Structural (X-ray), spectral (FT-IR and Raman) and quantum chemical investigations of a series of 6-benzylaminopurine derivatives

Article abstract of DOI:10.1016/j.molstruc.2011.03.049

The structural and spectroscopic properties of 6-(2-methylbenzylamino) purine 1, 6-(4-methylbenzylamino)purine 2, 6-(3,4-dimethoxybenzylamino)purine 3, 2-chloro-6-(3-bromobenzylamino)-9-isopropylpurine 4 and 2-chloro-6-(3,4- dichlorobenzylamino)-9-isoprop

Full text of DOI:10.1016/j.molstruc.2011.03.049

Journal of Molecular Structure 994 (2011) 350–359
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural (X-ray), spectral (FT-IR and Raman) and quantum chemical
investigations of a series of 6-benzylaminopurine derivatives
a
b,
⇑
ˇ
ˇ
ˇ
Michal Cajan , Zdenek Trávnícek
a Department of Inorganic Chemistry, Faculty of Science, Palacky´ University, 17. listopadu 12, CZ-771 47 Olomouc, Czech Republic
b Regional Centre of Advanced Technologies and Materials, Department of Inorganic Chemistry, Faculty of Science, Palacky´ University, 17. listopadu 12,
CZ-771 46 Olomouc, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
The structural and spectroscopic properties of 6-(2-methylbenzylamino)purine 1, 6-(4-methylbenzyla-
mino)purine 2, 6-(3,4-dimethoxybenzylamino)purine 3, 2-chloro-6-(3-bromobenzylamino)-9-isopropyl-
purine 4 and 2-chloro-6-(3,4-dichlorobenzylamino)-9-isopropylpurine 5 have been investigated by
means of single crystal X-ray diffraction analysis, FT-IR and Raman spectroscopy, and quantum chemical
calculations, where HF, DFT, RI-MP2 and MP2 methods in combination with the cc-pVDZ basis set have
been used. The theoretically obtained structural as well as spectral parameters have been compared with
those experimentally obtained. One of the unusual structural features is the finding that the electroneu-
tral form of 6-(2-methylbenzylamino)purine 1 is protonated at the N7 position of the purine ring, which
is not a typical protonation site for N9-unsubstituted adenine derivatives.
Received 11 October 2010
Received in revised form 21 March 2011
Accepted 21 March 2011
Available online 25 March 2011
Keywords:
X-ray structure
Purine derivatives
Adenine derivatives
Vibrational spectra
Quantum chemical calculations
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
studied owing to their possible medical application as enzyme
inhibitors [13], antiviral [14], anti-bacterial [15], and anti-cancer
6-Benzylaminopurine (Bap) derivatives represent heterocyclic
compounds showing a large scale of biological activities. As the
plant growth hormones, called cytokinins, they have been inten-
sively studied since the 1960s. The key role of the cytokinins lies
principally in participation in the controlling of the processes re-
lated to plant cell division and senescence [1–6]. It has been found
that the appropriate structural modification of the Bap molecule
can lead to a substantial change of its biological and physiological
properties. Thus, Bap derivatives substituted at the C2 and N9
positions of the purine moiety show the inhibition activity against
cyclin-dependent kinases (CDKs) [7–9], and some of them
(e.g. olomoucine = 6-(benzylamino)-2-[(2-hydroxyethyl)amino]-9-
methylpurine, bohemine = 6-(benzylamino)-2-[(3-hydroxypropyl)-
agents [16,17].
Coordination abilities as well as physiological activity of both
cytokinins and CDK inhibitors are strongly influenced by molecular
geometry, electron density distribution within the appropriate
molecule, and finally by possible tautomeric equilibria related to
the proton position at the unsubstituted nitrogen atoms of the pur-
ine ring. Thus, this work is devoted to the detailed analysis of
structural and spectroscopic properties within two structurally dif-
ferent types of 6-benzylaminopurine derivatives, i.e. 6-(2-meth-
ylbenzylamino)purine 1, 6-(4-methylbenzylamino)purine 2, and
6-(3,4-dimethoxybenzylamino)purine 3 as the compounds with
the unsubstituted imidazole moiety, and 2-chloro-6-(3-bro-
mobenzylamino)-9-isopropylpurine
4 and 2-chloro-6-(3,4-dic-
amino]-9-isopropylpurine,
hydroxymethyl-propyl)amino]-9-isopropylpurine
roscovitine = 6-(benzylamino)-2-[(1-
also show
hlorobenzylamino)-9-isopropylpurine 5 as the second group of
compounds, where the purine ring is modified by the chloro and
isopropyl substituents at the C2, and N9 position, respectively.
Although the compounds 1 and 2 are chemically very similar,
their molecular structures differ in the position of the hydrogen
atom at the imidazole moiety of the purine ring. The molecule of
1 is protonated at the N7 position, while the compound 2 prefers
protonation at the N9 position as is usual for most of similar purine
systems of this type. To our best knowledge, only one electroneu-
tral analog with the hydrogen atom positioned just at N7 has been
prepared up to now [18]. All the compounds presented in this work
were experimentally characterized by elemental analysis, FT-IR
significant both in vitro and in vivo cytotoxicity against some
human cancer cell lines [10–12]. Except for the above-mentioned
organic skeleton derivatization, the resulting cytotoxicity may be
also increased after complex formation of such heterocyclic com-
pounds with suitable transition metals, like Fe, Co, Pt, Pd, Cu, etc.
To date, many of these metal complexes have been extensively
⇑
Corresponding author. Tel.: +420 585 634 352; fax: +420 585 634 954.
E-mail address: zdenek.travnicek@upol.cz (Z. Trávnícek).
ˇ
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.03.049

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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
351
and Raman measurements, and single crystal X-ray analysis. The
experimentally found structural as well as spectroscopic data were
compared with those obtained by quantum chemical calculations
performed at the DFT, RI-MP2 and MP2 levels of theory.
2. Material and methods
2.1. Syntheses and characterizations
Compounds 1–3: 6-Benzylaminopurine derivatives were pre-
pared according to the well known synthetic strategy which is de-
picted in Scheme 2, i.e. by the reaction of 6-chloropurine with the
appropriate R-substituted benzylamine and triethylamine (Et3N) in
the butanol solution, in a molar ratio of 3:4:5 [19]. The yields
obtained were 70–80%. The single crystals of the discussed
compounds were obtained by re-crystallization from N,N0-
dimethylformamide.
Scheme 2. A general pathway for the preparation of 6-benzylaminopurine deriv-
atives (R: CH3 or OCH3).
Compounds 4 and 5: 2,6-dichloro-9-isopropylpurine (L1) was
prepared from 2,6-dichloropurine according to the previously re-
ported general preparation of 2,6-dihalogen-9-alkylpurine deriva-
tives [20]. The synthesis of
4 and 5 follows the published
procedure of C2,N9-substituted 6-benzylaminopurine derivatives
[21] (see Scheme 3), where a mixture of L1 and the corresponding
benzylamine derivative (in a molar ratio of 1:1) was stirred in
150 ml of ethyl acetate at the temperature of 78 °C for 5 h. Then,
the products were filtered off, washed with ethanol and diethyl
ether, and dried at 40 °C. The yields ranged from 76% to 88%. The
single crystals were prepared by slow evaporation of the isopropa-
nol/acetone mixture (1:1) at laboratory temperature.
6-(2-Methylbenzylamino)purine 1 Yield: 77%. Anal. Calc. for
C
13N5H13: C, 65.3; H, 5.5; N, 29.3. Found: C, 64.9; H, 5.5; N,
29.5%. 6-(4-Methylbenzylamino)purine 2. Yield: 80%. Anal. Calc. for
13N5H13: C, 65.3; H, 5.5; N, 29.3. Found: C, 65.6; H, 5.3; N,
C
29.1%. 6-(3,4-Dimethoxybenzylamino)purine 3. Yield: 78%. Anal.
Calc. for C14N5O2H15: C, 58.9; H, 5.3; N, 24.5. Found: C, 59.1; H,
5.2; N, 24.8%. 2-Chloro-6-(3-bromobenzylamino)-9-isopropylpurine
4. Yield: 73%. C15N5ClBrH15: C, 47.3; H, 4.0; N, 18.4. Found: C,
47.6; H, 4.4; N, 18.4%. 2-Chloro-6-(3,4-dichlorobenzylamino)-9-iso-
propylpurine 5. Yield: 76%. Anal. Calc. for C15N5Cl3H14: C, 48.6; H,
3.8; N, 18.9. Found: C, 48.9; H, 3.8; N, 18.5%.
2.2. X-ray crystallography, FT-IR and Raman Spectroscopy
Diffraction data were collected on an Xcalibur™ 2 diffractome-
ter (Oxford Diffraction, Ltd.) equipped with Sapphire2 CCD detec-
tor using Mo K
Diffraction, Ltd.) and
a
radiation (monochromator Enhance, Oxford
-scan rotation techniques at 100 K. Data col-
x
lection, cell parameter refinements and data reduction were per-
formed with the CrysAlis software package (Version 1.171.33.52,
Oxford Diffraction, Ltd., Abingdon, England, 2009). The structures
were solved by direct methods and refined anisotropically on F2
using full-matrix least-squares approach (SHELX-97 software
package) [22]. Hydrogen atoms were found from Fourier maps
and refined with the riding model [CAH distance of 0.95 and
0.98 Å, NAH distance of 0.88 Å, and with Uiso(H) values of
1.2Ueq(CH, CH2, NH) or 1.5Ueq(CH3)]. The molecular and crystal
structures were drawn with Diamond 3.2d program [23], which
was also used for interpretation of the additional structural
parameters.
FT-IR spectra were measured on a Nexus 670 FT-IR spectrome-
ter (ThermoNꢀic1olet) by the KBr pellets technique in the range of
400–4000 cm . Raman spectra were measured in the range of
150–4000 cmꢀ1 on a Nicolet NXR 9650 device with a liquid nitro-
gen cooled NXE Genie germanium detector (ThermoNicolet) using
the laser line 1064 nm and laser power 1.002 W.
Scheme 1. Structural formulas of the studied compounds (6-(2-methylbenzyl-
amino)purine 1, 6-(4-methylbenzylamino)purine 2, and 6-(3,4-dimethoxybenzyla-
mino)purine 3, 2-chloro-6-(3-bromobenzylamino)-9-isopropylpurine
4
and
2-chloro-6-(3,4-dichlorobenzylamino)-9-isopropylpurine 5), showing the nitrogen
atoms numbering and rings labeling (A – benzene, B – pyrimidine and C – imidazole).

ˇ
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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
Scheme 3. A general pathway for the preparation of 2-chloro-6-benzylamino-9-isopropylpurine derivatives (R = Br or Cl).
2.3. Quantum chemical calculations
lead to significant differences in the solid state molecular as well as
crystal structure. In the group of derivatives with the unsubstitut-
ed pyrimidine and imidazole moieties, i.e. the compounds 1–3, the
compound 1 crystallizes in the P21/c space group, while 2 as well
as 3 in the P1 space group. The purine rings of both compounds
4 and 5 are modified by the chloro and isopropyl substituents at
Geometries of the studied compounds as well as their infrared
and Raman spectral properties were calculated at the DFT, RI-
MP2 and MP2 levels. It is well known that HF and DFT do not often
correctly describe the molecular structure, especially in the cases,
when the geometry of a molecule is influenced by weak non-
covalent intramolecular and intermolecular interactions [24], and
thus, we decided to perform the geometry optimization also using
the RI-MP2 and MP2 approaches with the aim to compare these
results with those obtained by the non-correlated methods. In
the RI-MP2 method, 4-center 2-electron integrals are approxi-
mated by 3-center 2-electron integrals using optimized auxiliary
basis functions. This leads to an enormous speedup of the calcula-
tions and significant decreasing in memory requirements without
the loss of accuracy when compared to the conventional MP2
method [25–27]. As input geometries, the geometries determined
by single crystal X-ray analysis were used. DFT calculations were
performed with a Gaussian 03 program [28] based on the B3LYP
functional and the cc-pVDZ basis set. RI-MP2 and MP2 calculations,
both also with the cc-pVDZ basis set were performed with a Turbo-
mole 5.10 program [29]. Harmonic frequency analysis was used to
verify the nature of determined stationary points as the minima as
well as for the calculation of zero-point energies (ZPE). The calcu-
lated infrared frequencies were scaled by the 0.9084 factor in the
case of HF, 0.9709 factor in the case of B3LYP, 0.9543 factor in
the case of MP2 [30], and universal scaling factor of 0.9560 for
the RI-MP2 approach [31].
ꢀ
the C2, and N9 position, respectively. Concerning their crystal
ꢀ
structures, compound 4 crystallizes in P1 while compound 5 in
the P21/c space group.
Each of the molecules investigated contains nearly planar ben-
zene (A), pyrimidine (B) and imidazole (C) ring systems (Scheme
1). Maximum deviations from ring planarity were experimentally
determined as follows: compound 1: ꢀ0.0052(14) Å for C13 (ring
A), 0.0095(13) Å for C6 (ring B) and ꢀ0.0012(13) Å for C4 (ring
C); compound 2: ꢀ0.0029(14) Å for C10 (ring A), ꢀ0.0077(14) Å
for C4 (ring B) and ꢀ0.0025(14) Å for C8 (ring C); and compound
3: ꢀ0.0039(13) Å for C10 (ring A), 0.0194(13) Å for C4 (ring B)
and 0.0055(13) Å for C8 (ring C). The pyrimidine (B) and imidazole
(C) rings in the molecules of 1 and 2 are nearly coplanar, making
the dihedral angle of 2.10(4)° for 1 and 1.37(5)° for 2. In the case
of compound 3, the purine system is more deformed and the
experimental value of the mentioned dihedral angle was found
to be 4.37(4)°. The dihedral angles between the benzene and pur-
ine planes are quite different, i.e. 67.14(4)° for 1, 80.34(4)° for 2,
and 88.73(3)° for 3. The torsion angles between the bonds connect-
ing benzene and purine planes are 173.95(12)° for 1, ꢀ78.48(15)°
for 2, and ꢀ98.2(1)° for 3 in the case of the C6AN6AC9AC10 angle,
and 114.06(13)° for 1, ꢀ67.58(16)° for 2, and 1.2(2)° for 3 in the
case of the N6AC9AC10AC15 one. Concerning the second group
of the compounds, the maximum deviations from rings planarity
have been determined as follows: compound 4: 0.006(2) Å for
C13 (ring A), 0.012(2) Å for C6 (ring B), and 0.006(2) Å for C4 (ring
C); compound 5: ꢀ0.008(2) Å for C11 (ring A), 0.011(2) Å for C6
(ring B) and 0.0029(15) Å for C4 (ring C). The pyrimidine (B) and
imidazole (C) rings are in fact coplanar, with the dihedral angle
of 0.71(7)° for 4 and 0.95(5)° for 5. The dihedral angles between
the benzene and purine planes are 76.78(6)° for 4, and 80.34(4)°
for 2. The values of the related torsion angles have been found to
3. Results and discussion
3.1. Structural analysis (X-ray crystallographic and QM study)
The molecular structures of the compounds 1–5 together with
the atom numbering scheme are shown in Figs. 1 and 2. Crystal
data and structure refinements are given in Table 1, selected bond
lengths and angles together with the corresponding quantum
chemical data obtained at the HF, DFT, RI-MP2 and MP2 levels
are summarized in Table 2.
Although the prepared Bap derivatives are structurally very
similar within both the studied groups, i.e. compounds 1–3 versus
4 and 5, the subtituent’s type and its position on the phenyl group
be 126.7(2)° for
4 and 105.4(2)° for 5 in the case of the
C6AN6AC9AC10 angle, and ꢀ146.2(2)° for 4, and ꢀ47.6(2)° for 5
in the case of the N6AC9AC10AC15 one.
Regarding the crystal structure description, the compounds 1
and 2 are substituted only by the methyl group at the phenyl ring.

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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
353
Fig. 2. The molecular structures of compounds 4 and 5 together with the atom
numbering scheme. Non-hydrogen atoms are drawn as thermal ellipsoids at the
50% probability level.
In this case, the secondary structure is stabilized by intermolecular
hydrogen bonds of the NAHꢁ ꢁ ꢁN type (N6AHꢁ ꢁ ꢁN9 and N7AHꢁ ꢁ ꢁN3
for 1, N6AHꢁ ꢁ ꢁN7 and N9AHꢁ ꢁ ꢁN3 for 2, for details see Fig. 4), and
other non-covalent interactions of the CAHꢁ ꢁ ꢁN and CAHꢁ ꢁ ꢁC types.
The molecules of the compounds 3–5 contain also the oxygen,
chlorine and bromine atoms. Thus, besides NAHꢁ ꢁ ꢁN hydrogen
bonds (N6AHꢁ ꢁ ꢁN7 and N9AHꢁ ꢁ ꢁN3 for 3 and N6AHꢁ ꢁ ꢁN7 for 4
and 5) and CAHꢁ ꢁ ꢁN and CAHꢁ ꢁ ꢁC interactions, their secondary
structures are additionally formed by several CAHꢁ ꢁ ꢁX weak non-
covalent interactions of the van der Waals type, where X stands
for the O atom in CH3O (3), Br atoms in 4 and Cl atom in 5.
In the case of the compounds 1–3, the above-mentioned
NAHꢁ ꢁ ꢁN hydrogen bonds arrange the molecules into infinite 1D
chains (Fig. 3), with the Nꢁ ꢁ ꢁN distances ranging from 2.834 to
3.035 Å (for more detailed information see Supplementary mate-
rial). It was observed that the N3ꢁ ꢁ ꢁN9 and N3ꢁ ꢁ ꢁN7 distances are
generally shorter by approximately 0.1 Å in comparison with those
Fig. 1. The molecular structures of compounds 1, 2 and 3 together with the atom
numbering scheme. Non-hydrogen atoms are drawn as thermal ellipsoids at the
50% probability level.

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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
354
Table 1
Crystal data and structure refinements for 6-(2-methylbenzylamino)purine 1, 6-(4-methylbenzylamino)purine 2, and 6-(3,4-dimethoxybenzylamino)purine 3, 2-chloro-6-(3-
bromobenzylamino)-9-isopropylpurine 4 and 2-chloro-6-(3,4-dichlorobenzylamino)-9-isopropylpurine 5.
1
2
3
4
5
Empirical formula
Formula weight
Crystal system
Space group
C
13N5H13
C13N5H13
239.28
Triclinic
C14N5O2H15
285.31
Triclinic
C15H15BrClN5
380.68
Triclinic
C15H14Cl3N5
370.66
Monoclinic
P21/c
239.28
Monoclinic
P21/c
P1
P1
P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
9.2557(3)
11.2039(3)
11.3211(4)
90.00
100.550(4)
90.00
4.8792(2)
8.0596(3)
15.1224(6)
88.983(3)
82.091(4)
80.131(3)
2
580.29(4)
1.369
100(2)
7.5546(3)
8.3225(3)
10.3124(4)
85.698(3)
87.665(3)
88.714(3)
2
645.89(4)
1.467
105(2)
7.1968(2)
10.3372(3)
11.6119(3)
96.480(2)
101.680(2)
108.128(2)
2
789.51(3)
1.601
108(2)
12.7552(2)
9.58947(12)
14.1985(3)
90.00
110.387(2)
90.00
a
(ꢁ)
b (ꢁ)
c
(ꢁ)
Z
4
4
V (Å3)
1154.15(7)
1.377
100(2)
1627.90(5)
1.512
110(2)
Dcalc. (g cmꢀ3
T (K)
)
l
(mmꢀ1
)
0.089
0.088
0.103
2.776
0.568
Tmax/Tmin
Index ranges
0.9782 / 0.9739
ꢀ11 6 h 6 10
ꢀ11 6 k 6 13
ꢀ13 6 l 6 13
3.19 6 h 6 25.00
8956/2020
0.0343
0.9826/0.9741
ꢀ5 6 h 6 5
ꢀ9 6 k 6 7
ꢀ17 6 l 6 17
2.91 6 h 6 25.00
3973/1956
0.0227
0.9648/0.9599
ꢀ8 6 h 6 8
ꢀ8 6 k 6 9
ꢀ12 6 l 6 12
3.04 6 h 6 25.00
5378/2261
0.0214
0.6067/0.4897
ꢀ8 6 h 6 8
ꢀ8 6 k 6 12
ꢀ13 6 l 6 13
3.04 6 h 6 25.00
5350/2785
0.0156
0.8480/0.8046
ꢀ15 6 h 6 15
ꢀ11 6 k 6 11
ꢀ16 6 l 6 16
3.06 6 h 6 25.00
13711/2867
0.0105
h Range (ꢁ) for data collection
Reflection collected/unique
Rint
Data/restrains/parameters
2020/0/164
1.043
1956/0/164
1.013
2261/0/192
1.105
2785/0/201
1.101
2867/0/210
1.097
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0343
wR2 = 0.0889
R1 = 0.0463
wR2 = 0.0927
0.182 and ꢀ0.204
R1 = 0.0355
wR2 = 0.0918
R1 = 0.0468
wR2 = 0.0961
0.194 and ꢀ0.151
R1 = 0.0328
wR2 = 0.0944
R1 = 0.0377
wR2 = 0.0996
0.208 and ꢀ0.182
R1 = 0.0280
wR2 = 0.0736
R1 = 0.0301
wR2 = 0.0747
0.619 and ꢀ0.606
R1 = 0.0286
wR2 = 0.0827
R1 = 0.0312
wR2 = 0.0845
0.512 and ꢀ0.263
Largest peak and hole (e Åꢀ3
)
Table 2
Selected geometric parameters (bond lengths in Å, and angles in °) of compounds 1–5 as determined by single crystal X-ray analysis and various quantum-chemical methods (all
with the cc-pVDZ basis set).
Method N1AC2
N1AC6
C2AN3
N3AC4
C5AC6
N7AC5
N7AC8
N9AC4
N9AC8
C2AN1AC6 C2AN3AC4 C5AN7AC8 C4AN9AC8
1
2
3
4
5
X-ray
HF
B3LYP
RI-MP2 1.3664
MP2
1.337(2) 1.351(2) 1.328(2) 1.356(2) 1.410(2) 1.383(2) 1.338(2) 1.377(2) 1.324(2) 118.51(11) 112.10(11) 106.28(10) 103.36(10)
1.3398
1.3530
1.3162
1.3377
1.3369
1.3352
1.3041
1.3278
1.3341
1.3341
1.3366
1.3483
1.3551
1.3541
1.3996
1.4102
1.4143
1.4137
1.3851
1.3863
1.3748
1.3747
1.3539
1.3762
1.3832
1.3833
1.3737
1.3848
1.3869
1.3862
1.2899
1.3122
1.3229
1.3214
118.49
118.31
117.94
118.07
113.28
112.94
112.70
112.69
105.26
105.92
106.12
106.08
104.57
104.48
103.95
103.99
1.3647
X-ray
HF
B3LYP
RI-MP2 1.3581
MP2
1.333(2) 1.356(2) 1.335(2) 1.349(2) 1.407(2) 1.392(2) 1.311(2) 1.368(2) 1.362(2) 118.35(12) 110.48(12) 103.29(12) 105.98(12)
1.3321
1.3465
1.3292
1.3479
1.3477
1.3472
1.3124
1.3368
1.3428
1.3416
1.3323
1.3422
1.3481
1.3472
1.4071
1.4170
1.4184
1.4179
1.3835
1.3854
1.3835
1.3819
1.2827
1.3138
1.3328
1.3325
1.3628
1.3785
1.3817
1.3791
1.3717
1.3816
1.3761
1.3748
118.64
118.46
118.16
118.21
111.26
110.88
110.36
110.45
104.13
103.90
102.98
103.02
106.45
106.76
106.82
106.91
1.3573
X-ray
HF
B3LYP
RI-MP2 1.3583
MP2
1.337(2) 1.352(2) 1.334(2) 1.352(2) 1.406(2) 1.388(2) 1.315(2) 1.367(2) 1.361(2) 117.95(12) 110.93(11) 103.65(11) 106.42(11)
1.3322
1.3459
1.3275
1.3469
1.3468
1.3470
1.3127
1.3374
1.3428
1.3419
1.3315
1.3420
1.3477
1.3473
1.4064
1.4171
1.4186
1.4170
1.3835
1.3855
1.3836
1.3830
1.2828
1.3139
1.3324
1.3319
1.3632
1.3789
1.3808
1.3807
1.3715
1.3815
1.3759
1.3746
118.58
118.43
118.11
118.17
111.34
110.88
110.36
110.37
104.13
103.90
102.99
103.00
106.43
106.76
106.87
106.82
1.3571
X-ray
HF
B3LYP
RI-MP2 1.3475
MP2
1.325(3) 1.347(3) 1.318(3) 1.348(3) 1.410(3) 1.387(3) 1.317(3) 1.370(3) 1.364(3) 117.6(2)
109.4(2)
111.11
110.52
109.72
109.85
103.5(2)
103.85
103.71
102.86
102.94
105.6(2)
105.24
105.53
105.76
105.73
1.3214
1.3340
1.3298
1.3478
1.3480
1.3473
1.3017
1.3253
1.3340
1.3323
1.3360
1.3452
1.3522
1.3499
1.4050
1.4165
1.4196
1.4167
1.3792
1.3820
1.3793
1.3774
1.2848
1.3162
1.3374
1.3368
1.3613
1.3783
1.3795
1.3792
1.3744
1.3854
1.3800
1.3791
117.93
117.84
117.54
117.77
1.3480
X-ray
HF
B3LYP
RI-MP2 1.3486
MP2 1.3477
1.326(2) 1.350(2) 1.325(2) 1.351(2) 1.415(2) 1.383(2) 1.314(2) 1.373(2) 1.366(2) 117.61(13) 109.25(12) 103.47(12) 105.44(12)
1.3222
1.3359
1.3310
1.3492
1.3488
1.3475
1.3006
1.3240
1.3339
1.3322
1.3367
1.3457
1.3516
1.3510
1.4045
1.4156
1.4184
1.4174
1.3789
1.3816
1.3778
1.3768
1.2850
1.3163
1.3370
1.3362
1.3606
1.3777
1.3788
1.3780
1.3745
1.3853
1.3799
1.3790
117.95
117.81
117.69
117.73
111.12
110.63
109.83
109.85
103.83
103.69
102.89
102.92
105.26
105.52
105.72
105.74
of N7ꢁ ꢁ ꢁN6 or N9ꢁ ꢁ ꢁN6. The crystal structures of both the com-
pounds 4 and 5 are formed by centrosymmetric dimers connected
through the N6AHꢁ ꢁ ꢁN7 hydrogen bonds, where Nꢁ ꢁ ꢁN interaction
distances were found to be 3.012(3) Å for 4 and 2.975(2) Å for 5. All
the discussed non-covalent interactions as well as their symmetry
codes are summarized in Tables S1–S5 and Figs. S1 and S2 in
Appendix A: Supplementary material section. The above-
mentioned nonbonding interactions within the crystal structures
resulted in significant differences in dihedral angles between
benzene and purine rings as well as in the C6AN6AC9AC10 and

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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
355
N6AC9AC10AC15 torsion angles, as has been discussed above. For
the same reason, the used theoretical approaches have provided
more or less different values. Comparable results have been ob-
tained only in the case of the RI-MP2 and MP2 levels, which well
confirm the profitability of the resolution identity approximation.
Quantitative agreement between the experimental and theoretical
results is observable only in the case of the compound 1, as it is evi-
dent from Table 3.
absorptions with strong intensity at 1619–1633 cmꢀ1 belong to
(C@N)aromatic purine skeletal vibrations. The letter mentioned
m
maxima reflect on similarity within the group of the studied com-
pounds (see Fig. 3). The regions at 2800–3000 cmꢀ1 and 3050–
3135 cmꢀ1 relate to the
m(CaliphaticAH), and m(CaromaticAH) valence
vibrations, respectively. The bands of weak or medium intensities
observable within the 3258–3286 cmꢀ1 and 3424–3430 cmꢀ1 re-
gions should be classified as the
tions, respectively [32,33].
m(N9(7)AH), and m(N6AH) vibra-
Proton positioning at the N7 atom of the compound 1 leads to
significant geometric changes compared to the N9-protonated as
well as N9-substituted derivatives, particularly at the imidazole
part of the purine ring. The found differences are generally caused
by the hybridization type of the corresponding nitrogen atom,
which is specifically sp2 for the unsubstituted and sp3 for the
substituted/protonated one. Thus, the apparent differences be-
tween the N7-protonated compound 1 and N9-substituted/proton-
ated compounds 2–5 have been found for the N9AC8 and N7AC8
bond lengths, and principally for the C5AN7AC8 and C4AN9AC8
internal angles (see Table 2). The CAN bonds formed by protonated
nitrogen have been found longer by 0.014 Å for 1, and 0.051 and
0.046 Å for 2, and 3, respectively. Similarly, nitrogen substitution
leads to the CANAC internal angle value typically higher by
approximately 3.0° in comparison with the unprotonated system.
Thus, the experimental bond distances are 1.324(2) Å (1),
1.362(2) Å (2), 1.361(2) Å (3), 1.364(3) Å (4), and 1.366(2) Å (5)
for the N9AC8 bond length; 1.338(2) Å (1), 1.311(2) Å (2),
1.315(2) Å (3), 1.317(3) Å (4), 1.314(2) Å (5) for the N7AC8 bond
length. The experimental values of the internal angle C4AN9AC8
are 103.36(10)° for 1, 105.98(12)° for 2, 106.42(11)° for 3, and
105.6(2)° for 4, 105.44(12)° for 5. The values of the internal angle
C5AN7AC8 are 106.28(10)° for 1, 103.29(12)° for 2, 103.65(11)°
for 3, 103.5(2)° for 4, 103.47(12)° for 5. The values obtained by
the MP2/cc-pVDZ approach (as the most accurate from those used)
are rather similar, i.e. 1.3214 Å (1), 1.3748 Å (2), 1.3746 Å (3),
1.3791 Å (4), and 1.3790 Å (5) for the N9AC8 bond length, and
1.3833 Å (1), 1.3325 Å (2), 1.3319 Å (3), 1.3368 Å (4), and
1.3362 Å (5) for the N7AC8 bond length. Also in this case, bond
lengths calculated for protonated nitrogen are longer by approxi-
mately 0.05 Å. The values of internal angles calculated at the same
level are 103.99° (1), 106.91° (2), 106.82° (3), 105.73° (4), and
105.74° (5) for the C4AN9AC8 angle, and 106.08° (1), 103.02°
(2), 103.00° (3), 102.94° (4), and 105.74° (5) for the C5AN7AC8
angle.
Other typical bands should be observed in dependence on struc-
tural differences of each individual studied compound. Thus, the
strong maximum at 1268 cmꢀ1 in the spectrum of 3 have been as-
signed to the
found at 668 and 1155 cmꢀ1, and observable only in the spectra of
4 and 5, originate from the (CphenylABr) vibration, and (Cphe-
nylACl) vibration, respectively.
m(CphenylAO) vibration. The weak or medium maxima
m
m
The calculated frequencies enable more detailed analysis of the
FT-IR spectra measured. Important vibrational frequencies ob-
tained at the HF, B3LYP, RI-MP2 and MP2 levels of theory are sum-
marized in Table 4. Generally speaking, all the methods used have
given slightly overestimated frequency values in most cases. Such
results should be undoubtedly assigned partly to the methodology
errors, partly to the crystal field effects neglected. The frequencies
of the m(C@C)aromatic vibrations of the benzene and purine moieties
have been found overestimated by approximately 100 cmꢀ1, and
the best results have been obtained at the B3LYP level (in the range
of 1560–1619 cmꢀ1). Surprisingly, both RI-MP2 and MP2 ap-
proaches have provided worse results in this case. Regarding the
intensity of signals, the evident correspondence between experi-
mental and theoretical data has not been found for any calculation
approach used. Where experimental values are rather medium in-
tense, the HF as well as B3LYP approaches has also provided peaks
of strong or very strong intensities. Both the RI-MP2 and MP2
calculations have contrariwise led to absorptions with very low
In general, the accuracy of the calculated bond lengths is com-
parable in the whole range of the methods used. The deviations
from the experimental crystallographic values do not exceed
0.05 Å. The calculated values of the key bond angles at the purine
ring correspond much better with those obtained by X-ray analy-
sis, where the deviations of the values obtained by both MP2 meth-
ods does not exceed 1.0°. As can be evident from Table 2, the best
accuracy has been achieved at the RI-MP2 and MP2 levels as
expected.
3.2. FT-IR and Raman spectroscopy
All the FT-IR as well as Raman spectra measured are presented
in Figs. S3–S8 in Appendix A: Supplementary material section. Se-
lected maxima observed in the experimentally measured FT-IR
spectra and their assignments are presented in Table 4.
Due to the structural similarity of the studied compounds, sev-
eral common characteristic features should be found, specifically
in the purine and phenyl parts of the molecules. Most of the bands
observable within the 640–900 cmꢀ1 region originate from the
purine skeletal vibrations. Similarly, the medium or strong intense
peaks observed at 1460–1598 cmꢀ1 belong to the
skeletal vibrations of the both phenyl and purine moieties, while
m
(C@C)aromatic
Fig. 3. Superposition of the maxima belonging to
within the group of the studied compound 1–5.
m(CAN), showing on the similarity

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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
356
intensities. However, it must be said, that it is relatively difficult to
separate the (C@C)aromatic and (C@N)aromatic skeletal vibrations
within the purine moiety.
The (C@N)aromatic skeleton vibrations of mostly strong or
mediumꢀi1ntensities have been found within the region of 1518–
1688 cmꢀ1 RI-MP2 and 1493–1688 cmꢀ1 for MP2 approach. As it
is evident from Table 4, their values are not significantly influenced
by the substitution of the purine ring. The best agreement with
experimental results has been found for both MP2 approaches.
m
m
Similarly, the m(CaromaticAH) vibrations have been found within
m
the region of 3020–3079 cmꢀ1 for HF, 3063–3122 cmꢀ1 for B3LYP,
3038–3124 cmꢀ1 for RI-MP2 and 3059–3126 cmꢀ1 for the MP2
method, which has provided the best results. Majority of the values
found are of weak intensity (contrary to experimental medium val-
ues). The band of weak intensity observable at 3096–3106 cmꢀ1
1663 cm
for HF, 1468–1596 cmꢀ1 for B3LYP, for 1512–
Fig. 4. Parts of the crystal structures of compounds 1, 2 and 4, showing the NAHꢁ ꢁ ꢁN hydrogen bonds (dashed lines), and depicting the formation of infinite one-dimensional
chains of 1 and 2, and centrosymmetric dimers (for 4).

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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
357
Table 3
Selected torsion angles (°) of compounds 1–5 determined by single crystal X-ray analysis and various quantum-chemical methods (all with the cc-pVDZ basis set).
Method
C6AN6AC9AC10
N6AC9AC10AC15
1
2
3
4
5
1
2
3
4
5
X-ray
HF
B3LYP
RI-MP2
MP2
173.95(12)
179.28
176.12
177.83
178.05
ꢀ78.4(2)
ꢀ98.2(2)
126.7(2)
157.40
132.25
75.46
105.4(2)
90.46
92.88
73.24
73.44
114.06(13)
102.31
105.29
104.54
104.48
ꢀ67.6(2)
ꢀ109.87
ꢀ109.52
ꢀ95.62
1.2(2)
146.2(2)
128.34
143.44
88.74
ꢀ47.6(2)
ꢀ82.49
ꢀ75.57
ꢀ90.94
ꢀ90.76
ꢀ101.33
ꢀ100.26
ꢀ81.77
ꢀ82.26
ꢀ162.13
ꢀ136.93
ꢀ77.34
ꢀ77.79
46.21
40.27
89.30
88.87
75.72
ꢀ96.33
89.03
Table 4
Selected experimental and calculated (all with the cc-pVDZ basis set) FT-IR vibration frequencies (cmꢀ1) of compounds 1–5 and their assignments.
Method
Exp.
Comp.
m
(C@C)aromatic
m
(C@N)aromatic
m
(CaromaticAH)
m
(C8AH)
m
(NpurineAH)
m
(N6AH)
m
(CphenylAX)
m
(CpurineACl)
1
2
3
4
5
1565m, 1530w, 1460m
1598s, 1516w, 1460m
1592m, 1515s, 1487w
1568s, 1536m, 1472m
1574m, 1539m, 1492m
1625vs
1620vs
1623vs
1619vs
1633vs
3113m, 3050m
3100m, 3062m
3133m, 3071m
3132m, 3073m
3129m, 3074m
3262m
3258m
3286m
3427m
3426m
3430w
3429w
3424w
1268sa
668mb
1155mc
HF
1
2
3
4
5
1641w, 1610w
1645s, 1605w
1646s, 1622m
1645vs, 1623s
1631vs, 1622s
1663s, 1551m, 1518s
1653s, 1569w, 1534s
1652s, 1565m, 1526m
1645vs, 1571w, 1521s
1647s, 1573w, 1525s
3059–3024w/m
3050–3020w
3077–3047w/m
3077–3037w
3079–3057w
3096w
3102w
3102w
3105w
3106w
3548m
3538m
3539m
3478w
3499m
3493m
3489m
3500m
1324s, 1258sa
660wb
937m
961m
1020mc
B3LYP
RI-MP2
MP2
1
2
3
4
5
1618s, 1610w, 1582w
1619w, 1613s, 1577w
1614vs, 1609m, 1590w
1612vs, 1598w, 1570m
1610vs, 1591w, 1561w
1555s, 1497m, 1469m
1594s, 1516m, 1471s
1596s, 1516m, 1472s
1579s, 1517w, 1468s
1575s, 1518w, 1469w
3105–3070w
3094–3063w/m
3122–3067w/m
3121–3080w
3120–3100w
3143w
3149w
3148w
3152w
3153w
3533m
3530m
3530m
3473w
3495m
3496m
3493m
3499m
1266s, 1230sa
658wb
912m
906m
1010wc
1
2
3
4
5
1673m, 1637w
1686m, 1628w
1670w, 1640m
1659w, 1630m
1662w, 1610m
1685s, 1606s, 1545s
1688s, 1645s, 1540m
1687s, 1647s, 1512m
1679vs, 1610s, 1585s
1679vs, 1608s, 1585s
3103–3066w
3103–3038w
3124–3092w
3119–3068w
3120–3086w
3161w
3159w
3159w
3171w
3172w
3522m
3519m
3520m
3425w
3456m
3452m
3461m
3464m
1343s, 1317sa
692wb
1063w
954m
957m
1
2
3
4
5
1675w, 1637w
1687w, 1646m
1671w, 1641m
1660w, 1631m
1663w, 1610s
1686s, 1606s, 1543s
1688s, 1587w, 1512s
1687s, 1646s, 1513s
1680vs, 1611s, 1493s
1679vs, 1612s, 1494s
3106–3068w
3105–3059w
3126–3094w
3122–3071w
3123–3087w
3163w
3161w
3161w
3173w
3175w
3522m
3520m
3521m
3429w
3459w
3455m
3464m
3466m
1344s, 1288sa
692wb
953m
956m
1062mc
vs = Very strong, s = strong, m = medium, w = weak.
a
m
m
m
(CaromaticAO).
(CaromaticABr).
(CaromaticACl).
b
c
(HF), 3143–3153 cmꢀ1 (B3LYP), 3159–3172 cmꢀ1 (RI-MP2), and
3163–3175 cmꢀ1 (MP2), belongs to the
(C8AH) vibration.
The (N6AH) vibration has been identified in the 3478–
form infinite 1D chains in the crystal structures, while molecules
of compounds 4 and 5 have been found to be arranged as
m
m
3500 cmꢀ1 (HF), 3473–3499 cmꢀ1 (B3LYP), 3425–3463 cmꢀ1 (RI-
MP2), and 3429–3466 cmꢀ1 (MP2) regions. All the values are
slightly overestimated compared to experimental data (3420–
3429 cmꢀ1). Similarly to experimental observations, the vibration
intensities have been found to be weak or medium.
A substantial difference between experimental and calculated
frequency values has been observed for the m(N9(7)AH) vibration
of the compounds 1–3. In this case, the frequency is more influ-
enced by N7AHꢁ ꢁ ꢁN3 or N9AHꢁ ꢁ ꢁN3 hydrogen bonds formed be-
tween the neighboring purine moieties in the crystal structure
(Fig. 4). Thus, all the calculated values of this vibration are gener-
ally shifted by approximately 300 cmꢀ1 to higher wavenumbers
due to neglecting all the intermolecular interactions during the cal-
culations. Both RI-MP2 and MP2 methods have provided the same
results (3519–3522 cmꢀ1 and 3520–3522 cmꢀ1). The HF and B3LYP
calculations have led to slightly higher values (3538–3548 cmꢀ1
and 3530–3533 cmꢀ1, contrary to the experimentally determined
value of 3260 cmꢀ1).
Fig. 5. Superposition of the experimentally measured (black line) and calculated
FT-IR spectra for compound 5 (dotted line for isolated monomer, dashed line for
centrosymmetric dimer), showing the influence of NAHꢁ ꢁ ꢁN hydrogen bonds on the
As has been discussed above, molecules of compounds 1–3 are
connected together via the N6AHꢁ ꢁ ꢁN9 and N7AHꢁ ꢁ ꢁN3 (for 1)
or N6AHꢁ ꢁ ꢁN7 and N9AHꢁ ꢁ ꢁN3 (for 2 and 3) hydrogen bonds to
m
(NAH) and (CAN) vibrational maxima.

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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
358
Table 5
Selected Raman spectral data (cmꢀ1) of compounds 1–5 and their assignments.
Method
Exp.
Comp.
m
(C@C)aromatic
m
(C@N)aromatic
m
(CaromaticAH)
m
(CaliphaticAH)
m(CAX)
1
2
3
4
5
1568w, 1493w, 1461w
1562w, 1489w, 1452w
1532w, 1460w,
1573w, 1534w, 1478m
1571m, 1532w, 1474m
1604w
1610w
1595m
1592w
1596w
3113w, 3048w
3130w, 3055w
3133w, 3082w, 3055w
3142w, 3072w, 3053w
3132w, 3074w, 3057m
3000w, 2925w, 2880w
3009w, 2912w, 2919w
3003w, 2937w, 2835w
2981m, 2930m, 2868w
2985w, 2929m, 2872w
1164w
1167w
X = Cl, Br.
vs = Very strong, s = strong, m = medium, w = weak.
centrosymmetric dimers connected thorough the N6AHꢁ ꢁ ꢁN7
hydrogen bonds. Thus, the comparative HF, DFT and RI-MP2 calcu-
lations have been performed for the systems of compounds 2, 4
and 5, with aim to investigate the influence of the above-
mentioned hydrogen bonds on the values of calculated infrared
frequencies. Significant differences have been found for the
4. Conclusions
In this work, we have investigated structural and vibrational
properties of several 6-benzylaminopurine derivatives using a
combination of single crystal X-ray diffraction analysis, FT-IR and
Raman spectroscopy, and quantum chemical calculations. The
studied compounds should be divided into two structurally differ-
ent groups. The compounds 1, 2 and 3 represent the derivatives
with the unsubstituted imidazole moiety, while the compounds 4
and 5 have been additionally modified by the chloro and isopropyl
substituents at the C2, and N9 position, respectively. Concerning
the molecular structures of the studied compounds, the electro-
neutral form of 1 shows the non-typical protonation at the N7 po-
sition of the purine ring. The crystal structures of all the
compounds are stabilized by the hydrogen bonds of the NAHꢁ ꢁ ꢁN
type accompanied by several weak non-covalent interactions of
the CAHꢁ ꢁ ꢁC and CAHꢁ ꢁ ꢁX (X = O, Cl, Br) types. The molecules of
1, 2 and 3 form infinite 1D chains bound by hydrogen bonds, while
compounds 4 and 5 form centrosymmetric dimers.
m(N9AH) and m(N6AH) vibrations, which values are generally
shifted to lower wavenumbers and are also very close to the exper-
imentally determined ones. Superposition of experimental and cal-
culated spectra of compound 5 is shown in Fig. 5 Selected maxima
calculated for these ‘‘dimers’’ and their comparison with results
obtained for isolated molecules are presented in Table S6 in
Appendix A: Supplementary material section.
Concerning the m(CphenylAO) vibrations of 3, the wavenumbers
1266 and 1230 cmꢀ1 obtained by the B3LYP approach represent
the best agreement with the experimental values. The MP2,
RI-MP2 and HF methods have generally provided values overesti-
mated by 60–80 cmꢀ1
. Two types of the m(CACl) vibration
expected in the spectra of the compounds 4 and 5 have been
identified. The first one, which is located at higher wavenumbers
belongs to the m(CphenylACl) vibration. The MP2 approaches have
In general, the accuracy of the calculated bond lengths is com-
parable in the whole range of the methods used. The deviations
from the experimental crystallographic values do not exceed
0.05 Å. The calculated values of the key bond angles at the purine
ring correspond much better with those obtained by X-ray
analysis, when the deviations of the obtained values do not exceed
1.0°.
In order to assign important molecular vibrations, the quantum
chemical calculations of infrared as well as Raman spectra based
on the HF, DFT, RI-MP2 and MP2 approaches were used. Generally
speaking, both RI-MP2 and MP2 methods have provided results
comparable with the experimental data, while the HF and DFT fre-
quencies have been generally underestimated. Observed devia-
tions are given partly due to the methodology errors, partly due
to the crystal field effects neglecting. A substantial difference be-
tween the experimental and calculated frequency values has been
observed only for the m(N9(7)AH) and m(N6AH) vibrations of the
compounds. In these cases, the frequency is more influenced by
hydrogen bonds formed between the neighboring purine moieties
in the crystal structure. Similarly, the m(NAH) vibrations have been
found to be active only in the calculated Raman spectra if com-
pared with those experimentally measured. Regarding the inten-
sity of signals, the evident correspondence between experimental
and theoretical data has not been generally found for any calcula-
tion approach used.
led to the best agreement with the experimental value, when the
calculated values are 1063 cmꢀ1 for RI-MP2 and 1062 cmꢀ1 for
MP2. The second one corresponds to the
m(CpurineACl) vibration
and has been found within the region of 953–957 cmꢀ1 (also for
both MP2 methods). The
found at 692 cmꢀ1 (MP2).
m(CphenylABr) vibration of 4 has been
Selected maxima observed in Raman spectra and their assign-
ments are summarized in Table 5. The maxima observed in the
range of 842–889 cmꢀ1 belong to the d(CaromaticAH) vibrations.
The weak or medium maxima in the range of 1452–1573 cmꢀ1
may be assigned to the
or medium intensity found between 1592 and 1610 cmꢀ1 relate to
the
(C@N)aromatic vibration. The bands found at 2835–3009 cmꢀ1
and 3048–3142 cmꢀ1 belong to the
(CaliphaticAH), and (Caro-
maticAH) vibration, respectively [34–36].
The intensities of the (C@C)aromatic vibration range from weak
to medium, while the (C@N)aromatic vibration have been found to
be generally weak. The (CaromaticAH) vibration shows the med-
ium or strong intensity, contrary to weak intensity observed in
the infrared spectra. The (N6AH) Raman vibrations show med-
ium intensity and are generally more intense than those from
the infrared spectra. The (N9(7)AH) vibrations have been found
to be strong intense. Compared with the experimentally mea-
sured spectra, both (NAH) vibrations show the activity in the
m(C@C)aromatic vibration. The bands of weak
m
m
m
m
m
m
m
m
m
calculated spectra only. This difference is also probably given by
the presence of the NAHꢁ ꢁ ꢁN intermolecular hydrogen bonds,
whose role has been neglected in the calculation. Finally, the
Acknowledgements
m
(CAO),
m
(CACl) and
m
(CABr) vibrations have been found to be
This research was supported by the Ministry of Education,
Youth and Sports of the Czech Republic (MSM6198959218), Grant
Agency of the Academy of Science of the Czech Republic
(IAA401370901), and by the Operational Program Research and
Development for Innovations – European Social Fund (CZ.1.05/
weak, contrary to medium or strong intensities observed in the
infrared spectra. Concerning the results obtained by RI-MP2 and
MP2 methods, the Turbomole program package does not provide
the Raman intensities, and thus these could not be discussed
here.
ˇ
2.1.00/03.0058). The authors would like to thank Mr. Lukáš Dvorák

ˇ
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M. Cajan, Z. Trávnícek / Journal of Molecular Structure 994 (2011) 350–359
359
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Appendix A. Supplementary material
The hydrogen bonds and non-covalent interaction parameters
of compounds 1–5, the figures showing the crystal packing as well
as FT-IR and Raman spectra of all the compounds studied are pre-
sented in the Supplementary material section. Crystallographic
data for the structures of the compounds 1–5 have been deposited
within the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; email: de-
posit@ccdc.cam.ac.uk, or at http://www.ccdc.cam.ac.uk with the
deposition numbers CCDC 794403–794407. These data can be ob-
tained free of charge via www.ccdc.cam.ac.uk/data_request/cif.
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