A one-flask synthesis and characterization of novel symmetrical pyridyl monoselenides and X-ray crystal structure of bis(5-bromo-2-pyridyl) selenide and bis(2-bromo-5-pyridyl) selenide

Article abstract of DOI:10.1016/j.jorganchem.2009.11.034

The present work reports an efficient one-pot synthesis of symmetrical pyridyl monoselenides by the reaction of bromo-/iodopyridines with the isopropylmagnesium chloride, ⁱPrMgCl followed by quenching with selenyl chloride, SeCl₂. The current methodology constitutes a convenient synthesis of bis(5-bromo-2-pyridyl) selenide (I), bis(2-bromo-5-pyridyl) selenide (II) and bis(2,5-dibromo-3-pyridyl) selenide (III) under cryogenic conditions requiring shorter time duration to give satisfactory yields. The hitherto unknown compounds have been characterized by elemental analysis and various spectroscopic techniques i.e., ¹H NMR, ¹³C NMR, FT-IR, mass spectrometry and X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2009.11.034

Journal of Organometallic Chemistry 695 (2010) 648–652
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A one-flask synthesis and characterization of novel symmetrical pyridyl
monoselenides and X-ray crystal structure of bis(5-bromo-2-pyridyl) selenide
and bis(2-bromo-5-pyridyl) selenide
*
K.K. Bhasin , Rishu, Sukhjinder Singh, H. Kumar, S.K. Mehta
Department of Chemistry and Center of Advanced Studies, Panjab University, Chandigarh 160 014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2009
Received in revised form 20 November 2009
Accepted 24 November 2009
Available online 30 November 2009
The present work reports an efficient one-pot synthesis of symmetrical pyridyl monoselenides by the
reaction of bromo-/iodopyridines with the isopropylmagnesium chloride, iPrMgCl followed by quenching
with selenyl chloride, SeCl2. The current methodology constitutes a convenient synthesis of bis(5-bromo-
2-pyridyl) selenide (I), bis(2-bromo-5-pyridyl) selenide (II) and bis(2,5-dibromo-3-pyridyl) selenide (III)
under cryogenic conditions requiring shorter time duration to give satisfactory yields. The hitherto
unknown compounds have been characterized by elemental analysis and various spectroscopic tech-
niques i.e., 1H NMR, 13C NMR, FT-IR, mass spectrometry and X-ray crystallography.
Keywords:
Bis(5-bromo-2-pyridyl) selenide
Bis(2-bromo-5-pyridyl) selenide
Bis(2,5-dibromo-3-pyridyl) selenide
Selenyl chloride
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Curiously, this methodology remained untouched for the pyridyl
systems to synthesize the symmetrical pyridyl monoselenides.
Organoselenium chemistry has been exploited to present an
extensive range and high diversity of products that find an inevita-
ble place in the area of synthetic [1,2] applications. In addition,
organoselenium compounds are known to be suitable antioxidants
because of their unique ability to imitate the enzymatic activities
of glutathione peroxidase (Gpx) that catalyze the decomposition
of hydroperoxides in various biochemical reactions [3,4]. Organo-
selenium compounds containing selenium in bivalent oxidation
state play prominent role in coordination chemistry [5,6]. An
extensive use of organoselenium compounds in semiconductors
and MOCVD techniques consign these compounds a noticeable po-
sition in electronic chemistry [7,8].
Pyridyl monoselenides display a unique competitive coordina-
tion behavior [24,25] owing to the mixed donor characteristics of
Se (soft donor) and N (hard donor) of the pyridine ring towards
the same metal atom, in addition to their usefulness in biological
systems [26]. The present procedure involves direct selenylation
of the pyridine ring using selenyl chloride, SeCl2 as compared to
the existing procedures that employ multiple steps involving the
preparation of diselenide, its cleavage to selenolate ion followed
by arylation [20–22].
2. Results and discussion
A number of methods [9–13] have been developed to obtain an
array of aryl alkyl monoselenides and symmetrical diselenides
[14–16]. Symmetrical dialkyl/diaryl monoselenides have also been
prepared by the cleavage of dialkyl/diaryl diselenides [17–19],
while other methods use transition metal complexes [20–22].
However, the use of transition metal complexes not only increases
the cost of these reactions but requires elevated temperature, high
boiling solvents and longer time durations. In order to overcome
these limitations, metal–halogen exchange route has been used
to introduce electrophilic selenium into phenyl systems [23] that
affords the symmetrical diphenyl monoselenides in good yields.
2.1. Synthesis
The present write up reveals the synthesis of symmetrical pyri-
dyl monoselenides (Scheme 1) wherein selenyl chloride has been
used as an electrophilic reagent that introduces dicationic selenium
on the pyridyl moieties conveniently. The generation of pyridyl-
magnesium chloride using iPrMgCl makes the introduction of –SeCl
on the pyridine ring easier. This method of introduction of electro-
philic selenium into pyridyl moieties has an advantage over the
use of bromo-/iodopyridines as electrophiles into the pyridylsele-
nomagnesium chlorides where poor electrophilicity of the halopyri-
dines becomes a barrier for the synthesis of monoselenides.
It has been noted that the conventional methods [14–19] for the
synthesis of diaryl monoselenides suffer from the limitations like
* Corresponding author. Tel.: +91 172 253 4407; fax: +91 172 254 5074.
E-mail address: kkbhasin@pu.ac.in (K.K. Bhasin).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.11.034

K.K. Bhasin et al. / Journal of Organometallic Chemistry 695 (2010) 648–652
649
Scheme 1. Substrates, reagents and conditions used for the preparation of monoselenides I, II and III.
harsh refluxing conditions, use of high-boiling solvents, which are
difficult to remove during work-up and require long time span for
completion. However, the current methodology overcomes the
above-mentioned limitations as the reaction can be carried out
conveniently in one-flask under cryogenic conditions in shorter
duration of time and the solvent can be easily removed during
work-up. Moreover, selenyl chloride can be easily and freshly pre-
pared at room temperature and is an effective electrophilic reagent
[27].
Attempted preparations of symmetrical monoselenides from 2-
bromopyridine, 3-bromopyridine and 4-bromopyridine were not
met with success in spite of the complete magnesium–halogen
exchange of bromopyridines with iso-propylmagnesium chloride.
It is probably because the carbon–magnesium bond in pyridyl-
magnesium chloride, formed from monobromopyridines, is strong
enough to cause the electrophilic displacement of –MgCl with –
SeCl of selenyl chloride. As a result, the reaction did not yield
the corresponding monoselenide while the unused pyridylmagne-
sium chloride on hydrolysis gave pyridine that is soluble in water.
However, the presence of additional electron-withdrawing halo-
gen group in pyridylmagnesium chlorides prepared from poly-
halopyridines facilitates the selenylation due to the weaker
carbon–magnesium bond. In case of methyl substituted bromo-
pyridines (2,5-dibromo-3-methylpyridine, 2,5-dibromo-4-methyl-
pyridine, 2,5-dibromo-6-methylpyridine) the selenylation did
not take place as the electron-releasing methyl group on the
pyridylmagnesium chloride, makes the carbon–magnesium bond
stronger enough to cause electrophilic displacement of –MgCl
with –SeCl of selenyl chloride.
Using 2,5-dibromopyridine and 2-bromo-5-iodopyridine as
substrates, we got the same product II in both cases because the
metal–halogen exchange takes place efficiently at C-5 position of
the pyridine ring giving 2-bromo-5-pyridylmagnesium chloride
rather than 5-bromo-2-pyridylmagnesium chloride. This is be-
cause, in the later case, inter-electronic repulsions due to the co-
planarity of lone pair on the nitrogen of pyridine ring with elec-
trons of carbon–magnesium bond at C-2 position destabilizes the
2-magnesiated pyridine. The results obtained are in good agree-
ment with the reactions carried by Queguiner et al. [28] for the
functionalisation of 2,5-dibromopyridines. However, the yield
was better in case of 2-bromo-5-iodopyridine because of the pres-
ence of good leaving group i.e., iodide at the C-5 position of the
pyridyl ring. Similarly, in case of 2-iodo-5-bromopyridine the C-2
position is less electrophilic than C-5 position but the metal–halo-
gen exchange occurs conveniently at this position because of the
presence of iodide (a good leaving group) giving I in good yield.
In case of 2,3,5-tribromopyridine, intramolecular coordination of
bromine at C-2 with magnesium at C-3 position favors the Grig-
nard formation at C-3 position and subsequently yielded monosel-
enide III. These results are also in agreement with previously
obtained results of metal–halogen exchange reactions of 2,3,5-trib-
rompyridine with iPrMgCl in our laboratory [29]. It is seen that the
C-5/C-3 halopyridines undergo efficient metal–halogen exchange
reactions. The presence of additional halogen in halopyridines also
facilitates the reaction. However, the methyl substituents on halo-
pyridines have been found non-suitable for these reactions. As a re-
sult, the dependence of this methodology on the metal–halogen
exchange route limits its scope and applicability.
2.2. Proposed mechanism
In order to justify the pathway of the reaction, a tentative mech-
anism has been proposed for the method employed to synthesize
the symmetrical pyridyl monoselenides by schematic representa-
tion (Scheme 2). It has been suggested that bromo-/iodopyridines
(i) undergo complete metal–halogen exchange reaction with one
equivalent of iPrMgCl as indicated by initial color change from light
yellow to deep red colored solution and finally giving the reddish-
brown suspension of corresponding pyridylmagnesium chloride
(ii) in the reaction mixture. Pyridylmagnesium chloride formed re-
acts with half (0.5) equivalent of selenyl chloride (SeCl2) followed
by elimination of magnesium dichloride (MgCl2) utilizing the two
chlorides of SeCl2 simultaneously to give the corresponding sym-
metrical monoselenide (iii) in satisfactory yields as depicted in
the table included in Scheme 1. During the work-up of the reaction,
unreacted selenium in colloidal (red coloured) form was separated
by filtration.
A number of reactions were carried out with an objective to ex-
plore the utility of the present methodology to prepare the unsym-
metrical pyridyl monoselenides by treating the separately
prepared Grignard (1) of 2-iodo-5-bromopyridine with one equiv-
alent amount of SeCl2 at ꢀ78 °C followed by the addition of Grig-
MgCl
Y
Y
X
Y
Y
Se
1
equiv.
1equiv.
N
(ii)
0.5equiv.SeCl2
-2MgCl2
1equiv. i PrMgCl
N
(i)
N
N
X,Y=Br/I
(iii)
Scheme 2. General reaction pathway for the halopyridines.

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K.K. Bhasin et al. / Journal of Organometallic Chemistry 695 (2010) 648–652
(M+) at m/z; 394. The peaks corresponding to other isotopes of
selenium were observed at 396 [C10H6N2Br282Se]+, 392 [C10H6N2
Br278Se]+, 391 [C10H6N2Br277Se]+, 390 [C10H6N2Br276Se]+, 388
[C10H6N2Br274Se]+, respectively. In the mass spectrum of monosel-
enide III the molecular ion peak at m/z; 552 [C10H4N2Br480Se]+ was
not observed. However, the fragmented peaks at m/z; 391
[C10H4N2Br280Se]+ꢀ1 and at m/z 231 [C10H4N280Se]+ꢀ1 were ob-
served by the subsequent loss of two and four bromines respec-
tively from the molecular ion.
Table 1
Crystallographic data and structural refinement I and II.
I
II
Empirical formula
Formula weight (g mol)
Crystal system
Space group
Unit cell dimensions
a (Å)
C10H6Br2N2Se
C10H6Br2N2Se
392.95
Monoclinic
P21/c
392.95
Monoclinic
C2/c
7.645(5)
13.180(5)
11.310(5)
1080.2(9)
4
2.40651
0.0228
10.838
3340
0.0865
0.1076
1324/0/69
1.329
9.3322(5)
16.1847(8)
7.7901(4)
1127.46(10)
4
2.315
0.1003
10.384
45241
0.0640
0.1579
4162/6/137
1.020
b (Å)
c (Å)
Cell volume (Å3)
Z
2.5. X-ray crystallography
Calculated density (g/cm3)
R indices (all data)
Absorbed coefficients (mmꢀ1
Perspective view of the compounds I and II is shown in Fig. 1
and X-ray data of the prepared monoselenides is presented in Ta-
ble 1. It was found that compounds I and II were monoclinic crys-
tals with C2/c and P21/c space group, respectively. The perspective
view of crystals structures (I, II) also exhibits some secondary
Seꢁ ꢁ ꢁBr [36,37], Brꢁ ꢁ ꢁN and interactions as shown in Fig. 1. The C–
Se bond distances are depicted in Table 2. In case of compound I,
the C1–Se1 and C1a–Se1 bond distances are same i.e., 1.927 Å.
However, C3–Se1 and C6–Se1 bond distances for compound II
are 1.906 Å and 1.910 Å, respectively.
The bond angles as depicted in Table 2 for the compounds I and
II showed that angle C1Se1C1a (97.4°) for compound I is smaller
than angle C3Se1C6 (100.8°) for compound II. In structure II, C–
Se carbon is in contact with the adjacent carbon atoms bearing
hydrogen atoms on both the sides. Thus the steric repulsion caused
due to the presence of substituents on the pyridyl rings increases
the C–Se–C bond angle. On the other hand, in case of compound
I the carbon atoms of the two pyridine rings; C1 and C1a have
one adjacent naked nitrogen atom and one adjacent carbon atom
bearing hydrogen atom only, thus causing lesser steric crowding
responsible for decreased bond angle in case of I as compared to
that in structure II. The steric crowding and the bond angles are
also responsible for the variation in the orientation of the mole-
cules and their arrangement in the cubic lattice.
)
Number of observed reflections [I > 2
Final R(F)[ I > 2 (I)]
R(F2) [I > 2
(I)]
r
(I)]
r
x
r
Number of data/restraints/parameters
Goodness-of-fit
nard (2) of 2,5-dibromopyridine. Curiously, the expected unsym-
metrical product was not obtained in any of the cases. Instead, a
trace amount of the corresponding symmetrical monoselenides
along with diselenide corresponding to Grignard (1) i.e., bis(5,50-
dibromo pyridyl) diselenide was obtained. The unexpected disele-
nide might have formed due to the insertion of the elemental sele-
nium, left unreacted during the preparation of SeCl2, into the
Grignard (1) to afford the corresponding pyridyl selenomagnesium
chloride followed by hydrolysis and aerial oxidation and is well
supported by methodology practiced in our laboratory for the
preparation of diselenides [29]. The diselenide formed was charac-
terized by m.p. 110–112 °C, 1H NMR (d ppm) 8.414–8.425 (d, 2H,
J = 3.3 Hz), 7.563–7.591 (m, 4H, J = 8.4 Hz) and 13C NMR (d ppm)
152.66 (C-6), 150.49 (C-2), 139.81 (C-4), 125.01 (C-3), 118.74 (C-
5). The formation of the diselenide was avoidable under rigorously
dried conditions during the preparation of the SeCl2.
2.3. 1H NMR and 13C NMR spectroscopy
3. Materials and methods
From the spectroscopic data given in Section 3.3, the replace-
ment of halogen with selenium can be justified by noticeable var-
iation in the chemical shift (d ppm) of the aromatic protons of the
prepared compounds (I, II and III) in comparison to those of the
starting materials [30,31]. In 13C NMR spectroscopic data obtained
for the three compounds, the order of chemical shifts observed for
substituted and unsubstituted carbons of pyridyl ring is in fair
agreement with those assigned for the substituted pyridines in lit-
erature [32,33]. The assignment of the peaks to each carbon of the
prepared molecules is based on the numbering followed for the
compounds in Scheme 1.
All the experimental manipulations were carried out in dry and
deoxygenated nitrogen atmosphere. Tetrahydrofuran (THF) was
dried over sodium–benzophenone and distilled. All the starting
materials were prepared according to the methods reported in lit-
erature [30,31]. Selenyl chloride (SeCl2) was freshly prepared by
reacting elemental selenium (Loba) with sulfuryl chloride (Aldrich)
[27]. All the compounds prepared were fully characterized using
elemental analysis on a Perkin–Elmer 2400 CHN analyzer. 1H, 13C
NMR spectra were recorded on a Jeol AL 300 MHz spectrometer
in CDCl3/CCl4. Tetramethylsilane (TMS) was used as an internal
standard for 1H NMR and 13C NMR. Infrared spectra were obtained
between KBr plates using CCl4 as mulling agent on a Perkin–Elmer
model 1430 spectrophotometer. Mass spectrometry was carried
out on ES-MS Q-TOF while X-ray crystallography was carried out
on Bruker Smart Apex.
2.4. Infrared spectroscopy and mass spectrometry
IR data confirms the formation of the titled compounds as the
C–H stretching band appears in the region 3100–2900 cmꢀ1 while
the strong bands corresponding C@C and C@N appear in the region
1630–1430 cmꢀ1. The absorption peaks due to C–Br bonds for both
the compounds I, II and III appear at 622 cmꢀ1, 620 cmꢀ1 and
673 cmꢀ1, respectively and are in agreement with the recorded val-
ues in the literature that are generally in the region 600–800 cmꢀ1
[34]. Similarly, the peaks corresponding to the C–Se bonds appear
at 466 cmꢀ1 for compound I, 477 cmꢀ1 for compound II and
467 cmꢀ1 for compound III, thus are in the expected range (400–
500 cmꢀ1) [35].
3.1. General procedure for the synthesis of symmetrical pyridyl
monoselenides (Scheme 1)
i
A 2 M solution of PrMgCl (20 mmol) in THF was added drop
wise to the well stirred solution of (20 mmol) 5-bromo-2-iodopyr-
idine/2,5-dibromopyridine/2-bromo-5-iodopyridine/2,3,5-trib-
romopyridine in THF at room temperature leading to a perceptible
change in color from orange to reddish brown at room tempera-
ture. After two hours of continuous stirring at room temperature,
a freshly prepared selenyl chloride (SeCl2) solution (10 mmol)
Mass spectrometry studies of both monoselenides I and II
showed the appearance of molecular ion peak [C10H6N2Br280Se]+,

K.K. Bhasin et al. / Journal of Organometallic Chemistry 695 (2010) 648–652
651
Fig. 1. ORTEP representations and perspective view of bis(5-bromo-2-pyridyl) selenide (I) showing Brꢁ ꢁ ꢁN secondary interactions, and bis(2-bromo-5-pyridyl) selenide (II)
showing the Seꢁ ꢁ ꢁBr and Nꢁ ꢁ ꢁBr secondary interactions.
Table 2
Structural comparison of selenides I and II on the basis of selected C–Se and C–Br bond distances in terms of [Å] and bond angles in terms of [°].
I
II
Atoms 1,2
d 1,2 [Å]
Atoms 1,2,3
Angle 1,2,3 [°]
Atoms 1,2
d 1,2 [Å]
Atoms 1,2,3
Angle 1,2,3 [°]
C1–Se1
C1a–Se1
C4–Br1
–
1.927(9)
1.927(8)
1.896(9)
–
C1–Se1–C1a
N1–C1–Se1
C2–C1–Se1
C5–C4–Br1
C3–C4–Br1
97.4(5)
C1–Br1
C8–Br2
C3–Se1
C6–Se1
–
1.895(5)
1.903(5)
1.906(5)
1.910(5)
–
C3–Se1–C6
C10–C6–Se1
C7–C6–Se1
C2–C3–Se1
C4–C3–Se1
100.8(2)
123.3(3)
117.7(4)
116.3(4)
125.3(4)
117.0(9)
118.1(7)
120.4(7)
119.5(6)
–
–
was added in situ at ꢀ78 °C via cannulation ensuing a red colored
suspension and was then left for stirring at room temperature.
The progress of the reaction was monitored by thin layer chroma-
tography. After completion of the reaction, the resulting solution
was poured into water and extracted with dichloromethane
(3 ꢂ 50 mL). The organic layer was then filtered through celite
and dried over anhydrous sodium sulfate. Evaporation of the sol-
vent afforded the reddish brown colored solid that was purified
in silica 60–120 (hexane:ethyl acetate; 5:1).
unweighted and weighted agreement factors of R = 0.0228 and
R = 0.1076 for structure I and R = 0.1003 and R = 0.1579 for
structure II. Anisotropic thermal parameters were employed for
non-hydrogen atoms and all the hydrogen atoms were geometri-
cally fixed and allowed to refine using a riding model.
x
x
3.3. Spectroscopic data of the titled compounds
3.3.1. Bis(5-bromo-2-pyridyl) selenide (I)
Orange-yellow colored crystalline, m.p. 94–95 °C, Yield: 85%,
Anal. Calc. (%) for C10H6Br2N2Se: C, 30.64; H, 1.52; N, 7.10. Found:
C, 30.64; H, 1.48; N, 6.71%. 1H NMR: (300 MHz, CDCl3/CCl4, d
ppm) 8.53–8.55 (d, 2H, J = 6 Hz), 7.63–7.67 (dd, 2H, J = 12 Hz),
7.40–7.48 (d, 2H, J = 24 Hz); 13C NMR: (75 MHz, CDCl3/CCl4, d
ppm) 152.90 (C-6), 151.35 (C-2), 139.40 (C-4), 129.06 (C-5),
3.2. Single crystal X-ray analysis
Compounds I and II were recrystallised in dichloromethane/
hexane (1/4) mixture at room temperature and fine diffraction
quality crystals of the respective compounds were obtained. A suit-
able crystal was mounted on glass capillaries of Bruker Smart Apex.
The structures were solved by the direct methods (SHELXL-97) [38]
and refined by full-matrix least squares method. The final cycle
of full-matrix least squares refinement for structure I and II was
based on 1324 (diffraction temperature 100 K) and 4162 (diffrac-
tion temperature 150 K) observed reflections, at 69 and 137 vari-
119.53 (C-3); IR(KBr/CCl4,
m
cmꢀ1) 2922, 1591, 1436, 1249, 1091,
999, 836, 794, 705, 622, 466 cmꢀ1; ES-MS: m/z (R.I.) 394 (M+,
100), 396 (46), 392 (85), 390 (36), 388 (9), 155 (3), 120 (16).
3.3.2. Bis(2-bromo-5-pyridyl) selenide (II)
White crystalline, m.p. 108–110 °C, Yield: 80%, Anal. Calc. (%) for
C10H6Br2N2Se: C, 30.64; H, 1.52; N, 7.10. Found: C, 30.66; H, 0.71;
able parameters respectively for [I > 2r(I)] converged with

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K.K. Bhasin et al. / Journal of Organometallic Chemistry 695 (2010) 648–652
N, 6.66%. 1H NMR: (300 MHz, CDCl3/CCl4, d ppm) 8.45–8.46 (d, 2H,
J = 3 Hz), 7.59–7.62 (dd, 2H, J = 9 Hz), 7.42–7.44 (d, 2H, J = 6 Hz);
13C NMR: (75 MHz CDCl3/CCl4, d ppm) 153.44 (C-6), 153.22 (C-2);
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ES-MS: m/z (R.I.) 394 (M+, 100), 396 (52), 392 (83), 390 (35), 388
(10), 155 (27), 120 (90).
3.3.3. Bis(2,5-bromo-3-pyridyl) selenide (III)
Off-white crystalline, m.p. 120–122 °C, Yield: 83%, Anal. Calc. (%)
for C10H4Br4N2Se: C, 21.74; H, 1.01; N, 5.07. Found: C, 21.97; H,
0.97; N, 4.55%. 1H NMR: (300 MHz, CDCl3/CCl4, d ppm) 8.33–8.35
(d, 2H, J = 6 Hz), 7.50–7.57 (d, 2H, J = 21 Hz); 13C NMR: (75 MHz,
CDCl3/CCl4, d ppm) 150.30 (C-6), 143.77 (C-2), 140.38 (C-4),
132.09 (C-3), 120.45 (C-5); IR(KBr/CCl4,
m ) 2913, 1591,
cmꢀ1
1384, 1249, 1110, 1063, 1015, 840, 794, 705, 673, 467; ES-MS:
m/z (R.I.) 231 (11), 391 (5).
4. Conclusions
In this paper the authors have developed a convenient method-
ology for the synthesis of hitherto unknown symmetrical pyridyl
monoselenides. The crystal structures of the synthesized com-
pounds display, Seꢁ ꢁ ꢁBr and Brꢁ ꢁ ꢁN non-bonding interactions that
are usually known to impart supramolecular [39] characteristics
to these compounds.
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5. Supplementary material
CCDC 736024 and 736025 contain the supplementary crystallo-
graphic data for compounds I and II. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
[33] J. Oszczapowicz, Int. J. Mol. Sci. 6 (2005) 11.
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Organic Structures, John Wiley and Sons, Chichester, 1993.
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Structure, Gottingen, Germany, 1997.
Acknowledgement
Authors are thankful to CSIR and DST, New Delhi for their finan-
cial assistance.
[39] D.J. Sandman, J.C. Stark, B.M. Foxman, Organometallics 1 (1982) 739.
References
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Modern