Polymer complexes. LVIII. Structures of supramolecular assemblies of vanadium with chelating groups

Article abstract of DOI:10.1016/j.saa.2010.12.063

Oxovanadium(IV) polymer complexes of formulation {[(VO)L]₂} _n (1) and [(VO)LB]_n (2-4), where H₂L is tridentate and dianionic ligand (allylazorhodanine) and B is planar heterocyclic and aliphatic base have been p

Full text of DOI:10.1016/j.saa.2010.12.063

Spectrochimica Acta Part A 78 (2011) 1119–1125
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Polymer complexes. LVIII. Structures of supramolecular assemblies of vanadium
with chelating groups
A.Z. El-Sonbatia,∗, A.A.M. Belalb, M.A. Diaba, M.Z. Balboulaa
a Chemistry Department, Faculty of Science, (Demiatta), Mansoura University, Egypt
b Chemistry Department, Faculty of Science, Port Said University, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 October 2010
Received in revised form 6 December 2010
Accepted 14 December 2010
Oxovanadium(IV) polymer complexes of formulation {[(VO)L]2}n (1) and [(VO)LB]n (2–4), where H2L is
tridentate and dianionic ligand (allylazorhodanine) and B is planar heterocyclic and aliphatic base have
been prepared and characterized by elemental analyses, IR, 1H NMR, electronic spin resonance spectra,
magnetic susceptibility measurements, molar conductance and thermal studies. The molecular structure
shows the presence of a vanadyl group in six-coordinate VNO3/VN3O3 coordination geometry. The N,N-
donor heterocyclic and aliphatic bas displays a chelating mode of binding with an N-donor site trans
to the vanadyl oxo-group. In all polymeric complexes (1–4) the ligand coordinates through oxygen of
phenolic/enolic and azodye nitrogen. The molar conductivity data show them to be non-electrolytes.
All the polymer complexes are ESR active due to the presence of an unpaired electron. The calculated
bonding parameters indicate that in-plane ␴ bonding is more covalent than in-plane ␲ bonding. From
the electronic, magnetic and ESR spectral data suggest that all the oxovanadium(IV) polymer complexes
have distorted octahedral geometry. The thermal decomposition process of the polymeric complexes
involves three decomposition steps.
Keywords:
Oxovanadium(IV) polymer complexes
ESR spectrometry
Thermal studies
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
also act as inhibitors of enzymes [8] and antifungal/antibacterial
agents [9].
Interest in coordination chemistry is increasing continuously
with the preparation of organic ligands containing a variety of
donor groups and it is multiplied manifold when the ligands have
biological importance [1]. The number and diversity of nitrogen,
oxygen and sulfur chelating agents used to prepare new coordina-
tion and organometallic compounds has increased rapidly during
the past few years [2–4].
The coordination chemistry and biochemistry of allyl hetero-
cyclic have attracted increased interest due to their chelating ability
and their pharmacological application [1]. The pharmacological
activity is found to be more in the case of metal polymer com-
plexes when compared to the free ligand, and some side effects
may decrease upon complexation [5].
The potential catalytic abilities of vanadium compounds have
lead to an increasing interest in vanadium coordination chemistry
in recent years [10]. Coordination polymers i.e. polymeric metal
complexes derived from simple or polymeric coordination ligands
are generally insoluble in common solvents and added advantage,
over monomer analogues, of easy separation from the catalytic
reaction mixture leading to operational flexibility and recyclabil-
ity [11,12]. Synthesis and structural studies of a interesting series of
heterocyclic adducts of oxovanadium(IV) complexes of some aroyl-
hydrazones have been reported [13]. Vanadium(IV) complexes
containing SNO donor sets have also been reported [14]. In the case
of oxovanadium complexes, monomeric and five coordinated oxo-
vanadium(IV) complexes are formed with several bidentate Schiff
bases, but dimeric and five or six coordinated are formed with
tridentate Schiff bases [15]. Recently reported oxovanadium(IV)
based coordination polymers by Ando et al. [16] are insoluble in
common solvents and their catalytic oxidation reactions are het-
erogeneous in nature [16]. The objective of the present work is to
synthesis, spectral and ESR investigations of some polymeric oxo-
vanadium(IV) complexes with different ONO donor ligand derived
from allylazorhodanine. Heterocyclic and aliphatic bases viz. 2,2ꢀ-
bipyridine (bipy), pyridine (py) and ethylenediamine (en) were
used as auxiliary ligands for coordination. .
The chemistry of vanadium has received considerable attention
due to the discovery that vanadium is an essential element in bio-
logical system. Schiff base and related vanadium complexes have
important application in biology and medicine [6] as well as in the
catalysis associated with chemical and petrochemical processes [7],
∗
Corresponding author. Tel.: +20 60081581; fax: +20 502254000.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.12.063

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A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 78 (2011) 1119–1125
OH
NaNO2 / HCl
+
-
NH2
R
N
N Cl
(1)
(2)
X
O
CH3COONa
N
CH3OH
(3)
S
S
N
X
X
N
O
N
O
N
H
N
OH
S
OH
S
N
S
S
X = CH2= CH
H2C−
Fig. 1. The structure of azodye (H2L).
2. Experimental
2.3. Preparation of poly
{3-allyl-2-thioxo-1,3-thiazolidine-4,5-dione-5-[(o.hydroxyl
All reagents used for the preparation of the ligand and polymer
complexes were of analytical grade.
phenyl)] (PH2L) homopolymer
PH2L homopolymer was prepared by free radical initiation of
H2L using 0.1% (w/v) AIBN as initiator and DMF as solvent for ∼7 h.
The polymer product was precipitated by pouring in distilled water
and dried in a vacuum oven for several days at 40 ◦C. The PH2L
homopolymer has been characterized by IR, 1H NMR. The inherent
viscosity (ꢀinh = lnr/c‘, C = 0.49 g/dl), measured in a Desreux–Bishoff
suspended level viscometer at 30 0.01 ◦C, using chloroform as
solvent is ꢀinh =1.24.
2.1. Reagents
2-Aminophenol and Allyl rhodanine (Aldrich Chemical Co. Inc.)
were used without further purification.
2,2ꢀ-Azobisisobutyronitrile (AIBN) (Aldrich Chemical Co. Inc.)
was purified by dissolving in hot ethanol and filtering [17]. The
solution was left to cool. The pure material then being collected by
filtration and dried.
2.4. Synthesis of the solid polymer complexes
2.2. Preparation of the
3-allyl-2-thioxo-1,3-thiazolidine-4,5-dione-5-[(o.hydroxyl
phenyl)] (H2L) monomer
Method A: TheVO(IV) chelates with H2L was prepared by reflux-
ing VOSO4·5H2O (0.001 mole) with the corresponding ligand (0.001
mole) in 20 ml DMF as a solvent, and 0.1% (w/v) AIBN as initiator
were used. The resulting mixture was heated at reflux for 4 h (Fig. 2).
The hot solution was precipitated by adding a large excesses of
distilled water, containing dilute hydrochloric acid, to remove the
metal salts that were incorporated into the polymer complexes.
The ligand H2L (Fig. 1) was prepared and purified according
to El-Sonbati School [18–22]. Monomer (H2L) was typically pre-
pared by adding a 25 mL of distilled water containing hydrochloric
acid (12 M, 2.68 mL, 32.19 mmol) to allyl rhodanine (10.73 mmol).
To the resulting mixture, stirred and cooled to 0 ◦C, a solution of
sodium nitrite (10.73 mmol, in 20 mL of water) was added drop
wise. The so-formed diazonium chloride was consecutively cou-
pled with an alkaline solution (2-aminophenol) (10.73 mmol) in
20 mL of ethanol containing 602 mg (10.73 mmol) of potassium
hydroxide. The red precipitate, which formed immediately was fil-
tered and washed several times with water. The crude product
obtained was purified by crystallization from hot ethanol (yield
∼ 65%). The analytical data confirmed by expected composition.
Found: C, 49.22; H, 3.88; N, 14.05; S, 21.55%; C12 H11N3O2S2, Cal.
C, 49.15; H, 3.75; N, 14.35; S, 21.84%. The ligand was also charac-
terized by 1H NMR and IR spectroscopy. The IR spectrum of the
monomer showed the presence of an N N (1485) and OH (3330)
cm−1. 1H NMR (300 MHz, DMSO-d6): ı (ppm) ∼12.8 (OH); 6.25, 5.12
(CH2 CH).
N
O
O
O
V
V
O
O
O
N
Fig. 2. Tentative structure of polymer complex {[VOL]2}n (1).

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 78 (2011) 1119–1125
1121
Table 1
Analytical data of the polymer complexes (for molecular structure see Figs. 1 and 4).
Complexa
No.
Method of
Experimental (Calcd.) %
Preparationb
C
H
N
Sc metal
Molar ratio
{[(VO)L]2}n
A
B
B
B
40.34
(40.23)
46.80
(46.69)
40.08
(40.20)
51.50
2.40
(2.51)
3.32
(3.21)
4.22
(4.07)
3.42
11.87
(11.73)
13.05
(12.82)
17.01
(16.75)
13.62
!8.12 14.51
(17.88) (14.23)
14.84 11.85
(14.65) (11.66)
15.05 12.37
(15.31) (12.19)
12.71 10.30
1:1
1
[(VO)L.Py]n
2
[(VO)L.en]n
3
1:1:1
1:1:1
1:1:1
[(VO)Lbipy]n
4
(51.37)
(3.31)
(13.80)
(12.45) (9.91)
a
H2L is the ligand as given in Fig. 1 and L is the anion; air-stable; no-hygroscopic.
See text.
Estimated gravimetrically.
b
c
The polymer complex (1) (see Table 1) was filtered, washed with
water, and dried in a vacuum oven at 40 ◦C for several days.
Method B: The polymer complexes (2–4) were prepared from
a general synthetic procedure in which the ligand (0.001 mole) in
DMF (15 ml) was reacted with VOSO4·5H2O (0.001 mole) in 10 ml
DMF. The resulting mixture was stirred 30 min to obtain a homo-
geneous and clear solution that was subsequently reacted with the
corresponding heterocyclic base (Py/en/bipy) (0.001 mol) taken in
10 ml DMF as a solvent, and 0.1% (w/v) AIBN as initiator were used.
The resulting mixture was heated at reflux for 4 h (Fig. 3). The hot
solution was precipitated by adding a large excesses of distilled
water, containing dilute hydrochloric acid, to remove the metal
salts that were incorporated into the polymer complexes. The poly-
mer complexes were filtered, washed with water, and dried in a
vacuum oven at 40 ◦C for several days.
3. Results and discussion
3.1. General
The azo group can act as a proton acceptor in hydrogen bonds
[18,19]. The role of hydrogen bonding in azo aggregation has been
accepted for some time. Intramolecular hydrogen bonds involving
o.OH or o.COOH groups with the –N N– group increased their sta-
bilities through chelate ring structure [18,24]. The strength of the
hydrogen bond of o.hydroxyazo compounds depends on the nature
of substituents present in the coupling component from the aryl
azo group. Chelating rings formed by NH. . .N bonds are less stable
than corresponding rings formed by OH. . .N bonds [25]. The U.V.
spectra of acetylaminoazobenzene showed that the chelate ring
is stable in dioxan and in methanol solvents, whereas the chelate
ring in 2-hydroxy-4-methylazobenzene is stable in dioxan and
hydroxylic solvents. Chelate rings involving NH. . .N N bonds in
azo compounds (e.g. 2-amino-4-dimethylaminoazobenzene) have
been treated theoretically and have been studied in the IR and
UV spectra where both five and six membered chelate rings with
NH. . .N bonds have been suggested [26]. The attachment of the
OH group to o- or p-position increase the acidity, for exam-
ple 1-phenylazo-2-naphthol, was found to be stronger than in
the 2-hydroxyazobenzene forming intramolecular hydrogen bond
leading to a larger resonance system [27].
2.5. Measurements
C, H, and N microanalyses were carried out at the Cairo Uni-
versity Analytical Center, Egypt. 1H NMR spectrum was obtained
with a Jeol FX90 Fourier transform spectrometer with DMSO-d6
as the solvent and TMS as an internal reference. Infrared spec-
tra were recorded using Perkin-Elmer 1340 spectrophotometer.
Ultraviolet-Visible (UV-Vis) spectra of the polymer were recorded
in nuzol solution using a Unicam SP 8800 spectrophotometer.
The magnetic moment of the prepared solid complexes was
determined at room temperature using the Gouy method. Mer-
cury(II) (tetrathiocyanato)cobalt(II), [Hg{Co(SCN)4}], was used for
the calibration of the Gouy tubes. Diamagnetic corrections were
calculated from the values given by Selwood [23] and Pascal’s
In general, most of the azo compounds give spectral
localized bands in the wavelength range 47,620–34,480 and
31,250–27,000 cm−1. The first region is due to the absorption of
the aromatic ring compared to 1Bb and 1Lb of mono substituted
benzene and the second region is due to the conjugation between
the azo group and the aromatic nuclei with intermolecular charge
transfer resulting from ␲-electron migration to the diazo group
from electron donating substituents.
constants. Magnetic moments were calculated using the equation,
coor.
(eff. = 2.84 [T(M
]
1/2. EPR measurements of powdered samples
were recorded at room temperature (Tanta University, Egypt) using
an X-band spectrometer utilizing a 100 kHz magnetic field modula-
tion with diphenylpicrylhydrazyle (DPPH) as a reference material.
TG measurements were made using a Du Pont 950 thermobal-
ance. Ten milligram samples were heated at a rate of 10 ◦C/min
in a dynamic nitrogen atmosphere (70 ml/min); the sample holder
was boat-shaped, 10 mm × 5 mm × 2.5 mm deep; the temperature
measuring thermocouple was placed within 1 mm of the holder.
3.2. Synthesis and general properties
Oxovanadium(IV) polymer complexes of formulation
{[(VO)L]2}n (1) and [(VO)L.B]n (2–4), where H2L is tridentate
and dianionic ligand (allylazorhodanine) and B is planar hetero-
cyclic and aliphatic base (bipy; py; en), are prepared in high yield
from a general synthetic procedure in which vanadyl sulphate
is reacted with the azodye and B in DMF. The results of elemen-
tal analysis of the mixed ligand and polymer complexes are in
good agreement with those required by the proposed formula
(Figs. 2 and 3). Selected physicochemical data are given in Table 1.
The non-electrolytic complexes are soluble in DMF and DMSO.
They show characteristic vanadyl (V O) and azonitrogen (–N N–)
infrared bands at 750 and 1485 cm−1, respectively. The polymer
O
N
O
V
N
N
O
complexes are one-electron paramagnetic giving
moment value of ∼1.60 B.M.
a magnetic
Fig. 3. Ternary structures of [VOLB]n (2–4) and the bases (B) used.

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Table 2
3.3. Elemental analyses of the polymer complexes
Electronic spectral assignments (cm−1) of oxovanadium(IV) Polymer complexes.
Speciesa
Intraligand transition
LMCT
d-d
Analytical data indicated that the diazo coupling reaction
between 2-aminophenol and allyl rhodanine occurred in 1:1 molar
ratio and the product formed well defined polymer complexes
with vanadium sulphate. The generalized equation for the reac-
tion leading to the formation of the polymeric complexes is shown
as follows:
H2L
1
2
3
4
26250, 30674, 33550, 39470
36355, 30300
34700, 31685
34010, 31750
34000, 31745
–
–
26173
25775
27115
27115
18378
18278
17540
18265
a
See Table 1.
VOSO4·5H2O + H2L → {[VOL]2}n + H2SO4
iv) The intramolecular hydrogen bonds in o.OH group with –N N–
group increased their stabilities through chelate ring structure
[24]. Thus, the (i) case is more favoured than (ii).
VOSO4·5H2O + H2L + B → [VOLB]n + H2SO4
Formation of the polymer complexes has been done on the
basis of their elemental analytical data, molar conductance val-
ues and magnetic susceptibility data. All the complexes show
1:1{[VOL]2}n/1:1:1[VOLB]n metal:ligand/metal:ligand:base stoi-
chiometry. They are non-hygroscopic, decompose and possess good
keeping qualities. All the polymer complexes are insoluble in
common organic solvents except DMF and DMSO. The molar con-
ductance values in DMSO reveal the non-electrolytic nature of the
metal complexes [28].
The following features for some of the prepared polymer com-
plexes are observed:
i) The infrared spectra of the free ligands show no characteristic
absorption assignable to NH2 function. This confirms the forma-
tion of the azo compounds.
ii) The ligand exhibit bands in ∼1728, 3185 and 3325 cm−1 due
to C O, N–H and O–H stretches, respectively. These bands
are absent in polymeric complexes, which suggests deprotona-
tion of the phenolic group indicating the coordination through
phenolic oxygen, and enolisation of the carbonyl group, fol-
lowed by deprotonation [31]. A new band appearing in the
∼1285 5 cm−1 in the polymer complexes was assigned to the
ꢁ(C–O) (enolate) mode [32].
3.4. 1H NMR spectrum
The 1H NMR spectrum of ligand show two singlets correspond-
ing to phenolic –OH and –NH. The singlet at ı = ∼12.8 ppm and
ı = ∼10.9 ppm represent –OH and –NH, respectively of the forma-
tion of intramolecular hydrogen bonding with azonitrogen. The
ligand do not show any peak attributed to enolic–OH proton indi-
cating that they exist in keto form. Upon addition of D2O the
intensities of both OH and NH protons significant decrease. Fur-
ther, the CH signal vanish and a new NH signal appear i.e., change
from azo to hydrazone form (Fig. 4). This supports the assign-
ment. The protons of the aromatic ring resonate downfield in the ı
7.3–8.4 ppm range.
The NMR spectrum of H2L monomer showed the expected peaks
and pattern of the vinyl group (CH2 CH), ı 6.25 ppm (dd, J = 17,
11 Hz) for the vinyl CH proton and proton ı 5.12 ppm (AM part of
AMX system dd, J = 17, 1 Hz) for the vinyl CH2 protons, respectively.
These peaks disappeared on polymerization while a triplet at ı 1.86
(t, J = 7 Hz) and a doublet at 1.80 ppm (d, J = 7 Hz) appeared, indicat-
ing that the polymerization of H2L monomer occurs on the vinyl
group [4,27]. It is worth noting that the rest of the proton spectrum
of the monomer and polymer remain almost without change.
iii) The disappearance of the phenolic–OH group is an evidence for
the ligand coordination around the metal ion in its deprotonated
form [32]. This causes ꢁ(C–O) to shift to lower frequencies and a
new band in the range ∼507 cm−1, assigned to ꢁ(V–O) is found
in polymer complexes which confirm the coordination of the
ligand via phenolic oxygen [31].
iv) The shifting of (–N N–) to lower wavenumbers in the metal
polymeric complexes by 25–35 cm−1 indicates the coordina-
tion of azo nitrogen to the metal. Furthermore, the bands in
the regions 550–565 and 420–430 cm−1 can be assigned to the
stretching modes of the metal to ligand bonds, ꢁ(V–O) and
ꢁ(V–N), respectively [33]. In addition, the compounds exhibit
a strong band in the 955–965 cm−1 range due to the terminal
V
O stretching [34], indicates hexa-coordinated environment
around the metal center (Fig. 3). Complex (1) has a band in
the region 830 cm−1 indicating V–O–V bridge vibration [35].
Tentative structure of complex (1) is shown in Fig. 2. The fre-
quency range observed in polymer complexes indicates that
3.5. Infrared spectra
V
O bond is weakened by strong ␴ and ␲ electron donation
by enolate and phenoxy groups to the antibonding orbital of the
O group [36]. The variation in frequency suggests that the d␲-
p␲ overlap between vanadium and oxygen atom is influenced
by substituents and coligands [32].
The structural elucidation of the polymer complexes is also
supports by IR spectra and comparison of IR spectrum of the lig-
and (H2L) with those of isolated metal complexes indicate the
mode of bonding. The infrared spectrum of ligand exhibit strong
to medium broad bands in the frequency ∼3325 cm−1. These
bands can be attributed to intramolecular hydrogen bonded –OH
group [18,29,30]. Furthermore, ligand exhibit a strong band due
to C O [18,29,30]. The discussed infrared features beside the band
V
v) In the spectra of mixed bipy-polymeric complexes the bands
of bipy-free ligand at 750 cm−1 are shifted to higher frequency
around 780 cm−1 in the polymeric complexes. The spectra of
mixed en-polymeric complexes show two characteristic band at
3235 and 3295 cm−1 assigned to ꢁsym and ꢁasym vibration of NH2
suggesting coordination through NH2 [36]. Also, in compound
(2) a new band appears in 1617 cm−1, attributable to coordi-
nated pyridine. Thus, the nitrogen of pyridine is coordinated to
metal ion.
appeared at ∼1615 cm−1 can guide to assume the presence of C
N
structure through resonating phenomena [24]. Such class of com-
pounds is with different types of hydrogen bonding [29,30].
i) H-bonding of the type O–H. . .N between the –OH group and
–N N– group (Fig. 4-C1 & 4-C2).
ii) H-bonding of the type N–H. . .O between the –NH group and
3.6. Electronic spectra
C
O group (Fig. 4-D).
iii) Intermolecular hydrogen bonding of the O–H. . .N (Fig. 4-E) or
N–H. . .O (Fig. 4-F) type of one molecule to another one.
Electronic spectral data of the ligand and polymer complexes
in DMF solution are summarized in Table 2. The ligand (H2L)

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 78 (2011) 1119–1125
1123
X
X
O
OH
N
C
N
C
H
N
OH
N
OH
S
N
S
S
S
N
(A)
(B)
X
O
X
O
H
N
N
H
N
C
OH
C
N
OH
S
S
N
S
S
N
(D)
(C1)
R1
X
S
O
X
S
N
O
O
H
N
C
N
HN
N
C
H
O
N
C
NH
X
S
S
N
S
S
N
R1
(C2)
(F)
R1
X
S
S
OH
N
N
S
N
C
N
C
N
N
S
HO
X
R1
(E)
X = CH2= CH
H2C−
R1 = o.OHC6H4
Fig. 4. General formula and proton numbering of 3-allyl-2-thioxo-1,3-thiazolidine-4,5-dione[(2-aminophenol)] azodaye (H2L).
∼
exhibits bands at 381 nm (CS) (n → ␲*), 326 nm (CO) (n → ␲*),
298 nm (H-bonding and association), 253 nm (phenyl) (ph–ph*,
␲–␲*) [18] and 340 nm transition of phenyl rings overlaped by
composite broad ␲–␲* of azo structure. In the VO(IV) complexes,
the (CS)(n–␲*) transition shifts slightly to lower energy and remain
tion moves to lower energy at ( 400 nm). Spectra of VO(IV) with
=
various ligand arising from the tetragonal compression caused
by V O bonds, which results in further splitting of d orbitals
and give rise to 2B2 → E (dxy → dxz,dyz), 2B2 → B1 (dxy → dx2-y2),
2
2
2
2B2 → A1(dxy → dz2) These values are consistent with distorted
almost constant. The (CO) (n → ␲*) transition disappears with
octahedral structure for oxovanadium(IV) [38].
∼
the simultaneous appearance of a new bands ( 339 nm), being
=
attributed to ␲ → ␲* (C C) as a sequences of enolization. An
intense band observed at ∼360–385 nm could be due to ligand-
to-metal charge-transfer (LMCT: PhO → V(d␲)] transition and the
remaining bands appearing in the UV-region are assignable to
the intraligand transitions [37]. The band due to ␲ → ␲* transi-
3.7. ESR spectra
All spectra of all the oxovanadium(IV) polymer complexes (1–4)
were recorded. In polycrystalline state at room temperature and
in DMF solution at 77 K, the compound (1) is axial with g = 1.982
ꢁ

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Table 3
complexes commensurate with absence of coordinations through
the sulphur atom of the CS group [24].
ESR and bonding parameters of the polymer complexes.a
Based on various studies like elemental analyses, conductance
measurements, magnetic susceptibilities, infrared, UV–vis and ESR
spectral studies a octahedral geometry as a shown in Figs. 2 and 3,
may be proposed for all the polymeric complexes.
{[(VO)L]2}n (1) and [(VO)L.B]n (2–4), L is the doubly deproto-
nated allylazorhodanine ligand and B is the bidentate heterocyclic
base viz., bipy, Py and aliphatic en as shown in Figs. 2 and 3.
We report here on some unknown chemistry of oxovana-
dium(IV) polymeric complexes showing ESR activity. Three ternary
oxovanadium(IV) complexes having ONO-donor ligand and bases
are synthesized and structurally characterized.
1
2
3
4
gll
1.952
1.985
1.955
1.984
1.950
1.985
1.951
1.980
g
⊥
All
159.60 × 10−4
51.66 × 10−4
0.916
141.51 × 10−4
50.86 × 10−4
0.818
159.67 × 10−4
51.32 × 10−4
0.712
162.68 × 10−4
52.41 × 10−4
0.938
A
˛
B2
⊥
2
0.938
0.870
0.937
0.962
a
See Table 1.
and g = 2.069 and the other compounds are isotropic with ∼1.985.
⊥
All the compounds in DMF solution (Table 3) show well-resolved
A high affinity of chelation of the ligand towards VO(IV) ions was
noticed according to the increasing charge density of the metal ion
towards the increasing of their coordination affinities.
axial anisotropy with g < g and A
Al relationship characteris-
tic of an axially compressed dxy configuration [39]. The absence
ꢁ
⊥
ꢁ
of any ligand hyperfine lines in the g features due to nitrogen
ꢁ
The results arising from the present investigations confirm
that the selected 3-allyl-2-thioxo-1,3-thiazolidine-4,5-dione-5-
[(o.hydroxyl phenyl)](H2L) ligands are suitable for building a
supramolecular structure. Moreover, since the azo polymer com-
pounds experience photochemical isomerization and are therefore
of interest for applicative purposes, polymer complexes contain-
ing the 3-allyl-2-thioxo-1,3-thiazolidine-4,5-dione-5-[(o.hydroxyl
phenyl)](H2L) moiety combine features which could be useful in
molecular materials.
indicates that the unpaired electron, for most of the times staying
in the b2g (dxy,
2B2 ground state) orbital localized on metal, thus
excluding the possibility of its direct interaction with the ligand
[40,41].
The ESR parameters g , g , A and A and energies of d-d tran-
||
⊥
||
⊥
sitions were used to evaluate the molecular orbital coefficients ˛2
and ˇ2 for the polymer complexes by using the following equations:
2
˛
= (2.00277 − g )Ed−d/8ꢂˇ2
||
ꢀꢁ
ꢂ
ꢁ
ꢂ
ꢁ
ꢁ
ꢂ
ꢂ
ꢁ
ꢂ
ꢃ
7
6
All
P
A
5
14
9
14
⊥
ˇ2
=
−
+
+
gll
−
g )
⊥
−
ge
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P
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