Structure and properties of a series of 2-cinnamoyl-1,3-indandiones and their metal complexes

Article abstract of DOI:10.1007/s13738-011-0024-9

A series of seven 2-cinnamoyl-1,3-indandiones and their metal(II) complexes were synthesized and characterized by means of spectroscopic (IR, NMR, electron absorption and emission spectroscopy) and/or single-crystal X-ray diffraction methods. The optical

Full text of DOI:10.1007/s13738-011-0024-9

J IRAN CHEM SOC (2012) 9:297–306
DOI 10.1007/s13738-011-0024-9
ORIGINAL PAPER
Structure and properties of a series of 2-cinnamoyl-1,3-
indandiones and their metal complexes
•
Anife Ahmedova Petja Marinova
•
•
Gordana Pavlovic Maya Guncheva
•
´
•
Neyko Stoyanov Mariana Mitewa
Received: 24 June 2011 / Accepted: 19 August 2011 / Published online: 3 January 2012
ꢀ Iranian Chemical Society 2011
Abstract A series of seven 2-cinnamoyl-1,3-indandiones
and their metal(II) complexes were synthesized and char-
acterized by means of spectroscopic (IR, NMR, electron
absorption and emission spectroscopy) and/or single-crys-
tal X-ray diffraction methods. The optical spectra of the
organic compounds show very strong absorption in the
visible region and weak fluorescence with moderate to
strong Stokes shift. The effect of concentration, water
addition and metal ion complexation on the optical prop-
erties was also studied. In search of potential practical
application, the complexation of 2-cinnamoyl-1,3-indan-
diones with metal(II) ions was investigated. A series of
non-charged complexes with Cu(II), Cd(II), Zn(II), Co(II)
and Ni(II) was isolated and analyzed by elemental analyses
and IR. Most of the complexes show presence of water
molecules, most probably coordinated to the metal ion,
thus forming octahedral geometry. For the paramagnetic
Cu(II) complexes a distorted, flattened tetrahedral structure
is proposed, basing on the EPR data. The optical properties
of the metal complexes, however, do not differ appreciably
from those of the free ligands.
Keywords Indan-1,3-dione ꢀ Crystal structure ꢀ
Optical properties ꢀ Metal complexes
Introduction
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-011-0024-9) contains supplementary
material, which is available to authorized users.
The 2-substituted 1,3-indandiones show interesting photo-
physical properties and therefore were continuously the
subjects of intense experimental and theoretical studies [1–
5]. Intramolecular isomerization, electron and/or proton-
transfer processes are responsible for most of the observed
optical properties and potential applications of these
compounds [6–8]. The 1,3-indandione fragment is a very
strong electron acceptor and coupling with electron
donating substituents modulates the photophysical proper-
ties of the so-formed dipolar ‘‘push–pull’’ molecules.
Excited state twisting was observed in N,N-dimethylamino-
benzylidene-1,3-indandione [3, 5, 9] and its solid-state
optical properties were studied in details [5, 10] with
respect to the potential application of its derivatives in non-
linear optics [2]. On the other hand, derivatives possessing
intramolecular hydrogen bond, such as 2-acyl-1,3-indan-
diones, were investigated for possible tautomeric equilibria
in ground or excited states [11–13]. In most of the cases
the fundamental findings on the structural and optical
A. Ahmedova (&) ꢀ M. Mitewa
Faculty of Chemistry, University of Sofia, 1,
J. Bourchier av., 1164 Sofia, Bulgaria
e-mail: ahmedova@chem.uni-sofia.bg
P. Marinova
Faculty of Chemistry, University of Plovdiv, 24, Tzar Assen str.,
4000 Plovdiv, Bulgaria
´
G. Pavlovic
Laboratory of General Chemistry, Department of Applied
Chemistry, Faculty of Textile Technology, University of Zagreb,
´
Prilaz baruna Filipovica 28a, HR-10000 Zagreb, Croatia
M. Guncheva
Institute of Organic Chemistry and with Centre of
Phytochemistry, Bulgarian Academy of Sciences,
Acad. G. Bonchev str. bl.9, Sofia 1113, Bulgaria
N. Stoyanov
Rousse University, Technological Branch, Razgrad, 3,
Aprilsko vastanie str., 7200 Razgrad, Bulgaria
123

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J IRAN CHEM SOC (2012) 9:297–306
properties of these compounds led to their practical appli-
cations; the suggested fast and reversible tautomerization
of 2-acetyl-1,3-indandione, 2AID [11] for example, gave
the first indication that this compound should be photo-
stable upon UV irradiation. Later this was experimentally
proven and showed that 2AID has much higher photosta-
bility than the widely used sunscreens in practice such as
benzophenone-3 and octylmethoxycinnamate [7]. More-
over, we also found that the Zn(II) and Cu(II) complexes of
2AID show even better photostability in the hydrogen-bond
breaking solvent DMSO, which allowed us to propose
them as promising sunscreen agents, too [7].
compounds and the way they are affected by the structure,
solvent, concentration and metal ion complexation.
Experimental part
X-ray diffraction and spectroscopic experiments
The single-crystal X-ray and general data for structure 4
are reported in Table 1. The data collection was performed
on an Oxford Xcalibur Nova with CCD detector with
graphite-monochromated CuKa radiation at ambient tem-
perature using x-scans. Programs CrysAlis CCD and
CrysAlis RED (Version 1.171.32.29) [28] were employed
The strong chelation ability of 2-acyl-1,3-indandiones,
in addition to the diversity of their optical properties,
opened up a new door for searching potential application of
their metal complexes. There are several suggestions for
using 2-acyl-1,3-indandiones as extraction agents for metal
ions [14–16] or their evaluation as optical sensors for metal
ions [17–19]. Recently, we started a detailed study of the
structural, optical, and complexation properties of 2AID
[20–22] and its derivatives containing extended p-conju-
gated system [23–26].
Table 1 General and crystal data and summary of intensity data
collection and structure refinement for compound 4
Compound
4
Formula
C19H14O3
Mr
290.30
Crystal system, color and habit
Monoclinic, orange, prism
P 21/c
In this study, we describe the structural and optical
properties of a series of 2-cinnamoyl-1,3-indandiones with
a common structure depicted in Fig. 1. The synthesis,
spectroscopic and complexation properties of compounds 1
and 2 have been described elsewhere [23, 24]. The
molecular and crystal structure of compound 7 is known
since 1980 [27]. Presently, the crystal structure of com-
pound 4 was solved from single-crystal X-ray diffraction
data and will be compared with the available data for
similar compounds. Metal complexes of compounds 3–7
with Cu(II), Zn(II), Co(II), Ni(II) and/or Cd(II) were also
synthesized and investigated by means of various experi-
mental methods. The main focus of this work is the optical
(absorption and emission) properties of the studied
Space group
Crystal dimensions (mm3)
Unit cell parameters:
0.24 9 0.19 9 0.11
˚
a (A)
6.9931 (1)
˚
b (A)
12.5465 (1)
˚
c (A)
17.0219 (2)
a/ꢁ
b/ꢁ
c/ꢁ
–
101.1202 (12)
–
3
˚
V (A )
1465.44 (3)
Z
4
Dc (g cm-3
T/K
)
1.316
296
l (mm-1
)
0.718
F (000)
608
h range for data collection (ꢁ)
h, k, l range
4.4–72.5
-7 to 8, -14 to 15, -21 to 20
Scan type
x
No. measured reflections
No. independent reflections (Rint
12,926
)
2,910 (0.023)
No. observed reflections, I C 2r(I) 2,503
No. refined parameters/restraints
g1, g2 in w
205/0
0.0691, 0.1667
0.0402, 0.1178
0.0455, 0.1217
1.06
R, wR [I C 2r(I)]
R, wR [all data]
Goodness of fit on F2, S
Extinction coefficient
0.0009 (6)
0.14, -0.13
0.001
-3
)
˚
Max., min electron density (e A
Maximum D/r
Fig. 1 Structure of the studied 2-cinnamoyl-1,3-indandiones
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J IRAN CHEM SOC (2012) 9:297–306
299
for data collection, cell refinement and data reduction. The
Lorentz-polarization effect was corrected and the diffrac-
tion data have been scaled for absorption effects by the
multi-scanning method.
DRX-250 spectrometer operating at 250.13 MHz for
1H- and 62.90 MHz—for the 13C-nuclei. The chemical
shifts are related to TMS used as reference. The EPR
spectra were recorded on a Bruker B-ER 420 spectrometer
at 293 K.
The structure was solved by direct methods and refined
on F2 by weighted full-matrix least-squares. All non-
hydrogen atoms were refined anisotropically. Hydrogen
atoms were placed in geometrically idealized positions
The photostability assessment of compounds 1 and 5
was performed with a medium-pressure mercury lamp,
transmitting light between 250 and 450 nm. To remove IR
rays, the light was filtered through a saturated solution of
CuSO4 in 5 cm long quartz cell. Irradiation was performed
on ethanol solutions in fluorimetric quartz cells, well sealed
to prevent evaporation at room temperature. The UV–vis
absorption spectra were recorded during the irradiation at
different time intervals.
3
2
˚
˚
[Csp -H 0.96 A, Csp -H 0.93 A with Uiso(H) = 1.5 or
1.2 Ueq (C)] and were constrained to ride on their parent
atoms using the appropriate SHELXL97 HFIX instructions.
The hydrogen atom which belongs to hydroxyl group in 4
˚
is found in difference Fourier maps at distances 0.93(2) A
and was refined freely. Calculations were performed with
programs SHELXS97 [29] and SHELXL97 [29] both
integrated in the WinGX program package [30]. The
molecular geometry calculations were done using PLA-
TON [31] and the molecular graphics were done with
ORTEP-3 [32], and Mercury [33].
Synthesis and characterization
Compounds 1–7 were obtained by refluxing 4.7 g
(0.025 mol) 2-acetyl-1,3-indandione, 0.05 mol of the cor-
responding aldehyde (1, benzaldehyde; 2, p-fluoro-benz-
aldehyde; 3, p-chloro-benzaldehyde; 4, p-methyl-benz-
aldehyde; 5, p-cyano-benzaldehyde; 6, p-methoxy-benzal-
dehyde; 7, p-dimethylamino-benzaldehyde) in presence of
0.012 mol piperidine for 1 h. To the formed polycrystalline
precipitate 50 cm3 ethanol was added and the reaction
mixture was boiled for a half hour more. After cooling
down the formed crystals were filtrated and repeatedly
washed with ethanol. The filtrate was further diluted with
water, acidified and the additionally formed amount of the
product was collected. The total amount of the products
were recrystalized from ethanol.
The main geometrical features along with hydrogen
bond geometry for compound 4 are given in Table 2.
The IR spectra were recorded on a Specord 75-IR
(Carl-Zeiss, Jena, Germany) in Nujol mulls. Elemental
analyses were performed on a Vario EU III instrument.
The UV–vis absorption spectra were recorded on a
JASCO V-570-UV/Vis/NIR. Fluorescence spectra were
obtained using a Perkin-Elmer LS-5 and a Varian Eclipse
fluorometers. All solvents were of spectroscopic grade
and were used without further purification. Acetonitrile
was dried over P2O5 and freshly distilled before use. The
NMR spectra were recorded in CDCl3 using a Bruker
˚
˚
Table 2 Selected interatomic distances (A) and valence angles (ꢁ) as well as hydrogen bond geometry (A, ꢁ) for the compound 4
Bond distances
Bond angles
O1–C9
1.217 (2)
1.232 (2)
1.326 (2)
1.450 (2)
1.468 (2)
1.377 (2)
1.439 (2)
1.337 (2)
1.457 (2)
C2–C1–C6
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C1–C6–C5
117.7 (1)
121.3 (1)
121.3 (1)
117.6 (1)
121.2 (1)
120.9 (1)
O2–C7
O3–C10
C7–C8
C8–C9
C8–C10
C10–C11
C11–C12
C12–C13
Hydrogen bond geometry
D–HꢀꢀꢀA
D–H
HꢀꢀꢀA
DꢀꢀꢀA
\D–HꢀꢀꢀA
Symmetry code
O3–H1O3ꢀꢀꢀO2
C3–H3ꢀꢀꢀO2
C15–H15ꢀꢀꢀO1
C17–H17ꢀꢀꢀO1
0.93 (2)
0.93
1.80 (2)
2.610
2.625 (1)
3.302 (2)
3.296 (2)
3.296 (2)
147 (2)
132
–
-x ? 1, y ? 1/2, -z ? 1/2 ? 1
-x, y-1/2, -z ? 1/2
-x, -1/2 ? y, 1/2-z
0.93
2.556
137
0.93
2.560
137
123

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J IRAN CHEM SOC (2012) 9:297–306
Synthesis of the metal complexes of compounds 3–7
Compound 1; 2-[1-hydroxy-3-phenyl-allylidene]-in-
dan-1,3-dione, Yield 70%, M.p. 186 ꢁC (Ref. [26]
186–187 ꢁC); the IR and NMR spectral data were also
found to be identical with the one described in Ref. [26].
Compound 2; 2-[1-hydroxy-3-(4-fluoro-phenyl)-ally-
lidene]-indan-1,3-dione, Yield 79%, M.p. 205 ꢁC. (Ref.
[23] 205–206 ꢁC); all the spectral data are identical with
the one described in Ref. [23].
All metal complexes were obtained after mixing methanol
solutions of the corresponding metal acetates and the cor-
responding ligands, compounds 3–7, dissolved in dioxane,
in metal-to-ligand ratio 1:2. Non-charged complexes were
formed as precipitates, which were further filtrated,
repeatedly washed with ethanol, and dried over P4O10 for
2 weeks. Elemental analyses data were found to be in good
agreement ( 0.5%) with the calculated values and are
provided in the Supplementary material along with the IR
data for the complexes.
Compound 3; 2-[1-hydroxy-3-(4-chloro-phenyl)-allylid-
ene]-indan-1,3-dione, Yield 79%, M.p. 200–201 ꢁC. Anal.
Found, %: C, 69.05; H, 3.55; Calc. for C18H11ClO3, %: C,
69.58; H, 3.57. IR (Nujol) m, cm-1: broad 3,450 (mO–H), 1,700
(mC=O), 1,650 (mC=O, mC=C), 1,630 (mC=O, mC=C, (Ph)), 1,590 (mC=O
C=C, (Ph)), 1,560 (mC=O, mC=C, (Ph)), 985 (c=C–H), 810 (cAr–H).
Compound 4; 2-[1-hydroxy-3-(4-methyl-phenyl)-ally-
,
m
Results and discussion
lidene]-indan-1,3-dione, Yield 96%; M.p. 181–182 ꢁC.
Anal. Found, %: C, 79.04; H, 4.96; Calc. for C19H14O3%:
C, 78.60, H, 4.86. IR (Nujol) m, cm-1: 3,500 (mO–H), 1,700
Synthesis and structures
(mC=O), 1,650 (mC=O, mC=C), 1,630 (mC=O, mC=C), 1,595 (mC=O
C=C, (Ph)), 1,580 (mC=O, mC=C, (Ph)), 1,545 (mC=O, mC=C, (Ph)),
990 (c=C–H), 835 (cAr–H).
Compound 5; 2-[1-hydroxy-3-(4-cyano-phenyl)-allylid-
ene]-indan-1,3-dione, Yield 65%; M.p. 193–194 ꢁC. Anal.
Found, %: C, 75.90; H, 3.68; N, 4.52. C19H11O3N. Calc., %:
C, 75.74; H, 3.68; N, 4.65. IR (Nujol) m, cm-1: 3,400 broad
,
Compounds 1–7 were obtained in good yields according to a
previously described procedure [34], namely by condensa-
tion of 2AID with the corresponding benzaldehyde in
presence of piperidine. All compounds were characterized
with M.p., FT-IR and elemental analyses. NMR spectros-
copy (1H and 13C) was used for the compounds well soluble
in DMSO. The synthesis and characterization of compounds
1 and 2 have been reported elsewhere [23, 26]. The 2-acyl-
1,3-indandiones are known to exist in their exocyclic enolic
form, as depicted in Fig. 1, stabilized by the presence of
intramolecular hydrogen bond. Such enolic group is seen in
the 1H NMR spectra, showing a resonance peak in the range
of 11.2–13.2 ppm, and a broad band in the IR spectra of the
m
(mO–H), 2,220, 1,700 (mC=O), 1,650 (mC=O, mC=C), 1,620 (mC=O
,
mC=C), 1,580 (mC=O, mC=C, (Ph)), 1,570 (mC=O, mC=C, (Ph)), 1,550
(mC=O, mC=C, (Ph)), 1,320 (mN–Ar), 1,285 (dOH), 1,150 (dCH),
985 (c=C–H), 820 (cAr–H), 780 (cAr–H).
Compound 6; 2-[1-hydroxy-3-(4-methoxy-phenyl)-ally-
lidene]-indan-1,3-dione, Yield 98%; M.p. 192–193 ꢁC.
Anal. Found, %: C, 74.36; H, 4.84. Calc. for C19H14O4, %:
C, 74.49; H, 4.61. IR (Nujol) m, cm-1: 3,500 (mO–H), 1,700
studied compounds, at ca. 3,200 cm-1
.
Good quality single crystals were obtained from
compound 4 by slow evaporation of a saturated ethanol
solution. The crystal structure of 4 was solved from single-
crystal X-ray diffraction data and is depicted in Fig. 2a. It
confirms that the compound exists in the exocyclic enolic
form. Selected geometrical parameters are listed in
Table 2. The structure has trans configuration regarding
spatial orientation of substituents at the central C11=C12
double bond of allylidene moiety. The molecule is not
planar; the dihedral angle between the 1,3-indandione
fragment and the phenyl plane is 11.34(7)ꢁ. Planarity of the
1,3-indandione moiety is confirmed by the dihedral angle
of 1.21(7)ꢁ between benzene and cyclopentane ring planes
in 4. Keto oxygen atoms O(1) and O(2) deviate insignifi-
cantly from the cyclopentane ring plane in opposite
(mC=O), 1,640 (mC=O, mC=C), 1,610 (mC=O, mC=C), 1,595 (mC=O
C=C, (Ph)), 1,570 (mC=O, mC=C, (Ph)), 1,540 (mC=O, mC=C, (Ph)),
1,250 (maCs–O–C), 980 (c=C–H), 810 (cAr–H).
,
m
Compound 7; 2-[1-hydroxy-3-(4-dimethylamino-phe-
nyl)-allylidene]-indan-1,3-dione, Yield 60%; M.p. 214–
215 ꢁC. Anal. Found, %: C, 75.11; H, 5.30; N, 4.68. Calc.
for C20H17NO3; %: C, 75.22; H, 5.37; N, 4.39. IR (Nujol)
m, cm-1: 3,400–3,500 (mO–H, mNH), 1,700 (mC=O), 1,635
(mC=O, mC=C), 1,630 (mC=O, mC=C), 1,590 (mC=O, mC=C, (Ph)),
1,570 (mC=O, mC=C, (Ph)), 1,560 (mC=O, mC=C, (Ph)), 1,550
(mC=O, mC=C, (Ph)), 1,515 (dCH ), 1,300 (mN–Ar), 1,280 (dOH),
3
1,230 (mN–C), 1,150 (dCH), 985 (c=C–H), 850 (cAr–H), 800
1
(cAr–H). H-NMR (CDCl3), d [ppm]: 11.7 (s, 1H), 7.8–7.9
(m, 2H), 7.7–7.8 (m, 4H), 7.5–7.7 (m, 4H), 2.8–3.2 (m,
6H). 13C-NMR (CDCl3), d [ppm]: 197.36 (C7), 188.99
(C9), 174.28 (C10), 152.50 (C16), 146.36 (C11), 140.79
(C6), 138.71 (C5), 134.28 (C3), 133.48 (C2), 131.51 (C12),
122.58 (C13), 122.12 (C1), 121.76 (C4), 111.79 (C14,
C18), 111.71 (C15, C17), 106.38 (C8), 40.10 (CH3).
˚
directions by 0.005(1) and -0.027(1) A, respectively.
The enol form is stabilized by the resonance-assisted
intramolecular hydrogen bond (RAHB) [35, 36] of the O–
HꢀꢀꢀO type with expected geometry (OꢀꢀꢀO distance is
˚
2.625(1) A and O–HꢀꢀꢀO angle is 147(2)ꢁ; Table 2). The
123

J IRAN CHEM SOC (2012) 9:297–306
301
Fig. 2 ORTEP drawing of 4
with the atom numbering
scheme. The thermal ellipsoids
are drawn at the 50%
probability level at 296 K (a);
crystal packing of 4 with zigzag
chains of R(32) rings viewed
down the a axis (b)
˚
˚
pseudoaromatic six-membered ring is formed. The RAHB
forms well-recognized supramolecular synthon described
by the graph-set analysis as the S(6) type. The geometry of
RAHB is comparable with those found in 2-(1-hydroxy-
3-thiophen-3-yl-allylidene)-1,3-indandione [26] and
2-(3-furan-2-yl-1-hydroxy-allylidene)-1,3-indandione [26],
i.e., the geometry of RAHB is not influenced by the type of
the substituent.
(2) A]. On the contrary, the O(3)–C(10) bond (1.326(2) A;
Table 2), has a character of r Car–OH bond such as that
found in phenols [37]. Such molecular geometry of the
b-diketone fragment in 4 is in agreement with that found in
similar 1,3-indandione and indan-1-one derivatives such
as 2-pivaloyl-1,3-indandione [38], 2-acetyl-1,3-indandione
[39], 2-(hydroxy(amino)methylidene)-1,3-indandione [12],
2-(1-hydroxy-3-thiophen-3-yl-allylidene)-1,3-indandione
[26] and 2-(3-furan-2-yl-1-hydroxy-allylidene)-1,3-indandi-
one [26] and 2-acylindan-1-one [40].
The participation of the keto O(2)–C(7) group in RAHB
formation has reflection on O(2)–C(7) bond distance value
(elongation) in relation to the keto O(1)–C(9) bond distance
Flattening of the b-diketone fragment is accompanied by
the conjugation within the 1,3-indandione moiety and with
˚
[O(1)–C(9) equal to 1.217(2) A and O(2)–C(7) of 1.232
123

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J IRAN CHEM SOC (2012) 9:297–306
the allylidene part of the molecule. Therefore, shortening
of the single C–C bonds and elongation of the double C=C
bonds in the conjugated chain of the allylidene moiety in 4
is observed; C(8)–C(10) and C(11)–C(12) bond distances
˚
amount to 1.376(2) and 1.337(2) A, while C(10)–C(11) and
˚
C(12)–C(13) bond distances are 1.439(2) and 1.456(2) A;
either in ground or excited state, on one hand, and strong
coordination ability with metal ions—on the other.
Therefore, we studied thoroughly the optical properties of
the compounds as well as their metal complexes. The
complexation properties of compounds 1 and 2 were
described earlier [23, 24], so we focused on compounds
3–7 and their complexes with metal(II) ions. The purpose
was to obtain initial information about the composition and
structure of the formed metal complexes prior searching for
potential practical applications. All complexes were iso-
lated as amorphous precipitates and have rather poor sol-
ubility in the most common organic solvents, except for
strongly coordinating solvents such as DMSO and DMF.
Therefore, the complexes were characterized mainly with
IR spectra in solid and qualitative absorption spectra in
DMSO.
respectively (Table 2).
The five-membered indane ring deformation reveals
general shortening of endocyclic C–C ring bonds in rela-
˚
tion to those in cyclopentane ring itself (C–C 1.543 A) [37]
2
2
˚
and are close to the C(sp )–C(sp ) bond length (1.474 A)
[37] with the pronounced conjugation of shorter and longer
˚
C–C bonds; C(7)–C(8) equal to 1.450(2) A and C(8)–
˚
C(9)—1.468(2) A; Table 2.
The crystal packing in 4 and intermolecular interactions
are presented in Fig. 2b. The molecules are linked by C–
HꢀꢀꢀO hydrogen bonds (Table 2) with phenyl CH groups
acting as proton donors and the keto O(1) and O(2)
atoms—as proton acceptors, thus producing zigzag chains
of R(32) rings running parallel to the b axis. Both atoms
O(1) and O(2) participate in intramolecular O–H…O type
of hydrogen bond and intermolecular C–H…O type of
hydrogen bond. There are no contacts and pꢀꢀꢀp stackings
between the chains except van der Waals’ interactions.
According to our experience with the structural prop-
erties of 2-acyl-1,3-indandiones conjugated with an aro-
matic ring via allylidene bridge, the molecular geometry
remains virtually the same changing the type of the aro-
matic or heterocyclic substituent [26]. What is affected is
the way of crystal packing and the intermolecular hydrogen
bondings. This can also be seen comparing the available
crystallographic data with the molecular structure of
compound 4, currently described. The enol form of com-
pound 4 is revealed in the crystalline state, similarly to
other 2-acyl derivatives, such as 2-pivaloyl-1,3-indandione
structure [38], 2-acetyl-1,3-indandione [39], 2-(hydroxy
(amino)methylidene)-1,3-indandione [12], 2-(1-hydroxy-3-
thiophen-3-yl-allylidene)-1,3-indandione [26], 2-(3-furan-
2-yl-1-hydroxy-allylidene)-1,3-indandione [26] and 2-(4-
dimethylamino-cinnamoyl)-1,3-indandione [27]. The
substituent in the benzene ring of compound 4 is a methyl
group and has no proton donor or acceptor and therefore it
is not surprising that there are no intermolecular interac-
tions in the crystal packing. As far as the molecular
structure is concerned, we expect that all other compounds
from the series have similar structure as compound 4, since
their spectroscopic characteristics are very similar. For all
compounds exocyclic enolic form is proposed with trans
configuration of the C(11)–C(12) double bond and s-trans
configuration of C(10)–C(11) bond, as depicted in Fig. 1.
The presence of intramolecular hydrogen bond and
b-diketone fragment in the structure of the compounds
implies a possibility for intramolecular proton transfer
The elemental analyses data show composition of the
complexes with 1:2 metal-to-ligand ratio. Coordination of
the 2-cinnamoyl-1,3-indandiones after deprotonation of the
enolic OH group is supposed after comparing the IR
spectra of the metal complexes with that of the free ligand.
The vibrational frequencies for the OH group are absent in
the spectra of the complexes. Thereby, the compounds 3–7
coordinate as bidentate monoanion ligands forming
6-membered chelate ring with the metal ion. More com-
plicated are the analyses of the IR spectra of the complexes
where water molecules are present in the composition of
the complexes. However, based on our previous studies on
the structure of metal complexes of 2-acetyl-1,3-indandi-
one [20, 22], it is supposed that the Zn(II), Cd(II), Co(II)
and Ni(II) complexes contain at least two water molecules,
axially coordinated to the metal center, and octahedral
structure of these complexes is suggested. This is not the
case for the Cu(II) complexes showing no presence of
water molecules in their IR spectra and confirmed by the
elemental analyses data. Additional information for the
Cu(II) complexes is obtained from their EPR spectra
recorded for powder samples at room temperature. The
estimated values of the g-factors are listed in Table 3. All
EPR spectra are characterized by axial anisotropy, except
Table 3 EPR parameters for the Cu(II) complexes of 1–7 obtained
for powder samples at ambient temperature
Complex
g\
gk
giso
1–Cu(II)
2–Cu(II)
3–Cu(II)
4–Cu(II)
5–Cu(II)
6–Cu(II)
7–Cu(II)
2.076
2.068
2.071
2.062
2.079
2.295
2.279
2.286
2.285
2.310
2.149
2.138
2.143
2.136
2.156
2.081
2.068
123

J IRAN CHEM SOC (2012) 9:297–306
303
Table 4 Absorption and
emission properties of
Solvent comp.
Acetonitrile
Absolute ethanol
DMSO
compounds 1–7 in various
solvents (excitation wavelength
is given in parentheses)
kabs
kemis
kabs
kabs
1
2
3
4
5
6
7
371, 385
510 (385)
513 (380)
512 (390)
500 (380)
510 (385)
494 (400)
588 (500)
372, 385
378, 391, 410 sh
376 sh, 391, 411 sh
380, 392, 414 sh
381 sh, 399, 419 sh
378, 390, 417 sh
415
370 sh, 387
373, 390, 408 sh
376, 392, 413 sh
371, 387, 409 sh
410
370, 390 sh
373, 390, 408 sh
375, 391, 414 sh
370, 386, 408 sh
415
500
503
519
Sh shoulder
for the Cu(II) complexes of compounds 6 and 7, which
show broad isotropic signal. No hyperfine structure due to
interaction with 63,65Cu nuclei is observed. The EPR data
are consistent with a d9 electronic structure of the metal
center in distorted tetrahedral environment.
Additional studies on the optical properties are per-
formed for some of the compounds regarding the effect of
concentration and water addition, as well as irradiation
with UV light. The absorption spectrum of compound 7 in
96% ethanol consists of a broad band with a maximum at
503 nm and a shoulder at 404 nm. Interestingly, changing
the concentration of the solution the relative intensity of
these bands changes as depicted in Fig. 3a. Reducing the
concentration 5 times the intensity of the band at 503 nm
rapidly decreases whereas the band at 404 nm becomes
Optical properties
The data from the absorption spectra of compounds 1–7, in
three different solvents, are summarized in Table 4. The
molar absorptivity of the studied compounds is relatively
high; 40,000–45,000 M-1 cm-1 and typical for p–p*
transitions. Increasing solvent polarity causes slight bath-
ochromic shift of the absorption maxima. The latter is
located at ca. 385 nm for compounds 1–5 in acetonitrile.
Increasing the electron donating strength of the substituent
in the benzene ring is reflected in an expected bathochro-
mic shift of the absorption maximum, as seen for com-
pounds 6 and 7. The qualitative absorption spectra of the
complexes were obtained in DMSO and show rather small
hypsochromic shifts compared with that of the free ligands
(ca. 20 nm, data not shown). The most intense absorption
bands actually correspond to the ligand’s transitions. Even
for the green-colored Cu(II) complexes, the broad band at
ca. 720 nm corresponding to the forbidden d–d-transitions
could be only seen in very concentrated DMSO solutions.
These data show that the intense ligands’ n–p* and p–p*
transitions dominate strongly in the absorption spectra of
the complexes. Besides, the position of the absorption
maxima are only slightly affected by the complexation with
the metal ions and therefore the studied compounds are not
appropriate for optical sensing of metal ions.
more pronounced; so that at concentration 1.3 9 10-5
M
both bands become of equal intensity. Such effect, but to a
much lesser extent, is observed also in absolute ethanol.
In this case, however, the shoulder at 404 nm is visible
only in solutions of very low concentration;
C \ 0.8 9 10-5 M (see Fig. 4). Obviously the presence
of the strong absorption band at 503 nm is sensitive not
only to the concentration of the solution, but also to the
presence of water. This effect is demonstrated through a
series of spectra of 7 in 96% ethanol with addition of
increasing amount of water and presented in Fig. 3b.
Compound 7 is characterized with a strong electron
delocalization between the conjugated strong electron
acceptor (the 1,3-indandione) and the strong electron
donor (the N,N-dimethylamino group) and high polarity
of the molecule is expected. Most probably possible
intermolecular interactions, such as dimerization and
water adduction, are competing processes leading to the
observed changes in the absorption spectra. Quantitative
estimation of these processes, however, is obscured by the
fact that the bands in the absorption spectrum are very
broad and may have composite structure (see Figs. 3, 4).
Obviously aggregation of neighboring molecules is highly
possible and has contribution to the long-wavelength band
in the spectrum. For accurate explanation of all these
effects on the absorption spectra of compound 7 more
sophisticated experimental studies would be required
including thorough theoretical investigation with an
explicit description of the solvent molecules. This is,
however, beyond the scope of the present work.
Steady-state fluorescence spectra of 1–7 in dry aceto-
nitrile are characterized by a broad and structureless
emission band. The observed Stokes shift is estimated to
about 120 nm for compounds 1–5 (see Table 4), and less
than 100 nm for compounds 6 and 7. These data imply
possible intramolecular isomerizations accompanying the
excitation of the molecule or strong electron redistribution
in excited state.
123

304
J IRAN CHEM SOC (2012) 9:297–306
Fig. 3 Effect of concentration
on the absorption spectra of
compound 7 in 96% ethanol
solution (a); effect of water
addition on the absorption
spectra of compound 7 in 96%
ethanol solution (b)
a
1,6
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
b
7 in EtOH
7 in EtOH + 6% water
7 in EtOH + 12% water
7 in EtOH + 18% water
300
400
500
600
700
800
Wavelength, nm
Similarly to the parent compound, 2AID, which is
characterized by very large Stokes shift in the fluorescence
spectra and high photostability, we did photostability
assessment of some of the compounds, namely 1 and 5.
The irradiation was performed with a mercury lamp at
room temperature. The absorption spectra were recorded at
different time intervals, and 2AID is used as a reference
compound with a proved high photostability [7]. The
spectra after 1 and 2 h of irradiation of ethanol solution of
compound 5 are presented in Fig. 5. For the sake of
comparison, the spectra for 2AID are given in the inset of
Fig. 5. The data show that after 1 h of irradiation with UV
light the intensity of the most intensive band in the spectra
of 1 and 5 is reduced by 10 and 16%, respectively. After
2 h of irradiation the intensity of 5 is further reduced with
7% more, while the spectrum of 1 remains unchanged. The
same experiment for 2AID confirmed our previous obser-
vation that its absorption spectrum remains virtually
unchanged; after 2 h of irradiation with UV light the
intensity is reduced by less than 4%. These data show that
123

J IRAN CHEM SOC (2012) 9:297–306
305
Fig. 4 Effect of concentration
on the absorption spectra of
compound 7 in absolute ethanol
(concentrations and cell lengths
given in the figure legend)
7 in 20 mm cell (0.8*10-5M)
7 in 10 mm cell (1.6*10-5M)
7 in 1 mm cell (1.6*10-4M)
1,0
0,8
0,6
0,4
0,2
0,0
200
300
400
500
600
700
λ [nm]
Fig. 5 Absorption spectra of
ethanol solution of compound 5
after 1 and 2 h of UV-
irradiation; analogous data for
2AID are given in the inset
compounds 1 and 5 are less photostable than 2AID. Similar
result is expected for the other compounds from the studied
series and their photostability was not studied.
earlier theoretical (quantum chemical) calculations of
possible isomerizations of similar 2-acyl-1,3-indandiones
in gas phase suggested that such processes would require
much higher energy and could not take place upon UV-
irradiation [26]. Therefore, it was proposed that the
observed large Stokes shift (ca. 100 nm) is caused most
probably by strong charge redistribution during the elec-
tronic transitions. Such explanation seems appropriate for
compounds 1–7, too. Moreover, the compounds having
strong electron-donating substituent in the cinnamoyl
All data for the optical and structural properties of
compounds 1–7 indicate for the possibility for several
photophysical phenomena. Firstly, the observed large
Stokes shift in the fluorescence spectra of compounds 1–7
rises the question of any intramolecular rearrangements
that could take place in excited state; such as ESIPT pro-
cess shown for 2AID [11], or cis–trans isomerizations. Our
123

306
J IRAN CHEM SOC (2012) 9:297–306
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shift in the absorption spectra as compared with compound
1 (see Table 4) and smaller Stokes shift in their fluores-
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contain both intramolecular hydrogen bonding and flexible
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transfer and cis–trans isomerization. According to the
photostability and the fluorescence data of compounds 1–7,
the former process most probably does not occur.
ˇ
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Acknowledgments Financial support by the Ministry of Science
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