Substituents effect on the spectral studies on rutheninum(III) complexes of 5(-4′-derivatives phenyldiazo)-3-phenyl-2-thioxo-4-thiazolidinone

Article abstract of DOI:10.1016/S1386-1425(01)00627-8

A novel series of Ru(III) complexes with 5(-4′-derivatives phenyldiazo)-3-phenyl-2-thioxo-4-thiazolidinone (HLn) have been prepared. The ligands and structural composition of complexes were confirmed and characterized by various physico-chemical techniques. The spectral data were utilized to compute the important ligand field parameters B, β and Dq. The effect of Hamett's constant on the ligand field parameters is also discussed. The spectral and magnetic results commensurate an octahedral environment around the Ru(III) ion. The B-values suggest a strong covalency in the metal-ligand σ-bond and the Dq-values indicate a medium-strong ligand-field. IR spectra show that the ligand is neutral bidentate forming thereby a six-membered chelating ring and concomitant formation of an intramolecular hydrogen bond. The ligands are present in associated form in solution via intermolecular hydrogen bond and act as neutral bidentate coordinated to ruthenium(III).

Full text of DOI:10.1016/S1386-1425(01)00627-8

Spectrochimica Acta Part A 58 (2002) 1623–1629
www.elsevier.com/locate/saa
Substituents effect on the spectral studies on
rutheninum(III) complexes of 5(-4%-derivatives
phenyldiazo)-3-phenyl-2-thioxo-4-thiazolidinone
A.Z. El-Sonbati a,*, A.A. El-Bindary a, A. El-Dissouky b, T.M. El-Gogary a,
A.S. Hilali a,1
a Chemistry Department, Faculty of Science, Mansoura Uni6ersity, Demiatta, Egypt
b Chemistry Department, Faculty of Science, Alexandria Uni6ersity, Egypt
Received 13 May 2001; accepted 6 September 2001
Abstract
A novel series of Ru(III) complexes with 5(-4%-derivatives phenyldiazo)-3-phenyl-2-thioxo-4-thiazolidinone (HLn)
have been prepared. The ligands and structural composition of complexes were confirmed and characterized by
various physico–chemical techniques. The spectral data were utilized to compute the important ligand field
parameters B, i and Dq. The effect of Hamett’s constant on the ligand field parameters is also discussed. The spectral
and magnetic results commensurate an octahedral environment around the Ru(III) ion. The B-values suggest a strong
covalency in the metal–ligand s-bond and the Dq-values indicate a medium–strong ligand-field. IR spectra show that
the ligand is neutral bidentate forming thereby a six-membered chelating ring and concomitant formation of an
intramolecular hydrogen bond. The ligands are present in associated form in solution via intermolecular hydrogen
bond and act as neutral bidentate coordinated to ruthenium(III). © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Rhodanine azodyes; Solid complexes; Effect Hamett’s constant on ligand field parameters
1. Introduction
plexes have been described. These ligands give
complexes which possess a unique stereochemical,
magnetic and spectral properties and can be used
as analytical reagents in trace element determina-
tion. Furthermore, some were found to possess
biological activity [11–13].
As part of our studies about simple inorganic
models of interest for the development of the
bioinorganic chemistry of ruthenium, we have
started investigations on Ru(III) complexes with
El-Dissouky, El-Sonbati and El-Bindary [1–10],
the preparation, characterization and spectro-
scopic properties of some heterocyclic nitrogen-
containing aldehydes and their Schiff bases and/or
azodyes as well as their transition element com-
* Corresponding author.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
1 Abstracted from her Ph.D. Thesis.
1386-1425/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1386-1425(01)00627-8

1624
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 58 (2002) 1623–1629
5(-4%-derivatives phenyldiazo)-3-phenyl-2-thioxo-
4-thiazolidinone (HLn) which appear to be suit-
able models due to the preference of
ruthenium(III) for oxygen and nitrogen donors in
biological systems.
Recently, our laboratories have initiated a se-
ries of studies of the effects of substituents at
p-position of the aromatic amine on the stereo-
chemistry of the complexes formed and deduced
the relation between Hamett’s constants and lig-
and field parameters.
purification. The experimental technique has been
described previously [1–10].
2.2. Preparation of 5(-4%-deri6ati6es
phenyldiazo)-3-phenyl-2-thioxo-4-thiazolidinone
(HLn)
In a typical preparation, 25 ml of distilled water
containing hydrochloric acid (12 M, 2.68 ml,
32.19 mmol) were added to aniline (0.979, 10.73
mmol) or a 4-alkyl-aniline. To the resulting mix-
ture stirred and cooled to 0 °C, a solution of
sodium nitrite (740 mg, 10.73 mmol, in 20 ml of
water) was added dropwise. The so formed diazo-
nium chloride was consecutively coupled with an
alkaline solution of 3-phenyl-2-thioxo-4-thiazo-
lidinone (31 mg, 10.73 mmol) in 10 ml of pyridine.
The orange precipitated, which formed immedi-
ately was filtered, washed several times with wa-
ter. The crude product was purified by
recrystallization from hot ethanol, yield 65%. The
analytical data confirmed the expected composi-
tions, Table 1. The ligands were also characterized
2. Experimental
2.1. Synthesis of the ligands
3-Phenyl-2-thioxo-4-thiazolidinone was pre-
pared according to the previously reported
method [6,10].
The standard chemical aniline and 4-alkyl-
anilines (alkyl:CH3, OCH3, Cl and NO2; Aldrich
Chemical Co.) were used without any further
1
by H-NMR and IR spectroscopy.
Table 1
Analytical data of the isolated complexes
Complex
Code
Experimental (calculated)%
Compositiona
C
H
N
Clb
Mc
HL1
HL2
HL3
HL4
HL5
1
2
3
4
5
65.0 (55.9)
32.7 (32.6)
3.7 (3.8)
2.6 (2.5)
12.5 (12.2)
7.2 (7.6)
–
–
[HL1RuCl3OH2]·H2O
[HL2RuCl3OH2]·H2O
[HL3RuCl3OH2]·H2O
[(HL4)2RuCl2]Cl
18.2 (18.5)
17.2 (17.5)
58.7 (58.6)
33.7 (33.6)
3.9 (4.0)
2.6 (2.6)
13.0 (12.8)
7.4 (7.6)
–
–
18.7 (18.5)
17.7 (17.5)
57.5 (57.5)
32.3 (32.3)
3.5 (3.5)
2.3 (2.2)
13.6 (13.4)
7.6 (8.0)
–
–
19.1 (19.4)
18.2 (18.0)
52.0 (51.8)
39.9 (40.0)
3.0 (2.9)
2.2 (2.2)
12.4 (12.1)
9.3 (9.7)
–
–
7.9 (8.2)
11.2 (11.0)
50.1 (50.2)
39.0 (39.0)
2.7 (2.6)
2.3 (2.2)
15.6 (15.7)
12.1 (12.4)
–
–
[(HL5)2RuCl2]Cl
7.7 (8.0)
11.0 (11.3)
0)\11.0 (11.3)\
The stoichiometry of the complexes obtained after drying at 100 °C shows the presence of water molecules present. On heating
complexes (1–3), the mass loss corresponding to the loss of water molecules present. The presence of coordinated water was
confirmed by TGA data, where the loss in weight corresponds to one water molecules for compounds (1–3). No coordinated water
molecules were found in the other complexes.
a HL1ꢀHL5 are the ligand as given in Scheme 1, air stable, non-hygroscopic, high melting points, colored, insoluble in water.
b Estimated gravimetrically.
c Estimated on an atomic absorption spectrophotometer.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 58 (2002) 1623–1629
1625
Scheme 1. General formula and proton numbering of the 5(-4%-derivatives phenyldiazo)-3-phenyl-2-thioxo-4-thiazolidinone.
washed with ethanol followed by Et2O and finally
2.3. Synthesis of the complexes
dried in vacuo over P2O5.
A stoichiometric amount of RuCl3·3H2O (0.01
mol) in ethanol was added to a hot solution of the
ligand (0.01 mol in HL1ꢀHL3) or (0.01 mol; 0.02
mol in HL4 or HL5) in absolute ethanol and the
reaction mixture was boiled under reflux for 1–2
h on cooling at room temperature. The deeply
colored precipitates were separated by filtration,
2.4. Elemental analyses
C, H and N were estimated at the Microan-
alysis Unit at Mansoura and Cairo Universities.
The data are given in Table 1.

1626
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 58 (2002) 1623–1629
2.5. Results and discussion
[Ru(HLn)Cl3·OH2]·H2O
(n=1–3)
and
[Ru(HLn)2Cl2]Cl (n=4 or 5). The proposed for-
mulation is supported by IR spectra.
Theoretical approaches made by Liang and
Lipscomb [14] indicate that the nitrogen atom is
more negatively charged than the oxygen atom in
the isolated metal ion and consequently, it may
account for the coordination of the nitrogen atom
rather than the oxygen atom, to the metal ion.
Moreover, these authors have found that in the
presence of the metal, the bidentate binding con-
formation with both N and O atoms coordinated
to the metal ions is favored.
The ligand HLn were obtained in excellent
yields, ca. 85%. While the ligands are soluble in
coordinating solvent but partially soluble in etha-
nol. Furthermore, the ligands solution were used
as suspension during complexation. As the reac-
tion proceeded, the ligands dissolved completely,
as shown by the colour change of the reaction
mixture. After ca. :2 h the desired product
precipitated as a powder.
Most complexes of the HLn (n=3–5) were
obtained in low yield, possibly due to the low
solubility of the ligands. In general, reactions with
HLn (n=1 or 2) were faster and gave better
yields than reactions with HLn (n=3–5). Molar
conductance data showed that the metal com-
plexes are non-electrolytes in DMSO [15].
Our earlier studies on coordination behavior
of rhodanine derivatives have shown that this
5(-4%-derivatives phenyldiazo)-3-phenyl-2-thioxo-
4-thiazolidinone presents a variety of chelating
coordination behavior, depending on the nature
of the metal ion and the deprotonation of the
ligand.
Microanalytical data as well as sulfur, metal
and chloride estimations are in good agreement
with stoichiometry proposed for complexes (Table
1). All complexes were found to be non-
conducting.
2.6. Mode of bonding
The infrared spectra of ligands exhibit strong to
medium broad bands in the frequency range
3240–2900 cm−1. These bands can be attributed
to intramolecular hydrogen bonded-OH group [7].
Elemental analysis indicate that the stoichiome-
try for all these complexes having general formula
Table 2
Electronic absorption spectra and ligand field parameters (cm−1) of Ru(III)-azodyes complexes
Complexa
4
Observed bands
Assigments
w2/w1
Dq
B
i
Zb
C
F2
F4
15280
18680
22250
2T2g“2A2g (w1) 1.22
2T2g“2T1g (w2)
2028
398
0.64
0.68
1592
625.4
45.5
2T2g“2Eg (w3)
1
3
2
5
16667
18867
23255
Do
Do
Do
Do
1.13
1.08
1.21
1.23
2167
2126
2139
2038
425
417
419
400
0.68
0.66
0.67
0.64
0.80
0.76
0.77
0.69
1700
1668
1676
1600
667.9
655.3
658.4
628.6
48.6
47.7
47.9
45.7
16270
17540
20399
16390
19800
23810
15380
18867
23245
a 24400–27700 ligand and C.T.
b 33333–35000 aromatic transition p“p*.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 58 (2002) 1623–1629
1627
Furthermore, all ligands exhibit a strong band at
1735–1720 cm−1. This is due to wCꢁO [8]. The
discussed infrared features beside the band ap-
peared at 1610–1595 cm−1 can guide to assume
the presence of CꢁN structure through resonating
phenomena [8]. Such class of compounds is with
different types of hydrogen bonding [16,7–9]:
1. H-bonding of the type OꢀH···N between the
ꢀOH group and ꢀNꢁNꢀ group (1C).
2. H-bonding of the type NꢀH···O between the
ꢀNH group and CꢁO group (1D).
3. Intermolecular hydrogen bonding of the
OꢀH···N (E) or NꢀH···O (F) type of one
molecule to another one. The (2) case is
more favored than (1). This is due to the
presence of a broad band located at 870–
970 cm−1 which could be taken as a good
evidence for the intermolecular hydrogen
bonding. This is illustrated in Scheme 1.
The following features for some of the prepared
complexes are observed:
1. The infrared spectra of the free ligands show
no characteristic absorption assignable to NH2
function. This confirms the formation of the
azo compounds.
2. The strong band observed at 1135–1140 cm−1
may be assigned to w(NꢀN) vibration modes
[16] is affected on complexation. It is blue
shifted and appeared as a weak band.
3. In all complexes 3490–3150 cm−1 is observed.
Such region is attributed to different probabil-
ities: (a) it is due to either free OH or NH; (b)
bondedꢀOH group or ꢀNH group; or (c) due
to the presence of coordinated water
molecules.
4. The spectra of ligands do not show absorption
characteristic of the NꢁN function owing to
the formation of the hydrazone. The sharp,
medium intensity band of CꢁN (hydrazone)
appears at 1610–1595 cm−1 for ligands.
5. The spectra exhibits a very strong band at
1720 cm−1. This is a powerfull indicative to
wCꢁO. However, the broad band located at
3420 cm−1 leads to characterize the wNH
rather than hydrogen bondedꢀOH with NꢁN.
This is rather confirmed from the observation
of Karabatoser [17] where the hydrazone form
is more than the azo structure for similar
compounds.
Fig. 1. The variation of p-substituted Hamett’s constants with:
(a) Dq; (b) B; (c) i; and (d) Z*.

1628
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 58 (2002) 1623–1629
This is also proved by the appearance of NꢁN
magnetic moments of the ruthenium(III) complexes
(1)–(3) (Table 1) lie in the 1.86–2.1 B.M. and are
markedly higher than the spin-only value of one
unpaired electron for low spin t52g ruthenium(III) in
an octahedral environment. This positive deviation
due to incomplete quenching of the orbital contri-
bution to the magnetic moment [19].
in splitted strong spectral bands at 1440 and 1530
cm−1 combined with the tracing of a strong bands
at 1225 cm−1 characteristic to NH stretching
vibration. All these data with lack of the wCꢀO of
enol in the IR spectrum leads us to assume the
structure (1D) for this compounds.
6. Introduction of a hydrazo group instead of
NꢁN leads to: (i) a change in the coordination
mode of the azo group from the azo-nitrogen
to the amine nitrogen (NH); (ii) stabilization
of the chelate ring by intermolecular hydrogen
bonding between hydrogen of water of this
chelate ring and the basic oxygen of the six-
membered chelate ring and the basic oxygen of
the six-membered chelate ring of an carbonyl
group (Scheme 1).
This hydrogen bonding interaction will prevent
the hydrazone group from rearranging to the
energetically more favorable N-coordination
mode. This behavior has been observed with other
metal azo compounds that contained the sub-
stituent CꢁNꢀNH instead of CꢁO in the vicinity
of the azo group.
2.8. Spectra and geometry of the complexes
The electronic absorption spectra of Ru(III)–
azodye complexes under study Table 2, show three
groups of bands. The bands with frequencies above
35 000 cm−1 (p–p*) transitions of the aromatic
system. The bands within the 20 000–35 000 cm−1
region represent various types of change transfer
interactions either intraligand or due to L“
Ru(III) or Ru(III)“L charge transfer interactions.
The third group of bands lying below 20 000
cm−1 usually exhibits three distinct peaks. These
three peaks can be attributed to three spin forbid-
den d–d transtions corresponding to low spin d5
complexes of Ru(III) in octahedral environment
2
(t52g) is T25g, then the separation between the two
low energy spin-forbidden transitions w1 and w2
corresponds to 8B [20]. The magnitude of this
separation is useful in evaluating the electronic
repulsion parameter B. The values of 10 Dq have
been calculated from the relation:
7. The broad, medium intensity band at ꢀ2900
cm−1 in the free ligand is shifted to ꢀ2400
cm−1 on complex formation, a behavior at-
tributed to the OH of the hydrogen bond
(OꢀH···O) [18].
2T2g“2A2g=10 Dq−3F2−20F4 [21]
The bands characteristic of coordinated water
molecules are observed at ca. 880 cm−1, including
the rocking, wagging and the metal–oxygen
The B-values are less than that of the free ion
indicating considerable orbital overlap with
strongly covalent metal–ligand bond. The nephe-
lauxetic parameter, i, is in the 0.64–0.68 range
indicating that HLn is in the middle nitrogen and
oxygen donor series. It is apparent that the
parameter, i, depends greatly upon the elec-
tronegativity of the donor atoms and the ligand
structure. According to Jørgensan [22], decrease
B-values are associated with a reduction in the
nuclear charge on the cation and an increased
tendency to be reduced. For 4d metal, the varia-
tion of the Racah interelectronic repulsion
parameter with the ionic charge, Z*, and the
number of the electrons in the partly fielled d-
state (q) is given by the equation: B=742+
28q+50(Z*+1)−500/(Z*+1). The Z*-values
of the ruthenium(III) in the complexes are listed
stretching vibrations at 900, 760 and 670 cm−1
,
respectively. Coordination of the carbonyl oxygen
and the amine nitrogen in the chelate ring is
suported by the appearance of new bands at
640–690 and 570–590 cm−1, which are assigned to
RuꢀN and RuꢀO, respectively. The coordinated
halogen in the complexes exhibits a far IR ab-
sorbance.
2.7. Magnetic studies
The experimental values of magnetic moment at
room temperature from Ru(III) complexes (4) and
(5) (1.56 and 1.37 B.M.), respectively correspond to
one unpaired electron indicating inner orbital octa-
hedral geometry around the metal ion. While the

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 58 (2002) 1623–1629
1629
[3] A. El-Dissouky, A.Z. El-Sonbati, Transition Met. Chem.
12 (1987) 14.
[4] A.Z. El-Sonbati, Spectrosc. Lett. 30 (1997) 459.
[5] A.A. El-Bindary, Spectrochim. Acta A 57 (2001) 49.
[6] A.A. El-Bindary, A.Z. El-Sonbati, Polish J. Chem. 74
(2000) 615.
in Table 2, and lie in the 0.68–0.80 range which is
considerably below the formal value of +3.
As can be seen from Table 2, the Racah
parameters (Dq, B, i%) and Z* values increased
from compound 5, 4, 3, 2 to 1. This can be at-
tributed to the fact that the effective charge expe-
rienced by the d-electrons decreased due to the
electron withdrawing p-substituent (HL4 and
HL5) while it increased by the electrons donating
character of HL1 and HL2. This is in accordance
with that expected from Hamett’s constant (|R)
(Fig. 1a–d) correlate the Racah parameter with
|R, it is clear that all these parameters decrease
with increasing |R.
The above results show clearly the effect of
substitution in the para position of the benzene
ring on the stereochemistry of both Ru(III) com-
plexes. It is important to note that the existence of
a methyl and/or methoxy group enhances the
electron density on the coordination sites and
simultaneously increases the values of Racah
parameters (Table 2).
[7] A.A. El-Bindary, A.Z. El-Sonbati, Polish J. Chem. 74
(2000) 621.
[8] A.F. Shoair, A.A. El-Bindary, A.Z. El-Sonbati, R.M.
Younes, Spectrochim. Acta A, 57 (2001) 1683.
[9] A.Z. El-Sonbati, A.Z. El-Bindary, E.M. Mabrouk, R.M.
Ahmed, Spectrochim. Acta, Part A, 57 (2001) 1751.
[10] A. El-Dissouky, A.A., El-Bindary, A.Z., El-Sonbati, A.S.
Hilali, Spectrochim. Acta, Part A, 57 (2001) 1163.
[11] C. Allan, J. Gibson, A. Neville, Anal. Chim. Acta 51
(1970) 249.
[12] Beliniski, Stamslow, U, Tadewz, Acta Pol. Pharm., 32
(1975) 159.
[13] J.C. Thomas, E.C. Berkoff, B.W. Flog, C. Pellerano, J.
Med. Chem. 18 (1975) 245.
[14] J. Liang, W. Lipscomb, Biochemistry 28 (1989) 9724.
[15] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[16] M. Mohan, P. Sharma, N.K. Jho, Inorg. Chim. Acta 106
(1985) 117.
[17] G.J. Karabatoses, B.L. Shapiro, E.M. Vane, J.S. Fleining,
J. Ratka, J. Am. Chem. Soc. 85 (1963) 2784.
[18] K. Dey, K. Mandel, M. Bandyopadlyay, Indian J. Chem.
31A (1992) 937.
[19] M.C. Day, J. Selbin, Theoretical Inorganic Chemistry,
2nd ed., Van Nostrand Reinhold, New York, 1969.
[20] M.C. Main, P.C. Jain, J. Inorg. Nucl. Chem. 39 (1977)
2183.
[21] S.E. Living, J.H. Maryfield, D.S. Moore, Aust. J. Chem.
28 (1975) 2531.
References
[1] A. El-Dissouky, A. Kasem, A.Z. El-Sonbati, Transition
Met. Chem. 11 (1986) 449.
[2] A. El-Dissouky, A.Z. El-Sonbati, Polyhedron 9 (1990)
2443.
[22] C.K. Jørgensen, Acta Chim. Scand. 10 (1956) 500.