Two new layered lead(II) diphosphonates with 1,3,5-benzenetricarboxylate ligands as an intercalated species or a multidentate metal linker

Article abstract of DOI:10.1016/j.molstruc.2005.03.008

Hydrothermal reactions of lead(II) carbonate with 1,3,5- benzenetricarboxylic acid (H₃BTC) and butylimino- bis(methylenephosphonic acid) (CH₃CH₂CH₂CH ₂N(CH₂PO₃H₂)₂, H ₄L¹) or lead(II) acetate with H₃BTC and isobutylimino-bis(methylenephosphonic acid) (Me₂CHCH ₂N(CH₂PO₃H₂)₂, H ₄L²) afforded two novel lead(II) carboxylate phosphonate hybrids, namely, Pb₅(HL¹)₂(L ¹)·H₃BTC 1 and Pb₄(BTC)(L ²)(CH₃CO₂)(H₂O)₂· 1.5H₂O 2. The structure of compound 1 contains a 〈002〉 lead(II) diphosphonate hybrid layer formed by Pb(II) ions interconnected by HL¹ and L¹ anions. In compound 2, the interconnection of Pb(II) ions through bridging diphosphonate L² anions lead to the formation of the 〈200〉 lead(II) diphosphonate 2D layer. In compound 1, the 1,3,5-benzenetricarboxylic acid acts as an intercalated species whereas in compound 2, the 1,3,5-benzenetricarboxylate anion adopts a hexadentate chelating and bridging coordination mode.

Full text of DOI:10.1016/j.molstruc.2005.03.008

Journal of Molecular Structure 748 (2005) 63–70
www.elsevier.com/locate/molstruc
Two new layered lead(II) diphosphonates
with 1,3,5-benzenetricarboxylate ligands as an intercalated
species or a multidentate metal linker
*
Shao-Ming Ying, Jiang-Gao Mao
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter,
Chinese Academy of Sciences, Fuzhou 350002, P.R. China
Received 16 February 2005; revised 2 March 2005; accepted 4 March 2005
Available online 26 April 2005
Abstract
Hydrothermal reactions of lead(II) carbonate with 1,3,5-benzenetricarboxylic acid (H3BTC) and butylimino-bis(methylenephosphonic
acid) (CH3CH2CH2CH2N(CH2PO3H2)2, H4L1) or lead(II) acetate with H3BTC and isobutylimino-bis(methylenephosphonic acid)
(Me2CHCH2N(CH2PO3H2)2, H4L2) afforded two novel lead(II) carboxylate phosphonate hybrids, namely, Pb5(HL1)2(L1)$H3BTC 1 and
Pb4(BTC)(L2)(CH3CO2)(H2O)2$1.5H2O 2. The structure of compound 1 contains a !002O lead(II) diphosphonate hybrid layer formed by
Pb(II) ions interconnected by HL1 and L1 anions. In compound 2, the interconnection of Pb(II) ions through bridging diphosphonate L2
anions lead to the formation of the !200O lead(II) diphosphonate 2D layer. In compound 1, the 1,3,5-benzenetricarboxylic acid acts as an
intercalated species whereas in compound 2, the 1,3,5-benzenetricarboxylate anion adopts a hexadentate chelating and bridging coordination
mode.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Hydrothermal synthesis; Layered compounds; Intercalation; Crystal structure
1. Introduction
phosphonic acids have been synthesized by using phosphoric
acid as the spacer [19,20]. Direct use of two types of ligands in
the preparation, such as the phosphonic acid with the
carboxylic acid [21–23], the sulfonic acids [21], the
oxalate ion [24,25], the 2,20-bipy [26], 4,40-bipy [27], or
1,10-phenanththroline [28], etc. has been found to be another
useful method to build hybrid open-frameworks. A 3D open-
framework of tin(II) phosphonopropionate oxalate and a
layered tin(II) methylphosphonate oxalate have been reported
by the Cheetham group [24,25], and a microporous zinc(II)
compound with phosphonopropionic acid and 1,3,5-benzene-
tricarboxylic acid (H3BTC) was isolated, in which the
tricarboxylate moiety remains non-coordinated and is also
severely disordered [2]. Several Pb(II) compounds of
phosphonopropionic acid with 1,3,5-benzenetricarboxylic
acid (H3BTC) or 3-HO3S–C6H4–CO2H were isolated by our
group [21–23]. We have initiated a research program to study
the intercalation chemistry of the layered metal dipho-
sphonates with carboxylic acids and sulfonic acids; such
hybrids may have good proton conductivity as well as ion-
exchange properties due to the presence of protons with
stronger acidity. As an expansion of our work, we have
Open-framework and microporous materials are a class of
veryimportant compoundsdue totheirtraditionalapplications
in catalysis, separations, sorbents, and ion-exchange as well as
their expected future use as hybrid composite materials in
electro-optical and sensing applications [1,2]. Studies of metal
phosphonates have shown that the use of bisfunctional or
multifunctional anionic units, such as diphosphonates,
aminophosphonates or phosphonocarboxylates can lead to a
number of new materials with microporous or open-
framework structures [3–17]. Recently we have also isolated
a microporous Cd(II) compound with N,N0-bis(phosphono-
methyl)-1,10-diaza-18-crown ether [18]. Several porous
Zr(IV) compounds with aza-crown ether functionalised
*
Corresponding author. Tel.: C86 591 8370 4836; fax: C86 591 8371
4946.
E-mail address: mjg@ms.fjirsm.ac.cn (J.-G. Mao).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.03.008

64
S.-M. Ying, J.-G. Mao / Journal of Molecular Structure 748 (2005) 63–70
synthesized two new aminodiphosphonic acids, namely
butylimino-bis(methylene-phosphonic acid) (CH3CH2CH2
CH2N(CH2PO3H2)2, H4L1) and isobutylimino-bis(methy-
lene-phosphonic acid) (Me2CHCH2N(CH2PO3H2)2, H4L2).
Hydrothermal reactions of lead(II) salts with 1,3,5-benzene-
tricarboxylic acid (H3BTC) and the above two
diphosphonate ligands afforded two new layered lead(II)
carboxylate phosphonates, namely Pb5(HL1)2(L1)$H3BTC
and Pb4(BTC)(L2)(CH3CO2)(H2O)2$1.5H2O. Herein we
report their syntheses, characterizations and crystal structures.
3.38 ppm (R-CH2–N, d, 2H, JH–HZ7 Hz), 3.57 ppm
(N–CH2–PO3, d, 4H, JH–PZ12.0 Hz). Elemental analysis for
H4L2, C6H17NP2O6 (MrZ261): C, 27.37; H, 6.10; N, 5.14%.
Calcd: C, 27.57; H, 6.51; N, 5.36%.
2.3. Syntheses of Pb5(HL1)2(L1)$H3BTC 1
A mixture of 0.271 g of PbCO3 (1.0 mmol), 0.130 g of
H4L1 (0.5 mmol), 0.106 g of 1,3,5-benzenetricarboxylic
acid (0.5 mmol) and 15 ml of deionized water were sealed
into a bomb equipped with a Teflon liner (20 ml), and then
heated at 180 8C for 5 days. The initial and final pH values
of solution were 4.0 and 5.0, respectively. Colorless plate
crystals of compound 1 were recovered in ca. 59% yield
based on Pb. Elemental analysis for 1, C27H47N3O24P6Pb5
(MrZ2019.45): C, 16.20; H, 2.03; N, 2.02%. Calcd: C,
16.04; H, 2.32; N, 2.08%. IR data (KBr, cmK1): 2959(s),
2873(s), 1735(s), 1710(s), 1610(s), 1521(s), 1435(s),
1350(s), 1263(s), 1207(s), 1015(vs), 731(s), 661(m),
591(s), 547(s), 507(s), 491(m).
2. Experimental
2.1. Materials and methods
All chemicals were obtained from commercial sources
and used without further purification. Elemental analyses
were performed on a Vario EL III elemental analyzer.
Thermogravimetric analyses were carried out with a
NETZSCH/STA 449C unit at a heating rate of 15 8C/min
under an oxygen atmosphere. IR spectra were recorded on a
Magna 750 FT-IR spectrometer photometer using KBr
2.4. Syntheses of Pb4(BTC)(L2)(CH3CO2)(H2O)2$1.5H2O 2
1
pellets in the 4000–400 cmK1. H and 31P NMR spectra
A mixture of 0.570 g mmol of Pb(CH3COO)2$3H2O
(1.5 mmol), 0.133 g of H4L2 (0.5 mmol), 0.102 g of 1,3,5-
benzenetricarboxylic acid (0.5 mmol) and 15 ml of deio-
nized water were sealed into a bomb equipped with a Teflon
liner (20 ml), and then heated at 180 8C for 5 days. The
initial and final pH values of the solution were 5.0 and 6.0,
respectively. Prismatic colorless crystals of compound
2 were recovered in ca. 70% yield based on Pb. Elemental
analysis for 2, C17H26NO17.5P2Pb4 (MrZ1415.09):
C, 14.50; H, 1.83; N, 1.00%. Calcd: C, 14.43; H, 1.85;
N, 0.99%. IR data (KBr, cmK1): 3371(m), 3189(m),
2959(m), 1680(m), 1611(s), 1544(s), 1432(s), 1364(vs),
1107(s), 1071(s), 1011(s), 980(s), 959(s), 769(m), 723(s),
601(m), 571(m), 537(m), 517(m), 477(m).
were recorded on a Varian Unity 500 NMR in D2O. H3PO4
was used as 31P standard reference. XRD powder patterns
were collected on a Philips X’Pert-MPD diffractometer
using graphite-monochromated Cu Ka radiation in the
angular range 2qZ5–708 with a step size of 0.028 and a
counting time of 3 s per step. Since the bulk reaction
products contain some impurities based on XRD powder
studies, single crystals for compounds 1 and 2 are selected
manually and used for EA, IR and TGA analyses.
2.2. Syntheses of H4L1 and H4L2
H4L1 and H4L2 were prepared by a Mannich type reaction
according to the procedures previously described [29].
Butylamine (100 mmol, about 10 ml) was mixed with
36% hydrochloric acid (16.0 cm3), deionized water (20 ml)
and phosphorous acid (400 mmol, 32.8 g). The mixture was
allowed to reflux at 120 8C for 1 h, then paraformaldehyde
(300 mmol, 9 g) was added in small portions over a period
of 1 h, and the mixture was then refluxed for an additional
hour. Removal of solvents afforded 18.1 g of a white
powder of H4L1 (yield 72% based on butylamine). Its purity
was confirmed by NMR measurements and elemental
2.5. X-ray crystallography
Single crystal of compounds 1 (size: 0.26!0.24!
0.06 mm) and 2 (size: 0.62!0.12!0.10 mm) were
mounted on a Siemens Smart CCD diffractometer equipped
with
a
graphite-monochromated Mo Ka radiation
˚
(lZ0.71073 A) respectively. Intensity data were collected
by the narrow frame method at 293 K. Both data sets were
corrected for Lorentz and Polarization factors as well as for
absorption by j scan technique. Both structures were solved
by direct methods and refined by full-matrix least-squares
on F2 by SHELX-97 [30]. Phosphonate oxygen atoms
(O(11), O(12), O(13), O(32) and O(33)) of compound 1 and
C(5), C(6) and O(2W) of compound 2 were disordered and
were split into two orientations each with 50% occupancy.
These atoms as well as C(5), O(31), O(52) and O(53) of
compound 1 as well as O(1) of compound 2 were refined
with isotropic thermal parameters. O(4w) atom with a short
1
analysis. 31P NMR shows a single peak at 8.5 ppm. H
NMR: 0.94 ppm (CH3–, t, 3H), 1.39 ppm (Me-CH2–, q, 2H),
1.75 ppm (Et-CH2–, t, 2H), 3.51 ppm (R-CH2–N, t, 2H),
3.56 ppm (N–CH2–PO3, d, 4H, JH–PZ9.5 Hz). Elemental
analysis for H4L1, C6H17NP2O6 (MrZ261.12): C, 27.38; H,
6.75; N, 5.20%. Calcd: C, 27.57; H, 6.51; N, 5.36%.
H4L2 waspreparedbya methodsimilartothatforH4L1. 31
P
NMR shows a single peak at 9.0 ppm. H NMR: 1.02 ppm
1
(CH3–, d, 6H, JH–HZ6.5 Hz), 2.19 ppm (Me2CH–, t, 1H),

S.-M. Ying, J.-G. Mao / Journal of Molecular Structure 748 (2005) 63–70
65
Table 1
Crystal data and structural refinements for compounds 1 and 2
Table 3
Selected bond lengths (A) for compound 2
˚
Compound
1
2
Pb(1)–O(22)
Pb(1)–O(13)
Pb(2)–O(1W)
Pb(2)–O(3)
2.340(11)
2.474(11)
2.51(2)
Pb(1)–O(23)#1
Pb(1)–N
2.349(12)
2.655(16)
2.58(4)
Empirical formula
Formula weight
Crystal system
Space group
C27H47N3O24P6Pb5
2019.45
C17H26NO17.5P2Pb4
1415.09
Pb(2)–O(2W)
Pb(2)–O(1)#2
Pb(3)–O(13)
Pb(3)–O(6)#3
Pb(3)–O(4)#5
Pb(4)–O(12)
Pb(4)–O(11)#4
P(1)–O(11)
P(1)–O(13)
P(2)–C(2)
Triclinic
Triclinic
2.619(14)
2.534(12)
2.577(15)
2.674(12)
2.730(12)
2.375(12)
2.68(2)
2.70(3)
PK1 (No. 2)
0.26! 0.24!0.06
12.6374(3)
19.6463(6)
76.4100(10)
81.6600(10)
76.4730(10)
2354.65(13)
2
PK1 (No. 2)
0.62!0.12!0.10
10.1260(7)
16.0737(10)
99.4650(10)
98.7020(10)
105.8750(10)
1512.43(17)
2
Pb(3)–O(5)#3
Pb(3)–O(2)
2.543(11)
2.626(12)
2.727(13)
2.362(15)
2.378(14)
1.547(13)
1.519(12)
1.806(17)
1.514(12)
1.22(3)
Crystal size (mm)
˚
b (A)
˚
c (A)
Pb(3)–O(11)#4
Pb(3)–O(21)#1
Pb(4)–O(21)#2
Pb(4)–O(8)
a (8)
b (8)
g (8)
P(1)–O(12)
1.533(15)
1.840(17)
1.532(11)
1.510(13)
1.24(2)
3
˚
V (A )
P(1)–C(1)
Z
P(2)–O(21)
P(2)–O(22)
C(13)–O(1)
C(14)–O(3)
C(15)–O(5)
C(17)–O(8)
Dc (g cmK3
)
2.848
3.107
P(2)–O(23)
m(Mo Ka) (mmK1)
F(000)
18.104
22.377
C(13)–O(2)
1.25(2)
1844
1276
C(14)–O(4)
1.24(2)
1.24(2)
Reflections collected
Unique reflections
Observed data
10,983
7918
C(15)–O(6)
1.29(2)
1.226(18)
7597 (RintZ0.0459) 5289 (RintZ0.0793)
6677
C(17)–O(7)
1.27(3)
4611
Hydrogen bonds
O(1w)/O(4w)
O(2w)/O(1)#2
O(4w)/O(8)#7
O(2w0)/O(4w)
O(2w)/O(3)#6
[IO2s(I)]
2.42(4)
2.81(5)
2.81(4)
2.40(5)
2.77(5)
Goodness-of-fit on F2
R1, wR2 [IO2s(I)]
R1, wR2 (all data)
1.207
1.055
0.0613, 0.1317
0.0751, 0.1440
0.0611, 0.1540
0.0715, 0.1661
Symmetry transformations used to generate equivalent atoms: #1 KxC1,
Ky, KzK1; #2 x, yK1, z; #3 KxC2, KyK1, KzK1; #4 KxC1, KyK1,
KzK1; #5 x, yC1, z; #6 KxC2, KyC2, Kz; #7 KxC2, KyC2, KzK1.
ꢀ
P
2ꢁ1=2
2
P
P
P
2
2
2
R1Z jjF0jKjFcjj= jF0j; wR2Z
w½ðF0Þ KðFcÞ ꢀ = w½ðF0Þ ꢀ
.
Table 2
Selected bond lengths (A) for compound 1
˚
O(4w)/O(4w) separation of 2.2 A (symmetry code: 3Kx,
˚
K2Ky, Kz) and a high thermal parameter were also
considered to be disordered and refined with 50%
occupancy. All other non-hydrogen atoms were refined
with anisotropic thermal parameters. The final difference
Pb(1)–O(13)
Pb(1)–O(22)
Pb(1)–N(1)
Pb(2)–O(32)#2
Pb(2)–O(42)#2
Pb(3)–O(33)#6
Pb(3)–O(51)
Pb(3)–O(11)#5
Pb(4)–O(52)#7
Pb(4)–O(31)#6
Pb(5)–O(53)
Pb(5)–O(43)
Pb(5)–O(21)#3
P(1)–O(12)
P(1)–C(5)
2.397(18)
2.536(16)
2.732(17)
2.19(2)
Pb(1)–O(51)
Pb(1)–O(42)#1
Pb(1)–O(53)#1
Pb(2)–O(12)#3
Pb(2)–O(31)
Pb(3)–O(13)
Pb(3)–O(22)
Pb(4)–O(23)
Pb(4)–O(21)#3
Pb(4)–O(61)
Pb(5)–O(61)
Pb(5)–O(22)
P(1)–O(11)
P(1)–O(13)
P(2)–C(6)
2.515(15)
2.645(13)
2.758(13)
2.313(16)
2.65(2)
Fourier maps showed featureless residual peaks of
K3
(for compound 1, 0.917 A from Pb(2) atom)
2.601(14)
2.460(18)
2.631(16)
2.75(2)
˚
2.770 e A
˚
2.592(19)
2.705(14)
2.281(13)
2.479(12)
2.750(14)
2.516(14)
2.712(15)
1.563(15)
1.512(14)
1.814(19)
1.525(13)
1.430(15)
1.542(16)
1.79(2)
K3
˚
˚
or 3.92 e A (for compound 2, 0.716 A from Pb(4) atom),
respectively. All hydrogen atoms were located at geome-
trically calculated positions. The hydrogen atoms of the
water molecules were not included in the refinements.
Crystallographic data and structural refinements are sum-
marized in Table 1. Selected bond lengths and angles are
listed in Tables 2 and 3, respectively, for compounds 1 and
2. More details about the crystallographic data have been
deposited as supplementary materials.
2.436(11)
2.71(2)
2.422(12)
2.569(14)
2.751(14)
1.418(15)
1.82(2)
P(2)–O(21)
P(2)–O(23)
P(3)–O(31)
P(3)–C(11)
1.501(12)
1.537(14)
1.476(14)
1.80(2)
P(2)–O(22)
P(3)–O(32)
P(3)–O(33)
P(4)–C(12)
P(4)–O(43)
P(5)–O(52)
P(5)–O(53)
P(6)–C(18)
P(6)–O(61)
C(27)–O(1)
C(28)–O(3)
C(29)–O(5)
CCDC-232745 and -232746 contain the supplementary
crystallographic data for this paper. These data can be
P(4)–O(41)
P(4)–O(42)
P(5)–O(51)
P(5)–C(17)
1.497(14)
1.566(15)
1.524(15)
1.845(19)
1.498(14)
1.552(14)
1.30(4)
1.538(14)
1.521(13)
1.532(13)
1.787(19)
1.505(16)
1.17(4)
P(6)–O(63)
P(6)–O(62)
C(27)–O(2)
C(28)–O(4)
C(29)–O(6)
1.26(4)
1.22(4)
1.33(4)
1.24(4)
Hydrogen bonds
O(2)/O(41)#7
2.49(2)
O(63)/O(3)
2.63(3)
Symmetry transformations used to generate equivalent atoms: #1 KxC1,
KyC1, KzC1; #2 KxC2, Ky, KzC1; #3 KxC2, KyC1, KzC1; #4
xC1, yK1, z; #5 KxC1, KyC2, KzC1; #6 x, yC1, z; #7 xC1, y, z; #8
KxC2, KyC1, KzC2.
Fig. 1. The coordination geometries around the lead(II) ions in compound 1.

66
S.-M. Ying, J.-G. Mao / Journal of Molecular Structure 748 (2005) 63–70
Fig. 2. The coordination modes of aminodiphosphonate anions in compound 1.
obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: (internat.) C44 1223 336 033; E-mail: deposit@ccdc.
cam.ac.uk].
linker. The diphosphonate anion containing P(3) and P(4) is
heptadentate. It chelates with Pb(2) bidentately (O(32) and
O(42)) and bridges with five other Pb(II) ions. One
phosphonate oxygen (O(41)) remains non-coordinated.
Two phosphonate oxygen atoms (O(31) and O(42)) are
bidentate metal linkers. Its amine group is singly protonated
and remains non-coordinated. The diphosphonate anion
containing P(5) and P(6) is also heptadentate, it chelates
with Pb(5) bidentately (O(53) and O(61)) and bridges with
five other Pb(II) ions. Two phosphonate oxygen atoms
(O(62) and O(63)) remain non-coordinated and O(62) is
considered to be singly protonated based on its longer P–O
3. Results and discussion
Compound 1 contains five lead(II) ions, one full
deprotonated L1 anions, two single-protonated anions, and
one neutral 1,3,5-benzenetricarboxylic acid in its asym-
metric unit. As shown in Fig. 1, Pb(1) is six-coordinated by
a tridentate chelating L1 anion (N(1), O(13) and O(22)) and
three phosphonate oxygen atoms from three HL1 anions in
an irregular PbO5N polyhedron. Pb(2) is four-coordinated
by four phosphonate oxygen atoms from two HL1 and one
L1 anions. The coordination geometry around Pb(2) can be
described as a severely distorted j-PbO4 square pyramid
with one square site occupied by the lone pair of the Pb(II)
ion. Pb(3) is five-coordinated by a bidentate chelating L1
anion (O(13), O(22)) and three phosphonate oxygen atoms
from two HL1 and one L1 anions. The coordination
geometry around Pb(3) can be described as a j-PbO5
octahedron with one apex occupied by the lone pair of the
Pb(II) ion. Pb(4) is five-coordinated by five phosphonate
oxygen atoms from two HL1 and three L1 anions. Pb(5) is
five-coordinated by a bidentate chelating HL1 anion (O(53)
and O(61)) and three phosphonate oxygen atoms from one
HL1 and two L1 anions. Pb(4) and Pb(5) have coordination
geometry similar to that of Pb(3). The Pb–O distances range
˚
distance (1.552(14) A compared with 1.505(16) and
˚
1.498(14) A for two other P–O bonds). Three phosphonate
oxygens (O(51), O(53) and O(61)) are bidentate metal
linkers. The amine group is non-coordinated.
The interconnection of the lead(II) ions via diphosphonate
ligands lead to a !002O lead(II) diphosphonate layer
(Fig. 3). Based on C–O distances as well as the requirement
for charge balance, all three carboxylate groups of the 1,3,5-
benzenetricarboxylate remain protonated (Table 2). This
neutral carboxylate ligand acts as an intercalated species
between two metal phosphonate layers (Fig. 4), forming
strong hydrogen bonds with the uncoordinated phosphonate
˚
from 2.19(2) to 2.758(13) A and Pb(1)–N(1) distance is
˚
2.732(17) A (Table 2), which are comparable to those
reported for other Pb(II) aminodiphosphonates [21–23].
The diphosphonate anions in compound 1 adopt three
different types of coordinated modes (Fig. 2). The dipho-
sphonate anion containing P(1) and P(2) is undecadentate, it
chelates with Pb(1) tridentately (N(1), O(13) and O(22)),
and chelates with Pb(3) bidentately (O(13) and O(22)) and
also bridges with six other Pb(II) ions. All six phosphonate
oxygen atoms are involved in metal coordination, hence this
diphosphonate ligand has been deprotonated completely.
Two phosphonate oxygen atoms (O(13) and O(21)) are
bidentate metal linkers and O(22) acts as a tridentate metal
Fig. 3. View of a !002O 2D layer of lead(II) diphosphonate in compound
1 along the c-axis. The butyl groups were omitted for clarity. The C–PO3
tetrahedra are shaded in gray. Pb and N atoms are represented by open and
octanded circles.

S.-M. Ying, J.-G. Mao / Journal of Molecular Structure 748 (2005) 63–70
67
Fig. 4. View of the structure of compound 1 along the b-axis. The C–PO3 tetrahedra are shaded in gray. Pb, N, O and C atoms are represented by open,
octanded, crossed and black circles. Hydrogen bonds are drawn as dotted lines.
oxygen atoms (O(41) and O(63)) of the L1 ligands. The O/O
one pyramidal site occupied by the lone pair of the Pb(II)
ion. Pb(3) is seven-coordinated by three carboxylate groups
from three BTC anions, one in a bidenate chelating fashion
and the other two in a unidentate fashion, as well as three
phosphonate oxygens from three diphosphonate anions in an
irregular PbO7 polyhedron. Pb(4) is four-coordinated by
three phosphonate oxygen atoms from three diphosphonate
anions and an oxygen atom from an acetate anion (O(8)).
The coordination geometry around Pb(4) can be viewed as
j-PbO4 trigonal bipyramid with one trigonal site occupied
by the lone pair of the Pb(II) ion. The Pb–O distances are in
˚
contacts are 2.49(2) and 2.63(3) A, respectively (Table 2).
There is no p/p interaction between neighboring H3BTC
molecules since the shortest distance between two parallel
˚
benzene rings is 5.435 A.
Pb4(BTC)(L2)(CH3CO2)(H2O)2$1.5H2O 2 has a layered
structure in which the 1,3,5-benzenetricarboxylate ligand
functioned as a multidentate metal linker. Compound 2 is
composed of one full deprotonated L2 ligand, one fully
deprotonated 1,3,5-benzenetricarboxylate anion, two aqua
ligands as well as two lattice water molecules. As shown in
Fig. 5, Pb(1) is four-coordinated by three phosphonate
oxygen atoms and one N atom from two diphosphonate
ligands, its coordination geometry can be viewed as j-PbO4
square pyramid with the pyramidal site occupied by the lone
pair of the Pb(II) ion. Pb(2) is four-coordinated by two
carboxylate oxygen atoms from two 1,3,5-benzenetricar-
boxylate anions and two aqua ligands, its coordination
geometry can be viewed as j-PbO4 trigonal bipyramid with
˚
the range from 2.340(11) to 2.730(12) A, and the Pb(1)–N
˚
distance is 2.655(16) A (Table 3), which are comparable to
those reported for other Pb(II) aminodiphosphonates
[21–23]. The iso-butyl-substituted aminodiphosphonate
ligand adopts a coordination mode which is different from
those of the n-butyl-substituted aminodiphosphonate
ligands in compound 1. The diphosphonate anion is
decadentate, it chelates with one Pb tridentately and also
Fig. 5. The coordination geometries around the lead(II) ions and the coordination modes of aminodiphosphonate anions in compound 2.

68
S.-M. Ying, J.-G. Mao / Journal of Molecular Structure 748 (2005) 63–70
The acetate ligand is unidentate (O(8)) and one carboxylate
oxygen atom (O(7)) remains non-coordinated. The inter-
connection of Pb(II) ions via bridging L2 anions lead to a 1D
chain along b-axis, whereas the cross-linkage of Pb(II) by
BTC anions resulted in a 1D chains along b-axis (Fig. 6).
The interconnection of the above two types of 1D chains
lead to the formation of a !002O lead(II) carboxylate–
phosphonate layer (Fig. 7). The lattice water molecules are
located at the cavities of the lead(II) carboxylate–phospho-
nate layer and are involved in hydrogen-bonding (Fig. 8,
Table 3). These 2D layers are held together via hydrogen
˚
bond between O(2w) and O(3) (2.77(5) A, symmetry code:
2Kx, 2Ky, Kz) (Fig. 8).
IR spectra of compound 1 shows the absorption bands of
the non-coordination carboxyl groups (nCOO at 1710 and
1435 cmK1 (see Supporting materials). These bands are
shifted to 1611 and 1432 cmK1 in compound 2 due to the
coordination of the carboxylate groups with the lead(II)
ions. The vibrations of the phosphonate groups are in the
region 900–1100 cmK1 [18].
Fig. 6. A 1D chain of lead(II) diphosphonate (a) and a 1D double chain of
lead(II) tricarboxylate (b) in compound 2. The C–PO3 tetrahedra are shaded
in gray. The Pb, N, O and C atoms are represented by open, octanded,
crossed and black circles, respectively.
TGA curves of compound 1 exhibit two steps of weight
losses (see Supporting materials). Compound 1 is stable up
to 292 8C. The first step started at 292 8C and completed at
537 8C corresponding to the release of the intercalated
H3BTC molecules and the partial decomposition of the
diphosphonate ligands. The observed weight loss is 19.8%.
The second started at 820 8C and continued up to 1000 8C,
corresponding to the further burning of the aminodipho-
sphonate anions. The final product is Pb2P2O7. The total
weight loss of 27.9% is close to the calculated value
(27.2%). The TGA curves of compound 2 reveal three main
steps of weight losses (see Supporting materials). The first
step started at about 60 8C and completed at about 151 8C
bridges with seven other Pb atoms (Fig. 5). Several factors
that may affect the coordination mode of the diphohphonate
ligand include the pH value, the different substituents on the
amine group, the nature of the second ligand, the metal/
ligand ratio, and the nature of the metal ion used [18,22]. In
current case, we deem that the pH value, the metal/
ligand ratio as well as the substituent are key factors.
Unlike non-coordination H3BTC in compound 1, the BTC
anion in compound 2 is hexadentate, it chelates one Pb atom
bidentately and bridges with other four Pb atom (Fig. 5).
Based on coordination modes as well as P–O and C–O
distances, both 1,3,5-benzenetricarboxylate anion and
the L2 anion have been fully deprotonated (Table 3).
Fig. 7. A !002O lead carboxylate–phosphonate hybrid layer in compound 2 down the c-axis. The C–PO3 tetrahedra are shaded in gray, and Pb, N, O and C
atoms are represented by open, octanded, crossed and black circles, respectively. The water molecules are omitted for clarity.

S.-M. Ying, J.-G. Mao / Journal of Molecular Structure 748 (2005) 63–70
69
b
a
c
Fig. 8. View of the structure of compound 2 along the a-axis. The C–PO3 tetrahedra are shaded in gray, and Pb, N, O and C atoms are represented by open,
octanded, crossed and black circles, respectively.
corresponding to the release of aqua ligands and lattice
water molecules, the observed weight loss of 4.56% is close
to the calculated value (4.45%). The second weight loss
started at 378 8C and complete at about 509 8C correspond-
ing to the loss of the BTC anion, and the acetate anion. The
observed weight loss of 20.4% is slightly large than the
calculated value (18.8%). The third step started at 802 8C
and continued up to 1000 8C, corresponds to the burning of
the diphosphonate ligand. The final product is PbO. The
total weight loss (35.4%) is slightly smaller than the
calculated value (37.4%).
Appendix. Supplementary Material
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2005.
03.008
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