The chelating behaviour of 3-(4-X-phenyl)-2-sulfanylpropenoic acids with the PbII ion - Relevance of the lone electron pair in the supramolecular structures of the 2:1 complexes

Article abstract of DOI:10.1002/ejic.201300633

The interaction of 3-(4-X-phenyl)-2-sulfanylpropenoic acids [H ₂(X-pspa); X = -F, -Cl, -Br, -I, -OCH₃, -OCF₃, -OH] with lead(II) acetate in an alcoholic medium was explored in the search for new chelating agents for the Pb²⁺ ion. The direct reactions afforded [Pb(X-pspa)] complexes in yields of 67 (X = -Br) to 95 % (X = -OCH ₃). When the Pb^II/H₂(X-pspa) reaction was performed in the presence of diisopropylamine (Q), the derivatives [HQ] ₂[Pb(X-pspa)₂] (X = Cl, Br) were obtained. All of the complexes were characterized by spectrometric (FAB-MS and ESI-MS) and spectroscopic (IR, ¹H and ¹³C NMR spectroscopy) methods and these showed the permanence of the O,S coordination of the ligands to the metal ion in dimethyl sulfoxide (DMSO) solution. H₂(Cl-pspa), [HQ]₂[Pb(Cl-pspa)₂] and [HQ]₂[Pb(Br-pspa) ₂] were also fully characterized in the solid state by X-ray diffraction. The importance of the stereochemically active lone electron pair of the Pb^II ion in the supramolecular arrangement of [HQ] ₂[Pb(X-pspa)₂] (X = Cl, Br) is discussed. The characteristics of complexes formed by 3-(4-X-phenyl)-2-sulfanylpropenoic acids with lead(II) cations have been explored both in the solid state and in solution. The importance of the stereochemically active lone electron pair of the Pb^II ion in the supramolecular arrangement of [HQ] ₂[Pb(X-pspa)₂] (X = Cl, Br; Q = diisopropylamine) is discussed. Copyright

Full text of DOI:10.1002/ejic.201300633

FULL PAPER
DOI:10.1002/ejic.201300633
The Chelating Behaviour of 3-(4-X-Phenyl)-2-
sulfanylpropenoic Acids with the PbII Ion – Relevance of
the Lone Electron Pair in the Supramolecular Structures
of the 2:1 Complexes
José S. Casas,[a] M. Victoria Castaño,*[a] Maria D. Couce,*[b]
Agustín Sánchez,[a] José Sordo,[a] M. Dolores Torres,[a] and
Ezequiel M. Vázquez López[b]
Dedicated to Professor Antonio Laguna on the occasion of his 65th birthday
Keywords: Lead / Chelates / Supramolecular chemistry / Lone electron pairs
The interaction of 3-(4-X-phenyl)-2-sulfanylpropenoic acids
[H2(X-pspa); X = –F, –Cl, –Br, –I, –OCH3, –OCF3, –OH] with
lead(II) acetate in an alcoholic medium was explored in the
search for new chelating agents for the Pb2+ ion. The direct
reactions afforded [Pb(X-pspa)] complexes in yields of 67 (X
= –Br) to 95% (X = –OCH3). When the PbII/H2(X-pspa) reac-
tion was performed in the presence of diisopropylamine (Q),
the derivatives [HQ]2[Pb(X-pspa)2] (X = Cl, Br) were ob-
tained. All of the complexes were characterized by spectro-
metric (FAB-MS and ESI-MS) and spectroscopic (IR, 1H and
13C NMR spectroscopy) methods and these showed the per-
manence of the O,S coordination of the ligands to the metal
ion in dimethyl sulfoxide (DMSO) solution. H2(Cl-pspa),
[HQ]2[Pb(Cl-pspa)2] and [HQ]2[Pb(Br-pspa)2] were also fully
characterized in the solid state by X-ray diffraction. The im-
portance of the stereochemically active lone electron pair of
the PbII ion in the supramolecular arrangement of
[HQ]2[Pb(X-pspa)2] (X = Cl, Br) is discussed.
Introduction
“Inorganic lead” poisoning [i.e., intoxication with
lead(II) derivatives] remains a serious occupational and en-
vironmental hazard.[1] The presence of this ion in mammals
is known to provoke dysfunction in the renal, cardiovascu-
lar, reproductive and central nervous systems.[2] In children,
a particularly sensitive section of the population, PbII ions
may cause reduced growth and neuropsychological deficits
even at very low metal blood levels.[3]
Chelation therapy is the usual clinical approach to re-
duce the body burden of lead in poisoned individuals.[4]
Several examples of the drugs that are currently considered
for the treatment of lead(II) decorporation are shown in
Scheme 1.[5]
Scheme 1.
The compounds shown in Scheme 1 were not designed
to mobilize specifically the lead(II) ion and none fulfil the
characteristics required for an ideal chelating agent.[6] Thus,
the preparation of new and more effective antidotes to treat
PbII poisoning remains an important goal.
To achieve this goal, it is very important to consider the
coordination preferences of the PbII cation. In this respect,
the chelating agents shown in Scheme 1 constitute a rather
heterogeneous group of ligands. For example, fully or par-
[a] Departamento de Química Inorgánica, Universidade de Santi-
ago de Compostela,
tially
deprotonated
ethylenediaminetetraacetic acid
Campus Vida, 15782 Santiago de Compostela, Galicia, Spain
E-mail: mvictoria.castano@usc.es
(H4EDTA) chelates the metal ion through the two aminic
N atoms and four carboxylic O atoms, one from each carb-
oxylate group.[7] In [Pb(PEN)] (PEN = d-penicillaminato),
the ligand is N,O,S tridentate in the solid state.[8] In turn,
the meso-2,3-dimercaptosuccinato ligand (m-DMSA4–)
binds PbII ions through one O atom and two S atoms in
[b] Departamento de Química Inorgánica, Universidade de Vigo,
36310 Vigo, Galicia, Spain
Fax: +34-986812556
E-mail: delfina@uvigo.es
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300633.
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aqueous solution.[9] Nevertheless, this variety of coordina- are sparingly soluble. All of the complexes melt with de-
tion modes is probably consistent with the behaviour of composition at temperatures close to 200 °C, except for the
PbII ions as a borderline acid according to the hard and hydroxy derivative (X = –OH), which melted at 150 °C.
soft acids and bases (HSAB) principle of Pearson.[10]
However, although PbII ions are eclectic in terms of coor-
dination mode, one would expect PbII ions to have a fa-
voured combination of donor atoms. In this respect, it was
pointed out that mixed O,S donor ligands may have the
optimal hard/soft Lewis basicity to match the preferences
of the lead(II) ion.[11] This is the chelating mode of DMSA
and this may be the reason why this antidote has been re-
Scheme 3.
commended as a first choice chelator in cases of low-to-
moderate lead(II) poisoning.[5]
The reaction of lead(II) acetate with H2(X-pspa) in the
In the search for new and better O,S donor molecules,
we have explored the interaction of lead(II) with several 3-
(4-X-phenyl)-2-sulfanylpropenoic acids [H2(X-pspa), see
Scheme 2], at present only from the point of view of coordi-
nation.
presence of diisopropylamine (Q) in a molar ratio close to
1:2:4 (Scheme 3) produced the complexes [HQ]2[Pb(Cl-
pspa)2] and [HQ]2[Pb(Br-pspa)2]. The formation of these
compounds implies the requirement for an excess of Q with
respect to the stoichiometric relationship (1:2:4 instead of
1:2:2). This probably ensures complete deprotonation of
H2(X-pspa) and facilitates the formation of the anionic
complex. The other H2(X-pspa) acids afforded unidentified
solids, possibly mixtures of the 1:1 and 2:1:2 derivatives.
[HQ]2[Pb(Cl-pspa)2] and [HQ]2[Pb(Br-pspa)2] are more sol-
uble in DMSO and DMF than the corresponding 1:1 com-
plexes, but they are insoluble in water and other common
organic solvents and melt with decomposition at a rather
high temperature (ca. 250 °C).
Scheme 2.
It would be expected that these compounds would bind
to the PbII ion to form O,S chelates once their –COOH
and –SH groups are deprotonated. It is also reasonable to
expect that the para-X groups would have some influence
on the electron charge on the donor atoms and the bio-
availability of the compounds in biological media. The pres-
ence of the phenyl group will also possibly favour the lipo-
solubility of the ligand and increase its ability to cross the
cell membrane. H2(I-pspa) behaves as a neuroprotective
agent because it inhibits calpain, a class of protease located
within the cell, in the cytosol.[12]
X-ray Diffraction
The single crystals of H2(Cl-pspa) obtained by slow
evaporation of the solvent from a solution of the compound
in dichloromethane are composed of planar [root mean
square (rms) deviation: 0.0232 Å] molecules (Figure 1). Se-
lected bond lengths [Å] and angles [°] are listed in Table 1.
We describe here the solubility and spectroscopic and
structural characteristics of the PbII complexes formed by
H2(X-pspa) To the best of our knowledge, previous research
in this field has been limited to the preparation of the re-
lated PbII complexes with 3-(2-furyl)-2-sulfanylpropenoic
acid,[13] 3-(phenyl)-2-sulfanylpropenoic acid[14] and 3-
(phenyl)-3-(methyl)-2-sulfanylpropenoic acid.[15]
Results and Discussion
Figure 1. Molecular structure of H2(Cl-pspa) with numbering
scheme.
Synthesis and Properties of the Complexes
The reaction of Pb(OAc)2·3H2O and H2(X-pspa) (1:1
molar ratio) in a mixture of EtOH/H2O almost immediately
The S(1)–C(2) bond length [1.752(2) Å] is close to the
afforded coloured solids with the [Pb(X-pspa)] stoichiome- sum of the covalent radii for the two atoms (1.78 Å)[16] and
try (Scheme 3) in yields from 67 (X = –Br) to 95% (X = also to those found in the structurally related 3-(phenyl)-
–OCH3). All of the solids are insoluble in water and com- [1.749(3) Å][17] and 3-(2-chlorophenyl)-2-sulfanylpropenoic
monly used organic solvents except for dimethyl sulfoxide [1.766(7) Å][18]
acids
and
2-sulfanylbenzoic
acid
(DMSO) and dimethylformamide (DMF), in which they [1.766(3) Å].[19] The O(1)–C(1) and the O(2)–C(1) distances
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Table 1. Selected bond lengths [Å] and angles [°] in H2(Cl-pspa) and [HQ]2[Pb(Cl-pspa)2].
H2(Cl-pspa)
[HQ]2[Pb(Cl-pspa)2]
Pb environment
Pb–S(1)
Pb–S(2)
2.5899(16)
2.6326(16)
2.448(4)
Pb–O(11)
Pb–O(21)
2.431(4)
99.04(5)
73.52(10)
76.60(10)
90.90(10)
72.51(9)
S(1)–Pb–S(2)
S(1)–Pb–O(11)
S(1)–Pb–O(21)
S(2)–Pb–O(11)
S(2)–Pb–O(21)
O(11)–Pb–O(21)
Ligand 1
142.88(14)
Ligand 2
O(21)–C(10)
O(22)–C(10)
S(2)–C(11)
C(10)–C(11)
C(11)–C(12)
C(12)–C(13)
O(21)–C(10)–O(22)
O(21)–C(10)–C(11)
O(22)–C(10)–C(11)
S(2)–C(11)–C(12)
C(10)–C(11)–C(12)
C(11)–C(12)–C(13)
O(1)–C(1)
O(2)–C(1)
S(1)–C(2)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
O(1)–C(1)–O(2)
O(1)–C(1)–C(2)
O(2)–C(1)–C(2)
S(1)–C(2)–C(3)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
1.227(3)
1.305(3)
1.752(2)
1.483(3)
1.345(3)
1.464(3)
122.6(2)
122.2(2)
115.2(2)
124.94(19)
119.6(2)
131.5(2)
O(11)–C(1)
O(12)–C(1)
S(1)–C(2)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
O(11)–C(1)–O(12)
O(11)–C(1)–C(2)
O(12)–C(1)–C(2)
S(1)–C(2)–C(3)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
1.281(7)
1.239(7)
1.743(6)
1.536(8)
1.350(8)
1.460(8)
124.2(5)
117.9(5)
117.9(5)
124.9(5)
116.4(5)
131.2(6)
1.270(7)
1.242(7)
1.759(6)
1.515(8)
1.338(8)
1.461(8)
121.7(5)
119.6(5)
118.7(5)
125.4(5)
117.0(5)
132.4(6)
are in the ranges 1.21–1.25 and 1.31–1.35 Å, which fall the van der Waals radii, 3.50 Å);[21] additionally, the Cl
within the ranges suggested[20] to define C=O(1) and a C– atom is 3.404 Å from C(1) of a molecule of a parallel sheet.
O(2) bonds in ordered carboxylic acid dimers supported by
O–H···O bonds, as was found in this case (Table 2).
The structures of [HQ]2[Pb(Cl-pspa)2] and [HQ]2[Pb(Br-
pspa)2] are isotypic, so only the chloro derivative will be
discussed {the data for the [HQ]2[Pb(Br-pspa)2] complex
are given in Tables S1 and S2 and Figure S1}. A representa-
tion of the [Pb(Cl-pspa)2]2– anion is displayed in Figure 2
(a). Selected bond lengths and angles are given in Table 1.
The lattice consists of [Pb(Cl-pspa)2]2– anions and [HQ]2+
cations. In the former, the PbII ions are O,S-chelated by
two fully deprotonated sulfanylpropenoate ligands to give a
coordination number of four. The distribution of the Pb–O
and Pb–S bonds on one side of the PbII ion suggest the
presence of a stereochemically active lone pair (SALEP)
projected out in the opposite direction. This hemidirected
coordination sphere[22] can be described as a pseudo-trigo-
nal bipyramid in which the two O atoms are apical and the
two S atoms plus the SALEP are in the equatorial positions.
A similar kernel was depicted for some neutral PbII com-
plexes with thiomaltol,[11] 3-hydroxy-1,2-dimethyl-4(1H)-
pyridinethione[11] and thiohydroxamic acids.[23] As ex-
pected, the Pb–O bond lengths are shorter than those in
other PbII complexes with stereochemically active lone
pairs, but with higher coordination numbers.[24]
Table 2. Structural parameters [Å and °] describing intra- and inter-
molecular hydrogen bonding in [H2(Cl-pspa)] and [HQ]2[Pb(Cl-
pspa)2].
D–H···A
d(D–H) d(H···A) d(D···A) ЄDHA
[H2(Cl-pspa)]
S(1)–H(1S)···O(1)
1.29(4)
2.07(4)
1.88(4)
2.91(4)
2.9416(19) 120(2)
2.649(3) 172(4)
3.7587(12) 122(2)
O(2)–H(1O)···O(1)[a] 0.77(4)
S(1)–H(1S)···Cl(1)[b]
1.29(4)
[HQ]2[Pb(Cl-pspa)2]
N(2)–H(2B)···O(11)
N(1)–H(1A)···O(12)
0.92
0.92
1.95
1.86
1.97
2.38
1.80
2.867(6) 177.8
2.764(6) 168.1
2.865(6) 164.6
3.101(6) 135.0
2.718(6) 172.9
N(1)–H(1B)···O(21)[c] 0.92
N(1)–H(1B)···O(22)[c] 0.92
N(2)–H(2A)···O(22)[c] 0.92
[a] Symmetry code: –x + 2, –y, –z + 1. [b] x – 1, y – 1, z. [c] x, y
+ 1, z.
In addition to the O–H···O hydrogen bonds that link the
molecules into dimers, other intra- and intermolecular in-
The main distortion in this pseudo-trigonal-bipyramidal
teractions are present in H2(Cl-pspa). An intramolecular S– arrangement is associated with the bond angles O(11)–Pb–
H···O bond (Table 2), also detected in the two previously O(21) and S(1)–Pb–S(2), which are narrower [142.88(14)
cited[17,18] and similar sulfanylpropenoic acids but absent in and 99.04(5)°, respectively] than the ideal values (180 and
2-sulfanylbenzoic acid,[19] is present in this case. Further- 120°). In addition, the O(11)–Pb–S(1), O(21)–Pb–S(1) and
more, the S–H group and the Cl atom of a neighbouring O(21)–Pb–S(2) angles are smaller (73–77°) than the ideal
molecule are involved in an S–H···Cl hydrogen bond angle (90°), although O(11)–Pb–S(2) is close to this value
(Table 2) that links the dimers into sheets. In these sheets, [90.90(10)°]. As revealed previously,[23] these deviations
the Cl atom is located 3.296 Å from another Cl atom of a from the canonical geometry could be due to the influence
neighbouring molecule (a smaller distance than the sum of of the SALEP, which repels and compresses the bonding
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Figure 2. (a) Structure of [Pb(Cl-pspa)2]2– anion with numbering scheme. (b) View of the hydrogen-bonded chain formed between HQ+
cations and [Pb(Cl-pspa)2]2– anions.
pairs, but also the small bite of the ligand, which conditions volving N–H(1A) and the two carboxylate O atoms from
the O(11)–Pb–S(1) and O(21)–Pb–S(2) angles. These angles a neighbouring ligand. In one of these bonds [N–H(1A)
[73.52(10) and 72.51(9)°, respectively] are practically equal ···O(22)], the distance is larger, and the DHA angle is nar-
to those found in [PbPh2(pspa)2]2– [73.51(12) and rower than in the other [N–H(1A)···O(21), see Table 2].
71.23(11)°],[14] an anionic complex with a ligand similar to However, despite this difference, they are within the usual
Cl-pspa2– but without a SALEP as the complex is a PbIV range for this type of bond.[26] The same HQ+ cation forms
derivative. It is worth comparing the Pb–O and Pb–S bond an additional bond [N(1)–H(1B)··O(12)] with another li-
lengths in the [Pb(Cl-pspa)2]2– and [PbPh2(pspa)2]2– com- gand and, thereby, contributes to connect the [Pb(Cl-
plexes. In the PbII compound, the Pb–O distances are pspa)2]2– anions. The HQ+ cation containing N(2) forms
shorter [2.431(4) and 2.448(4) Å] than those in the di- only two bridging hydrogen bonds and these also contribute
phenyllead(IV) complex [2.480(5) and 2.569(5) Å], whereas to the catenation.
the Pb–S distances remain practically unchanged
In contrast to the situation in the complexes of the
[2.5899(16), 2.6326(16) and 2.5975(19), 2.6198(19) Å, thiohydroxamic acids,[23] in [Pb(Cl-pspa)2]2– there are no
respectively]. This suggests that PbII ions are possibly significant additional bonds with the metal ion. In the crys-
“harder” than PbPh22+, although the former is a borderline tal (Figure 3, a), the closest atoms to the PbII ion, other
Lewis acid.[25]
than those of the coordination sphere, are three H atoms
The bond lengths and angles of the ligand change only belonging to a phenyl ring [Pb···H(18) 3.198 Å, symmetry
marginally upon deprotonation and coordination. The code x, 3/2 – y, 1/2 + z] and to two diisopropylammonium
main modification occurs in the length of the two carboxyl- methyl groups [Pb···H(42B) 3.208 Å, symmetry code x,
ate C–O bonds, which became more similar in the complex 1/2 – y, 1/2 + z; Pb···H(50C) 3.427 Å, symmetry code x, 1
(Table 1). Moreover, the two ligands [Cl-pspaS(1)]2– and + y, z; Figure 3, b]. Although the formation of some agostic
[Cl-pspaS(2)]2– are not equivalent and differ mainly in their interactions between the SALEP and H–C bonds was con-
respective planarity, which is reduced in both cases with sidered,[27] it would be expected that, if such interactions
respect to that of the free ligand (vide supra). The dihedral occur, they would be located over the gap where the stereo-
angle between the two fragments that are approximately chemical lone pair is believed to reside and, in the present
planar in their backbones, namely, the phenyl ring and the complex, this is not the case (see magnified view in Fig-
sulfanylpropenoate moieties, is 23.35(19) for [Cl-pspaS(1)]2– ure 3, b).
and 18.66(24)° for [Cl-pspaS(2)]2–.
There is also one Cl atom (symmetry code –1 – x, 1 –
The [Pb(Cl-pspa)2]2– complex anions are associated in y, –z) located 3.896 Å from the metal centre. Although in
the lattice through hydrogen bonds, in which two types of this case a secondary interaction with PbII is plausible, this
diisopropylammonium cations participate; this results in distance is a little higher than the sum of the van der Waals
chains along the b axis (Figure 2, b). The HQ+ cation con- radii of the two atoms (2.00 and 1.75 Å for Pb[10] and Cl,[21]
taining N(1) forms a bifurcated donor hydrogen bond in- respectively).
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Figure 3. (a) Packing of the chains in the lattice of [HQ]2[Pb(Cl-pspa)2] along the b axis showing the SALEPs. (b) A view of the chains
along the a axis showing the π-stacking interactions and, in the enlarged detail, the unbound atoms closest to PbII. (c) View of the
packing in [HQ]2[Pb(Cl-pspa)2]. The HQ+ cations are in light yellow and cyan, and the two ligands of the [Pb(Cl-pspa)2]2– anions are in
brown and green.
The chains are held in pairs by π-stacking interactions ture in the IR spectra and this is the absence of the ν(S–H)
between the phenyl rings [C(5)···C(5)d 3.312 Å, symmetry band, which is consistent with the deprotonation of the S–
code 1 – x, –y, 1 – z], which are in a slipped alignment.[28] H group in all cases. In addition, the characteristic bands
The tapes thus formed pack together in the lattice without of the COOH group are replaced by the two typical bands
–
–
any relevant additional interactions.
A visual analysis of Figure 3 (a and b) suggests that the ing consistent with the deprotonation of the COOH group.
packing mode of [HQ]2[Pb(Cl-pspa)2] is somehow arranged Only for the second class of compounds was it possible
of the carboxylate group [νas(CO2 ) and νsym(CO2 )], a find-
to provide enough space to avoid destabilizing interactions to study some examples by X-ray diffraction. This study
involving the SALEP. The resulting packing efficiency is shows (vide supra) that in [HQ]2[Pb(Cl-pspa)2] and [HQ]2-
very good (see Figure 3, c) according to the Kitaigorodskii [Pb(Br-pspa)2] the carboxylate group of the ligand acts in a
packing index[29] (68% for the Cl-pspa2– derivative and 69% monodentate manner and is hydrogen bonded to the N–H
in the Br-pspa2– complex) calculated by using the CALC group of the diisopropylammonium cation. The IR spectra
VOID routine of PLATON.[30]
of both compounds show the carboxylate bands at 1520/
1317 (Cl) and 1522/1315 cm–1 (Br) and, thus, give values of
–
203 and 207, respectively, for the parameter Δν [νas(CO2 ) –
Spectroscopy Studies
–
νsym(CO2 )]. These values are close to those found pre-
The IR spectra of the H2(X-pspa) ligands show a ν(S– viously in similar complexes[13,14,31] and, bearing in mind
H) band in the range 2590–2560 cm–1. The bands of the the effect of the hydrogen bond,[32] fall inside the general
vibrations of the –COOH groups [ν(C=O), δ(OH) and ν(C– range for monodentate carboxylate groups.[33] The lower
O)] are in the ranges 1730–1680, 1440–1395 and 1320– value found for the F derivative, 188, can be attributed to
1210 cm–1, respectively.
the presence in the lattice of a stronger hydrogen bond,
The two classes of complexes described in this paper, though the participation of the carboxylate group in some
[Pb(X-pspa)] and [HQ]2[Pb(X-pspa)2], have a common fea- additional interaction cannot be ruled out.
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–
–
The positions of the νas(CO2 ) and νsym(CO2 ) bands in cases, the use of [D4]methanol as an alternative solvent was
the [Pb(X-pspa)] complexes led to values of 166–199 for the necessary.
parameter Δν. These values fall inside the general range[33]
In the 1H NMR spectra, the benzylidene rhodanines
for bridging carboxylate groups. However, it should be show a broad singlet at δ ≈ 14 ppm, assigned to the –NH
noted that for this specific class of sulfanylpropenoate li- group. The large deshielding of this signal could be ex-
gands, we have previously found values within this range plained by the persistence in solution of the hydrogen bond
for the bridging coordination mode[14,34] or bidentate and found in the solid state.[38] The benzylidene rhodanines also
bridge[35] mode of the carboxylate group. Therefore, both show a signal at δ ≈ 7.5 ppm, which corresponds to the
coordination modes would be compatible with the experi- –CH= group, and signals between δ = 8 and 7 ppm from
mental IR data for this class of compound.
the aromatic protons. The –OH proton of HOp-Rhod was
The mass spectra of the ligand and complexes were re- observed as a broad singlet at δ = 10.4 ppm.
corded by using FAB or ESI-TOF ionization methods (see
The spectra of the H2(X-pspa) ligands show a very broad
Experimental Section). Owing to its soft character, ESI-MS lowfield signal at δ ≈ 13 ppm, assigned to the proton of
is a good approach to explore the species present in the the –COOH group, and a broad peak at δ ≈ 5 ppm attrib-
solutions of a coordination compound.[36,37] The ESI-MS uted to the SH proton. For H2(HO-pspa), a broad singlet
data for [Pb(X-pspa)] and [HQ]2[Pb(X-pspa)2] (X = Cl, Br) was observed at δ = 9.48 ppm, and this is assigned to the
in DMSO solution will be discussed as representative phenol proton.
examples of the 1:1 and 1:2 derivatives prepared in this
study.
The [Pb(X-pspa)] and [HQ]2[Pb(X-pspa)2] complexes are
more stable than the ligands in DMSO solution, and insig-
In the positive ESI spectra of the [Pb(X-pspa)] com- nificant amounts of decomposition products were observed
plexes, the dominant metallated ion is [Pb(X-pspa) + H]+ during the time necessary to record the spectra. The pres-
and this confirms the permanence of the PbII–pspa2– coor- ence of the [X-pspa-S–S-pspa-X]2– anions is easily detected
dination even in the presence of a donor solvent such as by analyzing the position of the C(3)–H signal, which ap-
DMSO. Other subsidiary peaks appear in the spectra, and pears at lower field for the disulfides than in the free ligand,
these correspond to metallated ions that in some cases con- and in the complexes it appears at higher field (vide infra).
tain DMSO. Notably, once in solution, it can be expected Accordingly, it must be concluded that the oxidized species
that the limited coordination sphere of the PbII ion will in- observed in the ESI-MS measurements are derived from de-
crease, probably by incorporation of DMSO molecules in- sorption and the ionization process in the gas phase, despite
stead of the intermolecular interactions described in the so- the soft character of ESI. The possible partial dissociation
lid state. However, the negative-ion-mode experiments sug- of [Pb(X-pspa)2]2– in DMSO solution cannot be conclu-
gest that not all [Pb(X-pspa)] molecules remain unchanged sively established. There is no duplicity of signals, including
in the gas phase because some ions derived from X-pspa2– those of the free anions, but this could be the case if free
and their disulfide, such as [X-pspa + H]– and [X-pspa-S– and coordinated (X-pspa)2– anions interchange very
S-pspa–X]2–, appear in these spectra. The latter species con- rapidly. However, the very sharp signals observed in the
tain S–S bonds and these can be formed by oxidation of X- spectra are not consistent with an interchange process.
pspa2– during the ionization process or in DMSO solution
(vide infra).
The spectra of [Pb(X-pspa)] and [HQ]2[Pb(X-pspa)2]
were compared with those of the corresponding ligand. The
The ESI(+) MS data for [HQ]2[Pb(X-pspa)2] show weak spectra of the complexes lack the signals at δ ≈ 5 and
signals for the [Pb(X-pspa)2 + 3H]+ ions but the base peaks 13 ppm, which clearly shows that the ligand is bideproton-
correspond to the protonated 1:1 derivative, which suggests ated; furthermore, the C(3)–H signal is located at higher
a partial dissociation of the 1:2 complexes in the course of field that in the corresponding ligand, which indicates that
dissolution and/or ionization. The spectra in the negative the S coordination observed in the solid state remains in
mode give complementary information in this respect. Al- solution.[39] The spectrum of [Pb(HO-pspa)] contains the
though the signals corresponding to nonmetallated oxidized signal of the –OH substituent, and this shows that this
species are again predominant, several metallated group is not deprotonated. Integration of the [HQ]2[Pb(X-
monoanions such as [Pb(X-pspa)2 + H]– (Figure 4) are sig- pspa)2] spectra is consistent with the proposed stoichiome-
nificantly abundant; therefore, the total dissociation of try in the solid state and the location of the ligand signals,
[Pb(X-pspa)2]2– in the dissolution/ionization processes can which are sensitive to metallation, in similar positions to
be excluded.
those of the corresponding [Pb(X-pspa)] compounds dis-
The NMR signals (see Experimental Section) were as- cussed above also suggest an O,S coordination mode for the
signed by considering previous data for rhodanines,[38] sul- ligands. A septuplet and a doublet at high field in the spec-
fanylpropenoic acids[34,35] and complexes,[13,14,34,39] and on tra were assigned to the –C(H) and CH3 groups of the di-
the basis of gradient heteronuclear multiple quantum co- isopropylammonium cation, and the very broad signal at δ
+
herence (gHMQC) and gHMBC experiments when neces- ≈ 8 ppm was ascribed to the NH2 moiety of [HQ]+.
sary. Freshly prepared solutions of [D6]DMSO were used
As could be expected, in the 13C NMR spectra of the
to record the spectra, but even under these conditions H2(I- ligands an important dependence of the position of the C(7)
pspa) evolved very rapidly to give new species (possibly the signal on the nature of the para-X atom was observed. In
disulfide), which were not fully characterized. In these the complexes, the S coordination was confirmed by the
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Figure 4. Comparison of the [Pb(Br-pspa)2 + H]– signals in the experimental (upper trace) and simulated (lower trace) ESI(–) MS spectra
of [HQ]2[Pb(Br-pspa)2].
large deshielding of C(2) with respect to the corresponding
According to the results of IR studies, in the solid 1:1
ligands,[13,14,34,39] and the large downfield shift of C(1) pro- complexes the PbII ion is coordinated to the ligand through
vided evidence for the coordination of the carboxylate the deprotonated sulfhydryl and carboxylate groups, and
group.
the latter possibly form bridges between two metal centres
to give a polymeric arrangement. The NMR and ESI-MS
evidence indicate that the ligand remains coordinated to the
PbII centre in DMSO solution. In the gas phase, desorption
and ionization under ESI-MS conditions favours the partial
dissociation and oxidation of the ligand. These two phe-
nomena were not observed in solution, even after several
weeks.
Conclusions
The H2(X-pspa) acids readily coordinate to the PbII ion
in ethanol/water to give 1:1 [Pb(X-pspa)] complexes. When
the reactions were performed in the presence of an excess
of diisopropylamine (Q), which facilitates the deproton-
ation of the acids and can assume the role of counterion
once protonated, 1:2 [HQ]2[Pb(X-pspa)2] complexes were
isolated (X = –Cl and –Br).
The complexes with [HQ]2[Pb(X-pspa)2] stoichiometry
consist of [Pb(X-pspa)2]2– anions connected in chains
through hydrogen bonding with the [HQ]+ anions. The
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zaldehyde were used as supplied by Aldrich. The benzylidene rhod-
anines used as precursors for the sulfanylpropenoic acids [5-(4-fluo-
robenzylidene)rhodanine (Fp-Rhod), 5-(4-chlorobenzylidene)rhod-
anine (Clp-Rhod), 5-(4-bromobenzylidene)rhodanine (Brp-Rhod),
5-(4-iodobenzylidene)rhodanine (Clp-Rhod) and 5-(4-trifluorome-
thoxybenzylidene)rhodanine (F3COp-Rhod)] were prepared by
condensation of rhodanine with the appropriate aldehyde
(Scheme 4).[41] Rhodanine (0.02 mol in 40 mL of 0.4 m NaOH) was
added to the appropriate aldehyde in a solution of acetic acid
(10 mL) and ethanol (20 mL). After stirring of the mixture at 60–
anions contain two O,S-bonded ligands, and the distribu-
tion of the Pb–O and Pb–S bonds on one side of the PbII
ion suggest the presence of a stereochemically active lone
pair. The chains are held in pairs by π-stacking interactions
and arrange in a very efficient packing mode, which seems
to be adopted to provide enough space around the lone
pair to avoid repulsive interactions. Thus, these complexes
provide an interesting example of the relevance of the lone
pair in the supramolecular structures of PbII derivatives.
ESI-MS and NMR studies were not conclusive regarding 80 °C for 30 min, the resulting solid was collected by filtration and
the partial dissociation of [Pb(X-pspa)2]2– in DMSO solu-
vacuum dried. The synthesis and characterization of [5-(4-hydroxy-
benzylidene)rhodanine (HOp-Rhod) and 5-(4-methoxybenzyl-
tion. The ESI-MS data show that this partial dissociation
idene)rhodanine (CH3Op-Rhod) were described previously.[38]
occurs in the gas phase, but the NMR measurements did
not provide any evidence of this process; this suggests that
the dissociated species in the mass spectra are formed dur-
ing the desorption and ionization processes.
The stability of the complexes in solution, even in the
presence of donor solvents, supports the possibility that
H2(X-pspa) can efficiently capture PbII ions in biological
media and reduce its lethal effects. Although the simple
complexes prepared in the present work are not soluble in
aqueous media, they could evolve in vivo to more hydro-
soluble mixed species with natural ligands, which could be
Scheme 4.
susceptible to urinary excretion. These species could also be
decorporated from the liver into the faeces by bile by taking
advantage of the lipophilic character of the aromatic ring.
Some previous evidence for the antidotic action of sulfanyl-
propenoic acids against PbII toxicity in rodents has been
published.[40]
Fp-Rhod: Yellow solid, yield 85%, m.p. 215 °C. C10H6FNOS2
(239.29): calcd. C 50.20, H 2.53, N 5.85, S 26.80; found C 49.94,
1
H 2.52, N 5.88, S 25.98. H NMR ([D6]DMSO): δ = 7.42 (s, 1 H),
7.64 (pst, 2 H), 7.36 (pst, 2 H), 13.85 (br s, 1 H) ppm.
Clp-Rhod: Yellow solid, yield 94%, m.p. 225 °C. C10H6ClNOS2
(255.75): calcd. C 46.97, H 2.36, N 5.48, S 25.07; found C 46.47,
1
H 2.26, N 5.46, S 25.57. H NMR ([D6]DMSO): δ = 7.63 (s, 1 H),
7.61 (d, 2 H), 7.61 (d, 2 H), 13.75 (br s, 1 H) ppm.
Experimental Section
Brp-Rhod: Yellow solid, yield 82%, m.p. 234 °C. C10H6BrNOS2
Material and Methods
(300.20): calcd. C 40.01, H 2.01, N 4.67, S 21.36; found C 39.92,
H 1.78, N 4.68, S 21.32. H NMR ([D6]DMSO): δ = 7.61 (s, 1 H),
7.73 (d, 2 H), 7.53 (d, 2 H), 13.87 (br s, 1 H) ppm.
1
Elemental analyses were performed with a Carlo Erba 1108 micro-
analyzer. Melting points were determined with a Büchi apparatus.
Mass spectra were recorded by using FAB (Micro mass Autospec
spectrometer connected to a DS90 system, m-nitrobenzyl alcohol,
Xe, 8 eV; ca. 1.28ϫ 10–15 J) and ESI-TOF (positive and negative-
ion mode, Microtof® from Bruker Daltonics, DMSO, capillary
voltage 4.5 kV) ionization methods. IR spectra (from KBr pellets
or Nujol mulls) were recorded with a Bruker IFS66V FTIR spec-
trometer and are reported in the synthesis section with the follow-
ing abbreviations: vs = very strong, s = strong, m = medium, w =
Ip-Rhod: Yellow solid, yield 85%, m.p. 245 °C. C10H6INOS2
(347.20): calcd. C 34.60, H 1.74, N 4.03, S 18.47; found C 34.68,
1
H 1.72, N 4.04, S 18.39. H NMR ([D6]DMSO): δ = 7.56 (s, 1 H),
7.89 (d, 2 H), 7.35 (d, 2 H), 13.86 (br s, 1 H) ppm.
F3COp-Rhod: Yellow solid, yield 95%, m.p. 170 °C. C11H6F3NO2S2
(305.30): calcd. C 43.28, H 1.98, N 4.59, S 21.00; found C 43.01,
1
H 1.90, N 4.59, S 21.55. H NMR ([D6]DMSO): δ = 7.61 (s, 1 H),
7.57 (d, 2 H), 7.10 (d, 2 H), 13.77 (br s, 1 H) ppm.
weak, sh = shoulder, br. = broad. H and 13C NMR spectra were
1
Synthesis of Ligands: 3-(2-Aryl)-2-sulfanylpropenoic acids [H2(X-
pspa)] were prepared by hydrolysis of the appropriate benzylidene
rhodanine precursor (10–2 mol) in an alkaline medium (50 mL of
1 m NaOH) (Scheme 4). After stirring under reflux for 30 min, the
solution was cooled and neutralized with 1 m HCl. The resulting
solid was collected by filtration and vacuum dried. The synthesis
and characterization of H2(CH3O-pspa) were described pre-
viously.[32]
recorded at room temperature with a Bruker DPX 250 spectrome-
ter operating at 250.13 MHz, a Varian Mercury-300 or a Varian
Inova 400 system operating at 399.97 and 100.58 MHz or a Varian
Inova 500 spectrometer operating at 500.14 and 125.76 MHz with
5 mm o.d. tubes in [D6]DMSO or [D4]MeOD. Chemical shifts are
reported relative to tetramethylsilane (TMS) by using the solvent
signal (δ1H = 2.50 ppm, δ13C = 39.5 ppm and δ1H = 3.31 ppm,
δ13C = 49.00 ppm for DMSO and methanol, respectively) as refer-
ence. The signals are described as follows: chemical shift, multi-
plicity (s = singlet, d = doublet, dd = doublet of doublets, t =
triplet, pst = pseudotriplet, q = quadruplet, sept = septuplet, br. =
broad, vbr. = very broad). See Scheme 2 for atom numbering
scheme. The low solubility of the compounds precluded 207Pb
NMR experiments.
H2(F-pspa): Beige solid, yield 63%. Mp 115 °C. C9H7FO2S
(198.22): calcd. C 54.54, H 3.56, S 16.17; found C 54.88, H 3.19, S
16.82. MS (EI): m/z (%) = 197 (77) [M – H]+, 153 (100) [M –
COOH]+. IR (KBr): ν = 1668 [vs, ν(C=O)], 1421 [s, δ(OH)], 1234
˜
[vs, ν(C–O)], 2577 [s, ν(S–H)] cm–1. 1H NMR ([D6]DMSO): δ =
13.35 (vbr. s, 1 H, 1-OH), 5.34 (vbr. s, 1 H, 2-H), 7.73 (s, 1 H, 3-
3
3
Rhodanine, 4-fluorobenzaldehyde, 4-chlorobenzaldehyde, 4-bro-
mobenzaldehyde, 4-iodobenzaldehyde and 4-trifluoromethoxyben-
H), 7.73 (dd, J1H,1H = 7.7, J1H,19 = 5.8 Hz, 2 H, 5-H and 9-H),
F
3
3
7.31 (pst, J1H,1H = 7.8, J1H,19 = 7.8 Hz, 2 H, 6-H and 8-H) ppm.
F
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13C NMR ([D6]DMSO): δ = 166.3 (C-1), 124.0 (C-2), 132.5 (C-3), 0.51 mmol) in water (20 mL). The reaction mixture was stirred for
4
3
13C,19
131.5 (d, J
F
2
13C,19
F
= 2.46 Hz, C-4], 132.0 (d, J = 8.4 Hz, C-5,
3 h, and the resulting solid was isolated.
1
13C,19
F
F
C-9), 115.8 (d, J
248.3 Hz, C-7] ppm.
= 21.66 Hz, C-6, C-8), 161.9 (d, J1C,19 =
[Pb(F-pspa)]: Beige solid, yield 93%. C9H5FO2PbS (403.42): calcd.
C 26.80, H 1.25, S 7.95; found C 26.29, H 1.14, S 7.41. MS (FAB):
H2(Cl-pspa): Beige solid, yield 43%. Mp 175 °C. C9H7ClO2S
m/z (%) = 405 (30) [Pb(F-pspa) + H]+. IR (KBr): ν = 1504 [vs,
˜
νa(CO2 )], 1323 [s, νs(CO2 )] cm–1. 1H NMR ([D6]DMSO): δ = 7.53
–
–
(214.67): calcd. C 50.36, H 3.29, S 14.93; found C 50.18, H 3.11, S
14.96. MS (EI): m/z (%) = 213 (88) [M – H]+, 169 (100) [M – (s, 1 H, 3-H), 8.07 (dd, 2 H, 5-H and 9-H), 7.17 (pst, 2 H, 6-H and
COOH]+. IR (KBr): ν = 1684 [vs, ν(C=O)], 1421 [s, δ(OH)], 1258
8-H) ppm. 13C NMR ([D6]DMSO): δ = 182.7 (C-1), 137.5 (C-2),
133.1 (C-3), 134.1 (C-4), 132.5 (d, 3J
= 8.4 Hz, C-5, C-9),
˜
[vs, ν(C–O)], 2571 [s, ν(S–H)] cm–1. 1H NMR ([D6]DMSO): δ =
13.29 (vbr. s, 1 H, 1-OH), 5.41 (vbr. s, 1 H, 2-H), 7.71 (s, 1 H, 3-
H), 7.69 (d, 2 H, 5-H and 9-H), 7.54 (d, 2 H, 6-H and 8-H) ppm.
13C NMR ([D6]DMSO): δ = 166.2 (C-1), 125.3 (C-2), 132.1 (C-3),
133.3 (C-4), 131.4 (C-5 and C-9), 128.8 (C-6 and C-8), 133.8 (C-7)
ppm. Single crystals were grown by slow evaporation of a dichloro-
methane solution.
13C,19
F
114.7 (d, 2J
= 21.6 Hz, C-6, C-8), 160.6 (d, 1J
=
13C,19
F
13C,19
F
248.3 Hz, C-7) ppm.
[Pb(Cl-pspa)]: Orange solid, yield 78%. C9H5ClO2PbS (419.87):
calcd. C 25.75, H 1.20, S 7.64; found C 25.51, H 1.08, S 7.22. MS
(FAB): m/z (%) = 421 (10) [Pb(Cl-pspa) + H]+. MS (ESI+): m/z
(%) = 840 (5) [Pb2(Cl-pspa)2 + H]+, 710 (2) [Pb(Cl-pspa)2 + DMSO
+ 3H]+, 635 (5) [Pb(Cl-pspa)2 + 3H]+, 498 (2) [Pb(Cl-pspa) +
DMSO + H]+, 443 (4) [Pb(Cl-pspa) + Na]+, 421 (100) [Pb(Cl-pspa)
H2(Br-pspa): Beige solid, yield 58%. Mp 175 °C. C9H7BrO2S
(259.12): calcd. C 41.72, H 2.72, S 12.37; found C 41.63, H 2.57, S
11.59. MS (EI): m/z (%) = 259 (100) [M – H]+, 215 (70) [M – + H]+. MS (ESI–): m/z (%) = 427 (5) [(Cl-pspa-S–S-pspa-Cl) +
COOH]+. IR (KBr): ν = 1681 [vs, ν(C=O)], 1416 [s, δ(OH)], 1269
H]–, 319 (12) [(Cl-pspa-S–S-pspa-Cl)–COOH–COSH + H]–, 214
˜
[vs, ν(C–O)], 2561 [s, ν(S–H)] cm–1. 1H NMR ([D6]DMSO): δ =
13.20 (vbr. s, 1 H, 1-OH), 5.31 (vbr. s, 1 H, 2-H), 7.78 (s, 1 H, 3-
H), 7.65 (d, 2 H, 5-H and 9-H), 7.60 (d, 2,6-H and 8-H) ppm. 13C
NMR ([D6]DMSO): δ = 166.1 (C-1), 125.4 (C-2), 132.1 (C-3), 134.0
(40) [Cl-pspa + H]–, 213 (84) [(Cl-pspa-S–S-pspa-Cl)]2–, 197 (12)
[Cl-pspa–OH + H]–, 169 (100) [Cl-pspa–COO]–. IR (KBr): ν =
˜
1514 [vs, νa(CO2 )], 1321 [vs, νs(CO2 )] cm–1. 1H NMR ([D6]-
DMSO): δ = 7.45 (s, 1 H, 3-H), 8.00 (d, 2 H, 5-H and 9-H), 7.36
–
–
(C-4), 131.6 (C-5 and C-9), 131.5 (C-6 and C-8), 122.0 (C-7) ppm. (d, 2 H, 6-H and 8-H) ppm. 13C NMR ([D6]DMSO): δ = 182.1 (C-
1), 140.1 (C-2), 132.2 (C-3), 136.6 (C-4), 132.0 (C-5 and C-9), 127.7
(C-6 and C-8), 130.1 (C-7) ppm.
H2(I-pspa): Beige solid, yield 75%. Mp 160 °C. C9H7IO2S (306.12):
calcd. C 35.31, H 2.30, S 10.47; found C 35.94, H 2.34, S 9.73. MS
(EI): m/z (%) = 305 (100) [M – H]+, 261 (100) [M – COOH]+. IR
[Pb(Br-pspa)]: Orange solid, yield 67%. C9H5BrO2PbS (464.32):
(KBr): ν = 1676 [vs, ν(C=O)], 1414 [s, δ(OH)], 1256 [vs, ν(C–O)],
calcd. C 23.28, H 1.09, S 6.90; found C 23.72, H 0.96, S 6.51. MS
˜
1
2559 [s, ν(S–H)] cm–1. H NMR ([D6]DMSO): δ = 13.50 (vbr. s, 1 (ESI+): m/z (%) = 929 (1) [Pb2(Br-pspa)2 + H]+, 803 (31) [Pb(Br-
H, 1-OH), 7.65 (s, 1 H, 3-H), 7.83 (d, 2 H, 5-H and 9-H), 7.46 (d, pspa)2 + DMSO + 3H]+, 725 (28) [Pb(Br-pspa)2 + 3H]+, 541 (3)
2 H, 6-H and 8-H) ppm. 13C NMR ([D4]MeOD): δ = 167.9 (C-1),
[Pb(Br-pspa) + DMSO + H]+, 487 (3)[Pb(Br-pspa) + Na]+, 465
126.3 (C-2), 134.1 (C-3), 136.2 (C-4), 138.9 (C-5 and C-9), 132.6 (100) [Pb(Br-pspa) + H]+. MS (ESI–): m/z (%) = 537 (2) [(Br-pspa-
(C-6 and C-8), 95.4 (C-7) ppm.
S–S-pspa-Br) + Na]–, 515 (41) [(Br-pspa-S–S-pspa-Br) + H]–, 258
(93), [Br-pspa + H]–, 257 (100) [(Br-pspa-S–S-pspa-Br)]2–, 242 (9)
H2(F3CO-pspa): Beige solid, yield 79%. Mp 102 °C. C10H7F3O3S
(264.22): calcd. C 45.46, H 2.67, S 12.13; found C 45.80, H 2.75, S
11.69. MS (EI): m/z (%) = 527 (8) [2M – H]+, 263 (100) [M – H]+,
[Br-pspa–OH + H]–, 213 (51) [Br-pspa–COO]–. IR (KBr): ν = 1516
˜
–
–
1
[vs, νa(CO2 )], 1319 [vs, νs(CO2 )] cm–1. H NMR ([D6]DMSO): δ
= 7.43 (s, 1 H, 3-H), 7.94 (d, 2 H, 5-H and 9-H), 7.49 (d, 2 H, 6-
H and 8-H) ppm. 13C NMR ([D6]DMSO): δ = 182.1 (C-1), 140.3
(C-2), 132.2 (C-3), 136.9 (C-4), 132.3 (C-5 and C-9), 130.6 (C-6
and C-8), 118.7 (C-7) ppm.
247 (25) [M – OH]+, 219 (89) [M – COOH]+. IR (KBr): ν = 1668
˜
[vs, ν(C=O)], 1425 [s, δ(OH)], 1254 [vs, ν(C–O)], 2584 [s, ν(S–H)]
1
cm–1. H NMR ([D6]DMSO): δ = 13.19 (vbr. s, 1 H, 1-OH), 7.76
(s, 1 H, 3-H), 8.52 (d, 2 H, 5-H and 9-H), 7.79 (d, 2 H, 6-H and
8-H) ppm. 13C NMR ([D6]DMSO): δ = 166.3 (C-1), 125.8 (C-2),
[Pb(I-pspa)]: Orange solid, yield 77%. C9H5IO2PbS (511.32): calcd.
132.0 (C-3), 134.3 (C-4), 131.7 (C-5 and C-9), 121.2 (C-6 and C-
C 21.14, H 0.99, S 6.27; found C 21.35, H 1.18, S 5.84. IR (KBr):
1
–
–
1
8), 148.1 (C-7), 116.1 (q, J
= 256.9 Hz, C-10) ppm.
ν = 1516 [vs, ν (CO )], 1317 [vs, ν (CO )] cm–1. H NMR ([D ]-
˜
a 2 s 2 6
13C,19
F
DMSO): δ = 7.40 (s, 1 H, 3-H), 7.80 (d, 2 H, 5-H and 9-H), 7.66
(d, 2 H, 6-H and 8-H) ppm. 13C NMR ([D6]DMSO): δ = 182.1 (C-
1), 140.6 (C-2), 132.3 (C-3), 137.2 (C-4), 132.5 (C-5 and C-9), 136.5
(C-6 and C-8), 91.5 (C-7) ppm.
H2(HO-pspa): Brown solid, yield 54%. Mp 165 °C. C9H8O3S
(196.23): calcd. C 55.09, H 4.11, S 16.34; found C 54.94, H 4.08, S
15.96. MS (EI): m/z (%) = 195 (100) [M – H]+, 178 (3) [M –
OH]+, 150 (100) [M – COOH]+. IR (KBr): ν = 1686 [vs, ν(C=O)],
˜
1443 [vs, δ(OH)], 1256 [vs, ν(C–O)], 2580 [m, ν(S–H)] cm–1. 1H [Pb(CH3O-pspa)]: Yellow solid, yield 95%. C10H8O3PbS (415.45):
NMR ([D6]DMSO): δ = 13.29 (vbr. s, 1 H, 1-OH), 5.12 (vbr. s, 1
calcd. C 28.91, H 1.94, S 7.72; found C 28.80, H 1.90, S 7.49. MS
H, 2-SH), 7.66 (s, 1 H, 3-H), 7.55 (d, 2 H, 5-H and 9-H), 6.86 (d,
(FAB): m/z (%) = 417 (49) [Pb(CH O-pspa) + H]+. IR (KBr): ν =
˜
3
–
2 H, 6-H and 8-H), 10.05 (br s, 1 H, 7-OH) ppm. 13C NMR 1503 [vs, νa(CO2 )], 1329 [s, νs(CO2 )] cm–1. 1H NMR ([D6]DMSO):
–
([D6]DMSO): δ = 169.9 (C-1), 118.9 (C-2), 125.7 (C-3), 134.0 (C-
4), 131.8 (C-5 and C-9), 115.6 (C-6 and C-8), 158.4 (C-7) ppm.
δ = 7.45 (s, 1 H, 3-H), 7.94 (d, 2 H, 5-H and 9-H), 6.90 (d, 2 H, 6-
H and 8-H), 3.75 (s, 3 H, CH3O) ppm. 13C NMR ([D6]DMSO): δ
= 182.9 (C-1), 135.1 (C-2), 133.9 (C-3), 130.3 (C-4), 131.9 (C-5 and
C-9), 113.9 (C-6 and C-8), 157.6 (C-7), 54.9 CH3O ppm.
Synthesis of Complexes: The [Pb(X-pspa)] complexes were prepared
by the same general method: to a solution of lead(II) acetate trih-
ydrate in water was added a solution of the appropriate sulfanylcar-
boxylic acid in ethanol until a 1:1 molar ratio was achieved. The
mixture was stirred for several hours, and the resulting solid was
separated by centrifugation and dried under vacuum. For example,
a solution of H2(F-pspa) (0.10 g, 0.51 mmol) in ethanol (10 mL)
was added to a solution of lead(II) acetate trihydrate (0.19 g,
[Pb(F3CO-pspa)]: Yellow solid, yield 82%. C10H5F3O3PbS (469.42):
calcd. C 25.59, H 1.07, S 6.83; found C 25.94, H 0.91, S 6.40. MS
(FAB): m/z (%) = 471 (50) [Pb(F CO-pspa) + H]+. IR (KBr): ν =
˜
3
–
–
1506 [vs, νa(CO2 )], 1314 [vs, νs(CO2 )] cm–1. 1H NMR ([D6]-
DMSO): δ = 7.50 (s, 1 H, 3-H), 8.90 (d, 2 H, 5-H and 9-H), 7.31
(d, 2 H, 6-H and 8-H) ppm. 13C NMR ([D6]DMSO): δ = 182.1 (C-
Eur. J. Inorg. Chem. 2013, 5110–5120
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FULL PAPER
1), 140.5 (C-2), 131.9 (C-3), 137.2 (C-4), 132.1 (C-5 and C-9), 120.4
X-ray Crystal Structure Determination Studies: Single crystals were
mounted on glass fibres in a Bruker APEXII automatic dif-
fractometer, and data were collected at 293 K (or 110 K) with Mo-
Kα radiation (λ = 0.71073 Å). Corrections for Lorentz effects, po-
larization[42] and absorption[43] were made.
(C-6 and C-8), 146.1 (C-7), 120.2 (q, 1J
= 255.8 Hz, OCF3)
13C,19
F
ppm.
[Pb(HO-pspa)]: Red solid, yield 74%. C9H6O3PbS (401.43): calcd.
C 26.93, H 1.51, S 7.99; found C 26.72, H 1.73, S 7.95. MS (FAB):
Structure analyses were performed by direct methods.[44] Least-
squares full-matrix refinements on F2 were performed by using the
program SHELXL97.[44] Atomic scattering factors and anomalous
dispersion corrections for all atoms were taken from International
Tables for Crystallography.[45] All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were refined as riders at geometri-
cally calculated positions. Graphics were obtained with ORTEP-
3[46] and MERCURY.[47] The main crystal and refinement param-
eters for the compounds are given in Tables 3 and S3.
m/z (%) = 402 (4) [Pb(OH-pspa) + H]+. IR (KBr): ν = 1493 [vs,
˜
νa(CO2 )], 1329 [vs, νs(CO2 )] cm–1. 1H NMR ([D6]DMSO): δ =
7.43 (s, 1 H, 3-H), 7.82 (d, 2 H, 5-H and 9-H), 6.72 (d, 2 H, 6-H
and 8-H), 9.48 (br s, 1 H, 7-OH) ppm. 13C NMR ([D6]DMSO): δ
= 183.2 (C-1), 133.6 (C-2), 134.6 (C-3), 128.7 (C-4), 132.2 (C-5 and
C-9), 114.7 (C-6 and C-8), 156.1 (C-7) ppm.
–
–
The [HQ]2[Pb(X-pspa)2] complexes were prepared by following the
same general method: to a mixture of lead(II) acetate trihydrate
and diisopropylamine (Q) in ethanol was added a solution of the
appropriate sulfanylcarboxylic acid in the same solvent until a mo-
lar ratio of ca. 1:4:2 was achieved. The mixture was stirred at room
temperature, and the resulting solid was separated by centrifuga-
tion and dried under vacuum. For example, to a mixture of lead(II)
acetate trihydrate (0.18 g, 0.47 mmol) and diisopropylamine (Q,
0.26 mL, 1.9 mmol) in ethanol (15 mL) was added a solution of
H2(Cl-pspa) (0.20 g, 0.93 mmol) in ethanol (15 mL). The mixture
was stirred for 3 h, and the resulting solid was isolated.
Table 3. Crystal and refinement data for [H2(Cl-pspa)] and
[HQ]2[Pb(Cl-pspa)2].
Compound
[H2(Cl-pspa)]
[HQ]2 [Pb(Cl-pspa2)]
Empirical formula
M
C9H7ClO2S
214.66
C30H42Cl2N2O4PbS2
836.87
T [K]
293(2)
110.0(1)
monoclinic
P21/c
21.363(5)
10.531(3)
15.110(4)
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
triclinic
¯
P1
5.8339(14)
9.069(2)
9.940(3)
111.421(4)
104.628(4)
93.247(4)
467.2(2)
2
[HQ]2[Pb(Cl-pspa)2]: Beige solid, yield 48%. C30H42Cl2N2O4S2Pb
(836.93): calcd. C 43.06, H 5.06, N 3.35, S 7.66; found C 43.55, H
5.57, N 3.42, S 8.03. MS (FAB): m/z (%) = 421 (10) [Pb(Cl-pspa)
+ H]+. MS (ESI+): m/z = 710 (2) [Pb(Cl-pspa)2 + DMSO + 3H]+,
635 (5) [Pb(Cl-pspa)2 + 3H]+, 498 (2) [Pb(Cl-pspa) + DMSO +
H]+, 443 (4) [Pb(Cl-pspa) + Na]+, 421 (100) [Pb(Cl-pspa) + H]+.
MS (ESI–): m/z (%) = 871 (4) [Pb(Cl-pspa)3 + 2H + Na]–, 847 (26)
[Pb(Cl-pspa)3 + 3H]–, 633 (37) [Pb(Cl-pspa)2 + H]–, 480 (100) [(Cl-
pspa–S3–pspa-Cl) + Na]–, 449 (5) [(Cl-pspa-S–S-pspa-Cl) + Na]–,
427 (86) [(Cl-pspa-S–S-pspa-Cl) + H]–, 383 (8) [(Cl-pspa-S–S-pspa-
97.227(4)
γ [°]
V [Å3]
3372.3(15)
4
1.648
5.321
1664
Z
Dcalcd. [Mg/m3]
μ [mm–1]
F (000)
Crystal size [mm]
1.526
0.592
220
0.40ϫ0.30ϫ0.23 0.12ϫ0.10ϫ0.05
Cl)–COO + H]–, 319(3) [(Cl-pspa-S–S-pspa-Cl)–COOH–COSH +
θ range for data collec- 2.30 to 28.02
1.92 to 26.37
H]–. IR (KBr): ν = 1609 [vs, δ(NH +)], 1520 [vs, νa(CO2 )], 1317
–
˜
2
tion [°]
Reflections collected
Unique reflections,
–
[vs, νs(CO2 )] cm–1. 1H NMR ([D6]DMSO): δ = 7.38 (s, 2 H, 3-H),
3047
2131 [0.0179]
37283
6866 [0.0823]
8.06 (d, 4 H, 5-H and 9-H), 7.29 (d, 4 H, 6-H and 8-H), 1.18 (d,
24 H, CH3), 3.29 (sept, 4 H, CH), 8.92 (br s, 4 H, NH2+) ppm. 13
C
[R(int)
]
NMR ([D6]DMSO): δ = 179.9 (C-1), 143.8 (C-2), 129.1 (C-3), 137.7
(C-4), 131.2 (C-5 and C-9), 127.3 (C-6 and C-8), 131.2 (C-7), 19.1
(CH3 HQ), 45.8 (CH HQ) ppm. Single crystals were grown by slow
evaporation of the mother liquor.
Final R1, wR2
[I Ͼ 2σ(I)]
0.0467, 0.1206
0.0367, 0.0776
CCDC-922806 [for H2(Cl-pspa)], -922807 {for [HQ]2[Pb(Cl-
pspa)2]} and -922808 {for [HQ]2[Pb(Br-pspa)2]} contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[HQ]2[Pb(Br-pspa)2]: Beige solid, yield 54%. PbC30H42Br2N2O4S2
(925.83): calcd. C 38.92, H 4.57, N 3.03, S 7.22; found C 38.76, H
4.67, N 3.02, S 6.93. MS (FAB): m/z (%) = 465 (54) [Pb(Br-pspa)
+ H]+. MS (ESI+): m/z (%) = 803 (6) [Pb(Br-pspa)2 + DMSO +
3H]+, 725 (6) [Pb(Br-pspa)2 + 3H]+, 541 (8) [Pb(Br-pspa) + DMSO
+ H]+, 487 (4) [Pb(Br-pspa) + Na]+, 465 (100) [Pb(Br-pspa) +
H]+. MS (ESI–): m/z (%) = 1004 (2) [Pb(Br-pspa)3 + 2H + Na]–,
745 (16) [Pb(Br-pspa)2 + Na]–, 723 (21) [Pb(Br-pspa)2 + H]–, 570
(100) [(Br-pspa–S3–pspa-Br) + Na]–, 537 (8) [(Br-pspa-S–S-pspa-
Br) + Na]–, 515 (57) [(Br-pspa-S–S-pspa-Br) + H]–, 471 (7) [(Br-
pspa-S–S-pspa-Br)–COO + H]–, 425 (5) [(Br-pspa-S–S-pspa-Br)–
Supporting Information (see footnote on the first page of this arti-
cle): Crystallographic data for [HQ]2[Pb(Br-pspa)2].
Acknowledgments
The authors would like to thank the Spanish Ministry of Education
and Science (MEC) for financial support under Project CTQ 2006-
11805, the Spanish Ministry of Education and Innovation (MIC-
INN) for Project CTQ 2009-10738, and the Dirección Xeral de
I+D, Xunta de Galicia, Spain (IN845B-2010/121).
COOH–COSH + H]–, 258 (5) [HBr-pspa]–, 257 (4) [(Br-pspa-S–S-
pspa-Br)]2–. IR (KBr): ν = 1609 [vs, δ(NH +)], 1522 [vs, νa(CO2 )],
–
˜
2
1315 [vs, νs(CO2 )] cm–1. H NMR ([D6]DMSO): δ = 7.43 (s, 2 H,
3-H), 8.02 (d, 4 H, 5-H and 9-H), 7.40 (d, 4 H, 6-H and 8-H), 1.20
(d, 24 H, CH3), 3.32 (sept, 4 H, CH), 8.23 (br s, 4 H, NH2+) ppm.
13C NMR ([D6]DMSO): δ = 179.3 (C-1), 144.3 (C-2), 129.3 (C-3),
137.8 (C-4), 131.5 (C-5 and C-9), 130.3 (C-6 and C-8), 117.5 (C-
7), 19.2 (CH3 HQ), 46.0 (CH HQ) ppm. Single crystals were grown
by slow evaporation of the mother liquor.
–
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Received: May 16, 2013
Published Online: August 16, 2013
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