Stereochemistry of new nitrogen containing heterocyclic compound: XII. Polymeric uranyl complexes of hydrazone compounds

Article abstract of DOI:10.1016/j.saa.2004.06.058

Several dioxouranium(VI) heterochelates with tetradentate monobasic hydrazone compounds (HL_n) have been synthesized. The heterochelates of the type [(UO₂)₂(HL_n)(L_n) ₂(OAc)₂(OH

Full text of DOI:10.1016/j.saa.2004.06.058

Spectrochimica Acta Part A 61 (2005) 1847–1851
Stereochemistry of new nitrogen containing heterocyclic compound
XII. Polymeric uranyl complexes of hydrazone compounds
A.A. Al-Sarawya, A.A. El-Bindaryb,∗, D.N. El-Sonbatib
a
Mathematical and Physical Sciences, Faculty of Engineering, Mansoura University, Egypt
b
Chemistry Department, Faculty of Science (Demiatta), Mansoura University, Demiatta, Egypt
Received 21 April 2004; accepted 29 June 2004
Abstract
Several dioxouranium(VI) heterochelates with tetradentate monobasic hydrazone compounds (HLn) have been synthesized. The hete-
rochelates of the type [(UO2)2(HLn)(Ln)2(OAc)2(OH2)2]n have been characterized on the basis of elemental analyses, IR and electronic
spectra, conductance and magnetic susceptibility measurements. The complexes are polymeric, non-electrolytes, diamagnetic and eight-
coordinated.
Wilson, G.F. matrix method, Badger’s formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force
constants from which the U O bond distances were calculated. The bond distances of these complexes were also investigated.
© 2004 Published by Elsevier B.V.
Keywords: Polymeric complexes; Force constant; U O bond distance
1. Introduction
without any further purification. The experimental technique
has been described previously [1–3].
Hydrazone compounds of rhodanine usually react as
chelating ligands with transition metal ions by bonding
through the oxygen and hydrazinic nitrogen atoms [1,2], as
they form a stable six-membered characterization of 5-(4ꢀ-
alkylphenylazo)-3-phenylamino-2-thioxothiazolidin-4-one
(HLn) and their complexes with dioxouranium(VI). The
ligands act as tetradentate monobasic reacting with UO2(II)
through the CO (rhodanine moiety), hydrazinic N with
displacement of hydrogen atom, CS (rhodanine moiety) and
amidic N.
2.1. Preparation of 5-(4ꢀ-alkylphenylazo)-3-
phenylamino-2-thioxothiazolidin-4-one
(HLn)
In typical preparation, 25 ml of distilled water containing
hydrochloric acid (12 M, 2.68 ml, 32.19 mmol) was added
to aniline (0.979, 10.73 mmol) or a 4-alkyl-aniline. To the
resulting mixture stirred and cooled to 0 ◦C, a solution
of sodium nitrite (740 mg, 10.73 mmol, in 20 ml of wa-
ter) was added dropwise. The so-formed diazonium chlo-
ride was consecutively coupled with an alkaline solution
of 3-phenylamino-2-thioxothiazolidin-4-one (10.73 mmol)
in 20 ml of pyridine. The brown precipitate, which formed
immediately, was filtered, washed several times with wa-
ter. The crude product was purified by recrystallization
from hot ethanol, yielding 70%. The analytical data con-
firmed the expected compositions (Table 1). The ligands
2. Experimental
3-Phenylamino-2-thioxthiazolidin-4-one was prepared
according to El-Sonbati et al. [1].
The standard chemical aniline and 4-alkylanilines (alkyl:
CH3, OCH3, Cl and NO2; Aldrich Chemical Co.) were used
1
were also characterized by H NMR and IR spectroscopy
∗
(Fig. 1).
Corresponding author. Fax: +20 57403868.
1386-1425/$ – see front matter © 2004 Published by Elsevier B.V.
doi:10.1016/j.saa.2004.06.058

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3. Results and discussion
2+
The reaction of UO2
in ethanol with 5(-4ꢀ-
alkylphenylazo)-3-phenylamino-2-thioxothiazolidin-4-one
resulted in the formation of the complexes of the general
composition [(UO2)2(HLn)(Ln)2(OAc)2(OH2)2]n. Analyti-
cal results and some physical properties of the complexes
are listed in Table 1. All the complexes are powder-like,
stable in air and slightly soluble in methanol and ethanol.
Also, the complexes are soluble in DMF and dimethyl-
sulphoxide (DMSO). The isolated uranyl complexes have
Fig. 1. 5(-4ꢀ-alkylphenylazo)-3-phenylamino-2-thioxothiazolidin-4-one
(HLn); R OCH3 (n = 1), CH3 (n = 2), H (n = 3), Cl (n = 4) and NO2 (n =
5).
2.2. Synthesis of the complexes
a
general formula [(UO2)2(HLn)(Ln)2(OAc)2(OH2)2]n
A hot solution of UO2(OAc)2·2H2O (0.01 mol) in EtOH
(30 cm3) was added to the appropriate ligands (0.022 mol) in
EtOH (30 cm3). Polycrystalline solid complexes were imme-
diately formed in each case. The reaction mixture was then
maintained at the reflux temperature for 1.5 h to ensure com-
plete reaction. The solid complexes were filtered off while
hot and washed several times with EtOH, followed by Et2O,
and dried in vacuo over P2O5.
(where L: tetradentate monobasic hydrazone). The molar
conductivities of complexes in DMF at 25 ◦C are in the
2–11 ohm−1 cm2 mol−1 range, indicating a non-electrolytic
nature [4]. The magnetic susceptibility measurements
at room temperature indicate that the complexes are
diamagnetic as expected for a fo system.
3.1. Stoichiometries of the newuranyl complexes
The fact that HLn complexes with UO2(CH3COO)2·2H2O
2.3. Elemental analysis
2+
involving 2:1 ligand to UO2 (Table 1) have been isolated
clearly illustrates that the ligand under study does not
introduce sufficiently severe steric hindrance as to preclude
the formation of [(UO2)2(HLn)(Ln)2(OAc)2(OH2)2]n com-
plexes, but its steric feature and arrangement in space can
also favorably influence the stabilization of 2:3 complexes.
The ligands present three donor sites: azo nitrogen, the
The uranium content of each complex was determined
by igniting a definite mass of the complex at ∼800 ◦C and
weighing the residue as U3O8. Carbon, hydrogen and nitro-
gen contents were determined at the Microanalytical unit at
Cairo University, Cairo, Egypt. The analytical data are given
in Table 1.
Table 1
2+
Analytical data UO2 complexesa,b,c of HLn
Complex (colour)
Code
mp (◦C)
131
Experimental (calculated) (%)
Composition
C
H
N
Metal
–
HL1 (brown)
53.6
3.9
15.6
(53.6)
35.3
(4.0)
2.8
(15.6)
9.6
1
2
3
4
5
26.7
[(UO2)2(HL1)(L1)2(OAc)2(OH2)2]n
[(UO2)2(HL2)(L2)2(OAc)2(OH2)2]n
[(UO2)2(HL3)(L3)2(OAc)2(OH2)2]n
[(UO2)2(HL4)(L4)2(OAc)2(OH2)2]n
[(UO2)2(HL5)(L5)2(OAc)2(OH2)2]n
(35.3)
(2.8)
(9.5)
(27.0)
HL2 (brown)
HL3 (brown)
HL4 (brown)
55.8
(56.0)
36.2
4.1
(4.1)
3.0
16.4
(16.4)
10.1
–
161
164
164
178
27.3
(27.7)
(36.3)
(2.9)
(9.8)
54.8
(54.9)
35.0
3.6
(3.7)
2.7
16.9
(17.1)
10.3
–
28.0
(28.4)
(35.1)
(2.6)
(10.0)
49.6
(49.7)
32.9
3.0
(3.1)
2.4
15.4
(15.5)
9.1
–
26.4
(26.8)
(33.0)
(2.3)
(9.4)
HL5 (brown)
48.2
(48.3)
32.4
2.9
(3.0)
2.1
18.7
(18.8)
11.8
–
25.9
(32.5)
(2.3)
(11.6)
(26.3)
a
Microanalytical data as well as metal estimations are in good agreement with the stoichiometry of the proposed complexes.
The excellent agreement between calculated and experimental data supports the assignment suggested in the present work.
HL1–HL5 are the ligands and L1–L5 are the anions.
b
c

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1849
4. The spectra exhibit a very strong band at ∼1720 cm−1
This is a powerful indicative to ␯C O.
.
carbonyl oxygen and thionyl sulphur of rhodanine moiety
and the NH group of 3-phenylamino. However, it is clear that
the utilization of all the four bonding sites would introduce
certain steric restrictions and hence either both the azo
nitrogen and the carbonyl group would coordinate or the
NH group and the carbonyl group would coordinate. The
coordination of NH group and the carbonyl group seems
unlikely in view of the large size of the chelated ring.
5. In all complexes, 3480–3130 cm−1 is observed. Such re-
gion is attributed to –NH group (3-phenylamine).
6. The absence of any peak attributable to the N NH
(3180 and 3220 cm−1) moiety implies that in solution,
the ligands change to form. However, in solution and
in the presence of uranyl ion, these compounds exist in
equilibrium. The main change is observed in the azo
stretching vibration, thus suggesting that the form pre-
vails. The form reacts with uranyl ion by loss of proton
(of hydrazone) (C N NH) as mononegative chelating
agents producing (N2)/(NH) mode of the free ligands.
7. New bands assigned to ␯(NH) (hydrazone) in the free lig-
ands are absent, suggesting the cleavage of intramolecu-
lar hydrogen-bonded ␯NH [11] with subsequent depro-
tonation of NH group and coordination of nitrogen to the
metal ion.
3.2. Infrared spectra and nature of coordination
The mode of bonding of the azodyes to the uranyl ions
was elucidated by investigating the IR spectra of the chelates
2M:3L as compared to those of the free ligands.
The infrared spectra of ligands exhibit strong to medium
broad bands in the frequency range 3295–2950 cm−1. These
bands can be attributed to intramolecular hydrogen-bonded
–NH group [5]. Furthermore, all ligands exhibit a strong
band at 1730–1710 cm−1. This is due to ␯C O [2]. The
discussed infrared features beside the band appearing at
1640–1600 cm−1 can guide to assume the presence of C N
structure through resonating phenomena [6]. Such class of
compounds is with different types of hydrogen bonding
[7–9]:
8. Introduction of a hydrazo group instead of N N leads a
change in the coordination mode of the azo group from
theazo-nitrogentotheaminenitrogen(NH)(hydrazone).
9. Coordination of the carbonyl oxygen and the hydrazone
nitrogen in the chelate ring is supported by the appear-
ance of new bands at 625–685 and 580–580 cm−1, which
are assigned to M N and M O, respectively.
1. H-bonding of the type N H · · · O between the –NH (hy-
drazone) group and C O group;
10. The phenyl ring vibration appears at 1480–1510 cm−1
.
The presence of a p-substituted benzene ring in the
ligands as well as in the complexes is indicated by
strong and sharp bands around 610–635 cm−1. Bands
at 2930–3030 cm−1 for the ligands and at ∼2970 cm−1
for the complexes are assigned to ␯(C H) vibration of
the aromatic system.
2. intermolecular hydrogen bonding of the N H · · · O type
of one molecule to another one;
3. the case is more favored. This is due to the presence of
a broad band located at 870–965 cm−1 which could be
taken as a good evidence for the intermolecular hydrogen
bonding.
11. The strong bands around 3160 and 1615 cm−1 in the free
ligands are due to ␯N H and ␦N H. Practically, no affect
on these frequencies after complexation precludes the
possibility of complexation at (3-phenylamine) group.
12. An intensive strong band at 845 cm−1 in the free lig-
and spectrum is due to ␯(C S) which has been found to
shift to lower frequency by ∼50 cm−1 in the complexes,
pointing to the coordination of the sulphur to uranyl(II)
atom.
Thefollowingfeaturesforsomeofthepreparedcomplexes
are observed:
1. The infrared spectra of the free ligands show no char-
acteristic absorption assignable to NH2 function. This
confirms the formation of the azo compounds.
2. The strong band observed at ∼1110–1120 cm−1 may be
assigned to ␯(N N) vibration modes [9] and is affected
on complexation. It is blue shifted and appeared as a
weak band.
3.3. 1H NMR spectra
3. The spectra of ligands do not show absorption character-
istic of the N N function owing to the formation of the
hydrazone. The sharp, medium intensity band of C N
(hydrazone) appears at ∼1625–1610 cm−1 for ligands.
This is rather confirmed from the observation of Kara-
batores et al. [10] where the hydrazone form is more
than the azo structure for similar compounds. This is
also proved by the appearance of N N in splitted strong
spectral bands at 1435 and 1520 cm−1 combined with
the tracing of a strong band at 1230 cm−1 characteristic
of NH stretching vibration. All these data with lack of
the ␯C O of enol in the IR spectrum lead us to assume
the structure for this compound.
The proton magnetic resonance of the ligands and com-
plexes has been recorded in DMSO–d6 using TMS as the
internal standard. The broad signal exhibited by the ligands
can be assigned to intramolecular hydrogen bonded proton
of NH (hydrazone) at ∼11.4 ppm and NH(3-phenylamine) at
∼9.0 ppm were not affected by dilution and disappear in the
presence of D2O and the first band also disappears in uranyl
complex and the second shifted to ∼8.8 ppm indicating the
coordination of the nitrogen atoms with the metal ion. The
shifts are in the sequence: p-NO2 > p-Cl > H > p-OMe >
p-CH3.

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3.4. Spectral studies
HLn exhibits bands at 26,350–26,150 cm−1 (CS) (n →
␲*), 30,460–30,250 cm−1 (CO) (n → ␲*), 32,980–
33,100 cm−1 (h-bonding and association), 40,240–
39,890 cm−1 (phenyl) (ph–ph*, ␲–␲*) [12] and
29,610–29,350 cm−1 transition of phenyl rings over-
lapped by composite broad ␲–␲* of azo structure. In the
dioxouranioum(VI) complexes, the (CS and CO) (n–␲*)
transition shifts to lower energy. These shifts or the disap-
pearance of the bands are indicative of coordination of the
ligands to UO22+. The dioxouranium complexes exhibit a
new band at 24,490–24,310 cm−1, which is assigned to the
1 ꢀu
3
→ ␲ transition, typical of OUO for the symmetric
u
g
stretching frequency for the first excited state.
3.5. Complexation on uranyl ion spectra
Uranyl ion UO22+ is quite peculiar in its own structure and
in its identity over a wide range of vibrations in experimental
conditions and can be considered from the geometric point
of view, as a single particle. In the present investigation, the
␯(U O) in all the complexes has been assigned in 920–890
and845–815 cm−1 regionas␯3 and␯1, respectively(Table2).
The ␯ values decrease as the donor characteristic increase
3
as is observed for ␲-electron substituents, where the basicity
of the donating atom increases.
The experimental results reveal an excellent linear rela-
tion between ␯ and ␯ with the slope corresponding to (1
1
3
+ 2MO/MU)1/2 (MO and MU are the masses of oxygen and
uranium atoms, respectively).
Instead of the linear relation between ␯ and ␯ frequen-
1
3
cies, the El-Sonbati equation [13] has focused attention on
their normalized differences, which do not depend on the
masses of oxygen and/or uranium atoms.
˚
Fig. 2. The variation of p-substituted Hammet’s with (1) rU O (A); and (2)
FU
(mdyn A−1).
˚
O

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3.6. Force constant, FU O, and bond lengths, rU O, of
the uranyl complexes
Due to small scattering power of the oxygen atom, report
ofthedeterminationofU Obondlengthofsomeuranylcom-
plexes by X-ray study is scanty. From infrared spectra, the
stretching and interaction force constants in the present com-
plexes have been calculated [14–16]. The results are in turn
used to evaluate U O bond distances using Badger’s formula,
Jones equation [17,18] and El-Sonbati equation [13]. The val-
ues are given in Table 2 and such report is also found for other
uranyl complexes [13,14,18,19]. The variation of bond length
in the complexes is due to presence of electron-releasing or
electron-withdrawing substituents in the equatorial position.
References
Fig. 3. The relation between (1) ␯ vs. rn; (2) ␯ vs. r2; and (3) ␯ vs. r3.
3
3
3
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Our objective is to get El-Sonbati equation from which
the U O bond force constant should be eventually served as
a fairly accurate measure of the U O bond distance in given
compounds. The force constant for the U O bond [FU
O
S
(mdyn A−1)], (FU O) , (FUS ) and FUO,UO with neglecting
˚
ꢀ
O
t
o
the interaction of the spectral data used herein are presented in
Table2;aplotof␯1 +␯3 and/or␯3 versusforceconstantforthe
U O (FU O (mdyn A−1)) and the U O bond distance (rU
˚
O
˚
(A)) gives a straight line with the increase in the value of ␯1 +
␯3 and/or ␯3 decreases rU O and increases the force constant
of the U O bond. There is also a straight line relationship be-
tween rU and the p-substituent, Hammett’s constant (σR)
O
with negative slope, i.e. the higher the value of σR, the lower
the rU O and the higher the force constant of the U O bond
(Fig. 2). Also, plotting of the r1, r2 and r3 (bond distance,
rU O) versus ␯3 gives straight line with increase in the value
of ␯3 and decrease in rU O (Fig. 3). Our results also showed
an inverse relationship between ␯ and rU O. This can be
3
explained. The electron withdrawing p-substituent increases
the positive charge on the UO22+ leading to an increase in v3
and FU O and subsequently a decrease in rU O. Accordingly,
[16] A.Z. El-Sonbati, A. El-Dissouky, Transition Met. Chem. 12 (1986)
112.
[17] R.M.N. Badger, J. Chem. Phys. 3 (1935) 710.
[18] L.H. Jones, Spectrochim. Acta 10 (1985) 395;
L.H. Jones, Spectrochim. Acta 11 (1959) 409.
[19] S.P. McGlynn, J.K. Smith, W.C. Neely, J. Chem. Phys. 35 (1961)
105.
rU values can be arranged in the order, p-OCH3 > p-CH3
O
< H < p-Cl < p-NO2, which are consistent with the values of
their σR.