Syntheses, characterisation and structure of new diazoketiminato chelates of palladium(II) incorporating a tridentate (N,N,N) azo ligand

Article abstract of DOI:10.1016/j.poly.2006.03.019

The 1N-(2-pyridyl-2-methyl)-2-arylazo aniline, HL [where HL = ArN{double bond, long}NC₆H₄N(H)(CH₂C₅H₄N); Ar{double bond, long}C₆H₅ (for HL¹) or p-MeC₆H₄ (for HL²) or p-ClC₆H₄ (for HL³)], ligands were prepared by treating the appropriate 2-(arylazo) aniline with 2-chloromethyl pyridine. Reactions of Na₂PdCl₄ with HL afforded (L)PdCl complexes. HL binds palladium(II) in a tridentate fashion (N,N,N) forming a new diazoketiminato chelate, dissociating the amino proton. The X-ray structure of (L¹)PdCl was determined.

Full text of DOI:10.1016/j.poly.2006.03.019

Polyhedron 25 (2006) 2637–2642
www.elsevier.com/locate/poly
Syntheses, characterisation and structure of new diazoketiminato
chelates of palladium(II) incorporating a tridentate (N,N,N) azo ligand
Debprasad Patra, Jahar lal Pratihar, Biswaranjan Shee, Poulami Pattanayak,
*
Surajit Chattopadhyay
Department of Chemistry, University of Kalyani, Kalyani-741235, India
Received 23 February 2006; accepted 21 March 2006
Available online 7 April 2006
Abstract
The 1N-(2-pyridyl-2-methyl)-2-arylazo aniline, HL [where HL = ArN@NC6H4N(H)(CH2C5H4N); Ar@C6H5 (for HL1) or p-MeC6H4
(for HL2) or p-ClC6H4 (for HL3)], ligands were prepared by treating the appropriate 2-(arylazo) aniline with 2-chloromethyl pyridine.
Reactions of Na2PdCl4 with HL afforded (L)PdCl complexes. HL binds palladium(II) in a tridentate fashion (N,N,N) forming a new
diazoketiminato chelate, dissociating the amino proton. The X-ray structure of (L1)PdCl was determined.
Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: 1N-(2-pyridyl-2-methyl)-2-arylazo aniline; Sodium tetrachloropalladate; Diazoketiminato species
1. Introduction
erties were attributed to the low-lying ligand p* orbitals
[6].
The p-acidity and metal binding ability of the azo
nitrogen have drawn interest to the exploration of the
chemistry of transition metal complexes incorporating
azo ligands. Notable examples of these ligands are ary-
lazobenzene [1], arylazooxime [2], arylazophenol [3], ary-
lazopyridine [4], arylazoimidazole [5], arylazoaniline [6]
and related ligands. The coordination chemistry of transi-
tion metals with azo ligands is being studied due to the
observation of several interesting properties. Facile
metal–carbon bond formation and the subsequent reac-
tions of some orthometallated azobenzene and related
molecules demonstrated their importance in C–H bond
activation [3,7,8]. Fascinating electron transfer [3–5,9]
and photophysical [10] behaviour of delocalised transition
metal chelates of bi and tridentate azo ligands have drawn
attention during the recent years. Such remarkable prop-
Herein we describe the synthesis of some new azoamine
ligands, 1N-(2-pyridyl-2-methyl)-2-arylazo anilines, HL
(1) and reactions of these new ligands with Na2PdCl4.
The coordination mode of HL toward palladium (II)
has been compared critically with that of other 1N-
alkyl-2-arylazo aniline ligands, HLa (2), reported earlier
[7]. Formation of the diazoketiminato chelate, in the case
of HL, rather than orthometallation has been rationalised
on the basis of product formation and amino proton
dissociation.
R
R
Ligand
HL1
N
H
HL2
HL3
N
N
N
Me
Cl
H
*
Corresponding author. Fax: +91 33 25828282.
1
E-mail address: scha8@rediffmail.com (S. Chattopadhyay).
0277-5387/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.03.019

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D. Patra et al. / Polyhedron 25 (2006) 2637–2642
was plausible in the cases of HLa since these ligands also
underwent facile orthopalladation upon treatment with
Na2PdCl4 (Scheme 2). Whereas reaction of HL with
Na2PdCl4 did not afford the orthopalladated product and
the reaction pathway has been proposed as shown in
Scheme 3. Coordination of the amino nitrogen upon con-
comitant dissociation of its proton was assumed to occur
as a result of prior binding of the pyridyl nitrogen to
Pd(II). These preceding coordinations of pyridyl and
amido nitrogens enabled the ligand to form the diazoke-
timinato chelate upon subsequent binding through the
azo nitrogen and delocalisation of negative charge, which
grows upon amino proton dissociation.
R=alkyl group
N
N
N
R
H
(HLa)
2
2. Results and discussion
2.1. Syntheses
The 1N-(2-pyridyl-2-methyl)-2-arylazo aniline, HL (1),
ligands were prepared by refluxing 2-(arylazo) aniline with
2-chloromethyl pyridine in acetonitrile in the presence of
potassium carbonate and a catalytic amount of potassium
iodide (Scheme 1). The ligands were isolated as orange solids.
The reactions of the new HL ligands with Na2PdCl4 in
methanol afforded pink complexes of palladium (II) of
the composition (L)PdCl (3) incorporating a new tridentate
(N,N,N) ligand (Scheme 1). The deprotonated secondary
amino and the azo nitrogens bind the metal, forming a
six membered diazoketiminato chelate, while the other
1N-alkyl-2-arylazo aniline, HLa (2) [7] produced the ortho-
palladated species (La)PdCl (4) upon treatment with
Na2PdCl4. Formation of a six membered azoimine chelate
in the case of HL has been attributed to the delocalisation
of the negative charge within the ligand backbone.
2.2. Characterisation
All the ligands displayed characteristic UV–Vis spectra
with an absorption near 325 nm for the n–p* transition of
azo compounds [6]. The (L)PdCl complexes exhibited a
characteristic low energy absorption near 560 nm, which
was assigned to a MLCT transition. Representative UV–
Vis spectra of the ligand HL3and (L3)PdCl are shown in
Fig. 1. Relevant data are collected in Section 3.
The IR spectra of HL display a sharp singlet near
3189 cmÀ1 for mN–H which was absent in spectra of
(L)PdCl, indicating dissociation of the amino proton on
complexation. The mN@N band of the ligands
(ꢀ1510 cmÀ1) shifts to lower frequency after formation of
the Pd(II) chelates (1350–1400 cmÀ1), consistent with coor-
dination of the azo nitrogen [6]. The mPd–Cl of the palladium
complexes appear in the range 290–333 cmÀ1 [7]. Relevant
data are included in Section 3.
R′
The 1H NMR spectra of the ligands and the correspond-
ing palladium complexes are consistent with the formulae
and structures. Although the amino proton of HL appears
as a broad signal, due to the vicinal coupling of the methy-
lene protons its splitting into a broadened triplet can be
observed. On the other hand, the methylene proton reso-
nance also splits as a doublet due to vicinal coupling of
the N–H proton. In contrast, the 1H NMR spectra of
(L)PdCl do not display the N–H resonance and the methy-
lene protons appear as a singlet (the vicinal coupling of
N–H is absent), signifying the dissociation of the amino
proton upon complexation. The methylene proton reso-
Cl
Pd
N
R = CH2Ph
N
N
H
R′ = H, CH, Cl
R
3
4
The general mechanism of the formation of orthopalla-
dated azobenzene was described to proceed via initial coor-
dination of azo nitrogen followed by electrophilic
substitution at the pendant aryl ring [11]. This mechanism
R
R
R
HCl
.
N
Cl
CH2Cl
N
N
N
N
N
N
Na2PdCl4
Pd
N
N
N
N
K2CO3 / KI
NH2
H
HL
(
)
L PdCl
H or CH or Cl
R
=
3
3
Scheme 1.

D. Patra et al. / Polyhedron 25 (2006) 2637–2642
2639
2
Cl
Cl
Cl
R
R
Cl
Pd
Cl
N
R
Cl
H
Cl
Cl
N
Pd
Pd
Cl
Cl
-
- Cl
..
N
N
.
N
..
N
.
H
N
N
N
H
H
-HCl
R
Cl
Pd
N
N
N
H
Scheme 2.
2
Cl
Cl
Cl
R
R
Pd
R
Cl
Cl
N
Pd
Cl
Cl
.. Cl
Cl
HCl
N
-
.
.
N
.
N
.
.
Cl
-
.
N
Pd
.
N
N
.
N
N
N
H
N
N
H
- Cl
R
Cl
N
N
N
N
Pd
Scheme 3.
nance of (L)PdCl (ꢀd 5.24) is shifted downfield compared
1
to that of the HL ligands (ꢀd 4.68). The H NMR data
are given in Section 3.
2.3. X-ray structure
Suitable crystals of (L1)PdCl were grown by slow diffu-
sion of hexane into a dichloromethane solution. The X-ray
structure of the complex was determined and the perspec-
tive view of the (L1)PdCl molecule, along with the atom
numbering scheme, is shown in Fig. 2. Selected bond dis-
tances and angles are collected in Table 1. The geometry
about palladium is distorted square planar, where the
mono anionic deprotonated ligand (L1)À binds in a triden-
tate (N,N,N) fashion. A chloride ligand satisfies the tetrac-
oordination. Three chelating nitrogens are: azo (N(azo)),
pyridyl (N(py)) and amino (N(am)). The Pd–N(azo), Pd–
Fig. 1. UV–Vis spectra of HL3 (---) and (L3)PdCl (—). The arrows
indicate scales of the corresponding spectrum.
˚
˚
N(py) and Pd–Cl lengths (1.988(4) A, 2.037(5) A and

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D. Patra et al. / Polyhedron 25 (2006) 2637–2642
3. Experimental
C(3)
C(2)
C(1)
3.1. Materials
C(4)
The solvents used in the reactions were of reagent grade,
obtained from E. Merck, Kolkata, India and purified and
dried by reported procedures [6]. 2-(Arylazo) anilines were
prepared according to the reported procedure [6]. Palla-
dium chloride and potassium carbonate were purchased
from E. Merck, Kolkata, India. 2-(Chloromethyl) pyridine
hydrochloride was purchased from Lancaster, England.
Disodium tetrachloropalladate was prepared by a reported
procedure [6a].
Cl
C(5)
C(6)
N(1)
Pd
N(2)
C(7)
C(18)
N(4)
C(17)
C(8)
C(12)
N(3)
C(13)
3.2. Syntheses of the ligands
C(16)
C(14)
C(9)
All the ligands, HL1, HL2 and HL3, were prepared fol-
lowing similar procedures. A representative procedure for
HL1 is given below.
C(15)
C(10)
C(11)
Fig. 2. Perspective view of (L1)PdCl with the atom numbering scheme.
Hydrogen atoms are omitted for clarity.
3.2.1. HL1
A mixture of 2-(phenylazo) aniline (0.3 g, 1.52 mmol), 2-
chloromethyl pyridine hydrochloride (0.25 g, 1.52 mmol),
1 g of K2CO3 and a catalytic amount of KI (0.01 g,
0.06 mmol) in 30 cm3 dry acetonitrile was refluxed for
3 h. The orange solid mass that was obtained after evapo-
ration of the solvent, afforded the ligand, HL1, which was
isolated by column chromatography on silica gel (60–120
mesh) using the eluent petroleum ether–benzene (3/1 v/v).
Upon evaporation of the solvent after chromatography,
the orange-red solid of pure HL1 was obtained. Yield:
0.262 g, 60%. Anal. Calc. for C18H16N4, HL1: C, 75.00;
H, 5.20; N, 19.44. Found: C, 74.42; H, 5.35; N, 19.35%.
UV–Vis (kmax/nm (ꢀ/MÀ1 cmÀ1) in dichloromethane): 465
(1620), 420 (9430), 325 (10570). IR (KBr pellets, cmÀ1):
mN–H 3189, mN@N 1512. 1H NMR (CDCl3): d = 9.50 (b,
NH); 8.66 (d, 1H, J = 6.0); 7.90 (d, 3H, J = 9.0); 7.66 (t,
1H, J = 8.5); 7.49 (t, 2H, J = 7.5); 7.41 (d, 1H, J = 7.2);
7.36 (t, 1H, J = 6.0); 7.28 –7.20 (m, 2H); 6.81 (t, 1H,
J = 7.2); 6.73 (d, 1H, J = 8.4); 4.69 (d, 2H, J = 4.5).
Table 1
1
˚
Selected bond distances (A) and angles (°) for (L )PdCl
Pd–N(4)
Pd–N(1)
Pd–N(3)
Pd–Cl
N(1)–C(6)
N(1)–N(2)
N(2)–C(7)
C(7)–C(12)
C(7)–C(8)
2.037(5)
1.988(4)
1.968(5)
2.330(2)
1.454(8)
1.284(7)
1.346(8)
1.421(1)
1.344(2)
N(3)–C(12)
C(7)–C(8)
C(8)–C(9)
1.330(9)
1.429(9)
1.349(10)
1.385(13)
1.368(12)
1.419(10)
1.466(8)
1.454(10)
1.350(9)
C(9)–C(10)
C(10)–C(11)
C(11)–C(12)
N(3)–C(13)
C(13)–C(14)
C(14)–N(4)
N(4)–Pd–N(3)
N(1)–Pd–N(4)
N(1)–Pd–Cl
N(3)–Pd–Cl
C(6)–N(1)–Pd
C(13)–N(3)–Pd
82.3(2)
173.7(2)
94.8(2)
172.2(3)
123.9(4)
114.6(4)
N(1)–N(2)–C(7)
C(13)–C(14)–N(4)
C(14)–N(4)–Pd
Pd–N(1)–N(2)
C(7)–C(12)–N(3)
C(12)–N(3)–Pd
124.6(5)
118.0(6)
113.4(4)
126.7(4)
121.5(6)
126.6(5)
˚
2.330(2) A, respectively) are within the normal range [9a].
The geometry about palladium is planar (mean deviation
0.042 A) justifying the oxidation state of Pd(II) and the
˚
uninegative ligand since the complex is a non-electrolyte.
The delocalisation of the negative charge within the
ligand backbone causes the bond lengths to be suitably
3.2.2. HL2 and HL3
Ligands HL2 and HL3 were prepared using 2-(p-toly-
lazo) aniline and 2-(p-chlorophenylazo) aniline in place of
2-(phenylazo) aniline, respectively. Yield: HL2, 62% and
HL3, 65%.
˚
altered [6]. The C(12)–N(3) length (1.330(9) A) is shorter
compared to the C–N single bond (N(1)–C(6),
˚
1.454(8) A) in the same molecule and is similar to the imine
(C@N) distance [6]. Also the effect of imine formation due
to delocalisation has been reflected in the adjacent phenyl
ring (C(7), C(8), C(9), C(10), C(11) and C(12)) which is dis-
Anal. Calc. for C19H18N4, HL2: C, 75.50; H, 5.96; N,
18.54. Found: C, 75.42; H, 6.00; N 18.60%. UV–Vis
(kmax/nm (ꢀ/MÀ1 cmÀ1
)
in dichloromethane): 451
˚
˚
torted with two short (ꢀ1.35 A) and four long (ꢀ1.4 A)
bonds. Thus the formation of an azoimine chelate could
be inferred from the X-ray studies [6] and the structural
formula of (L1)PdCl has been drawn accordingly in 3 of
Scheme 1 (vide supra). All the non-hydrogen atoms of
(L1)PdCl, excluding the pendant phenyl ring (C(1)–C(6)),
(37287), 419 (32681), 321 (61303). IR (KBr pellets,
cmÀ1): mN–H 3196, mN@N 1512. 1H NMR (CDCl3):
d = 9.37 (b, NH); 8.65 (d, 1H, J = 5.0); 7.86 (d, 1H,
J = 8.0); 7.79 (d, 1H, J = 8.5); 7.64 (t, 1H, J = 7.5); 7.35
(d, 1H, J = 10.0); 7.29 (d, 2H, J = 8.0); 7.24–7.19 (m,
3H); 6.79 (t, 1H, J = 7.5); 6.73 (d, 1H, J = 8.5); 4.68 (d,
2H, J = 5.5); 2.42 (s, 3H).
˚
make a good plane (mean deviation 0.114 A).

D. Patra et al. / Polyhedron 25 (2006) 2637–2642
2641
Anal. Calc. for C18H15N4Cl, HL3: C, 66.97; H, 4.65; N,
17.37. Found: C, 66.50; H, 4.70; N, 17.25%. UV–Vis (kmax
Table 2
Crystallographic data for (L1)PdCl
/
nm (ꢀ/MÀ1 cmÀ1) in dichloromethane): 461 (10854), 426
(8483), 324 (17123), 253 (19435). IR (KBr pellets, cmÀ1):
mN–H 3196, mN@N 1511. 1H NMR (CDCl3): d = 9.55 (b,
NH); 8.66 (d, 1H, J = 4.0); 7.88 (d, 1H, J = 8.0); 7.84 (d,
2H, J = 7.0); 7.66 (t, 1H, J = 7.5); 7.46 (d, 2H, J = 9.0);
7.33 (d, 1H, J = 7.5); 7.25 (m, 1H); 7.22 (t, 1H, J = 6.5);
6.83 (t, 1H, J = 8.0); 6.75 (d, 1H, J = 8.5); 4.68 (d, 2H,
J = 5.0).
Chemical formula
Formula weight
Space group
C18H15ClN4Pd
429.21
Pna21 cab (no. 33)
orthorhombic
6.9300(11)
13.3390(13)
17.738(2)
0.71073
1639.7(4)
4
Crystal system
˚
a (A)
˚
b (A)
˚
c (A)
˚
k (A)
3
˚
V (A )
Z
Temperature (K)
qcalc (Mg/m3)
293
1.739
1.301
856
0.0300
1448/1269
0.0805
3.3. Syntheses of the complexes
l (mmÀ1
F (000)
R1
)
All the complexes, (L1)PdCl, (L2)PdCl and (L3)PdCl
were prepared following similar procedures. A representa-
tive procedure for (L1)PdCl, is given below.
Unique reflections/[I > 2r(I)]
wR2
Goodness-of-fit
1.04
3.3.1. (L1)PdCl
A solution of HL1 (0.150 g, 0.52 mmol) in 10 cm3 meth-
anol was added to a solution of Na2PdCl4 (0.153 g,
0.52 mmol) in 5 cm3 methanol. The mixture was stirred
for 5 h. The dark solid precipitate was separated by filtra-
tion and purified by column chromatography using silica
gel (60–120 mesh). The eluent was benzene–acetonitrile
(19/1 v/v) mixed solvent. Upon evaporation of the solvent,
a violet solid of pure (L1)PdCl was obtained. Yield: 0.122 g,
55%. Anal. Calc. for C18H15N4PdCl, (L1)PdCl: C, 50.32; H,
3.49; N, 13.04. Found: C, 50.35; H, 3.50; N, 13.00%. UV–
Vis (kmax/nm (ꢀ/MÀ1 cmÀ1) in dichloromethane): 565
(14660), 525 (3230), 325 (31870). IR (KBr pellets, cmÀ1):
mN@N 1357, mPd–Cl 333. 1H NMR (CDCl3): d = 9.39 (d,
1H, J = 6.0); 7.86 (t, 2H, J = 7.2); 7.52 (d, 1H, J = 7.8);
7.45–7.30 (m, 7H); 7.02 (d, 1H, J = 9.0); 6.68 (t, 1H,
J = 7.8); 5.24 (s, 2H).
3.4. Physical measurements
Microanalyses (C,H,N) were performed using a Perkin–
Elmer 240C elemental analyser. Infrared spectra were
recorded on a Perkin–Elmer L120-00A FT-IR spectrome-
ter with the samples prepared as KBr pellets. Electronic
spectra were recorded on a Shimadzu UV-2401 PC spectro-
1
photometer. H NMR spectra were obtained on Brucker
Avance DPX 300 and Brucker RPX 500 NMR spectrome-
ters in CDCl3, using TMS as the internal standard.
3.5. Crystallography
A crystal of C18H15N4PdCl was grown by slow diffusion
of hexane into a dichloromethane solution at 298 K. Data
were collected by the x-scan technique on a Enraf–Nonius
CAD4 diffractometer with Mo Ka radiation monochro-
mated by a graphite crystal. The structure solution was
done by the direct method with the SHELXS-97 program.
Full matrix least square refinements were performed using
the SHELX-97 program (PC version). All non-hydrogen
atoms were refined anisotropically using reflections
I > 2r(I). Hydrogen atoms were included in calculated
positions. The crystal data and data collection parameters
are listed in Table 2.
3.3.2. (L2)PdCl and (L3)PdCl
Complexes (L2)PdCl and (L3)PdCl were prepared using
the ligands HL2 and HL3 in place of HL1, respectively.
Yield: (L2)PdCl, 55% and (L3)PdCl, 55%.
Anal. Calc. for C19H17N4PdCl, (L2)PdCl: C, 51.46; H,
3.83; N, 12.64. Found: C, 51.40; H, 3.90; N, 12.70%.
UV–Vis (kmax/nm (ꢀ/MÀ1 cmÀ1) in dichloromethane): 563
(25711), 529 (22733), 460 (19844), 327 (37666). IR (KBr
1
pellets, cmÀ1): mN@N 1354, mPd–Cl 332. H NMR (CDCl3):
d = 9.40 (d, 1H, J = 5.5); 7.86 (m, 2H); 7.53 (d, 1H,
J = 8.0); 7.43 (t, 1H, J = 7.0); 7.35–7.31 (m, 3H); 7.18 (d,
2H, J = 8.0); 7.01 (d, 1H, J = 8.5); 6.67 (t, 1H, J = 7.5);
5.22 (s, 2H); 2.39 (s, 3H).
4. Conclusion
Reactions of transition metal substrates with preformed
ligands describe the actual metal–ligand interaction which
is important to rationalise several biological and catalytic
processes. The work presented here is a unique example
in this regard. In this report we have described that the
M–C interaction in polyfunctional organic molecules may
be influenced not only electronically but also by suitable
arrangements of the hetero donor atoms. The N-alkylated
arylazo anilines, HLa, were demonstrated to be appropriate
for C–H bond activation via orthometallation [7] while
Anal. Calc. for C18H14N4PdCl2, (L3)PdCl: C, 46.60; H,
3.02; N, 12.08. Found: C, 46.55; H, 3.00; N, 12.10%.
UV–Vis (kmax/nm (ꢀ/MÀ1 cmÀ1) in dichloromethane): 566
(21488), 534 (18813), 334 (40348), 247 (159395). IR
(KBr pellets, cmÀ1): mN@N 1357, mPd–Cl 333. 1H NMR
(CDCl3): d = 9.35 (d, 1H, J = 5.5); 7.86 (t, 1H, J = 7.5);
7.79 (d, 1H, J = 8.5); 7.53 (d, 1H, J = 7.5); 7.44–7.32 (m,
6H); 7.02 (d, 1H, J = 9.0); 6.68 (t, 1H, J = 7.5), 5.23 (s,
2H).

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D. Patra et al. / Polyhedron 25 (2006) 2637–2642
[3] (a) R. Acharyya, S.-M. Peng, G.-H. Lee, S. Bhattacharya, Inorg.
Chem. 42 (2003) 7378;
reactions of the newly synthesised ligands, HL with
Na2PdCl4 afforded the remarkable azoimine chelates. A
plausible rationale has been given considering the logical
progress of the reactions.
(b) S. Nag, P. Gupta, R.J. Butcher, S. Bhattacharya, Inorg. Chem. 43
(2004) 4814;
(c) P. Gupta, R.J. Butcher, S. Bhattacharya, Inorg. Chem. 42 (2003)
5405;
Acknowledgments
(d) R. Aharyya, F. Basuli, R.Z. Wang, T.C. Mak, S. Bhattacharya,
Inorg. Chem. 43 (2004) 704, and references therein.
[4] (a) A.H. Velders, K. van der Schilden, A.C.G. Hotze, J. Reedijk,
H. Kooijman, A.L. Spek, J. Chem. Soc., Dalton Trans. (2004)
448;
We are thankful to the DST (New Delhi) for funding
and fellowship to J.P. under the DST-SERC project. The
necessary laboratory and infrastructural facility are pro-
vided by the Department of Chemistry, University of Kaly-
ani. We are thankful to Prof. G.K. Lahiri (IIT, Mumbay)
for his continuous help. The support of the DST under
the FIST program to the Department of Chemistry, Uni-
versity of Kalyani is acknowledged.
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Appendix A. Supplementary data
Figs. S1–S6, UV–Vis spectra; Figs. S7–S12, IR spectra
and Figs. S13–S18, H NMR spectra are supplied as sup-
1
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and references therein;
plementary material. Crystallographic data for the struc-
tural analysis have been deposited with the Cambridge
Crystallographic Data Center, CCDC reference number
250543. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, e-mail: deposite@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online
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