Synthesis, spectral and quantum chemical studies on NO-chelating sulfamonomethoxine-cyclophosph(V)azane and its Er(III) complex

Article abstract of DOI:10.1016/j.saa.2014.02.061

Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of novel ethane-1,2-diol-dichlorocyclophosph(V)azane of sulfamonomethoxine (L), and its binuclear Er(III) complex. Differe

Full text of DOI:10.1016/j.saa.2014.02.061

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 724–729
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral and quantum chemical studies on NO-chelating
sulfamonomethoxine–cyclophosph(V)azane and its Er(III) complex
c
d
e
Abdel-Nasser M.A. Alaghaz a,b, , Reda A.A. Ammar , Gottfried Koehler , Karl Peter Wolschann ,
⇑
Tarek M. El-Gogary f,
⇑
a Department of Chemistry, Faculty of Science (Boys), Al-Azhar University, Nasr City, Cairo, Egypt
b Department of Chemistry, Faculty of Science, Jazan University, Jazan, Saudi Arabia
c Department of Chemistry, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
d Max F Perutz Laboratories, University of Vienna, 1030 Vienna, Austria
e Institute for Theoretical Chemistry, University of Vienna, 1090 Vienna, Austria
f Department of Chemistry, Faculty of Science, Damietta University, Damietta, Egypt
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
A novel cyclodiphosph(V)azane
ligand, was synthesized and
characterized by different tools.
Quantum chemical calculations were
used to support the measured results.
Geometry optimization was
performed at the level of B3LYP/6-
31G(d).
ꢀ
ꢀ
ꢀ
ꢀ
Simulated IR and UV–VIS spectra
showed agreement with the
measured values.
Reactivity of the title compound was
discussed in terms of accommodation
of charge and HOMO picture.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 October 2013
Received in revised form 10 February 2014
Accepted 13 February 2014
Available online 27 February 2014
Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural
and spectroscopic properties of novel ethane-1,2-diol-dichlorocyclophosph(V)azane of sulfamonome-
thoxine (L), and its binuclear Er(III) complex. Different tautomers of the ligand were optimized at the
ab initio DFT level. Keto-form structure is about 15.8 kcal/mol more stable than the enol form (taking
zpe correction into account). Simulated IR frequencies were scaled and compared with that experimen-
tally measured. TD–DFT method was used to compute the UV–VIS spectra which show good agreement
with measured electronic spectra. The structures of the novel isolated products are proposed based on
elemental analyses, IR, UV–VIS, 1H NMR, 31P NMR, SEM, XRD spectra, effective magnetic susceptibility
measurements and thermogravimetric analysis (TGA).
Keywords:
Cyclodiphosph(V)azane
Sulfamonomethoxine erbium(III) complex
B3LYP
Ó 2014 Elsevier B.V. All rights reserved.
TD–DFT
⇑
Corresponding authors. Address: Department of Chemistry, Faculty of Science (Boys), Al-Azhar University, Nasr City, Cairo, Egypt (A.-N.M.A. Alaghaz). Tel.: +966
500972289 (T.M. El-Gogary).
E-mail address: tarekelgogary@yahoo.com (T.M. El-Gogary).
http://dx.doi.org/10.1016/j.saa.2014.02.061
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

Abdel-Nasser M.A. Alaghaz et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 724–729
725
mass spectrometer using the direct inlet system. The molar
conductance measurements were carried out using a Sybron–
Barnstead conductometer. Magnetic susceptibilities were
measured at room temperature using the Faraday method with a
Cahn–Ventron RM-2 balance standardized with HgCo(NCS)4;
diamagnetic corrections were estimated from Pascal’s
constants. Thermogravimetric analysis was performed under a
nitrogen atmosphere using a Shimadzu TGA-50H with a flow rate
Introduction
In recent years, the structural feature of four-membered P2N2 ring
compounds in which the coordination number of P varies from three
to five have attracted considerable attention [1,2]. Heterocycles with
PAC, PAN, PAO, and PAS bonds, in addition totheir great biochemical
and commercial importance [3,4], play a major role in some substitu-
tion mechanisms heterocycles had been found to be potentially
carcinostatics [3] among other pharmacological activities. The
introduction of tervalentP centers in thering enhanced the versatility
of the heterocycles in complexing with both hard and soft metals.
Since the tervalent P centers could stabilize transition metals in low
oxidation states [3,4], such complexes could be potential homoge-
neous or phase-transfer catalysts in various organic transformations
[3]. There is considerable current interest in compounds containing
spiro and ansa organic P rings [5]. Although the ammonolysis of some
1,3-diaryl-2,4-dichlorocyclodiphosph(V)azans had been investigated
in some detail, little was known about the interaction of
hexachlorocyclodiphosph(V)azanes with bifunctional reagents.
The reaction of bifunctional reagents with cyclodiphosph(V)azanes
could give rise in principle to four types of structures named
spiro, ansa, cross-linking, and only one functionality attached,
while the other remains free. Spiro, ansa, and cross linking
structures of phosphazanes were now well studied synthetically,
spectroscopically, and crystallographically [5]. The reaction of
hexachlorocyclodiphosph(V)azanes with amino compounds, active-
methylene-containing compounds, and bifunctional reagents had
been investigated in some details [6,7]. Sulfonamides were the oldest
class of antimicrobials and were still the drug of choice for many
diseases such as cancer and tuberculosis [8]. Cyclophosphamide
and its derivatives were examples of phosphorus compounds
which were one of the most effective anticancer agents with
proven activity against a large variety of human cancers [9].
Hexachlorocyclodiphosph(V)azanes of sulfonamides and their
complexes had been prepared [6,10–13]. In continuation to our
interest to prepare hexachlorocyclodiphosph(V)azane of sulfa
drugs [14,15], the present paper aims chiefly to prepare ethane-
1,2–diol-dichlorocyclodiphosph(V)azane L. The behavior of this
ligand toward erbium(III) ion was studied. The characterization
of the prepared compounds was performed using different physico-
chemical methods.
of 20 ml minꢁ1
.
Synthesis of L ligand
1,3-bis(N1-4-amino-6-methoxypyrimidinebenzenesulfonamide)-
2,2,2,4,4,4-hexachlorocyclodiphosph(V)azane(0.1 mol, 83.1 g) in
100 ml cold dry benzene was added in small portions to a well
stirred cold solution of ethan-1,2-diol (0.2 mol, 12.4 g) in 100 ml
cold dry benzene during half an hour at ꢂ15 °C under dry
conditions. After completion of the reaction (HCl gas ceased to
evolve), filtration and removal of all solvent in vacuo, a residue
was obtained which on crystallization (Fig. 1).
L: White solid, Yield, 81%; m.p. 126 °C. Molar conductance
(
KM): 1.14 X
ꢁ1 cm2 molꢁ1. Anal. calcd. for C30H32Cl2N4O10P2S2
(M.Wt. 805.58): C, 44.73; H, 4.00; Cl, 8.80; N, 6.95; O, P, 7.69; S,
7.96. Found: C, 44.25; H, 3.86; Cl, 8.43; N, 6.41; P, 7.60; S, 7.78.
1H NMR (CDCl3) (300 MHZ, 298 K); d = 6.73 (2H, t, aromatic,
J1 = 8.4 HZ, J2 = 10.8 HZ), 6.95 (2H, d, aromatic J = 8.1 HZ), 6.95
(2H, d, aromatic, J = 7.4 HZ), 7.32 (2H, t, aromatic J1 = 8.4 HZ,
J2 = 6.8 HZ), 7.36 (1H, d, J = 8.21 Hz), 7.13 (1H, d, J = 8.52 Hz), 5.12
(2H, s, ASO2NH), 3.72 (6H, s, AOCH3), 3.66 (8H, s, AOACH2).
Synthesis of erbium complex
The erbium complex was prepared by adding dropwise hot
aqueous (60 °C) solution (100 ml) of ErCl3ꢃ6H2O (0.76 g;
0.002 mol) to a solution of L (0.805 g; 0.001 mol) in tetrahydrofu-
ran (THF) (20 ml) while stirring continuously. After complete
addition of the ErCl3ꢃ6H2O solution, the reaction mixture was
heated under reflux for about 28 h under dry conditions. The
complex obtained was filtered, washed with water, ethanol, and
THF and then dried in vacuo (Fig. 2).
Experimental
O
O
N
O
O
O
S
O
Cl
Melting points (°C, uncorrected) were determined in open cap-
illaries on a Gallen Kemp melting point apparatus. Elemental anal-
ysis (C, H, N and S) were performed on Carlo Erba 1108 Elemental
Analyzer. The chlorine content was determined by the Schöninger
method, phosphorus content was determined by the vanadomo-
lybdato–phosphoric acid spectrophotometric method and water
molecules were determined by the thermogravimetric analysis.
Analysis of the erbium complex started with decomposition of
the complex with concentrated nitric acid. The resultant solution
was diluted with distilled water, filtered to remove the precipi-
tated ligand. The solution was then neutralized with aqueous
ammonia solution and the metal ions titrated with EDTA. The
infrared spectra were recorded on a Shimadzu FT-IR spectrometer
using KBr disks. Electronic spectra were recorded for solution of
the ligand, L in DMF, and for the metal complexes as Nujel Mull
on a Jasco UV–VIS spectrophotometer model V-550-UV–VIS. 1H
NMR spectra (in CDCl3) were recorded on Bruker Ac-300 ultra-
shield NMR spectrometer at 300 MHz, using TMS as internal stan-
dard. 31P NMR spectra were run, relative to external H3PO4 (85%),
with a Varian FT-80 spectrometer at 36.5 MHz. The mass spectrum
of L ligand was performed using a Shimadzu-Ge–Ms–Qp 100 EX
N
P
H
N
H
N
N
O
N
N
S
O
P
N
O
Cl
O
Fig. 1. Proposed structure of L ligand.
Fig. 2. Suggested structure of erbium-L binuclear complex.

726
Abdel-Nasser M.A. Alaghaz et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 724–729
Table 1
Characteristic IR bands of the ligand (L) and its [Er2(L)(H2O)6Cl6]H2O complex as KBr
pellets.
Assignments
asym(SO2)
msym (SO2)
L
[Er2(L)(H2O)6Cl6]H2O
m
1346s
1084s
3366br
3024m
2937m
1622m
–
1325s
1090s
3370br
3024m
2936m
1557m
824s
m
m
m
m
(NH)
(CH)aromatic
(CH)aliphatic
(C@N)
qr(H2O)
qw(H2O)
–
775s
m
m
m
m
m
m
m
m
m
(MAO)
(MAN)
(MACl)
(PAN)cyclic
(PAN)linear
(PACl)
(PAOAC)
(PANAP)
(NAPAN)
–
–
–
489s
422s
486m
1225m
984m
584m
1116m
990w
813m
1225m
1005m
586m
1114m
1014m
816m
Fig. 3. IR spectrum of (a) ligand (L) and (b) Er(III) complex.
[Er2(L)(H2O)6Cl6]H2O: Pink solid, Yield, 73%; m.p. 198 °C: Molar
conductance (KM): 2.24
Cl8Er2N8O17P2S2.
(M.Wt. 1482.87): C, 21.06; H, 2.85; Cl, 19.13; Er, 22.56; N, 7.56;
P, 4.18; S, 4.32. Found: C, 20.98; H, 2.47; Cl, 19.02; Er, 22.48; N,
7.33; P, 4.11; S, 4.24.
X
ꢁ1 cm2 molꢁ1. Anal. calcd. for C26H42
to the metal ion [22]. The stretching vibration band; m(NH), of the
sulfonamide group, which found at 3365 cmꢁ1 in the free ligand,
were shifted to higher frequencies in the spectra of the isolated
complex. The presence of coordinated water molecules renders it
difficult to confirm the enolization of the sulfonamide group. The
blue shift of the SO2 stretching vibration to lower frequencies
may be attributed to the transformation of the sulfonamide to the
enol form as a result of complex formation to give a more stable
six-membered ring [14,15]. This transformation would result in
the loss of the amide proton and the appearance of the absorption
Computational methods
All quantum chemical calculations were performed using the
Gaussian09 suite of programs [16]. Geometry optimization of the
ligand have been performed using the ab initio Density Functional
Theory (DFT) at the B3LYP functional [17–19] in conjunction with
the 6-31G(d) basis set. For each stationary point, we carried out a
force constant harmonic frequency calculation at the same levels
to characterize their nature as minima or transition states and to
correct energies for zero-point energy and thermal contribution.
The frequencies are scaled by a factor of 0.98. The vibrational
modes were animated using the ChemCraft program [20]. Natural
charges were computed within full Natural Bond Orbital analysis,
using NBO program implemented in Gaussian 09 [16]. Erbium
binuclear complex was optimized at B3LYP/UGBS1P [21] for the er-
bium atoms and 6-31G(d) for other atoms of the complex.
peak for enol m
(OH) stretching mode at 2923 cmꢁ1 for the complex,
together with a change in position and intensities of the sulfone
group [14,15]. This is supported by the 1H NMR data. The enolic
OH group is formed through the following tautomerism [15,22,23].
The lower frequencies of the enolic OH groups can be taken as
evidence for the participation of this group in complex formation
[14,15]. The strong and sharp bands at 1621 cmꢁ1 of the pyrimi-
Results and discussion
dine-N; m
(C@N) in the free ligand is shifted to 1595 cmꢁ1 in the
Experimental studies
erbium complex. This indicates the participation of the pyrimidine-N
in complex formation [14,15]. The presence of medium-to-strong
bands in the region between 816 and 765 cmꢁ1 in the spectrum
of the erbium complexes were attributed to coordinated water
molecules [14,15]. New bands were found in the spectrum of the
complex in the regions 488 and 421 cmꢁ1 which were assigned
The L structure is unambiguously assigned by 1H NMR (Fig. S1),
13C NMR (Fig. S2), 31P NMR (Fig. S3), and FTIR (Fig. 3). The 1H NMR
spectrum (Fig. S1) of the ligand L revealed its formation by the
presence of ANH proton signal at d = 5.12 ppm. This is further sup-
ported by the appearance of stretching vibration band m(NH) imine
at 3365 cmꢁ1. Also, the 1H NMR of the ligand exhibits signals at
d(ppm) = 3.66 (s, 6H, 2OCH3) and 9.82 (br, 2H, AOH, exchangeable
with D2O). This is an experimental evidence for the tautomeriza-
tion. The 13C NMR spectrum shows an obvious peak of the carbon
of CAP on the ligand at 47.62 ppm, the carbon of ACH3 and ACH2-
appears in 16.34 and 62.87 ppm, respectively. The 31P NMR spec-
trum shows a strong singlet at 24.96 ppm, indicating that the
two phosphorus groups in the molecule have the same chemical
environment.
to
m
(MAO) and
m(MAN) stretching vibrations, respectively [14,15].
Therefore, the IR data reveal that L ligand behaves as neutral
bidentate ligand and bind to the metal ion through enolic sulfon-
amide OH and pyrimidine-N.
The UV spectrum (Fig. 4) of the ligand in DMF solvent showed
absorption band at 276 nm, which are due to the electron delocal-
ization within the four membered ring of the dimeric structure for
the ligand [14,15].
The IR data are listed in Table 1. The SO2 group modes of the
ligand appear as medium to small bands at 1345 cmꢁ1
(masym) and
Computational studies
1083 cmꢁ1
(msym) for L ligand. In the complex, the asymmetric and
symmetric modes are shifted to 1324 cmꢁ1 and 1099 cmꢁ1for the
asymmetric and symmetric modes, respectively, upon coordination
Since single crystal X-ray structure for the novel hexa-
chlorocyclophosph(V)azane of sulfamonomethoxine ligand is not

Abdel-Nasser M.A. Alaghaz et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 724–729
727
Fig. 4. Electronic spectrum of (a) ligand (L) and (b) Er(III) complex.
available, quantum chemical calculations were utilized to find the
geometry optimized structures for the L at B3LYP/6-31G(d) quan-
tum mechanical method. Fig. S4 shows the optimized structure
of the L at B3LYP/6-31G(d). An inspection of the resulting structure
easily shows two close contacts H-bonding interactions. Table S1
in the supplementary material presents computed geometrical
parameters of L. Although the system is big-sized (46 non-hydro-
genic atoms) the optimization process goes smoothly till reached
a local minimum after 29 steps as shown in Figs. S5 and S6.
Figs. S7 and S8 in the supplementary material present the structure
of the ligand L, showing the atom symbols and atomic numeration
respectively. Since dispersion energies do not play a considerable
role in these types of structure, electron correlations are not so
important consequently DFT methods would provide a good qual-
ity structures. The P2N2 ring is almost planar and PAN bonds in the
ring are not of equal length. The average bond length is 1.754 Å.
The PACl bond length is 2.089 Å. Our structural data given in
Table S1 in Supplementary material agrees well with the available
X-ray data on P2N2 ring-containing compounds [23,24] and also
with our previous computations [24,25] add also the new paper
[24–26].
Fig. 5. Simulated IR spectrum of keto-form of L.
HOMO and LUMO pictures of the hexachlorocyclophosph
(V)azane of sulfamonomethoxine (L) are shown in Figs. S9 and
S10. HMO are located at the tail of the structure on the pyrimidine
ring, and sulfamonomethoxine. This part of the molecule is inter-
acting with the metal ions. Where this part behaves as a bidentate
ligand from the OH (after tautomerization) and the pyrimidine N.
Possibility of keto-enol tautomerism has been taken into ac-
count. The enol structure was computed and optimized at the same
level. The optimized enol structure is shown in Fig. S11. The keto
structure is more stable than the enol form by about 16.3 kcal/
mol. This difference is reduced to 15.8 kcal/mol if zero-point
Simulated IR spectra of L were calculated at the level B3LYP/
6-31G(d). Fig. 5 displays the simulated IR spectra for the keto
tautomer scaled by 0.98 as a scale factor [26]. Inspection of the
calculated frequencies shows that they agree with the experimen-
tally measured IR spectra Fig. 3a and Table 1. The vibrational
frequencies were animated with ChemCraft to assign frequencies
to their normal modes. The C@N stretching frequency measured
as a medium peak around 1620 computed as a very strong peak
at 1647. The asymmetric stretching of SO2 which measured around
1346 was computed at 1391 cmꢁ1
The electronic spectrum of L in DMF showed absorption bands at
272 nm regions which is due to intra ligand
pꢄ and n ? pꢄ tran-
.
p
?
sitions involving molecular orbital of the pyrimidine ring. DT–DFT
calculations were performed for the free ligand in the molecular
gas state. The UV–VIS spectrum of L keto-form is shown in Fig. 6.
The UV–VIS data as shown in Fig. 4 shows a sharp band at 233 nm.
Natural charges (Table 2) were computed within full Natural
Bond Orbital analysis, using NBO implemented in Gaussian 09
[16]. Positive and negative charges are accommodated on some
centers of the L molecule. Positive charges are found on S, P, H
and some C atoms. The highest positive charge is found on S
(2.351), and the next highest charge is found on P (2.256). On the
other hand, negative charges are on N, O, Cl and some C atoms.
The highest negative is found on N (ꢁ1.143). The coordination is
processed from N20 (ꢁ0.541) and N32 (ꢁ0.544) which accommo-
date fairly negative charge. Coordination also links oxygen atoms
that carry approximately (ꢁ0.900) of negative charge. The
distribution of charge on the ligand accounts for the importance
of the electrostatic interaction for the course of bonding with the
erbium(III) metal ion upon complexation.
Fig. 6. Simulated UV–VIS spectrum of keto-form of L.

728
Abdel-Nasser M.A. Alaghaz et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 724–729
Table 2
1 ꢁ b
dð%Þ ¼
ꢅ 100;
ð2Þ
ð3Þ
Computed natural charge of all atoms in the L.
b
Atom
Charge
Atom
Charge
Atom
Charge
ꢀ
ꢁ
1
2
b1=2
¼
ð1 ꢁ bÞ
:
1=2
N1
P2
N3
P4
C5
C6
C7
C8
ꢁ1.143
2.256
C27
C28
S29
N30
C31
N32
C33
C34
N35
C36
O37
C38
O39
O40
Cl41
O42
O43
Cl44
O45
O46
C47
C48
C49
C50
H51
H52
ꢁ0.193
ꢁ0.206
2.351
H53
H54
H55
H56
H57
H58
H59
H60
H61
H62
H63
H64
H65
H66
H67
H68
H69
H70
H71
H72
H73
H74
H75
H76
H77
H78
0.275
0.258
0.443
0.253
0.218
0.223
0.218
0.220
0.252
0.264
0.276
0.259
0.440
0.242
0.220
0.236
0.207
0.206
0.223
0.236
0.240
0.221
0.235
0.222
0.220
0.238
ꢁ1.143
2.256
ꢁ0.873
0.164
0.425
Computational studies on the complex
ꢁ0.209
ꢁ0.208
ꢁ0.328
ꢁ0.194
ꢁ0.207
2.351
ꢁ0.951
ꢁ0.913
ꢁ0.873
0.413
ꢁ0.544
ꢁ0.423
0.276
Erbium binuclear complex was optimized at B3LYP/UGBS1P
[21] for the erbium atoms and 6-31G(d) for other atoms of the
complex. Fig. S12 shows the optimized structure of the binuclear
Er complex. The ligand behaves a bidentate from the enolic struc-
ture. The complex appeared in an dodecahedral structure. Coordi-
nation occurs from O and N where ErAO and ErAN bond lengths
are 2.221 and 2.251 Å respectively. The ErAO of the coordinated
water is a slightly longer (2.258 Å).
C9
ꢁ0.518
C10
S11
O12
O13
N14
C15
C16
C17
N18
C19
N20
O21
C22
C23
C24
C25
C26
0.569
ꢁ0.497
ꢁ0.324
ꢁ0.913
ꢁ0.951
ꢁ0.312
ꢁ0.826
ꢁ0.823
ꢁ0.314
ꢁ0.823
ꢁ0.825
ꢁ0.129
ꢁ0.139
ꢁ0.129
ꢁ0.138
0.252
ꢁ0.379
0.574
Fig. S13 presents the TG and derivative thermogravimetric
(DTG)curves of [Er2(L)(H2O)6Cl6]H2O in nitrogen, which shows that
[Er2(L)(H2O)6Cl6]H2O undergoes three-steps thermal degradation.
The first decomposition step was found in the temperature range
of 85–145 °C with an estimated mass loss of 1.14% (calculated
mass loss of 1.21%) could be assigned to the successive loss of
one hydrated water molecule. There is a slight exothermic process
observed in the DTA curve from 85 to 145 °C. The second decompo-
sition steps found within temperature range of 145–260 °C with an
estimated mass loss of 7.16% (calculated mass loss 7.29%), could be
assigned to the successive loss of two coordinated water
molecules. The third decomposition step was found within tem-
perature range 260–450 °C with an estimated mass loss of
63.14% (calculated mass loss 63.22%), which are reasonably ac-
counted by the removal of the organic moieties (C23H26Cl8N8O7P2
S2), one spilt exothermic peak observed in the DTA curve at
408 °C. The decomposition of the Er(III) complex molecule ended
with the metallic residue (2Er2O3) and three carbon residue with
an estimated mass loss of 28.19% (calculated mass loss of 28.26%).
Fig. S14 depicts the SEM photographs of the synthesized ligand
L and [Er2L(H2O)6Cl6]H2O complex. The morphology and particle
size of the ligand L and [Er2L(H2O)6Cl6]H2O complex have been
illustrated by the scanning electron micrography (SEM). It was
noted that there is a uniform matrix of the synthesized complex
in the pictograph which leads to believe that it is a homogeneous
phase material. An ice fogs like shape is observed in the ligand L
ꢁ0.569
0.281
ꢁ0.541
ꢁ0.514
ꢁ0.320
0.165
ꢁ0.210
ꢁ0.208
ꢁ0.329
0.264
energy (zpe) correction has been taken into consideration. This
large difference permits separable isomers. This allows tautomer-
ization prior to complexation.
Characterization of erbium(III) complex
Er(III) complex (Fig. 4b) display five electronic spectral bands in
the range of 679, 616, 527, 468, and 415 nm, characteristic to an
dodecahedral geometry [27]. These bands may be assigned to the
following transitions:
4I15/2 ? 4F9/2 4I15/2 ? 4S3/2 4I15/2 ? 2H11/2 (Er–I), 4I15/2 ? 4F7/2
, , ,
and 4I15/2 ? 4G11/2 (Er–II), respectively. Magnetic moment of the
erbium(III) complex at room temperature lie in the range 9.43
B.M. These values are in tune with a high spin configuration and
show the presence of an distorted dodecahedra environment
[27,28] around the Er(III) ion in the complex. This magnetic
behavior of the complex indicating that the 4f electrons in the com-
plexes Er(III) atoms are well-shielded by the outermost 5s and 5p
electrons. The values of the bonding parameters b (nephelauxetic
ratio), d (Sinha’s parameter) and b1/2 (covalent factor), calculated
[27,29–34] from the solid-state f–f spectra by Eqs. (1-3), are listed
in Table 3. The values indicate that the interaction between Er(III)
and the ligand is essentially electrostatic and that there is a minor
participation of the 4f orbitals in bonding [29–34].
with the particle size of 5
plex is an ice granules shaped morphology with 5
l
m. However [Er2L(H2O)6Cl6]H2O com-
m particle size.
l
Single crystal of the complex could not be prepared to get the
XRD and hence the powder diffraction data was obtained for struc-
tural characterization. X-ray powder patterns of one representative
complex [Er2(L)(H2O)6Cl6]H2O has been given in Fig. S15 along
with the prominent data. The peak broadening at lower angle is
more meaningful for the calculation of particle size; therefore the
size of the particle has been calculated using Debye–Scherrer for-
mula [35] using reflection from the XRD pattern. Debye–Scherrer
formula is given by D = 0.94k/bCosh, where D is the size of the par-
ticle, k is the wavelength of X-ray, b is the full width at half max-
imum (FWHM) after correcting the instrument peak broadening
(b is expressed in radians,) and h is the angle. The size of the par-
ticles has been found to be 33–35 nm. The size for the representa-
tive complex was obtained 16.0 nm and on this basis it could be
concluded that the complex [Er2(L)(H2O)6Cl6]H2O is a nano-sized
complex of erbium(III) with an dodecahedral structure. The ob-
served X-ray pattern of the free ligand sample studied in the pres-
ent investigation indicates amorphous nature.
n
X
1
2 n¼1
Vcomplex
Vaquo
b ¼
;
ð1Þ
Table 3
Bonding parametersa,b for the [Er2L(H2O)6Cl6]ꢃ2H2O complex.
Compound
b
d
b1/2
0.058
[Er2(L)(H2O)6Cl6]H2O
0.995
+0.72
On the basis of spectral, thermal and magnetic studies, a
plausible structure for the complexes is established (Fig. 2) in
which erbium(III) is situated in an dodecahedral environment.
a
Calculated from solid-state f–f spectra taking into account the bwavenumbers of
4
4
the I15/2
?
4F9/2
, , , , ,
4S3/2 2H11/2 4F7/2 4F5/2 4F3/2, (2G, 4F, 2H)9/2 and G11/2 transitions.
b
For the definition of the bonding parameters b, d (%) and b1/2
.

Abdel-Nasser M.A. Alaghaz et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 724–729
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a
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cyclodiphosph(V)azane ligand (L), obtained from the reaction of
1,3-bis(N1-4-amino-6-methoxypyrimidinebenzene-sulfonamide)-
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Acknowledgment
The Authors extend their appreciation to the Deanship of Scien-
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.02.061.
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