Influence of neutral amine ligands on the network assembly of lead(II) 4-sulfobenzoate complexes

Article abstract of DOI:10.1016/j.molstruc.2007.03.006

Two new lead(II) 4-sulfobenzoate complexes with amine ligands, [Pb(4-sb)(2,2′-bipy)]_n (1) and {[Pb(4-sb)(4,4′-bipy)_1/2] · (4,4′-bipy)_1/2}_n (2) (2,2′-bipy = 2,2′-bipyridine; 4,4′-bipy = 4,4′-bipyridine; 4-sb = 4-sulfobenzoate dianion), were synthesized and characterized by single-crystal X-ray analyses, IR, TG, elemental analyses and fluorescent studies. Complexes 1 and 2, in addition to previously reported [Pb(4-sb)(H₂O)₂]_n (3) and {[Pb(4-sb)(phen)] · (H₂O)}_n (4) where phen is 1,10-phenanthroline, all contain [Pb(4-sb)] building units, while four [Pb(4-sb)] networks in 1-4 are very different, which is significantly influenced by the neutral ligands. The coordination array of complex 1 is a 2-D network in which each 4-sb acts as a η₅-μ₃ mode while the complex 2 is a 3-D architecture in which each 4-sb performs a η₅-μ₆ mode. Both coordination modes of 4-sb ligands in 1-2 are novel and first reported in this paper.

Full text of DOI:10.1016/j.molstruc.2007.03.006

Available online at www.sciencedirect.com
Journal of Molecular Structure 873 (2008) 61–68
www.elsevier.com/locate/molstruc
Influence of neutral amine ligands on the network assembly
of lead(II) 4-sulfobenzoate complexes
*
Li-Ping Zhang, Long-Guan Zhu
Department of Chemistry, Zhejiang University, Hangzhou 310027, People’s Republic of China
Received 29 January 2007; received in revised form 28 February 2007; accepted 3 March 2007
Available online 12 March 2007
Abstract
Two new lead(II) 4-sulfobenzoate complexes with amine ligands, [Pb(4-sb)(2,20-bipy)]n (1) and {[Pb(4-sb)(4,40-bipy)1/2]Æ(4,40-bipy)1/2
}
n
(2) (2,20-bipy = 2,20-bipyridine; 4,40-bipy = 4,40-bipyridine; 4-sb = 4-sulfobenzoate dianion), were synthesized and characterized by sin-
gle-crystal X-ray analyses, IR, TG, elemental analyses and fluorescent studies. Complexes 1 and 2, in addition to previously reported
[Pb(4-sb)(H2O)2]n (3) and {[Pb(4-sb)(phen)]Æ(H2O)}n (4) where phen is 1,10-phenanthroline, all contain [Pb(4-sb)] building units, while
four [Pb(4-sb)] networks in 1–4 are very different, which is significantly influenced by the neutral ligands. The coordination array of
complex 1 is a 2-D network in which each 4-sb acts as a g5–l3 mode while the complex 2 is a 3-D architecture in which each 4-sb performs
a g5–l6 mode. Both coordination modes of 4-sb ligands in 1–2 are novel and first reported in this paper.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: 4-Sulfobenzoate; Lead(II); Coordination polymer; Network assembly
1. Introduction
4-sb coordination modes in all transition metal complexes
were observed in the Cambridge Structural Database
(CSD; May 2006 update) [20], as depicted in Scheme 1.
Interestingly, our previous exploration exhibited that the
PbII salts used in the synthetic chemistry instead of transi-
tion metals led to the {[Pb(4-sb)(phen)]Æ(H2O)}n and [Pb(4-
sb)(H2O)2]n complexes [21,22], in which the 4-sb ligands
perform interesting coordination modes, therefore, we rea-
soned that further exploration using different bridging or
chelating amine ligands to tune networks may induce more
diverse structures. Herein, we report the influence of neu-
tral ligands on the network assembly of lead(II) 4-sul-
fobenzoate complexes.
In recent decade, network or framework construction is
an interesting issue in the pursuing of functional materials
[1–3]. A large number of 1,4-benzenedicarboxylate (bdc)
coordination polymers with metal-organic frameworks
have been synthesized and these coordination polymers
can be potentially used in gas adsorption, chemical sensor,
and catalysis [4–14]. The bdc ditopic ligand has two poten-
tially equivalent coordinating carboxylate groups, thus the
variable topologies in assembled networks constructed by
this ligand are largely limited. The sulfonate group has a
very different coordination ability compared to the carbox-
ylate, therefore a ligand with the sulfonate and carboxylate,
4-sulfobenzoate (4-sb), has been chosen for constructing
novel diverse networks in our lab [15–17] and other
research groups [18,19]. Unexpectedly, only four of the
2. Experimental
2.1. Materials and instruments
All chemicals and solvents used in this work were com-
mercially obtained and were used as received without fur-
ther purification. Elemental analyses (C, H, and N) were
*
Corresponding author. Tel.: +86 571 87963867; fax: +86 571
87951895.
E-mail address: chezlg@zju.edu.cn (L.-G. Zhu).
0022-2860/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.03.006

62
L.-P. Zhang, L.-G. Zhu / Journal of Molecular Structure 873 (2008) 61–68
822(w), 797(m), 779(m), 729(m), 641(s), 622(m), 606(w),
569(m), 550(w), 466(m).
These two complexes are insoluble in water and com-
mon organic solvents, such as methanol, ethanol, acetone,
benzene, chloroform, THF, and N,N0-dimethylformamide.
M
O
S
M
O
S
M
O
S
O
O
O
O
O
O
-
SO3
2.2. X-ray structure determination
Data collection for complexes 1 and 2 were carried out
by a Brucker SMART diffractometer equipped with a
CCD area detector. The data were integrated by use of
the SAINT program, and the intensities were corrected
for Lorentz factor polarization and absorption [23]. The
two structures were solved by Patterson method and suc-
cessive Fourier syntheses. Full-matrix least squares refine-
ments on F2 were carried out using SHELXL-97 package
[24]. All hydrogen atoms were placed in calculated posi-
O
M
O
O
O
O
O
O
O
M
M
M
M
Scheme 1. Coordination modes of the 4-sb in all reported transition metal
complexes.
˚
tions and refined as riding, with CAH = 0.93 A and Uiso(-
H)=1.2Ueq(C). All the programs used are included in the
WinGX Suite with the version of 1.70 [25]. The highest
and lowest peaks in the final difference Fourier maps for
complexes 1 and 2 are near Pb atoms, indicating meaning-
less for real atoms. Detail crystal data and structure refine-
ments for 1–2 are listed in Table 1.
carried out on a ThermoFinnigan Flash EA1112. The IR
spectra were recorded on a Nicolet Nexus 470 spectropho-
tometer in the range 400–4000 cmꢀ1 in KBr pellets. Ther-
mogravimetric analyses (TGA) were performed by a
NETZSCH STA 409 in a N2 atmosphere with a heating
rate of 10 ꢁC minꢀ1 using Al2O3 crucibles. The fluorescence
study was carried out on a powder sample at room temper-
ature using a Hitachi 850 spectrometer.
3. Results and discussion
Single-crystal X-ray analysis revealed that the coordina-
tion array of complex 1 is a 2-D network, in which each
2.1.1. Synthesis of [Pb(4-sb)(2,20-bipy)]n (1)
A mixture of Pb(NO3)2 (0.173 g, 0.52 mmol), 4-sulfo-
benzoic acid monopotassium salt (0.114 g, 0.48 mmol),
2,20-bipyridine (0.098 g, 0.5 mmol) and H2O (15 ml) was
placed in a 30-mL stainless-steel reactor with Teflon liner
and heated at 150 ꢁC for 24 h. The vessel was then slowly
cooled to room temperature, and light yellow block crys-
tals of 1 were collected by filtration. Yield: 62% based on
the PbII salt. Anal. Calcd for C17H12N2O5SPb: C,
36.23%; H, 2.14%; N, 4.97%. Found: C, 36.41%; H,
2.25%; N, 4.86%. IR (KBr pellet, cmꢀ1): 1590(s), 1536(s),
1496(m), 1478(s), 1437(s), 1389(s), 1323(m), 1255(s),
1172(s), 1150(s), 1110(s), 1004(s), 854(s), 784(s), 768(s),
739(s), 700(m), 642(s), 558(s), 477(s), 417(m).
Table 1
Crystal data and details of structural determination of complexes 1 and 2
Complex
1
2
Formula
Mr
Crystal color, shape
Crystal size/mm
Space group
C
563.56
17H12PbN2O5S
C17H12PbN2O5S
563.56
Light yellow/block
0.08 · 0.15 · 0.15
Monoclinic, P21/c
9.6464(7)
16.4821(12)
10.6570(7)
90
91.307(1)
90
1694.0(2)
4
2.210
295
10.115
2.1–26.0
9320
3321
3033
1064
0.022, 0.054
0.025, 0.055
235
1.041
0.483, ꢀ1.710
Light yellow/prism
0.11 · 0.15 · 0.19
Monoclinic, P21/c
10.1711(10)
28.951(3)
5.6154(5)
90
97.619(2)
90
1638.9(3)
4
2.284
295
10.455
2.0–26.0
9187
3211
2984
1064
0.039, 0.074
0.043, 0.075
235
1.212
1.839, ꢀ1.739
˚
a/A
˚
b/A
˚
c/A
a/ꢁ
b/ꢁ
c/ꢁ
3
˚
V/A
2.1.2. Synthesis of {[Pb(4-sb)(4,40-bipy)1/2]Æ
Z
D/g cmꢀ3
(4,40-bipy)1/2}n (2)
T/K
l/mmꢀ1
h range/ꢁ
Measured reflections
Unique reflections
Observed reflections
F(000)
2
2
A mixture of Pb(NO3)2 (0.165 g, 0.5 mmol), 4-sulfoben-
zoic acid monopotassium salt (0.120 g, 0.5 mmol), 4,40-
bipyridine (0.098 g, 0.5 mmol) and H2O (15 ml) was added
in a 30-mL stainless-steel reactor with Teflon liner and
heated at 150 ꢁC for 22 h. After cooling naturally, light yel-
low prism crystals of 2 were collected by filtration. Yield:
47% based on the PbII salt. Anal. Calcd for
C17H12N2O5SPb: C, 36.23%; H, 2.14%; N, 4.97%. Found:
C, 36.17%; H, 2.12%; N, 4.98%. IR (KBr pellet, cmꢀ1):
1605(m), 1585(s), 1525(s), 1493(m), 1382(s), 1231(m),
1187(s), 1162(m), 1143(m), 1119(s), 1031(m), 1006(s),
R1 and wR2 (I > 2r(I))
R1 and wR2 (all data)
Number of variables
Goodness of fit (GOF)
Largest differenꢀce3 peak
˚
and hole/e A

L.-P. Zhang, L.-G. Zhu / Journal of Molecular Structure 873 (2008) 61–68
63
PbII center adopts a seven-coordinated geometry com-
Table 2
˚
pleted by two nitrogen donors from one 2,20-bipyridine,
two oxygen atoms from one carboxyl group, and three
oxygen atoms from two sulfonate groups, as shown in
Fig. 1. Each PbII atom is surrounded by three 4-sb ligands
(Table 2).
Selected bond lengths (A) and angles (ꢁ) for complex 1
Pb1AO1
2.409(3)
2.794(3)
2.943(3)
2.435(3)
52.19(9)
139.21(9)
82.84(9)
104.32(9)
130.94(9)
79.88(9)
124.49(9)
138.65(9)
116.08(9)
69.75(9)
66.79(10)
Pb1AO2
Pb1AO3ii
Pb1AN1
2.598(3)
2.969(3)
2.475(3)
Pb1AO3i
Pb1AO5ii
Pb1AN2
O1APb1AO2
O1APb1AO3ii
O1APb1AN1
O2APb1AO3i
O2APb1AO5ii
O2APb1AN2
O3iAPb1AO5ii
O3iAPb1AN2
O3iiAPb1AN1
O5iiAPb1AN1
N1APb1AN2
O1APb1AO3i
O1APb1AO5ii
O1APb1AN2
O2APb1AO3ii
O2APb1AN1
O3iAPb1AO3ii
O3iAPb1AN1
O3iiAPb1AO5ii
O3iiAPb1AN2
O5iiAPb1AN2
73.65(9)
141.87(8)
77.77(9)
91.54(8)
129.06(9)
141.69(9)
80.41(9)
47.56(8)
77.84(9)
67.43(9)
The complex 2, {[Pb(4-sb)(4,40-bipy)1/2]Æ(4,40-bipy)1/2}n,
displays a 3-D network, in which each PbII center is eight-
coordinated in a dicapped trigonal prism with a [PbNO7]
chromophore. The coordination geometry of the PbII atom
consists of one nitrogen atom from one 4,40-bipyridine,
three oxygen atoms from three carboxyl groups, and four
oxygen atoms from three sulfonate groups (Fig. 3). Each
PbII atom is totally surrounded by six 4-sb ligands (Table 3).
Recently, we have reported two PbII complexes contain-
ing 4-sb ligands under similar hydrothermal synthetic
conditions, {[Pb(4-sb)(H2O)2]}n (3) and {[Pb(4-sb)(phen)]Æ
H2O}n (4) [21,22]. In contrast to complexes 1 and 2 without
water moiety, complexes 3 and 4 contain two and one
water molecules, respectively. In these four complexes,
there are some similarities and differences in PbAN and
PbAO bond distances, coordination modes of 4-sb, and
assembly of molecular structures.
Symmetry codes, i: ꢀ1 + x, y, z; ii: ꢀ1 + x, 0.5 ꢀ y, 0.5 + z.
Table 3
˚
Selected bond lengths (A) and angles (ꢁ) for complex 2
Pb1AO1
2.548(5)
2.428(5)
2.804(5)
Pb1AO1i
2.863(5)
2.696(5)
2.875(5)
Pb1AO2ii
Pb1AO3iii
Pb1AO4iv
Pb1AO4v
Pb1AO5v
2.669(5)
Pb1AN1
2.623(6)
O1APb1AO1i
O1APb1AO3iii
O1APb1AO4v
O1APb1AN1i
O1iAPb1AO3iii
O1iAPb1AO4v
O1iAPb1AN1
O2iiAPb1AO4iv
O2iiAPb1AO5v
O3iiiAPb1AO4iv
O3iiiAPb1AO5v
O4ivAPb1AO4v
O4ivAPb1AN1
O4vAPb1AN1
74.73(13)
88.19(16)
147.92(16)
81.47(19)
141.38(16)
79.39(14)
130.33(17)
133.86(17)
82.50(17)
74.39(16)
77.69(16)
67.11(12)
150.88(18)
130.34(18)
O1APb1AO2ii
O1APb1AO4iv
O1APb1AO5v
O1iAPb1AO2ii
O1iAPb1AO4iv
O1iAPb1AO5v
O2iiAPb1AO3iii
O2iiAPb1AO4v
O2iiAPb1AN1
O3iiiAPb1AO4v
O3iiiAPb1AN1
O4ivAPb1AO5v
O4vAPb1AO5v
O5vAPb1AN1
103.61(18)
86.30(16)
159.60(16)
69.40(17)
70.23(15)
125.24(15)
149.18(18)
84.29(17)
74.97(19)
100.81(15)
78.88(18)
103.64(15)
51.05(15)
81.41(18)
˚
The PbAN bond distance in 2 is 2.623(6) A, which is
slightly longer than those in 1, but all are in the normal
range and are corresponding to those in PbII-complexes
containing N-donor ligands, such as [Pb2(2-sb)2(phen)2]Æ
2H2O [26], {[Pb(4-sb)(phen)]ÆH2O}n, [Pb(3-sb)(phen)(-
H2O)]n [27], [Pb(3-sb)(2,20-bipy)(H2O)]n [28] and a series
of lead(II) 5-sulfosalicylate complexes [29]. The
PbAO(COOꢀ) bond distances in 1 and 2 except the
Pb1AO1i in 2 are similar, and also are corresponding to
those in 3, but slightly different from those in 4, which is
mainly attributed to the different coordination modes of
the carboxylate groups. Bond distances of PbAO(SOꢀ3 ) in
3 and 4 are similar, but are somewhat different from those
Symmetry codes, i: x, 0.5 ꢀ y, 0.5 + z; ii: x, y, ꢀ1 + z; iii: 1 + x, y, z; iv:
1 + x, 0.5 ꢀ y, 0.5 + z; v: 1 + x, y, 1 + z.
Fig. 1. An ORTEP view of complex 1 showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. (Symmetry
codes, i: ꢀ1 + x, y, z; ii: ꢀ1 + x, 0.5 ꢀ y, 0.5 + z).

64
L.-P. Zhang, L.-G. Zhu / Journal of Molecular Structure 873 (2008) 61–68
Fig. 2. A view of 2-D network constructed by [Pb(4-sb)] units in complex 1.
Fig. 3. An ORTEP view of complex 2 showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. (Symmetry
codes, i: x, 0.5 ꢀ y, 0.5 + z; ii: x, y, ꢀ1 + z; iii: 1 + x, y, z; iv: 1 + x, 0.5 ꢀ y, 0.5 + z; v: 1 + x, y, 1 + z; vi: ꢀx, ꢀy, ꢀz; vii: 1 ꢀ x, ꢀy, ꢀz ).
in 1 and 2, which is also caused by the different coordina-
tion modes of the sulfonate groups.
lead(II) complexes, which can potentially extend structures
into high-dimensional assembly. The coordination mode of
the 4-sb in 1 is g5–l3 with the chelating carboxyl and che-
lating-bridging sulfonate, and g7–l6 in 2, g4–l3 in 3, and
g5–l4 in 4. Therefore, three 2-D networks in 1, 2 and 4
have different networks and these diverse networks are sig-
nificantly influenced by the neutral ligands. It is obvious
that the coordination of 2,20-bipyridine, 1,10-phenanthro-
line or aqua ligands lead to the modification of basic
metal-4-sb networks, which substantially depend upon
These four complexes all contain [Pb(4-sb)] units, but
the coordination modes of 4-sb ligands are different as
shown in Scheme 2, resulting in four different networks.
The networks constructed by [Pb(4-sb)] units in complexes
1, 2, and 4 are 2-D (Figs. 2, 4, and 5), but 1-D for complex
3 (Fig. 6). Unlike the monodentate mode or uncoordina-
tion of the sulfonate group of the 4-sb in transition metal
complexes, it provides two or three coordination sites in

L.-P. Zhang, L.-G. Zhu / Journal of Molecular Structure 873 (2008) 61–68
65
Pb
Pb
Pb
Pb
Pb
Pb
O
O
S
Pb
O
S
O
S
O
S
Pb
Pb
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Pb
Pb
Pb
Pb
Pb
Pb
Pb
4
3
1
2
Scheme 2. Coordination modes of 4-sb ligands in complexes 1–4.
Fig. 5. A view of 2-D network constructed by [Pb(4-sb)]units in complex 4.
Fig. 6. A view of 1-D chain constructed by [Pb(4-sb)]units in complex 3.
The co-planarity in 1 is higher than that in 2, but the
twisted angle between two rings of the 2,20-bipyridine
[6.8(2)ꢁ] is larger than that of the 4,40-bipyridine in 2, in
the latter two pyridine rings are nearly co-planar.
Different networks in 1–4 lead to different Pb. . .Pb dis-
tances separated by 4-sb. The shortest distances between
two PbII atoms bridged by the 4-sb in 1 are 9.6464(7) A,
˚
˚
˚
˚
10.1711(10) A in 2, 10.6687(8) A in 3, and 9.8647(5) A in
4, respectively, clearly indicating the shortest separation
distances of Pb. . .Pb by 4-sb in 1 and 4 are shorter than
those in 2 and 3 without neutral chelating ligands. More-
over, the shortest distances of Pb. . .Pb by sulfonates are
˚
˚
˚
5.4399(3) A in 1, 4.1552(5) A in 2, 5.1220(4) A in 3, and
7.1706(4) A in 4. The large distance of Pb. . .Pb in 4 is
Fig. 4. A view of 2-D network constructed by [Pb(4-sb)]units in complex 2.
˚
caused by the anti-bridging coordination mode of the sul-
fonate. The short distance of Pb. . .Pb in 2 may indicate
the weak Pb. . .Pb interaction [30,31]. Complex 2 has the
second linker, 4,40-bipyridine, but this linker only serves
as dimeric bridge, consisting of a dimeric unit, [Pb2(4,40-
bipy)(4-sb)2], in which distance of two Pb atoms is
the topology of the donating sites and volume and shape of
the terminal ligands.
In these four complexes, the sulfonate groups act as
bridging ligands, whereas the carboxyl groups are only
associated with the bridging in complexes 2 and 4. Investi-
gating many complexes containing sulfonate groups, we
can conclude that the PbII atom is favorably coordinated
to sulfonate groups compared with the mono-coordination
or non-coordinating behaviors for transition metals in 4-
sulfobenzoate complexes.
The planarity of carboxylate groups with benzene rings
is largely different in 1–4. The dihedral angles between car-
boxyl and benzene ring are 4.6(5)ꢁ in 1, 7.6(5)ꢁ in 2,
19.6(5)ꢁ in 3, and 10.2(9)ꢁ in 4. The largest dihedral angle
occurs in complex 3, indicating the non-planarity in 3.
0
0
˚
12.3400(11) A and similar to that in [Pb2(2,2 -bipy)2(4,4 -
˚
bipy)(NO3)4] [12.3526(5) A] [32]. The [Pb(4-sb)] 2-D layers
in 2 are further extended by dimeric linker of 4,40-bipyri-
dine into 3-D dimensional architecture without any inter-
penetration, and the free 4,40-bipyridine molecules occupy
the channel of the 3-D network (Fig. 7).
Compared to several 2-sb or 3-sb lead(II) complexes
reported very recently, the 4-sb complexes have some
advantages in the network assembly. Each network of
two PbII/3-sb complexes, [Pb(3-sb)(phen)(H2O)]n and

66
L.-P. Zhang, L.-G. Zhu / Journal of Molecular Structure 873 (2008) 61–68
Fig. 7. A view of 3-D network of complex 2. Uncoordinated 4,40-
bipyridine molecules occupy the channels.
[Pb(3-sb)(2,20-bipy)(H2O)]n, is 1-D, in which each 3-sb
ligand acts as a chelating-bridging mode, whereas the
molecular structure of the PbII/2-sb complex, [Pb(2-
sb)(phen)]2 Æ2H2O, is only a dimer. Therefore, 4-sb ligands
in lead(II) complexes exhibit abundant coordination modes
which are achieved by chelating or bridging neutral amine
ligands, resulting in high-dimensional structures.
Fig. 8. The fluorescence spectrum of complex 1 in solid state at room
temperature.
It is also interesting note that in complex 1 p–p stacking
interactions exist only between 2,20-bipyridine rings, with
˚
the centroid-to-centroid distance of 3.759(2) A. But in com-
plex 2 p–p interactions exist not only between coordinated
4,40-bipyridine and free 4,40-bipyridine ligands, but also
between coordinated 4,40-bipyridine and 4-sb, and between
free 4,40-bipyridine ligand and 4-sb.
4. Characterizations
4.1. IR spectra
In the IR spectra of complexes 1 and 2 there is no any
absorption near 1700 cmꢀ1, indicating the absence of the
proton on the carboxylate group. The mas(COOꢀ) and
ms(COOꢀ) are at 1590 and 1389 cmꢀ1 in 1 and at 1585
and 1382 cmꢀ1 in 2, respectively, indicating the carboxy-
lates are associated with coordination. Bands in the range
3200–2900 cmꢀ1 for complexes 1 and 2 correspond to the
stretching vibrations of CAH group occurring in pyri-
dine-type complexes. Several characteristic peaks of 4,40-
bipyridine or 2,20-bipyridine are overlapping with some
peaks of carboxylate or sulfonate, such as peak at 1590
cmꢀ1 with shoulder can be verified as the absorptions of
mas(COOꢀ) and mC@N, and in the range 1000–1200 cmꢀ1
sulfonate and inplane deformations and ring-breathing
modes of pyridine occur, but the mC@C peaks at
1537 cmꢀ1 in 1 and at 1525 cmꢀ1 in 2 can be clearly recog-
nized [33]. The peak 622 cmꢀ1 in 2 may be attributable to
the existence of non-coordinated 4,40-bipyridine molecule
[34].
Fig. 9. The fluorescence spectrum of complex 2 in solid state at room
temperature.

L.-P. Zhang, L.-G. Zhu / Journal of Molecular Structure 873 (2008) 61–68
67
4.2. TGA analysis
can be found, in the online version, at doi:10.1016/
j.molstruc.2007.03.006.
The thermogravimetric analyses (TGA) have been per-
formed on complexes 1–2 by heating each complex to
800 ꢁC. TGA for 1 showed the loss of one 2,20-bipyridine
in the range 200–326 ꢁC (calculated 27.7%, observed
28.2%), and further weight loss began at 450 ꢁC. TGA
for 2 showed that 4,40-bipyridine was partly lost in the tem-
perature range 140–180 ꢁC, then followed by the further
loss of 4,40-bipyridine ligand in the range 220–340 ꢁC.
The sum of weight loss in the range 140–180 ꢁC is 20.9%,
corresponding to the removal of 0.75 4,40-bipyridine mole-
cule (calculated 20.8%). Then complex 2 further lost mass
in the temperature range 480–560 ꢁC (observed 16.3%).
Totally, the weight loss in the range 140–560 ꢁC is 45.6%
and the residue is 54.4%, which corresponds to the residue
of PbSO4 (calculated 53.8%), indicating the TGA process
in complex 2 is more complicated.
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