphthol group for the nickel/copper. The band at 695 cm–1
for the nickel complex is also assigned to the vs(CH) mode
from the naphthol group as an intense band, whereas for the
copper complex the same vibrational mode can be seen at
699 cm–1 as a weak band. Most of the medium intensity
bands, such as those found at 1618/1614, 1548/1548,
1304/1307, 1147/1149 and 1000/995 cm–1, are assigned as
the symmetric n(CC) modes, containing a contribution
from the ds(CH) angular deformation. Two other IR bands
are also important: at 1377 cm–1 for the copper complex,
assigned as the [ns(CN) þ ns(CC) þ n(CvO) þ ds(CH3)]-
coupled vibrational mode, and at 1321 cm– 1, of
medium intensity, for the nickel complex, assigned to the
[ns(CN) þ ns(CC) þ ds(CH)] mode.
The observed Raman spectra can be seen in Figure 4
and the calculated spectra are shown in Figure S6 in
Supplementary Material. In the low wavenumber region,
the vibrational modes are related to the metal–ligand
bonds; for the nickel complex the band at 263 cm–1 is
assigned to the d(NiN) mode, the band at 228 cm– 1 to the
Figure 4. Experimental Raman spectra (a) for bis-1-
(phenylazo)-2-naphtholatenickel(II) and (b) for bis-1-(2,4-
xylylazo)-2-naphtholatecopper(II).

Supramolecular Chemistry
7
[d(NiO) þ v(CH)] and the band at 200 cm– 1 to d(NiO).
Supplementary material
For the copper complex, the same bands are observed at
280 cm– 1, assigned to the d(CuN) mode, at 234 cm– 1 as
d (CuO) and at 199 cm– 1 as d(CuO). The band at
510 cm– 1 can be attributed to the [ns(NiN) þ v(CH)]
mode; this band is observed in the nickel complex
spectrum but it is not present for the copper complex.
Several medium and weak intensity bands with
contribution of the symmetric ns(CC) mode and angular
deformation d(CH) can also be noted, as for instance the
ones at 1543/1550, 1250/1241, 1199/1205, 1095/1099
and 996/998 cm21 for the nickel/copper complexes,
respectively. The nickel complex spectrum presents
three bands with medium intensity in the region around
1360 cm– 1, assigned as [d(CH) þ ns(CvO) þ ns(CC)]-
coupled mode. Less important bands, which can be used
Figure S1 shows the optimised geometries for both compounds at
B3LYP/6-311þþG(d,p) theory level, and Figures S2 and S3
shows the molecular electrostatic potentials (MEP) from total
SCF density for the nickel complex and cooper complex,
respectively, calculated at B3LYP/6-311þþG(d,p) theory level.
The Figure S4 and S5 show the experimental and theoretical
infrared spectra for both compounds, and Figure S6 shows the
calculated Raman spectra at B3LYP/6-311þþG(d,p) level for
nickel and copper complex, respectively. Tables S1 and S2
display the structural parameters obtained from X-ray diffraction
and calculated at B3LYP/6-311þþG(d,p) level. Cambridge
Crystallographic Data Centre (CCDC) 882018 and 882019
contains the supplementary crystallographic data for Sudan I
complex nickel and Sudan II complex copper. These data can be
obtained free of charge at http://www.ccdc.cam.ac.uk or from the
CCDC, 12 Union Road, Cambridge CB2 IEZ, UK [Fax:
(internet.) 1 44-1223/336-033; Email: deposit@ccdc.cam.ac.uk].
to characterise the ligands, are the ones at 520 cm– 1
,
assigned to d(CCC), and at 427 cm– 1, assigned to v
(CH). Previous assignments are consistent with struc-
tures observed in the solid state (Figure 1) and can be
further used for characterisation of azo dyes complexes
in which crystal diffractions are not available.
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Supramolecular Chemistry
9
Gilson Rodrigues Ferreira,
Bruna Luana Marcial,
Humberto Costa Garcia, Fabiano
´
R.L. Faulstich, Helio F. Dos Santos and
Luiz Fernando C. de Oliveira
Supramolecular compounds of azo dyes
derived from 1-phenylazo-2-naphthol
and their nickel and copper complexes
1–9