Structural insights into the coordination and extraction of Pb(II) by disulfonamide ligands derived from o-phenylenediamine

Article abstract of DOI:10.1021/ic051103r

The o-phenylenediamine-derived disulfonamide ligands 1 and 2 complex and efficiently extract Pb(II) from water into 1,2-dichloroethane via ion-exchange, in combination with 2,2′-bipyridine (97.5% and 95.0%, respectively, for 1:1 ligand-to-Pb ratios). The

Full text of DOI:10.1021/ic051103r

Inorg. Chem. 2005, 44, 7951−7959
Structural Insights into the Coordination and Extraction of Pb(II) by
Disulfonamide Ligands Derived from o-Phenylenediamine
Robert J. Alvarado,† Jay M. Rosenberg,† Aileen Andreu,† Jeffrey C. Bryan,§ Wei-Zhong Chen,‡
Tong Ren,‡ and Konstantinos Kavallieratos*,†
Department of Chemistry and Biochemistry, Florida International UniVersity,
Miami, Florida 33199, Department of Chemistry, UniVersity of Miami,
Coral Gables, Florida 33146, and Department of Chemistry, UniVersity of
Wisconsin-La Crosse, La Crosse, Wisconsin 54601
Received July 1, 2005
The o-phenylenediamine-derived disulfonamide ligands 1 and 2 complex and efficiently extract Pb(II) from water
into 1,2-dichloroethane via ion-exchange, in combination with 2,2 -bipyridine (97.5% and 95.0%, respectively, for
1:1 ligand-to-Pb ratios). The corresponding Pb(II) sulfonamido binary complexes of ligands 1 and 2 (3 and 4,
respectively), and ternary complexes with 2,2 -bipyridine (5 and 6, respectively), were isolated and characterized.
1H NMR spectra of the organic phases after extraction show the formation of ternary Pb
sulfonamido bipy complexes.
′
−
′
−
−
X-ray characterization of 3, 4, and the ternary complex 5 consistently demonstrates four primary coordination sites
and a stereochemically active lone pair on Pb. The X-ray structure of 3 shows a pseudo trigonal bipyramidal
configuration on Pb, with the lone pair occupying one of the equatorial sites, and the formation of an unusual
“hemidirected” coordination polymer via axial S
with two DMSO molecules is observed in the structure of 4
the binary complexes in strongly coordinating solvents. In contrast, the X-ray structure of the ternary complex 5
reveals a distorted four-coordinate configuration with only weak S Pb coordination leading to dimer formation,
thus explaining its higher solubility in weakly coordinating solvents. FT-IR spectroscopy confirms the X-ray data,
since the ligand νS stretching frequencies shift to lower values in the binary Pb(II) sulfonamido complexes and
bipy complexes, as would be expected for
dO−Pb coordination. The same axial S
dO−Pb coordination pattern
‚[2(CH3)2SO)], thus rationalizing the high solubility of
dO−
−
dO
are again altered upon formation of the ternary Pb(II)−sulfonamido−
2,2 -bipy complexation and hindered S Pb coordination.
′
dO−
Introduction
active.6,7 For low coordination numbers (2-5), the lone pair
is stereochemically active and the ligand-to-metal bonds are
distributed unevenly around the metal center with an identifi-
able void (presumably the location of the lone pair) present
Lead exposure continues to be one of the most serious
environmentally related threats to human health in the United
States and worldwide.1 Therefore, there is a strong need to
design ligands that can complex Pb(II),2 which is the most
mobile form of lead in the environment, efficiently and
selectively for Pb(II) extraction and transport3 and for sensing
applications.4
The design of selective ligands for Pb(II) should take into
account its unique coordination chemistry.2,5 Pb(II) com-
plexes can adopt many different ligand geometries with
coordination numbers as low as 2 and as high as 10.6 The
geometry of Pb(II) complexes is highly dependent on whether
the lone electron pair of the metal is stereochemically
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* To whom correspondence should be addressed. E-mail: kavallie@fiu.edu.
† Florida International University.
‡ University of Miami.
§ University of Wisconsin.
10.1021/ic051103r CCC: $30.25
Published on Web 09/30/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 22, 2005 7951

Alvarado et al.
a,b
Scheme 1
in the coordination sphere, resulting in a “hemidirected”
ligand environment.6 On the other hand, complexes with high
coordination numbers (9-10) adopt a holodirected geometry
in which the ligands are distributed evenly throughout the
coordination sphere with a stereochemically inactive lone
pair. For intermediate coordination numbers (6-8), the
stereochemical activity of the lone pair, and hence the
geometry, depends strongly on the nature of the ligands and
the donor atoms. In general, complexes with large, bulky
ligands and with soft donors have a stereochemically inactive
lone pair and holodirected geometries.6
Although numerous successful macrocyclic ligands for
binding and extraction of Pb(II) have been reported in the
literature,2a,8,9 their synthesis is often time-consuming and
expensive, making their large-scale application for extraction
and detection of Pb(II) cost-prohibitive.10 By contrast, the
synthesis of ionizable chelates,11,12 which can extract via an
ion-exchange mechanism, is generally more straightforward.
Moreover, chelates generally exhibit more favorable com-
plexation-decomplexation kinetics13 and offer great potential
for combinatorial ligand strategies14 due to their synthetic
versatility.14 Therefore, there is a strong interest in developing
practical low-coordinate Pb(II) ion-exchangers that take
advantage of the preference of Pb(II) for hemidirected
geometries with a stereochemically active lone pair in order
to enhance selectivity against other competing metals.
Recently, we reported that disulfonamide ionizable chelates
derived from o-phenylenediamine can complex and ef-
ficiently extract Pb(II) via an ion-exchange mechanism.15,16
Deprotonation of the sulfonamide ligand by an organic base
results in the formation of a Pb(II) complex, and the metal
a Complex formation results in extraction of Pb(II) into the organic phase
(extraction stage). b Contact of the organic phase with dilute acid transfers
the extracted metal to a second aqueous phase for analysis (stripping stage).
is extracted into the organic phase (Scheme 1a). A secondary
coligand may be used to improve the solubility of the
complex in the organic medium and the extraction selectivity.
The metal can be isolated and the ligand recovered after
extraction by contacting the organic phase with dilute
aqueous acid (stripping stage), which results in decomplex-
ation and transfer of the Pb(II) to a new aqueous phase
(Scheme 1b). 2,2′-Bipyridine (2,2′-bipy) was used as a
coligand for Pb(II) extraction by 1 and 2 due to the poor
solubility of the binary Pb(II)-sulfonamido complexes in
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7952 Inorganic Chemistry, Vol. 44, No. 22, 2005

Coordination and Extraction of Pb(II) by Disulfonamides
1
water-immiscible solvents.15 Herein, we report in full on the
coordination of Pb(II) by these extractants using X-ray
crystallography, IR, and H NMR. The X-ray structures of
the binary complex 4 and the ternary complex 5, which is
formed during the extraction process, give us insight on
coordination by solvent molecules and 2,2′-bipy. This
structural data in combination with FT-IR spectroscopy
elucidate the role of the 2,2′-bipy coligand during extraction.
a white powder. H NMR (CDCl3, 20 °C): 7.60 (d, 4H, J ) 8.5
Hz), 7.42 (d, 4H, J ) 8.5 Hz), 7.02 (dd, 2H, J ) 6.0 and 3.5 Hz),
6.96 (dd, 2H, J ) 5.9 and 3.5 Hz), 6.73 (s br, 2H), 1.29 (s, 18H).
13C-{1H}-NMR (CDCl3, 20 °C): 157.73, 135.87, 131.18, 127.85,
127.72, 126.52, 126.43, 35.70, 31.52. FT-IR (KBr): N-H, 3316,
3272, and 3238 cm-1; SdO, 1337 and 1166 cm-1. Elemental anal.
Calcd for C26H32N2S2O4: C, 62.37; H, 6.44; N, 5.60. Found: C,
61.98; H, 6.45; N, 5.50.
1
Pb[1,2-C6H4(NSO2C6H5)2] (3). A solution of Pb(NO3)2 (0.853
g, 2.58 mmol) in 100 mL of MeOH was added dropwise to a
solution of 1 (1.00 g, 2.56 mmol) and 2.2 equiv of NEt3 (0.569 g,
5.63 mmol) in 400 mL of MeOH. After stirring for 1 h, the reaction
mixture was added dropwise to an equal volume of H2O. After
removal of most of the methanol, a white precipitate was collected,
washed with CH2Cl2, and recrystallized from MeOH/H2O yielding
Experimental Section
Materials and Methods. All materials (purchased from Aldrich
Chemical Co., ACROS organics, or TCI) were standard reagent
grade and were used without further purification, with the exception
1
of 1,2-dichloroethane (DCE), which was distilled from CaH2. H
and 13C NMR spectra were recorded on either a 400 or a 600 MHz
Bruker NMR spectrometer and were referenced, using the residual
solvent resonances. All chemical shifts, δ, are reported in ppm.
FT-IR spectra were recorded on a Nicolet Magna-IR 560 spec-
trometer. ICP-MS measurements were carried out on a Hewlett-
Packard 4500 series plus or a Perkin-Elmer Elan-II DRC. Positive-
mode electrospray ionization mass spectra were obtained on a
Finnigan ThermoQuest LC-MS instrument using 0.01 mg/mL
solutions directly infused to the MS chamber at a rate of 0.01
mL/min.
1
1.28 g of 3 (84%). H NMR (CD3OD, 20 °C): 7.93 (dd, 4H, J )
6.0 and 2.1 Hz), 7.43 (m, 6H), 6.53 (dd, 2H, J ) 6.0 and 3.5 Hz),
6.30 (dd, 2 H, J ) 6.0 and 3.5 Hz). 13C-{1H}-NMR (CD3OD,
20 °C): 144.61, 141.37, 133.02, 130.00, 128.43, 121.26, 120.44.
FT-IR (KBr): SdO, 1257 and 1129 cm-1. Elemental anal. Calcd
for PbC18H14N2S2O4: C, 36.42; H, 2.38; N, 4.72. Found: C, 36.01;
H, 2.58; N, 4.66.
Pb[1,2-C6H4(NSO2C6H4-p-But)2] (4). Synthesized in a method
similar to that for 4, from 2 (0.648 g, 1.29 mmol) and 2.2 equiv of
NEt3 (0.287 g, 2.85 mmol) dissolved in 80 mL of MeOH by the
addition of Pb(NO3)2 (0.429 g, 1.30 mmol) dissolved in 85 mL of
N,N′-Diphenyl-1,2-benzenedisulfonamide (1).17 A solution of
1,2-phenylenediamine (2.01 g, 18.6 mmol) and pyridine (5.12 g,
64.7 mmol) in 75 mL of CH2Cl2 was added dropwise to a solution
of benzenesulfonyl chloride (6.56 g, 37.1 mmol) dissolved in 50
mL of CH2Cl2. The reaction mixture was stirred at room temperature
for 22 h and was monitored by TLC (70:30, hexanes/EtOAc). The
reaction mixture was diluted with an additional 200 mL of CH2Cl2
and washed sequentially with 1M HCl, 1M NaHCO3, and H2O.
The resulting organic phase was separated and dried by pouring it
through a Na2SO4 column. The volatiles were removed and the
residue was recrystallized from MeOH/H2O to give 5.91 g of 1
(82%) as a white powder. 1H NMR (CDCl3, 20 °C): 7.66 (dd, 4H,
J ) 7.3 and 1.8 Hz), 7.54 (tt, 2H, J ) 7.5 and 1.4 Hz), 7.41 (t, 4H,
J ) 7.8 Hz), 7.03 (dd, 2H, J ) 6.0 and 3.5 Hz), 6.92 (dd, 2H, J )
5.9 and 3.6 Hz), 6.80 (s, 2H). 13C-{1H}-NMR (CDCl3, 20 °C):
140.06, 134.43, 132.31, 130.31, 128.57, 128.09, 126.6. FT-IR
1
MeOH. Yield: 0.913 g (95%). H NMR (CD3OD, 20 °C): 7.84
(d, 4H, J ) 8.6 Hz), 7.46 (d, 4H, J ) 8.6 Hz), 6.56 (dd, 2H, J )
6.0 and 3.5 Hz), 6.33 (dd, 2H, J ) 5.9 and 3.5 Hz), 1.22 (s, 18H).
13C-{1H}-NMR (CD3OD, 20 °C): 155.80, 140.61, 140.43, 127.31,
125.96, 120.20, 119.44, 34.91, 30.50. FT-IR (KBr): SdO 1271
and 1138 cm-1. Elemental anal. Calcd for PbC26H30N2S2O4: C,
44.24; H, 4.28; N, 3.97. Found: C, 44.24; H, 4.50; N, 3.99.
Pb[1,2-C6H4(NSO2C6H5)2][2,2′-bipy] (5). Compound 1 (0.264
g, 0.680 mmol), 1 equiv of 2,2′-bipy (0.106 g, 0.679 mmol), and
2.2 equiv of diisopropylamine (0.20 mL, 1.42 mmol) were dissolved
in 45 mL of DCE. Pb(NO3)2 (0.699 g, 2.11 mmol) was dissolved
in 45 mL of H2O and added to the DCE solution. The two phases
were contacted under vigorous stirring for 36 h at room temperature.
The organic phase was separated and dried by pouring through a
Na2SO4 column. The DCE was removed under vacuum, and the
isolated solid was washed many times with ether. The product was
recrystallized from CH2Cl2/hexanes and dried under vacuum for
(KBr): N-H, 3276 and 3225 cm-1; SdO, 1336 and 1165 cm-1
.
N,N′-Di-(4-tert-butylbenzene)-1,2-benzenedisulfonamide (2).
The compound was synthesized in a method similar to that for 1:
4-tert-butylbenzenesulfonyl chloride (2.17 g, 9.34 mmol) was
dissolved in 20 mL of CH2Cl2. 1,2-Phenylenediamine (0.505 g, 4.67
mmol)/pyridine (1.30 mL, 1.19 g, 13.1 mmol) dissolved in 25 mL
of CH2Cl2 was added, and the mixture was stirred for 10.5 h.
Recrystallization from CH2Cl2/hexanes gave 2.01 g (86%) of 2 as
1
12 h at 40 °C. Yield: 0.204 g (40%). H NMR (DMSO-d6, 20
°C): 8.67 (ddd, 2H, J ) 4.8, 1.0, and 0.8 Hz), 8.36 (td, 2H, J )
8.1 and 1.0 Hz), 8.00 (m, 4H), 7.94 (td, 2H, J ) 7.7 and 1.8 Hz),
7.54 (m, 6H), 7.44 (ddd, 2H, J ) 7.3, 4.8 and 1.3 Hz), 6.54
(dd, 2H, J ) 6.0 and 3.5 Hz), 6.34 (dd, 2H, J ) 6.0 and 3.5 Hz).
13C-{1H}-NMR (DMSO-d6, 20 °C): 155.50, 149.57, 143.57,
140.46, 137.65, 131.89, 129.10, 127.45 124.51, 120.76, 119.68,
118.81. FT-IR (KBr): SdO 1261 and 1129 cm-1. ESI-MS
(CH3OH): 751 (M+H+).
Pb[1,2-C6H4(NSO2C6H4-p-But)2][2,2′-bipy] (6). The compound
was synthesized in a method similar to that for 5 from 2 (0.130
g, 0.260 mmol), 1 equiv of 2,2′-bipy (0.041 g, 0.260 mmol), and
2.3 equiv of diisopropylamine (0.08 mL, 0.56 mmol) dissolved
in 30 mL of DCE contacted with Pb(NO3)2 (0.435 g, 1.31
mmol) dissolved in 30 mL of H2O. Yield: 0.165 (74%). 1H NMR
(DMSO-d6, 20 °C): 8.68 (d, 2H, J ) 4.1 Hz), 8.37 (d, 2H, J ) 8.0
Hz), 7.95 (td, 2H, J ) 7.9 and 1.7 Hz), 7.92 (d, 4H, J ) 8.5 Hz),
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Inorganic Chemistry, Vol. 44, No. 22, 2005 7953

Alvarado et al.
Table 1. Crystallographic Data for 3, 4‚[2(CH3)2SO)], and
7.55 (d, 4H, J ) 8.5 Hz), 7.46 (dd, 2H, J ) 6.9 and 5.1 Hz), 6.61
(dd, 2H, J ) 5.8 and 3.5 Hz), 6.38 (dd, 2H, J ) 5.9 and 3.4 Hz),
(s, 18H). 13C-{1H}- NMR (DMSO-d6, 20 °C): 155.99, 155.42,
150.15, 141.12, 141.05, 138.31, 127.89, 126.49, 125.15, 121.38,
120.26, 119.33, 35.58, 31.69. FT-IR (KBr): SdO 1267 and 1137
5‚[1.5(CH3)2CO]
3
4‚[2(CH3)2SO)]
5‚[1.5(CH3)2CO]
formula
C18H14N2O4PbS2
C30H36N2O6PbS4
C
32.50H31N4O5.50PbS2
formula weight
crystal system
593.6
monoclinic
856.04
monoclinic
836.92
monoclinic
cm-1
.
crystal size (mm3) 0.40 × 0.35
0.11 × 0.08 × 0.03 0.40 × 0.25 × 0.21
Distribution Experiments (ICP-MS). Typical ICP-MS ex-
periments were performed as follows: All glassware was contacted
with 8 M HNO3 overnight and then washed with water. The DCE
was distilled and vigorously stirred with water for 1 h. A stock
solution of ligand (0.15-3 mM), 2.2 equiv of NH(i-Pr)2, and 1
equiv of 2,2′-bipy was prepared in DCE. An appropriate amount
of stock solution and DCE was used in preparing 800 µL of organic
phase samples. Stock solutions of M(NO3)2 (3 µM to 3 mM) were
prepared. 800 µL of the aqueous phases were subsequently prepared
using appropriate amounts of the metal stock solution and equili-
brated H2O. The two phases were contacted for 12 h in a rotating
wheel and then separated. For stripping, 500 µL aliquots of the
organic phases were contacted with 500 µL of a 0.1 M HNO3
solution for 3 h. The source aqueous phases and stripped aqueous
phases for each sample were diluted twice before the ICP-MS
runs so that the final metal concentration before measurement did
not exceed 125 ppb. A 2% HNO3 thallium internal standard solu-
tion was prepared and used for the dilution of the aqueous
phases, as well as for the determination of a calibration curve.
Internal standards solutions for Co, Ni, Cu, Cd, and Zn were
prepared in the same fashion using Sc or In (for Cd). Calibration
curves were determined with known metal ICP-MS standards
(GFS Chemicals, Inc.) and a minimum of seven points ranging
from 0 to 150 ppb. For Pb, the total isotopic counts for m/z of 206,
207, and 208 were measured for the calibration curve and samples.
All samples were adjusted using a blank sample, which contained
metal and DCE only. The distribution ratios were calculated from
the corrected amounts of metal present in the two phases. All
extraction experiments were performed in independent triplicate
samples.
space group
a, Å
b, Å
P21/n
P21/n
C2/c
9.8201(15)
19.358(3)
9.8553(12)
90
99.828(10)
90
10.4577(19)
13.246(3)
25.935(9)
90
92.566(16)
90
19.4207(11)
13.4855(8)
25.6477(14)
c, Å
R, deg
â, deg
γ, deg
V (Å3)
Z
95.1590(10)
1846.0(5)
4
3589.1(16)
4
6689.9(7)
8
T, °C
λ, Å
-173
0.71073
2.14
0.028
0.075
27
0.71073
1.584
0.042
0.067
27
0.71073
1.662
0.036
0.078
Dc, g cm-3
R1a
wR2b
a R1
)
[Σ||Fo|
c
-
|Fc||]/[Σ |Fo|], based on
o
I > )
2σI. b wR2
[Σw(F -F 2)2]/[Σw(F )2]
2
2
x
o
analysis, and the detector was placed at a distance of 4.997 cm
away from the crystal. For 5‚[1.5(CH3)2CO], a yellowish block of
approximate dimensions 0.40 × 0.35 × 0.21 mm3 was mounted in
a 0.3 mm capillary, which was filled with mother liquor. The
capillary was sealed with epoxy glue, and the detector was placed
at a distance of 5.020 cm away from the crystal. Data were
measured using omega scans of 0.3° per frame for 5 s such that a
hemisphere was collected. A total of 1271 frames were collected
with a final resolution of 0.75 Å. No decay was indicated by the
recollection of the first 50 frames at the end of data collection.
The frames were integrated with the Bruker SAINT software
package using a narrow-frame integration algorithm, which also
corrects for the Lorentz and polarization effects. Absorption
corrections were applied using SADABS supplied by George
Sheldrick. With the use of the Bruker SHELXTL (version 5.1)
software, the structure of 4‚[2(CH3)2SO)] was solved and re-
fined in the space group P21/n. The structure of 5‚[1.5(CH3)2CO]
was solved and refined in the space group C2/c. For 4‚[2(CH3)2-
SO)], the asymmetric unit contains one independent molecule with
two DMSO molecules coordinating to Pb. Both S atoms in
DMSO, C28, C29, and C30 (methyl groups in DMSO) are
disordered over two positions (54% and 46%) and were refined
with occupancy. For 5‚[1.5(CH3)2CO], the asymmetric unit con-
tains one independent molecule, one and half acetone molecules,
which are not involved in the coordination. For both structures, all
non-hydrogen atoms were derived from the direct method solu-
tion. With all non-hydrogen atoms being anisotropic and all
hydrogen atoms being isotropic, the structures were refined to
convergence by a least-squares method on F2, using SHELXL-93,
incorporated in SHELXTL.PC V 5.03. The results are summarized
in Table 1.
X-ray Crystallography. Single crystals of 3 were grown in
50:50 MeOH/H2O. X-ray intensity data were collected at 100 K
on an Enraf-Nonius, CAD4 diffractometer fitted with a 1.1 mm
collimator and an Oxford Cryosystems 600 series low-temperature
device. A pale yellow hexagonal plate, measuring 0.40 × 0.35 ×
0.16 mm3, was mounted on the end of a glass fiber. A total of
7764 reflections were collected of which 3935 were independent
(Rint ) 0.036). Data reduction was carried out using XCAD4,
supplied by Klaus Harms. Bruker’s SHELXTL (version 5.1, IRIX)
was used for absorption correction, structure solution/refinement,
and molecular graphics. A lamina absorption correction, based on
a set of psi-scans was applied. All non-hydrogen atoms were refined
anisotropically. Each H-atom was placed in a calculated position,
refined using a riding model, and given an isotropic displacement
parameter equal to 1.2 times the equivalent isotropic displacement
parameter of the atom to which it is attached. Full-matrix least-
squares refinement against |F| of the quantity ∑w(Fo2 - Fc2)2 was
2
Scheme 2. Synthesis of Sulfonamide Ligands
used to adjust the refined parameter. Structural analysis was
performed by Ton Speck’s PLATON.
Single crystals of 4‚[2(CH3)2SO)] and 5‚[1.5(CH3)2CO] were
grown in 50:50 DMSO/H2O and via slow evaporation of acetone,
respectively. The X-ray intensity data were measured at 300 K on
a Bruker SMART 1000 CCD-based X-ray diffractometer system
equipped with a Mo-target X-ray tube (λ ) 0.71073 Å) operated
at 2000 W of power. For 4‚[2(CH3)2SO)], a colorless block of
approximate dimensions 0.11 × 0.08 × 0.03 mm3 cemented onto
a quartz fiber with epoxy glue was used for the crystallographic
7954 Inorganic Chemistry, Vol. 44, No. 22, 2005

Coordination and Extraction of Pb(II) by Disulfonamides
Scheme 3. Synthesis of Pb(II) Binary and Ternary Complexes
Table 2. Selected Bond Distances (Å) and Angles (deg) for 3,
4‚[2(CH3)2SO)], and 5‚[1.5(CH3)2CO]
Results and Discussion
Synthesis of Ligands and Complexes. The aryldisul-
fonamide ligands 1 and 2 were synthesized by a modification
of previously reported procedures (Scheme 2).17 The one-
step synthesis is carried out in good yields by reacting two
equiv of the corresponding arylsulfonyl chloride with o-phen-
ylenediamine in the presence of two equiv of pyridine.
Binary complexes 3 and 4 were prepared in MeOH by
reacting the ligand with Pb(NO3)2 in the presence of Et3N
or NH(i-Pr)2 (Scheme 3). By contrast, ternary complexes 5
and 6 were prepared using a two-phase method in which
the ligand, 2,2′-bipy, and the base are all dissolved in 1,2-
dichloroethane (DCE) (Scheme 3). The organic layer is then
contacted with an aqueous solution of the Pb(NO3)2, and the
Pb(II) complex is isolated from the organic phase.
3
Pb-N(1)
Pb-N(2)
Pb-O(2)′
Pb-O(4)′′
Pb‚‚‚O(1)
Pb‚‚‚O(3)
Pb‚‚‚S(1)
2.296(4)
2.329(4)
2.599(4)
2.524(3)
2.869(4)
3.043(3)
3.221(1)
Pb‚‚‚S(2)
3.314(1)
1.445(4)
1.458(4)
1.571(4)
1.448(4)
1.459(4)
1.569(4)
S(1)-O(1)
S(1)-O(2)
S(1)-N(1)
S(2)-O(3)
S(2)-O(4)
S(2)-N(2)
N(1)-Πâ-N(2)
N(1)-Πâ-O(1)
N(1)-Πâ-O(2)′
N(1)-Πâ-O(3)
N(1)-Πâ-O(4)′′
68.4(1)
53.7(1)
95.0(1)
119.5(1)
81.5(1)
N(2)-Πâ-O(1)
N(2)-Πâ-O(2)′
N(2)-Πâ-O(3)
N(2)-Πâ-O(4)′′
O(2)′-Pb-O(4)′′
120.4(1)
89.6(1)
51.2(1)
92.5(1)
175.0(1)
4‚[2(CH3)2SO)]
Pb(1)-N(1)
Pb(1)-N(2)
Pb(1)-O(6)
Pb(1)-O(5A)
S(1)-O(1)
2.326(6)
2.321(4)
2.521(5)
2.53(3)
S(2)-O(3)
S(2)-O(4)
S(1)-N(1)
S(2)-N(2)
S(4A)-O(6)
S(3B)-O(5A)
1.442(4)
1.448(4)
1.581(5)
1.591(5)
1.518(9)
1.51(2)
X-ray Crystallography. The X-ray crystal structure of 3
(Figure 1) indicates that the Pb(II) is coordinated to two
1.458(5)
1.452(5)
S(1)-O(2)
N(1)-Pb(1)-N(2)
N(1)-Pb(1)-O(6)
N(2)-Pb(1)-O(6)
68.38(18)
88.29(19)
80.90(16)
N(1)-Pb(1)-O(5A)
N(2)-Pb(1)-O(5A)
O(6)-Pb(1)-O(5A)
83.2(7)
81.7(6)
162.5(6)
5‚[1.5(CH3)2CO]
Pb(1)-N(1)
Pb(1)-N(2)
Pb(1)-N(3)
Pb(1)-N(4)
N(1)-S(2)
2.411(5)
2.338(5)
2.568(5)
2.651(5)
1.565(4)
N(2)-S(1)
O(1)-S(1)
O(2)-S(1)
O(3)-S(2)
O(4)-S(2)
1.578(4)
1.437(5)
1.431(5)
1.445(4)
1.462(4)
N(1)-Pb(1)-N(2)
N(2)-Pb(1)-N(3)
N(1)-Pb(1)-N(3)
67.34(16)
100.85(17)
80.72(16)
N(2)-Pb(1)-N(4)
N(1)-Pb(1)-N(4)
N(3)-Pb(1)-N(4)
86.92(16)
130.10(14)
62.38(15)
simply coordinates to the metal in a bidentate fashion through
the two nitrogen atoms, and no polymeric structure is
formed.19 The relatively short Pb-N bond lengths (2.296-
(4) and 2.329(4) Å) (Table 2) are consistent with the obser-
vation that Pb-N bonds opposite the location of the stereo-
chemically active lone pair tend to be shorter in length than
the average value.2a,6 The distances between the Pb and the
O atoms in the axial positions (2.524(3) and 2.599(3) Å)
are within the range for Pb-O covalent bonds (ranging from
2.46 to 2.96 Å).20,21 Longer distances are observed between
Pb and the two sulfonyl oxygen atoms of the coordinated
sulfonamide O(1) (2.869(4) Å) and O(3) (3.043(3) Å).
Figure 1. PLUTO representation of the extended structure of 3, showing
the formation of a coordination polymer. Hydrogen atoms have been omitted
for clarity.
sulfonamide nitrogen atoms of the deprotonated ligand, as
well as by two oxygen atoms from neighboring complexes,
resulting in the formation of an unusual coordination polymer
with a hemidirected geometry.18 A pseudo trigonal bipyra-
midal (tbp) configuration is observed, in which the equatorial
positions are occupied by the Pb-N bonds and the lone pair.
The axial positions are occupied by the Pb-O bonds
responsible for the formation of the coordination polymer.
Interestingly, in all previous studies of metals bound to
N,N′-1,2-arenebis(benzenesulfonamide) ligands, the ligand
(19) (a) Evans, C.; Henderson, W.; Nicholson, B. K. Inorg. Chim. Acta
2001, 314, 42. (b) Cheng, P.-H.; Cheng, H.-Y.; Lin, C.-C.; Peng, S.
M. Inorg. Chim. Acta 1990, 169, 19. (c) Cheng, H.-Y.; Cheng, P.-H.;
Lee, C.-F.; Peng, S. M. Inorg. Chim. Acta 1991, 181, 145.
(20) Holloway C. E.; Melnik, M. Main Group Met. Chem. 1997, 20, 399.
(21) Based on a search of the Cambridge Structural Database (CSD) for
all Pb(II)-(NS(O)2C) fragments containing a Pb-O bond. Allen, F.
H. Acta Crystallogr. 2002, B58, 380. CSD reference codes FUYDOS,
IGIGEK, IGIGIO, TEZMIU, and XAQNAE were found.
(18) For other Pb(II) coordination polymers see: (a) Harrowfield, J.;
Miyamae, H.; Skelton, B. W.; Soudi, A. A.; White, A. H. Aust. J.
Chem. 1996, 49, 1165. (b) Mann, K. L. V.; Jeffery, J. C.; McCleverty,
J. A.; Ward, M. D. Polyhedron 1999, 18, 721. (c) Meng, X.; Song,
Y.; Hou, H.; Fan, Y.; Zhu, Y. Inorg. Chem. 2003, 42, 1306. (d) Shi,
Y.; Li, L.; Li, Y.; Tai, X.; Xue Z.; You, X. Polyhedron 2003, 22,
917.
Inorganic Chemistry, Vol. 44, No. 22, 2005 7955

Alvarado et al.
Figure 2. ORTEP plot of 4‚[2(CH3)2SO)] (30% probability ellipsoids).
For clarity, the hydrogen atoms have been omitted.
Figure 3. ORTEP representation of the ternary complex 5 (30% probability
ellipsoids).
Further examination of the vacancy in the coordination
sphere reveals that the space is partially filled by two
aromatic rings from neighboring molecules (symmetry
equivalents of the sulfonyl phenyl rings). While weak Pb-π
interactions are fairly common, the shortest Pb-C distances
reported here (C(14) 3.695(6) Å, C(23) 3.786(5) Å, C(24)
3.724(5) Å) are generally longer than those typically
observed in the literature,22 suggesting that if any Pb-π
interactions are present they are very weak. This observation
is consistent with the presence of a stereochemically active
lone pair in the vacant site.
The X-ray crystal structure of 4‚[2(CH3)2SO)] (Figure 2)
shows that the Pb(II) is coordinated to two sulfonamide
nitrogen atoms of ligand as well as two molecules of DMSO.
Although the O-Pb-O angle (162.5(6)°) is smaller than in
3 (175.0(1)°), the geometry is also hemidirected and assumes
a pseudo tbp configuration in which the lone pair occupies
the vacant axial site. Similar to 3, relatively short Pb-N
(2.321(4) and 2.326(6) Å) distances are observed. The
distances between the Pb and the two O atoms of the DMSO
molecules (2.521(5) and 2.53(3) Å) are also comparable to
the Pb-O distances for complex 3.
In the same fashion as 3 and 4, the X-ray crystal structure
of ternary complex 5 (Figure 3) shows a four-coordinate
metal center with a hemidirected geometry and a stereo-
chemically active lone pair. However, slightly longer Pb-N
bond distances (2.388(5) and 2.411(5) Å) than in 3 and 4
are observed between the sulfonamide ligand and the metal
(Table 2). In addition, the Pb(II) is also coordinated to the
nitrogen atoms of the 2,2′-bipy. The distances between the
metal center and the 2,2′-bipy nitrogen atoms are significantly
larger (2.568(5) and 2.651(5) Å) than those observed for the
sulfonamide nitrogen atoms and are also slightly larger than
those observed before for PbI2(2,2′-bipy).23 However, the
distances are similar to those reported for a related Pb(II)-
sulfonamide-2,2′-bipy complex.12a
Figure 4. Packing diagram of 5, showing the formation a dimer. The
packing is enhanced by π-π interactions between two bipyridine molecules.
Hydrogen atoms have been omitted for clarity.
In contrast to complexes 3 and 4, where coordination to
neighboring molecules is strong, complex 5 exhibits only
weak interactions with neighboring molecules as shown by
the rather long Pb-O and Pb-S distances (3.238 and 4.034
Å, respectively). Nevertheless, as shown in Figure 4, the
interaction between neighboring molecules results in the
formation of a dimer, and the crystal packing is further
enhanced by π-π interactions involving the 2,2′-bipy
molecules (the center-to-center distance between the two
2,2′-bipy molecules is 2.696 Å). Further examination of the
packing diagram (Figure 4), shows that the Pb-N bonds
between the 2,2′-bipy and the metal center are closer to the
lone pair (presumably located in the large vacancy in the
coordination sphere) than the Pb-N bonds of the sulfona-
mide ligand. This observation correlates well with previous
studies which show that ligands close to the lone pair exhibit
longer Pb-N bond lengths than those away from the lone
pair.2a,6
Comparison of the bond lengths in 3, 4, and 5 with those
(22) (a) Edelmann, F. T.; Buijink, J.-K. F.; Brooker, S. A.; Herbst-Irmer,
R.; Kilimann, U.; Bohnen, F. M. Inorg. Chem. 2000, 39, 6134 and
references therein. (b) No, K. H.; Kim, J. S.; Shon, O. J.; Yang, S.
H.; Suh, I. H.; Kim, J. G.; Bartsch, R. A.; Kim, J. Y. J. Org. Chem.
2001, 66, 5976.
for the free ligand, 1,24 shows that the S-N bonds are
(23) Zhu, H.; Xu, Y.; Yu, Z.; Wu, Q.; Fun, H.; You, X. Polyhedron 1999,
18, 3491.
7956 Inorganic Chemistry, Vol. 44, No. 22, 2005

Coordination and Extraction of Pb(II) by Disulfonamides
Table 3. IR Frequencies (cm-1) of the N-H and SdO Bonds of 1-6a
significantly shorter (averaging 1.57 Å in 3 and 1.64 Å in
1) when the ligand is bound to Pb(II). However, a corre-
sponding lengthening of the SdO bond cannot always be
observed based on the standard uncertainties in the crystal-
lographic data. Such lengthening is expected based on the
observed decrease of the SdO stretching frequency in the
IR (vide infra).
N-H
SdO
type of IR
1
1
1
1
2
2
2
2
3276, 3225
3253
1336, 1165 KBr
1336, 1165 film
1331, 1170 solution
3331
3332b
1330, 1164 solution + NH(i-Pr2)
3316, 3272, 3238 1337, 1166 KBr
3255
3333
3333b
1330, 1165 film
1340, 1165 solution
1337, 1166 solution + NH(i-Pr2)
1332, 1158 KBr
The coordination of Pb(II) to the oxygen atoms of neigh-
boring molecules or DMSO in complexes 3 and 4 explains
why the binary Pb-sulfonamide complexes are poorly sol-
uble in relatively less polar solvents such as DCE, yet sol-
uble in more polar, highly coordinating solvents, such as
CH3OH and DMSO. By contrast, in the ternary complex 5,
the coordination of 2,2′-bipy significantly interferes with self-
association through Pb-OdS bonding, thus increasing the
solubility in less polar solvents.
C6H5NHSO2C6H5 3206
C6H5NHSO2C6H5 3257
C6H5NHSO2C6H5 3349, 3257
C6H5NHSO2C6H5 3352b
3
4
5
6
1332, 1153 film
1348, 1165 solution
1348, 1168 solution + NH(i-Pr2)
1257, 1129 KBr
1271, 1138 KBr
1261, 1129 KBr
none
none
none
none
1267, 1137 KBr
a For reference, the data of model compound C6H5NHSO2C6H5 is also
included. b The intensity of the N-H peak decreases significantly upon
IR Studies. The changes in the FT-IR stretching frequen-
cies upon complexation complement the information ob-
tained from the X-ray structures. The IR data of binary
complexes 3 and 4 show a significant decrease in the
stretching frequencies of the SdO bonds as compared to their
corresponding ligands. The lower frequency implies that the
SdO bonds weaken upon complexation and correlates well
with the X-ray crystal structure of 3 which shows that the
sulfonamide oxygens are coordinated to Pb(II) centers of
neighboring molecules, forming a coordination polymer.
Interestingly, the SdO frequency of ternary complex 5 is
slightly larger than that of the corresponding binary com-
plex 3. This is unexpected considering the electron-do-
nating ability of the 2,2′-bipy ligand, which should actually
decrease the SdO stretching frequency even further. These
observations suggest that the addition of the 2,2′-bipy dis-
rupts the self-association via SdO-Pb coordination, thus
slightly strengthening the SdO bond, and increasing its
stretching frequency. This interference with SdO-Pb co-
ordination by 2,2′-bipy is indicated in the X-ray crystal
structure and also by the higher solubility of 5 compared to
that of 3 in noncoordinating solvents. The balance of
electronic effects and hindered SdO-Pb coordination after
the complexation of 2,2′-bipy is somewhat altered for the
t-Bu-substituted analogues 6 and 4, leading only to a very
slight change to the opposite direction upon complexation.
For the free ligands (Table 3), the N-H infrared stretching
frequency varies significantly between solution and film. In
solution, the N-H stretch appears at higher frequencies as
compared to those from the KBr or thin-film measurements.
The lower frequency of the N-H stretch in the solid state is
indicative of a higher degree of self-association between the
sulfonamide molecules as a result of hydrogen bonding.
Addition of 2.2 equiv of NH(i-Pr)2 to a ligand solution causes
a significant decrease in the intensity of the N-H peak.
addition of the base.
and 6. Attempts to extract Pb(II) in the absence of 2,2′-bipy
were hindered by the low solubility of the binary com-
1
plexes 3 and 4 in DCE. The H NMR spectrum of the or-
ganic phase after extraction of Pb(II) by 1 exhibits reso-
nances for both the ternary complex and the free ligand.
Furthermore, it is apparent that the ligand and the com-
plex are in slow exchange on the NMR time scale, because
after extraction there are two different sets of peaks for the
two species. To determine whether there is fast exchange
between complex 5 and free 2,2′-bipy molecules in so-
lution, 2,2′-bipy was added to a solution of isolated 5. The
fact that only one set of peaks is observed for the four
2,2′-bipy resonances, and that the chemical shifts are dif-
ferent than those observed for free 2,2′-bipy and 5, clearly
indicate that the free and coordinated 2,2′-bipy are in fast
exchange on the NMR time scale. A control dilution ex-
1
periment of 2,2′-bipy gave no changes in the H NMR
spectrum.
With the use of the following protocol, it is possible to
indirectly determine the distribution ratio for Pb(II) (de-
fined as DPb ) [Pb2+]org/[Pb2+]aq, where org and aq refer to
the concentrations in the organic and aqueous phases, after
extraction, respectively) from the 1H NMR data. Equation 1
relates DPb to the concentration of the ternary complex
([Pb(L)(2,2′-bipy)]org) and the initial concentration of Pb(II)
([Pb2+]i).
DPb ) [Pb(L)(2,2′-bipy)]org/[Pb2+]i - [Pb(L)(2,2′-bipy)]
(1)
Although the concentration of the ternary complex cannot
1
be directly determined by H NMR, the ratio of ternary
complex to free ligand can be determined from the integration
ratio (defined as Ω ) [Pb(L)(2,2′-bipy)]org/[L]org) of the
central aromatic peaks from the complex to the ones from
the free ligand. Substituting Ω into (1) and defining Θ as
the ratio of the initial concentrations of Pb(II) to ligand
([Pb2+]i/[L]i) gives eq 2.
1H NMR Studies. Ligands 1 and 2 were shown to ex-
tract Pb(II) from water into DCE by ion-exchange at the
liquid-liquid interphase when used in synergistic combina-
tions with 2,2′-bipy, by forming the ternary complexes 5
(24) Bryan, J. C.; Rosenberg, J. M.; Kavallieratos, K. Acta Crystallogr.,
Sect. E. 2005, 61, o396.
DPb ) Ω[L]org/Θ[L]i - Ω[L]org
(2)
Inorganic Chemistry, Vol. 44, No. 22, 2005 7957

Alvarado et al.
Figure 6. Extraction of M(NO3)2 by 1 in the presence of 1.0 equiv
of 2,2′-bipy and 2.2 equiv of NH(i-Pr)2. M(II) was kept constant at
2.70 mM.
Figure 5. Extraction of Pb(II) by 1 and 2 in the presence of 1.0 equiv of
2,2′-bipy and 2.2 equiv of NH(i-Pr)2. The distribution ratio D is defined as
[Pb2+
]
org/[Pb2+]aq. [Pb] is constant at 6.30 mM (error in concentration is
<5%).
Pb(II), Cd(II), Zn(II), Cu(II), and Ni(II) (Figure 6) shows
that at a metal concentration of 2.70 mM and ligand
concentration of 3.00 mM the extraction efficiency increases
as follows: Cd(II) < Ni(II) < Pb(II) < Zn(II) < Cu(II).
The higher D values of Zn(II) and Cu(II) over Pb(II) are
likely attributed to stronger complexation of Zn(II) and
Cu(II) to 2,2′-bipy.12c,d Such a conclusion is supported by
the fact that the analogous o-phenylenediamine-derived
dansylamide has been shown to selectively extract Pb(II)
without the need for a coligand addition via the formation
of the binary complex.16
Using the fact that [L]i is equal to the sum of [Pb(L)(2,2′-
bipy)]org and [L]org and substituting into (2) gives (3), which
can be further simplified to (4).
DPb ) Ω[L]org/Θ([Pb(L)(2,2′-bipy)]org + [L]org) - Ω[L]org
(3)
DPb ) Ω/Θ(Ω + 1) - Ω
(4)
Substitution of the actual values of Ω and Θ gave a DPb
of 61.26 for an initial Pb (II) concentration of 4.079 mM
and a ligand concentration of 5.301 mM.
Distribution Experiments (ICP-MS). Extraction of
Pb(II) by ligands 1 and 2 was also studied using ICP-MS.
For extraction of Pb(II), aqueous phases containing Pb(NO3)2
(0.15-6.30 mM) were contacted with DCE containing 1 or
2 (0-5 mM), 2.2 equiv of NH(i-Pr)2, and 1.0 equiv of 2,2′-
bipy. Subsequently, the organic phases were stripped with
0.1 M HNO3. The concentration of Pb(II) at both the source
aqueous phase and the stripping phase was determined by
ICP-MS, allowing direct determination of the distribution
ratios. The synergistic extraction of Pb(II) for a 1:1 ratio of
ligand to Pb(II) was found to be as high as 97.5% for 2
and 95.0% for 1 (Figure 5). Double stripping of the or-
ganic phase showed no significant decrease in the distribution
ratios obtained. Control experiments, using 2,2′-bipy only,
NH(i-Pr)2 only ligand only, as well as combinations of those
in pairs, demonstrated that all components are necessary for
the Pb(II) extraction. Further control experiments demon-
strated the HNO3 used for stripping does not react with either
1 or 2 and that both 1 and 2 are recoverable after extraction
Conclusions
In conclusion, the simple sulfonamide ion-exchangers 1
and 2 can coordinate Pb(II), resulting in the formation of
binary complexes 3 and 4. X-ray crystallography shows that
the metal center of these complexes can also accommodate
coordination by either neighboring sulfonamide molecules,
forming a coordination polymer, or by solvent molecules.
These observations compare well with the tendency of
Pb(II) to recruit additional ligand or solvent molecules in
order to achieve desired coordination patterns. Self-associa-
tion through SdO-Pb coordination explains why complexes
3 and 4 exhibit low solubility in weakly coordinating sol-
vents, limiting their application to extraction. By contrast,
ternary complex 5 is only weakly coordinated by neigh-
boring molecules and is far more soluble in less polar
solvents. Apparently, the addition of 2,2′-bipy disrupts the
coordination of the metal center by additional molecules. As
1
1
demonstrated by both H NMR and ICP-MS studies, the
(>97% measured by H NMR with 4,4′-dimethylbiphenyl
enhanced solubility of ternary complexes 5 and 6 allows the
efficient extraction of Pb(II) from water into DCE, albeit
with no selectivity against Cu(II) and Zn(II). Future work
will focus on the effects that changes of the peripheral
sulfonamide groups may have on the ability of the metal to
recruit additional molecules into the coordination sphere.
Improving the solubility and extraction properties of the
metal-ligand binary complexes, without the need for a
coligand addition, could potentially lead to selective Pb(II)
extraction.
as internal standard). The pH of the aqueous phase after
contact was measured at 7.0 ((0.2). The control aniline
derivative (C6H5NHSO2C6H5) did not extract under any
conditions, indicating the need for coordination through the
two chelating nitrogens for extraction. This synergistic
system, showed 420 (for 1) and 430 (for 2) times higher
extraction than 18-crown-6 (18C6) or combinations of 18C6
and 2,2′-bipy.
Further distribution studies were performed with other
divalent metals. A plot of log [M(II)]org vs [1]t for M(II) )
7958 Inorganic Chemistry, Vol. 44, No. 22, 2005

Coordination and Extraction of Pb(II) by Disulfonamides
Acknowledgment. We thank Mr. Michael T. Lago for
synthetic experimental help and Dr. Weihua Zhang for help
with the ESI-MS characterization. We also thank Drs. J.
Martin Quirke and Stanislaw F. Wnuk for useful discussions
and suggestions. This project was supported by NIH-NIEHS/
ARCH (S11 ES11181). J.M.R. was supported through a
RISE Award from the National Institutes of Health (MBRS/
RISE-R25-GM061347). The support of U.S. Army Research
Office (W911NF-04-1-0022) for the purchase of the 600
MHz NMR spectrometer is gratefully acknowledged.
Supporting Information Available: Crystal data for complexes
3, 4, and 5; partial 1H NMR spectra of ligands, complexes, and the
organic phase after extraction. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC051103R
Inorganic Chemistry, Vol. 44, No. 22, 2005 7959