Crystal structure and conformational analysis of 1-[N-(2-bromophenyl)]naphthaldimine

Article abstract of DOI:10.1016/S0022-2860(03)00277-1

1-[N-(2-bromophenyl)]naphthaldimine (C₁₇H₁₂NOBr) (1) was synthesised and its crystal structure was determined. The compound 1 is orthorhombic, space group P2₁2₁2₁, with a = 12.653(2), b = 13.7311(14),

Full text of DOI:10.1016/S0022-2860(03)00277-1

Journal of Molecular Structure 655 (2003) 369–374
www.elsevier.com/locate/molstruc
Crystal structure and conformational analysis
of 1-[N-(2-bromophenyl)]naphthaldimine
a,
H. Unver , T. Nuri Durlu
a,b
¨
*
a
˘
Department of Physics, Faculty of Science, Ankara University, TR-06100 Tandogan, Ankara, Turkey
bDepartment of Physics, Faculty of Art and Science, University of Kırıkkale, Yahs¸ihan Campus, TR-71450 Kırıkkale, Turkey
Received 3 June 2002; revised 8 April 2003; accepted 14 April 2003
Abstract
1-[N-(2-bromophenyl)]naphthaldimine (C17H12NOBr) (1) was synthesised and its crystal structure was determined. The
ꢀ
compound 1 is orthorhombic, space group P212121 with a ¼ 12:653ð2Þ; b ¼ 13:7311ð14Þ; c ¼ 7:9799ð12Þ A; V ¼ 1386:4ð4Þ
ꢀ 3
A ; Z ¼ 4; Dc ¼ 1:563 g cm23; mðMo KaÞ ¼ 2:959 mm21; R ¼ 0:032 for 499 reflections I . 2sðIÞꢀ: There is an
˚
intramolecular hydrogen bond of distance 2.473(3) A between the hydroxyl oxygen atom and imine nitrogen atom, the
hydrogen atom essentially being bonded to the oxygen atom. Minimum energy conformation was calculated as a function of
torsion angle u (C10–C11–N1–C12) varied every 5 degrees. The optimized geometry of the crystal structure corresponding to
the non-planar conformation is the most stable conformation in all calculations. The results strongly indicate that the minimum
energy conformation is primarily determined by hydrogen–hydrogen repulsions between the ortho-hydrogen atoms on the
1
aldehyde rings. Complementary IR, H NMR and UV measurements in solution and in the solid state were carried out.
q 2003 Elsevier B.V. All rights reserved.
Keywords: Schiff base; Photochromism; Conformational analysis; Crystal structure; Intramolecular hydrogen bonding
1. Introduction
applications of photochromic materials were realised
in various areas such as the control and measurement
of radiation intensity, optical computers and display
systems [9]. The Schiff base complexes have also
been used in catalytic reactions [10] are used as
models for biological systems [11,12].
Schiff bases from 2-hydroxy-1-naphthaldehyde
have often been used as chelating ligands in the
field coordination chemistry [1]. The Schiff base
compounds can be classified by their photochromic
and thermochromic characteristics [2]. Photochro-
mism is produced by intramolecular proton transfer
associated with a change in the p-electron configur-
ation [3–8]. Studies on the photochromic compounds
have been increased ever since the potential
There are two types of intramolecular hydrogen
bonds [either N–H· · ·O (keto form) or N· · ·H–O (enol
form), Fig. 1] in 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 (alkyl or aryl) [13–17] (Table 1). In the
aldimine compounds derived from 2-hydroxy-1-
naphthaldehyde, both types of hydrogen bonds were
*
Corresponding author.
E-mail address: unver@science.ankara.edu.tr (H. Unver).
¨
0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-2860(03)00277-1

¨
H. Unver, T. Nuri Durlu / Journal of Molecular Structure 655 (2003) 369–374
370
Table 2
˚
Bond lengths (A) and bond angles (deg) in naphthaldehyde ligands
O· · ·H H–N
O–H· · ·N CyO
C–N
O· · ·N
Ia
1.846(8) 0.827(9) 2.544(2) 1.310(8) 1.319(6) 141
1.852(3) 1.00(3) 2.583(3) 1.260(4) 1.329(4) 127(3)
1.83(3) 0.91(3) 2.532(3) 1.281(4) 1.322(4) 133(3)
1.96(5) 0.66(4) 2.530(4) 1.303(5) 1.30(4) 146(6)
1.759(4) 0.90(4) 2.572(4) 1.274(4) 1.345(4) 150(3)
IIb
IIIc
IVd
Ve
Fig. 1. Enol and keto tautomerism of 1.
found [18–27] (Table 2). In this study, we investi-
gated the structure of the title compound in order to
reveal the presence of either the enol or keto forms
related with hydrogen bonding by using IR, 1H NMR,
UV and X-ray crystallographic techniques in the
solution and solid states, respectively. The tautomer-
ism of the title compound has also been investigated
by AM1 semi-empirical quantum mechanical method.
O–H
H· · ·N O–H· · ·N C–O
CyN
O–H· · ·N
VIf
1.130 1.534 2.547(3) 1.337(4) 1.273(4) 145
VIIg 0.95(3) 1.70(3) 2.540(2) 1.334(2) 1.290(2) 146.3
VIIIh 0.97
1.71
2.553(4) 1.321(5) 1.291(4) 143.2
2.570(3) 1.323(3) 1.290(3) 152
IXi
Xj
XIk
0.83
0.88(4) 1.76(4) 2.574(3) 1.357(3) 1.294(3) 153(4)
1.01(3) 1.66(3) 2.473(3) 1.331(5) 1.280(5) 136(3)
a
1-[N-(4-bromophenyl)]aminomethylidene-2(1H)naphthalenone
[18].
b
1-[N-(6-metyl-2-pyridyl)]aminomethylidene-2(1H)naphthale-
none [19].
c
2. Experimental
1-[N-(4-metyl-2-pyridyl)]aminomethylidene-2(1H)naphthale-
none [20].
d
1-[N-(4-iodophenyl)]aminomethylidene-2(1H)naphthalenone
2.1. Reagents and techniques
[21].
e
1-[N-(2-pyridyl)]aminomethylidene-2(1H)naphthalenone [22].
2-Hydroxy-1-naphthaldehyde and 2-bromoaniline
were purchased from Merck (Germany). Melting
points were measured on a Gallonkamp apparatus
using a capillary tube. Infrared absorption spectra
were obtained from a Mattson 1000 FTIR spec-
trometer in KBr discs and reported in cm21. UV–vis
spectra were measured using a Perkin Elmer Lambda
2 series spectrometer. 1H NMR (400 MHz) were
recorded with a Bruker DPX FT-NMR spectrometer
(CDCl3 as internal standard).
f
g
h
i
1-[N-(4-fluorophenyl)]naphthaldimine [23].
N-(2-aminophenyl)]naphthaldimine [24].
N-(2-bromo-4-methylphenyl)]naphthaldimine [25].
N-(3,5-dichlorophenyl)]naphthaldimine [26].
4-Ethyl-2-(2-hydroxynaphthymethylidene)-amino-5-methyl-3-
j
thiophenecarbonitrile [27].
k
Present study [1-[N-(2-bromophenyl)]naphthaldimine].
2.2. Synthesis of compound 1
Compound 1 was prepared by addition of 100 ml
hot ethanol solution of 0.001 mol of 2-bromoaniline
(0.172 g) to 75 ml hot ethanol solution of 0.001 mol of
2-hydroxy-1-naphthaldehyde (0.172 g). The mixture
was refluxed for 5 h and during reflux process brown
coloured prismatic crystals were formed [28], m.p.
145 8C, 0.312 g (91%) yields. Found: C, 62.43; H,
3.82; N, 4.20. Calcd for C17H12NOBr; C, 62.60;
H, 3.71; N, 4.29%. UV/vis (C2H5OH): lmax
ðlog 1Þ ¼ 344 nm (4.90). IR (KBr, cm21): n(CyN)
1623s, n(CyC) 1421–1619, n(C–O) 1321s, n(C–H)
Table 1
˚
Bond lengths (A) and bond angles (deg) in salicylaldehyde ligands
O–H
H· · ·N O· · ·N
C–O
CyN
O–H· · ·N
Ia
0.95(5) 1.73(5) 2.577(6) 1.353(4) 1.325(5) 151(3)
IIb 0.95(3) 1.73(3) 2.604(2) 1.346(3) 1.276(2) 150(2)
IIIc 0.84(4) 1.83(4) 2.604(3) 1.354(3) 1.281(3) 154(3)
IVd 0.97(3) 1.71(3) 2.607(3) 1.351(2) 1.287(2) 153(2)
Ve 1.154(3) 1.488(3) 2.578(3) 1.356(3) 1.270(3)
a
2-(3-Methoxy-2-hydroxyphenyl)benzimidazole [13].
b
N-(2,5-methylphenyl)salicylaldimine [14].
c
N-(2-methyl-5-chlorophenyl)salicylaldimine [15].
1
3069–3071, n(O–H) 3402vwb. H NMR (CDCl3):
d ¼ 15.18 (s, 1H, NH), 9.26 (s, 1H, CHyN), 6.84–
d
4-([(1E)-(2-hydroxyphenyl)methylidene]amino(-1,5-dimethyl-
2-phenyl-2,3-dihydro-1H-pyrazol-3-one [16].
e
1,8-di[N-2-oxyphenyl-salicylidene]-3,6-dioxaoctane [17].
8.18 (m, 10H).

¨
H. Unver, T. Nuri Durlu / Journal of Molecular Structure 655 (2003) 369–374
371
2.3. X-ray structure determination
density. H atom displacement parameters were
restricted to be 1:2Ueq of the parent atom. Fractional
atomic coordinates and equivalent isotropic thermal
parameters for non-hydrogen atoms are given for in
Table 4. Bond distances and bond angles for 1 are
listed in Table 5 and an ORTEP view of the molecular
structure is given in Fig. 2. [33].
The data collection was performed on a RIGAKU
AFC7-S diffractometer employing graphite-mono-
ꢀ
chromatized Mo Ka radiation ðl ¼ 0:71073 AÞ [29].
The details of the X-ray data collection, structure
solution and structure refinements are given in Table 3.
Data reduction and corrections for absorption and
crystal decomposition (1.1%) were carried out using
the TEXSAN Single Crystal Structure Analysis
Software [30]. The structure was solved by SHELXS-
97 [31] and refined with SHELXL-97 [32]. The
positions of H atoms bonded to C atoms were
2.4. Conformation analyses
Theoretical calculations were carried out with the
standard parameters using a locally modified version
of the MOPAC 6.0 program package [34] which
includes the AM1 Hamiltonian [35] running on a
Pentium II PC starting with the optimized X-ray
crystallographic coordinates [36] of 1. The geometry
optimizations of the crystal structure of 1 were carried
out by using the Fletcher–Powell–Davidson algor-
ithm [37,38], which is implemented in the MOPAC
6.0 package, and the PRECISE option was used
to improve the convergence criteria. To determine
˚
calculated (C–H distances 0.93 A), and included in
the structure factor calculation using a riding model
(except HO1). The hydrogen atom HO1 riding on the
O1 atom was found from a difference map at the end
of the refinement process as a small positive electron
Table 3
Crystal data and structure refinement
Compound
C17H12NOBr
Brown/prismatic
326.19
Table 4
Atomic coordinates ( £ 1024) and equivalent isotropic displace-
Color/shape
2
ment parameters ( £ 1023 A ) for 1. Ueq is defined as one third of
˚
Formula weight
Crystal system
Space group
Cell constants
Orthorhombic
P212121
the trace of the orthogonalized Uij tensor
Atom
x
Y
Z
Ueaq
ꢀ
a ¼ 12:653ð2Þ A
ꢀ
b ¼ 13:7311ð14Þ A
ꢀ
c ¼ 7:9799ð12Þ A
O1
3276(3)
2544(4)
1528(4)
788(4)
2821(2)
2126(3)
2377(3)
1741(4)
776(4)
3631(5)
3617(6)
4308(7)
4268(6)
3604(6)
3544(6)
2900(6)
2236(6)
2252(6)
2922(6)
2961(6)
2421(6)
2436(4)
1994(6)
2421(6)
2054(7)
1262(7)
823(6)
73(2)
53(2)
65(2)
78(2)
55(2)
70(2)
72(2)
64(2)
53(2)
43(2)
42(2)
38(2)
51(1)
45(2)
57(2)
64(2)
72(2)
65(2)
47(2)
76(1)
46
3
˚
Cell volume
Formula units/unit cell
Dx
1386.4(4) A
C1
4
C2
1.563 g cm23
2.959 mm21
Rigaku AFC7-S/v–2u
C3
mðMo KaÞ
Diffractometer/Scan
lðMo KaÞ
C4
918(4)
C5
73(4)
100(4)
˚
0.71073 A
C6
195(4)
2816(4)
21073(4)
2444(3)
516(3)
Crystal size
T
0.10 £ 0.15 £ 0.05 mm3
C7
1183(4)
2008(3)
1915(3)
2753(4)
3812(3)
4535(3)
5588(4)
6064(3)
7111(4)
7724(4)
7258(3)
6240(4)
5612(1)
385(2)
293 K
656
C8
Fð000Þ
C9
Index ranges
0 # h # 15
0 # k # 19
0 # l # 11
1871
C10
C11
N1
1203(4)
994(3)
1635(3)
1384(3)
515(4)
Number of reflections measured
C12
C13
C14
C15
C16
C17
Br1
HO1
Number of reflections used
499
Number of parameters
185
323(3)
R
0.032
1018(4)
1873(4)
2068(3)
3273(1)
268(2)
Rw
0.055
Goodness-of-fit
ðDðsÞmax
ðDðrÞmax
ðDðrÞmin
1.002
1221(6)
586(1)
0.004
23
˚
0.356 eA
˚
20.390 eA
273(4)
23
Ueaq ¼ ð1=3ÞSiSjUij api ajp ai·aj:

¨
H. Unver, T. Nuri Durlu / Journal of Molecular Structure 655 (2003) 369–374
372
Table 5
˚
Bond lengths (A) and angles (deg)
3. Results and discussion
3.1. Spectroscopic study
O1–C1
1.331(5)
1.432(6)
1.432(6)
1.423(6)
1.407(7)
1.431(6)
1.416(6)
1.444(5)
1.397(6)
1.389(7)
1.342(6)
1.01(3)
C1–C10
1.406(6)
1.285(6)
1.413(7)
1.369(7)
1.366(6)
1.422(6)
1.280(5)
1.373(6)
1.387(6)
1.352(7)
1.901(4)
1.66(3)
C1–C2
C2–C3
Absorption bands were observed of 1623 cm21
(nCyN), 3071 cm21, (nC – H, Ar–H), 1605 cm21
C3–C4
C4–C5
C4–C9
C5–C6
C6–C7
C7–C8
(nCyC). Observation of
a phenolic nC – O at
C8–C9
C9–C10
1321 cm21 is evidence for the existence of the enol
form (N· · ·H–O) intramolecular hydrogen bonding
only in the solid state.
C10–C11
C11–N1
N1–C12
C12–C13
C12–C17
C13–C14
C14–C15
C15–C16
The UV–visible spectra of the compound were
studied in polar, non-polar solvents and with the
addition acid and base. Absorption in the range
above 400 nm is observed in DMSO, ethanol,
chloroform, benzene and cyclohexane [17]. The
new band (above 400 nm) belongs to the keto form
was observed in polar (DMSO, ethanol and
chloroform) and non-polar (benzene and cyclohex-
ane) solvents and in acidic (CF3COOH) solutions
of chloroform and benzene and basic [(C2H5)3N]
solutions of DMSO, ethanol, chloroform, benzene
and cyclohexane but it is not observed in acidic
solutions of DMSO and ethanol [17].
C16–C17
C17–Br1
O1–HO1
HO1· · ·N1
O1–C1–C2
C3–C2–C1
C5–C4–C9
C9–C4–C3
C5–C6–C7
C7–C8–C9
C10–C9–C8
C1–C10–C11
C11–C10–C9
C11–N1–C12
C13–C12–N1
C12–C13–C14
C15–C16–C17
C12–C17–Br1
O1–C1–C10
C10–C1–C2
C2–C3–C4
C5–C4–C3
C6–C5–C4
C8–C7–C6
C10–C9–C4
C4–C9–C8
C1–C10–C9
N1–C11–C10
C13–C12–C17
C17–C12–N1
C13–C14–C15
C16–C17–Br1
O1–HO1· · ·N1
122.0(4)
119.4(4)
124.2(5)
122.5(4)
122.5(5)
121.4(5)
117.7(4)
117.1(4)
120.6(4)
122.2(4)
117.9(5)
120.7(4)
120.5(5)
121.3(4)
136(3)
118.6(4)
119.8(5)
119.2(5)
118.3(4)
118.2(5)
121.5(4)
125.2(4)
118.5(5)
120.8(5)
124.5(4)
121.2(4)
120.2(5)
122.1(5)
117.6(3)
The enol tautomer is dominant only in the acidic
solutions of DMSO and ethanol, while it is dominant
in polar and non-polar solvents and in both acidic
solutions of chloroform and benzene and basic
solutions of DMSO, ethanol, chloroform, benzene
and cyclohexane [17,21,28]. Absence of the keto
form in the acidic solutions of DMSO and ethanol
may be explained by the hydrogen bonding to
CF3COOH.
the conformation energy profiles, heat of formation
energies were calculated as a function of the torsion
angle u (C10–C11–N1–C12) varied from 0 to 3608,
for every 58.
The phenolic function in compound 1 was
neutralized with NaOH (Fig. 3). According to this
result compound 1 is in the enol tautomer as expected.
Fig. 2. The molecular structure of the title compound. Displacement
ellipsoids are plotted at the 50% probability level.
Fig. 3. Chemical reactions in enol tautomeric form.

¨
H. Unver, T. Nuri Durlu / Journal of Molecular Structure 655 (2003) 369–374
373
3.2. Crystallographic studies
the molecular model of the enol and keto tautomeric
form.
The heat of formation energy profile shows that the
minimum energy value is 56.42 kcal/mol for keto
tautomeric form while 41.46 kcal/mol for enol form
(Fig. 4). The energy profile of keto and enol forms of 1
as a function of u show maximum near 190 and 2508,
respectively, due to the steric interaction between H13
and HO1. Besides, the interactions of the hydrogen
atom H8 attached to the C8 on the naphthaldehyde
ring and the hydrogen atom (H11) on the ‘bridge’
carbon atom of C11 is repulsive in conformation
analysis in the planar conformation, but it is reduced
with increasing the non-planarity for the enol form.
The results confirm the X-ray data so the most stable
non-planar conformation of 1 is the enol form.
Bu¨rgi and Dunitz [39] carried out an extensive
theoretical and experimental study on the non-
planar conformation of N-benzylideneaniline and
related compounds. Their explanation for the non-
planarity of N-benzylideneaniline involves a com-
petition between two principal factors: (i) the
interaction of the ortho hydrogen on the aniline
ring and the hydrogen on the bridge carbon is
repulsive in the planar conformation but reduced
with increasing non-planarity, (ii) the p-electron
system, itself divisible into two components,
including, on the one hand, delocalisation between
the –HCyN– double bond and the aniline phenyl
ring (which is maximised for a planar confor-
mation) and, on the other hand, delocalisation of
the nitrogen lone pair of electrons into the aniline
ring which is essentially zero for the planar
conformation but increases with increasing non-
planarity (where the lone pair density on the
nitrogen may interact with the p systems of the
ring).
The title molecule is not planar; Schiff base
moieties A[C1–C11, O1; planar with a maximum
˚
deviation of 0.0798 (0.0018) A for the O1 atom] and
B[N1, C12, C13, C14, C15, C16, C17, Br1; planar
˚
with a maximum deviation of 20.0353(0.0003) A for
the N13 atom] are inclined at angle of 41.67(2)8
reflecting mainly the twist about N1–C12 [C11–N1–
C12–C13, 38.1(2)8]. The title molecule contains an
intramolecular hydrogen bonds (O–H· · ·N) [O1–H1
˚
˚
˚
1.01(3) A, H1· · ·N1 1.66(3) A, O· · ·N 2.473(3) A,
O1–HO1· · ·N1 136(3)8]. X-ray structure determi-
nations reveal that the enol tautomer is favoured
over the keto tautomer. This is evident from the
observed O1–C1 bond distance of 1.331(5) which is
consistent with the O–C single bond, similarly the
˚
N1–C11 distance of 1.280(5) A is also consistent
with the NyC double bonding.
3.3. Conformation analyses
Semi-empirical AM1 calculations were carried out
to complement the experimental investigations and to
clarify the tautomerism of 1. Results are shown in
Fig. 4. The theoretical calculations were performed on
the torsion angles u (C10–C11–N1–C12) (Fig. 4),
that control the planarity of 1. In order to find the most
stable conformation in the solid state, we studied
In summary, the AM1 optimized geometry of the
crystal structure of the investigated compound
corresponding to non-planar conformation is the
most stable conformation in all considered calcu-
lations. The results strongly indicate that the most
stable conformation is primarily determined by non-
bonded hydrogen–hydrogen repulsions. The inter-
action between the N-lone pair and the p electrons of
the rotated naphthaldehyde ring, however, might also
contribute to the conformational energy of the title
compound.
Fig. 4. AM1 conformation energies of the enol and keto form as a
function of the u (C10–C11–N1–C12) torsion angle (X) enol, (B)
keto.

¨
H. Unver, T. Nuri Durlu / Journal of Molecular Structure 655 (2003) 369–374
374
¨
[21] H. Unver, M. Kabak, D.M. Zengin, T.N. Durlu, Z. Naturforsch.
References
56b (2001) 1003.
¨
[22] T. Hokelek, Z. Kılıc¸, M. Is¸ıklan, M. Toy, J. Mol. Struct. 523
[1] A.D. Garnovski, A.L. Nivorozhkin, V.I. Minkin, Coord.
Chem. Rev. 126 (1993) 1.
(2000) 61.
¨
[23] H. Unver, D.M. Zengin, T.N. Durlu, Anal. Sci. 16 (2001)
[2] E. Hadjoudis, M. Vittorakis, I. Maustakali-Mavridis, Tetra-
hedron 43 (1987) 1345.
1021.
[24] L. Govindasamy, D. Velmurugan, T.M. Rajendran, Acta
Crystallogr. C55 (1999) 1368.
[3] P.F. Barbara, P.M. Rentzepis, L.E. Brus, J. Am. Chem. Soc.
102 (1980) 2786.
[25] A. Elmali, Y. Elerman, E. Kendi, Acta Crystallogr. C54 (1998)
1137.
[4] P. Gilli, V. Bertolasi, V. Ferretti, G. Gilli, J. Am. Chem. Soc.
122 (2000) 10405.
[26] A. Elmali, Y. Elerman, I. Svoboda, H. Fuess, Acta Crystallogr.
C54 (1998) 974.
¨
[27] Y. Elerman, A. Elmali, E. Kendi, S. Ozbey, V. Ertu¨zu¨n, Acta
[5] R. Herzfeld, P. Nagy, Curr. Org. Chem. 5 (2001) 373.
[6] H. Joshi, F.S. Kamounah, C. Gooijer, G.V.D. Zwan, L.
Antonov, J. Photochem. Photobiol. 152 (2002) 183.
[7] M. Rospenk, I. Krol-Starzomska, A. Filarowski, A. Koll,
Chem. Phys. (2003) 287.
Crystallogr. C53 (1997) 1158.
¨
[28] H. Unver, Spectrosc. Lett. 34 (2001) 783.
[29] Molecular Structure Corporation, MSC/AFC Diffractometer
Control Software, MSC, 3200 Research Forest Drive, The
Woodlands, TX 77381, USA, 1994.
[8] L. Antonov, W.M.F. Fabian, D. Nedeltcheva, F.S. Kamounah,
J. Chem. Soc. Perkin 2 (2000) 1173.
[9] H. Du¨rr, Angew. Chem. Int. Ed. 28 (1989) 413.
[10] D.E. Hamilton, R.S. Drago, A. Zombeck, J. Am. Chem. Soc.
109 (1987) 374.
[30] Molecular Structure Corporation, TEXAN for Windows
Version 1.03, Single Crystal Structure Analysis Software
Version 1.03, MSC, 3200 Research Forest Drive, The
Woodlands, TX 77381, USA, 1997.
[11] J.W. Pyrz, A.L. Roe, L.J. Stern, L. Que Jr., J. Am. Chem. Soc.
107 (1985) 614.
[31] G.M. Sheldrick, SHELXS-97, Program for the solution of
[12] J. Costamagna, J. Vargas, R. Latorre, A. Alvarado, G. Mena,
Coord. Chem. Rev. 119 (1992) 67.
¨
Crystal Structures, University of Gottingen, Germany, 1997.
[32] G.M. Sheldrick, SHELXL-97, Program for the refinement of
[13] Y. Elerman, M. Kabak, Acta Crystallogr. C53 (1997) 372.
[14] A. Elmali, Y. Elerman, C.T. Zeyrek, J. Mol. Struct. 443 (1998)
123.
¨
Crystal Structures, University of Gottingen, Germany, 1997.
[33] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[34] J.P. Stewart, MOPAC Version 6.0, Quantum Chemistry
Program Exchange 581, Indiana University, USA, 1989.
[35] M.J.S. Dewar, E.G. Zeobisch, E.F. Healy, J.J.P. Stewart,
J. Am. Chem. Soc. 197 (1985) 3902.
[15] A. Elmali, Y. Elerman, J. Mol. Struct. 442 (1998) 31.
¨
[16] T. Hokelek, M. Is¸ıklan, Z. Kılıc¸, Acta Crystallogr. C57 (2001)
117.
¨
[17] M. Yıldız, Z. Kılıc¸, T. Hokelek, J. Mol. Struct. 441 (1998) 1.
¨
[18] H. Unver, D.M. Zengin, K. Gu¨ven, J. Chem. Crystallogr. 30
[36] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G.
Orpen, J. Chem. Soc. Perkin Trans. 2 (1987) 1.
(2000) 359.
¨
[19] T. Hokelek, M. Is¸ıklan, Z. Kılıc¸, Anal. Sci. 16 (2000) 99.
[37] R. Fletcher, M.J.D. Powell, Comput. J. 6 (1963) 163.
[38] W.C. Davidson, Comput. J. 10 (1968) 406.
[20] Y. Elerman, M. Kabak, A. Elmali, I. Svoboda, Acta Crystal-
logr. C54 (1998) 128.
[39] H.B. Bu
¨rgi, J.D. Dunitz, Helv. Chim. Acta. 54 (1971) 1255.