Synthesis and structural characterization of a flexible tetradentate ligand and its copper(I) coordination polymers

Article abstract of DOI:10.1016/j.ica.2011.06.050

A tetradentate Schiff-base ligand, N,N′-bis-(4-chlorobenzylidene)-1, 2-bis(2-aminophenylthio)ethane, L, and its copper(I) coordination polymers, [Cu₂(μ-I)₂-μ-L]_n·2n(CH ₃CN), LCuIS, and [Cu₂(μ-Cl)

Full text of DOI:10.1016/j.ica.2011.06.050

Inorganica Chimica Acta 376 (2011) 408–413
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and structural characterization of a flexible tetradentate ligand
and its copper(I) coordination polymers
a
c
Katayoun Marjani a, Mohsen Mousavi b, , Elham Ahmadi , David L. Hughes
⇑
a Faculty of Chemistry, Tarbiat Moalem University, 49 Mofateh Avenue, 15614 Tehran, Iran
b Department of Chemistry, Saveh Branch, Islamic Azad University, P.O. Box 39187/366, Saveh, Iran
c School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK
a r t i c l e i n f o
a b s t r a c t
A tetradendate Schiff-base ligand, N,N0-bis-(4-chlorobenzylidene)-1,2-bis(2-aminophenylthio)ethane, L,
and its copper(I) coordination polymers, [Cu2( -I)2- -Cl)2- -L]n, were
prepared. The products were characterized via their analytical and spectral properties. The crystal struc-
tures of the ligand molecule, L, and the complex, LCuIS, were determined by single-crystal X-ray diffraction
methods. In both the free molecule and the complex, L adopts an anti, staggered, extended conformation. In
LCuIS, prepared from L and CuI in acetonitrile, each Cu atom has a distorted tetrahedral coordination sphere
composed of a nitrogen atom and a sulfur atom from L and two iodine ligands. LCuIS is a sheet polymer,
Article history:
Received 13 February 2011
Received in revised form 18 June 2011
Accepted 30 June 2011
l
l
-L]nꢀ2n(CH3CN), LCuIS, and [Cu2(
l
l
Available online 19 July 2011
Keywords:
Bridging ligand,
Coordination polymer
Copper(I)
Crystal structure
Cyanacure
formed from coordination polymer chains containing the dimetal clusters Cu2(
linked through interactions of phenyl rings.
ꢀ ꢀ ꢀ
l-I)2; the chains are cross-
p
p
Ó 2011 Elsevier B.V. All rights reserved.
N2S2-donor ligand
1. Introduction
weak interactions (H-bonding, p–p stacking, van der Waals) may
also play a major role in ultimately controlling the network
The design and construction of metal–organic coordination
polymers are of current interest in the fields of supramolecular
chemistry and crystal engineering [1–3]. This interest arises from
their intriguing variety of architectures and topologies [3–6]. Fur-
thermore, research on the synthesis and characterization of
metal–organic coordination polymers is greatly motivated by their
potential applications ranging from catalysis [3–10], gas storage
[3,5,6,8–10], magnetism [3–7,9,10], molecular sensing [3,6,9,10],
non-linear optics [4,5,7,10], ion-exchange [3,4,6], electric conduc-
tivity [4,7,9], molecular separation [8,9], host–guest chemistry
[4,9], and medicine [5]. Therefore, rational design and synthesis
of materials with specific networks has become an important
research concern [3].
A large number of coordination polymers with a wide variety of
structural motifs has been prepared through the variation of
reagents and reaction conditions [6,10]. The structure and the
properties of such materials depend on several factors, such as
the oxidation state and coordination geometry of central metals,
structural chemistry of organic spacers, nature of solvents, pH va-
lue, temperature, the counter-anion and molar ratio of central
metal to organic ligand [3,4,6,8–12]. In addition to these factors,
[11,13].
Among these factors, the selection of appropriate organic spac-
ers has the greatest influence on determining the structural out-
come of target polymers [4,12,14]. The organic spacers serve to
link metal sites and to propagate structural information through-
out the extended structure. Properties of the organic spacers, such
as solubility, coordination preference, length, geometry and rela-
tive orientation of the donor groups, play a very important role
in dictating polymer framework topology [12,15]. With conforma-
tionally flexible spacers, the competition between bridging and
chelating coordination modes is an important factor in controlling
the self-assembly process [16,17]. So, structural control of metal–
organic reactions involving flexible ligands is a great challenge
and unexpected topologies often result [6].
Cyanacure (1,2-bis(2-aminophenylthio)ethane) is
a flexible
dithio-arylether with two ortho–amino substituents, enabling it
to form various Schiff-base ligands. Cyanacure itself is capable of
forming metal complexes via chelation to metal ions from both
nitrogen and sulfur atoms [1,18–21]. Cyanacure-derived Schiff-
bases can adopt various binding modes such as tetradentate
[1,17] or hexadentate [22,23] chelation to one metal center, triden-
tate chelation to one metal center [24], bridging in bis-bidentate
[17,21] or bis-tridentate [23] mode between two metal centers to
form bimetallic species, and bridging in bis-bidentate mode
⇑
Corresponding author. Tel.: +98 255 2241511; fax: +98 255 2240111.
E-mail address: drmousavi@hotmail.com (M. Mousavi).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.06.050

K. Marjani et al. / Inorganica Chimica Acta 376 (2011) 408–413
409
S
N
S
N
Ar
M
M
M
Ar
L
X
N
N
X
S
N
S
M
M
M
a)
b)
Ar
Ar
S
X
Ar
X
X
N
S
Ar
N
Ar
X
S
M
M
S
S
M
S
N
X
X
M
L
N
Ar
N
X
Ar
c)
d)
Ar
Scheme 1. Usual binding modes of cyanacure-derived Schiff-bases; (a) tetradentate chelating mode; (b) tridentate chelating mode; (c) monomeric bis-bidentate chelating
mode; (d) polymeric bis-bidentate chelating mode.
between two metal halide clusters to form polymeric networks [2]
(Scheme 1).
added and the mixture was refluxed for 30 min. An orange precip-
itate was formed on cooling, which was filtered, washed with hot
ethyl acetate and dried in vaccuo.
The formation of metal complexes by combination of Cu(I)
halides and bidentate bridging ligands has been studied extensively
and shown to results in 1D chain or 2D sheet networks through the
linking of Cu2X2 moieties by bidentate bridging ligands [25].
A 1D coordination polymer composed of CuI and a cyanacure-de-
rived Schiff-base, N,N0-bis-(2-thenylidene)-1,2-bis(2-aminophenyl-
thio)ethane [2] has been reported previously. We report herein the
preparation and structural characterization of N,N0-bis-(4-chloro-
benzylidene)-1,2-bis(2-aminophenylthio)ethane, L, and its cop-
per(I) halide coordination polymers.
2.3.1. [Cu2(
Yield: 82%, mp 233 °C. Anal. Calc. for C28H22Cl4Cu2N2S2: C, 46.74;
H, 3.08; N, 3.89. Found: C, 46.60; H, 2.80; N, 3.93%. FTIR (KBr pellet,
cmꢁ1): 1621 (C@N). UV–Vis: kmax (nm) ( , L molꢁ1 cmꢁ1) in CH3CN:
350(9020), 268(51870). KM
ꢁ1 cm2 molꢁ1 (10ꢁ3 mol dmꢁ3 in ace-
l-Cl)2-l-L]n
m/
e
/X
tonitrile, 25 °C) 102.7. 1H NMR (DMSO-d6, ppm): d 3.10 (s, 4H), 7.31–
7.44 (m, 6H), 7.46 (d, J = 8.3, 4H), 7.67 (br s, 2H), 8.01 (d, J = 8.3, 4H),
8.85 (s, 2H). 13C NMR (DMSO-d6, ppm): d 32.4, 120.0, 127.9, 128.2,
128.7, 130.5, 132.1, 133.6, 137.0, 138.8, 150.1, 161.9.
2. Experimental
2.1. Material and physical measurements
2.3.2. [Cu2(
l
-I)2-
l
-L]n and [Cu2(
l
-I)2-
l
-L]nꢀ2n(CH3CN), LCuIS
Yield: 76%, mp 230–231 °C. Anal. Calc. for C28H22Cl2Cu2I2N2S2: C,
1,2-Bis(2-aminophenylthio)ethane (Cyanacure) was prepared
using a reported procedure [26]. Other reagents were commer-
cially available and used as received. Elemental analyses (CHN)
were performed using a Perkin-Elmer 2400 series (II) CHN elemen-
tal analyzer. 13C NMR and 1H NMR spectra were recorded on a Bru-
ker Avance-300 MHz spectrometer employing tetramethylsilane as
an internal reference. FTIR spectra were measured on a Perkin-El-
mer 843 spectrometer. UV–Vis spectra were recorded on a Perkin-
Elmer Lambda 25 instrument. Molar conductance measurements
were carried out on a Metrohm Herisau E 382 conductometer.
37.27; H, 2.46; N, 3.10. Found: C, 36.98; H, 2.21; N, 3.10%. IR (KBr pel-
let,
CH3CN: 360 (9750), 266 (71065), 252 (70895). KM
m e
/cmꢁ1): 1623 (C@N). UV–Vis: kmax (nm) ( , L molꢁ1 cmꢁ1) in
/X
ꢁ1 cm2 molꢁ1
(10ꢁ3 mol dmꢁ3 in acetonitrile, 25 °C) 106.2. 1H NMR (DMSO-d6,
ppm): d 3.13 (s, 4H), 7.26–7.38 (m, 6H), 7.47 (d, J = 8.5, 4H), 7.51
(d, J = 7.6, 2H), 8.01 (d, J = 8.5, 4H), 8.69 (s, 2H). 13C NMR (DMSO-
d6, ppm): d 31.8, 119.3, 127.5, 128.0, 128.8, 130.7, 131.7, 134.1,
136.1, 136.7, 149.8, 161.4.
Salmon-pink crystals of [Cu2(
able for X-ray diffraction were obtained by slow evaporation of sol-
l
-I)2-
l
-L]nꢀ2n(CH3CN), LCuIS, suit-
2.2. Synthesis of the ligand, N,N0-bis-(4-chlorobenzylidene)-1,2-bis(2-
aminophenylthio)ethane, L
vent from a solution of [Cu2(l-I)2-l-L]n in acetonitrile.
4-Chlorobenzaldehyde (0.53 g, 2 mmol) was added to a solution
of 1,2-bis(2-aminophenylthio)ethane (0.276 g, 1 mmol) in EtOH
(25 cm3). The mixture was stirred for 45 min to form a yellow pre-
cipitate which was then filtered, washed with cold ethanol and
dried in vaccuo. Yield: 0.41 g (78%), mp 147 °C. Anal. Calc. for
2.4. X-ray crystallography
Crystals of L and LCuIS were mounted in oil on glass fibers and
fixed in the cold nitrogen stream on an Oxford Diffraction Xcalibur-
3/Sapphire3-CCD diffractometer, equipped with Mo K
(k = 0.71073 Å) and graphite monochromator. Intensity data were
measured at 140 K by thin-slice - and -scans. Data were pro-
cessed using the CrysAlisPro-CCD and -RED [27] programs. The
structures were determined by the direct methods routines in
the SHELXS program [28] and refined by full-matrix least-squares
methods, on F2’s, in SHELXL [28]. The non-hydrogen atoms were
refined with anisotropic thermal parameters. Hydrogen atoms
were included in idealized positions and their Uiso values were
set to ride on the Ueq values of the parent carbon atoms. Scattering
factors for neutral atoms were taken from reference [29]. Com-
puter programs used in this analysis have been noted above, and
were run through WinGX [30] on a Dell Precision 370 PC at the
University of East Anglia. A summary of crystal and refinement
data for L and LCuIS is given in Table 1.
a radiation
C
28H22Cl2N2S2: C, 64.48; H, 4.25; N, 5.37. Found: C, 64.59; H,
4.07; N, 5.36%. IR (KBr pellet,
/cmꢁ1): 1621 (C@N). UV–Vis: kmax
(nm) (
, L molꢁ1 cmꢁ1) in CH3CN: 351(10775), 267(65915). 1H
m
x
u
e
NMR (DMSO-d6, ppm): d 3.17 (s, 4H), 7.13–7.29 (m, 8H), 7.58 (d,
J = 8.4, 4H), 7.93 (d, J = 8.4, 4H), 8.53 (s, 2H). 13C NMR (DMSO-d6,
ppm): d 30.1, 118.2, 126.3, 126.7, 126.8, 129.0, 130.4, 131.1,
134.8, 136.3, 149.1, 159.3. Pale yellow crystals suitable for X-ray
diffraction were obtained from slow diffusion of n-hexane in a
solution of L in ethylacetate.
2.3. Syntheses of the complexes
To a boiling suspension of L (0.61 g, 1 mmol) in CH3CN (15 cm3),
a solution of CuX (X = I or Cl) (2 mmol) in CH3CN (15 cm3) was

410
K. Marjani et al. / Inorganica Chimica Acta 376 (2011) 408–413
Table 1
Crystal and structure refinement data for L and LCuIS.
Compound
L
LCuIS
Elemental formula
Formula weight
Crystal system
Space group
Crystal color and shape
Crystal size (mm)
a (Å)
C
28H22Cl2N2S2
C28H22Cl2Cu2I2N2S2, 2(C2H3N)
984.5
monoclinic
P21/c (no. 14)
521.5
monoclinic
P21/c (no. 14)
pale yellow prism
salmon-pink plate
0.39 ꢂ 0.26 ꢂ 0.25
0.30 ꢂ 0.24 ꢂ 0.12
8.2795(2)
9.85515(11)
b (Å)
12.6140(2)
15.64116(16)
c (Å)
12.2250(2)
11.22348(12)
b (°)
107.667(2)
1216.53(4)
96.5560(10)
1718.74(6)
V (Å3)
Z
2
2
Dcalc (mg mꢁ3
F(0 0 0)
)
1.424
540
0.459
1.902
956
3.340
l
(mmꢁ1
)
h range (°)
3.5–30.0
3.7–30.0
Limiting indices
ꢁ11 ꢃ h ꢃ 11, ꢁ17 ꢃ k ꢃ 17, ꢁ17 ꢃ l ꢃ 17
ꢁ13 ꢃ h ꢃ 13, ꢁ22 ꢃ k ꢃ 22, ꢁ15 ꢃ l ꢃ 15
Completeness to h = 30.0 (%)
Maximum and minimum transmission
Reflections collected
99.8
99.8
1.090 and 0.884
23 277
1.243 and 0.765
28 141
Unique reflections (Rint
)
3547 (0.030)
2856
4990 (0.033)
4292
Reflections with I > 2 (I)
r
Data/restraints/parameters
3547/0/154
1.089
4990/0/200
0.993
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.028, wR2 = 0.076
R1 = 0.039, wR2 = 0.078
0.36 and ꢁ0.22
R1 = 0.018, wR2 = 0.040
R1 = 0.024, wR2 = 0.041
0.39 and ꢁ0.56
Largest difference peak and hole (e Åꢁ3
)
S
N
S
N
O
H
S
S
EtOH
2
+
NH2 H2N
Cl
Cl
Cl
Cyanacure
L
Scheme 2. Preparation of L.
formed the reaction of L with Cu(I) halides in acetonitrile, in order to
obtain and examine the coordination polymers produced.
3. Results and discussion
3.1. Synthesis
N,N0-Bis-(4-chlorobenzylidene)-1,2-bis(2-aminophenylthio)
ethane, L, was prepared from a 1:2 mixture of 1,2-bis(2-aminophe-
nylthio)ethane (cyanacure) and 4-chlorobenzaldehyde in ethanol
(Scheme 2).
L is a N2S2-donor ligand with two rigid N,S-donor moieties con-
nected through a flexible –CH2–CH2– spacer. While L can act as a
simple tetradentate ligand chelating to a single metal ion, it can also
act as a bis-bidentate ligand, bridging between two metal ions.
These different coordination modes are usual for cyanacure-derived
Schiff-bases. For instance, in treatment of N,N0-bis-(3-phenylprop-
2-en-1-ylidene)-1,2-bis(2-aminophenylthio)ethane with Cu(I) per-
chlorate, the metal ion releases its labile ligand, and the flexible
Schiff-base chelates it in tetradentate mode [17]. On the other hand,
in treatment with Cu(I) halides which do not have labile ligands, the
flexible Schiff-base ligand coordinates to each Cu(I) halide center in
bidentate mode, which allows it to bridge between two metal cen-
ters. In the latter case, if a suitable monodentate ligand (such as
PPh3) is present, the tetragonal coordination sphere of Cu(I) is satu-
rated with the additional ligand and a bimetallic complex will result
[17]. Otherwise, halide ions may bridge between tri-coordinated
Cu(I) ions to form a 1D coordination polymer [2]. Therefore, we per-
Fig. 1. View of a molecule of L, indicating the atom numbering scheme. Thermal
ellipsoids are drawn at the 50% probability level.

K. Marjani et al. / Inorganica Chimica Acta 376 (2011) 408–413
411
Fig. 2. Chains of L molecules linked through
pꢀ ꢀ ꢀp
interactions between the C(1–6) and C(215–265) rings and the C(21–26) and C(15–65) rings.
Table 2
Selected bond lengths (Å) and angles (°) for L and LCuIS.
L
C(11)–C(111)
C(11)–S(1)
S(1)–C(1)
1.531(2)
1.8081(12)
1.7693(11)
N(2)–C(20)
C(20)–C(21)
C(2)–N(2)
1.2746(14)
1.4656(15)
1.4158(14)
C(111)–C(11)–S(1)
C(1)–S(1)–C(11)
113.04(11)
103.10(5)
C(20)–N(2)–C(2)
N(2)–C(20)–C(21)
119.75(10)
122.51(10)
C(111)–C(11)–S(1)–
C(1)
C(11)–S(1)–C(1)–
C(6)
67.06(12)
C(2)–N(2)–C(20)–
C(21)
C(1)–C(2)–N(2)–
C(20)
ꢁ177.75(10)
ꢁ152.42(11)
18.95(11)
LCuIS
Cu–I
2.6265(2)
2.6047(2)
2.3613(4)
Cu–N(2)
Cu...Cu2
2.1020(12)
2.6416(4)
Cu–I2
Cu–S(1)
I–Cu–I2
S(1)–Cu–I
N(2)–Cu–I
S(1)–Cu–I2
119.343(7)
104.441(12)
108.56(3)
N(2)–Cu–I2
N(2)–Cu–S(1)
Cu–I–Cu2
123.29(3)
85.98(4)
60.657(7)
108.131(12)
Fig. 3. View of a portion of the polymer chain of LCuIS, indicating the atom
numbering scheme. Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms are omitted for clarity.
Cu2–I–Cu–N(2)
148.53(4)
ꢁ18.39(12)
ꢁ24.11(9)
ꢁ87.71(5)
144.21(5)
I–Cu–N(2)–C(2)
I2–Cu–N(2)–C(2)
N(2)–Cu–S(1)–C(1)
Cu–N(2)–C(2)–C(1)
C(20)–N(2)–C(2)–
C(1)
79.79(10)
ꢁ133.20(8)
20.43(6)
19.19(17)
ꢁ149.65(14)
Cu–S(1)–C(1)–C(2)
S(1)–Cu–N(2)–C(2)
I–Cu–S(1)–C(1)
I2–Cu–S(1)–C(1)
The Cu(I) complexes, [Cu2(l-Cl)2-l-L]n and [Cu2(l-I)2-l-L]n,
were prepared from a 1:2 mixture of L and CuX (X = Cl or I) in ace-
tonitrile. We obtained suitable single crystals for X-ray crystallog-
Cu2–I–Cu–S(1)
ꢁ120.891(14) C(2)–N(2)–C(20)–
ꢁ169.26(14)
C(21)
raphy from solutions of L and its CuI complex, [Cu2(
ethyl acetate and acetonitrile solutions, respectively. The latter
crystallized with solvent molecules to form crystals of [Cu2( -I)2-
-L]nꢀ2n(CH3CN), LCuIS. However, our efforts to obtain single crys-
tals from [Cu2( -Cl)2- -L]n were unsuccessful.
l
-I)2-
l
-L]n, in
C(1)–S(1)–C(11)–
C(111)
S(1)–C(1)–C(2)–N(2) 2.06(19)
78.4(2)
N(2)–C(20)–C(21)–
C(22)
8.3(2)
l
Symmetry transformations used to generate equivalent atoms: In L: 11 ꢁ x, 1 ꢁ y,
1 ꢁ z. In LCuIS: 12 ꢁ x, 1 ꢁ y; 1 ꢁ z; 21 ꢁ x, 1 ꢁ y, 1 ꢁ z.
l
l
l
are some downfield shifts especially for the imine protons (from
d 8.53 to 8.69 and 8.85, respectively), and for the two protons of
the aminothiophenyl rings in the ortho position to the amino sub-
stituent groups; from around d 7.29 to 7.51 and 7.67, respectively.
These downfield shifts relative to the corresponding signals in the
free ligand can be attributed to the deshielding effect resulting
from the coordination of the imine nitrogens. 13C NMR spectra of
L show a signal at d 30.1 for ethylene moiety, 10 signals from d
118.2 to 149.1 for aromatic rings, and a signal at d 159.3 for imine
carbons. The same pattern is observed in 13C NMR spectra of both
complexes.
3.2. Analytical and spectral characterization
The elemental analysis data are in good agreement with the
calculated values for the proposed formulae of the ligand and its
complexes. Both the chloride and iodide complexes are non-elec-
trolyte species, according to molar conductance measurements
[31]. The IR spectrum of the free ligand, L, shows a relatively strong
C@N stretching band at 1621 cmꢁ1, which is also present as a med-
ium band in the IR spectra of both complexes, at approximately the
same wave number. The 1H NMR spectrum of L presents a singlet
at d 3.17 for the central ethylene moiety, a multiplet at d 7.13–7.29
for protons of the electron-rich aminothiophenyl rings, a doublet of
doublets centered at d 7.75 for the protons of the electron-poor 4-
chlorophenyl rings, and a singlet at d 8.53 for the imine protons. A
similar pattern may be observed in the 1H NMR spectra of [Cu2
3.3. Description of crystal structures
In the solid state, the central –S–CH2–CH2–S– moiety of the
molecule L adopts an anti, staggered conformation (Fig. 1). The
(l-I)2-l-L]n and [Cu2(l-Cl)2-l-L]n complexes; nevertheless, there

412
K. Marjani et al. / Inorganica Chimica Acta 376 (2011) 408–413
Fig. 4. A sheet of LCuIS, viewed down the crystallographic b axis. The C6 rings of C(21–26) and C(215–265) are overlapping.
molecule lies about a center of symmetry at the mid-point of the
C(11)–C(111) bond; this is typical of molecules with this linking
group [22,32–34]. There is a rotation about the C(2)–N(2) bond
so that the planes of the two six-membered rings are rotated
21.64(5)° apart. Each Cl–C6H4–CH@N–C6H4 unit of the molecule
overlies a symmetry-related unit, with the C6 rings approximately
data: CCDC 808928 and 808927 contain the supplementary crys-
tallographic data for L and LCuIS, respectively. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
parallel (Fig. 2) allowing
p p interactions and closest interatom
ꢀ ꢀ ꢀ
contacts of C(6). . .C(254) 3.372(2) and C(1). . .C(264) 3.397(2) Å.
Molecules are thus linked in chains parallel to the (1 0 1) vector.
In crystals of the complex LCuIS, the ligand L again shows an ex-
tended form and lies about a center of symmetry at the mid-point
of the C(11)–C(111) bond. It is therefore able to coordinate, through
its two pairs of S,N donor atoms, to two Cu atoms, labeled Cu and
Acknowledgment
We gratefully acknowledge financial support from the Tarbiat
Moalem University.
Cu1 (Fig. 3). The Cu atom is part of a Cu2(
l-I)2 group which also lies
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been noted in [Cu2(l-I)2(l
-N,N0-di-(thiophenecarbaldehyde)-1,2-
di(o-aminophenylthio)ethane}]n [2]; the principal difference in
the pattern of the polymer chain is in the torsion angles about
the C–S–C–C link which for C(1)–S(1)–C(11)–C(111) in our complex
is 78.4(2)° (Table 2), compared with ꢁ53.8(4)° for the correspond-
ing angle in the previous structure. In our complex, pairs of chloro-
phenyl groups overlap, ca. 3.220 Å apart, about a further center of
symmetry, and form crosslinks of
chains to give a sheet polymer (Fig. 4).
p p interactions between the
ꢀ ꢀ ꢀ
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