Spectroscopic studies on some fluorescent mixed-ligand titanium(IV) complexes

Article abstract of DOI:10.1016/j.saa.2011.09.017

A novel route to synthesize some titanium(IV) complexes containing acetylacetone, straight chain carboxylic acid and hydroxycarboxylic acid ligands has been investigated. Complexes with the general formula [Ti(acac)Cl _2-n(OOCR*)_n(OOC

Full text of DOI:10.1016/j.saa.2011.09.017

Spectrochimica Acta Part A 84 (2011) 125–129
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectroscopic studies on some fluorescent mixed-ligand titanium(IV) complexes
Balram Prasad Baranwal∗, Alok Kumar Singh, Anand Varma
Coordination Chemistry Research Laboratory, Department of Chemistry, DDU Gorakhpur University, Gorakhpur 273009, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 June 2011
Received in revised form 8 September 2011
Accepted 9 September 2011
A novel route to synthesize some titanium(IV) complexes containing acetylacetone, straight chain car-
boxylic acid and hydroxycarboxylic acid ligands has been investigated. Complexes with the general for-
mula [Ti(acac)Cl2−n(OOCR*)n(OOCC15H31)] (where Hacac = acetylacetone, R*COOH = hydroxycarboxylic
acids and n = 1 or 2) have been isolated and characterized. Molecular weight determinations indicated
mononuclear nature of the complexes. LMCT bands were observed in the electronic spectra. Infrared
spectra suggested bidentate nature of the ligands. Fluorescent behaviour of the complexes was noticed
on the basis of fluorescence spectra. Powder XRD indicated them to be semi-crystalline having the crys-
tallite size in 136–185 nm range. Transmission electron microscopy (TEM) indicated spherical particles
of ∼200 nm diameter. On the basis of physico-chemical studies, it is suggested that titanium is having
coordination number 7 or 8 in these complexes.
Keywords:
Titanium(IV)
Fluorescent
Mononuclear
Mixed-ligand complexes
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
titanium is attached with all the different type of four ligands. The
ligands chosen in this work were electron rich bearing hydroxy
Although the chemistry of hydroxy (OH) rich ligands with
(OH) group keeping in view to result in a hydrolysis resistant prod-
ucts. Carboxylic and hydroxycarboxylic acids have been used in
the light that incorporation of these ligands in titanium(IV) com-
plexes may enhance the cytotoxicity providing a better candidate
for anticancer agents [10]. These complexes are characterized using
different spectral techniques and their coordination behaviour is
discussed.
oxometal centres such as VO2+, VO3+, cis-VO2+, cis-MoO2 and
2+
trans-UO22+, is well understood [1], their coordination behaviour
towards non-oxo metal species has received a limited attention [2].
The coordination role of hydroxy rich ligands with non-oxo metal
centres, particularly in case of titanium(IV) is reported showing
reactivity of cis-bis(acetylacetonate) and other bis(␤-diketonate)
complexes for many applications [3,4]. A perusal of the literature
reveals that a number of transition metals form complexes with
hydroxycarboxylic ligands [5], but studies on titanium(IV) com-
plexes with such ligands are very limited. It has also been found
that the mixed-ligand complexes of titanium(IV) with higher fatty
acids and hydroxycarboxylic acids are not reported so far. Research
on the synthesis and applications of fluorescent titanium(IV) com-
plexes are currently considered as one of the most expanding areas
in biomedical and inorganic chemistry [6].
Most of the titanium complexes are sensitive to hydrolysis
which may cause a subsequent reduction in their catalytic property
[7]. Their rate of hydrolysis can significantly be reduced resulting
in better photocatalytic activity by using bulky electron-rich lig-
ands [8]. In this light we have recently reported some titanium(IV)
complexes having Ti–O–C bond and increased resistance towards
hydrolysis [9].
2. Experimental
2.1. Materials and analytical methods
All the reactions were carried out under anhydrous conditions.
Organic solvents (Qualigens) were dried and distilled before use by
standard methods [11]. Sodium palmitate, acetylacetone, hydrox-
ycarboxylic (salicylic, mandelic and benzilic) acids (Aldrich) and
TiCl4 (BDH) were used as received. Titanium and chlorine were
estimated gravimetrically as TiO2 and AgCl, respectively [12].
2.2. Physico-chemical measurements
Electronic spectra were recorded on Hitachi U-2000 spec-
trophotometer in toluene. Fluorescence spectra were recorded
on a Hitachi F-2500 spectrophotometer with the scan speed of
300 nm/min and PMT voltage at 400 V in toluene. Excitation source
was 150 W Xenon lamp. Infrared spectra were recorded on a Perkin-
Elmer RX1 FTIR spectrophotometer using KBr discs. 1H NMR spectra
were recorded at 300 MHz on a Bruker DRX-300 NMR spectrome-
ter in CDCl3. Molecular weights were determined in a semi-micro
In this paper we report an easier method of synthesis for nano-
sized, fluorescent mixed-ligand complexes of titanium(IV) in which
∗
Corresponding author. Tel.: +91 551 2203459.
E-mail address: drbpbaranwal@gmail.com (B.P. Baranwal).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.09.017

126
B.P. Baranwal et al. / Spectrochimica Acta Part A 84 (2011) 125–129
ebulliometer (Gallenkamp) with a thermistor sensing device. Pow-
der XRD data were collected on a PW 1710 diffractometer. The
operating voltage of the instrument was 30 kV and the operat-
ing current was 20 mA. The intensity data were collected at room
temperature over a 2ꢀ range of 5.025–79.925◦ with a continuous
scan mode. Transmission electron microscopy (TEM) images were
obtained on a Tecnai 30 G2S – Twin electron microscope with an
accelerating voltage of 300 kV on the surface of a carbon coated
copper grid. Molar conductance were measured on century CC-
601 digital conductivity meter at 10−2 to 10−3 molar solutions in
nitrobenzene. Solid state conductance measurements were carried
out with Keithley 6220 Precision current source and keithley 2182 A
nanovoltmeter. Elemental analyses (C, H) were done on a Vario EL
III Carlo Erba 1108 elemental analyzer.
chloride formed during the reaction was filtered out. Excess solvent
from the soluble part was removed in vacuo to yield an orange solid.
It was purified in dichloromethane-n-hexane mixture (1:1 ratio).
2.4. Synthesis of [Ti(acac)(OOCC6H4OH)2(OOCC15H31)] (2)
Sodium salt of salicylic acid (1.04 g, 6.50 mmol) was added in the
solution of B (1.54 g, 3.25 mmol) in benzene (50 mL). The contents
were stirred (10 h) followed by refluxing (6 h). Insoluble sodium
chloride formed during the reaction was filtered out. Excess solvent
from the soluble part was removed in vacuo to yield dark orange
solid. It was purified by using a mixture of dichloromethane and
n-hexane (1:1 ratio).
An analogous procedure was adopted to synthesize other tita-
nium(IV) complexes being reported in this communication and the
details of analytical results are summarized in Table 1.
2.3. Synthesis of [Ti(acac)Cl(OOCC6H4OH)(OOCC15H31)] (1)
Synthesis of this complex was completed in following steps:
3. Results and discussion
2.3.1. Preparation of sodium salicylate
A solution of sodium metal (0.45 g, 19.57 mmol) in 25 mL of iso-
propanol (sodium isopropoxide formed in situ) was slowly added to
Some mixed-ligand complexes of titanium(IV) were synthe-
sized by stepwise substitutions of chloride ions from titanium
tetrachloride as depicted below:
Benzene
TiCl4 + Hacac
[Ti(acac)Cl3] + HCI ↑
Reflux
A
Benzene
↑
A + C15H31COONa
[Ti(acac)Cl2(OOCC15H31)] + NaCl
Reflux
B
Benzene
↑
B + nR*COONa
[Ti(acac)Cl2-n(OOCR*)n(OOCC15H31)] + nNaCl
Reflux
HO
COONa
COONa
COONa
HO
OH
Ρ'ΧΟΟΝα
Ρ’’ΧΟΟΝα
Ρ’’’ΧΟΟΝα
where Hacac = acetylacetone; R* = C6H4OH (Rꢀ); C6H5CH(OH)
(Rꢀꢀ) or (C6H5)2C(OH) (Rꢀꢀꢀ) and n = 1 or 2.
salicylic acid (2.70 g, 19.55 mmol) in isopropanol (25 mL). The con-
tents were boiled to reflux for 3 h. Removal of excess isopropanol
under vacuum yielded solid sodium salicylate (yield: calcd. = 3.13 g;
found = 2.68 g).
Benzene was chosen a solvent in these substitutions because
sodium chloride formed during the reaction was insoluble and the
titanium(IV) complexes were soluble which could made the sepa-
ration easy. The molar conductance of complexes at 10−2 to 10−3
molar concentrations in nitrobenzene was obtained in the range
3–9 ꢁ−1 cm2 mol−1 which indicated them to be non-electrolytes
[14]. Solid state conductance measurements were done for all the
complexes and were found in the range 1.4 × 106–2.5 × 106 ꢁ at
295 K using current 1 × 10−8 A and voltage 1.4 × 10−2 V. This clearly
indicated them to show high resistance or they could be said
to behave like insulators. Room temperature magnetic moment
measurements indicated diamagnetic nature of the complexes,
showing absence of unpaired electrons in these complexes. They
are characterized by elemental analyses too. Ebullioscopic method
of molecular weight determinations showed that all the complexes
were monomeric in refluxing benzene (Table 1).
2.3.2. Preparation of [Ti(acac)Cl3] (A)
Acetylacetone (1.66 g, 16.68 mmol) was added to titanium tetra-
chloride (3.51 g, 16.61 mmol) taken in benzene (40 mL). Hydrogen
chloride gas was evolved and the reaction was exothermic with a
sharp colour change from yellow to red. The contents were refluxed
for 4 h. Excess solvent was removed in vacuo and a dark red solid
product A was obtained (yield: calcd. = 4.21 g; found = 3.49 g) [13].
2.3.3. Preparation of [Ti(acac)Cl2(OOCC15H31)] (B)
Sodium palmitate (2.54 g, 9.12 mmol) was added to A (2.31 g,
9.12 mmol) taken in benzene (40 mL). The reaction mixture was
stirred for 8 h followed by refluxing for 2 h. The contents were fil-
tered using G 4 sieve to remove insoluble sodium chloride formed
during the reaction. Excess solvent was removed in vacuo and
a yellow coloured solid, B was obtained (yield: calcd. = 4.32 g;
found = 3.72 g) [9].
To a solution of B (1.70 g, 3.59 mmol) in benzene (50 mL), sodium
salt of salicylic acid (0.58 g, 3.62 mmol) was added. The contents
were stirred for 10 h followed by refluxing for 4 h. Insoluble sodium
3.1. Electronic and fluorescence spectra
Two bands were observed in the range 202–208 nm and
288–305 nm in the electronic spectra of the complexes which could
be assigned to ꢂ–ꢂ* and n–ꢂ* transitions, respectively. The elec-
tronic transitions observed in the range 362–445 nm are due to

B.P. Baranwal et al. / Spectrochimica Acta Part A 84 (2011) 125–129
127
Table 1
Analytical results for titanium(IV) complexes.
Reactants (g, mmol)
Product (colour) (% yield)
MP (◦C)
Found (calculated) %
Molecular weight
found (calcd.)
Ti
Cl
C
H
[Ti(acac)Cl2(OOCC15H31)] + RꢀCOONa
TiC28H43O7Cl
(Orange) (86) (1)
TiC35H48O10
(Dark orange) (89) (2)
TiC29H45O7Cl
(Dark yellow) (81) (3)
TiC37H52O10
215
224
172
184
198
210
8.28
(8.33)
7.21
(7.08)
8.19
(8.13)
6.63
(6.79)
7.08
(7.20)
5.45
6.26
(6.17)
58.41
(58.49)
62.28
(62.12)
59.05
(59.13)
63.01
(63.06)
63.32
(63.20)
68.81
7.33
(7.55)
7.10
(7.17)
7.57
(7.72)
7.29
(7.45)
7.33
(7.44)
7.01
587
(574)
668
(676)
595
(589)
715
(704)
677
(665)
848
(1.70, 3.59)
[Ti(acac)Cl2(OOCC15H31)] + RꢀCOONa
(1.54, 3.25) (1.04, 6.50)
[Ti(acac)Cl2(OOCC15H31)] + RꢀꢀCOONa
(1.84, 3.89) (0.68, 3.91)
[Ti(acac)Cl2(OOCC15H31)] + RꢀꢀCOONa
(1.61, 3.40) (1.19, 6.83)
(0.58, 3.62)
–
5.95
(6.02)
(Dark yellow) (78) (4)
[Ti(acac)Cl2(OOCC15H31)] + RꢀꢀꢀCOONa TiC35H49O7Cl
5.18
(5.33)
(1.16, 2.45)
[Ti(acac)Cl2(OOCC15H31)] + RꢀꢀꢀCOONa TiC49H60O10
(1.53, 3.23) (1.62, 6.47) (Yellow) (84) (6)
(0.62, 2.48)
(Yellow) (88) (5)
(5.59)
–
(68.68)
(7.07)
(856)
Table 2
Fluorescence spectral data for titanium(IV) complexes.
Complex
Excitation ꢃmax
Apex (nm)
Region
Band
Height
Area (Data nm)
1
2
3
4
5
6
388
413
409
427
425
435
432.5
438.0
430.7
442.4
447.0
459.5
Blue
Blue
Blue
Blue
Blue
Blue
B
B
B
B
B
B
466.7
458.3
407.0
462.4
465.0
483.2
6787.440
6763.271
6327.327
6587.791
7513.319
7971.241
Fig. 1. (a) UV–vis; (b) fluorescence spectra of 1 (
) and 6 (- - - -).
strong charge-transfer absorption from ligand ꢂ-orbital to vacant
titanium orbital (ligand to metal charge-transfer, LMCT bands)
which are strongly affected by the chemical nature of the lig-
ands giving colours to the complexes [15]. The electronic and
fluorescence spectra of complexes 1 and 6 are given in Fig. 1. In
fluorescence spectra of all the complexes one B band in blue region
is observed. The data (Table 2) indicated them to behave like a
fluorescent material.
antisymmetric stretches, ꢅ [ꢄasymOCO − ꢄsymOCO] were found in
the range 110–132 cm−1. This indicated that carboxylate groups of
both palmitic acid and hydroxycarboxylic acids were coordinated
to titanium in a bidentate chelating mode involving coordination of
both the oxygen atoms of –COOH group [16]. No band was found in
1626–1700 cm−1 region indicating the CO group of acetylacetone
was not free in the complexes. Two splitted new bands observed
at ∼1615 cm−1
(
) and ∼1530 cm−1
(
) indicated the
vC
O
vC
C
chelating nature of acetylacetonate ion in the complexes [17]. The
bands around 670 and 465 cm−1 could be assigned to ring deforma-
tion ꢄTi–O and ꢄTi–O vibrations, respectively [16]. A representative
infrared spectrum of complex 1 is given in Fig. 2.
3.2. Infrared spectra
In infrared spectra of all the complexes, the characteristic
ꢄ(C O) and ı(O–H) of free carboxylic acids at 1710 cm−1 and
935 cm−1, respectively, were found absent. The O–H stretching
vibration of free hydroxyl group of hydroxycarboxylic acid was
noticed at ∼3400 cm−1 in the spectra of the complexes, which
indicated that the hydroxyl group of hydroxycarboxylic acid was
not bound to titanium and remained free. Two strong bands
were observed in the range 1592–1545 cm−1 and 1460–1435 cm−1
which could be assigned due to (ꢄasymOCO) (antisymmetric)
and (ꢄsymOCO) (symmetric) vibrations of the carboxylate ions,
respectively [16]. The differences between the symmetric and
3.3. Hydrolytic stability of the complexes
The complex [Ti(acac)Cl2(OOCC15H31)] (B) is moisture sensitive
[9]. Its sensitivity towards hydrolysis is reduced by substituting
chloride ions by hydroxycarboxylic acids. This stability was tested
by dissolving the complexes in benzene and 1% water was added
and stirred the contents for 14 h open in the air. Following cor-
relation in the hydrolytic stability may be sought: 1, 3, 5 < 2, 4,
6.

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B.P. Baranwal et al. / Spectrochimica Acta Part A 84 (2011) 125–129
Table 3
1H NMR spectral data (ı, ppm) for titanium(IV) complexes.
Complex
1H
2
3
4
5
6
0.90 [s, 3H, CH3], 1.27 [s, 26H, (–CH2)13], 1.64 [t, 2H, ␣-CH2], 2.06 [s, 6H, acac], 5.63 [s, 1H, CH, acac], 7.68–6.79 [m, 8H, arom], 10.04 [s, 2H, OH, PhOH]
0.89 [s, 3H, CH3], 1.26 [s, 26H, (–CH2)13], 1.64 [t, 2H, ␣-CH2], 2.06 [s, 6H, acac], 5.60 [s, 1H, CH, acac], 5.23 [s, 1H, OH, –HCOH], 7.58–6.97 [m, 5H, arom]
0.90 [s, 3H, CH3], 1.26 [s, 26H, (–CH2)13], 1.65 [t, 2H, ␣-CH2], 2.06 [s, 6H, acac], 5.60 [s, 1H, CH, acac], 5.26 [s, 2H, OH, –HCOH], 7.59–6.81 [m, 10H, arom]
0.89 [s, 3H, CH3], 1.27 [s, 26H, (–CH2)13], 1.64 [t, 2H, ␣-CH2], 2.05 [s, 6H, acac], 5.63 [s, 1H, CH, acac], 5.37 [s, 1H, OH, –COH], 7.61–6.94 [m, 10H, arom]
0.89 [s, 3H, CH3], 1.27 [s, 26H, (–CH2)13], 1.64 [t, 2H, ␣-CH2], 2.06 [s, 6H, acac], 5.64 [s, 1H, CH, acac], 5.38 [s, 2H, OH, –COH], 7.61–6.72 [m, 20H, arom]
Fig. 2. Infrared spectrum of 1.
Fig. 3. 1H NMR spectrum of 1.
Fig. 4. Powder XRD pattern of 1.
3.5. Powder XRD and TEM studies
3.4. 1H NMR spectra
Powder XRD was done for all the complexes which show first
order reflection. The pattern and results of XRD suggested that the
crystals of the complexes are not perfect but lying in between amor-
phous and crystalline character. Due to this reason, the complexes
were not found suitable for single crystal XRD. A representative
spectrum of complex 1 is given in Fig. 4. In this case, first order
reflection occurs at 5.05◦ for (1 0 0) face, 12.71◦ for (0 1 0) face and
20.49◦ for (0 0 1) face. Using Bragg’s equation, it can be shown
that relative spacing between planes of the faces (1 0 0), (0 1 0)
In 1H NMR spectrum of 1 (Fig. 3) a singlet was appeared at
ı = 0.89 ppm (3H) corresponding to methyl protons of palmitate ion
[–OOCCH2(CH2)13CH3] and a singlet at ı = 1.26 ppm due to 26H of
13-CH2 groups. A peak at ı = 1.64 ppm (2H) indicated the ␣-CH2
protons of palmitate ion. A singlet at ı = 2.05 ppm (6H) indicated
the methyl protons of acetylacetonate ion while its methine pro-
ton was observed as a singlet at ı = 5.62 ppm (1H). A multiplet
from ı 7.65 ppm to 6.88 ppm corresponded to aromatic ring pro-
tons of hydroxycarboxylate anion while the free hydroxyl proton
attached to the ring appeared at ı = 10.02 ppm. The signal posi-
tions observed in the spectra for other complexes are given in
Table 3.
˚
˚
˚
and (0 0 1) are 8.69 A, 3.50 A and 2.21 A, respectively. Values of the
˚
˚
˚
unit cell dimensions are a = 8.69 A, b = 3.50 A and c = 2.21 A. The data
obtained can be attributed to the fact that
a =/ b =/ c and ˛ =/ ˇ =/ ꢆ =/ 90◦.

B.P. Baranwal et al. / Spectrochimica Acta Part A 84 (2011) 125–129
129
Table 4
character and possess Ti–O–C linkage too, which is mainly required
for their catalytic property. They have high hydrolytic stability and
coordination number of titanium is assigned to seven or eight in
the complexes.
Powder XRD structural data for complex 1.
Parameters
1
Empirical formula
Crystal system
Bravice lattice
Space group
TiC28H43O7Cl
Triclinic
Primitive
P1
Acknowledgements
˚
a (A)
8.69
3.50
2.21
5.05
12.71
20.49
Authors are thankful to the CSIR [no. 01(2293)/09/EMR-II] and
[no. 09/057/(0200)/2010/EMR-I], and UGC [F. no. 37-132/2009
(SR)], New Delhi for financial support. They also thank CDRI, Luc-
know for spectral and microanalysis.
˚
b (A)
˚
c (A)
˛ (◦)
ˇ (◦)
ꢆ (◦)
Limiting indices
References
˚
h (A)
8.69
3.50
2.21
337
˚
k (A)
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Kꢃ
D =
(ˇ cos ꢀ)
where D is the crystallite size; K is a constant (=0.94); ꢃ is X-ray
wavelength (ꢃ = 1.5406 A); ꢀ is Bragg diffraction angle and ˇ is inte-
gral peak width which is converted into radian while calculation.
The values obtained were in the range 136–185 nm.
The morphology of complex 1 was observed to have spherical
particles (Fig. 5) of ∼200 nm average diameter.
˚
4. Conclusions
Designing of a novel type of mononuclear, non-oxo, mixed-
ligand complexes of titanium(IV) containing different ligands
around the metal has been made which have spherical shaped par-
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