Cobalt(III) complexes of unsaturated carboxylic acids: Synthesis, characterization, and photochemical studies in aqueous medium

Article abstract of DOI:10.1007/s11164-012-0850-0

Cobalt(III) ammine complexes coordinated to carboxylic acids are classic examples showing photoredox reactions originating from the ligand to metal charge transfer excited states. Cobalt(III) pentaammine complexes coordinated to unsaturated carboxylic acids as ligands were synthesized and characterized by spectroscopic methods. The photolysis of these complexes produces a carboxylate free radical. This free radical undergoes further transformation to form organic photoproducts. The organic photoproducts were characterized by spectroscopic methods. The nature of the decomposition products from the organic photoproduct was examined in detail. The quantum yields were also determined. The photochemical reactions have the potential to produce novel compounds from the decarboxylation of unsaturated acids, which shows interesting reaction pathways.

Full text of DOI:10.1007/s11164-012-0850-0

Res Chem Intermed
DOI 10.1007/s11164-012-0850-0
Cobalt(III) complexes of unsaturated carboxylic acids:
synthesis, characterization, and photochemical studies
in aqueous medium
•
Kandasamy Jothivenkatachalam
•
Singaravelu Chandra Mohan
Paramasivan Natarajan
Received: 20 July 2012 / Accepted: 1 October 2012
ꢀ Springer Science+Business Media Dordrecht 2012
Abstract Cobalt(III) ammine complexes coordinated to carboxylic acids are
classic examples showing photoredox reactions originating from the ligand to metal
charge transfer excited states. Cobalt(III) pentaammine complexes coordinated to
unsaturated carboxylic acids as ligands were synthesized and characterized by
spectroscopic methods. The photolysis of these complexes produces a carboxylate
free radical. This free radical undergoes further transformation to form organic
photoproducts. The organic photoproducts were characterized by spectroscopic
methods. The nature of the decomposition products from the organic photoproduct
was examined in detail. The quantum yields were also determined. The photo-
chemical reactions have the potential to produce novel compounds from the
decarboxylation of unsaturated acids, which shows interesting reaction pathways.
Keywords Photolysis Á Carboxylatopentaamminecobalt(III) complex Á
Ligand to metal charge transfer Á Carboxylic acid
Introduction
Cobalt(III) complexes undergo redox reactions from the charge transfer to metal
(LMCT) excited states, leading to the reduction of the metal center and the
Electronic supplementary material The online version of this article (doi:10.1007/s11164-012-0850-0)
contains supplementary material, which is available to authorized users.
K. Jothivenkatachalam (&) Á S. Chandra Mohan
Department of Chemistry, Anna University, BIT Campus, Tiruchirappalli 620 024, India
e-mail: jothivenkat@yahoo.com
P. Natarajan
National Centre for Ultrafast Processes, University of Madras, Taramani Campus, Chennai 600 113,
India
e-mail: pnatrajan@hotmail.com
123

K. Jothivenkatachalam et al.
hv
.
RCOOCoIII L5
RCOO CoL5
254nm; H3O+
.
.
solvent
RCOO + SCoII L5
RCOO CoL5
.
.
RCOO
R
+ CO2
.
Products
R
Scheme 1 Mechanism for the photoredox reaction of carboxylatopentaamminecobalt(III) complex
corresponding oxidation of ligands on excitation with ultraviolet and visible light
[1–4]. The general reaction mechanism for the photochemistry of carboxylatopen-
taamminecobalt(III) is shown in Scheme 1 [5–8].
Earlier studies have concentrated on these photochemical reactions for exploring
the nature of products formed using amino acids and carboxylic acids as ligands [4,
9–14]. In the present investigation, the photoredox chemistry of cobalt(III) ammine
complexes coordinated with unsaturated carboxylic acids such as itaconic acid and
sorbic acid as ligands has been carried out with a view to elucidate the
photoproducts from the photo-oxidized ligands, which may lead to the synthesis
of value-added products.
The structure of the carboxylatopentaamminecobalt(III) complexes 1 and 2 is
shown below:
O
C
OH
C
O
O
O
O
H3N
NH3
NH3
H3N
NH3
NH3
Co
(ClO4)2
Co
(ClO4)2
H3N
H3N
NH3
NH3
1
2
Detailed investigations on the continuous photolysis of complexes 1 and 2 were
systematically carried out. The nature of the photochemically formed R• radical of
the complex is of particular interest [where R• for complex 1; HOOC–C(=CH2)–
123

Cobalt(III) complexes of unsaturated carboxylic acids
CH•2 and for complex 2; CH3–CH=CH–CH=CH•]. The effect of the substituent R in
the carboxylic acid ligand, the quantum yield of product formation, the identifi-
cation of the R• radical, and its subsequent behavior are important in order to be
able to understand the nature of the primary processes occurring in the
photochemistry of the cobalt(III) carboxylato complexes.
Experimental
Materials and methods
Cobaltous nitrate hexahydrate, acetone, diethyl ether, perchloric acid (70 %), and
liquid ammonia were purchased from Merck Chemicals. Itaconic acid and sorbic
acid used in this investigation were obtained from Aldrich Chemicals. Dowex 50W-
X4 cation exchange resin (200–400 mesh) was purchased from Sigma Chemicals.
All other reagents used in this investigation were of laboratory grade.
The absorption spectra were recorded using a Hewlett-Packard Model-8452A
UV–Visible diode-array spectrophotometer. The fluorescence spectra were recorded
using a Perkin-Elmer LS-5B luminescence spectrometer interfaced with a PC via an
RS-232C interface. The infrared spectra were recorded in a Perkin Elmer Model-
783 spectrophotometer in the spectral range 4,000–400 cm-1, using KBr pellets.
NMR spectra were recorded using JEOL GSX400 and Bruker 300-MHz spectrom-
eters. Gas chromatography/mass spectrometry (GC-Mass) spectra of photoproducts
were recorded in a Shimadzu QP-5000 GC/MS instrument using a DB-1 non-polar
column, and a Perkin-Elmer AutoSystem XL Gas TurboMass mass spectrometer
(EI, 70 eV), with helium as the carrier gas at a flow rate of 1 ml/min. The elemental
analyses were carried out by using a Carlo Erba Model 1106 elemental analyzer
performed at the catalysis division, IIT, Chennai.
Fluorescence lifetime measurements were carried out in a picosecond laser-
excited, time-correlated, single-photon counting (TCSPC) spectrometer. The
excitation source is the tunable Ti-sapphire laser (Tsunami, Spectra Physics,
USA). The laser pulse (pulse width of \2 ps and repetition rate of 82 MHz) was
derived from the frequency-doubled output (532 nm) of the locked mode, which
is based upon the regeneratively initiated technique (Spectra Physics, USA). The
Ti-sapphire rod is refringent, and uninterrupted tuning is achieved when the rod
is aligned coplanar with the polarization of the electric field within the cavity.
The tuning range is 840–1,000 nm. A polarized picosecond laser pulse at 295 nm
excites the sample. The fluorescence emission was monitored at right angles to
the excitation path and the first photon was detected by an MCP-PMT detector
(Hamamatsu-R 3809U). When the first excitation pulse occurs, a synchronization
pulse triggers the charging of the capacitor in the TAC through the
discriminator. The voltage on the capacitor increases linearly until a stop timing
pulse is detected on repeating the start–stop cycle. A histogram representative of
the fluorescence decay is obtained, which is further analyzed using the IBH
software.
123

K. Jothivenkatachalam et al.
100000
10000
1000
100
1
2
10
1
200
300
400
500
600
wavelength /nm
Fig. 1 Electronic spectra of complexes 1 [Co(NH3)5It](ClO4)2 and 2 [Co(NH3)5SR](ClO4)2
Synthesis of carboxylatopentaamminecobalt(III) complexes 1 and 2
The complexes employed in this investigation were prepared by following the
general procedure reported in the literature [9–11, 15–17], and, in some cases, a
modified procedure was adopted. The general procedure for the synthesis of
carboxylatopentaamminecobalt(III) complexes involves the treatment of 20 mol of
the carboxylic acids (itaconic acid and sorbic acid) with 1.75 N sodium hydroxide
(10 ml), heating at 80 ꢁC for 10 min, and then filtering. The pH of the filtrate was
adjusted to \6.5 and the filtrate was added to a solution of aquapentaammine-
cobalt(III) perchlorate (1.0 g) in hot water (2 ml). The mixture was kept at
75–80 ꢁC for *4 h, then was cooled, and then added to a large separating funnel
containing a mixture of water (5 ml), 70 % HClO4(25 ml), and ether (150 ml). The
unreacted parent carboxylic acid becomes dissolved in the ether layer on shaking.
On standing for 30 min, the layers separated and the aqueous layer was extracted
again with 200 ml of ether. The solution was cooled and then added to precooled
70 % perchloric acid (15 ml), and the mixture was allowed to stand overnight at
-10 ꢁC. The precipitated complex was filtered off, washed with ice cold water,
dissolved in a minimum quantity of hot water (90 ꢁC), and the solution was cooled
to 0 ꢁC. The recrystallized complex was then filtered off and dried in vacuum at
35 ꢁC for 10 h.
The parent carboxylic acid compound is present as an impurity which had to be
removed, after several recrystallizations. The purity of the sorbatopentaammineco-
balt(III) complex was acceptable when [502 had a value in the 65–70 M-1 cm-1
123

Cobalt(III) complexes of unsaturated carboxylic acids
range. The above procedure with slight modification is used for the itaconato-
pentaamminecobalt(III) complex. In the case of itaconic acid, since two carboxylic
acid groups are present, in order to avoid the formation of bidentate coordination, an
excess amount of itaconic acid was used and the pH of the medium was maintained
at 6.5. The complex was recrystallized from distilled water at 60 ꢁC. Recrystal-
lization was repeated until the measured molar absorptivity remains unchanged
(kmax 500 nm; [500 = 63 M-1 cm-1). The yields tend to be small, often \20 %.
The presence of vinyl group in the unsaturated carboxylic acids leads to the
formation of polymers at higher temperatures. In order to avoid the polymerization
of free acid, the synthesis of these complexes was carried out under dark conditions
and at a moderate temperature of 70–80 ꢁC. (Caution: perchlorate is a potentially
highly dangerous oxidant in the presence of organic material; hence, care should be
taken in the handling of these complexes).
Continuous photolysis
Continuous photolysis experiments for complexes 1 and 2 were performed at the
intense ligand to metal charge transfer bands using a 254-nm low-pressure
mercury pen-ray lamp (Ultraviolet Products Inc) in acidic aqueous medium
(pH = 1) at 5 ꢁC. The apparatus used for photolysis is shown as supplementary
material S1. Light intensities were measured using ferrioxalate actinometry [18–
20].
During photolysis, the electronic absorption spectral changes were recorded in
the UV–visible region for definite intervals of time. The formation of cobalt(II) was
confirmed by analyzing the reduced metal ions spectrophotometrically on
complexation with thiocyanate ions (molar absorptivity at 625 nm for
[Co(NCS)4]2- &1,868 M-1 cm-1).
Photolysis of complexes 1 and 2 in acidic medium liberates ammonia, which
is dissolved in the photolysis solution. The pH of the photolysed solution
increased after photolysis due to the presence of ammonia in the solution. To
confirm the presence of ammonia, the solution was photolysed for about 75 %
decomposition of the complex and, through this solution, dry nitrogen was
passed and the resulting gas was passed through Nessler’s reagent. During this
process, a few pellets of sodium hydroxide were added to the photolysed
solution. Ammonia was liberated and a red–brown color developed in the
Nessler’s reagent. This test confirmed the liberation of ammonia during
photolysis.
After the completion of photolysis, following separation of the oxidized
photoproduct from cobalt(II) ions, the photolysed solution was passed through a
column loaded with a cation exchange resin (Dowex 50W-X4, 200–400 mesh). The
column temperature was maintained at 5 ꢁC by circulating cold water and the
organic photoproducts in the column were eluted with cold water at 5 ꢁC in the
dark. Then, the solution was concentrated and evaporated to dryness by means of a
freeze-drying.
123

K. Jothivenkatachalam et al.
Results and discussion
Of the carboxylatopentaamminecobalt(III) complexes used in the present investi-
gation, complex 1 shows two low-intensity absorption bands in the visible region
(500 nm, e = 62.89 M-1 cm-1, d–d transition) and one in the near-ultraviolet
region (350 nm, e = 61.88 M-1 cm-1, CT transition), which are illustrated in
Fig. 1. These two low-intensity bands are assigned as the spin-allowed ligand field
1
1
1
1
transitions, A1g ? T1g and A1g ? T2g, and the intense charge transfer band in
the ultraviolet region as the charge transfer transition. In the case of complex 2
[501 nm, e = 61.94 M-1 cm-1, d–d transition, and 350 (sh). 275 (sh)nm, CT
transition], the charge transfer absorption is shifted to the longer wavelength region
due to the presence of conjugation in the carboxylic acid.
IR (KBr, cm-1): 1,700 (–C=O stretching of free –COOH group), 1,600 (–C=O
stretching of coordinated –COO- group). For complex 1: 1,580 (–C=O stretching of
Fig. 2 Electronic spectral changes accompanying 254-nm photolysis of complexes
1 [Co
(NH3)5It](ClO4)2 and 2 [Co(NH3)5SR](ClO4)2 in acidic aqueous solution at 5 ꢁC. U unphotolysed
solution
123

Cobalt(III) complexes of unsaturated carboxylic acids
Table 1 Quantum yield of cobalt(II) ion formation for carboxylatopentaamminecobalt(III) complexes
2?
/
Co
Complex
Graphical
Experimental
[Co(NH3)5It] (ClO4)2
[Co(NH3)5SR] (ClO4)2
0.49 0.02
0.19 0.02
0.50 0.02
0.19 0.02
Fig. 3 Formation of cobaltous ions on the photolysis of carboxylatopentaamminecobalt(III) complexes
(change of absorbance at 625 nm vs. time of photolysis): 1 [Co(NH3)5It]2? ions and 2 [Co(NH3)5SR]2?
ions
coordinated –COO- group), 1,700 (uncoordinated carboxylic acid). For complex 2:
1,618 (–C=O asymmetric stretching of coordinated –COO- group), 1,396 (–C=O
symmetric stretching of coordinated –COO- group), 1,100 (stretching mode of
ClO4–).
123

K. Jothivenkatachalam et al.
Fig. 4 The emission spectrum (a) and the excitation spectrum (b) of organic photoproduct obtained from
[Co(NH3)5It]2? ions excited at 290 nm in water
1H-NMR (300 MHz, D2O, d/ppm) for complex 1: 3.9 (2H, s, –CH2), 6.04, 6.42
(1H, s, two olefinic protons) and also one of the acid protons is exchanged with
1
solvent D2O. H-NMR (300 MHz, acetone d6, d/ppm) for complex 2: 1.9 (3H, s,
CH3), 7.12, 6.67 (1H, m, two olefinic protons).
Elemental analysis for complex 1: anal. calcd. for C5H20N5O4: C, 12.68; H, 4.23;
N, 14.79; found: C, 12.48; H, 4.13; N, 14.47. Elemental analysis for complex 2:
anal. calcd. for C6H22N5O2: C, 15.82; H, 4.83; N, 15.38; found: C, 15.42; H, 4.78;
N, 15.32.
Continuous photolysis of cobalt ammine complexes
Most of the ultraviolet photochemistry of cobalt(III) complexes arising from the
irradiation of ligand-to-metal charge transfer bands at 254 nm results predominantly
in leading to photoreduction, with the formation of cobalt(II) ions and the oxidized
free radical of the ligand [21–23]. Carboxylatopentaamminecobalt(III) ions, on
123

Cobalt(III) complexes of unsaturated carboxylic acids
Table 2 The relative mass peak intensity of the photoproducts from carboxylatopentaamminecobalt(III)
complexes
Photoproduct from 1 [Co(NH3)5It](ClO4)2
Photoproduct from 2 [Co(NH3)5SR](ClO4)2
Mass peak
% intensity
Mass peak
% intensity
152
138
124
115
111
97
3.22
4.83
324
309
295
285
283
282
281
268
267
265
251
249
222
221
207
177
147
133
74
10.50
4.20
6.45
2.52
3.27
2.31
14.51
20.96
25.80
33.87
83.87
100.00
9.24
19.33
71.00
3.15
83
69
55
6.09
41
15.55
5.04
9.87
1.68
7.77
13.86
6.09
34.87
5.88
9.45
73
100.00
excitation of the carboxylato-to-cobalt(III) charge transfer bands, lead to carbox-
ylate radical (RCOO•) and cobalt(II) complex [24–26] in acidic aqueous solution.
A homolytic bond fission mechanism for the charge transfer to the metal-excited
state is generally proposed for the photochemical reactions of all the carbox-
ylatopentaamminecobalt(III) complexes. This involves a one-electron transfer from
the carboxylate ligand to the central cobalt(III) metal ion, leading to a reduced
species producing cobalt(II) ions and oxidized ligand radicals. The typical
absorption spectral changes are shown in Fig. 2. The photoproducts were analyzed
by various spectral techniques.
Quantum yield of cobalt(II) ion formation
The photolysis of cobalt(III) complexes in acidic aqueous solution in the LMCT
band leads to the formation of cobalt(II) ions, and the amount of cobalt(II) ions
formed on photolysis was determined by Kitson’s method by complexing it with
ammonium thiocyanate. The quantum yield values of cobalt(II) ion formation on
254-nm irradiation of carboxylatopentaamminecobalt(III) complexes 1 and 2 are
given in Table 1, and the plots of absorbance versus time are shown in Fig. 3. The
123

K. Jothivenkatachalam et al.
Fig. 5 The gas chromatography/mass spectrometry (GC-Mass) spectrum of organic product from
[Co(NH3)5It]2? ions in methanol
linear plot observed shows that no significant secondary photolysis occurs under
these conditions.
Analysis of photoproduct from complex 1
The absorption maximum for the photoproduct is observed at 270 nm. The emission
maximum observed at 420 nm is shown in Fig. 4.
123

Cobalt(III) complexes of unsaturated carboxylic acids
Fig. 6 The fluorescence emission decay profile of organic photoproduct excited at 375 nm
1
IR (KBr, cm-1): 1,700 (–C=O stretching). H NMR (300 MHz, D2O, d/ppm):
2.32 (–CH2–), 5.92 (d, 44, j = 3 Hz) olefinic protons and acid protons are
exchanged with D2O. 13C-NMR (300 MHz, D2O, d/ppm at 5 ꢁC): 178 (acidic
carbons), 133.48, 129.08 (olefinic carbons), and 39.4 (aliphatic carbons).
The GC-Mass spectrum of the photoproduct was recorded using methanol as the
solvent, and the relative mass intensity is shown in Table 2. The GC trace of the
compound shows two major compounds at retention periods (rt) of 33.28 and 33.92,
as shown in Fig. 5. This indicates the presence of two major compounds in the
organic photoproduct. From the GC-Mass spectra, it is confirmed that the
photoproduct is a mixture of isomers. The mass spectra of the compound showed
a molecular ion peak at m/z 152.
The lifetime of the emissive excited state of the compound was measured by
exciting at 295 nm and monitoring the emission at 420 nm. The emission decay
profile does not fit a single exponential and fits to the biexponential with lifetimes of
1.5 0.1 and 5.5 0.5 ns, respectively. This observation, again, supports the
presence of two products that have similar character in the excited state emission.
The fluorescence emission decay profile of organic photoproduct of complex 1
excited at 375 nm is shown in Fig. 6.
From the above spectral studies, a mechanism is proposed for the formation of
photoproduct (IT 4), as shown in Scheme 2. The primary photoproduct A
123

K. Jothivenkatachalam et al.
2+
O
CH2
IT 2
(NH3)5Co OC
.
hv, 254 nm
H2O, H+
+
COO
5 NH4
CH2
Co (II)
+
+
HOOC
HOOC
CH2
CH2
.
CO
-
COO
2+
2
.
HOOC
HOOC
CH2
IT 3
IT 2
O
CH2
CH2
CH2
IT 3
(NH3)5Co OC
+
+
COOH
+
CH2
+ 5 NH4
CO2
.
HOOC
HOOC
HOOC
IT 1
CH2
Co (II)
+
CH2
IT 4
CH2
COOH
CH2
.
HOOC
HOOC
CH2
2
IT 3
IT 4
C
H
CH2
3
COOH
COOH
CH2
HOOC
HOOC
C
H
3
A
B
Scheme 2 Formation of photoproduct from complex 1
isomerizes to structure B to give a signal at m/z 138, due to the loss of H• and CH3•
from M? •
.
From the Scheme 2, it is inferred that the luminescent photoproduct is a
conjugated molecule with olefinic groups. The presence of the carbonyl absorption
in the 13C NMR spectrum and a band at 1,700 cm-1 in the IR spectrum confirms the
presence of a carbonyl group. The formed photoproduct is stable at low temperature
and the proton NMR spectrum of the compound at room temperature showed
additional peaks, which confirm that the photoproduct had undergone
decomposition.
Analysis of photoproduct from complex 2
After continuous photolysis of complex 2, the separated photoproduct was analyzed
by the spectral methods. The organic photoproduct dissolved in methanol was
analyzed by the GC-Mass spectral method. In GC, the major peak was obtained with
123

Cobalt(III) complexes of unsaturated carboxylic acids
Fig. 7 The GC-Mass spectrum of organic product from [Co(NH3)5SR]2? ions in methanol
the retention period (rt) of 10.25, whereas the other peaks were of low intensity and
the corresponding mass spectrum of the major peak is given in Fig. 7. In this case
also, the major GC-Mass peaks are considered for detailed interpretation. The
123

K. Jothivenkatachalam et al.
O
2+
hv 254 nm
H2O H+
O
.
+
(H3N)5 Co
+
Co(II)
+
5 NH4
O
O
SR 2
SR 1
O
O
O
.
O
2
O
O
SR 3
+ 2 H2O
O
O
O
OH
O
OH
SR 4
A
Scheme 3 Formation of photoproduct from complex 2
relative intensity of the mass peaks is given in Table 2 and the fragmentation
schemes are given in supplementary material S2. The structure of the photoproduct
was also confirmed by IR spectra and NMR spectra.
IR (KBr, cm-1): 1724, 1,709 (–C=O stretching), and 1,637 (–C=C–H stretching),
1,430 (C–H bending vibration CH3), 3,050–3,500 (C–H stretching vibrations CH3
and O–H stretching vibrations, broad signal).
1H NMR (300 MHz, D2O, d/ppm): 6.21–7.98 (m, olefinic protons), 1.23 and 1.87
(d, CH3). The methylene protons and methyne protons appear as multiplets in the
respective regions. 13C-NMR, the compound ‘‘SR 4’’ shows peaks for two carbonyl
carbons at d 195.65 and 198.29. Eight olefinic carbons appear in the olefinic region
separately. The methyl, methylene, and methyne carbons appear in the respective
regions d 17.57, 21.73, 23.25, 58.31, and 58.49. From the above spectral studies, the
structure of the photoproduct is confirmed as SR 4. Based on the spectral analysis,
Scheme 3 has been proposed for the structure of the major compound SR 4.
In Scheme 3, the two sorbato carboxyl radicals undergo dimerization reaction
before the loss of carbon dioxide to form the compound SR 3. This compound
abstracts OH• radical from the solvent. This abstracted OH• radical attacks the
double bond conjugated to the carbonyl group at the a-position, thereby generating a
radical in the b-carbon. The new radical abstracts CH3–CH=CH–CH=CH• radical
formed from sorbatocarboxylic radical after the elimination of carbon dioxide
molecules. The addition of water is subjected to the d-carbon. The mass spectra
illustrate that the addition of water takes place on the d-carbon based on the mass
unit m/z 309 signal. Hence, the proposed structure of the major compound (SR 4)
‘‘A’’ is named as 7,8-dioxahexadeca-4,12,14-trien-6,9-dione.
123

Cobalt(III) complexes of unsaturated carboxylic acids
Conclusion
The photolysis of carboxylatopentaamminecobalt(III) complexes in their LMCT
band results in the reduction of the cobalt(II) ions and the oxidation of ligand
carboxyl radicals. This work gives evidence that the two possible mechanisms for
the formation of photoproduct from carboxyl radicals depends on the nature of the
coordinating ligand. In the case of complex 1, the photoproduct is suggested to form
as a result of photochemical reactions of cobalt(III) ammine complex with
carboxylate ligand, showing decarboxylation of the coordinated ligand from the
CTTM excited state and the resulting free radicals produce interesting photoprod-
ucts. But for complex 2, the photoproduct was formed as the result of dimerization
of carboxyl radicals. This is the first report where dimerization of the carboxyl
radical has been observed.
The observation of the difference in the photoproducts formed from complexes 1
and 2 is attributed to the stabilization of the carboxyl radicals by the presence of the
olefinic bonds in the neighboring carbons. Itaconic acid is a non-fluorescent
compound of importance in the polymer industry as a monomer. At present, no
synthetic derivative of itaconic acid is known as a fluorescent molecule. However, it
has been reported more recently that a long-chain fluorescent derivative of itaconic
acid has been isolated as a fungal metabolic product [27, 28]. The fluorescence
spectrum of the photoproduct shows a similar spectrum of the existing metabolite.
Acknowledgments This work was supported by a grant from the Department of Science and
Technology (DST), Government of India, New Delhi, Sanction No. SR/FT/CS-042/2008.
References
1. K.K. Rohatgi-Mukherjee, Fundamentals of Photochemistry (Wiley Eastern Limited, New Delhi,
1986), p. 235
2. D.A. Braden, E.E. Parrack, D.R. Tyler, Coord. Chem. Rev. 277, 279 (2001)
3. G. Stochel, A. Wanat, E. Kulis, Z. Stasicka, Coord. Chem. Rev. 171, 203 (1998)
4. C.A. Otter, R.M. Hartshorn, Dalton Trans. 1, 150 (2004)
5. A.L. Poznyak, V.I. Pavlovskii, L.V. Stopolyanskaya, Russ. J. Coord. Chem. 35, 101 (2009)
6. H. Kunkley, A. Vogler, J. Photochem. Photobiol. A 151, 45 (2002)
7. R.B. Jordan, Reaction Mechanisms of Inorganic and Organometallic Systems (Oxford University
Press, New York, 2007)
8. S.K. Weit, C. Kutal, Inorg. Chem. 29, 1455 (1990)
9. S.K. Weit, G. Ferraudi, P.A. Grutsch, C. Kutal, Coord. Chem. Rev. 128, 225 (1993)
10. E. Natarajan, P. Natarajan, Inorg. Chem. 31, 1215 (1992)
11. K. Subramani, V.S. Srinivasan, Indian. J. Chem. 28A, 378 (1989)
12. R.M. Hartshorn, S.G. Telfer, J. Chem. Soc. Dalton. Trans. 9, 2801 (2000)
13. R.M. Hartshorn, S.G. Telfer, J. Chem. Soc. Dalton. Trans. 18, 3217 (1999)
14. D.M. Tonei, L.-J. Baker, P.J. Brothers, G.R. Clark, D.C. Ware, Chem. Commun. 23, 2953 (1998)
15. C. Busset, P. Mazellier, M. Sarakha, J.D. Laat, J. Photochem. Photobiol. A 185, 127 (2007)
16. M.A. Ilyushin, M.A. Aleksandrova, I.V. Bachurina, A.V. Smirnov, I.V. Tselinskii, Russ. J. Appl.
Chem. 83, 92 (2010)
17. A.L. Poznyak, V.I. Pavlovski, Angew. Chem. Int. Ed. Engl. 27, 789 (1988)
18. A.M. Braun, M.T. Maurette, E. Oliveros, Photochemical Technology, Chap. 2 (Wiley: Chichester,
1991)
123

K. Jothivenkatachalam et al.
19. S.L. Murov, I. Carmichael, G.L. Hug, Handbook of Photochemistry, Chap. 13 (Marcel Dekker, New
York, 1993)
20. H.J. Kuhn, S.E. Braslavsky, R. Schmidt, Pure Appl. Chem. 76, 2105 (2004)
21. O. Horvath, K.L. Stevenson, Charge-Transfer Photochemistry of Coordination Compounds (VCH,
New York, 1993)
22. D.M. Roundhill, Photochemistry and Photophysics of Metal Complexes (Plenum Press, New York,
1994)
23. M. Montalti, A. Credi, L. Prodi, M.T. Gandolfi, Handbook of Photochemistry (Taylor & Francis
Group, Boca Raton, 2006), p. 601
24. H. Kawaguchi, M. Yoshida, T. Yonemura, T. Ama, K. Okamoto, T. Yasui, Bull. Chem. Soc. Jpn. 68,
874 (1995)
25. J.C. Scaiano, W.J. Leigh, G.J. Ferraudi, Can. J. Chem. 62, 2355 (1984)
26. A.L. Poznyak, V.E. Stelmashok, Inorg. Chim. Acta 83, L59 (1984)
27. M. Enoki, T. Watanabe, Y. Honda, M. Kuwahara, Chem. Lett. 29, 54 (2000)
28. S. Jung, S.E. Lowe, R.I. Hollingsworth, J.G. Zeikus, J. Biol. Chem. 268, 2828 (1993)
123