Structural model of dioxouranium(VI) with hydrazono ligands

Article abstract of DOI:10.1016/j.saa.2004.06.036

Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized

Full text of DOI:10.1016/j.saa.2004.06.036

Spectrochimica Acta Part A 61 (2005) 1163–1170
Structural model of dioxouranium(VI) with hydrazono ligands
Ahmed T. Mubarak
Department of Chemistry, Faculty of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia
Received 18 February 2004; accepted 18 June 2004
Abstract
Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono
compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized by
various physico-chemical techniques. The bond lengths and the force constant have been calculated from asymmetric stretching frequency of
O U O groups. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and hydrazo nitrogen donor system.
The effect of Hammett’s constant on the bond distances and the force constants were also discussed and drawn. Wilson’s matrix method,
Badger’s formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force constant from which the U O
bond distances were calculated. The bond distances of these complexes were also investigated.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Force constant; U O bond distance; McGlynn and Badger’s formula; Hammett’s constant
2+
1. Introduction
ligand (Scheme 1), (ii) the synthesis of UO2 complexes
derived from this ligand, (iii) assigning the stereochemistry
of the complexes based on the infrared and (iv) knowing
the mode of bonding of these complexes from the infrared
(IR) spectral data, and (v) The nature of binding of nitrate
group.
The azo compounds have gained much attention because
of their use as models for biological systems [1]. In our
laboratory, the coordination behaviour and chemical equi-
libria of some azo compounds have been investigated in
depth. Heterocyclicnitrogen-containinghydrazonesandtheir
metal complexes have shown very important biological ef-
fects [2–4]. Some of these compounds are used in analytical
separation of many metal ions in a mixture and as analytical
reagents [4], the coordination chemistry, new structural fea-
tures and biological activity [5]. A literature survey indicates,
however, the lacking of research on the synthesis and prop-
erties of azodyes. These molecules are capable of possessing
azo-hydrazo tautomers (Scheme 1).
2. Experimental
All the chemical used were of BDH quality. 1-Phenyl-
3methyl-(4-dervitives phenylhydrazo)-5-pyrazolone was
prepared by the methods outlined by El-sonbati and co-
workers [5–8], and the experimental techniques have been
described therein.
El-Sonbati and co-workers [5–8] found that the bis-
bidentate azodyes ligands play a key role in our under-
standing of coordination chemistry of transition metal ions.
In this paper the coordination compounds of these ligands
with UO2 nitrate are presented. The major interest of this
paper are: (i) the synthesis of new substituted 1-phenyl-
3-methyl-(4-derivatives phenylhyrazo)-5-pyrazolone (HLn)
2.1. Preparation of the azo compounds
New azodyes prepared from aniline or its p-substituted
derivatives (10 mmol) was dissolved in hydrochloric acid
(20 mmol/25 ml distilled H2O). The hydrochloric compound
was diazotized below −5 ◦C with a solution of sodium nitrate
(0.8 g, 10 mmol; 30 ml distilled H2O). The diazonium chlo-
ride was coupled with an alkaline solution of start in 20 ml of
2+
E-mail address: ahmadtahir20@hotmail.com (A.T. Mubarak).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.06.036

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A.T. Mubarak / Spectrochimica Acta Part A 61 (2005) 1163–1170
Scheme 1. General formula and proton numbering of the 1-phenyl-3-methyl-(4-derivatives phenylhydrazo)-5-pyrazolone.
ethanol. The crude dye was collected by filtration and crys-
tallized from dimethylformamide; then dried in a vacuum
desiccator over P2O5.
2.3. Physical measurements
C, H and N microanalyses were carried out at King Khalid
University, Analytical Center, Saudi Arabia, using a Perkin-
Elmer 2400 Series II Analyzer. The uranium content of each
complex was determined by igniting a definite mass of the
complex at ∼1000 ◦C and weighing the residue as U3O8. The
1H NMR spectra was obtained with a Jeol FX 900 Q Fourier
Transform spectrometer with DMSO-d6 as the solvent and
tetramethylsilane (TMS) as an internal reference. Infrared
spectra (IR) were recorded using Perkin-Elmer 1340 spec-
trophotometer. UV spectra of the compounds were recorded
in Nujol using a Unicam SP 8800 Spectrophotometer. TG
measurements were made using a DuPont 950 thermobal-
ance. Ten milligrams samples were heated at 10 ◦C min−1
in a dynamic nitrogen atmosphere (70 ml min−1); the sam-
2.2. Synthesis of the complexes
A hot solution of UO2(NO3)2·6H2O (0.01 mol) in ethanol
(30 cm3) was added to the appropriate ligands (0.012 mol) in
ethanol (30 cm3). Polycrystalline solid complexes were im-
mediately formed in each case. The reaction mixture was then
maintained at reflux temperature for 1/2 h to ensure complete
reaction. The solid complexes were filtered off while hot and
washed several times with EtOH, followed by Et2O, and dried
in vacuo over P2O5.

A.T. Mubarak / Spectrochimica Acta Part A 61 (2005) 1163–1170
1165
solvents, and it is thus difficult to determine the molecular
weight.
3.2. 1H NMR Spectra
The 1H data are in agreement with the proposed structures.
1
The H spectrum of the ligand (HL3) and uranyl complex
(Table 1) supports the occurrence of the form depicted in
Scheme 1. A broad signal in HL3 observed at δ 11.3 ppm is
attributed to the NH proton. The latter proton disappears in
the presence of D2O. Further, the CH signal vanish and a new
NH and C N signal appears, i.e., change from azo to hydrazo
form (Scheme 1). The protons of the aromatic ring resonate
downfield in the δ 7.3−8.4 ppm range [5].
3.3. Thermal analysis measurements
The thermogravimetric analysis of the free ligand and their
corresponding complexes were carried out to get informa-
tion as to whether decomposition occurs and on the relative
volatility of the complexes. It was found that the ligands are
stable up to about 150 ◦C and then start losing weight very
rapidly and volatilize completely at about 450−550 ◦C. In
most cases, U3O8 is obtained as the final product beyond
∼500 ◦C. The volatilization of the ligands proceeds simulta-
neously. It is clear from the thermograms that the complexes
containingthebidentateligandshavenoH2Omoleculewhich
is coordinate. Coordinated NO3 could be removed within the
range of 210–315 ◦C. [UO2LnNO3]H2O (n = 4, 5) loses the
H2O molecule at ∼115 ◦C to give [UO2LnNO3], which de-
composes to give U3O8; whereas the [UO2LnNO3]2H2O (n =
1–3) loses the two H2O molecules in two steps at ∼100 and
∼125 ◦C and then decompose further to give finally U3O8
at ∼500 ◦C. The oxide U3O8 is formed around 650 ◦C via
the formation of UO3, following which there is no mea-
surable change in weight. In brief, these changes can be
shown as:
∗
Fig. 1. The relation between (a) ν1 vs. ν3 and (b) ν1 vs. ν3.
ple holder was boat-shaped, 10 mm × 5 mm × 2.5 mm deep;
the temperature measuring thermocouple was placed within
1 mm of the holder.
3. Results and discussion
3.1. Stoichiometries of the new uranyl complexes
The fact that the complexes with UO2(NO3)2·6H2O in-
2+
volving 1:1 ligand to UO2 ratio (Table 1), have been iso-
lated, clearly illustrates that the ligands under study does not
introduce sufficiently severe steric hindrance as to preclude
the formation of [UO2(Ln)NO3]·nH2O complexes, but its
stericfeaturesandarrangementinspacecanalsofavorablyin-
fluence the stabilization of 1:1 complexes. All complexes are
diamagnetic and sparingly soluble in most common organic
Table 1
Elemental analysis data for UO22+ complexesa with hydrazono ligands derived from 1-phenyl-3-methyl-5-pyrazolone (for molecular structures see Scheme 1)b
Complexc
Code
Experimental (calculated) (%)
Composition
C
H
N
Metal
HL1
HL2
HL3
HL4
1
2
3
4
5
66.1 (66.2)
30.2 (30.2)
5.1 (5.2)
2.2 (2.2)
18.5 (18.2)
10.4 (10.7)
35.3 (35.3)
[UO2L1NO3]2H2O
[UO2L2NO3]2H2O
[UO2L3NO3]2H2O
[UO2L4NO3]2H2O
[UO2L5NO3]2H2O
69.8 (69.9)
30.9 (31.0)
5.6 (5.5)
2.3 (2.3)
19.4 (19.2)
10.9 (10.6)
36.5 (36.1)
37.1 (36.9)
35.7 (35.4)
36.3 (36.0)
69.0 (20.1)
29.7 (29.8)
5.1 (5.0)
1.9 (2.0)
20.3 (20.1)
11.1 (10.9)
59.0 (59.4)
28.5 (28.6)
3.9 (4.0)
1.9 (1.8)
21.9 (21.7)
12.6 (12.5)
HL5
61.5 (61.4)
28.9 (29.0)
4.1 (4.2)
1.7 (1.8)
20.1 (20.3)
10.5 (10.6)
a
Microanalytical data as well as metal are in good agreement with the stoichiometry of the proposed complexes.
The excellent agreement between calculated and experimental data supports the assignment in the present work.
HL1–HL5 are the ligand as given in Scheme 1 and L1–L5 are anions.
b
c

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A.T. Mubarak / Spectrochimica Acta Part A 61 (2005) 1163–1170
Table 2
Thermogravimetric analysis of uranyl complexes of 1-phenyl-3-methyl-(4-derivatives phenyl hydrazo)-5-pyrazolone ligands (for molecular structures see
Scheme 1)a
Complexesb
Temperature
range (◦C)
60–110
215–255
275–455
Mass loss (%)
(found)
5.33
Effect type
Assignment
1
5.63
Endo
Exo
Exo
Loss of 2H2O molecules
Loss of NO3 group
Decomposition of complex and formation of metal oxide (UO3)
14.92
54.35
15.34
60.09
2
3
4
90–110
235–300
460
5.46
15.32
61.24
5.78
15.73
61.64
Endo
Exo
Exo
Loss of 2H2O molecules
Loss of NO3 group
Decomposition of complex and formation of metal oxide (UO3)
70–120
250–290
420–530
5.57
15.92
62.81
5.72
16.12
63.16
Endo
Exo
Exo
Loss of 2H2O molecules
Loss of NO3 group
Decomposition of complex and formation of metal oxide (UO3)
105–125
210–250
380–460
2.68
12.32
52.91
2.79
11.94
52.24
Endo
Exo
Exo
Loss of 1H2O molecule
Loss of NO3 group
Decomposition of complex and formation of metal oxide (UO3)
5
100–120
225–252
350–500
2.72
12.05
56.05
2.96
12.43
56.88
Endo
Exo
Exo
Loss of 1H2O molecule
Loss of NO3 group
Decomposition of complex and formation of metal oxide (UO3)
a
The excellent agreement between calculated and experimental data supports the assignment in the present work.
See Table 1 and Scheme 1.
b
◦
[UO2(Ln)NO3]2H2O 60−−1→20 C[UO2(Ln)NO3]
stretching frequency for the first excited state [8]. Also, the
bands observed in the spectra of the ligands as well as the
uranyl complexes in the 47,200–47,840, 43,100–43,500 and
n=1−3
◦
◦
550 ◦C
215−−→300 C UO2L 275−−→530 C UO3 −→ U3O8
34,400–36,400 cm−1 regions are assigned to ␲–␲∗ and n–␲
∗
transitions, respectively. Another band at ∼34,900 cm−1 in
the spectra of the HLn is assigned to complex formation with
UO22+ and to the disappearing of hydrogen bonding and as-
sociation [9].
◦
[UO2(Ln)NO3]H2O 100−−→130 C[UO2(Ln)NO3]
n=4,5
◦
◦
550 ◦C
210−−→250 C UO2L 380−−→500 C UO3 −→ U3O8
3.5. Mode of bonding
The determined temperature ranges, % losses in mass and
thermal effects accompanying the changes in the solid com-
plexes on heating are given in Table 2. The results of the metal
contents [%M], calculated from the masses of the residual ox-
ides, support the stoichiometry obtained from the elemental
analyses.
The bonding of the ligands to different metal ion was in-
vestigated by comparing the IR spectra of the free ligands
with those of their solid complexes (Table 3). The following
conclusions can be drawn:
The infrared spectra of ligands exhibit a strong band at
1650–1625 cm−1. This is due to ␯(CO of the pyrazolone
ring) [10]. The discussed infrared features beside the band ap-
peared at 1595–1575 cm−1, can guide to assume the presence
of ␯C N (attached to the hydrazo group) structure through
resonating phenomena [11]. In general, the presence of elec-
tron attracting group minimizes the charge transfer from the
phenyl ring and this leads to increase the CO band modes. The
3.4. Electronic spectra
The UV spectra of the uranyl complexes exhibit a band
1
3
in the 20,800–22,600 cm−1 region assigned to Eg+ → πu
transition. This band is similar to the O–U–O symmetric
Table 3
Solid state infrared frequencies (cm−1) of uranyl complexes of 1-phenyl-3-methyl- (4-derivatives phenyl hydrazo)-5-pyrazolone ligands (for molecular structures
see Scheme 1)a
Complexa
νOH
νCO
νNO3 (coordinated)
νM
O
νM N
1
2
3
4
5
a
3500–3400
3500–3400
3500–3400
3500–3400
3500–3400
1667
1655
1650
1645
1642
1505, 1270, 1030
1500, 1280, 1040
1495, 1283, 1043
1493, 1285, 1045
1490, 1288, 1048
612, 452
604, 466
602, 470
600, 475
595, 478
560,370
572,360
575,358
577,355
580,350
See Table 1 and Scheme 1.

A.T. Mubarak / Spectrochimica Acta Part A 61 (2005) 1163–1170
1167
␤C H, ␦C H and ␥C H modes of vibrations are identified
by the presence of strong bands in the 1180–1110, 1030–930
and 840–780 cm−1 regions, respectively. The C C vibrations
are also identified by the presence of several bands at fre-
quencies lower than 755 cm−1. Generally, the electron donor
methoxy group enhances the change transfer from the phenyl
ring to the heterocyclic moiety. This leads to increase both po-
larizability of the carbonyl group. Such class of compounds,
as illustrated in Scheme 1, have different types of hydrogen
bonding [12–14], as follows:
1. H-bonding of the type O H· · ·N between the OH group
and N N group (1B).
2. H-bonding of the type N H· · ·O between the NH group
and C O group (1C).
3. Intermolecular hydrogen bonding of the O H· · ·N (1D)
or N H· · ·O (1E) type of one molecule to another. The (2)
case is more favored than (1). This is due to the presence
of a broad band located at 875–975 cm−1, which could be
taken as a good evidence for the intermolecular hydrogen
bonding [5]. This is illustrated in Scheme 1.
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 1130–1140 cm−1, which
may be assigned to ␯(N N) vibration modes [14] is af-
fected on complexation. It is blue shifted and appeared
as a weak band.
3. In all complexes, 3480–3150 cm−1 is observed. Such a
region is attributed to different probabilities: (a) it is due
to either free OH or NH; (b) bonded OH group or NH
group; or (c) due to presence of water molecules.
4. 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 1595–1575 cm−1 for ligands.
5. The spectra exhibit a strong band at 1650 cm−1, which
is indicative to ␯CO. However, the broad band located at
3430 cm−1 leads to characterize the ␯NH rather than hy-
drogen bonded OH with N N. This is rather confirmed
from the observation of Karabatoses et al. [15] where the
hydrazone formed is more than the azo structure for sim-
ilar compounds. This is also proved by the appearance−o1f
N N in splitted strong spectra bands at 1435–1535 cm
combined with observing a strong bands at 1230 cm−1
characteristic to NH stretching vibration. All these data
with lack of the ␯C O of enol in the IR spectrum lead
us to assume the structure (1C) for this compounds.
6. Introduction of a hydrazo group instead of N N leads
to a change in the coordination mode of the azo group
from the azo-nitrogen to the amine nitrogen (NH)
(Scheme 1).

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A.T. Mubarak / Spectrochimica Acta Part A 61 (2005) 1163–1170
7. Coordination of the carbonyl oxygen and the amine ni-
The experimental results reveal an excellent linear rela-
tion between ν1 and ν3 with the slope corresponding to (1 +
2Mo/Mu)1/2 (Mo and Mu are the masses of oxygen and ura-
nium respectively, Fig. 1a), and the data satisfy the equations:
(i) νs = −115 + 1.0νas for compounds (1), (2), and (4) and (ii)
νs = −100 + 1.0νas for compounds (3) and (5). Similar results
have been reported by McGlenn et al. [19]. It is obvious that
good linearity obtained in the case of ν¯1 and ν¯2.
trogen in the chelate ring is supported by the appear-
ance of new bands which are assigned to U N and U O
(Table 3).
8. The infrared spectrum of the nitrate complex shows
bands corresponding to coordinated nitrate group.
These should show absorptions [16] at 1505–1475 cm−1
(ν1), 1325–1275 cm−1 (ν5), 1045–1020 cm−1 (ν2) and
803 cm−1 (ν6). The complexes under study show IR
bands at ∼1430 cm−1 (ν1), 1384 cm−1 (ν3), 1274 cm−1
(v5), 1010 cm−1 (v2) and 839 cm−1 (v6). The separation
of ∼200 cm−1 between ν1 and ν5 indicates the bidentate
nature of the nitrate group [16].
9. There is no coordinated H2O in the complexes as is clear
from the IR and TGA curves and thus the equatorial
coordination number for UO22+ is 4.
10. The ligandorbitals ofhydrazopyrazolonesaregroupthe-
oretically, energetically and occupationally suitable for
participation in both donor (U → L) and acceptor (L →
U) ␲-interactions with the uranyl ion [17]. Convincing
evidence [17] has been adduced that U → L ␲-bonding
makes a significant contribution to the bonding in uranyl
complexes.
11. Electron-withdrawing substituents appear to decrease
the donor capacity of the carbonyl groups. This is evi-
dent from the ␯(C O) values of these complexes and is a
general feature of all transition and non-transition metal
␤-ketoenolates with electron-withdrawing substituents
[18]. In the mean time, U → O ␲-bonding will be facil-
itated by such substituents, leading to a positive contri-
bution to ␯(U O).
Instead of the linear reaction between ν1 and ν3 frequen-
cies, El-Sonbati equation [20] has focused attention on their
normalized differences with a slope A (0.000192) and con-
stant B (1.835) do not depend on the masses of oxygen
and/or uranium atoms. The objective in using El-Sonbati
equation, from which the U O bond force constant is cal-
culated, should serve as fairly an accurate measure for U O
bond distance in given compounds. The force constant for the
U O (FU O mdyn A−1), (FsU O)t, (FsU O)o and (FUO,UO ),
˚
−
when neglecting the interaction of the U O bonds with the
˚
ligands and the U O bond distance [rU O A], were calcu-
lated [19,21] (Table 4). Another observation is that a plot
of (ν1 + ν3) and/or ν3 versus force constant for the U O
(FU O mdyn A−1) or (F∗U O mdyn A−1) and the U O bond
˚
˚
˚
˚
distance (rU O A or r3U O A) gives a straight line with in-
creasing value of ν1 + ν3 and/or ν3, accompanied by decreas-
ing rU O and increasing the force constant of the U O bond
(Figs. 2–4). There is also a straight line relationship between
rU O and the p-substituents, when Hammett’s constant (σR)
was applied, giving a negative slope, i.e. the higher the value
of σR, the lower rU O and the higher the force constant of the
U O bond (Fig. 5). Moreover, plotting of r1, r2, r3, and rt
(bond distance, rU O) versus ν3 gives a straight lines with an
increase in the values of ν3 and a decrease in rU O (Fig. 6).
The electron withdrawing p-substituents increases the
3.6. Complexation effect on uranyl ion spectra
2+
positive charge on the UO2 leading to an increase in ν3
Substituent effects on reactivities depend mainly on the
rate controlling step and the nature of the transient species.
Hammett’s related the reactivity trends in ligands and com-
plexes with the stability, i.e., the lower the stability the higher
the reactivities. Based on Hammett’s relationship, electron-
withdrawing substituents to ligands in their complexes en-
hance the stabilities of these complexes owing to the decrease
of electron density at the metal central atom and thus the in-
crease of the positive charge on the metal. Therefore, this
effect results in decreasing reactivity. In contrast, the elec-
tron donating substituents increase the electron density at the
metal and leading to decrease the stability of the chelates.
and FU O and subsequently a decrease in rU O. Accordingly,
rU O value can be arranged in the order p-OCH3 > p-CH3 >
H > p-Cl > p-NO2, which are consistent with the values of
their σR.
2+
Uranyl ion UO2 is quite peculiar in its own structure
and in its coordination compounds [5–8,11]. The ion retains
its identities over a wide range of vibrations in experimen-
tal conditions and can be considered from the geometrical
point of view as a single particle. In the present investiga-
tion, the ␯(U O) in all the complexes has been assigned in
938–910 and 840–792 cm−1 regions as ν3 and ν1, respec-
tively (Table 4). The ν3 values decrease as the donor char-
acteristic increase as is observed for ␲-electron substituents,
when the basicity of the donating atom increases.
Fig. 2. The relation between ν1 and ν1 + ν3.

A.T. Mubarak / Spectrochimica Acta Part A 61 (2005) 1163–1170
1169
Fig. 3. The relation between rU (A) and FU (mdyn A−1) vs. ν3.
˚
˚
O
O
El-Sonbati equation [20], which has been used to deter-
mined the symmetric stretching frequency (ν1∗) data should
eventually serve as a fairly accurate evaluation for (FU O),
(rU O) and (Fuo,uo−) [Table 4]. There is also a straight line
relationship between (ν1∗) and ν3 (O U O) (Fig. 1b).
˚
Fig. 5. The variation of p-substituted Hammett’s with (a) rU (A) and (b)
O
FU (mdyn A−1).
˚
O
The results are in turn used to evaluate U O bond distances
following Badger’s formula [24].
In the equatorial bonding, the more effective overlap of
O U O group orbital by nitrogen than by oxygen in the lig-
ands leading to lowering ν3 values for UO22+ complexes with
the former. The force constant of U O bond in the present
investigation has been calculated following McGlenn et al.
[19], and the U O bond distance for corresponding com-
3.7. Stereochemistry and structure of the complexes
1-Phenyl-3-methyl-(4-dervitives phenylhdrazo)-5-pyraz-
olone reacts with UO2(NO3)2·6H2O (molar ratio 1:1) giving
solid complexes. The proposed structure of uranyl complexes
are given in Scheme 1. The spectra of all complexes show two
bands attributed to the asymmetric and symmetric stretching
frequency. A group theoretical consideration [22] shows that
plexes are evaluated using the Jones equation [21] Ru o
=
1.08 F−1/3 + 1.17. The evaluated values are given in Table 4,
and such a report is also found for other uranyl complexes,
which is due to the presence of electron donating or electron
withdrawing substituents in the equatorial position.
2+
a linear and symmetrical triatomic UO2 ion possessing
D␣h symmetry gives rise to three fundamental modes of vi-
brations. Wilson’s matrix method [23] has been also used
to determine the stretching and interaction force constants.
Fig. 6. The relation between (1) r1 vs. ν3, (2) r2 vs. ν3, (3) r3 vs. ν3 and (4)
rt vs. ν3.
Fig. 4. The relation between r3 UO and F∗ vs. ν3.
UO

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A.T. Mubarak / Spectrochimica Acta Part A 61 (2005) 1163–1170
[9] A.I.I. Hsieh, R.M. Sheahan, B.O. West, Aust. J. Chem. 28 (1975)
In the present investigation, it is well established that
885.
uranyl ion possesses planar hexagonal structure with nitro-
gen and oxygen atoms in the axial position. HLn behaves
as a chelating bidentate monobasic ligand, bonding through
oxygen and amine nitrogen.
[10] D.P. Powell, N. Sheppard, Spectrochim. Acta A 17 (1961) 68.
[11] A.F. Shoair, A.A. El-Bindary, A.Z. El-Sonbati, R.M. Younes, Spec-
trochim. Acta A 57 (2001) 1683.
[12] A.Z. El-Sonbati, A.A. El-Bindary, E.M. Mabrouk, R.M. Ahmed,
Spectrochim. Acta A 57 (2001) 1751.
[13] A.Z. El-Sonbati, A.A. El-Bindary, M.A. Diab, Spectrochim. Acta A
59 (2003) 443.
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