Synthesis and X-ray crystal structure of dichloro[S-1-phenyl-N-(S- pyrrolidin-2-ylmethyl)ethanamine]zinc(II) and its catalytic application to rac-lactide polymerization

Article abstract of DOI:10.1016/j.poly.2010.11.002

New dichloro zinc(II) complex ligated by the homochiral bidentate ligand S-1-phenyl-N-(S-pyrrolidin-2-ylmethyl)ethanamine (PPMA) was synthesized and characterized by X-ray crystallography. The geometry of the (PPMA)ZnCl ₂ is a distorted tetrahe

Full text of DOI:10.1016/j.poly.2010.11.002

Polyhedron 30 (2011) 405–409
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and X-ray crystal structure of dichloro[S-1-phenyl-N-(S-pyrrolidin-2-
ylmethyl)ethanamine]zinc(II) and its catalytic application
to rac-lactide polymerization
⇑
Saira Nayab, Hyosun Lee, Jong Hwa Jeong
Department of Chemistry, Kyungpook National University, Sankyuk-dong, Taegu 702-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
New dichloro zinc(II) complex ligated by the homochiral bidentate ligand S-1-phenyl-N-(S-pyrrolidin-2-
ylmethyl)ethanamine (PPMA) was synthesized and characterized by X-ray crystallography. The geome-
try of the (PPMA)ZnCl2 is a distorted tetrahedron comprising of zinc metal as a center linked with two N
atoms of the PPMA in a bidentate coordination mode along with two chloro ligands. The catalytic capac-
ity of the complex was evaluated in ring opening polymerization (ROP) of rac-lactide. The active catalyst
species was generated in situ by treating MeLi to complex (PPMA)ZnCl2. The dimethyl derivative of the
(PPMA)ZnCl2 showed highly activity in ROP of rac-lactide and gave preference to heterotactic polylactide.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 29 September 2010
Accepted 4 November 2010
Available online 18 November 2010
Keywords:
Polylactide
S-1-phenyl-N-(S-pyrrolidin-2-
ylmethyl)ethanamine
Zinc complex
Ring opening polymerization
Heterotacticity
1. Introduction
iron [13–15], zinc [16–23] on one hand and highly toxic metals
such as tin [24,25], lead [26] and lanthanides [27,28] on the other
Polyesters represent a class of polymers that can serve as prom-
ising substitutes for petrochemical-based polymers [1] because of
the depleting petrochemical feedstocks and increasing environ-
mental awareness. Polylactides are aliphatic polyesters obtained
by polymerizing lactide, a cyclic diester of lactic acid, which is ob-
tained by fermentation of 100% bio-renewable resources such as
sugar (beet or cane) or starch (corn, wheat, potatoes) or even from
food wastes compared to the most of other polymeric materials.
The consumption of petrochemical resources would be signifi-
cantly reduced by polylactide production, as 150 million tons of
these nonrenewable resources are consumed annually for plastic
production. These polymeric materials are biodegradable, biore-
newable and biocompatible and have great potential to be used
as a new class of environmental friendly thermoplast [2–4] and
will offer a practical solution to the ecological problems associated
with bioresistant wastes.
hand. In particular, the polymerization of lactide by zinc(II)
complexes is advantageous due to their unique features, such
as lack of color, low-toxicity, low cost, biocompatibility, and
environmentally friendly nature. As polylactide is mainly used
in biomedical [29], pharmaceuticals, agriculture, and packaging
applications [30,31], so it is highly recommended to remove
the catalyst residue completely from the polymer. Since the
complete removal of the catalytic residues is practically not pos-
sible, biocompatible and environmentally friendly metals are
preferable.
Stereochemistry is one of the main factors that determine the
physical and mechanical properties of a polymeric material [32]
and hence, the stereoselective polymerization of lactide, has be-
come a subject of considerable attention in order to elucidate
the structure–property relationship. Polylactides can exhibit dif-
ferent microstructures depending both on the monomer (rac-lac-
Ring opening polymerization of lactide to synthesize polylac-
tide has been proven to be the most effective and versatile strat-
egy using homogenous single site metal catalysts. Many different
types of metal-based catalysts have been employed for the
synthetic protocol of these valuable materials that include non
hazardous lithium [5,6], magnesium [7–9], aluminum [10–12],
tide, meso-lactide, -lactide) involved and on the course of the
L
polymerization reaction [33,34]. Isotactic polylactides, contain
sequential stereocenters of the same relative configuration, while
syndiotactic polylactides have sequential stereocenters of oppo-
site relative configuration. By changing the composition and tac-
ticity of the polymers, the physical properties can be tuned and
significantly improved. Therefore, the extent of stereocontrol
exhibited by catalytic system is very important as the rate of
chemical and biological degradation, mechanical and thermal
⇑
Corresponding author. Tel.: +82 53 950 6343; fax: +82 53 950 6330.
E-mail address: jeongjh@knu.ac.kr (J.H. Jeong).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.11.002

406
S. Nayab et al. / Polyhedron 30 (2011) 405–409
properties of polylactide depend upon the tacticity of the poly-
mer. With single-site catalysts, the monomer attachment occurs
at a metal center that in turn bound to an organic ligand. The
metal center reactivity is being modulated by the ancillary
ligand, which remains bound throughout the catalytic reaction.
Furthermore, the structure of ancillary ligand has a substantial
influence on the stereoregularity and hence, the tacticity of the
final polymeric material for appropriate applications.
Recently, the zinc-based catalysts for polymerization of lactide
have been reported by several groups [35–38]. Additionally, zinc
acetate in the presence of BnOH reported by Chakraborty group
has been shown the highest catalytic activity with no stereoregu-
larity over the microstructure of the obtained PLA using rac-lactide
[39].
2.3. Synthesis and characterization of ligand and complex
2.3.1. 5-Oxo-pyrrolidine-2-carboxylic acid (1-phenyl-ethyl)-amide
To the 2-amino-pentanedioic acid (5.0 g, 33.98 mmol) was
added S-methylbenzylamine (6 mL, 47.13 mmol) slowly at ambi-
ent temperature. The reaction mixture was stirred at 150 °C for
1 day and the progress of the reaction was monitored by TLC. Light
brown solid product was obtained after pouring the reaction mix-
ture into dichloromethane and slowly evaporating the solvent at
room temperature followed by washing the solid residue several
times with diethyl ether (6.52 g, 83.0%). 1H NMR (400 MHz, CDCl3)
d 7.31–7.00 (m, 1H), 5.12–5.05 (m, 1H), 4.04–4.03 (m, 1H), 2.47–
2.06 (m, 5H), 1.47 (d, J = 6.8 Hz, 3H). Analysis calculated for
C13H16N2O2: C, 67.22%; H, 6.94%; N, 12.06%. Found: C, 66.99%; H,
In this regard zinc based initiators for ROP of rac-lactide have
been reported by Coates group [(BDI)Zn(OiPr)]2 [(BDI) = 2-((2,
6-dialkylphenyl)amido)-4-((2,6-diiso-propylphenyl)imino)-2-pen-
tene] that showed high activity along with high stereoselective
for polylactide. The high heterotacticity (Pr) value obtained was
found to be 0.94, which is the highest ever reported [40]. Keeping
in view these facts, we describe herein, the synthesis, and struc-
tural characterization of mononuclear zinc complex (PPMA)ZnCl2
and the ability of its dimethyl derivative generated in situ to ini-
tiate the polymerization of rac-lactide, resulted in a high activity
and a high stereoselectivity compared to our previous reported
initiator ZnEt2(S-EPP) [41]. Further included in these studies is
the effect of inherent chirality on the tacticity of polylactide
afforded from ROP of rac-lactide. The X-ray crystal structure of
the pre-catalyst, (PPMA)ZnCl2, will also be described.
7.01%; N, 12.10%.
2.3.2. S-1-phenyl-N-(S-pyrrolidin-2-ylmethyl)ethanamine (PPMA)
To the THF (20 mL) solution of 5-oxo-pyrrolidine-2-carboxylic
acid (1-phenyl-ethyl)-amide (2.0 g, 8.6 mmol) was added slowly
the THF (20 mL) solution of LiAlH4 (0.65 g, 17.2 mmol) at À78 °C.
The reaction mixture was stirred for one day at reflux temperature
after warming to room temperature. The progress of the reaction
was monitored by TLC. Excess of LiAlH4 was quenched with 2N
(10 mL) NaOH. The residue obtained after removing the solvent
was dissolved in 30 mL CH2Cl2 and washed with distilled water
(3 Â 20 mL). The CH2Cl2 solution of product was dried over anhy-
drous MgSO4. The solvent was evaporated to give yellow oil
(1.30 g, 74.0%). 1H NMR (400 MHz, CDCl3) d 7.32–7.20 (m, 5H),
3.75 (m, 1H), 3.23–3.12 (m, 1H), 2.90–2.82 (m, 2H), 2.43–2.27
(m, 2H), 1.85–1.60 (m, 5H), 1.34 (d, J = 6.4 Hz, 3H), 1.287–1.20
(m, 1H). Analysis calculated for C13H20N2: C, 76.42%; H, 9.87%; N,
13.71%. Found: C, 75.56%; H, 9.76%; N, 13.82%. IR (solid neat;
cmÀ1): 3060 (m), 2959 (w), 1664 (br, w), 1492 (w), 1450 (br,
m),1368 (w), 1351 (w), 1208 (w), 1128 (br, w), 1026 (w), 911
(w), 760 (s), 698 (s), 594 (w).
2. Experimental
2.1. Materials
All manipulations involved in the synthesis of ligands and com-
plexes were carried out by the use of bench top techniques in air
unless otherwise specified. All polymerizations were carried out
by the use of standard schlenk techniques, high vacuum, and glove
box under argon. THF was dried over Na/benzophenone ketyl,
while CH2Cl2 was dried over CaH2, these solvents were deoxygen-
ated by distillation under argon prior to use. EtOH and Et2O were
purchased from high grade commercial supplier and used as received.
Starting materials were obtained from high-grade commercial
suppliers and used without further purification. 3,6-dimethyl-1-
dioxane-2,5-dione (rac-lactide) was purchased from Aldrich and
stored in glove box and used without further purification. S-meth-
ylbenzylamine, zinc chloride and methyl lithium (1.6 M in diethyl
ether) were purchased from Aldrich and were used without further
purification. NMR solvents were purchased from Aldrich and stored
over 3 Å molecular sieves.
2.3.3. (PPMA) ZnCl2
A 100 mL, one-necked round-bottom flask was charged with
ZnCl2 (0.66 g, 4.90 mmol) and EtOH (5 mL) and stirred to make
homogenous solution followed by the addition of EtOH solution
(5 mL) of PPMA (1.0 g, 4.90 mmol). The mixture was stirred at
ambient temperature for 12 h and the progress of reaction was
monitored by TLC. The solid product was filtered and washed with
cold EtOH (3 Â 5 mL) and dried in vacuo (1.4 g, 84.0%). 1H NMR
(400 MHz, CDCl3) d 7.35–7.23 (m, 5H), 3.94 (m, 1H), 3.60–3.75
(m, 2H), 3.24 (m, 2H), 3.00–3.16 (m, 2H), 2.32–2.36 (m, 1H),
2.04–2.14 (m, 1H), 1.68–1.95 (m, 4H), 1.60 (d, J = 6.8 Hz, 3H). Anal-
ysis calculated for C13H20Cl2N2Zn: C, 45.84%; H, 5.92%; N, 8.22%.
Found: C, 45.80%; H, 5.90%; N, 8.19%. IR (solid neat; cmÀ1): 3233
(br, w), 3207 (w), 2970 (w), 1464 (w), 1453 (w), 1428 (w), 1382
(w), 1281 (w), 1222 (w), 1197 (m), 1129 (w), 1074 (s), 1047 (s),
1025 (m), 1005 (w), 985 (w), 964 (w), 936 (w),1368 (w), 896
(s),778 (m), 764 (s), 703 (s), 656 (w), 625 (m), 594 (w), 565 (m).
2.2. Instrumentation
1H NMR (400 MHz) spectra were recorded on a Bruker Advance
Digital 400-NMR spectrometer and chemical shifts were recorded
in ppm units using SiMe4 as an internal standard. Infrared (IR)
spectra were recorded on Bruker FT/IR-Alpha (neat) and the data
are reported in reciprocal centimeters. Elemental analyses were
performed by Fison-EA1108. Gel permeation chromatography
(GPC) analyses were carried out on a Waters Alliance GPCV2000,
equipped with differential refractive index detectors at the Chem-
ical Analysis Laboratory of the Center for Scientific Instruments of
Kyungpook National University. The GPC columns were eluted
using THF with 1 ml/min rate at 25 °C and were calibrated with
monodisperse polystyrene standards.
2.4. Polymerization of rac-lactide with in situ generated
(PPMA)ZnMe2
(PPMA)ZnCl2 (0.18 g, 0.5 mmol) and dried THF (7.3 mL) were
added to a 100 mL of schlenk flask to make a homogenous solution.
To this solution was added MeLi (0.65 mL of 1.6 M solution in
diethyl ether, 1 mmol) drop wise at À78 °C. After being stirred
for 2 h at room temperature, the resulting solution of
(PPMA)ZnMe2 was used as a catalyst for polymerization reaction.
The general procedure for the polymerization reaction was as fol-
lows: a 100 mL of schlenk flask was charged with rac-lactide
(0.991 g, 6.8 mmol) in the glove box. Dried CH2Cl2 (5 mL) was

S. Nayab et al. / Polyhedron 30 (2011) 405–409
407
transferred to the flask via syringe and stirred to make a clear solu-
tion. The reaction was initiated by adding the catalyst solution
(1.0 mL, 0.0625 mmol) with gas tight syringe under argon. The
reaction mixture was stirred at room temperature and À25 °C for
12 h. The polymerization reaction was quenched after prescribed
duration by adding water (1 mL). Hexane (2 mL) was added to pre-
cipitate the polymer followed by washing with Et2O. The resultant
sticky polymeric material was dried in vacuo. A white solid was ob-
tained finally (0.87 g, 97% based on rac-lactide). 1H NMR (400 MHz,
CDCl3): d 5.12–5.25 (m, 1H), 1.51–1.63 (m, 3H).
refined anisotropically and all hydrogen atoms of carbon atoms
were refined positioned geometrically using riding model with
fixed isotropic thermal factors. And amine hydrogen atoms were
refined using riding model with 0.87 Å separations and fixed isotropic
thermal factors. The final cycle of the refinement converged with
R1 = 0.038 and wR2 = 0.090.
3. Results and discussion
3.1. Synthesis and X-ray crystal structure of the (PPMA)ZnCl2 complex
2.5. X-ray crystallographic analysis
The synthesis of bidentate ligand PPMA has been successfully
carried out by two steps process comprising of condensation reac-
tion of S-2-aminopentandioic acid and S-methylbenzylamine un-
der neat conditions at 150 °C, followed by the reduction of amide
to amine analog by treating with stoichiometric amount of LiAlH4
in THF at refluxing temperature. The air and moisture stable di-
chloro zinc complex of PPMA was synthesized by treating ZnCl2
with PPMA at ambient temperature for 12 h in EtOH (Scheme 1).
The synthesized ligand and complex were characterized by 1H
NMR, IR, elemental analysis, and X-ray crystal determination.
The X-ray crystal structure of (PPMA)ZnCl2 has two indepen-
dent molecules per asymmetric unit. The ORTEP drawing of the
complex is shown in Fig. 1 with atomic labels. Crystal data, details
of the data collection, and refinement parameters are listed in
Table 1. Selected bond distances and angles are listed in Table 2.
An X-ray quality single crystals were obtained by diffusion of
hexane into solution of (PPMA)ZnCl2 in CH2Cl2. A single crystal
was mounted in a thin-walled glass capillary on an Enraf-Noius
CAD-4 diffractometer with MoKa radiation (k = 0.71073 Å). Unit
cell parameters were determined by least-squares analysis of 25
reflections (10° < h < 13°). Intensity data were collected with h
range of 1.79–25.47° in
x/2h scan mode. Three standard reflections
were monitored every 1 h during data collection. The data were
corrected for Lorentz-polarization effects and decay. Empirical
absorption corrections with
w-scans were applied to the data.
The structure was solved by using Direct method and refined
by full-matrix least-squares techniques on F2 using SHELXS-97 and
SHELXL-97 program packages [42]. All non hydrogen atoms were
NH2
O
HO
OH
-2H2O
H2N
+
150 oC, 24h
N
O
O
H
N
O
H
Ph
LiAlH4
THF, Reflux, 24h
ZnCl2
N
HN
N
H
EtOH, R.T, 12h
H
N
Zn
H
Ph
Ph
Cl
Cl
Scheme 1. Synthesis of (PPMA)ZnCl2.
Fig. 1. An ORTEP drawing of (PPMA)ZnCl2 with the numbering scheme at 40% probability level.

408
S. Nayab et al. / Polyhedron 30 (2011) 405–409
Table 1
of C–N single bond upon coordination of N(1) atom to mental
center. In addition the d-conformation has been confirmed for
Crystal data and structure refinement of (PPMA)ZnCl2.
the five-membered ring made by Zn–N(1)–C(4)–C(5)–N(2).
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C13H20Cl2N2Zn
681.16
Orthorhombic
P212121
3.2. Polymerization of rac-lactide with in situ generated Zn catalyst
Ring opening polymerization of rac-lactide employing
(PPMA)ZnMe2 as an initiator is systematically examined under in-
ert atmosphere. The dimethyl zinc complex (PPMA)ZnMe2 was
prepared in situ from the air stable (PPMA)ZnCl2 by treating with
two equivalents of MeLi (1.6 M solution in diethyl ether) in THF.
The appearance of the resonance for protons of (PPMA)ZnMe2 in
the high-field region (d À0.61) demonstrated the formation of
the desired complex. Conversion of monomer to polylactide is
determined on the basis of 1H NMR spectroscopy. The polymeriza-
tion was carried out at 25 °C and at À25 °C in CH2Cl2 using THF
solution of (PPMA)ZnMe2 (0.0625 mmol) as initiator. The polymer-
ization results are listed in Table 3. The resultant polymers were
isolated and purified using water and hexane followed by Et2O
and dried in vacuo for overnight at 40 °C. The well controlled poly-
merization process indicated from experimental results is shown
in Table 3. As the narrow polydispersities over the range of 1.21–
1.23 and Mn of the produced polylactides have linear relationship
with calculated values predicted from [monomer]/[catalyst], indi-
cated the living polymerization process of single active site. The
polymerization was carried out at two different temperatures in
order to sort out the relationship between the Pr and polymeriza-
tion temperature, keeping the [monomer]/[catalyst] constant i.e.
[1]/[110]. The fact is revealed that the dimethyl derivative pre-
pared in situ is a highly efficient initiator for the polymerization
of rac-lactide. Viscous solution has been observed within an hour
at the desired [monomer]/[catalyst] ratio in dichloromethane at
room temperature. Furthermore the polymerization rate at the
same [monomer]/[catalyst] ratio at low temperature was slightly
decreased.
As described earlier, the physical, mechanical, and degradation
properties of the polylactides are dramatically dependent on the
tacticity of the polymer. The stereoselectivity of the produced poly-
mer is determined by the Bernoullian statistics based on the data
obtained by homonuclear decoupled 1H NMR spectroscopy
[43,44] and the calculated values are summarized in Table 3. The
representative homonuclear decoupled 1H NMR spectrum of
methine proton region of polylactide is shown in Fig. 2 and the cal-
culation of Pr values was carried out from the ratio of the area of
(rmr and mrm)/total area of methine proton region from the
decoupled spectra. As demonstrated from the table and 1H NMR
spectra, the (PPMA)ZnMe2 produced high degree of heterotactic
polylactides. Pr values [45–48] for polylactides were found to be
0.71 at room temperature compared to 0.55 for the previous com-
plex [ZnCl2(S-EPP)]. The inherent chirality at C(6) in complex
(PPMA)ZnCl2 provides the polylactide with high degree of hetero-
tacticity (Pr = 0.71), since the ligand architecture is expected to
play a major role in stereoselectivity [49,50]. These values are
higher than those of obtained in the previous work [41] where a
chiral center exists but that cannot affect much the microstructure
of the polylactide. As mentioned earlier that ligand coordinate to
the metal core influence the microstructure of PLA. The study on
polymerization of lactide with the zinc acetate complex coupled
with the lack of ancillary ligands around the zinc core revealed that
10.7971(4)
b (Å)
13.4236(10)
21.5761(11)
3127.2(3)
8
1.447
1.897
1408
1.79–25.47
À13 6 h 6 13, À16 6 k 6 16,
À26 6 l 6 26
20650
5800 [Rint = 0.0088]
4284
c (Å)
V (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmÀ1
F(0 0 0)
)
h range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Reflections observed (>2d)
Data Completeness
1.000
Refinement method
Full-matrix least-squares on F2
5800/0/331
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2d (I)]
R indices (all data)
1.002
R1 = 0.0383 wR2 = 0.0899
R1 = 0.0683 wR2 = 0.1034
0.006(15)
0.512 and À0.343
Absolute structure parameter
Largest diff. peak and hole (e ÅÀ3
)
Table 2
Selected bond lengths (Å) and angles (°) for (PPMA)ZnCl2.
Zn–N(1)
Zn–N(2)
Zn–Cl(1)
Zn–Cl(2)
N(1)–Zn–N(2)
N(2)–Zn–Cl(2)
N(2)–Zn–Cl(1)
N(3)–Zn(1)–N(4)
N(4)–Zn(1)–Cl(4)
N(4)–Zn(1)–Cl(3)
2.046(5)
2.090(4)
2.227(1)
2.209(1)
86.6(2)
114.3(1)
109.3(1)
86.1(2)
Zn(1)–N(3)
Zn(1)–N(4)
Zn(1)–Cl(3)
Zn(1)–Cl(4)
N(1)–Zn–Cl(2)
N(1)–Zn–Cl(1)
Cl(2)–Zn–Cl(1)
N(3)–Zn(1)–Cl(4)
N(3)–Zn(1)–Cl(3)
Cl(4)–Zn(1)–Cl(3)
2.052(4)
2.108(4)
2.238(1)
2.218(1)
113.0(1)
108.0(10)
120.42(6)
126.6(1)
109.1(1)
114.68(5)
107.0 (1)
108.1(1)
The geometry of the (PPMA)ZnCl2 complex is a distorted tetrahe-
dron comprising of zinc metal as a center linked with two N atoms
of the PPMA in a bidentate coordination mode along with two
chloro ligands. The planes of two independent molecules between
Cl–Zn–Cl and N–Zn–N are 89.9(1)° and 84.5(1)° and the two bite
angles for Cl–Zn–Cl and N–Zn–N are 117.55(6)° and 86.4(2)°,
respectively. These values are similar with those found in [ZnCl2
(S-EPP)] complex [41] having similar skeleton to (PPMA)ZnCl2.
Larger Cl–Zn–Cl than N–Zn–N bite angle is due to the fact that
the two binding sites in tetrahedron are occupied by bidentate
ligand forming chelate while the other two sites are bounded by
large chloride ions.
Two stereogenic N atoms with two chiral centers from the
bidentate PPMA ligand exist in (PPMA)ZnCl2. The induced chirality
of N(2) was RN configuration and C–N single bond was rotated to
form head-to-tail configuration of hydrogen atoms of C(6) and
N(2). The configuration of N(1) was also RN and the configuration
of hydrogen atoms of C(4) and N(1) was head-to-head, which was
thermodynamically favorable resulted from interfering rotation
Table 3
Polymerization of rac-lactide with in situ prepared (PPMA)ZnMe2.
Entry
[Monomer]/[catalyst]
Temp. (°C)
Conversion
Mn  103
Mw  103
PDI
Pr
1
2
110
110
25
À25
97
96
15.4
16.4
19.0
19.9
1.23
1.21
0.71
0.75

S. Nayab et al. / Polyhedron 30 (2011) 405–409
409
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Fig. 2. Homonuclear decoupled 1H NMR spectrum of polylactide (for the prepara-
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Acknowledgment
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This research was supported by Basic Science Research Programs
through the National Research Foundation of Korea (NRF), funded
by the Ministry of the Education, Science, and Technology (Grant
No. 2009-0075742).
Appendix A. Supplementary data
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CCDC 802824 contains the supplementary crystallographic data
for (PPMA)ZnCl2. 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
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.
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