Bidentate coordinating behaviour of chalcone based ligands towards oxocations: VO(IV) and Mo(V)

Article abstract of DOI:10.1016/j.saa.2013.03.002

We synthesized and studied the coordinating behaviour of chalcone based ligands derived from DHA and n-alkoxy benzaldehyde and their complexes of VO(IV) and MoO(V). The chalcone ligands are characterized by elemental analyses, UV-visible, IR, 1H NMR, and

Full text of DOI:10.1016/j.saa.2013.03.002

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Bidentate coordinating behaviour of chalcone based ligands towards oxocations:
VO(IV) and Mo(V)
⇑
B.T. Thaker , R.S. Barvalia
Department of Chemistry, Veer Narmad South Gujarat University, Surat 395 007, India
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
ꢀ
ꢀ
Chalcon containg ligands are
associated with biological activities.
The VO(IV) and MoO(V) metal
containing compounds are highly
biological active materials.
ꢀ
ꢀ
Such compounds are also used as
catalyst.
The main aim to synthesize such
compounds as mesomesogens, due to
shorter length of the ligands it will
not exhibit mesomorphic property.
The main findings are
ꢀ
characterization of such compounds
by spectroscopic, thermal and
magnetic properties and determine
the geometry.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 August 2012
Received in revised form 26 December 2012
Accepted 3 March 2013
Available online 15 April 2013
We synthesized and studied the coordinating behaviour of chalcone based ligands derived from DHA and
n-alkoxy benzaldehyde and their complexes of VO(IV) and MoO(V). The chalcone ligands are character-
ized by elemental analyses, UV–visible, IR, 1H NMR, and mass spectra. The resulting oxocation complexes
are also characterized by elemental analyses, IR, 1H NMR, electronic, electron spin resonance spectra,
magnetic susceptibility measurement and molar conductance studies. The IR and 1H NMR spectral data
suggest that the chalcone ligands behave as a monobasic bidentate with O:O donor sequence towards
metal ion. The molar conductivity data show them to be non-electrolytes. From the electronic, magnetic
and ESR spectral data suggest that all the chalcone ligand complexes of VO(IV) and MoO(V) have distorted
octahedral geometry.
Keywords:
Oxovanadium(IV)
Oxomolybdenum(V)
Chalcone ligands
Dehydroacetic acid
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
research due to their importance in medical, agriculture, analytical,
biological and industrial fields. Chalcones are the condensation
Chalcones based ligands and their metal complexes play a
prominent role in modern coordination chemistry. These com-
pounds possessing novel structure features, interesting spectral
and magnetic properties, have been the subject of intensive
product of acetophenonne with aromatic aldehydes in the pres-
ence of strong base. In resent years a number of b-dicarbonyl com-
pounds in which the carbonyl function(s) bonded to olefinic
linkage(s) have gained considerable importance [1–3] mainly
because of the fact that such compounds are structurally related
to the active chemical constituents of several traditional medicinal
plants. Chalcone is an aromatic ketone that forms the central core
for a variety of important biological compounds, which are known
⇑
Corresponding author. Tel.: +91 261 2267957; fax: +91 261 2227312.
E-mail address: btthaker1@yahoo.co.in (B.T. Thaker).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.03.002

102
B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
collectively as chalcones. They show antibacterial, antifungal,
antitumor and anti-inflammatory properties. Some chalcones
demonstrated the ability to block voltage-dependent potassium
channels [4].
The antimalarial activity of chalcones was first noted when lic-
ochalcone-A, a natural product isolated from Chinese liquorice
roots, was reported to exhibit potent in vivo and in vitro antimalar-
ial activity [5]. Subsequently, a synthetic analogue, 2,4 dimethoxy-
4-butoxychalcone, was reported to have outstanding antimalarial
activity [6].
100 mg sample of VO(IV) complexes were placed in a silica cruci-
ble, decomposed by gentle heating and then treated with 2–3 ml
of nitric acid, 2–3 times and igniting at 600 °C. Orange colored res-
idues of V2O5 were obtained after decomposition and complete
drying and weighing [15]. Similarly, Molybdenum was estimated
gravimetrically as MoO3, yellowish white colored residues of
MoO3 were obtained after decomposition and complete drying
and weighing [16]. The conductance of oxo cation complexes were
carried out on the Equip-Tronics conductivity meter, model No.
EQ-664 with range 20 lO to 20 mO at 306 K temperature. IR spec-
The photo-alignment technique was introduced for the reduc-
tion of contamination that reduce the contrast ratio and the static
electricity buildup that cause cross-track shorts or failure of thin-
film transistors [7]. For the application of photo-alignment tech-
nique to VA-LCD, polyimide film was used as an alignment layer,
which is composed of DOCDA–DAP [5-(2,5-dioxotetrahydrofuryl)-
3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride1/1,4-diamin-
ophenol]. Generally, polyimides exhibit high anchoring energy and
good thermal stability. The chalcones derivatives were introduced
on the surface of the PI film through chemical modification. The
chalcone derivatives react fast with irradiation of UV light. The
anisotropy of the PI film was induced by irradiating LP–UV light
[8,9]. This study is designed for the elucidation of surface effects
on liquid crystal alignment mechanism.
Makita et al. synthesized poly(4-methacryloyloxy chalcone)
(PM4Ch) or poly(40-methacryloyloxy chalcone) (PMCh) and investi-
gated the photoreaction of their polymers. The authors also
reported that PM4Ch and PMCh would be employed as a photo-
alignment film. Hwang and Seo reported copolymers composed of
a cholesteryl monomer and a chalcone monomer [10]. However,
all the chalcone based polymers did not display mesomorphic prop-
erties. SLCPs with chalcone groups are little reported. Photosensi-
tive polymers possess, with a combination of properties such as
high photosensitivity, good solubility, good thermal stability, the
ability to form films, resistance towards solvents after cross linking,
as well as resistance towards plasmas and etching agents [11].
Yeap et al. [12] has been synthesized a series of new chalcone
trum of chalcone ligand and their complexes were recorded at
Centre of Excellence, Quality Testing Facility & R & D Centre, GIDC,
Vapi with a Perkin Elmer Spectrum-BX, IR spectrophotometer
(4000–450 cmꢂ1) using KBr pellets. The electronic spectrum of
complexes in the 200–800 nm were obtained in DMSO as a solvent
on a SHIMADZU UV 160 A using quartz cell of 1 cm3 optical path.
The magnetic measurement of metal complexes at room tempera-
ture was carried out on Gouy balance method [17] at M.S. Univer-
sity of Baroda, Vadodara. The mass spectrum were recorded by
Electro impact mass spectrometer (GC–MS) at SAIF, Punjab Univer-
sity, Chandigarh. ESR spectrum of all VO(IV) and MoO(V) com-
plexes were recorded by SAIF, IIT, Mumbai, at RT and LNT for
polycrystalline state. TGA and DTG were performed on an Al2O3
crucible and samples under investigation decomposed in the N2
atmosphere at a heating rate 10 °C/min at SAIF, Indian Institute
of Technology – Madras, Chennai.
Synthesis of chalcone ligands
Synthesis of [A] 4-hydrxy-3[3-(4-g-tetradecyloxyphenyl)aery-
loyl]6-methyl-2H-pyrane-2one.
[B]
4-hydrxy-3[3-(4-g-hexadecyloxyphenyl)aeryloyl]6-
methyl-2H-pyrane-2one.
Synthesis of 4–tetradecyloxy or 4-
4-hydroxy benzaldehyde (0.1 mol, 12.2 g), anhydrous K2CO3
(0.15 mol, 20.85 g) and corresponding -tetradecyl bromide
(0.12 mol, 33.24 g) or -hexadcaylbromide (0.12 mol, 35.4 g) were
g-hexadecyloxy – benzaldehyde
g
derivatives with
a
general formula of CH3CnH2nCOOC6H4-
g
CH:CHCOC6H4 where n = 10, 12, 14 and 16. All of the compounds
except undecylcarbonyloxy analogue exhibit Cr1–Cr2 transition
with smectic-like texture within the Cr2 phase. Thaker et al. [13]
have been synthesized and evaluation of thermal behaviour of
two novel series of chalcone-based liquid–crystalline compounds.
Rao et al. [14] synthesized the Co(II) complexes from chalcones
i.e., 3-(2-pyridyl)-1-(2-hydroxy-phenyl)-2-propen-1-one (PHPO),
added to dry acetone (60.00 mL) in a round-bottom flask fitted
with a reflux condenser. The reaction mixture was heated on water
bath for 12–14 h. The whole mass was then added to cold water
and the aldehyde thus separated in the form of oily layer. It was
extracted twice with ether. Ether extract was washed with dilute
NaOH solution to remove unreacted 4-hydroxy benzaldehyde,
followed by water and then dried. Ether was evaporated and the
3-(1-naphthyl)-1-(2-hydroxy-phenyl)-2-propen-1-one
(NHPO),
4-g-alkoxy benzaldehyde thus obtained were purified by distilla-
3-(3,4-dimethoxy-phenyl)-1-(2-hydroxy-phenyl)-2-propen-1-one
(DMPHPO).
tion under reduce pressure. Boiling points almost agreed with
those reported in literature [18–21].
Synthesis of compounds [A] and [B]
Experimental
Dehydroaceticacid (0.01 mol, 1.68 g) and 4-
-hexadecyloxy – benzaldehyde (0.02 mol, 6.36 g or 7.92 g) were
dissolved in the ethanol (80 mL). The ethanolic solution of dehydro-
acetic acid was added into the ethanolic solution of 4- -alkoxy
g-tetradecyloxy Or
4-g
Materials
g
For the synthesis of chalcone ligands and their metal com-
plexes, solvents like acetone, methanol, petroleum ether, (AR
grade), dehydroacetic acid (DHA) (Merk), 4-hydroxy benzaldehyde,
alkyl bromides (Lancaster, England) were used. HCl, K2CO3 and
KOH were made of Polypharm, Mumbai. The metal salts like
VOSO4ꢁ5H2O (National chemicals) and MoCl5 (Aldrich, USA) were
used as received.
benzaldehyde. The reaction mixture made alkaline by adding
chilled KOH solution to raise the PH up to 12. The reaction mixture
was heated at 80 °C for 6–7 h. After refluxing, the resulting solution
poured into the 50% HCl in cooled ice water and stirred. The result-
ing mixture was allowed to stand overnight; the precipitate was col-
lected by filtration. Crystallization was done with ethanol. The
synthetic route is given in scheme 1 (Fig. 1).
Instruments
Synthesis of binary metal complexes of VO(IV)
Elemental analyses (C,H,N) were performed at RSIC, Lucknow.
The vanadium metal was estimated gravimetrically as V2O5. A
The metal salt VOSO4ꢁ5H2O (0.001 mol, 0.253 g) was dissolved in
water (15 mL). The warmed methanolic solution (ꢃ65 °C) of the

B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
103
(0.002 mol, 0.992 g) added into the (40 mL) methanolic solution
(0.001 mol, 0.274 g) of MoCl5. The pH of the reaction mixture
was raised with NaOAcꢂ buffer up to six and stirred. The reaction
mixture was refluxed for 3–3.5 h. During the refluxing the color
of the reaction mixture was changed, the reaction mixture was
concentrated up to half of its volume. It was cooled and kept for
overnight. The resulting precipitates were filtered, washed with
petroleum ether and dried. The purity of the compounds was
checked by TLC. TLC shows only one spot indicating compounds
are single and pure.
Scheme 1.
Result and discussion
Physical data and elemental analysis of chalcone ligands [A] and
[B] and their metal complexes are shown in Table 1. The present
VO(II) and MoO(V) are stable in air at room temperature for longer
time. The elemental analyses are good agreement with expected
stochiometry of complexes which indicate that the metal to ligand
ratio in all VO(II) and MoO(V) complexes is 1:2.
Molar conductance measurements
The molar conductance of the oxovanadium(II) and oxomolyb-
denum(V) complexes in 10ꢂ3 M in DMSO as solvent obtained in
the range 0.67–7.32 ohmꢂ1 cm2 molꢂ1. The molar conductance of
VO(II) and MoO(V) complexes are shown in Table 1. The low con-
ductivity values in DMSO reveal that all complexes are non-elec-
trolytic in nature and there is no counter ion present outside the
coordination sphere of oxocations complexes [15,22,23].
FT-IR spectra of chalcone ligand and their oxocation complexes
Where, R = CnH2n+1, n = 14 and 16, n =14; A, n =16; B
In the IR spectral studies of ligands only few important absorp-
tion frequencies related to groups involved in the complex forma-
tion like enolic OAH, aromatic C@C, olefinic C@C, lactone C@O and
acetyl C@O in ligands are discussed. The OAH stretching frequency
is not observed as broad band and sharp band in the 3600–
3200 cmꢂ1 region. This result indicates that chalcone ligand in
the solid state remain in keto form (Fig. 1). The lactone carbonyl
band observed in the ligand at 1716 cmꢂ1 and 1720 cmꢂ1 in the
ligand [A] and [B], respectively. These bands remain unchanged
in complex formation, indicating non participation of this group
during the complex formation. In the present investigation, in li-
gands, the bands observed at 1638 cmꢂ1 are assigned to C@O
stretching vibration of acetyl carbonyl group [24,25]. A prominent
band at 985 cmꢂ1 and 995 cmꢂ1 typical of trans ACH@CHA
absorption [26].
[A] 4-hydrxy-3[3-(4-η-tetradecyloxyphenyl)aeryloyl]6-methyl-2H-pyrane-2one
[B] 4-hydrxy-3[3-(4-η-hexadecyloxyphenyl)aeryloyl]6-methyl-2H-pyrane-2one
Fig. 1. Synthetic pathway of chalcone ligands: A and B.
corresponding chalcone ligand [A] (0.002 mol, 0.936 g) or ligand [B]
(0.002 mol, 0.992 g) added into the metal solution. After addition
was over, 2 g of sodium perchlorate was added to the reaction
mixture for raising the PH up to 5–6. It was refluxed for 3–4 h and
then concentrated to half of its volume. It was cooled and kept for
overnight. The resulting precipitates were filtered, washed with
petroleum ether and dried. The purity of the compounds was
checked by TLC. TLC shows only one spot indicating compounds
are single and pure.
The IR spectrum of the metal complexes, the broad band ob-
served at 3420 cmꢂ1 [VO(A)2 (H2O)] and 3423 cmꢂ1 [VO(B)2
(H2O)] due to the coordinated water [27]. The sharp band observed
Synthesis of binary metal complexes of MoO(V)
at 1659–1653 cmꢂ1 due to
t(C@O) of acetyl group of DHA moiety.
The warmed (50 mL) methanolic solution (ꢃ65 °C) of the corre-
A band ꢃ40 cmꢂ1 down field of the acetyl group
t(C@O) has been
observed in the complexes as coordinated to ligands, suggesting
sponding chalcone ligand [A] (0.002 mol, 0.936 g) or ligand [B]
Table 1
Elemental analysis and some physical data of chalcone ligand and their oxocation complexes.
Elemental analysis found % (calculated %)
Compounds
Color
Yield (%)
Melting point (°C)
C
H
M
Molar conductivity (ohmꢂ1 cm2 molꢂ1
)
ueff (BM)
Ligand-A
Ligand-B
[VO(A)2 (H2O)]
[VO(B)2 (H2O)]
[MoO(A)2Cl]
[MoO(B)2Cl]
Bright yellow
Bright yellow
Green
Green
Brown
65
67
72
71
67
60
66
50
>250
>250
>250
>250
74.48(74.17)
8.46(8.37)
–
–
–
–
0.67
2.24
7.34
7.02
–
–
1.77
1.78
1.75
1.74
75.59(75.27)
68.53(68.32)
69.42(69.23)
64.56(64.35)
65.74(65.53)
8.63(8.55)
8.01(7.90)
8.45(8.24)
7.48(7.26)
7.83(7.61)
4.95(4.90)
4.92(4.73)
8.97(8.86)
8.63(8.42)
Brown

104
B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
Table 2
FT-IR spectral data of chalcone ligand and their oxocation complexes.
Functional group and IR frequencies (cmꢂ1
)
Compounds
t
(OH) coord.
t(C@O) lactone
t(C@O) acetyl carbonyl
t(C@O) coord.
ACH@CHA Trans
t
(M@O)
t
(MAO) stra.
t(MAN) stra.
Ligand-A
Ligand-B
[VO(A)2 (H2O)]
[VO(B)2 (H2O)]
[MoO(A)2Cl]
[MoO(B)2Cl]
–
–
1716
1720
1719
1722
1719
1717
1638
1638
1659
1654
1656
1653
–
–
985
995
1008
1006
1001
1009
–
–
975
974
958
955
–
–
553
551
509
504
–
–
471
469
485
483
3420
3423
–
1281
1279
1280
1278
Table 3
1H NMR spectral data of chalcone ligand and their oxocation complexes.
Functional group and chemical shifts d in ppm
a
b
c
d
e
f
g
h
Compounds
ACH3 alkoxy
chain
ACH2 alkoxy
chain
ACH3
DHA
AOACH2
H
proton
Phenyl proton
multiplets
Hb proton
aldehydic
(AOHꢁ ꢁ ꢁOA)
a
chalcone
enolic
Ligand-A
Ligand-B
[VO(A)2
0.84–0.88
0.86–0.89
0.85–0.87
1.27–1.89
1.25–1.88
1.23–1.89
2.27
2.27
2.27
2.68
2.66
2.46
5.92
5.93
5.92
6.97–8.0
6.82–8.01
6.88–7.84
9.88
9.87
9.87
16.70
16.69
–
(H2O)]
[VO(B)2
0.85–0.89
1.25–1.90
2.29
2.47
5.95
6.91–7.94
9.86
–
(H2O)]
[MoO(A)2Cl]
[MoO(B)2Cl]
0.85–0.87
0.88–0.90
1.25–1.98
1.26–2.0
2.16
2.17
2.58
2.57
5.92
5.96
6.65–7.71
6.67–7.80
9.78
9.81
–
–
Fig. 2. Mass spectra of chalcone ligand B.

B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
105
Table 4
Electronic spectral data of chalcone ligand and their oxocation complexes.
Complexes
d–d transition (cmꢂ1)/(m)
Charge transfer band (cmꢂ1)/(nm)
d–d transition (cmꢂ1)/(nm)
d
xy ? dxy,dyz, (m1
)
2B2
?
2E
2B2
?
2B1
2B2
?
2A1
dxy ! dx2 ; ðm2
Þ
dxy ! dz2 ðm3Þ
ꢂy2
O(
p) ? d(Mo)
[VO(A)2 (H2O)]
[VO(B)2 (H2O)]
[MoO(A)2Cl]
12,787(782)
13,793(725)
–
–
17,985(556)
16,722(598)
–
–
20,080(498)
19,880(500)
–
–
23,360(428)
32,809(305)
28,409(352)
27,624(362)
32,786(305)
32,776(305)
28,735(348)
28,985(345)
37,740(262)
39,215(255)
32,680(306)
32,470(308)
–
–
–
–
–
–
14,388(695)
13,888(720)
18,867(530)
18,518(540)
23,255(430)
22,883(437)
[MoO(B)2Cl]
Fig. 3. The power ESR spectra of [VO(A)2 (H2O)] complex at (a) RT and (b) LNT.
Fig. 4. The power ESR spectra of [MoO(A)2Cl]complex at (a) RT and (b) LNT.
the participation of acetyl C@O in complex formation. The shift is
mainly due to weakening of double bond between carbon and oxy-
gen and also, the pair of electrons from oxygen is involved in the
formation of coordinate bond with metal ion [28,29]. The medium
but sharp band appeared at 1281–1279 cmꢂ1 in complexes is due
of the t(Mo@O) grouping in complexes [33]. The bands in the re-
gion 553–504 cmꢂ1 and 485–469 cmꢂ1 which may be due to the
formation of MAO and MAN respectively [34]. The FT-IR spectral
data of [A]and [B] chalcone ligands and their complexes presented
in the Table 2.
to enolic t(CAO) after removing the proton during complexation.
This band is shifted towards higher wave number ꢃ27 cmꢂ1
1H NMR spectra of chalcone ligands [A] and [B] and their oxocation
complexes
[27,30,31]. The spectrum of all VO(IV) complexes show sharp in-
tense band at 975 cmꢂ1 and 974 cmꢂ1 is indicative of the
t(V@O)
1H NMR spectrum of chalcone ligand exhibits signals at d 0.84–
0.89 ppm as a triplet and d 1.25–1.89 ppm as a multiplet which are
grouping in complexes [32]. All MoO(V) complexes spectrum
shows sharp intense band at 958 cmꢂ1 and 955 cmꢂ1 is indicative

106
B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
Table 5
proton of DHA moiety, we concluded that the coordination occur
through the oxygen atom of AOH group of dehydroacetic acid,
after deprotanation. Their spectral data are presented in Table 3.
Thermal behaviour and thermodynamic parameters of [VODC16 (H2O)] and
[MoODC16Cl] complexes.
Complexes
Step Step analysis
temperature
°C
D
Eꢄ
(kcal molꢂ1
Cs =
Order of
)
Ws ꢂ Wf/ reaction
Mass spectral study
W0 ꢂ Wf
Ti
Tmax Tf
The mass spectrum of chalcone ligand [B] is represented in
(Fig. 2), which also gives molecular ion peak at 497.5 (M+ + 1),
which are also agreement with molecular masses of the ligand
[B] (C31H44O5 = 496.66).
I
120 150
255 275
410 425
170 15.10
315 10.01
565 5.38
0.291
0.345
0.333
1
1
1
[VO(B)2 (H2O)] II
III
I
195 205
270 310
405 425
235 12.13
330
600
0.314
0.408
0.397
1
1
1
[MoO(B)2Cl]
II
III
9.97
4.72
UV/visible spectra of chalcone ligand and their oxocation complexes
Ti = Initial decomposition temperature.
Tmax = Temperature for maximum rate of decompositions.
Tf = Final decomposition temperature.
The electronic spectrum of ligands [A] and [B] have been taken
in methanol solvent in the range of 200–400 nm. The high intensity
band observed at 246 nm (
to
pꢄ of >C@O group in the ligands [A] and [B], respectively.
The low intensity band observed at 383 nm = 3600) and
410 nm ( = 3600) are due to (ACH@CHA) chalcone group of li-
gands [A] and [B], respectively.
e = 4000) and 305 nm (e = 3900) are due
p
?
(
e
attributed to the methyl and methylene protons of alkoxy chain,
respectively. The doublet signal appeared at d 2.27 ppm due to
the methyl proton of dehydroacetic acid. A singlet observed at d
e
The electronic spectral results for the coordinate complexes of
VO(IV) and MoO(V) in solution are characteristic of an octahedral
geometry around the central metal ion [36,37]. From electronic
spectrum of VO(IV), three expected low-energy ligand field bands
observed at 12,789–13,793 cmꢂ1 (781.9–725.0 nm), 16,722–
17,985 cmꢂ1 (598.0–556.0 nm) and 19,880–20,080 cmꢂ1 (503.0–
5.92–5.93 ppm can be assigned to the olefinic protons of H proton
a
of chalcone group. The phenyl multiplets observed at
d
6.97–8.01 ppm. The aldehydic (Hb) proton gives singlet at d 9.88–
9.87 ppm. The 1H NMR spectrum shows the singlet at d 16.70–
16.69 ppm due to the presence of strong intramolecular hydrogen
bonding between the phenolic hydrogen and acetyl carbonyl group
of the ligands [35], which indicates the chalcone ligand in solution
state converted into enolic form.
498.0 nm) range are assigned as 2B2g ? 2E2g 2B2g ? 2B1g, and
,
2B2g ? 2A1g transitions, respectively. According to Ballhausen
[38,39], these bands are assigned to ligand field transitions:
In the spectrum of VO(IV) and MoO(V) complexes, weak singlet
observed up field at d 2.16–2.29 ppm due to the ACH3 protons of
DHA. The proton of the coordinated water molecule did not
observed in solution spectrum of VO(IV) complexes, this coordi-
nated water molecule is further confirmed by thermal analysis. A
d
xy ? (dxz, dyz), dxy ! dx2
and dxy ! dz2 corresponding to
ꢂy2
b2 ? eꢄ(
m
1), b2 ? b1ꢄ(
m
2), and b2 ? a1ꢄ(
m3) transitions, respectively
[40]. In the UV region, bands appeared at 23,360–32,809 cmꢂ1
(428.1–304.8 nm), 32,786–28,735 cmꢂ1 (305.0–348.0 nm) and
39,215–32,470 cmꢂ1 (254.8–307.9 nm). The three bands can be
due to the inter ligand transition, whereas the last band can be
due to the charge transfer [41]. Similarly, electronic spectrum of
MoO(V) exhibits, three expected low-energy ligand field bands ob-
served at 13,888–14,388 cmꢂ1 (746.9–695.0 nm), 18,518–
18,867 cmꢂ1 (540.0–530.0 nm) and 22,883–23,255 cmꢂ1 (437.0–
weak singlet observed at d 5.92–5.96 ppm can be assigned to H
a
– protons of ACHab@CHb A group. The phenyl multiplets ob-
a
served at d 6.65–7.94 ppm. The Hb chalcone proton gives singlet
at d 9.78–9.87 ppm. In the 1H NMR spectrum of VO(IV) and MoO(V)
complexes, the peak disappeared at d ꢃ16.70 ppm of enolic AOH
Fig. 5. TGA/DTG curve of [VO(B)2 (H2O)] complex.

B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
107
Fig. 6. TGA/DTG curve of [MoO(B)2Cl]complex.
430.0 nm) range are assigned as 2B2 ? 2E2
(m
1), 2B2 ? 2B1
(m
2), and
trum of [VO(A)2 (H2O)] complex consists of one signal line with
shape of the signals in polycrystalline state is lorentzian. The g val-
ues, |g| or g0 = 1.96 and 1.97, g\ = 1.98 and 1.99 and g|| = 1.94 at RT
and LNT respectively, are essentially the same for the entire com-
plex examined. The g|| < g\ relations are consistent with octahedral
geometry in complexes with C4v symmetry with the unpaired elec-
tron in the dxy orbital [44]. As expected, the g values are invariably
lower than the free electron value (ge = 2.0023). This lowering is re-
lated to the spin–orbit interaction of the ground state dxy level,
with the low lying excited states.
O( ) ? d(Mo)( 3) transitions, respectively [17,42]. In the UV re-
p
m
gion, bands appeared at 27,624–28,409 cmꢂ1 (362.0–352.0 nm),
28,735–28,985 cmꢂ1 (380.0–345.0 nm) and 32,470–32,680 cmꢂ1
(307.9–305.9 nm). The bands can be due to the inter ligand transi-
tion, whereas the last band can be due to charge transfer. These
spectral data are consistent with those predicted for six-coordinate
VO(IV) and MoO(V) complexes, whose structures are distorted
octahedral in C4 symmetry. The electronic spectral data of com-
m
plexes are presented in Table 4.
The EPR spectrum of oxomolybednum complex consists of six
ESR line signals arising from the interaction of a single unpaired
electron (S = ½) with the quenched orbital angular momentum of
molybdenum nucleus of spin I = 5/2. But 75% of molybdenum
atoms are isotopes 94Mo and 96Mo with the nuclear spin quantum
number I = 0 and these isotopes give 2I + 1 = 2 ꢅ 0 + 1 = 1 ESR line.
The polycrystalline ESR spectrum of [MoO(A)2Cl] complex show
one typical ESR line at RT and LNT (Fig. 4). The |g| = 1.91 and
1.99, g\ = 1.89 and 1.98, g|| = 1.95 and 2.02 at RT and LNT respec-
tively. The g|| > g\ relation is consistent with distorted octahedral
geometry in complexes with C4v symmetry with the unpaired elec-
tron in the dxy orbital [17,32].
Magnetic susceptibility
The magnetic susceptibility measurement of [VO(A)2 (H2O)] and
[VO(B)2 (H2O)] complexes were carried out by Gouy method at
room temperature. The observed magnetic moment (leff) values
are 1.77 BM and 1.78 BM, indicating the VO(IV) compounds in d1
configuration are normal paramagnetic behaviour having one un-
paired electron, s = 1/2. There is no reduced magnetic moment
for these compounds, ruling out any antiferromagnetic interaction
present in these molecules. Therefore, VO(IV) complexes are mono
nuclear. All the two complexes of [Mo(A)2Cl] and [Mo(B)2Cl] are
paramagnetic with effective magnetic moments are 1.75 and
1.74 BM respectively, (shown in Table 1) with no significant mag-
netic interactions between the neighboring oxomolybdenum(V)
ions, indicating mononuclear nature of chalcone ligand complexes
[42]. The ESR spectral studies indicate that the MoO(V)compounds
are magnetically dilute in nature.
Thermal study
From the TGA and DTG curves [VO(B)2 (H2O)]complex, it has
been observed that there are main three steps in the decomposi-
tion of [VO(B)2 (H2O)] complex. In complex, decomposition starts
from 120–170 °C, the first mass loss 1.75% (1.67% cal.) up to
170 °C is in good agreement with loss of one coordinated water
molecule. The second step and third step start from 255 to
315 °C and 410 to 565 °C respectively, which is due to the pyrolysis
of organic molecule into two steps. After 850 °C, the stable metal
oxide V2O5 was formed. From TGA and DTG curves of [MoO(B)2Cl]
complex, it has been also observed that there are mainly three
steps in decomposition of [MoO(B)2Cl] complex. The curves of
ESR spectra
EPR (ESR) spectroscopy has proven to be a powerful technique
revealing three important types of information about: (i) the envi-
ronment of the oxocations, (ii) the nature of the ligand types, and
(iii) the distortion of the complexes and degree of association with-
in the system [43]. The EPR spectrum of [VO(A)2 (H2O)] complex in
polycrystalline form at RT and LNT shown in (Fig. 3). The EPR spec-

108
B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
Fig. 7. Broido plots of [VO(B)2 (H2O)] complex.
Fig. 8. Broido plots of [MoO(B)2Cl] complex. Where M = V(IV); X = H2O and M = Mo(V); X = Cl, R = CnH2n+1, n = 14 and 16, n = 14; A, n = 16; B.
TGA show no loss up to 190 °C, which indicate that neither crystal-
line nor coordinated water molecule present in [MoO(B)2Cl] com-
plex. The curves exhibit the first step starts at 195–235 °C, is due
to the completely remove of the chlorine atom, found percentage
is 3.25% (calc. 3.11%), which is coordinated with the Mo atom.
Decomposition of organic ligand begins after 250–600 °C. The
DTG curve also shows endothermic peak at 195–235 °C. This is fol-
lowed by exothermic process with the mass loss 87.5–80.0%, due
to the pyrolysis of organic molecule into two steps. After 800 °C
the stable metallic oxide MoO3 formed.
Application of Broido’s [45] method used to determine the ki-
netic parameter for complexes.
The Horowitz–Metzger equation [46,47].
Cs ¼ n1=ð1ꢂnÞ
;
Cs ¼ Ws ꢂ Wf =W0 ꢂ Wf :
The above equation is used for the determination of the reaction
order, where Cs is the mass fraction of the substance, here Ws
stands for the mass remaining at a given temperature, W0 and Wf
are the initial and final masses of the substance, respectively. On
the basis of above studies the probable structure of the chalcone
ligand complexes of oxovanadium (IV) and oxomolybdenum (V)
have distorted octahedral geometry as shown in Fig. 9.
The thermal behaviour and thermodynamic parameters pre-
sented in the Table 5. The TGA/DTG curves of [VO(B)2 (H2O)] and
[MoO(B)2Cl] of binary complexes also shown in Figs. 5 and 6,
respectively. The plot of lnln(1/y) vs 1/T, results in straight line
are shown in Figs. 7 and 8. From these plots we calculated the acti-
vation energy
D
Eꢄ and also calculated order of reaction.

B.T. Thaker, R.S. Barvalia / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 101–109
109
Where M = V(IV); X = H2O and M = Mo(V); X = Cl, R = CnH2n+ ,n = 14 and 16, n =14; A, n =16; B
Fig. 9. Probable structures of chalcone ligand complexes of oxovanadium(IV) and oxomolybednum(V).
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Conclusion
The IR and 1H NMR spectral data suggest that the chalcone li-
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gands behave as a monobasic bidentate with O:O donor sequence
towards metal ion. The molar conductivity data show them to be
non-electrolytes. From the magnetic measurement, electronic
and ESR spectral data suggest that all the oxovanadium(IV) and
oxomolybdenum(V) complexes have distorted octahedral geome-
try. The presence of one coordinated water molecule in the oxova-
nadium(IV) complexes and one coordinated chlorine atom in the
oxomolybdenum(V) complexes are confirmed by thermal study
such as TGA and DTG.
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