Thermal transformation of 1D-Pb(en)2Cl2to 3D-PbCl2 via 2D-Pb(en)Cl2and their substantial modification of the coordination environment on Pb(II)

Article abstract of DOI:10.1016/j.poly.2010.04.008

The solvothermal synthesis and crystal structures of two new lead(II) compounds, bis(ethylenediamine)lead(II) chloride, Pb(en)₂Cl ₂ 1 and mono(ethylenediamine)lead(II) chloride, Pb(en)Cl₂ 2, are reported. A detailed comparison of the two structures is given. In 1, the Pb(II) center is coordinated by two chlorine atoms and four nitrogen atoms from three en ligands, which act as either chelating or bridging ligands, allowing links to other Pb(II) centers. This creates an infinite linear chain of Pb(Cn)₂Cl₂. In 2, the Pb(II) center is chelated by one en ligand and is coordinated by six chlorine atoms, including two unusually weak Pb-Cl bonds (>3.5?) connected through μ₂- and μ₄-Cl to build a neutral layer of Pb(en)Cl₂ units. Complex 1 contains a hemidirected Pb(II), while complex 2 has a (pseudo-)hemidirected Pb(II). TGA and high-temperature controlled powder-XRD studies show that compound 1 decomposes to compound 2 near 150°C, and finally to PbCl₂ above 320°C.

Full text of DOI:10.1016/j.poly.2010.04.008

Polyhedron 29 (2010) 2105–2110
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Thermal transformation of 1D-Pb(en) Cl to 3D-PbCl via 2D-Pb(en)Cl
2
2
2
2
and their substantial modification of the coordination environment on Pb(II)
a
a
a
a
b
Yoonsuk Cho , Seonhong Kim , Seungmoon Pyo , Yong Sun Park , Seung-Joo Kim ,
b
a,
*
Hoseop Yun , Junghwan Do
a
Department of Chemistry, Konkuk University, Seoul 143-701, South Korea
Department of Chemistry, Ajou University, Suwon 441-749, South Korea
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The solvothermal synthesis and crystal structures of two new lead(II) compounds, bis(ethylenedia-
mine)lead(II) chloride, Pb(en) Cl 1 and mono(ethylenediamine)lead(II) chloride, Pb(en)Cl 2, are
2 2 2
reported. A detailed comparison of the two structures is given. In 1, the Pb(II) center is coordinated by
two chlorine atoms and four nitrogen atoms from three en ligands, which act as either chelating or bridg-
Received 17 January 2010
Accepted 8 April 2010
Available online 14 April 2010
ing ligands, allowing links to other Pb(II) centers. This creates an infinite linear chain of Pb(en)
the Pb(II) center is chelated by one en ligand and is coordinated by six chlorine atoms, including two
unusually weak Pb–Cl bonds (>3.5 Å) connected through - and -Cl to build a neutral layer of
Pb(en)Cl units. Complex 1 contains a hemidirected Pb(II), while complex 2 has a (pseudo-)hemidirected
Pb(II). TGA and high-temperature controlled powder-XRD studies show that compound 1 decomposes to
compound 2 near 150 °C, and finally to PbCl above 320 °C.
2 2
Cl . In 2,
Keywords:
Solvothermal synthesis
Coordination polymer
Ethylenediamine lead(II) chloride
Thermal transformation
Hemidirected
l
2
l
4
2
2
Pseudo-hemidirected
Ó 2010 Elsevier Ltd. All rights reserved.
1
. Introduction
23 of 26 complexes in the CSD [13]. Only three crystal structures fell
into the hemidirected category; however, in these cases the differ-
ence between hemidirected and holodirected geometries was not
obvious [13,15,16].
The lone pair of electrons are important in determining stereo-
chemical activity and forming the preferred coordination geometry
around Pb(II) [1–12]. The role of such a lone pair of electrons on
Pb(II) was systematically investigated by Bock et al. through ab ini-
tio molecular orbital optimizations and crystallographic studies of
many Pb(II) complexes [13]. The lone pair of electrons can cause a
non-spherical charge distribution around Pb(II), leading to void for-
mation in the distribution of bonds to the ligands. Such geometries
with voids are called hemidirected, though not all Pb(II) complexes
with non-bonded electron pairs may belong to this category [14].
The presence of a void is usually taken as evidence for a stereo-
chemically active lone pair of electrons. On the other hand, holodi-
Here, we report the solvothermal syntheses and crystal struc-
tures of two hemidirected lead(II) coordination polymers, Pb(en)
Cl 1 and Pb(en)Cl 2 (en = ethylenediamine). Complex 1 possesses
2
2
2
chelating and bridging en, while complex 2 includes only chelating
en. Although en is one of the most common chelating and bridging
ligands [17–20], to our surprise, no previous studies were found of
Pb(II) complexes with bridging en ligands except for [Pb(en)
an analogue of Pb(en) Cl [21]. Interestingly, complex 1 decom-
posed to 2 near 150 °C and finally to PbCl above 320 °C. In this
process, the overall structure was altered 1D (1) ? 2D (2) ? 3D
(PbCl ), and the coordination sphere of Pb(II) was substantially
changed from hemidirected, C.N. = 6 (1) ? (pseudo-)hemidirected,
C.N. = 8 (2) ? holodirected, C.N. = 9 (PbCl ).
2 2
]Br ,
2
2
2
rected refers to complexes that include
a
spherical charge
2
distribution around Pb(II), without voids. The (non)-spherical
charge distributions around Pb(II) are known to be determined by
the number of ligands, ligand species, interactions among ligands,
and the number of electrons transferred from the ligand to the me-
tal [13]. Structures with coordination numbers 2–5 and 9–10 al-
ways occur with a hemidirected and holodirected arrangement,
respectively. For coordination number 6–8, both stereochemistries
are found; however, a holodirected Pb(II) coordination sphere is
dominant for C.N. = 8, probably due to ligand crowding, found in
2
2
. Experimental
.1. General methods
All the chemicals used in this work were of reagent grade and
2
they used as received from commercial sources without further
purification. Infrared spectra were recorded on a Hartmann &
Braun BOMEM FTIR spectrometer within
4000 cm using the KBr pellet method. Qualitative analyses of
a
range of 400–
*
Corresponding author. Tel.: +82 2 450 3416; fax: +82 2 3436 5382.
E-mail address: Junghwan@konkuk.ac.kr (J. Do).
ꢀ1
0
277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.04.008

2
106
Y. Cho et al. / Polyhedron 29 (2010) 2105–2110
the compounds were performed on a JEOL JSM-5200 scanning elec-
tron microscope (SEM) equipped with an EDAX Genesis energy dis-
persive spectroscopy (EDS) detector. Element analyses of the
compounds were carried out using a Perkin–Elmer ICP-AES, Opti-
ma 4300PV for Pb, and a ThermoQuest CE EA1110 for C, H and N.
4.1; N, 14.0%. Anal. Calc. for 2: Pb, 61.3; C, 7.1; H, 2.4; N, 8.3. Found:
Pb, 60.8; C, 7.2; H, 2.4; N, 8.6%.
2.3. Structure determination and refinement
Single-crystal data were collected on a Rigaku R-AXIS RAPID
diffractometer (graphite-monochromated Mo K
a radiation, k =
2.2. Synthesis
0
.71073 Å, T = 293 K). An empirical absorption correction was ap-
plied. The structures were solved by direct methods using SHELXS97,
refined on F by full-matrix least squares using SHELXL97 [22,23].
2
Complex 1 was synthesized from a mixture of PbCl (0.334 g,
.2 mmol) and en (1.0 ml, 14.8 mmol), which was sealed under
2
1
Hydrogen atoms associated with the en were placed geometrically
and refined by riding. All the non-hydrogen atoms were refined
anisotropically. Further details of the X-ray structural analysis
are given in Table 1. Selected bond distances and bond angles are
listed in Table 2. For drawings of the crystal structures the program
DIAMOND (Crystal Impact, Bonn, 1995) was used.
vacuum in a Pyrex tube and heated to 150 °C for 40 h, followed
by cooling to room temperature at 10 °C/h. The solid products were
recovered by vacuum filtration and washed with en. Colorless
plate-like crystals of 1 were found. The product 1 was slightly
unstable in water and in air. The yield of the 1 was ꢁ46 % based
on lead.
Complex 2 was synthesized from a mixture of PbCl
2
(0.334 g,
1
.2 mmol), en (0.1 ml, 1.5 mmol), and methanol (0.8 ml), which
2.4. Thermal analyses
was sealed under vacuum in a Pyrex tube and heated to 150 °C
for 40 h, followed by cooling to room temperature at 10 °C/h. The
solid products were recovered by vacuum filtration and washed
with N,N-dimethylformamide (DMF). Pale yellowish plate-like
crystals of 2, together with unidentified light brown polyhedral
crystals, were found. The product 2 was slightly unstable in water
and in air. The yield of 2 was ꢁ30 % based on lead. The product was
insoluble in common polar solvents.
Thermogravimetric analyses (TGA) were carried out in N2 at a
heating rate of 5 °C/min, using a high-resolution Perkin–Elmer
TGA7 Thermal Analyzer. Temperature controlled powder X-ray dif-
fraction analyses were performed using a PANalytical X’Pert PRO
Table 2
Selected bond lengths (Å) and angles (°) for 1 and 2.
EDS analysis for both complexes confirmed the presence of Pb
and Cl. The element analyses gave the following results: Anal. Calc.
for 1: Pb, 52.0; C, 12.1; H, 4.0; N, 14.1. Found: Pb, 52.2; C, 12.8; H,
1
Pb(1)–N(1)
Pb(1)–Cl(1)
2.447(3)
3.111(1)
Pb(1)–N(2)
2.602(3)
N(1)–C(1)
C(1)–C(1)#2
1.451(4)
1.522(7)
N(2)–C(2)
C(2)–C(2)#1
1.467(4)
1.501(6)
Table 1
Crystallographic details for 1 and 2.
1
2
N(1)–Pb(1)–N(1)#1
N(1)#1–Pb(1)–N(2)#1
N(1)–Pb(1)–Cl(1)#1
N(1)–Pb(1)–Cl(1)
70.19(12)
83.41(9)
140.06(6)
71.17(7)
148.53(4)
N(1)–Pb(1)–N(2)#1
N(2)#1–Pb(1)–N(2)
N(2)–Pb(1)–Cl(1)#1
N(2)–Pb(1)–Cl(1)
80.31(9)
160.08(13)
99.74(7)
85.68(7)
Empirical formula
Pb
396.3
monoclinic
C2/c
12.668(3)
7.4084(15)
13.068(3)
118.50(3)
1077.7(4)
4
1
C
4
H
16Cl
N
2 4
1 2 8 2 2
Pb C H Cl N
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
338.2
monoclinic
P2 /c
10.367(2)
9.2247(18)
7.3657(15)
97.80(3)
697.9(2)
4
Cl(1)#1–Pb(1)–Cl(1)
1
N(1)–C(1)–C(1)#2
110.1(2)
N(2)–C(2)–C(2)#1
Pb(1)–N(2)
110.8(3)
2
b (°)3
Pb(1)–N(1)
Pb(1)–Cl(2)
Pb(1)–Cl(1)
Pb(1)–Cl(2)#3
2.454(3)
2.473(3)
V (Å )
2.7605(10) Pb(1)–Cl(2)#1
3.1285(14) Pb(1)–Cl(2)#2
3.5633(11) Pb(1)–Cl(1)#4
3.1126(11)
3.1820(10)
3.5720(13)
Z
T (K)
290(1)
290(1)
k (Å)
0.71073
2.455
161.05
736
0.71073
3.219
248.31
600
q
l
calcd (g cmꢀ3)
N(1)–C(1)#1
C(1)–N(1)#2
C(2)–C(1)#1
1.454(5)
1.454(5)
1.514(6)
N(2)–C(2)
C(1)–C(2)#2
1.462(5)
1.514(6)
ꢀ
1
(cm
)
F(0 0 0)
3
Crystal size (mm ) 0.28 ꢂ 0.26 ꢂ 0.13
0.42 ꢂ 0.13 ꢂ 0.04
h Range (°)
3.30–27.47
3.56–27.48
N(1)–Pb(1)–N(2)
69.55(10)
77.84(8)
130.89(8)
91.86(8)
143.95(3)
142.50(7)
N(1)–Pb(1)–Cl(2)
91.50(8)
69.01(8)
78.09(3)
69.86(8)
135.95(3)
72.97(7)
Index ranges
ꢀ15 6 h 6 16, ꢀ9 6 k 6 9,
ꢀ13 6 h 6 13,
ꢀ11 6 k 6 10, ꢀ9 6 l 6 9
6701
N(2)–Pb(1)–Cl(2)
N(2)–Pb(1)–Cl(2)#1
N(1)–Pb(1)–Cl(1)
Cl(2)–Pb(1)–Cl(1)
N(1)–Pb(1)–Cl(2)#2
Cl(2)–Pb(1)–Cl(2)#2
Cl(1)–Pb(1)–Cl(2)#2
N(2)–Pb(1)–Cl(2)#3
Cl(2)#1–Pb(1)–Cl(2)#3 69.259(17) Cl(1)–Pb(1)–Cl(2)#3
Cl(2)#2–Pb(1)–Cl(2)#3 113.60(2)
N(2)–Pb(1)–Cl(1)#4 144.36(7)
Cl(2)#1–Pb(1)–Cl(1)#4 73.38(3)
Cl(2)#2–Pb(1)–Cl(1)#4 73.57(3)
N(1)–Pb(1)–Cl(2)#1
Cl(2)–Pb(1)–Cl(2)#1
N(2)–Pb(1)–Cl(1)
Cl(2)#1–Pb(1)–Cl(1)
N(2)–Pb(1)–Cl(2)#2
ꢀ
16 6 l 6 16
Reflections
collected
Independent
reflections
Data/parameters
Goodness-of-fit
4979
1251 [Rint = 0.0487]
1601 [Rint = 0.0216]
79.454(17) Cl(2)#1–Pb(1)–Cl(2)#2 141.456(16)
76.22(3)
140.70(7)
1251/52
1.073
1601/64
1.125
N(1)–Pb(1)–Cl(2)#3
Cl(2)–Pb(1)–Cl(2)#3
96.44(7)
140.737(17)
74.31(3)
142.20(7)
84.33(3)
113.19(3)
2
(
GOF) on F
a
R
1
[I > 2
wR (all data)
Extinction
coefficient
r
(I)]
0.0175
0.0374
0.0163(4)
0.0169
0.0363
n/a
N(1)–Pb(1)–Cl(1)#4
Cl(2)–Pb(1)–Cl(1)#4
Cl(1)–Pb(1)–Cl(1)#4
b,c
2
Cl(2)#3–Pb(1)–Cl(1)#4 66.16(2)
(D
q
)
max:(
D
q)
min
ꢀ1.19:1.01
ꢀ1.29:0.43
ꢀ
3
(
e Å
)
N(1)#2–C(1)–C(2)#2
108.9(3)
N(2)–C(2)–C(1)#1 109.7(3)
P
P
a
R = ||F
o
| ꢀ |F
c
|/ |F
o
|.
Symmetry transformations used to generate equivalent atoms for 1: #1 ꢀx, y,
ꢀz + 1/2; #2 ꢀx, ꢀy + 1, ꢀz.
P
P
b
2
1=2
1=2
w ¼ 1=½r2ðF Þ þ ð0:0000PÞ þ 0:00Pꢃ;
2
2
wR
2
¼ ½ wðjF
P
o
j ꢀ jF
c
jÞ = wjF
o
o
j2ꢃ
j2ꢃ
;
;
o
2
o
2
P ¼ ½MaxðF ; 0Þ þ 2F ꢃ=3.
Symmetry transformations used to generate equivalent atoms for 2: #1 ꢀx + 2,
ꢀy + 1, ꢀz + 1; #2 x, ꢀy + 1/2, z ꢀ 1/2; #3 ꢀx + 2, y + 1/2, ꢀz + 1/2; #4 ꢀx + 2, ꢀy + 1,
ꢀz.
c
P
c
2
w ¼ 1=½r2ðF Þ þ ð0:0134PÞ þ 0:83Pꢃ;
2
o
2
wR
2
¼ ½ wðjF
o
j ꢀ jF
c
jÞ = wjF
2
o
2
P ¼ ½MaxðF ; 0Þ þ 2F ꢃ=3.
c

Y. Cho et al. / Polyhedron 29 (2010) 2105–2110
2107
diffractometer (Cu K
a
radiation) on a platinum substrate. The 2h
distance of 3.111(1) Å complete a PbN
4
Cl
2
sphere with hemidirect-
range was 5–70° with a step size of 0.01° and accumulation time
of 0.2 s at a point. In the thermal in situ experiment, the sample
was heated in air stepwise at a rate of 5 °C/min at 25 °C ?
ed geometry, which is common in Pb(II) complexes with C.N. = 6
containing Pb–N, Pb–O and Pb–S bonds [24–31]. Of two crystallo-
graphically unique en ligands, one presents as a chelating ligand
and the other performs as a bridging ligand, which allow the lead
1
40 °C ? 150 °C ? 160 °C ? 400 °C and further cooling of the
sample to room temperature at a rate of 20 °C/min.
2 2
atoms to be linked in an infinite neutral zigzag chain, Pb(en) Cl
along the c-direction (Fig. 2).
3
. Results and discussion
For 1, it is noteworthy that the Pb–N distance (2.447(3) Å) to the
chelating ligand is shorter than the Pb–N distance (2.602(3) Å) for
the bridging ligands. This demonstrates the greater binding energy
of chelation compared to that of bridging. A similar trend can be
3.1. Structures
The structure of 1 is built up of infinite neutral Pb(en)
Fig. 1). One crystallographically independent lead atom is coordi-
nated by four nitrogen atoms from three en ligands to form a
slightly distorted seesaw geometry, with Pb–N bond lengths in
the range 2.447(3)–2.602(3) Å. Two additional Pb–Cl bonds at a
2
Cl
2
chains
observed in several other complexes. Examples include rac-
l
-
-
(
en[cis-CoCl(en)
en[cis-CoCl(en)
2
]
]
2
(ZnCl
(ZnCl
4
)
)
2
2 2
and [Pb(en) ]Br [21,19]. In rac-
l
2
2
4
2
, the two Co–N bond lengths to the
bridging en are 2.006(5) and 1.998(4) Å, while bond distances to
the chelating en are in the range 1.951(4)–1.970(4) Å. Interestingly,
b
c
a
C2 C2a
N1
N1a
N2a
N2
C1
Pb
Cl
Cla
C1a
N2b
2 2
Fig. 1. View parallel to [1 0 1] of 1 showing the infinite chain of Pb(en) Cl (thermal ellipsoids 50%). The H atoms are omitted for clarity.
a
c
Fig. 2. View along the b-axis showing the interchain packing of 1. The H atoms are omitted for clarity. The black, empty, cross-hatched, and light gray circles represent the
lead, chlorine, nitrogen and carbon atoms, respectively.

2
108
Y. Cho et al. / Polyhedron 29 (2010) 2105–2110
in rac-
l
-en[cis-CoCl(en)
2
] (ZnCl
2
4
2
) , the N–C–C angles (114.2(5)°,
due to the direct interactions of a lp between Pb(II) and C atoms in
1
17.0(5)°) of the bridging en are considerably wider than the non-
the crotonate anions, i.e., the formation of Pb(II)–lp–C bonds with
long Pb–C distances of ꢁ3.6 Å [25]. The shortest Pb–O distance of
2.35 Å is found in trans to the lone pair (axial), while the other five
Pb–O distances are about 2.5–2.6 Å in the equatorial directions.
There are two crystallographically independent chlorine atoms,
Cl1 and Cl2, acting as two- and four-donor bridging ligands in 2,
bridging en (109.8(2)°, 111.2(2)°). However, such a stretching is
not observed in the bridging en (110.8(3)°) of 1. In the isostructural
[
2 2
Pb(en) ]Br , the Pb–N distance (2.457(5) Å) to the chelating ligand
is also shorter than the Pb–N distance (2.624(6) Å) to a bridging
ligand, and a comparison of cell parameters with 1 shows the
expected trend that replacing the Cl by the larger Br is reflected in
increased lattice parameters and cell volume (for [Pb(en)
a = 13.076 Å, b = 7.586 Å, c = 13.248 Å, b = 117.88°, V = 1162 Å ).
Another important structural feature of complex 1 is the
arrangement of en between the lead atoms. The bridging en shows
an anti-conformation (crystallographic twofold symmetry, N–C–C–
N torsional angle = 180.0°), a phenomenon that is commonly found
in bridging en ligands. The conformations about Pb–en, however,
are gauche (Pb–N–C–C torsional angle = 76.94(1)°), which results
in an unusual gauche–anti–gauche arrangement with a Pb–Pb dis-
tance of 6.996(1) Å.
respectively (Fig. 3). The
centers forming dimeric building units. The l
l
2
-Cl1 atom bridges neighboring Pb(II)
-Cl2 atom connects
2
3
2
]Br ,
4
four lead atoms in a distorted square planar geometry to extend
these units into 2D corrugated layers on a bc-plane. The interlayer
packing of 2 is shown in Fig. 4. The structure is stabilized by van
der Waals interactions of the en molecules between the neutral
2
Pb(en)Cl layers. The interlayer distance is >3.87 Å.
In the IR spectra of 1 and 2, vibration modes are observed for
the C–H, N–H and C–N stretching and bending vibrations at
3260, 3223, 3142, 2927, 2931, 2868, 1598, 1576, 1458, 1148,
ꢀ
1
1113, 1061, 1021 and 1001 cm for 1; 3320, 3237, 3206, 3123,
The structure of 2 contains a PbN
2
Cl
4
sphere with a coordina-
2959, 2922, 2867, 1584, 1448, 1314, 1223, 1058, 1023 and
ꢀ
ꢀ
1
1
tion number of six. One crystallographically distinct Pb atom is
chelated by one en ligand (2.454(3) and 2.473(3) Å), and is coordi-
nated by four chlorine atoms (2.760(1), 3.113(1), 3.128(1) and
986 cm
for 2. The additional absorption bands at 669, 562,
ꢀ1
541 cm for 1 and at 652 and 502 cm for 2 are due to the C–H
and N–H rocking vibrations. These values are in good agreement
with those reported previously [34].
3
(
.182(1) Å) (Fig. 3). Interestingly, two additional weak bonds
3.563(1) and 3.572(1) Å) are observed, which is very rare, and
no structures with Pb–Cl distances >3.5 Å were found in the CSD
Cambridge Structural Database, 2009). These weak Pb–Cl bonds
cannot be considered as a regular Pb–Cl bond, taking into account
3.2. Thermal transformations
(
2
Thermogravimetric analysis of 1 shows that upon heating in N ,
the evolution of en occurs in several steps at temperatures ranging
2
+
ꢀ
the ionic radii (Pb , 0.98 Å for C.N. = 4; Cl , 1.81 Å, and mean Pb–Cl
distance for holodirected Pb(II) complexes in the CSD is 2.62(11) Å)
from ꢁ80 to 320 °C (Fig. 5). Assuming that the residue at 400 °C
[
13,32]; however, they are within the range of van der Waals inter-
actions (van der Waals radii, Pb, 2.0 Å; Cl, 1.7–1.9 Å) [33]. Thus,
considering the weak Pb–Cl bonds (<3.6 Å) the coordination sphere
2
corresponds to PbCl , the overall observed weight loss (31.1%) is
in good agreement with that calculated for the composition of
PbCl (30.3%). The final product after heat treatment shows an
excellent agreement with the powder-XRD pattern of PbCl
The thermogravimetric analysis of 2 upon heating in N remains
2
2 6
of Pb is PbN Cl with C.N. = 8. The lone pair of Pb becomes ‘‘less
2
.
active” when involved in two unusually weak Pb–Cl bonds, i.e., a
smaller void size in Pb(II). The two extraordinary weak bonds are
most probably due to the direct interactions of the lone pair of
electrons between Pb and Cl, Pb–lp–Cl bonds (3.563(1) and
.572(1) Å), which is much longer than the mean Pb–Cl distance,
.62(11) Å for holodirected Pb(II) complexes in the CSD [13].
Therefore, due to the two weak Pb–Cl interactions, the coordina-
tion sphere of Pb(II) could be best described as ‘‘pseudo-hemidirect-
ed” (i.e., transition between hemidirected and holodirected). The
shortest Pb–N distance of 2.454(3) Å is found in trans to the very
2
stable up to ꢁ150 °C. On further heating, a weight loss of 18.1% oc-
b
3
2
a
long Pb–Cl bonds.
0
A similar example is found in catena-[(
l
-crotonato-O,O )(croto-
0
nato-O,O )lead(II)] which contains six Pb–O bonds and unusually
long Pb(II)ꢄꢄꢄC (carbon atoms in crotonate anions) bonds, probably
Cl1b
C2
C1
N1
Cl2a
N2
Pb1h
Pb1g
Pb1b
Cl2
Cl2b
Pb1
Cl1a
Pb1c
Cl2c
Pb1f
Cl1
Pb1d
Pb1e
Fig. 3. Connectivities of Pb, Cl and en in 2 are represented by 50% thermal
ellipsoids. The H atoms are omitted for clarity. The dashed lines indicate weak
bonds.
Fig. 4. View along the c-axis showing the interlayer packing of 2. The H atoms are
omitted for clarity. The labeling scheme is the same as that in Figs. 2 and 3.

Y. Cho et al. / Polyhedron 29 (2010) 2105–2110
2109
2
, but at ꢁ80 °C for 1. For 1, at ꢁ150 °C, the temperature at which
decomposition begins for 2, a distinct weight change occurs. The
weight loss of 1 at this temperature, ꢁ150 °C, is in good agreement
with that calculated for one en (15.2%). The evolution of the
remaining en from the structure 1 ends at ꢁ320 °C. The TG curves
of 1 and 2 corresponding to the loss of one en in the temperature
range 150–320 °C are very similar to each other. This may imply
100
9
8
7
0
0
0
st
loss of 1 en: 15.2%
that the thermal evolution of one en in Pb(en)
2 2
Cl , 1 results in
Pb(en)Cl , 1
2
the transformation to Pb(en)Cl
2
, 2 at ꢁ150 °C.
Indeed, the high-temperature controlled powder-XRD con-
firmed the proposed thermal decomposition path obtained from
TGA results (Fig. 6). A sample of 1 was heated up to 400 °C on a
Pt stage. At 140 °C, compound 1 nearly decomposes to 2, and a
small amount of 1 remains as shown by the weak diffraction at
nd
Pb(en) Cl , 2
loss of 2 en: 15.2%
2
2
1
4.5°. The transformation to 2 completes at 150 °C, as shown by
an excellent agreement with the simulated powder pattern of 2.
At 160 °C, the diffractions of Pb(en)Cl were considerably de-
100
200
300
400
2
Temperature (deg.)
creased, and several strong reflections at 39.6, 46.1 and 67.3° from
the Pt stage suddenly appeared. This may due to the significant
Fig. 5. TG curves for 1 and 2.
curs in the range 150–320 °C, which is attributed to the evolution
of en molecules (Fig. 5). Assuming that the residue at 400 °C corre-
(a)
C2
C2a
N1a
N2a
sponds to PbCl
agreement with that calculated for the composition of PbCl
17.8%). The final product after heat treatment showed excellent
agreement with the powder-XRD pattern of PbCl
2
, the overall observed weight loss (18.1%) is in good
2
(
N1
N2
2
.
Comparing the TG curves shows important thermal relation-
ships between 1 and 2. The evolution of en starts at ꢁ150 °C for
Pb
(
a)
Cl
Cla
C1
(b)
C2
N2
(
b)
N1
Cl2a
Cl1
(c)
Cl2b
Pb1
Cl2
(
(
d)
e)
Cl2c
Cl1a
(c)
(f)
10
20
30
40
50
60
70
2
theta
2
Fig. 7. Coordination environments of Pb(II) in 1 (a), 2 (b), and PbCl (c), showing
Fig. 6. Simulated powder patterns of 1 (a) and 2 (f). In situ temperature dependent
powder X-ray diffraction patterns of 1 at 25 °C (b), 140 °C (c), 150 °C (d), 160 °C (e).
hemidirected, pseudo-hemidirected, and holodirected spheres, respectively. The
dashed lines indicate weak bonds.

2
110
Y. Cho et al. / Polyhedron 29 (2010) 2105–2110
reduction in volume of the sample by the evolution of en in
Pb(en)Cl . The volume reduction of the asymmetric units by re-
2
moval of each en are D(2-PbCl ) =
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.cam.ac.uk.
2
3
D
V(1–2) = 94.94 Å , ꢀ35% and
3
9
6.3 Å , ꢀ55%.
TG analysis confirms that the chelating en is thermally more
stable and more strongly bonded than the bridging en, as indicated
by the shorter Pb–N distance of the chelating en than the bridging
en. The overall thermal decomposition reactions of 1 are summa-
rized below:
Acknowledgements
This work was supported by the Konkuk University. H. Yun and
S.J. Kim were partially supported by the Korean Research Founda-
tion Grant funded by the Korean Government (MOEHRD) (KRF-
2007-412-J04001).
-
en
-en
1
D-PbðenÞ Cl
2
; 1 ꢀ! 2D-PbðenÞ Cl
2
; 2 ꢀ! 3D-PbCl
2
2
2
hemidirected
ðpseudo-Þhemidirected
holodirected
The structure of 1 can be transformed through two main steps
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[
CCDC 679745 and 679746 contain the supplementary crystallo-
graphicdata for1 and 2, respectively. These data canbe obtained free