Spectroscopic studies, antimicrobial activities and crystal structures of N-(2-hydroxy-3-methoxybenzalidene)1-aminonaphthalene

Article abstract of DOI:10.1016/j.molstruc.2004.10.030

Schiff base N-(2-hydroxy-3-methoxybenzalidene)1-aminonaphthalene has been synthesized from the reaction of 2-hydroxy-3-methoxybenzaldehyde with 1-aminonaphthalene. The compound were characterized by elemental analysis, FT-IR, ¹H NMR, ¹³C NMR and UV-visible techniques. The UV-visible spectra of the Schiff base were studied in polar and nonpolar solvents in acidic and basic media. The structure of the compound has been examined cyrstallographically. There are two independent molecules in the asymmetric unit. It crystallizes in the monoclinic space group P2₁/c, with unit cell parameters: a=14, 602(2), b=5,800(1), c=16, 899(1) ?, V=1394.4(2) ?³, D_x=1.321 g cm^-3 and Z=4. The crystal structure was solved by direct methods and refined by full-matrix least squares to a find R=0.041 of for 1179 observed reflections. The title compound's antimicrobial activities also have been studied. The antimicrobial activities of the ligand has been screened in vitro against the organisms Escherichia coli ATCC 11230, Staphylococcus aureus ATCC 6538, Klebsiella pneumoniae UC57, Micrococcus luteus La 2971, Proteus vulgaris ATCC 8427, Pseudomonas aeruginosa ATCC 27853, Mycobacterium smegmatis CCM 2067, Bacillus cereus ATCC 7064 and Listeria monocytogenes ATCC 15313, the yeast cultures Candida albicans ATCC 10231, Kluyveromyces fragilis NRRL 2415, Rhodotorula rubra DSM 70403, Debaryomyces hansenii DSM 70238 and Hanseniaspora guilliermondii DSM 3432.

Full text of DOI:10.1016/j.molstruc.2004.10.030

Journal of Molecular Structure 737 (2005) 159–164
www.elsevier.com/locate/molstruc
Spectroscopic studies, antimicrobial activities and crystal structures
of N-(2-hydroxy-3-methoxybenzalidene)1-aminonaphthalene
a,
Hu¨seyin Unver , Mustafa Yıldız , Bas¸aran Du¨lger ,
b
c
¨
*
d
Ozen Ozgen , Engin Kendi , Tahsin Nuri Durlu
d
a,e
¨
¨
a
˘
Department of Physics, Faculty of Science, Ankara University, TR-06100 Tandogan, Ankara, Turkey
bDepartment of Chemistry, Faculty of Science and Arts, C¸ anakkale Onsekiz Mart University, TR-17100 C¸ anakkale, Turkey
cDepartment of Biology, Faculty of Arts and Sciences, C¸ anakkale Onsekiz Mart University, TR-17100 C¸ anakkale, Turkey
dDepartment of Engineering Physics, Hacettepe University, TR-06532 Beytepe, Ankara, Turkey
e
¨
Department of Physics, Faculty of Arts and Sciences, University of Kırıkkale, Yahs¸ihan Kampus, TR-71450, Kırıkkale, Turkey
Received 14 August 2004; accepted 22 October 2004
Available online 23 November 2004
Abstract
Schiff base N-(2-hydroxy-3-methoxybenzalidene)1-aminonaphthalene has been synthesized from the reaction of 2-hydroxy-3-
1
methoxybenzaldehyde with 1-aminonaphthalene. The compound were characterized by elemental analysis, FT-IR, H NMR, 13C NMR
and UV–visible techniques. The UV–visible spectra of the Schiff base were studied in polar and nonpolar solvents in acidic and basic media.
The structure of the compound has been examined cyrstallographically. There are two independent molecules in the asymmetric unit. It
3
˚
˚
crystallizes in the monoclinic space group P21/c, with unit cell parameters: aZ14, 602(2), bZ5,800(1), cZ16, 899(1) A, VZ1394.4(2) A ,
DxZ1.321 g cmK3 and ZZ4. The crystal structure was solved by direct methods and refined by full-matrix least squares to a find RZ0.041
of for 1179 observed reflections. The title compound’s antimicrobial activities also have been studied. The antimicrobial activities of the
ligand has been screened in vitro against the organisms Escherichia coli ATCC 11230, Staphylococcus aureus ATCC 6538, Klebsiella
pneumoniae UC57, Micrococcus luteus La 2971, Proteus vulgaris ATCC 8427, Pseudomonas aeruginosa ATCC 27853, Mycobacterium
smegmatis CCM 2067, Bacillus cereus ATCC 7064 and Listeria monocytogenes ATCC 15313, the yeast cultures Candida albicans ATCC
10231, Kluyveromyces fragilis NRRL 2415, Rhodotorula rubra DSM 70403, Debaryomyces hansenii DSM 70238 and Hanseniaspora
guilliermondii DSM 3432.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Spectroscopic studies; Ligand; Enol-imine form; Tautomerism; Antimicrobial activities
1. Introduction
show photochromism in the solid state. The photochromism
is produced by intramolecular proton transfer from the
hydroxyl O atom to the imine N atom [7–10]. Apart from the
biological activities, photochromism is another character-
istic of these materials leading to its application in various
areas such as the control and measurement of radiation
intensity, display systems and optical computers. Tautomer-
ism in Schiff bases with OH group in ortho position to the
imino group both in solution and in solid state were
investigated using spectroscopy and X-ray crystallograpy
techniques [2–6,11,12]. Schiff bases with OH group in ortho
position to the imino group are of interest mainly due to the
existence of either O–H/N or O/H–N type of hydrogen
bond and tautomerism between enol-imine and keto-amine
Schiff bases have been widely used as ligands in the
formation of transition metal complexes [1]. Although many
structures of transition metal complexes with Schiff base
ligands have been determined, a relatively small number of
free Schiff bases have been structurally characterized [2–6].
However, knowing the structures of free Schiff base ligands
could be important in view of comparison with the structure
of Schiff base complexes. N-substituted salicylaldimines
* Corresponding author. Tel.: C90 312 212 6720; fax: C90 312 223
2395.
¨
E-mail address: unver@science.ankara.edu.tr (H. Unver).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.10.030

¨
H. Unver et al. / Journal of Molecular Structure 737 (2005) 159–164
160
nCaN; 1608s, nCaC; 1563 m, nC–N; 1392 m, nC–O; 1336
m, nC–O–C; 1252s, 1177s, 1090s. 1H NMR(DMSO); d
ppm, 13.06(s, 1H, Ar–OH); 8.77 (s, 1H, Ar–CHaN–Ar);
7.96–6.69 (m, 10H, Ar–H); 3.63 (s, 3H, Ar–OCH3). 13C-
NMR(DMSO); d ppm, 165.06 (CHaN), 151.42 (Cipso,
–OH, ArNaC), 148.86 (Cipso, –OCH3), 146.13, 134.46,
128.90, 128.62, 128.32, 127.59, 127.51, 127.13, 124.68,
123.29, 120.51, 119.66, 116.58, 115.31 (Ar–C) and 56
(–OCH3).
Scheme 1.
form. In these compounds, short hydrogen bonds between
the OH group in ortho position to the imino group and the
imine nitrogen are due to the stereochemistry.
2.3. Crystallography
The data collection was performed on a Enraf-Nonius
CAD-4 diffractometer employing graphite-monochroma-
In this paper, we investigated the structure of the title
compound (Scheme 1), in order to reveal the presence of
either the enol-imine or keto-amine forms related with
˚
tized Mo Ka radiation (lZ0.71000 A) [15]. The details of
1
hydrogen bonding by using FT-IR, H NMR, 13C-NMR,
the X-ray data collection, structure solution and structure
refinements were given in Table 1. Data reduction and
corrections for absorption and crystal decomposition (1.1%)
were carried out using the TEXAN Single Crystal Structure
Analysis Software [16]. The structure was solved by
SHELXSK97 [17] and refined with SHELXL-97 [18]. The
positions of the H atoms bonded to C atoms were calculated
UV–visible and X-ray crystallographic techniques in the
solution and solid states, respectively. In addition, we have
studied antimicrobial activities of compound. The anti-
microbial activities of compound has been screened in vitro
againts the microorganisms by disc diffusion method
[13,14].
˚
[C–H distance 0.93 A], and included in the structure factor
calculation using a riding model. The hydroxy atom HO1
was found from difference Fourier map calculated at
the refinement process as a small positive electron density.
The final fractional atomic coordinates and thermal
parameters were given in Table 2. Bond distances and
angles are listed in Table 3 and an ORTEP view of the
molecular structure is given in Fig. 1 [19].
2. Experimental section
2.1. Reagents and techniques
The 1H and 13C-NMR spectra were recorded on a Bruker
DPX FT-NMR spectrometer operating at 400 and
101.6 MHz. The 1H and 13C chemical shifts were measured
using SiMe4 as an internal standard. Infrared absorption
spectra were obtained from a Perkin Elmer BX II
spectrometer in KBr discs and were reported in cmK1
units. The UV–visible spectra were measured using a
SHIMADZU 1208 series spectrometer. Carbon, nitrogen
and hydrogen analysis were performed on a LECO CHNS-
932 analyzer. Melting point was measured on a Electro
Thermal IA 9100 apparatus using a capillary tube. 2-
hydroxy-3-methoxybenzaldehyde, 1-aminonaphthalene,
THF, CHCl3, EtOH, benzene, DMSO, CF3COOH and
[C2H5]3N were purchased from Merck (Germany).
Table 1
Crystal and experimental data
Compound
C18H15NO2
Yellow/prismatic
275.73
Colour/shape
Formula weight
Crystal system
Space group
Monoclinic
P21/c
˚
Unit cell dimensions
aZ14.602(2) A
˚
bZ5.800(1) A, bZ103.00(1)8
˚
cZ16.899(1) A
3
˚
Volume
1394(2) A
Z
4
Density (calculated)
Absorption coefficient
F (0 0 0)
1.321 g cmK3
0.086 mmK1
584
0.20!0.15!0.32 mm3
2.47–24.638
2.2. Synthesis of N-(2-hydroxy-3-methoxybenzalidene)
1-aminonaphthalene
Crystal size
q Range for data collection
Index ranges
K17%h%0; K6%k%0;
K19%l%19
2429
1-Aminonaphthalene (0.50 g; 3.49!10K3 mol) was
added to a dry THF (100 mL) solution of 2-hydroxy-3-
methoxybenzaldehyde (0.53 g; 3.49!10K3 mol). The mix-
ture was stirred and heated for 2 h. Compound was obtained
from the evaporation of THF. It was crystallized from
methanol as a red crystal, m.p. 92 8C, 0.65 g (67%) yields.
Found: C, 77.01; H, 5.02; N, 4.98. Calc. For C18H15NO2; C,
77.97; H, 5.40; N, 5.05%. IR(KBr, cmK1); nAr–H; 3045 w,
Reflections collected
Independent reflections
Reflections observed (IO2s(I))
Refinement method
2335
1179
Full-matrix least-squares on F2
Data/restraints/parameters
Goodness-of-fit on F2
2335/0/387
0.905
Final R indices [IO2s(I)]
Largest diff. peak and hole
R1Z0.041; wR2Z0.104
K3
˚
0.151 and K0.170 e A

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H. Unver et al. / Journal of Molecular Structure 737 (2005) 159–164
161
Table 2
Table 3
Selected bond lengths (A) and bond angles (8)
˚
Atomic coordinates and equivalent isotropic displacement parameters of
2
the title compound (A )
˚
C10–N1 1.424(2)
N1–C11 1.266(2)
C11–C12 1.455(2)
C12–C17 1.396(2)
C17–O2 1.379(2)
C28–N2 1.410(2)
Atom
x
y
z
Ueq
N2–C29 1.284(2)
C29–C30 1.442(2)
C30–C35 1.409(2)
C35–O4 1.316(2)
C1
0.725(1)
0.822(1)
0.887(1)
0.865(1)
0.773(1)
0.701(1)
0.605(1)
0.538(1)
0.559(1)
0.653(1)
0.682(1)
0.625(1)
0.655(1)
0.588(1)
0.616(1)
0.711(1)
0.776(1)
0.870(1)
0.749(1)
0.900(1)
0.815(1)
0.275(1)
0.179(1)
0.109(1)
0.137(1)
0.228(1)
0.299(1)
0.394(1)
0.465(1)
0.439(1)
0.349(1)
0.320(1)
0.377(1)
0.346(1)
0.410(1)
0.382(1)
0.289(1)
0.224(1)
0.128(1)
0.251(1)
0.098(1)
0.186(1)
K0.094(2)
K0.036(2)
K0.179(3)
K0.370(3)
K0.428(3)
K0.291(2)
K0.346(2)
K0.213(3)
K0.020(3)
0.034(2)
0.348(1)
0.358(1)
0.405(1)
0.444(1)
0.437(1)
0.388(1)
0.380(1)
0.334(1)
0.290(1)
0.299(1)
0.254(1)
0.217(1)
0.167(1)
0.123(1)
0.076(1)
0.073(1)
0.116(1)
0.118(1)
0.163(1)
0.073(1)
0.202(1)
0.653(1)
0.641(1)
0.595(1)
0.557(1)
0.566(1)
0.611(1)
0.617(1)
0.665(1)
0.704(1)
0.702(1)
0.747(1)
0.786(1)
0.834(1)
0.879(1)
0.925(1)
0.928(1)
0.885(1)
0.884(1)
0.838(1)
0.931(1)
0.800(1)
0.041(3)
0.049(3)
0.067(4)
0.064(5)
0.068(4)
0.046(4)
0.055(4)
0.072(5)
0.061(4)
0.050(4)
0.045(3)
0.052(4)
0.045(3)
0.049(3)
0.056(4)
0.050(3)
0.048(3)
0.078(3)
0.053(4)
0.085(5)
0.060(3)
0.048(3)
0.064(4)
0.065(4)
0.071(5)
0.053(3)
0.049(4)
0.067(5)
0.059(4)
0.052(4)
0.041(3)
0.052(3)
0.045(3)
0.042(3)
0.053(3)
0.055(4)
0.055(4)
0.051(3)
0.065(3)
0.044(3)
0.074(5)
0.076(3)
C2
C3
C1–C10–N1 116.1(1)
C9–C10–N1 121.2(1)
C11–N1–C10 122.7(1)
N1–C11–C12 121.6(1)
C17–C12–C11 121.3(1)
C13–C12–C11 119.5(1)
O2–C17–C16 119.2(1)
O2–C17–C12 120.2(1)
N2–C28–C19 116.2(1)
C29–N2–C28 123.2(1)
N2–C29–C30 122.2(1)
C31–C30–C35 119.3(1)
C31–C30–C29 121.1(1)
C35–C30–C29 119.5(1)
O4–C35–C30 123.5(1)
O4–C35–C34 118.9(1)
C4
C5
C6
C7
C8
C9
C10
N1
0.218(2)
C11
C12
C13
C14
C15
C16
O1
0.367(3)
0.544(2)
show absorption in the range greater than 400 nm in polar
and nonpolar solvents [2,3]. It is point out that the new band
belongs to the keto-amine form of the Schiff bases with OH
group in ortho position to the imino group in polar and
nonpolar solvents in both acidic and basic media [2,3,20].
The compound showed no absorption above 400 nm in polar
(DMSO, ethanol and chloroform) and nonpolar (benzene)
solvents and basic ([C2H5]3N; pH 9) DMSO, chloroform and
benzene solutions. The band was observed with value greater
than 400 nm in acidic (CF3COOH; pH 2) solutions of
ethanol, chloroform and benzene for compound. The enol-
imine tautomer is dominant in basic solutions of DMSO,
ethanol, chloroform and benzene, in same pure solvents and
in the acidic DMSO solution for compound. The keto-amine
tautomer is dominant only in the acidic of ethanol, chloro-
form and benzene solutions for compound. In conclusion,
0.699(2)
0.864(2)
0.889(3)
0.739(3)
0.753(2)
C17
C18
O2
0.566(2)
0.917(3)
0.411(2)
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
N2
0.733(2)
0.686(3)
0.809(2)
1.013(3)
1.066(2)
0.929(2)
0.980(3)
0.851(3)
0.662(2)
0.596(2)
0.416(2)
C29
C30
C31
C32
C33
C34
O3
0.264(2)
0.086(2)
K0.068(2)
K0.238(3)
K0.253(3)
K0.105(3)
K0.099(2)
0.076(2)
C35
C36
O4
K0.291(3)
0.220(2)
P P
Ueq Zð1=3Þ
j Uijaꢀi ajꢀðai; ajÞ. Ueq is defined as one third of the trace of
i
the orthogonalized Uij tensor.
3. Result and discussion
1
3.1. IR, H NMR, 13C NMR and UV–visible spectroscopy
The IR spectrum (Fig. 2) is given in synthetic
procedures. The stretching frequency observed at
2828 cmK1 shows the presence of O–H/N intramole-
cular hydrogen bond [2,3].
The 1H NMR and 13C NMR data are given in the
experimental section. According to the 13C-NMR spectra,
the title molecule has 18 signals (Fig. 3). The UV–visible
spectrum of the compound was studied in polar and nonpolar
solvents in both acidic and basic media. The Schiff bases
Fig. 1. The molecular structure of the title compound. Displacement
ellipsoids are plotted at the 50% probability level [19].

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H. Unver et al. / Journal of Molecular Structure 737 (2005) 159–164
162
Fig. 2. FT-IR spectrum of the title compound.
1
UV–visible, H NMR and 13C-NMR results show that in
DMSO solution the compound exist in the enol-imine form.
impregnated with 20 mL of solution. All the bacteria
mentioned above were incubates at 30G0.1 8C for 24 h by
inoculution into Nutrient Broth (Difco), and the yeasts
studied were incubated in Malt Extract Broth (Difco) for
48 h. An inoculum containing 106 bacterial cells or 108
yeast cells/mL was spread on Mueller–Minton Agar (Oxoid)
plates (1 mL inoculum/plate). The discs injected with
solutions were placed on the inoculated agar by pressing
slightly and incubated at 35 8C (24 h) for bacteria, and at
25 8C (72 h) for yeast. On each plate on appropriate
3.2. Screening for antimicrobial activities
The bacteria and yeast cultures were used in this study as
the test microorganisms. The compound dissolved in
DMSO to a final concentration of 30 mg/mL. Empty
sterilized antibiotic discs having a diameter of 6 mm
(Schleicher and Schull No 2668, Germany) were each
Fig. 3. 13C-NMR spectrum of the title compound.

¨
H. Unver et al. / Journal of Molecular Structure 737 (2005) 159–164
163
Table 4
bacterium, having the diameter zones of 21 mm. the title
compound is more active than those of the standard
antibiotics P10, SAM20 and CTX30 against Escherichia
coli, Bacillus cereus and Proteus vulgaris. While the
compound has higher antibacterial effect than those of the
all standard antibiotics except for OFX5 and TE30 against
Stapylococcus aureus, it has weak antimicrobial effect
against Micrococcus luteus. Besides, the compound is
equivalent to the standard antibiotic P10 against the acid-
fast bacterium Mycobacterium smegmatis.
Antimicrobial activity
Microorganisms
Diameter of inhibition zones (mm)
Staphylococcus aureus
Escherichia coli
17
15
12
11
21
18
15
17
12
19
17
11
13
12
15
Bacillus cereus
Micrococcus luteus
Proteus vulgaris
Enterobacter aerogenes
Mycobacterium smegmatis
Listeria monocytogenes
Pseudomonas aeruginosa
Klebsiella pneumoniae
Candida albicans
The compound has weak antimicrobial activity against
the yeast cultures used in this study, as compared to
the standard antifungal antibiotics Nystatin, Ketaconozole
and Clotrimazole. Against Debaryomyces hansenii, com-
pound is susceptible and equivalent to the standard
antibiotics KETO20 and NY100, respectively. The com-
pound differs significantly in their activity against tested
microorganisms. These differences may be attributed to fact
that the cell wall in Gram-positive bacteria of a single layer,
whereas the Gram-negative cell wall is multi-layered
structure and the yeast cell wall is quite complex [22].
Debaryomyces hansenii
Kluyveromyces fragilis
Rhodotorula rubra
Hanseniaspora guilliermondii
Inactive (K), moderately active (8–13); higher active (O14). Includes
diameter of disc (6 mm).
reference antibiotic disc was applied depending on the test
microorganisms [13–14]. The data reported in Table 4 are
the average data of three experiments.
Table 4 shows antimicrobial activities of compound.
Besides, the inhibition zones formed by standard antibiotic
discs are indicated in Table 5. As can clearly be seen from
Table 4, the compound is strong antimicrobial activities
against all tested microorganisms. In classifying the
antibacterial activity as Gram-positive or Gram-negative,
it would generally expected that a much greater number
would be active against Gram-positive than Gram-negative
bacteria [21]. However, in this study, the compound was
active against both Gram (C) and Gram (K) bacteria.
When the results obtained were compare to those of
standard antibiotics, Enterobacter aerogenes is the most
influenced bacterium against compound, having the diam-
eter zones of 24 mm. Proteus vulgaris is the most sensitive
3.3. Crystallographic study
Two types of intramolecular hydrogen bonds, either
N–H.O (keto-amine form) or N.O–H (enol-imine form)
can exist in 2-hydroxy Schiff bases. The Schiff bases
derived from salicylaldehyde always form the N.H–O type
of hydrogen bonding, regardless of the nature of the N
substituent [23,24]. The compounds derived from 2-
hydroxy-1-naphthaldehyde, both types of hydrogen bonds
were found [25–29]. These Schiff bases usually have keto-
amine form, and show photochromism because of the
hydrogen from the phenol group is reversible transferred to
the imine nitrogen [7]. Similar hydrogen transfer and
Table 5
Antimicrobial activities of some standard antibiotics
Microorganisms/antibiotics
Inhibition zone (mm)
P10
SAM20
CTX30
VA30
OFX5
TE30
NY100
KETO20
CLT10
Escherichia coli
18
13
18
8
12
16
14
10
16
12
21
12
32
–
10
12
13
54
18
14
11
16
32
–
22
13
22
10
20
18
20
26
34
–
30
24
28
44
28
30
32
30
28
-
28
26
30
34
26
25
24
28
22
–
–
–
–
Staphylococcus aureus
Klebsiella pneumoniae
Pseudomonas aeruginosa
Proteus vulgaris
–
–
–
–
–
–
–
–
–
10
14
15
10
36
–
–
–
–
Bacillus cereus
–
–
–
Mycobacterium smegmatis
Listeria monocytogenes
Micrococcus luteus
Candida albicans
–
–
–
–
–
–
–
–
–
20
18
18
21
16
21
16
22
24
14
15
18
16
22
18
Kluyveromyces fragilis
Rhodotorula rubra
H. guilliermondii
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Debaryomyces hansenii
–
–
–
–
–
–
P10: Penicillin G (10 Units), SAM20: Ampicillin 10 mg, CTX30: Cefotaxime 30 mg, V30: Vancomycin 30 mg, OFX 5: Oflaxacin 5 mg, TE30: Tetracyclin
30 mg, N30: Nystatin 100 mg, KETO20: Ketaconazole 20 mg: CLT10: Clotrimazole 10 mg.

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H. Unver et al. / Journal of Molecular Structure 737 (2005) 159–164
164
[4] G.Y. Yeap, S.T. Ha, N. Ishizawa, K. Suda, P.L. Poey,
W.A.K. Mahmood, J. Mol. Struct. 658 (2003) 87.
[5] M. Gavranic, B. Kaitner, E. Mestrovic, J. Chem. Crystallogr. 26
(1996) 23–28.
N–H/O type hydrogen bonds are not found in the
molecular structure of the compound.
The title compound has two crystallographically inde-
pendent molecules in the asymmetric unit. The two planar
phenyl rings bridged by the CaN imino moiety in the two
crystallographically independent molecules, however, are
inclined at angle of 11.10(4) and 11.54(4), respectively.
The crystal structure is stabilized by intramolecular
hydrogen bonding. Intramolecular hydrogen bonds occur
¨
[6] H. Unver, M. Kabak, D.M. Zengin, T.N. Durlu, J. Chem. Crystallogr.
31 (2001) 203–209.
[7] E. Hadjoudis, M. Vitterakis, I. Moustakali-Mavridis, Tetrahedron 43
(1987) 1345–1360.
[8] M. Hoshino, T. Inabe, T. Mitani, Y. Maruyama, Bull. Chem. Soc. Jpn.
61 (1988) 4207–4214.
[9] G.M.J. Schmidt, L. Leiserowitz, J. Bregman, J. Chem. Soc. 1964;
2068.
˘
[10] A. Elmali, M. Kabak, E. Kavlakoglu, Y. Elerman, T.N. Durlu, J. Mol.
˚
between hydroxyl O2.N1 [2.561(2) A], and hydroxyl
˚
O4.N2 [2.584(2) A] atoms. The sum of the Van der
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˚
Waals radius of the O and N atoms (3.07 A) is significantly
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¨
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longer than the intramolecular O.N hydrogen bond length
[30].
X-ray structure determinations reveal that the enol
359–364.
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tautomer is favoured over the keto tautomer. This is evident
˚
from the observed O2–C17 bond distance of 1.379(2) A and
˚
O4–C35 bond distance of 1.316(2) A, which is consistent
with the O–C single bond; similarly the N1–C11 distance of
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˚
1.266(4) A and the N2–C29 distance of 1.284(4) A are also
˚
consistent with the NaC double bonding, respectively.
[16] Molecular Structure Corporation. TEXAN for Windows version 1.03.
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¨
Structures, University of Gottingen, Germany, 1997.
Crystallographic data for the structure reported in the
paper have been deposited with the Cambridge Crystal-
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CCDC-209504. Copies of the data can be obtained on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax C44-1223/336-033; E-mail: deposit@ccdc.
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