Supramolecular structure and substituents effect on the spectral studies of dioxouranium(VI) azodyes complexes

Article abstract of DOI:10.1016/j.molstruc.2011.08.036

The synthesis of several coordination azo compounds of dioxouranium(VI) heterochelates with bidentate azo compounds derived from 4-alkylphenylazo-5- sulfo-8-hydroxyquinoline (HL_n) ligands, are described. The ligands and structural composition of azo complexes were confirmed and characterized by various physico-chemical techniques. The bonding sites of the azo compounds are deduced from IR and ¹H NMR spectra and the ligands were found to bond to the UO22+ ion in a bidentate fashion. The ligands obtained contain NN and phenolic functional groups in different positions with respect to the quinoline group. IR spectra show that the azo compounds (HL_n) acts as a monobasic bidentate ligand by coordinating via the azo nitrogen atom of azodye (NN) and oxygen atom of the phenolic group forming thereby a six-membered chelating ring and concomitant formation of an intramolecular hydrogen bond. The υ₃ frequency of UO22+ has been shown to be an excellent molecular probe for studying the coordinating power of the ligands. The values of υ₃ of the prepared complexes containing UO22+ were successfully used to calculate the force constant, F_UO (1n 10 ^-8 N/) and the bond length R_UO (in ) of the UO bond. A strategy based upon both theoretical and experimental investigations has been adopted. The theoretical aspects are described in terms of the well-known theory of 5d-4f transitions. Wilson's, matrix method, Badger's formula, and Jones and El-Sonbati equations were used to calculate the UO bond distances from the values of the stretching and interaction force constants. The most probable correlation between UO force constant to UO bond distance were satisfactorily discussed in term of Badger's rule and the equations suggested by Jones and El-Sonbati. The effect of Hamette's constant is also discussed.

Full text of DOI:10.1016/j.molstruc.2011.08.036

Journal of Molecular Structure 1007 (2012) 11–19
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Supramolecular structure and substituents effect on the spectral studies
of dioxouranium(VI) azodyes complexes
1
⇑
M.A. Diab, A.A. El-Bindary, A.Z. El-Sonbati , O.L. Salem
Chemistry Department, Faculty of Science (Demiatta), Mansoura University, Demiatta, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 May 2011
Received in revised form 21 August 2011
Accepted 22 August 2011
Available online 24 September 2011
The synthesis of several coordination azo compounds of dioxouranium(VI) heterochelates with bidentate
azo compounds derived from 4-alkylphenylazo-5-sulfo-8-hydroxyquinoline (HLn) ligands, are described.
The ligands and structural composition of azo complexes were confirmed and characterized by various
physico-chemical techniques. The bonding sites of the azo compounds are deduced from IR and 1H
NMR spectra and the ligands were found to bond to the UO22þ ion in a bidentate fashion. The ligands
obtained contain N@N and phenolic functional groups in different positions with respect to the quinoline
group. IR spectra show that the azo compounds (HLn) acts as a monobasic bidentate ligand by coordinat-
ing via the azo nitrogen atom of azodye (AN@NA) and oxygen atom of the phenolic group forming
thereby a six-membered chelating ring and concomitant formation of an intramolecular hydrogen bond.
Keywords:
Supramolecular structures
UO22þ complexes
Hydrogen bonded stabilities
Badger’s formula
Jones and El-Sonbati equations
The
t
3 frequency of UO2þ has been shown to be an excellent molecular probe for studying the coordinat-
2
ing power of the ligands. The values of t3 of the prepared complexes containing UO2þ were successfully
2
used to calculate the force constant, FUO (1n 10ꢀ8 N/Å) and the bond length RUO (in Å) of the UAO bond. A
strategy based upon both theoretical and experimental investigations has been adopted. The theoretical
aspects are described in terms of the well-known theory of 5d-4f transitions. Wilson’s, matrix method,
Badger’s formula, and Jones and El-Sonbati equations were used to calculate the UAO bond distances
from the values of the stretching and interaction force constants. The most probable correlation between
UAO force constant to UAO bond distance were satisfactorily discussed in term of Badger’s rule and the
equations suggested by Jones and El-Sonbati. The effect of Hamette’s constant is also discussed.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
sulfo-8-hydroxyquinoline (HLn). These are achieved by reporting
the studies of (i) the synthesis of novel 4-alkylphenylazo-5-
The chemical properties of quinoline complexes and their
derivatives are of interest due to their biological relevance [1],
coordination capacity [2,3] and their use as metal extracting agent
[4]. A number of recent papers from the laboratory of El-Sonbati
and co-workers [5–12] have described the preparation and isola-
tion of novel solid complexes of several quinoline derivatives. It
was reported that hydrogen bonded supramolecular quinoline
azodyes and/or hydrozone ligands moiety can be viewed as hy-
dride structure, composed of a carbonyl/azomethine function
and OH/@NANH group, which has mutual electronic and steric
influence on the hydrogen bonding formation dependent on the
conformation of the molecules, determined by the two competi-
sulfo-8-hydroxyquinoline (HLn) ligands, (ii) the synthesis of UO2(II)
complexes derived from these ligands, (iii) investigating the
stereochemistry of the complexes based on the electronic spectra
and other measurements, (iv) determining the vibrational mode
of bonding, stability and structures of the hydrogen-bonding com-
plexes, (v) deduced the correlation between UAO force constant to
UAO bond distance using Badger‘s rule and the equation suggested
by Jones and El-Sonbati [17,18], and also, the effect of Hamett‘s
constant is also discussed.
2. Experimental
tive conjugated p– p systems and steric effect [11–16].
p⁄ and n–
All the chemicals used were of BDH quality.
In this paper, we investigate the supramolecular chemistry of
azo 8-hydroxyquinoline derivatives namely 4-alkylphenylazo-5-
2.1. Synthesis of 4-alkylphenylazo-5-sulfo-8-hydroxyquinoline (HLn)
ligands
4-Alkylphenylazo-5-sulfo-8-hydroxyquinolines (HLn) were typ-
ically prepared by adding a 25 mL of distilled water containing
hydrochloric acid (12 M, 2.68 mL, 32.19 mmol) were added to
⇑
Corresponding author.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
Abstracted from her M.Sc.
1
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.08.036

12
M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
aniline (10.73 mmol) or p-derivatives. To the resulting mixture,
stirred and cooled to 0 °C, a solution of sodium nitrite (10.73 mmol,
in 20 mL of water) was added drop wise. The so-formed diazonium
chloride was consecutively coupled with an alkaline solution of
sulfooxine (10.73 mmol) in 20 mL of ethanol containing 602 mg
(10.73 mmol) of potassium hydroxide. The red precipitate, which
formed immediately was filtered and washed several times with
water. The crude product obtained was purified by crystallization
from hot ethanol (yield ꢁ60–80%).
2.3. Measurements
Microanalysis of all samples was carried out at Microanalytical
unit at Cairo University, Cairo, Egypt. Infrared spectra were re-
corded as KBr pellets using a Pye Unicam SP 2000 spectrophotom-
eter. 1H NMR spectra were obtained on a JEOL FX 900Q Fourier
transform spectrometer with deutrated dimethylsulfoxide
(DMSO-d6) as solvent and TMS as internal reference. The equation
suggested by El-Sonbati has been manipulated by using a com-
puter program developed in our laboratories using C Language.
The resulting formed ligands are: 4-methoxyphenylazo-5-
sulfo-8-hydroxyquinoline (HL1), 4-methyphenylazo-5-sulfo-8-
hydroxyquinoline (HL2), 4-phenylazo-5-sulfo-8-hydroxyquinoline
(HL3), 4-chlorophenylazo-5-sulfo-8-hydroxy quinoline (HL4) and
4-nitrophenylazo-5-sulfo-8-hydroxyquinoline (HL5) were charac-
terized by microanalyses, IR and 1H NMR spectroscopy.
3. Results and discussion
The analytical data of the ligands and their uranyl complexes
(1–5) are summarized in Table 1. The stoichiometry of the
NaNO2
HCl
.
H2O
-
/
N+
N
Cl
R
HCl
R
NH2
+
0-5οC
SO3H
PH=10-12
CH3OH, CH3COONa KOH
/
0-5οC
N
OH
SO3H
OH
N
N
N
R
:
SO3H
N
SO3H
=
N
HO
N
N
N
N
N
O
R
R
O
H
H
n=1, R = OCH3 (HL1); n=2, CH3 (HL2); n=3, H (HL3); n=4, Cl (HL4); and n=5, NO2 (HL5)
The formation mechanism of azodye ligands (HLn)
2.2. Synthesis of the uranyl complexes
prepared uranyl(II) complexes are consistent with the proposed
structure [UO2(Ln)2].
A hot solution of UO2(NO3)2ꢂ5H2O, (0.01 mol) in EtOH (30 cm3)
was added to the appropriate ligands (0.022 mol) in EtOH
(30 cm3). The reaction mixtures were maintained under reflux
temperature for 1.5 h to ensure complete reaction. Polycrystalline
solid complexes were immediately formed. The solid complexes
were filtered off while hot, washed several times with EtOH, fol-
lowed by Et2O, and finally dried in a vacuum over P2O5. The ura-
nium content of the complexes was determined by ignition of a
definite mass of each complex at ꢁ1000 °C and weighing the res-
idue as U3O8.
The fact that HLn complexes with UO2(NO3)2ꢂ5H2O involving 2:1
ligand to UO22þ ratio (Table 1), have been isolated, clearly illustrates
that the ligands under study does not introduce sufficiently severe
steric hindrance as to preclude the formation of [UO2(Ln)2] com-
plexes, but its steric feature and arrangement in space can also
favorably influence the stabilization of 2:1 complexes. The com-
plexes are microcrystalline or powder-like, stable under ambient
conditions, and partially soluble in warm DMF and DMSO to vary-
ing extents. The complexes do not melt but decompose on heating
and are converted to U3O8 around 700 °C [16].

M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
13
Table 1
Analytical data of HLn ligand and their UO2þ complexes.a
2
Compoundsb/Serial No.
Color
Yield (%)
Exp.(Calecd.)%
C
Compositions
H
N
S
Metal
HL1
1
HL2
2
HL3
3
HL4
4
Black
Brown
Red
Dark red
Pale red
Orange
60.4
69.3
62.0
70.3
64.7
72.0
68.8
74.3
78.0
80.0
53.88 (53.48)
39.21 (38.95)
56.12 (55.98)
40.33 (40.25)
54.87 (54.71)
39.02 (38.88)
49.64 (49.52)
36.30 (36.18)
48.30 (48.13)
35.66 (35.43)
3.82 (3.62)
2.45 (2.43)
3.90 (3.79)
2.55 (2.52)
3.45 (3.34)
2.22 (2.16)
2.84 (2.75)
2.01 (1.81)
2.72 (2.67)
2.15 (1.97)
12.21 (11.70)
8.81 (8.32)
12.72 (12.25)
8.99 (8.81)
13.22 (12.77)
9.42 (9.07)
11.93 (11.55)
8.75 (8.44)
9.35 (8.91)
6.83 (6.49)
9.71 (9.33)
6.90 (6.71)
10.10 (9.73)
7.32 (6.91)
9.21 (8.80)
6.74 (6.43)
8.83 (8.56)
6.71 (6.30)
–
24.60 (24.19)
–
25.40 (24.95)
–
26.25 (25.70)
–
24.50 (23.92)
–
23.80 (23.43)
[(UO2)2(L1)2]
[(UO2)2(L2)2]
[(UO2)2(L3)2]
[(UO2)2(L4)2]
[(UO2)2(L5)2]
Red
Dark orange
Dark red
Reddish brown
HL5
5
15.30 (14.97)
11.44 (11.02)
a
Microanalytical data as well as metal estimations are in good agreement with the stoichiometry of the proposed complexes.
L1–L5 are the anions.
b
DMF
UO2ðNO3Þ ꢂ 5H2O þ HLn
½UO ðL Þ ꢃðn ¼ 1—5Þ
ƒƒ!
2
n
2
2
Ligands
Complex
As shown in Table 1, the values of yield % is related to the nature
of the p-substituent as they increase according to the following or-
der p-(NO2 > Cl > H > CH3 > OCH3). This can be attributed to the fact
that the effective charge experienced by the d-electrons increased
due to the electron withdrawing p-substituent (HL4 and HL5) while
it decreased by the electrons donating character of (HL1 and HL2).
This is in accordance with that expected from Hamett’s constant
5
80
72
64
56
5
4
(r
R) as in Fig. 1 correlate the yield % values with (
all these values increase with increasing
r
R), it is clear that
3
r
R. The above results
2
1
4
show clearly the effect of substitution in the para position of the
benzene ring on the stereochemistry of UO2(II) complexes. It is
important to note that the existence of a methyl and/or methoxy
group enhances the electron density on the coordination sites
and simultaneously decreases the values of yield %.
3
2
1
The molarconductance of 10ꢀ3 M of solutions of the complexes in
DMSO is calculated as 25 2 °C. It is concluded from the results that
UO2(II) chelates with HLn ligand under investigation were found to
have molar conductance values in the range from 0.8 to
4.6 ohmꢀ1 cm2 moleꢀ1 which indicates that the complexes have mo-
lar ratio of metal:ligand as 1:2. The lesser molar conductance values
-0.5
0.0
0.5
1.0
Hammett substituation coefficient σR
(
)
Fig. 1. The relation between Hamette‘s t substitution coefficient (
r
R) and yield %.
SO3 H
N
N
O
O
N
N
O
R
O
U
O
O
N
R
U
N
N
O
N
O
Trans
SO3 H
n=1, R = OCH3 (HL1); n=2, R = CH3 (HL2); n=3, R = H (HL3); n=4, R = Cl (HL4);
n=5, R = NO2 (HL5);
The structure of UO2(II) complexes

14
M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
indicate that they are all non-electrolytic in nature. This is in accor-
dance with the fact that conductivity values for a non-electrolytes
are below 50 ohmꢀ1 cm2 moleꢀ1 in DMSO [19]. The elemental anal-
yses data concern well with the planned formulae for the ligands and
also recognized the [M(Ln)2] composition of the UO2(II) chelates.
which is assigned to the 1RgU
!
3pU transition, typical of OUO for
the symmetric stretching frequency for the first excited state [16].
In general, most of the azo compounds give spectral localized
bands in the wavelength range 46,620–34,480 and 31,250–
270,370 cmꢀ1. The first region is due to the absorption of the
aromatic ring compared to 1Bb and 1Lb of mono substituted ben-
zene and the second region is due to the conjugation between
the azo group and the aromatic nuclei with intermolecular charge
3.1. Electronic spectra
HLn exhibited bands at 32,500–32,150 cmꢀ1 (CN) (
33,340 cmꢀ1 (H-bonding and association), 40,038–39,460 cmꢀ1
(phenyl) (Ph–Ph⁄, p⁄) [13,14] and 29,340–29,230 cmꢀ1 transition
p–
p⁄), 33,450–
transfer resulting from
p-electron migration to the diazo group
from electron donating substituents. The p-substituents increase
the conjugation with a shift to a longer wavelength. Most of the
simple p-substituted compounds are in the azoid form in cyclohex-
ane and alcohols. The substituted effect is related to the Hamett’s
p–
of phenyl rings overlapped by composite broad (p–
p⁄) of azo struc-
ture. The band due to the n ? p⁄ transition obtained in the visible re-
constant values [8,14,16]. The position of the
p–
p⁄ transition of
gion is associated mainly with the color of the respective compound
p ?
p⁄ transition moves to lower energy.
the azo groups remains as one of the more interesting unanswer-
able questions of molecular spectroscopy. For azo benzenes, as
the possibilities of the mesomerism became greater, the stabiliza-
tion of the excited state is increased relative to that of the ground
state and a bathochromic shift of the absorption bands follow [16].
Based on MO theory [20] the energy terms of the molecular orbital
[14]. The band due to
These shifts or the disappearance of the bands are indicative of coor-
dination of the ligands to UO2(II). The position of their bands is
varied from one dye to the other which may be due attributed to
the p-phenylazosubstituent variabledonating power. The dioxoura-
nium complexes exhibits a new bands at 24,390–24,210 cmꢀ1
,
SO3H
O
SO3H
HO3S
O
Coupling
2
H
H
H
N
N
P-alkylamine, 0-5°C
N
N
N
N
OH
R
O
SO3H
(A/ )
(A)
SO3H
SO3H
SO3H
N
N
N
N
N
N
N
N
N
O
O
H
R
O
R
R
H
H
(C/ )
(B)
(C)
R
N
N
R
N
HO3S
O
O
SO3H
I
H
II
H
II
N
I
N
N
N
N
N
N
H
H
HO3S
O
O
SO3H
N
N
R
R
(B/)
(C2)
Fig. 2. Representation of the dimeric structure and intramolecular hydrogen bond.

M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
15
became more closely spaced as the size of the conjugated system
increases. Therefore, with every additional conjugated double bond
the energy difference between the highest occupied and the lowest
Much has been discussed about the AOH stretching frequency
and intensity of phenol derivatives depending on many factors
(e.g., constituents, medium, etc.). Hoyer [21] reviewed the relation-
ship between the hydrogen bond band and the AOH stretching fre-
quency. In addition to that, there have been many other research
workers who examined the problem in finer and more quantitative
data. This has attracted our attention to acquire the IR technique to
explain and justify the bonding in this study.
vacant p-electron level became smaller and the wavelength of the
first absorption band corresponds to this transition is increased.
The azo group can act as a proton acceptor in hydrogen bonds
[14,16]. The role of hydrogen bonding in azo aggregation has been
accepted for some time.
The free ligands exhibit broad and weak absorption bands in the
region 3310–3320 cmꢀ1 due to
m(OH) and strong bands at 1285–
1295 cmꢀ1 due to d(OH). This latter band is replaced by at a higher
frequency (1345–1350 cmꢀ1) in complexes indicating that the li-
gands coordinate to the metal ion as deprotonated species. The
3.2. IR spectra
The IR spectroscopy is known to be a powerful tool for struc-
tural determinations of the ligand and metal chelates. The assign-
ments of fundamental functional groups are basic for such
purposes.
disappearance of the bands due to t(OH) the complexes confirms
that the C8AOH group takes part in the complex formation through
Oꢀ owing to strong hydrogen bonding both intramolecular
[OAHꢂ ꢂ ꢂN (Fig. 3B), OAHꢂ ꢂ ꢂN (Fig. 3C)] and intermolecular hydrogen
bonding of the OAHꢂ ꢂ ꢂN type between N@N of one molecule and OH
group of another one (Fig. 4E), the frequency of the hydrogen bonded
OH is probably lowered to considerable extent and overlaps with the
OH vibrations, thus appearing as a broad band in the region 3310–
By tracing the IR spectra of the azo compounds, no NH2 stretch-
ing vibrations are apparent. This supports the formation of azodye
ligands. The mode of bonding of the HLn to the metal ions was
elucidated by investigating the IR spectra of the complexes on
the basis of a comparative analysis of the results with respect to lit-
erature data of related systems. The positions of the most relevant
and characteristic bands are due to: (i) azo nitrogen, (ii) OH group
and (iii) CNpy group. Due to the 1, 2-position of these donor groups
in the molecule, six-and/or five membered chelate ring formation
is possible on complexing.
3320 cmꢀ1. All the complexes exhibit
m
(C@C) in ffi1498 cmꢀ1. The
presence of an p-disubstituted benzene ring in the ligands as well
as in the complexes is indicated by strong and sharp bands around
720–740 cmꢀ1. Bands at 2950–3040 cmꢀ1 for the ligands and at
ꢁ2960–3040 cmꢀ1 for the complexes are assigned to
m(CAH)
SO3H
R
N
N
N
O
N
N
N
H O
SO3H
H
H
N
R
N
N
R
HO3S
O H
N
N
O
N
R
SO3H
(D)
SO3
(E)
H
R
N
N
N
O
N
NH
O
SO3
H
N
H
R
H
N
R
O
HO3
S
HN
R
N
O
N
N
N
(G)
(F)
SO3H
R
N
N
N
H
N
HO3
S
O
H
O
SO3H
N
N
R
(H)
Fig. 3. Intermolecular hydrogen bond.

16
M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
paper suggest that in the monomeric form a strong intramolecular
5
hydrogen bond is present. This is in agreement with a previous re-
sult [7–9,23]. The two such monomers lead to the dimmer by
forming an additional hydrogen bonding yielding the bifureated
hydrogen bonds and HANAH nitrogen bridges (Fig. 2A).
4
826
825
824
840
830
820
5
In addition to the two bifureated intra/intermolecular OHꢂ ꢂ ꢂN
hydrogen bonds (Figs. 2 and 3), two more intermolecular hydrogen
bonding interactions are observed between nitrogen atom of azo/
azomethine group and phenolic hydroxyl hydrogen oxygen atom.
This additional H-bonding does not influence the intramolecular
distance which shows a band at a lower frequency than the inter-
molecular interaction. Reason for this behavior might be due to the
additional H-bond which influences the hydrogen bonding ability
of the sulfonyl group by electronic and/or steric factors. The overall
structure of the dimmer is close to planar with a slight shift of the
two quinoline units from the plane. The dimmer is able to dissoci-
ate, while the intermolecular interaction can only be broken if
appropriate hydrogen bond acceptors are attached then acting as
competitors to the quinoline nitrogen atoms.
4
3
3
2
2
1
890
900
910
920
ν3
890
900
910
920
ν3
Fig. 4. The relation between (a) m1 vs. m3 and (b) (mÃ1) vs. m3 (cmꢀ1).
The two hydroxyquinoline units of the dimmer (Fig. 2B0 & 2C2)
are in one plane. The intermolecular (I) as well as intramolecular
(II) hydrogen bonding occur between the hydroxyl group and the
quinoline nitrogen atom. The intermolecular hydrogen bond dis-
tance is shorter than the intramolecular one. This observation
was also reported for other 8-hydroxyquinoline dimmers and
might be due to an unfavored small OAHAN angle for the intramo-
lecular interaction [24].
Hydrogen bonding represents one of the most versatile interac-
tions that could be used for molecular recognition. Several at-
tempts to modulate the strengths of hydrogen bonds in synthetic
host–guest systems [23] and in biological approach. In view of
the large differences in the substituent effects (e.g., the Hamette-
type substituent constants for p.positions and sulfonyl group); it
might be possible to tune the strength of the hydrogen bond effec-
tively by linking the hydrogen-bonding site to a reaction center
through a conjugated spacer, and by altering the charge state of
the reaction center in the solution. At the hydrogen-bonding end,
azo/azomethine is used as a proton acceptor to form a hydrogen
bond with OH group of ligand. The effects of protonation of the
OH on the strength of the hydrogen bond of the ligand are simu-
vibrations of the aromatic system. This is also in agreement with the
data reported by El-Sonbati and co-workers [6–14,16].
The assignment of the 1570 cmꢀ1 (N@N) and 1585 cmꢀ1 (CN)
(non-bonded groups) stretching modes is based on our previous
work [6–14,16], El-Sonbati [18] and Henry et al. [22]. Comparing
the position of these bands for the different ligands, it is obvious
that ring substitution results in a shift to lower frequencies. This
behavior can probably be explained by the lowering in the elec-
tronic density caused by electronegative groups.
1570 cmꢀ1 (N@N) occurs at higher frequency in the ligands
than in the respective complexes by 25–40 cmꢀ1, revealing its
involvement in complexation [11–14]. In this case, the decrease
of the electronic density of the ring may be correlated with the
donor character of the oxygen and/or N atoms in the MAO and
MAN bond. These is also another correlation, observed when com-
paring the position of the m(N@N) band in the free ligand and in the
corresponding complexes. In these cases, the higher shift corre-
sponds to higher electronegativity. Evidently, the presence of elec-
tronegative groups in the ring affects the donor capacity of the O
and N atoms.
These comparisons show that the electronegativity of the ring
substituents produces not only a decrease of the electronic density
lated as a function of the length of the p-conjugated.
over the ring, generating a dimination in the m(N@N) stretching fre-
quency, but also causes a lowering of the donor character of the N
atom.
The interaction of azo compounds, RAN@NAR, with some transi-
tion metal salts produced complexes of at least four different types:
An electron-withdrawing bridge would be expected to increase
the acidity of the proton donor and hence increase its binding abil-
ity. As the electron-withdrawing character of an azo group is rele-
vant to the interesting signal-amplifying behavior [25]. The results
indicate that in the HLn, the effects of the bridges are electron-
withdrawing and electron-donating, respectively. Accordingly,
the efficiency of sp2-hybridized bridges is N@N > C@N.
Coggeshell [26], El-Sonbati et al. [7–13] found three kinds of
bonded –OH structures on the basis of the frequencies: (i) only
the oxygen is in the bridge while the hydrogen is free, (ii) a poly-
mer chain is formed in which both hydrogen and oxygen atoms
participate in the hydrogen bond, (iii) dimmer associates are
formed.
(a) Containing the azo compound attached via nitrogen
bonds.
a-donor
(b) Containing the azo compound bonded via
the -electrons of the AN@NA system.
(c) In case of aromatic derivatives, containing a metallated
p-bonds involving
p
ligand attached via one nitrogen and a metal–carbon
to the ortho carbon of the ring.
r-bond
(d) Containing rearranged nitrogen-donor, e.g. o-semidine azo-
benzene acts as a fairly strong -acid.
Intramolecular hydrogen bond between the nitrogen atom of
C@N(CNPy)/AN@NA (five/six-membered) system and hydrogen
atom of the phenolic hydroxyl hydrogen atom and hydrogen
(C8AOH) are illustrated in (Fig. 2B, C and C0). Intermolecular hydro-
gen bonding can form cyclic dimmer through the OAHꢂ ꢂ ꢂOH type
between C8AOH/N@N of one molecule and C8AOH/N@N group of
another one (Fig. 3H, G and F) and/or ꢂ ꢂ ꢂN type between C8AOH
of one molecule and CNpy/AN@NA of another (Fig. 3D).
In general, hydrogen bonding involving OH groups are proton
donors and their O atoms are proton acceptors. Both intra and
intermolecular OHAN may form a number of structures in a simul-
taneous equilibrium.
p
The presence of a sulfonate group in the quinoline ring confers
special characteristics to the ligand, introducing changes in spec-
troscopic and structural properties of the metallic complexes. A
charge density redistribution trough the ring, due to this nega-
tively charged group, reinforces the ligand bonds counteracting,
in some cases, the weakening effect generated after the coordina-
tion of the metal.
It has been known [7–9,15] that 8-hudroxyquinoline exists, in
solution, in a monomer dimmer equilibrium. The results of this

M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
17
The assignments made from 13C NMR spectrum of the ligand
(HL5) are shown in Table 2.
Therefore, it is clear from these results that the data obtained
from the elemental analyses, IR and 1H NMR spectral measure-
ments are in agreement with each other.
Table 2
13C NMR and 1H NMR spectrum for HL5(ppm vs. TMS).a
b
HL5
13C NMR d, ppm
(C atoms, peak
assignment)
1H NMR d, ppm
(H atoms, peak
assignment)
14
11
07
02
10
08
04
05
06
13
15
09
12
16
03
157.68
157.68
147.15
147.04
146.45
136.87
135.88
129.37
128.22
124.89
124.89
123.58
121.12
121.12
116.89
–
–
9.87
8.44
–
–
8.77
–
4-Derivatives phenylazo-5-sulfo-8-hydroxyquinoline (HLn) re-
act with UO2(NO3)2.5H2O (molar ratio 2:1 in ethanol) giving solid,
color complexes with expected show [UO2(Ln)2] stoichiometry. The
IR spectra of all complexes show two bands attributable to the
asymmetric and symmetric cmꢀ1 stretching frequency. A group
theoretical consideration [31] shows that a linear and symmetrical
triatomic UO22þ ion possessing D symmetry gives rise to three
a
h
–
fundamental modes of vibrations.
8.26
8.26
8.26
7.77
7.77
7.38
In the equatorial bonding the more effective overlap of OAUAO
group orbital by nitrogen than by oxygen in the ligands leads to
lower
m
3 values for UO2þ complexes with the former. The force con-
2
stant of UAO bond in the present investigation has been calculated
following McGlynn et al. [32], and the UAO bond distance for the
corresponding complexes are evaluated using the Jones equation
[17] RUAO = 1.08 Fꢀ1/3 + 1.17. The variation of bond length in the
complexes is due to presence of electron releasing or electron
a
The excellent agreement experimental data supports the assignment suggested
in the present work.
SO3H
4
10
5
3
2
9
13
15
12
16
5
840
8
6
N
7
OH
O2N
N
N
4
1
11
14
.
830
3
3.3. 1H NMR spectra
820
2
The 1H NMR spectra of all the ligands were recorded in DMSO-
d6 at room temperature (Table 2) supports the occurrence of the
form depicted in Figs. 2 and 3. The signal due to methyl/methoxy
proton appeared as singlet in 1.55/3.9 ppm. In the aromatic region,
a few doublets and in few cases some overlapping doublets/multi-
plets are observed in the range d 6.78–8.40 ppm. These doublets/
multiplets are due to aryl protons of three benzene rings. Another
singlet corresponding to one proton for all compounds is observed
in the range d ꢁ 9.2–10.40 ppm. This signal disappeared when a
D2O exchange experiment was carried out. It can be assigned
either to OH or NH, in either case it is strongly deshielded because
of hydrogen bonding with the other atom (N/O) (Figs. 2 and 3). It
may be noted that the integration of this signal perfectly matches
with one proton and there is no other fragment(s) of this signal,
which suggests that only one tautomeric form of the ligand exist
in solution under the experimental conditions. Comparing with
the solid state study, we prefer to assign this signal to OH, how-
ever, assignment of this peak to NH cannot be ruled out provided
solid state structural evidence is not considered [27]. The main
proton chemical shifts of dyes (1–5 except 3) appeared at different
values depending upon the donating power effect of p-substituent
of p-phenylazo groups. As reported in a previous study [28,29], this
hydrogen bonding leads to a large deshielding of these protons.
The shifts are in the sequence: p-NO2 > p-Cl > H > p-OMe > p-CH3.
The 1H NMR spectral data are reported along with the possible
assignments was found as to be in their expected region [30].
The conclusion drawn from these studies lend further support to
the mode of bonding discussed in their IR spectra. In the spectra
of diamagnetic UO2(II) complexes, the resonance arising from
OH proton disappears, indicating the chelation of the ligands
through the deprotonated phenolic OH group. The appearance of
signals due to HC@N [ꢁ8.94 ppm (1H)] protons of the same posi-
tions in the ligand and its diamagnetic complexes shows the
non-involvement of this group in coordination.
1
810
860
880
ν3
900
`
Fig. 5. The relation between m01 vs. m30 (cmꢀ1).
Fig. 6. The relation rUAO (Å) and FUAO (10ꢀ8 N/Å) with m3 (cmꢀ1).

18
M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
Fig. 7. The relation between r3 (Å) and Fx  ð10ꢀ8 N=ÅÞ with m3 (cmꢀ1).
UAO
withdrawing substitutents in the equatorial position. The
m3 values
Fig. 9. The relation between: (1) m3 vs. r1; (2) m3 vs. r2 and (3) m3 vs. r3.
decrease as the donor characteristic increase as is observed for
p
-
electron substituents, where the basicity of the donating atom
increases.
of the bond length of the UAO bond. Assuming no interaction in
the spectral data, the force constant for the UAO bond [FUAO
Uranyl ion UO22þ is quite peculiar in its own structure and in its
identity over wide ranges of vibrations in experimental conditions.
Also, it can be considered from the geometric point of view, as a
10ꢀ8 N/Å], ðFUS ꢀOÞt, and FUO,UO are calculated. The plots of t1
+ t3
and/or t3 vs. force constant for the UAO (FUAO 10ꢀ8 N/
Å),(FxUAO Â 10ꢀ8 N=Å) and the UAO bond distance (rUAO Å),(r3UAO Å)
are linear (Figs. 6 and 7). An increase in the value of the force
single particle. In the present investigation, the
complexes has been assigned in 940–910 cmꢀ1 and 840–
795 cmꢀ1 cmꢀ1 region as t3 and
1, respectively. The t3 values
decreased as the donor characteristics increases as is observed for
-electron substituents, where is the basicity of the donating atom
increases. The experimental results revealed anexcellent linear rela-
t(U@O) in all the
t
constant of the UAO bond vs. t1
+ t3 and/or t3 (Fig. 6) and decrease
on rUAO with increasing t1 t3 and/or t3 were observed. The force
+
p
constant of the UAO bond (Fig. 7). There is also a straight line rela-
tionship between rUAO and the p-substituent, Hamett‘s constant
tion between t1 and t3 with the slope corresponding to (1 + 2 MO/
(r r
R) with negative slope, i.e. the higher the value of R, the lower
MU)1/2 (MO and MU are the masses of oxygen and uranium atoms
respectively, Fig. 4a). It is obvioused that good linearly obtains also
in case of m01 and m03 (Fig. 5).
rUAO and the higher the force constant of the UAO bond (Fig. 8).
Also plotting the values of r1, r2, r3 and rt (bond distance, rUAO
vs. m3 gave straight lines on increasing the value of 3. Our results
3 and rUAO (Fig. 9). The
)
t
Instead of the linear relation between t1 and t3 frequencies, the
also showed inversed relationship between
t
El-Sonbati equation [18] has focused attention on their normalized
differences, in which such differences does not depend on the
masses of oxygen and/or uranium atoms.
In the present investigation, El-Sonbati equation for the calcula-
tion of the UAO bond force constant of the prepared uranyl(II)
complexes should be eventually serve as a fairly accurate measure
electron withdrawing increases the positive charge on the UO22þ
leading to an increase in t3 and FUAO and subsequently a decrease
in rUAO. Accordingly to the rUAO the following order:
HL1 > HL3 > HL2 > HL4 > HL5
was achieved in consistent with the positive charge on the UO22þ
.
These data can be explained by El-Sonbati equation [18] by using
the spectral data of complexes for calculating the symmetric
stretching frequency (mÃ1). The (mÃ1) data served as a an accurate eval-
uation to the (FUAO), (rUAO) and (FꢀUO;UO). There is also a straight line
relationship between (mÃ1) and (
t3) (O@U@O) (Fig. 4b). Perhaps a
new light can be shed on the problem by looking at the values of
r1, r2 and r3 from a different point of view. It might be worthwhile
to focus attention on their normalized differences. Thus a new rela-
tionship between them with respect to rt was determined by Global
error which shows that the excellent validity is in the sequence:
p
p
p
2
2
2
ðr3 ꢀ rtÞ > ðr1 ꢀ rtÞ > ðr2 ꢀ rtÞ :
for the force constant, FUAO and bond lengths, RUAO of the uranyl
complexes.
Due to small scattering power of the oxygen atom, report of the
determination of UAO bond length of some uranyl complexes by
X-ray study is scantly. From the IR spectra, the stretching and
interaction force constants of the complexes have been calculated
[33–35]. The data were used to evaluate the UAO bond distances
using Badger’s formula, Jones equation [17,36] and El-Sonbati
equation [18]. The data are quite close to results reported earlier
for other uranyl complexes [18,17,36,32]. The variation of bond
Fig. 8. The variation of p-substituted Hamette‘s with; (1) rUAO (Å) and (2) FUAO
(10ꢀ8 N/Å).

M.A. Diab et al. / Journal of Molecular Structure 1007 (2012) 11–19
19
length in the complexes is due to presence of electron releasing or
References
electron withdrawing substituents in the equatorial position.
[1] A.E. Comys, Chem. Rev. 60 (1960) 115.
[2] S.D. Conradson, D. Mamera, F. Wastin, D.L. Clark, G.H. Lander, L.A. Morales, J.
Rebizant, V.V. Rondinella, Inorg. Chem. 43 (2004) 6922.
[3] E.N. Rizkalla, G.R. Choppin, Handbook on the Physics and Chemistry of Rare
Earth, vol. 18, Elsevier, Amsterdam, 1994.
[4] K.L. Nash, Solv. Extract Ion Exc. 11 (1993) 729.
[5] A.T. Mubarak, A.Z. El-Sonbati, A.A. El-Bindary, R.M. Issa, H.M. Kera, Appl.
Organomet. Chem. 20 (2006) 819.
[6] M.A. Diab, A.Z. El-Sonbati, R.H. Mohamed, Spectrochim. Acta A 77 (2010) 795.
[7] A.Z. El-Sonbati, M.A. Diab, M.M. El-Halawany, N.E. Salam, Spectrochim. Acta A
77 (2010) 795.
[8] A.Z. El-Sonbati, M.A. Diab, M.M. El-Halawany, N.E. Salam, Met. Chem. Phys. 123
(2010) 439.
[9] A.Z. El-Sonbati, A.A. El-Bindary, A.A. Sarawy, Spectrochim. Acta A 58 (2002)
2771.
[10] A.Z. El-Sonbati, A.S. Shihri, A.A. Bindary, Spectrochim. Acta A 60 (2004) 1763.
[11] A.Z. El-Sonbati, A.A. El-Bindary, A.F. Shoair, Spectrochim. Acta A 58 (2002)
3003.
[12] A.Z. El-Sonbati, R.M. Issa, A.M. Abd El-Gawad, Spectrochim. Acta A 74 (2009)
643.
[13] A.Z. El-Sonbati, A.A. Belal, S.I. El-Wakel, M.A. Hussien, Spectrochim. Acta A 60
(2004) 965.
[14] Ahmed T. Mubarak, A.Z. El-Sonbati, S.M. Ahmed, Coord. Chem. 60 (2007) 1877.
[15] M. Albrecht, K. Witt, E. Wegelins, K. Rissanen, Tetrahedron 56 (2000) 591.
[16] A.Z. El-Sonbati, M.A. Diab, M.S. El-Shehawy, M. Moqbal, Spectrochim. Acta A 75
(2010) 394.
[17] L.H. Jones, Spectrochim. Acta A 11 (1959) 409.
[18] A.Z. El-Sonbati, Spectrosc. Lett. 30 (1997) 459.
[19] J.A. Dean, 14th ed., Lange‘s Hand Book of Chemistry, MEGRAW-Hill, New York,
1992.
[20] S. Millifiori, G. Favini, Z. Phys. Chem. 75 (1971) 23.
[21] H. Hoyer, Z. Electrochem. 49 (1943) 97.
[22] R.P. Henry, P.C.H. Mitchell, J.E. Pure, Inorg. Chim. Acta 7 (1975) 885.
[23] G. Cook, V.M. Rotello, Chem. Soc. Rev. 31 (2002) 275.
[24] M. Albrecht, O. Blau, E. Wegelins, K. Rissanen, New J. Chem. 23 (1999) 667.
[25] H. Suzuki, Electronic Absorption Spectra and Geometry of Organic Molecules,
Academic Press, New York, 1967.
[26] N.D. Coggeshell, J. Am. Chem. Soc. 69 (1947) 1620.
[27] R.N. Jadeja, J.R. Shah, E. Suresh, P. Paul, Polyhedron 23 (2004) 2465.
[28] A.Z. El-Sonbati, A. El-Dissouky, A.A. El-Bindary, A.S. Hilali, Spectrochim. Acta A
57 (2001) 1163.
4. Concluding remarks
HLn behaves as a chelating bidentate monobasic ligand, bonding
through the azo nitrogen atom of azodye (AN@NA) and oxygen
atom of the phenolic group. HLn was characterized by analytical
and spectral methods before using it for the preparation of
complexes.
Substituent effects on reactivities depend mainly on the rate
controlling step and the nature of the transient species. Hamett,s
related the reactivity trends in ligands and complexes with the
stability, i.e., the lower the stability the higher the reactivities.
Based on Hamett‘s relationship, electron withdrawing substituents
to ligands in their complexes enhance the stabilities of these
complexes owing to the decrease of electron density at the metal
central atom and thus the increase of the positive charge on the
metal. Therefore, this effect results in decreasing reactivity. In
contrast, the electron donating substituents increase the electron
density at the metal and leading to decrease the stability of the
metal chelates.
The results arising from the present investigations confirm that
the selected 4-alkylphenylazo-5-sulfo-8-hydroxyquinolines (HLn)
ligands are suitable for building a supramolecular structure.
Moreover, since the azo compounds experience photochemical
isomerization and are therefore of interest for applicative pur-
poses, uranyl complexes containing the 4-alkylphenylazo-5-
sulfo-8-hydroxyquinolines (HLn) moiety combine features which
could be useful in molecular materials. Work is underway on the
synthesis and characterization of further uranyl compounds of this
family of ligands and towards the development of the materials
they produce.
The satisfactory analytical data coupled with the studies pre-
sented above indicate that the complexes under this investigation
are of the general composition, [UO2(Ln)2], where HLn = 4-alkylph-
enylazo-5-sulfo-8-hydroxyquinoline. In view of the well character-
ized of bis[(4-alkylphenylazo)-5-sulfo-8-hydroxyquinoline]uranyl
(II) (involving a monoprotic bidentate (O, N-donor) azo ligand,
octahedral structures with axial oxo group) and O, N-donor at
the equatorial positions in cis-arrangement have been proposed
for these complexes.
[29] A.F. Shoair, A.A. El-Bindary, A.Z. El-Sonbati, R.M. Younes, Spectrochim. Acta A
57 (2001) 1683.
[30] W.W. Simmons, The Sadtler Handbook of Proton NMR Spectra, Sadtler
Research Laboratories, Philodelphia, PA, 1978.
[31] V.K. Rastogi, A.N. Pandey, S.L. Gupta, R.C. Saxena, Ind. J. Pure Appl. Phys. 19
(1980) 379.
[32] S.P. McGlynn, J.K. Smith, W.C. Neely, J. Chem. Phys. 35 (1961) 105.
[33] A.Z. El-Sonbati, A.A. El-Bindary, M.A. Diab, Spectrochim. Acta A 59 (2003) 443.
[34] A. El-Dissouky, A.Z. El-Sonbati, A.A. El-Bindary, A.S. Hilali, Spectrochim. Acta A
57 (2001) 1163.
[35] A.Z. El-Sonbati, A. El-Dissouky, Transition Met. Chem. 12 (1986) 112.
[36] R.M.N. Badger, J. Chem. Phys. 3 (1935) 710.