Investigation of 9-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)-3,3-dimethyl-2,3,4,9-tetrahydro-1H-xanthen-1-one: Crystal structure, AIM and NBO analysis

Article abstract of DOI:10.1016/j.molstruc.2016.11.082

Single crystal X-ray analysis reveals that the 9-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)-3,3-dimethyl-2,3,4,9-tetrahydro-1H-xanthen-1-one, crystallizes in the centrosymmetric space group P2₁/c. In the crystal, molecules form as a dimer

Full text of DOI:10.1016/j.molstruc.2016.11.082

Journal of Molecular Structure 1133 (2017) 510e518
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Investigation of 9-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-
1-yl)-3,3-dimethyl-2,3,4,9-tetrahydro-1H-xanthen-1-one: Crystal
structure, AIM and NBO analysis
Mani Udayakumar a, Kothandapani Jagatheeswaran b, Subramaniapillai Selva Ganesan b,
Natarajan S. Venkataramanan c, Shankar Madan Kumar d, Kullaiah Byrappa e,
,
*
Subbiah Thamotharan a
a Biomolecular Crystallography Laboratory, Department of Bioinformatics, School of Chemical and Biotechnology, SASTRA University, Thanjavur 613 401,
India
b Department of Chemistry, School of Chemical and Biotechnology, SASTRA University, Thanjavur 613 401, India
c Centre for Computational Chemistry and Materials Science, SASTRA University, Thanjavur 613 401, India
d PURSE Laboratory, Mangalagangotri, Mangalore University, Mangalore 574 199, India
e Department of Materials Science, Mangalore University, Mangalore 574 199, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Single crystal X-ray analysis reveals that the 9-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)-3,3-
dimethyl-2,3,4,9-tetrahydro-1H-xanthen-1-one, crystallizes in the centrosymmetric space group P21/c.
In the crystal, molecules form as a dimer through a keto-enol type hydrogen-bonding pattern along with
intermolecular CeH/O interactions. The crystal structure of the title compound is further stabilized by
intermolecular H/H interactions. Various intermolecular interactions present in the crystal structure are
quantified by Hirshfeld surface analysis, PIXEL energy, NBO, AIM and DFT calculations. The energetics of
the title compound is also compared with that of the two closely related analogs. Further, the vibrational
modes of the interacting groups are characterized using both the experimental and simulated FT-IR and
FT-Raman spectra. The experimental and calculated UVevisible spectra are compared and agree well.
The time-dependent DFT spectra suggest that the ligand-to-ligand charge transfer within the molecule is
responsible for the intense absorbance.
Received 19 September 2016
Received in revised form
26 November 2016
Accepted 28 November 2016
Keywords:
Xanthene
Hirshfeld surface
Intermolecular interactions
PIXEL
AIM
NBO
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
formation of the tetraketone intermediate (see Scheme 1). Several
derivatives have been structurally characterized in their tetrake-
Xanthene derivatives show important biological activities such
as anti-viral, anti-bacterial, anti-inflammatory and anti-nociceptive
due to the presence of pyran ring and incorporate into a wide va-
riety of these therapeutic agents [1e4]. Specifically, xanthene-1,8-
dione derivatives are a part of the structural unit in several natu-
ral products [5]. These heterocycles have also been used as dyes and
as fluorescent materials [6]. In view of these, we synthesized the
title compound by the one-pot condensation reaction of two
equivalents of dimedone and one equivalent of 2-
hydroxybenzaldehyde and zinc chloride is used as a catalyst. This
reaction was conducted at room temperature and it leads to the
tone intermediate forms [7e11]. In all of these derivatives, two
intramolecular keto-enol type hydrogen-bonding patterns are
observed. The title compound was obtained at room temperature
from the tetraketone intermediate form by the intramolecular
nucleophilic addition of phenolic hydroxyl group with dimedone
carbonyl group.
In this work, we present the crystal and molecular structure of
the tetrahydro-1H-xanthen-1-one derivative, namely 9-(2-
hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)-3,3-dimethyl-
2,3,4,9-tetrahydro-1H-xanthen-1-one. The crystal structure anal-
ysis reveals that the title compound exists in the enol form. The
crystal structures of the two closely related analogs of the title
compound have already been reported [12,13]. We also report a
comparative study in the context of molecular conformation, lattice
energy and Hirshfeld surface analysis for the title compound along
* Corresponding author.
E-mail address: thamu@scbt.sastra.edu (S. Thamotharan).
http://dx.doi.org/10.1016/j.molstruc.2016.11.082
0022-2860/© 2016 Elsevier B.V. All rights reserved.

M. Udayakumar et al. / Journal of Molecular Structure 1133 (2017) 510e518
511
Scheme 1. Synthetic route for (I).
with two of its analogs. The structure of the title compound was
optimized in the gas phase using the M05-2X functional with the 6-
31þG(d) basis set. The harmonic vibrational frequencies are
computed at the same level of theory to confirm the global minima.
To get a better understanding of how various intermolecular in-
teractions contribute toward crystal packing, we quantified the
energetics of these interactions using PIXEL method. Moreover, the
intermolecular interactions in the crystal structure are visualized
using Hirshfeld surface analysis and the relative contributions of
various interactions were estimated using 2D fingerprint plots.
Furthermore, the existence of various intra-and intermolecular
interactions was confirmed through the atoms-in-molecules (AIM)
analysis and the natural bond orbital (NBO) study.
structure of the title compound was solved by the SIR92 program
[14] and all the non-hydrogen atoms were refined anisotropically
using the SHELXL2014 program [15]. The hydrogen atoms were
placed in idealized geometrical positions (CeH ¼ 0.93e0.98 Å) and
constrained to ride on their parent atoms. The hydrogen atoms
bonded to the methyl carbons were allowed to rotate freely about
the CeC bonds. The ORTEP and packing figures were produced
using the program MERCURY [16]. Crystal data:
C23H26O4,
M ¼ 366.46, 0.40 ꢁ 0.25 ꢁ 0.25 mm3, monoclinic, space group P21/
c, a ¼ 7.060(3), b ¼ 20.290(10), c ¼ 13.680(7) Å,
a
¼ 90ꢂ,
b
¼
93.379(7)ꢂ,
g
¼
90ꢂ,
V
¼
1956.2(16) Å3,
radiation,
Z
¼
4,
Dc ¼ 1.244 Mg mꢀ3, F000 ¼ 784, MoK
a
l
¼ 0.71075 Å,
2
q
max
¼
50ꢂ, 18418 reflections collected, 3439 unique
(Rint ¼ 0.0432), Final GooF ¼ 1.188, R1 ¼ 0.0615, wR2 ¼ 0.1153, R
indices based on 2956 reflections with I > 2s
(I) (refinement on F2),
2. Experimental
248 parameters,
m
¼ 0.084 mmꢀ1. CCDC-1499266 contains the
supplementary crystallographic data for this paper. These data can
be obtained free of charge at www.ccdc.cam.ac.uk/data_request/cif
or from the Cambridge Crystallographic Data Centre (CCDC), 12
Union Road, Cambridge CB2 1EZ, UK; fax: þ44(0) 1223 336 033;
email:deposit@ccdc.cam.ac.uk.
In order to prepare the title compound (I), a reaction mixture of
dimedone (140 mg, 1 mmol), aromatic aldehyde (0.5 mmol),
ammonium acetate (231 mg,
3 mmol) and ZnCl2 (17 mg,
0.125 mmol) were successively added and stirred at room tem-
perature for 30 min. After completion, cold water (5 mL) was added
and the mixture was stirred for 10 min. The solid product of (I) were
isolated by simple filtration, washed with hexane and a portion of
the sample was recrystallized from absolute ethanol for spectral
analysis. Single crystals of (I) were obtained from ethanol by the
slow evaporation method. A plausible mechanism for the formation
of the product is shown in Scheme 1 and the details were given in
the supplementary information section.
The FT-IR spectrum of the title compound was measured in the
frequency region of 4000e400 cmꢀ1 on a Perkin Elmer FTeIR
spectrophotometer using the KBr pellet technique. The Raman
spectrum was recorded using the 1064 nm line of Nd:YAG laser as
excitation wavelength in the region of 4000e50 cmꢀ1 on a Bruker
RFS-27 FT-Raman spectrometer. The UVeVis absorption spectrum
was recorded (200e700 nm) on an Eppendorf Bio-
spectrophotometer in DMSO solvent.
2.2. Hirshfeld surface analysis and pixel energy calculation
The Hirshfeld surface (HS) and 2D fingerprint plots were
generated for the title structure using the program CrystalExplorer
3.1 [17] as mentioned in our earlier work [18e20]. A comparative
analysis of Hirshfeld surfaces mapped with different properties
such as di, de, dnorm, electrostatic potential, shape index and curv-
edness of the title compound and two of its analogs were per-
formed. In order to quantify the energies associated with the
various intermolecular interactions exist in the crystal structure,
PIXEL calculation was carried out as reported earlier [18e20].
Briefly, the distances involving hydrogen atoms are moved to their
neutron values (CeH ¼ 1.083 Å and OeH ¼ 0.986 Å) before the
calculation. The electron density of the molecule has been obtained
at the MP2/6-31G** level of theory using Gaussian 09 [21]. The total
energy is partitioned into the corresponding Coulombic, polariza-
tion, dispersion and repulsion energies.
2.1. Single crystal X-ray diffraction
The Xeray intensity data for the title compound was collected
on
a
Rigaku AFC12 Saturn724 þ diffractometer. The crystal

512
M. Udayakumar et al. / Journal of Molecular Structure 1133 (2017) 510e518
2.3. Theoretical calculation
puckering parameters [Q
¼
0.480(2) Å, q2
¼
0.418(2) Å,
q3 ¼ ꢀ0.238(2) Å,
q
¼ 119.7(2)ꢂ and 4 ¼ 359.0(3)ꢂ for the atom
2
The crystal structure of the title compound was used as the
starting conformation for the gas phase geometry optimization for
the monomer with the Gaussian 09 program package [21]. Further,
two most stabilized dimers were considered on account of their
interaction energies from the PIXEL energy calculation. These di-
mers were optimized without any geometrical constraints using
the dispersion corrected M05-2X functional [22] with the 6-
31þG(d) basis set. Based on the previous studies, we selected the
M05-2X functional [20,23]. The CPCM method was used to include
the effect of the DMSO solvent. Furthermore, the vibrational fre-
quencies were computed to confirm the proper convergence to
global minima. The results obtained confirmed that no imaginary
frequencies were present. Moreover, the interaction energy Eint was
calculated for two different dimers after incorporating the zero
point vibrational energy (ZPVE) and counterpoise correction with
an account of basis set superposition error (BSSE) [24]. The second
order perturbation energies E(2) were computed for the two
different dimers using the natural bond orbital (NBO) program as
implemented in Gaussian 09 program. The topological analysis was
performed using the AIMALL package [25]. The time dependent-
DFT (TDDFT) calculation was carried out by extracting a mini-
mum of 100 roots using the time dependent Kohn-Sham formalism
[26].
sequence C18eC19eC20eC21eC22eC23]. In ring D, atom C21
is ꢀ0.327(2) Å from the plane containing the five remaining atoms.
The dihedral angle between ring D and the A/B/C rings are 65.13(6),
71.66(6) and 73.57(5)ꢂ, respectively. It is of interest to note that the
ring C exhibits a distorted envelope conformation. Atoms C11 and
C12 deviate by 0.344(2) and ꢀ0.284(2) Å, respectively from the
mean plane formed by ring C atoms. The Cremer & Pople puckering
parameters for this ring are Q ¼ 0.492(2) Å, q2 ¼ 0.413(2) Å,
q3 ¼ 0.267(2) Å,
q
¼ 57.1(2)ꢂ and 4 ¼ 134.0(3)ꢂ for the atom
2
sequence C9eC10eC11eC12eC13eC14. The C11eC15 and C11eC16
bonds are oriented equatorially and axially, respectively. Similarly,
the C21eC25 and C21eC26 bonds are oriented equatorially and
axially, respectively. In the methyl (II) and bromo analogs (III), rings
C and D have envelope conformations. These substitutions do not
affect the conformations of rings C and D.
The HS diagram and the two dimensional fingerprint plots are
given in Fig. 2. This analysis suggests that the intermolecular H/H
contacts contribute more (66.2%) to the crystal packing when
compared to the other contacts present in the crystal structure of
(I). As shown in Fig. 2, the shortest H/H contact in the fingerprint
plot as characteristic spikes (di þ de y 2.2 Å). The crystal structure is
also dominated by the intermolecular O/H/H/O and C/H/H/C
type contacts. The relative contributions of the O/H/H/O and
C/H/H/C contacts are 18.5% and 14.2%, respectively, to the total
HS area of the molecule. The shortest O/H/H/O contacts are
represented as sharp spikes (di þ de y 1.7 Å). The C/H/H/C
contacts are appeared as wings in the fingerprint plot with the
shortest contact di þ de y 2.8 Å. This type of contact is mainly
3. Results and discussion
3.1. Description of crystal structure
represented for CeH/p interactions. In (II) and (III), the intermo-
The single crystal X-ray diffraction data for the title compound
reveals that the crystal has the space group P21/c and belongs to the
monoclinic system. The title compound (I) crystallizes with just one
molecule in the asymmetric unit and ORTEP diagram of the title
compound with atom-numbering scheme is shown in Fig. 1. It is
clearly seen from the bond length [C19eO24 ¼ 1.337(2) Å] that the
title compound exists in the enol form. The values of the dihedral
angles between every two rings, i.e. A and B, A and C, and B and C
pairs, are 6.97(6), 14.38(7) and 9.60(6)ꢂ, respectively. Ring D adopts
an envelope conformation as shown by the Cremer & Pople [27]
lecular H/H contacts are predominant as observed in (I). For these
two structures, the HS diagram and the 2D fingerprint plots are
given in the supplementary section (Figs. S1eS2). Due to the
presence of methyl (II) and bromine (III) substituents on ring A, the
H/H contributions are altered [68.8% in (II) and 55% in (III)]. The
reduction of H/H contacts in (III) is compensated by the inter-
molecular H/Br contacts (11.9%). The intermolecular O/H/H/O
type contacts are nearly the same in (I) and (II). However, these
contacts are slightly reduced by ca. 2% in (III). Similar reduction is
also observed for C/H/H/C type contacts in (II) and (III) when
compared to (I).
The lattice energy is calculated at the crystal geometry using the
PIXEL method. Comparative lattice energy of structures (IeIII) is
given in the supplementary section (Table S1). The total lattice
energy was calculated to be ꢀ47.9 kcal molꢀ1 for (I). The corre-
sponding Coulombic, polarization, dispersion and repulsion en-
ergies are ꢀ13.5, ꢀ14.2, ꢀ38.4 and 18.1 kcal molꢀ1, respectively. It is
worthy to note that the dispersion contribution (58%) is greater
than the Coulombic (20%) and polarization (21%) contributions.
Moreover, lattice energy calculation shows that structure (II) is
5.2 kcal molꢀ1 more stable than structure (I) and structure (III) is
4.4 kcal molꢀ1 more stable than structure (I). Structures (II) and (III)
were observed to have similar lattice energies (see Table S1).
The interacting pair of molecules in (I) along with various en-
ergy components is listed in Table 1. In the crystal structure of the
title compound, the hydroxy group (O24eH24) is participating in
an intermolecular OeH/O hydrogen bonding interaction with the
carbonyl oxygen atom (O27). As a result, two molecules form a keto-
enol type hydrogen-bonded dimer (motif I; Dimer-I) as clearly seen
as an intense red spot on the HS diagram shown in Fig. 2. This dimer
is further stabilized by three intermolecular CeH/O interactions.
One of the carbonyl atom (O17) acts as an acceptor for these
intermolecular CeH/O interactions. It is of interest to note that the
two different methyl groups (via H15A and H16A) from ring C act as
Fig. 1. ORTEP diagram and atom-numbering scheme for title compound (I). Rings are
labelled.

M. Udayakumar et al. / Journal of Molecular Structure 1133 (2017) 510e518
513
Fig. 2. (aeb) Two different views of Hirshfeld surface mapped with dnorm and key intermolecular contacts are labelled (C1: O24eH24/O27; C2: C16eH16A/O17; C3:
C15eH15A/O17 and C4: O8/O24) (c) 2D fingerprint plots showing various intermolecular contacts in (I).
Table 1
Interaction energy (in kcal molꢀ1) for various molecular pair along with centroid-centroid distance in (I).
Motifs
I
Centroid-centroid distance (Å)
7.060
Symmetry code
ECoul
Epol
Edisp
Erep
Etot
Possible interactions
Geometry(Å,ꢂ)a
xꢀ1, y, z
ꢀ16.6
ꢀ7.9
ꢀ10.4
19.5
ꢀ15.4
O24eH24/O27
C10eH10B/O17
C15eH15A/O17
C16eH16A/O17
O8/O24
1.714, 163
2.636, 140
2.516, 145
2.485, 146
3.008
II
III
6.982
9.638
x, ꢀyþ1/2, zþ1/2
ꢀ3.1
ꢀ1.1
ꢀ1.4
ꢀ0.8
ꢀ10.6
ꢀ6.4
6.0
3.8
ꢀ9.1
ꢀ4.4
C22eH22B/C14
C20eH20A/H10A
C20eH20A/C10
C12eH12A/H4
C25eH25C/H26A
C26eH26A/H26A
2.886,156
2.312, 120
2.871, 141
2.188, 152
2.286, 146
2.318, 145
x-1, ꢀyþ1/2, zꢀ1/2
IV
V
10.287
10.151
ꢀxþ1, yꢀ1/2,ꢀzþ3/2
ꢀxþ1, ꢀy, ꢀzþ1
ꢀ1.1
ꢀ0.8
ꢀ0.7
ꢀ0.5
ꢀ4.6
ꢀ5.1
3.0
3.3
ꢀ3.4
ꢀ3.3
a
Neutron values are given for all DeH/A interactions.
donors for intermolecular CeH/O interactions and these two
contacts are clearly visible on the HS diagram. The third intermo-
lecular CeH/O interaction comes from H10B which is bonded to
atom C10. Furthermore, the keto-enol dimers are extended as a
chain that runs parallel to the a axis. The stabilization energy for
this molecular pair (motif I) was found to be ꢀ15.4 kcal molꢀ1 as
evaluated from the PIXEL method. This pair is mainly stabilized by
the contributions of Coulombic (48%) and dispersion (30%) in-
teractions. Interestingly, there is a non-bonded contact observed
between atoms O8 and O24 with a distance of 3.008 and this
contact is also visible as a light red spot on the HS. Motif II (Dimer-
II) is formed by an interaction between the atoms H22B and C14.
This interaction links the molecules into a chain that runs parallel
3.2. DFT and wavefunction analysis
The monomeric structure (I) is optimized in the gas phase using
the DFT method. The bond lengths, angles and torsion angles of the
optimized structure are compared with the geometrical parameters
of the experimental structure. A comparison of geometrical pa-
rameters between the gas phase structure and the crystal structure
is given in the supplementary section (Tables S2eS4). The atoms of
rings A, B and C are used for the structural superimposition to
compare the conformation of the experimental and the optimized
monomeric structures and the RMSD (root mean squared devia-
tion) between them is 0.08 Å (Fig. S3). The maximum deviation
(0.022 Å) of bond length was observed for the C18eC23 bond. In the
calculated structure, the endo cyclic angles of ring D are slightly
deviated from the X-ray geometry. The larger deviation is observed
for C18eC19eC20 (6.4ꢂ) and C18eC23eC22 (5.4ꢂ). The torsion
angles of the calculated structure are very close to the experimental
torsion angles. Moreover, the inclusion of intrinsic solvent (DMSO)
has only a marginal effect.
To identify the nature of interactions that exists between the
molecules in the crystal structure, the two most stabilized molec-
ular dimers (motif I: Dimer-I and motif-II: Dimer-II) are considered
based on the PIXEL calculation. The above dimeric pairs are sub-
jected to geometrical relaxation without any constraints on the
positions and symmetry. The structural optimization in gas phase
also showed that the dimer-I was found to be more stable by
7.4 kcal molꢀ1 than dimer-II. This energy difference is close to the
value of 6.3 kcal molꢀ1 obtained from the PIXEL method. As dis-
cussed earlier, there are one intermolecular hydrogen bonding, the
OeH/O interaction, and three intermolecular CeH/O in-
teractions in Dimer-I. To find the reason for the near isoenergetic
to the
c
axis. The interaction energy for this dimer
was ꢀ9.1 kcal molꢀ1. This dimer is predominantly stabilized by the
contribution of the dispersion interactions (70%). Motif III is stabi-
lized by the presence of two intermolecular interactions through
the H10A/H20A and H20A/C10 contacts. The stabilization inter-
action energy for this molecular pair was calculated to
be ꢀ4.4 kcal molꢀ1 and the dispersion contributes nearly 77% for
the stabilization. The molecular pair (motif IV) was formed by an
intermolecular H4/H12A contact. This weak dimer scores an
interaction energy of ꢀ3.4 kcal molꢀ1 and mainly stabilized by the
dispersion (72%) in nature. The hydrogen atoms of the dimethyl
groups in ring D participate in the intermolecular H/H interactions
with the hydrogen atoms of the dimethyl groups in ring D of the
neighbouring molecule (motif V). The interaction energy for this
dimer was ꢀ3.3 kcal molꢀ1 and this molecular pair is mainly sta-
bilized by the dispersion (~80%) interactions. The above discussed
intermolecular interactions are shown in Fig. 3.

514
M. Udayakumar et al. / Journal of Molecular Structure 1133 (2017) 510e518
Fig. 3. Selected molecular pairs stabilized by various intermolecular interactions in the crystal structure of (I).
nature of Dimers-I and II, we performed the atoms-in-molecules
(QTAIM) analysis for these dimers. The molecular graphs for
Dimer-I and Dimer-II are provided in Fig. 4. The topological pa-
rameters at the bond critical point (BCP) of various intermolecular
Fig. 4. Molecular topography analysis obtained from AIM analysis for (a) Dimer-I and (b) Dimer-II. Small green spheres indicate the bond critical points (BCPs). (For interpretation of
the references to colour in this figure legend, the reader is referred to the web version of this article.)

M. Udayakumar et al. / Journal of Molecular Structure 1133 (2017) 510e518
515
interactions present in Dimers-I and II are given in Table S5. The
value for rBCP at the intra-and intermolecular BCP's offers the
strength of the hydrogen bonding interactions present in the
molecules. In Dimer-I, there are 12 intermolecular BCP's observed,
in which the methyl hydrogens of ring C make five intermolecular
BCPs. The rBCP values for these interactions lie in the range of
0.003e0.009 a.u. The carbonyl oxygen (O27) of the ring D makes
two bondings with the methylene hydrogen and hydroxy group
(OeH/O). Furthermore, the molecules are stabilized by two
interacts
with
the
antibonding
O24eH24
orbital
(LP(2) / s
*(O24eH24) of another monomer molecule with a sta-
bilization energy of 17.36 and 0.51 kcal molꢀ1. Similarly, the oxygen
atom (O17) for the carbonyl groups with its lone pair orbitals 1 and
2 interacting with CeH antibonding orbital of the methylene
hydrogen of the adjacent monomer with an stabilization energy of
0.83 kcal molꢀ1. Furthermore, the oxygen lone pairs also interact
with the methyl hydrogen atoms with a stabilization energy of
0.90 kcal molꢀ1
.
intramolecular
interactions
(C16eH16B/O27
and
In Dimer-II, the lone pair donor orbitals 1 and 2 on the oxygen
atom of the carbonyl group of monomer interacts with the anti-
bonding C10eH10A orbital, methylene group hydrogen atoms with
a stabilization energy of 1.16 and 1.43 kcal molꢀ1, respectively.
Furthermore, we observe the interaction between the bonding
orbital of the C9eC14 carbon atoms and antibonding orbitals of the
C22eH22B methylene hydrogen atom, with an interaction energy
of 0.89 kcal molꢀ1. Furthermore, similar bonding interactions were
observed between the C2eC7 and C12eH12B groups. These CeC
C26eH26C/O17) in each of the monomer. These intramolecular
interactions are also observed in the AIM analysis of pure monomer.
The computed rBCP values for OeH/O lie in the range of 0.031 a.u.,
while the rBCP value for the C]O/methylene interaction was
found to be 0.006e0.008 a.u. It is of interest to note that there is an
interaction between the oxygen atom in ring B and hydroxy oxygen
in the ring D with a rBCP value of 0.005 a.u. The computed
OeH/O]C values lie closer to the values proposed by Popelier and
Koch for the hydrogen bonding interaction [28]. Moreover, the
intramolecular C]O/methylene interaction has a rBCP value of
0.004 a.u. It was found from the rBCP value that the intermolecular
C]O/methylene interaction contributes more to the stabilization
than the intramolecular C]O/methylene interaction.
interactions with methylene hydrogen resemble that of CeH/
p
supports the AIM result observed previously [31]. In addition to the
above intermolecular bondings, the bonding orbital of the carbonyl
oxygen interacts with the antibonding orbital of methylene
hydrogen atom with a stabilization energy of 0.46 kcal molꢀ1
.
In Dimer-II, we observe nine intermolecular BCPs and each
monomer consists of three intramolecular BCPs. Among the inter-
molecular BCPs observed six are of the CeH/C type interactions
with a rBCP ranging from 0.004 to 0.008 a.u., whose values are
3.4. Infrared and Raman spectrum
In order to understand the nature of the interactions present in
the crystal structure, we recorded the IR and Raman spectra for the
title compound. We also calculated the IR and Raman spectra for
the monomer, Dimer-I and Dimer-II of the title compound. The
computed IR and Raman spectra without any scaling are shown in
Fig. 5. It is obviously clear in the figure that the simulated spectra
resemble the experimental spectra. However, we observed a
spectra shift in their stretching frequencies. It is a well-known fact
that the DFT levels systematically overestimate the vibrational
wave-numbers [32]. The experimental IR spectrum for the title
compound exhibited intense absorption bands at 1666, 2922 and
2954 cmꢀ1 which were assigned to the C]O stretching, methyl and
methylene hydrogen CeH stretching, respectively. The broad peak
at 3410 cmꢀ1 was assigned to the intermolecular O/H stretching
band. In the calculated IR spectra for the monomer, the C]O
stretching is at 1770 and 1784 cmꢀ1. The methyl group in the
monomer has a CeH stretching frequency at 3180 cmꢀ1 while the
closer to CeH/p interaction observed in similar systems [29].
There are two C]O/methylene hydrogen interactions one with a
rBCP value of 0.011 and other with 0.005 a.u. Furthermore, an
intermolecular H/C interaction is observed with a rBCP value of
0.008 a.u. This interaction also exists in the crystal structure. The
accounted high number of intermolecular BCP's is responsible for
the high stabilization of Dimer-II and for the near isoenergetic
nature.
3.3. NBO analysis
For forming a stable donor-acceptor bond, delocalization of
electron density occurs between occupied bond or lone pair NBO
orbital and unoccupied antibonding orbital. Furthermore, the larger
the E(2) value, the more intensive is the interaction between the
donor and acceptor [30]. The NBO calculations for Dimer-I and
Dimer -II molecular pairs are reported in Table 2. In Dimer-I, the
lone pair donor orbitals 1 and 2 on oxygen atom of one monomer
methylene groups have the CeH stretching frequency at 3153 cmꢀ1
When compared with the experiment values, a shift in the C]O
.
Table 2
The intermolecular donor-acceptor interactions and second order perturbation energies (in kcal molꢀ1) for Dimer-I and Dimer-II of the title compound. The symbol ($) denotes
atom-numbering of the second monomer in the dimer.
Dimer-I
Dimer-II
Donor (i)
Donor (i)
Acceptor (j)
*(1) C26$eH26$
E(2)
Acceptor (j)
E(2)
s
s
s
(1) C22eC23
(1) O24eH24
(1) O24eH24
s
0.47
0.71
0.50
0.83
0.83
0.90
0.94
1.77
0.45
0.68
0.49
0.48
17.36
0.51
s
s
s
(2) C9eC14
s
s
s
s
s
*(1) C22$eH22B$
*(1) C12eH12B
*(1) C12eH12B
*(1) C10eH10A
*(1) C10eH10A
0.89
0.37
0.46
1.16
1.43
RY*(3) O27$
(2) C2$eC7$
(2) C23$eO27$
s
s
s
s
s
s
s
*(1) C23$eO27$
*(1) C10$eH10B$
*(1) C15$eH15$
*(1) C16$eH16$
*(1) C15$eH15A$
*(1) C26$eH26A$
*(1) C26$eH26A$
LP(1) O17
LP(1) O17
LP(1) O17
LP(2) O17
LP(1) O27$
LP(2) O27$
s
s
s
s
s
*(2) C3eC4
*(2) C9eC14
(1) C23$eO27$
(1) C23$eO27$
(2) C23$eO27$
RY*(1) H24
s
s
s
s
*(1) O24eH24
*(1) O24eH24
*(1) O24eH24
*(1) O24eH24
LP(1) O27$
LP(2) O27$

516
M. Udayakumar et al. / Journal of Molecular Structure 1133 (2017) 510e518
Fig. 5. Experimental and simulated (a) FT-IR and (b) FT-Raman spectra of title compound.
stretching to the lower frequency is observed which is the conse-
quence of the formation of intermolecular interaction between the
C]O group with methyl and methylene hydrogen along with the
OeH intermolecular hydrogen bonds.
the Time Depended-Density Functional Theory (TD-DFT) along
with the experimental spectra are shown in Fig. 6(a). The computed
and experimental spectra show a reasonable resemblance. The
experimental spectra show a broad peak at ca. 345 nm. A similar
broad hump is observed in the computed spectra at ca. 350 nm. The
intensive absorption is observed for the compound at 252 nm and
at 246 nm in the experiment and in the computed spectra,
respectively. The excitation energies, oscillator strengths (f) and the
electron configurations for the main excited states obtained using
PBE0/6-31þG(d) method with polarizable continuum model (PCM)
with Klamt sphere radii are presented in Table 3. The selected
preponderant mono excitations are presented in Fig. 6(b) using the
isodensity plots of the MOs involved. The maximum absorption
bands were observed at 327, 311, 292, 271, 266 and 246 nm. The
intense absorption band at computed at 311 nm is mainly consti-
tuted by the H-2 / LUMO (26%), H-1 / LUMO (31%) with an
oscillatory strength of 0.003, which corresponds to the broad band
observed at 316 nm. The excitation at 327 nm with orbital contri-
bution mainly from the HOMO / LUMO (69%) has an oscillatory
strength of 0.022. However, this transition is too broad to be
observed experimentally. Furthermore, the special diagram shows
that the HOMO orbitals are localized over the benzene partly while
the LUMO orbital is localized on the entire molecule. Thus, the
intense absorption that occurs at 311 nm is mainly due to the
charge transfer HOMO-1 / LUMO and HOMO-2 / LUMO orbital
and is of Ligand to Ligand charge transfer in nature.
In Dimer-I, the calculated band at 3166 is attributed to the free
methyl CeH stretching. This upon interaction with hydroxyl group
of the adjacent molecule undergoes a red shift and a stretching
frequency is observed at 3138 cmꢀ1. Similarly the methyl groups
upon interacting with C]O show a red shift to 3144 cmꢀ1, while the
free C]O group shows a blue shift to 1764 cmꢀ1. The methylene
CeH shows a blue shift from 3153 cmꢀ1 in free monomer to
3166 cmꢀ1 in Dimer-I. In Dimer-II, the calculated band for the free
C]O is at 1774 and 1783 cmꢀ1, which are closer to the values
observed for the gas phase monomer. There is a red shift with a
peak observed at 1760 cmꢀ1 which is due to the possible involve-
ment of C]O and methylene hydrogen interaction. Furthermore,
the methyl CeH groups show a red shift from 3180 cmꢀ1 in free
monomer to 3163 cmꢀ1 indicating their involvement in intermo-
lecular bonding.
In the experimental Raman spectra, the most intense peaks
appeared at 1589 and 1645 cmꢀ1, which are assigned to the C]C
stretching band in ring A and ring D. The corresponding stretching
frequencies in the monomer molecule are calculated at 1687 and
1746 cmꢀ1. In Dimer-I, the calculated results showed that the C]C
stretching bands are at 1716 cmꢀ1 and 1735 cmꢀ1 for the rings of D
and A, respectively. In Dimer-II, the carbon-carbon bond stretching
frequency of ring D is calculated at 1735 cmꢀ1 and A ring is
observed at 1748 cmꢀ1. In the experimental spectra, a broad peak in
the region of 2900e3000 cmꢀ1 is assigned to the symmetric
stretching mode of CeH methylene hydrogen. In computed
5. Conclusions
The title compound was synthesized and characterized by
means of the experimental and theoretical methods. The crystal
structure analysis revealed that the title compound exists in the
enol form. As observed in the related structures, the keto-enol type
hydrogen-bonded pattern is observed in the title compound along
with the intermolecular CeH/O interactions. Further stabilization
comes from the intermolecular H/H interactions. The lattice en-
ergy calculation using the PIXEL method suggests that the title
compound is less stable than that of the two closely related analogs.
Further, the strengths of the various intermolecular interactions
were quantified. These interactions also appeared in the AIM and
NBO analysis. The experimental and simulated IR and Raman
spectra support the presence of these interactions in the crystal.
monomer, CeH methylene has
a symmetric stretching at
3089 cmꢀ1 while the asymmetric stretching is observed at
3161 cmꢀ1. In Dimer-I, the symmetric CeH stretching of methylene
is observed at 3085 cmꢀ1 and the asymmetric stretching is
observed at 3154 cmꢀ1, while in Dimer-II the respective frequencies
are calculated at 3094 cmꢀ1 and 3171 cmꢀ1. All these findings
indicate the involvement of bonds during the crystal formation.
4. UVevisible spectrum
The UVevisible absorption for the title compound was recorded
in the DMSO solvent. Our simulated spectra in this solvent using

M. Udayakumar et al. / Journal of Molecular Structure 1133 (2017) 510e518
517
Fig. 6. (a) Observed and calculated UVeVis absorption spectra (b) HOMO and LUMO orbitals.
Authors thank DST-PURSE Lab, Mangalore University for providing
single crystal X-ray diffraction facility.
Table 3
Excitation energies (nm), oscillators strengths, configurations, and experimental
data for (I) in DMSO solvent. TD-DFT calculations were performed using PBE0/6-
31þG(d) functional.
Appendix A. Supplementary data
Excitation energy
327
f
Main configuration
Expt.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2016.11.082.
0.0221
HOMO / LUMO (69%)
HOMO / Lþ1 (12%)
H-3 / LUMO (18%)
H-2 / LUMO (26%)
H-1 / LUMO (31%)
H-3 / LUMO (11%)
HOMO / LUMO (30%)
HOMO / Lþ1 (34%)
H-2 / LUMO (28%)
H-1 / LUMO (50%)
H-3 / LUMO (28%)
HOMO / Lþ1 (41%)
H-4 / LUMO (14%)
HOMO / Lþ2 (70%)
H-3 / LUMO (10%)
H-1 / Lþ1 (70%)
311
292
0.0031
0.1295
316 (br)
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