Spectral and thermal studies for some transition metal complexes of bis(benzylthiocarbohydrazone) focusing on EPR study for Cu(II) and VO2+

Article abstract of DOI:10.1016/j.saa.2007.07.058

The coordination behavior of bis (benzylthiocarbohydrazone) as a macrocyclic ligand (H₂BBTC), towards Co(II), Ni(II), Cu(II) nitrates, Cd(II) and Pt(IV) chlorides as well as VO²⁺ sulphate has been investigated. The elemental analysis, magnetic moments, spectral (UV-vis, IR, ¹H NMR and EPR) with thermal studies were used to characterize the isolated complexes. The IR spectra showed that the ligand acts as a binegative hexadentate donor through NH groups and thiol S atoms. Electronic and magnetic data proposed the octahedral structure for all complexes under investigation, except VO²⁺, is a square-pyramidal geometry. EPR spectra for VO²⁺ and Cu(II) reveal data confirmed the proposed structures. The ionization constants (pK₁ = 8.3 and pK₂ = 7.7) of the ligand and the stability constants of its complexes in solution were determined. The TG analysis for most complexes supports the absence of solvent molecules in or out the coordination sphere through the high thermal stability observed on the thermal curves for the investigated complexes.

Full text of DOI:10.1016/j.saa.2007.07.058

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 277–283
Spectral and thermal studies for some transition metal complexes
of bis(benzylthiocarbohydrazone) focusing on EPR
study for Cu(II) and VO2+
Khlood S. Abu-Melhaa, Nashwa M. El-Metwallyb,∗
a Department of Chemistry, Faculty of Education, King Khaled University, Abha, Saudi Arabia
b Department of Chemistry, Faculty of Science, Mansoura University, Egypt
Received 30 November 2006; received in revised form 21 July 2007; accepted 31 July 2007
Abstract
The coordination behavior of bis (benzylthiocarbohydrazone) as a macrocyclic ligand (H2BBTC), towards Co(II), Ni(II), Cu(II) nitrates, Cd(II)
and Pt(IV) chlorides as well as VO2+ sulphate has been investigated. The elemental analysis, magnetic moments, spectral (UV–vis, IR, 1H NMR and
EPR) with thermal studies were used to characterize the isolated complexes. The IR spectra showed that the ligand acts as a binegative hexadentate
donor through NH groups and thiol S atoms. Electronic and magnetic data proposed the octahedral structure for all complexes under investigation,
except VO2+, is a square-pyramidal geometry. EPR spectra for VO2+ and Cu(II) reveal data confirmed the proposed structures. The ionization
constants (pK1 = 8.3 and pK2 = 7.7) of the ligand and the stability constants of its complexes in solution were determined. The TG analysis for most
complexes supports the absence of solvent molecules in or out the coordination sphere through the high thermal stability observed on the thermal
curves for the investigated complexes.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Thiocarbohydrazone; EPR study; VO2+ complexes
1. Introduction
complexes was elucidated. In which, the ligand coordinated
in protonated and deprotonated forms by losing of hydrazinic
protons (Scheme 1).
Formerly the complexes containing four or two nitrogen and
oxygen atoms in an equatorial plane was extensively studied
[1–3]. The macrocyclic ligands containing nitrogen and oxygen
atoms are of great interest due to their elaborated versatility
[4], through the flexibility and the ability to coordinate in either
neutral or deprotonated form [5].
They also contain N C C N structure unit, which displays
a strong chelating ability through the electron delocalization,
which associated with extended conjugation, that may affect
on the nature of the complex formed. They can yield mono or
polynuclear complexes, some of which are biologically relevant
[6]. Particularly, first row of transition metal complexes with
such ligands have a wide range of biological properties [7–11].
The ligand under investigation is expected to form additional
complexes. The ligitional behavior appeared with the prepared
nitrogen–sulphur ligand (Scheme 1) with some 3d metal ion
2. Experimental
All chemicals used Co(NO3)2·6H2O, Ni(NO3)2·6H2O,
Cu(NO3)2·2.5H2O, VOSO4·2H2O, CdCl2·2.5H2O, H2PtCl6,
benzyl, ethanol, diethylether, DMF and DMSO were of ana-
lytical reagent grade (BDH) and used as supplied.
2.1. Synthesis of ligand
An ethanolic solution of benzyl (40 mmol, 8.40 g) was added
to thiocarbohydrazide, which was prepared using a published
procedure [12], in glacial acetic acid (80 mmol, 8.48 g). The
reaction mixture was refluxed on a hot plate for 1 h. The orange
precipitate formed was separated out, filtered off, recrystallized
from ethanol, and dried in desiccators over anhydrous CaCl2.
The proposed chemical structure of the ligand is in a good agree-
ment with the stoichiometry abstracted from its analytical data
and confirmed from the IR, 1H NMR and mass spectral data.
∗
Corresponding author.
E-mail address: n elmetwaly00@yahoo.com (N.M. El-Metwally).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.07.058

278
K.S. Abu-Melha, N.M. El-Metwally / Spectrochimica Acta Part A 70 (2008) 277–283
2.4. Physical measurements
Carbon and hydrogen contents were determined at the Micro-
analytical Unit in Cairo University. The analysis of metal and
chloride ions was carried out according to the standard meth-
ods [13]. The infrared spectra, as KBr discs, were recorded on
a Mattson 5000 FTIR Spectrophotometer. The electronic and
1H NMR (200 MHz) spectra were recorded on UV2 Unicam
UV–vis, and a Varian Gemini Spectrophotometers, respectively.
The mass spectra were recorded on a Varian MAT 311 instru-
ment. The thermal studies were carried out on a Shimadzu
thermogravimetricanalyzerataheatingrateof10 ◦C min−1. The
protonation constants of the ligand and the formation constants
of its complexes were determined pH-metrically by Irving and
Rossotti method. ESR spectrum was obtained on a Bruker EMX
Spectrometer working in the X-band (9.78 GHz) with 100 kHz
modulation frequency. The microwave power was set at 1 mW,
and modulation amplitude was set at 4 G. The low field signal
was obtained after 4 scans with a 10-fold increase in the receiver
gain. Apowderspectrumwasobtainedina2 mmquartzcapillary
at room temperature.
Scheme 1. Thione form of H2BBTC.
2.2. Synthesis of complexes
The solid complexes were prepared by the reaction of calcu-
lated amount for 1:1 (M:L) ratio of both metal salts and ligand in
ethanol–water (v/v) solution. The reaction mixture was heated
under reflux on a water bath for 2–3 h. During the prepara-
tion of Pt(IV) and VO2+ complexes sodium acetate was added
by about 0.3 g. The reaction product was filtered immediately,
washed several times with hot EtOH followed by diethylether
and dried in a desiccator over anhydrous CaCl2. The analytical
and physical data are given in Table 1.
3. Results and discussion
The macrocyclic ligand used in this study is elucidated by
different tools as, the elemental analysis, which used to propose
the ligand formulae and the molecular ion peak in mass spectrum
supported this. 1H NMR spectrum is the final confirming tool for
the ligand structure and displayed a singlet peak at δ = 7.34 by
integration assigned to 20 H referring to the four phenyl groups.
Also, the two singlet peaks at δ = 8.4 and 8.8 each peak by inte-
gration assigned to the two hydrogen atoms aggregated from two
similar NH groups. The relative down field appearance of the
second peak (δ = 8.8) may be due to the intramolecular hydro-
gen bonding between NH and C S groups [14]. All the isolated
complexes are stable under atmospheric conditions and insolu-
ble in most common organic solvents except DMF and DMSO
dissolved all of them except [Cu(C30H22N8S2)] which is par-
tially soluble. The soluble complexes having a non-conducting
feature. [Pt(BBTC)]Cl2 deviates from this behavior by showing
a relative high conductivity value (110 ꢀ−1 cm2 mol−1) which
may refer to the presence of two ionizable chloride ions in the
crystal lattice. All the complexes have melting points above
2.3. Procedure for the pH-metric titrations
The titrations were carried out at room temperature
(25 1 ◦C). The titrant was added from burette and the contents
of the titration vessel were stirred magnetically. The titration
was carried out for the following solutions:
(1) 2.5 ml of HCl (10−2 mol l−1) + 1.25 ml KCl + 10 ml ethanol.
(2) 2.5 ml of HCl + 1.25 ml KCl (6.1 mol l−1) + 0.25 ml
(10−2 mol l−1) of ligand + 9.75 ml of ethanol.
(3) Solution (2) + 0.05 ml (10−2 mol l−1) of metal ion.
All the above solutions were completed to 25 ml with twice-
distilled water and titrated against 0.978 × 10−2 mol l−1 NaOH.
Table 1
Analytical and physical data for the metal complexes
No.
Complex
Color
Found (calcd.%)
F.W. founda
C
N
H
M
1
2
3
4
5
6
7
[C30H24N8S2]
Yellow
Yellow
Brown
Green
Green
Green
65.2(64.3)
52.7(53.7)
59.8(58.4)
56.6(57.7)
44.0(43.7)
56.7(58.4)
46.4(45.7)
19.2(20.0)
15.9(16.7)
17.8(18.1)
17.5(18.0)
12.9(13.6)
17.5(18.1)
14.9(14.2)
4.75(4.32)
4.3(4.32)
3.1(3.6)
3.8(3.6)
3.2(2.7)
3.4(3.6)
3.3(2.8)
–
563(560.7)
–((671.1)
619(617.6)
–((622.2)
–((824.7)
618(617.4)
626(625.7)
[Cd (C30H22N8S2)]
[Co (C30H22N8S2)]
[Cu (C30H22N8S2)]
[Pt(C30H22N8S2)]Cl2
[Ni (C30H22N8S2)]
[(VO)2 (C30H22N8S2) SO4]
17.2(16.7)
9.6(9.5)
10.9(10.2)
24.1(23.6)
9.8(9.5)
12.1(12.9)
Dark green
a
Values obtained from mass spectra.

K.S. Abu-Melha, N.M. El-Metwally / Spectrochimica Acta Part A 70 (2008) 277–283
279
Table 2
Significant IR spectral bands (cm−1) of H2BBTC and its metal complexes
Complex
ν(NH)
υ(NH· · ·S)
υ(C N)
υI(C S)
υIV(C S)
υ(N N)
δ(NH)
υ(M N)
υ(M S)
1
2
3
4
5
6
7
3220
3127
1640
1623
1598
1600
1630
1619
1635
1580
1485
1482
1483
1556
1535
1538
873
–
–
–
–
1025
1070
1065
1098
1028
1105
1111
1533
–
–
–
–
–
–
420
400
420
420
422
420
380
340
380
394
397
390
3059
3058
3100
3023
3060
1482
1483
1500
1535
–
–
300 ◦C. The elemental analysis and the color of the complexes
are listed in Table 1.
well as the band at 1111 and 1040 cm−1 is due to ν(V O)and
ν(N N) vibration, respectively. This is the further evidence for
square-pyramidal geometry proposed for VO2+ complex [19].
3.1. IR spectral studies
3.2. Electronic spectra and magnetic measurements
The characteristic bands of the ligand and its complexes are
collected in Table 2. The infrared spectrum of H2BBTC shows
bands at 3220 and 3127 cm−1 assigned for νNH groups, the
lower appearance of the second NH (3127 cm−1) group may
support its participation in hydrogen bonding [15]. The two
bands at 1640 and 1025 cm−1 for ν(C N) and ν(N N) vibra-
tions, respectively [16]. The band at 873 cm−1 is assigned to
ν(C S) vibration. The careful comparison between IR spectra
of H2BBTC and each complex spectrum reflects the follow-
ing observations: (i) the negative shift (50–90 cm−1) observed
on ν(C N) band, (ii) the positive shift (40–80 cm−1) observed
for ν(N N) band, (iii) the coordination of azomethine nitrogen
is also consistent with the presence of new band at the range
(400–480 cm−1) assignable to the ν(M N) vibration [17]; and
finally, (iv) the coordination via thiolate sulphur is indicated by
the absence of ν(C S) vibration with the simultaneous appear-
ance of new bands at the ranges 619–697 and 340–420 cm−1
attributed to the ν(C S) [18] and ν(M S) vibrations, respec-
tively. Such observations proposed the binegative hexadentate
feature of the ligand with all investigated metal ions in a
mononuclear structure (Scheme 2) except with VO2+ ion, which
appeared as a binuclear complex. In which, the band at 1190 and
1020 cm−1 is assigned to ν(SO4) in its bidentate nature [19] as
The magnetic moments and the significant electronic absorp-
tion bands (in DMF) for all complexes under investigation
are shown in Table 3. Nujol mull spectra for some complexes
were done and displayed conformity for DMF results. The data
abstracted reflect true insight about the geometry of the com-
plexes which asserted by other tools. The magnetic moment
of [Ni(BBTC)] is found to be 2.1 BM, which is not suitable
with the normal values of Ni(II) geometries. This may suggest
a mixed stereochemistry between octahedral and square-planar
geometries [20] with 3A2g ground state term symbol. The elec-
tronic spectral bands support such postulation by the presence
3
of 24,690 (ν3) and 14,810 (ν2) bands attributed to the A2g
3
3
(F) → T1g (F) and 3A2g (F) → T1g (P) transitions, respectively
in an octahedral structure. Also, the presence of 20,000 cm−1
band in the spectrum assigned to the A1g → A2g transition
in a square-planar [21] geometry. This verified the presence of
square-planar by 25% in the geometry mix.
1
1
The electronic spectrum of the [Cu(BBTC)] complex, in
2
DMF, shows band at 17,540 cm−1 assigned to the 2Eg → T2g
transition which may suggest a distorted octahedral arrange-
ment around the metal ion. The distortion may be due to Jahn
Teller effect. The charge transfer band at 23,810 may be due
to S → Cu(II) which is previously mentioned [22] in which the
S → Cu(II) charge transfer band are in the region from 21,785 to
24,750 cm−1. The normal magnetic moment (1.75 BM) supports
the absence of any metal–metal interaction with the neighbor-
ing molecules, which appeared on the clear resolution of EPR
spectrum.
The electronic spectrum of [Co(BBTC)] in DMF dis-
plays two bands at 19,455 and 14,830 cm−1 assignable to the
4
4
4T1g → T1g(P) (ν3) and 4T1g → A2g (ν2) transitions, respec-
tively corresponding to octahedral configuration [23]. The
calculated values of 10Dq, B and β (Table 3) lie in the range
reported for the proposed structure. The magnetic moment value
(3.4 BM) is near the spin only moment (3.87 BM) [24].
The electronic spectrum of [(VO)2(BBTC)SO4] in DMF
shows two bands at 12,370 and 16,000 cm−1 may assign to
Scheme 2. (a) The modeling for Co(II) complex in which the phenyl groups
were excluded, after the minimization energy steps, to clarify the figure and (b)
is the proposed structure for the complexes, where M = Co(II), Ni(II), Cu(II) and
Cd(II).
2
2
2
2B2 → E and B2 → B1, respectively, which are well char-
acteristic for square-pyramidal geometry [25]. The magnetic
moment value (1.4 BM) measured for the individual atom is

280
K.S. Abu-Melha, N.M. El-Metwally / Spectrochimica Acta Part A 70 (2008) 277–283
Table 3
Magnetic moments, electronic spectral data (in DMF) and ligand field parameters of some complexes
Complex
μeff (BM)
υmax (cm−1
)
Ligand field parameters
10Dq
B
β
2
3
4
5
6
7
Diamagnetic
2.36
1.75
Diamagnetic
2.08
1.4
17,857
19,455; 14,830
17,540
23,310; 12,195
24,690; 20,000; 14,810
12,270; 16,000
24,570
25,125
23,810
25,000
–
4493
898
0.91
9031
903.1
0.88
29,410
lower than that reported (1.7–2.1 BM), this may support the
presence of vanadyl complex in a binuclear with strong inter-
action between the two VO2+ ions. The octahedral geometry
is the most acceptable structure for [Pt(BBTC)]Cl2 referring
The residual part measured at 650 ◦C agrees with NiS + N2C2S
fragment by 27.5(27.4).
The TGA curve of [Cu(BBTC)] shows a gradual degrada-
tion steps. The first started at 185.84 ◦C refers to the removal of
2(ph-C) by 28.4 (28.6%) weight loss as a terminal part in the
ligand. The second decomposition step started at 330 ◦C is cor-
responding to the removal of another terminal part (2 ph + C) by
26.5 (26.7%) weight loss. The third decomposition step started
at 485 ◦C is corresponding to the removal of another fragment
(N5H2C3) by 16.5(17.2%). The residual part observed at 660 ◦C
by 27.5 (27.5%) is due to CuS beside N3S fragment.
The TGA curve of [Co(BBTC)] shows three decomposition
stages started at 210 ◦C corresponds to the dissociation of 3 ph
groups by 36.4 (37.4%) weight loss, followed by C2N3H as a
part expelled in the second step at 426 ◦C by 9.3 (10.8%) weight
loss. The final step started at 529 ◦C represents the removal of
ph + C3N3 fragment by 22.2 (23.1%) weight loss. The residual
part representing CoS beside C2H2N2S fragment is measured at
660 ◦C by 31.4 (28.7%) weight percent. The difference between
the found and calculated values may be due to the overlapping
between each successive steps.
The TGA curve of [Cd(BBTC)] showed three degradation
steps started at 179 ◦C. The first step ended at 303 ◦C is attributed
to the removal of phenyl group by 12.87 (11.50%) weight loss.
The second step ended at 440 ◦C may attribute to the removal of
3 ph groups by 35.8 (34.4%) weight loss. The third step ended
at 677 ◦C is attributed to the removal of N4C6H2 fragment by
18.5 (19.3%). The final residue measured at 660 ◦C is due to
CdS beside SN4 fragment by 32.8 (34.6%).
to the low spin d6 system having A1g as ground state. Two
1
spin allowed absorption bands at 23,310 and 12,195 cm−1 are
1
1
to be expected corresponding to transitions A1g → T2g and
1
1A1g → T1g, respectively [26]. The spectrochemical parame-
ters Dq, B and β of Co(II) and Ni(II) complexes are given in
Table 3. the Dq values (4.49 × 103 and 9.03 × 103 cm−1) are
found close to that observed for the complexes containing oxy-
gen, nitrogen and/or sulphur. The observed Dq values ordered
the ligand in the middle range of the spectrochemical series and
provides that the C N and C S of the ligand are complexed
to the Co(II) and Ni(II) ions in an octahedral geometry. The B
values of the complexes were found by ∼90%, indicating con-
siderable overlap with strongly ionic bond character [27]. The
high B values are most likely associated with the unchangeable
nuclear charge of the cation. The nephelauxetic parameter, β
values (0.91 and 0.88 for Co(II) and Ni(II), respectively) are
indicating that the ligand is in the middle of the nephelauxetic
of other nitrogen and sulphur donor series. The values are higher
than that reported for NiN6 or NiO6, confirming the coordination
via N and S atoms (Scheme 2).
3.3. Thermal analysis
The thermogravimetric (TGA and DTGA) analysis for most
investigated complexes was recorded at temperature range
25–800 ◦C. The thermograms exhibit several thermal events.
The relative high thermal stability observed in all thermally
investigated complexes, which may correspond to the absence
of solvent molecules in/out the coordination sphere. This is pro-
posed referring to the higher thermal stability observed for all
investigated complexes in which the first decomposition step is
started at relatively higher temperature. Also, the high weight
percent of the residual part reflects the stability of the chelate
structure, which is considered as a logical behavior especially
with S and N sites.
The curve of [Pt(BBTC)]Cl2 showed stability till 170 ◦C
above which a weight loss by 18.8 (17.8%) corresponds to
the removal of ph + 2Cl fragment. The second stage started at
282 ◦C is assigned to the elimination of 3 ph + N8C6H2S by
53.7 (54.5%) as a residual organic fragment. The third step
(458–618 ◦C) can be ascribed to the residual part (PtS) by 27. 5
(27.8%) weight percent.
3.4. Mass spectra
The TG curves obtained for [Ni(BBTC)] showed high ther-
mal stability up to 234 ◦C, followed by a sudden decomposition
stage ended at 422 ◦C may be attributed to the removal of 4 ph
groups by 49.4 (49.9%) weight loss. The second decomposition
stage followed the previous one ended at 659.3 ◦C, also may be
attributed to the removal of N6H2C4 as the organic fragment.
The mass spectra for most investigated complexes and the
molecular ion peaks confirmed the proposed formulae. Calcu-
lated and found molecular weights are given in Table 1. As
a typical example, the mass spectrum (Fig. 1) of H2BBTC
shows peaks corresponding to the successive degradation of the
molecule. The first peak at m/e = 563 (calcd. = 560.7) represents

K.S. Abu-Melha, N.M. El-Metwally / Spectrochimica Acta Part A 70 (2008) 277–283
281
dx2 − y2 orbital as a ground state [28]. No band correspond-
ing to the forbidden magnetic dipolar transition for the complex
was observed at half-field (ca. 1500 G, g = 4.0). This reveals the
absence of any Cu–Cu interaction which supporting the mono
nuclear complex. In axial symmetry the g-values are related to
the G-factor by the expression, G = (g − 2)/(g − 2) = 4, which
ꢀ
⊥
measures the exchange interaction between copper centers in the
solid. According to Hathaway [29], if the value of G is greater
than 4, the exchange interaction between copper(II) centers in
the solid state is negligible, whereas when it is less than 4, a
considerable exchange interaction exists in the solid complex.
The calculated G values are given in (Table 4). The G values are
greater than 4, this supports the absence of exchange coupling
between copper(II) centers in the solid state [30]. In hexaco-
ordinated complex, tetragonal distortion from the octahedral
symmetry due to the Jahn–Teller distortion is very common.
The low g-value (g = 2.17) obviously corresponds to regular
octahedral Cu(II) complex. Superhyperfine structures for these
complexes are not seen at higher fields excluding any interac-
tion of the nuclear spins of the nitrogen (I = 1) with the unpaired
electron density on Cu(II). Molecular orbital coefficients, a2 (a
measure of the covalence of the in-plane ␴-bonding between the
3d orbital and the ligand orbitals) and β2 (the covalent in-plane
␲-bonding), were calculated by using the following equations
[31]:
Fig. 1. Mass spectrum of H2BBTC.
ꢀ
ꢁ
A
3
ꢀ
α2 =
β2 =
+ (g − 2.0023) + (g − 2.0023) + 0.04,
ꢀ
⊥
0.036
7
(g − 2.0023)E
−8λα2
where λ = −828 cm−1 for the free copper(II) ion and E is the
electronic transition energy. The lower value of β2 compared to
α2 indicates that the in-plane ␲-bonding is more covalent than
the in-plane ␴-bonding, the data in a good agreement with the
data reported earlier [29]. The α2 value for copper(II) complex
indicates a considerable covalency in the bonding between the
Cu(II) ion and the ligand.
Fig. 2. Solid state X-band ESR spectra for Cu(II) complex (a) and VO2+ (b) at
room temperature.
The EPR spectra of VO2+ complex at room temperature
exhibit an eight-line pattern corresponding to the usual par-
allel and perpendicular components of g- and hyperfine (hf)
A-tensors. As a representative, the EPR spectrum of the com-
plex is shown in (Fig. 2b). It can be seen that the parallel and
perpendicular components are well resolved. Nitrogen superhy-
perfine splitting is not observed in the complex, which indicates
that the unpaired electron is in the dxy orbital [30]. The pattern
suggests that g and A are axially symmetric in nature. The spin
Hamiltonian parameters derived from the spectrum are given in
Table 4 with MO parameters computed from experimental data.
The parameters A and g are found to be in agreement with the
the molecular ion peak of the complex (M+ + 2) with 9.2% abun-
dance. The sharp peak (base peak) with m/e = 92 (calcd. = 91)
may represent the residual part (C6H5N) of the ligand.
3.5. ESR spectra
The room temperature solid-state ESR spectrum of copper
complex (Fig. 2a) exhibits axially symmetric g-tensor parame-
ters with g > g > 2.0023. The g values reflect that, the Cu(II)
ꢀ
⊥
center has a tetragonal distorted octahedral geometry with
Table 4
Spin-Hamiltonian parameters at room temperature
Complex
g
ꢀ
g
⊥
g0
A × 10−4
g /A
A
⊥
A0
α2
β2
ꢀ
ꢀ
ꢀ
(4)
(7)
2.17
1.937
2.03
1.964
2.12
1.955
187
−181.25
132.3
–
–
−70
–
0.59
1.432
0.50
0.943
−107.08

282
K.S. Abu-Melha, N.M. El-Metwally / Spectrochimica Acta Part A 70 (2008) 277–283
values generally observed for the vanadyl complex with square-
pyramidal geometry [31]. The molecular orbital coefficient α2
and β2 were calculated using the following equations [32]:
Taking A and A to be negative values the expression for K is
ꢀ
⊥
[35]:
ꢀ
ꢁ
A0
ꢀ
ꢁ
K = −
− (ge − g0)
7
6
A
A
5
9
p
ꢀ
⊥
β2 =
α2 =
−
+
+ g − g − ge
,
ꢀ
⊥
p
p
14
14
Thus K (Fermi-contact term) can be evaluated (0.88).
2.0023 −
8β2λ
g
where g = (g − g ) × 10−3
⊥
ꢀ
3.6. pH-metric studies
The negative values of β2 lead to negative values of α2. Since
hyperfine coupling constants are negative, calculations were
done taking A and A as negative, which gave positive values
The association constant measured for organic molecules
in solution is becoming important. This elaborates the insight
during the investigation of their complexation behavior in aque-
ous or solid state. The protonation constants of the ligand were
determined through a plot between pH and n¯A, where n¯A is the
average number of protons associated per ligand molecule. This
is easily calculated from the Irving and Rossotti equation [36]:
ꢀ
⊥
of β2 and α2. In this study, α2 is less than β2 indicating that in-
plane ␴-bonding is more covalent than in-plane ␲-bonding. The
spectrum of the complex shows two bands at 16,000 cm−1 (E1)
2
2
and 12,270 cm−1 (E2) which are assigned to B2 → B1 and
2B2 → E, transitions, respectively. Assuming pure d-orbitals
2
(V1 − V2)([A] + [B])
and using first- and second-order perturbation theory, the spin
Hamiltonian parameters can be related to the transition energies
by the following expressions:
n¯A = Y +
(V0 + V1)TL
where Y is the ionizable proton of the ligand, (2H+) V1 and
V2 are the volumes of alkali required to reach the same pH
value in the free acid and in the ligand mixture, respectively
V0 is the initial volume of the titrated mixture, TL is the lig-
and concentration in the initial volume, and [A] and [B] are
the concentrations of the free acid and the alkali, respectively.
The association constants (pK1 and pK2) are determined [37]
by interpolation at n¯A = 0.5 and 1.5, respectively. pK1 = 8.3 and
pK2 = 7.7 is determined by indirect method using pK (at n¯A = 1)
and pK1 by applying this equation pK1 + pK2 = 2 pK (at n¯A = 1).
The low pK values may indicate the relative acidity of the ligand
which facilitate the deprotonation as well as the little difference
between the two values may refer to the stepwise deprotonation
process even for the symmetric centers of ionization (NH C S).
This may support the binegative behavior of the ligand which
appeared, as the major trend towards the metal ions in the solid
complexes. The stability constants (Table 5) of all metal ion
complexes under investigation were determined. This by using
the relation between the free ligand exponent (pL) and the aver-
age number of ligands attached per metal ion (n¯A). The values
were evaluated applying the following equations:
ꢀ
ꢁ
ꢀ
ꢁ
8λ
E1
2λ
E2
g = ge −
ꢀ
and
g
= ge −
⊥
where ge is the free-electron g value (2.0023). Using E1 and
E2 values, the spin–orbital coupling constant (λ) value (182.79)
is evaluated. A value for λ of 250 cm−1 is reported [33] for
the free V4+ ion. The reduction in the magnitude of λ for the
double bonded oxovanadium complex (V O)2+ is attributed to
substantial ␲-bonding. While, the value is within the reasonable
limits of predicated values.
3.5.1. Calculation of dipolar term (p)
The p value is calculated from the following equation:
7(A − A )
ꢀ
⊥
p =
6 + 3/2(λ/ΔE1)
If A is taken to be negative and A positive, the p value will be
ꢀ
⊥
more than 270 G, which is far from the expected value. Thus, the
signs of both A and A are taken as negative and are indicated
ꢀ
⊥
in the form of isotropic hf constant (A0). McGarvey theoretically
calculated the value of p to be +136 G for vanadyl complexes
[34] and the value (129.42) of this complex do not deviate much
from this expected value.
(V3 − V2)([A] + [B])
n¯ =
(V0 + V1)−nATM
Table 5
The association constants of the ligand and the formation constants of its
complexes
3.5.2. Calculation of MO coefficients and bonding
parameters
System
Half method
The g values observed so far for most vanadyl complexes are
generally lower than 2.0023 and the data in this work support
this observation. This lowering is related to the spin–orbit inter-
action of the ground state dxy level with low-lying excited states.
The isotropic and anisotropic (g and A) parameters have been
calculated from equations:
log K1
log K2
log β*
1
2
3
4
5
6
7
8.3
4.6
6.4
9.6
8.2
8.5
6.5
7.7
2.2
2.8
8.7
5.7
5.3
4.3
–
6.8
9.2
18.3
13.9
13.8
10.8
A + 2A
g + 2g
ꢀ
⊥
ꢀ
⊥
A0 =
,
g0 =
3
3
β* is the overall stability constant.

K.S. Abu-Melha, N.M. El-Metwally / Spectrochimica Acta Part A 70 (2008) 277–283
283
1 + K1[H+] V3V0
[7] E.M. Jouad, A. Riou, M. Allian, M.A. Khan, G.M. Bovet, Polyhedron 20
(2001) 67.
pL = log
pL = log
·
for a monobasic ligand
TL − n¯ TM
V0
[8] Z. Xinde, C. Wang, Z. Lu, Y. Dang, Trans. Met. Chem. 22 (1997) 13.
[9] S. Chandra, K. Gupta, Trans. Met. Chem. 27 (2002) 196.
[10] A.M. Dhiman, K.N. Wadodkar, Ind. J. Chem. B 40 (2001) 636.
[11] S. Chandra, K. Gupta, Trans. Met. Chem. 27 (2002) 329.
[12] G.C. Saha, K. Khayer, M.R. Islam, Ind. J. Chem. B 31 (1992) 547.
[13] A.I. Vogel, A Text Book of Quantitative Inorganic Analysis, Longmam,
London, 1994.
1 + K1[H+] + K1K2[H+]2 V3V0
·
TL − n¯ TM
V0
for a dibasic ligand
[14] N.M. Elmetwaly, A.A. El-Asmy, A.A. Abou-Hussen, JPAC 1 (1) (2006)
75.
[15] S. Chanda, X. Sangeetila, Spectrochim. Acta A 60 (2004) 147.
[16] A.A. El- Asmy, M.E. Khalifa, M.M. Hassanian, Ind. J. Chem. A 43 (2004)
92.
[17] R.M. El-shazly, G.A.A. El-Hazmi, S.E. Ghazy, M.S. El-Shahawi, A.A.
El-Asmy, Spectrochim. Acta A 61 (2005) 243.
[18] F.A. El-Said, A.A. El-Asmy, W. Kaminsky, D.X. West, Trans. Met. Chem.
28 (2003) 954.
[19] N.M. El-Metwaly, R.M. El-shazly, I.M. Gabr, A.A. El-Asmy, Spectrochim.
Acta 61 (2005) 1113.
[20] A.A. El-Asmy, Y.M. Shaibi, I.M. Shedaiwa, M.A. Khattab, Synth. React.
Inorg. Met. Org. Chem. 18 (1988) 231.
where V3 is the volume of alkali required to reach the
desired pH in the complex solution, TM the initial con-
centration of the metal ion. The data reveal a good
agreement with the Irving and Williams [38] series with
Cu(II) > Ni(II) > VO2+ > Co(II) > Cd(II) order in which, the sta-
bility of the complex increases with the size of metal ion
decrease. The formation constants (8.2 and 5.7) for the Pt(IV)
complexes in solution show a high stability for the different
ratios (1:1 and 1:2 as M:L) appeared, which is the expected
behavior for highly charged metal ion.
[21] R. Srinivasan, I. Sougandi, R. Venkatesan, P. Sambasiva, Proc. Indian Acta
Sci. Chem. 115 (2003) 91.
4. Conclusion
[22] E. Franco, E. Lopez-Torres, M.A. Mendiola, M.T. Sevilla, Polyhedron 19
(2000) 441.
[23] N.M. El-Metwaly, I.M. Gabr, A.M. Shallaby, A.A. El-Asmy, Coord. Chem.
58 (2005) 1145.
[24] A.O. Baghiaf, M. Ishaq, O.A.S. Ahmed, M.A. Al-Julani, Polyhedron 4
(1985) 853.
[25] A.A. Abou-Hussen, N.M. El-Metwaly, E.M. Saad, A.A. El-Asmy, Coord.
Chem. 58 (2005) 1735.
[26] L. Petrilli, F. Tarli, G. Chiozzini, C. Riccueci, Polyhedron 16 (1997)
275.
[27] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam,
1986.
[28] H.I. Park, L.J. Ming, J. Inorg. Biochem. 27 (1998) 57–62.
[29] (a) B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143;
(b) B.J. Hathaway, Struct. Bonding (Berlin) 57 (1984) 55.
[30] H. Montgomery, E.C. Lingefetter, Acta Cryst. 20 (1966) 728.
[31] C.J. Carrano, C.M. Nunn, R. Quan, J.A. Bonadies, V.L. Pecoraro, Inorg.
Chem. 29 (1990) 944.
[32] T.M. Dunn, Trans. Faraday Soc. 57 (1961) 1441.
[33] B.R. McGarvey, J. Phys. Chem. 71 (1967) 51.
[34] M. Salagram, N. Satyanarayana, S. Radhakrishna, Polyhedron 5 (1986)
1171.
A series of novel complexes have been prepared and fully
characterized. The ligand bind mainly as a binegative in all
investigated complexes. The potentiometric studies supported
the behavior of the ligand in solid complexes, also the forma-
tion constants for the complexes in solution proposed the high
stability of Cu(II) an Pt(IV) complexes, which related to their
smaller atomic size. EPR spectra for VO2+ and Cu(II) complexes
supportedthebinuclearsquarepyramidalandmononuclearocta-
hedral structures proposed for the two complexes, respectively.
Proposed fragmentation and thermal decomposition patterns for
some of the complexes are also given.
References
[1] A. Biggotto, G. Costa, M. Mestroni, G. Pellizer, A. Puxeddu, E. Reisen-
hofer, L. Stefan, G. Tauzer, Inorg. Chim. Acta Rev. 4 (1970) 41.
[2] G. Costa, G. Mestroni, J. Orgnaomet. Chem. 11 (1968) 325.
[3] G. Costa, G. Mestroni, G. Tauzher, L. Stefani, J. Organomet. Chem. 6
(1966) 181.
[4] P. Sbuza, M.A. Mendiola, A. Arquero, V. Fernandez, E.G. Puebla, C.R.
Valero, Z. Natureforsch. 496 (1994) 263.
[5] M.A. Ali, A.H. Mirza, A. Monsur, S. Hussain, M. Nizamuddin, Polyhedron
20 (2001) 1045.
[35] R.C. Maurya, S. Rajput, J. Mol. Struct. 687 (2004) 35–44.
[36] H.M. Irving, H.S. Rossotti, J. Chem. Soc. (1954) 2904.
[37] A.Z. El-Sonbati, M.A. Diab, A.A. El-Asmy, Synth. React. Inorg. Met. Org.
Chem. 19 (1989) 731.
[38] H.M. Irving, R.J.P. Williams, J. Chem. Soc. 3192 (1954).
[6] F.M. Belicchi, F. Bisceglie, G. Pelosi, J. Inorg. Biochem. 83 (2001) 169.