Back to the coordination modes of the thiosemicarbazonate chain: New insights from diorganolead(IV) and lead(II) derivatives of isatin-3- thiosemicarbazone

Article abstract of DOI:10.1002/ejic.201000669

The syntheses and characterizations of the new heteroleptic complexes [PbPh₂(OAc)(N²-L¹)]?MeOH?EtOH, [PbPh₂(OAc)(N³-L²)]?H₂O, [Pb(OAc)(N²-L¹)], [Pb(OAc)(N³-L ¹)]?3H₂O and [Pb(OAc)(N²-L²)] {HL¹ = isatin-3-thiosemicarbazone, HL² = isatin-3-(N ¹-methylthiosemicarbazone); N²-L^x = thiosemicarbazonate bound through O,S and the hydrazinic [N(2)] nitrogen atom; N³-L^x = thiosemicarbazonate bound through the O,S and the iminic [N(3)] nitrogen atom} are described. The single-crystal X-ray structures of HL², [PbPh₂(OAc)(N²-L¹)] ?MeOH?EtOH, [PbPh₂(OAc)(N³-L²)] ?H₂O, [Pb(OAc)(N²-L¹)] and [Pb(OAc)(N ³-L¹)]?3H₂O have been solved. The organometallic compounds [PbPh₂(OAc)(N²-L ¹)]?MeOH?EtOH and [PbPh₂(OAc)(N ³-L²)]?H₂O have a roughly similar distorted bipyramidal pentagonal stereochemistry, with apical phenyl groups and both the O,N^x,S-coordinated L^x- and the anisobidentate AcO^- ligands in the equatorial plane. In [PbPh₂(OAc) (N²-L¹)]?MeOH?EtOH, the (N²-L ¹)^- ligand forms a four- and a six-membered chelate ring with the metal, whereas in PbPh₂(OAc)(N³-L ²)]?H₂O the two chelate rings formed by (N ³-L²)^- are five-membered. The Pb^II complexes, [Pb(OAc)(N²-L¹)] and [Pb(OAc)(N ³-L¹)], which were isolated from the same solution, are linkage isomers. These compounds have a rather irregular stereochemistry that suggests the presence of a stereochemically active lone electron pair; in [Pb(OAc)(N²-L¹)] the (L¹)^- ligand is O,N²,S-coordinated and in [Pb(OAc)(N³-L¹)] this ligand is O,N³,S-coordinated. Analyses of all these systems in solution by ¹H and ¹³C NMR spectroscopy showed that during synthesis the kinetically controlled O,N²,S isomer formed first due to the rigidity of the ligand. If the compound remains in solution, slow partial evolution to the O,N³,S isomer occurs. DFT calculations predict that [Pb(OAc)(N³-L¹)] is slightly more stable than [Pb(OAc)(N²-L¹)] both in the gas phase and in DMSO solution. The calculations also modelled structures for the two isomers close to those obtained by X-ray diffraction studies. Solid state and solution studies indicated that, in the title derivatives, the thiosemicarbazone chain is initially bound by N²,S coordination, but evolves with time to form the N³,S-linkage isomer.

Full text of DOI:10.1002/ejic.201000669

FULL PAPER
DOI: 10.1002/ejic.201000669
Back to the Coordination Modes of the Thiosemicarbazonate Chain:
New Insights from Diorganolead(IV) and Lead(II) Derivatives of
Isatin-3-thiosemicarbazone
José S. Casas,*[a] Noelia Casanova,[a] María S. García-Tasende,[a] Agustín Sánchez,[a]
José Sordo,[a] Ángeles Touceda,[a] and Saulo Vázquez[b]
Keywords: Lead / Coordination modes / Thermodynamics
The syntheses and characterizations of the new heteroleptic
complexes [PbPh2(OAc)(N2-L1)]·MeOH·EtOH, [PbPh2(OAc)-
(N3-L2)]·H2O, [Pb(OAc)(N2-L1)], [Pb(OAc)(N3-L1)]·3H2O and
whereas in PbPh2(OAc)(N3-L2)]·H2O the two chelate rings
formed by (N3-L2)– are five-membered. The PbII complexes,
[Pb(OAc)(N2-L1)] and [Pb(OAc)(N3-L1)], which were isolated
from the same solution, are linkage isomers. These com-
pounds have a rather irregular stereochemistry that suggests
the presence of a stereochemically active lone electron pair;
in [Pb(OAc)(N2-L1)] the (L1)– ligand is O,N2,S-coordinated
and in [Pb(OAc)(N3-L1)] this ligand is O,N3,S-coordinated.
Analyses of all these systems in solution by 1H and 13C NMR
spectroscopy showed that during synthesis the kinetically
controlled O,N2,S isomer formed first due to the rigidity of
the ligand. If the compound remains in solution, slow partial
evolution to the O,N3,S isomer occurs. DFT calculations pre-
dict that [Pb(OAc)(N3-L1)] is slightly more stable than
[Pb(OAc)(N2-L1)] both in the gas phase and in DMSO solu-
tion. The calculations also modelled structures for the two
isomers close to those obtained by X-ray diffraction studies.
[Pb(OAc)(N2-L2)] {HL1 = isatin-3-thiosemicarbazone, HL2
=
isatin-3-(N1-methylthiosemicarbazone); N2-Lx
= thiosemi-
carbazonate bound through O,S and the hydrazinic [N(2)] ni-
trogen atom; N3-Lx = thiosemicarbazonate bound through
the O,S and the iminic [N(3)] nitrogen atom} are described.
The single-crystal X-ray structures of HL2, [PbPh2(OAc)(N2-
L1)]·MeOH·EtOH, [PbPh2(OAc)(N3-L2)]·H2O, [Pb(OAc)(N2-
L1)] and [Pb(OAc)(N3-L1)]·3H2O have been solved. The orga-
nometallic compounds [PbPh2(OAc)(N2-L1)]·MeOH·EtOH
and [PbPh2(OAc)(N3-L2)]·H2O have a roughly similar dis-
torted bipyramidal pentagonal stereochemistry, with apical
phenyl groups and both the O,Nx,S-coordinated Lx– and the
anisobidentate AcO– ligands in the equatorial plane. In
[PbPh2(OAc)(N2-L1)]·MeOH·EtOH, the (N2-L1)– ligand forms
a four- and a six-membered chelate ring with the metal,
of an N3···H–N1 hydrogen bond, so coordination mode A
in Scheme 2 involves the spatial rearrangement of the free
ligand (with the S atom trans to N3) by rotating the thio-
amide group 180° around the N2–C1 bond.
Introduction
Although thiosemicarbazones (HTSC, Scheme 1) are
weakly acidic molecules (pKa ≈ 11–12),[1] in the presence of
metal ions they easily lose a proton from the N3-N2H moi-
ety to generate the thiosemicarbazonate anion, which
adopts the tautomeric thiolic form (TSC–, Scheme 1). This
form reacts with the metal ion and gives stable complexes
that, in the solid state, usually contain the TSC– ligand
bound to the Mn+ species through the thiolic sulfur and the
azamethinic nitrogen (N3), giving rise to a five-membered
chelate ring (A, Scheme 2). When R3 and/or R4 are hydro-
gen atoms, the general conformation of HTSC is that
shown in Scheme 1. This arrangement allows the formation
Scheme 1.
[a] Departamento de Química Inorgánica, Facultade de Farmacia,
Universidade de Santiago de Compostela,
15782 Santiago de Compostela, Galicia, Spain
Fax: +34-981-547102
E-mail: sergio.casas@usc.es
[b] Departamento de Química Física, Facultade de Química,
Universidade de Santiago de Compostela,
Scheme 2.
15782 Santiago de Compostela, Galicia, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000669.
The isolation and structural identification of (p-
anisaldehyde thiosemicarbazonato)dimethylthallium(III)[2]
View this journal online at
wileyonlinelibrary.com
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Eur. J. Inorg. Chem. 2010, 4992–5004

Back to the Coordination Modes of the Thiosemicarbazonate Chain
showed that another coordination mode for the thiosemi- presence of the R groups, but it is very often influenced
carbazonate chain is possible, namely, N2,S-chelation (B, by a stereochemically active lone electron pair that heavily
Scheme 2). In this case, in which a less stable four-mem- restricts the spatial distribution of the PbII–ligand donor
bered chelate ring is formed, large changes in the structure bonds.[13] In the present work it will therefore be possible
of the free ligand are not needed. Since this first example to explore if the existence of significant differences in the
of N2,S-chelation was described, more than forty complexes steric demand of the metal centre can influence the O,N2,S-
with coordination mode B have been identified by X-ray or O,N3,S-coordination mode adopted by the selected li-
diffraction (CSD[3]) – although this number is still a very gands (hereafter denoted N2-Lx-coordination and N3-Lx-
low percentage of all the thiosemicarbazonates studied to coordination).
date.
There have been several attempts to rationalize the for-
Results and Discussion
mation of a four-membered chelate ring instead of the more
usual five-membered ring. For example, Bhattacharya et
al.[4] suggested that the size of the C2-substituent trans to
N2 (R2, Scheme 1) determines the coordination mode, with
the unusual N2,S-coordination sterically favoured by the
bulky R2 groups. Subsequent contributions[5,6] support the
idea that coordination may be determined by small differ-
ences in weak bonding interactions and/or by the steric
requirements of the packing.
In the work described here, an analysis of the interaction
between isatin-3-thiosemicarbazone (HL1) and isatin-3-(N1-
methylthiosemicarbazone) (HL2) with diphenyllead(IV) and
lead(II) was carried out. The results shed new light on the
coordination modes of the thiosemicarbazonate chain. Isa-
tin-based thiosemicarbazones (Scheme 3) have very interest-
ing chemotherapeutic properties[7] that, in some cases, are
amplified by the presence of metal ions such as CuII.[8] Al-
though the role of metal complexes in this amplification has
been questioned,[9] it is somewhat surprising that very little
attention has been payed to the coordination chemistry of
isatin thiosemicarbazones in general and, in particular, to
the structural characterization of their complexes. Accord-
ing to the limited information available, isatin-3-thio-
semicarbazonates behave mainly as O,N3,S-tridentate li-
gands,[10,11] although some N3,S-chelates have also been
identified.[12]
The complexes were obtained by adding a freshly pre-
pared solution of PbPh2(OAc)2 or Pb(OAc)2·3H2O in meth-
anol (see Exp. Section) to a solution of the corresponding
thiosemicarbazone in ethanol or methanol. The [PbPh2-
(OAc)(Lx)] or [Pb(OAc)(Lx)] stoichiometry of the isolated
complexes did not change when 1:1 and 2:1 ligand:metal
molar ratios were used in the synthesis. No attempts were
made to prepare the homoleptic [PbPh2(Lx)2] and [Pb(Lx)2]
complexes using molar ratios higher than 2:1.
The organolead(IV) derivatives were isolated as crystal-
line solids. In the case of [Pb(OAc)(L1)], besides the pre-
vious formation of a microcrystalline orange precipitate
with this composition, two types of single crystals were
grown from the mother liquor: yellow-coloured prismatic
crystals with the same stoichiometry as that of the former
precipitate and octahedral-shaped orange crystals with the
formula [Pb(OAc)(L1)]·3H2O.
Description of the Structures
HL2·H2O
The structure and numbering scheme for this compound
are shown in Figure 1 and the significant structural param-
Scheme 3.
The metal ions selected for this work (PbPh22+ and Pb2+
)
will result in HL1 and HL2 being confronted with two
rather different coordination demands. Diorganolead(IV)
cations are almost linear and bonding to the ligand is usu-
ally in the equatorial plane of a bipyramid; the R groups
occupy the apical positions. The coordination of lead(II),
Figure 1. The crystal structure of HL2·H2O showing the intramo-
however, clearly lacks the limitations associated with the lecular hydrogen bonds.
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J. S. Casas et al.
FULL PAPER
eters are listed in Table 1. The asymmetric unit consists of between H(2) and H(7), which occurs in the E conforma-
one molecule of thiosemicarbazone and one water mole- tion (Scheme 4).[14] Furthermore, the sulfur atom is trans to
cule. The isatin moiety and the thiosemicarbazone back- N(3).
bone are both practically planar and form a dihedral angle
of 9.73°. As in all examples of free isatin thiosemicarb-
azones studied to date by X-ray diffraction,[3] the configura-
tion of HL2 about the C(2)=N(3) bond is Z, probably be-
cause this arrangement permits the formation of the strong
intramolecular hydrogen bond N(2)–H···O(1) (see Figure 1
and Table 2) and simultaneously avoids the steric hindrance
Scheme 4.
Table 1. Selected bond lengths [Å] and angles [°] in HL2·H2O.
Although the C(1)–N(2) bond is formally a single bond,
S(1)–C(1)
O(1)–C(3)
N(1)–C(1)
N(1)–C(10)
N(2)–N(3)
N(2)–C(1)
N(3)–C(2)
N(4)–C(3)
N(4)–C(9)
C(1)–N(1)–C(10) 122.96(9)
N(3)–N(2)–C(1) 119.98(8)
C(2)–N(3)–N(2) 116.29(8)
C(3)–N(4)–C(9) 110.92(8)
N(1)–C(1)–N(2) 117.03(9)
N(1)–C(1)–S(1) 125.25(8)
N(2)–C(1)–S(1) 117.72(7)
N(3)–C(2)–C(8) 126.21(9)
N(3)–C(2)–C(3) 127.41(9)
C(8)–C(2)–C(3) 106.22(8)
O(1)–C(3)–N(4) 127.19(9)
O(1)–C(3)–C(2) 126.16(9)
1.6923(10)
1.2385(12)
1.3187(12)
1.4575(13)
1.3576(11)
1.3708(12)
1.2914(12)
1.3505(13)
1.4107(13)
C(2)–C(8)
C(2)–C(3)
C(4)–C(9)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
1.4566(13)
1.5086(13)
1.3838(14)
1.3991(15)
1.3941(16)
1.3964(14)
1.3874(13)
1.4046(13)
theoretical studies[15] indicate that there is a restricted rota-
tion around it, so the observed mutual arrangement of S(1)
and N(3) in HL2·H2O can be labelled as the E configura-
tion. The structure of this part of the thiosemicarbazone
chain in free isatin thiosemicarbazones is not homogeneous
in the solid state and both Z and E configurations have
been identified.[3] Nevertheless, a close look at the available
structures shows that the Z configuration occurs only when
N(1) is fully substituted, probably because, if an N(1)–H
group exists, the E configuration allows the formation of
an additional intramolecular hydrogen bond [N(1)–H(1)···
N(3), see Figure 1 and Table 2]. This bond is not possible
in the Z configuration.
N(4)–C(3)–C(2) 106.64(8)
C(9)–C(4)–C(5) 117.05(9)
C(6)–C(5)–C(4) 121.57(10)
C(5)–C(6)–C(7) 120.83(10)
C(8)–C(7)–C(6) 118.03(9)
C(7)–C(8)–C(9) 120.59(9)
C(7)–C(8)–C(2) 133.02(9)
C(9)–C(8)–C(2) 106.31(8)
C(4)–C(9)–C(8) 121.92(9)
C(4)–C(9)–N(4) 128.19(9)
C(8)–C(9)–N(4) 109.88(8)
There are several additional intermolecular hydrogen
bonds in the compound (Table 2). One is formed between
N(1)–H(1) and the S atom of another molecule [so H(1) is
involved in a bifurcated hydrogen bond], which associates
the molecules in chains along the c axis. Within the chain,
the molecules are distributed into two planes that form a
dihedral angle of ca. 118° (see Figure S1). The water mole-
cule is involved in three hydrogen bonds (see Table 2), which
connect the chains to give double layers in the bc plane
stacked along the a axis (Figure 2).
Table 2. Hydrogen bonding parameters (Å, °) in HL2·H2O.
D–H···A[a]
d(D–H)
d(H···A) d(D···A)
Ͻ(DHA)
N(1)–H(1)···N(3)
0.875(15) 2.251(14) 2.6489(12) 107.5(11)
0.875(15) 2.620(15) 3.3999(9)
0.839(19) 2.506(19) 3.3395(9)
0.838(15) 2.044(15) 2.7240(11) 137.9(14)
0.81(2) 1.99(2) 2.7987(11) 178.2(19)
0.852(17) 1.933(17) 2.7764(12) 170.3(15)
N(1)–H(1)···S(1)i
148.9(12)
172.6(16)
O(1W)–H(1W)···S(1)ii
N(2)–H(2)···O(1)
[PbPh2(OAc)(N2-L1)]·MeOH·EtOH and [PbPh2(OAc)-
(N3-L2)]·H2O
O(1W)–H(2W)···O(1)iii
N(4)–H(4A)···O(1W)
The molecular structure of the former complex is shown
in Figure 3 and the most significant structural parameters
are given in Table 3. The asymmetric unit consists of a mo-
[a] Symmetry operators, i: x, –y + 1/2, z – 1/2; ii: –x – 1, y + 1/2,
–z + 3/2; iii: –x – 1, –y + 1, –z + 2.
Figure 2. The double layers of HL2·H2O stacked along the a axis.
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Eur. J. Inorg. Chem. 2010, 4992–5004

Back to the Coordination Modes of the Thiosemicarbazonate Chain
lecule of the complex and one each of MeOH and EtOH.
When the structure of the isatin thiosemicarbazonate
2+
In [PbPh2(OAc)(N2-L1)], the PbPh2 moiety is bound to a moiety in [PbPh2(OAc)(N2-L1)] is compared with that of
monodeprotonated O,N2,S-coordinated thiosemicarb- HL1,[12] it is evident that coordination did not induce sig-
azonate and to an anisobidentate acetate, both located on nificant changes in the configuration of the free ligand.
the equatorial plane of a distorted pentagonal bipyramidal There are some adjustments in bond lengths and angles
coordination sphere in which the two phenyl groups are in [e.g., the length of C(1)–S(1) increases from 1.663(4) in free
apical positions. The main distortions affect the O(1)–Pb– HL1[12] to 1.724(5) Å in the complex, in accordance with
O(3) and O(2)–Pb–O(3) angles – due to the small bite size the usual thione to thiol evolution in this type of complex]
of the ligands
–
and the C(20)–Pb–C(30) angle but the initial configuration of the thiosemicarbazone re-
[156.58(16)°], which bends towards the equatorial position mains “frozen” during deprotonation, metallation and pre-
with less steric hindrance. As a result, this complex consti- cipitation. This finding is quite consistent with the observed
tutes a new example of the rare N2,S-coordination mode of slow change in the configuration about the C(2)=N(3) bond
the thiosemicarbazonate chain, and the isatin-3-thiosemi- when derivatives of HL1 lose their proton in solution,[14]
carbazonate forms with the metal atom a four- and a six- and also with the calculated partial double bond character
membered chelate ring.
of the N(2)–C(1) bond.[15] In the present case it appears
that the N2,S-coordination is the result of the slow confor-
mational evolution of the ligand and of the sparing solubil-
ity of the N2,S-bound complex, which precipitates before
the donor atoms of the ligand can be rearranged appropri-
ately to afford the N3,S-coordination mode. Additionally,
there are several weak bonding interactions in the lattice
of the [PbPh2(OAc)(N2-L1)]·MeOH·EtOH compound
(Table 4). A hydrogen bond [N(4)–H(4)···O(3)] links the
molecules into dimers and these are connected in chains
through the N(1)H2 group and the oxygen atom of the
methanol molecules (Figure S2). Finally, the chains are
linked by the ethanol molecules and form stacked layers, as
shown in Figure S3.
Table 4. Hydrogen bond parameters (Å, °) in [PbPh2(OAc)(N2-L1)]·
MeOH·EtOH.
D–H···A[a]
d(D–H) d(H···A) d(D···A)
Ͻ(DHA)
N(1)–H(1A)···O(1S)i
N(1)–H(1B)···O(1S)ii
O(1S)–H(1S)···O(2S)
O(2S)–H(2S)···O(2)iii
N(4)–H(4)···O(3)iv
N(1)–H(1A)···N(3)
0.86
0.86
0.82
0.82
0.86
0.86
2.31
2.03
1.85
1.92
1.95
2.42
2.944(5)
2.884(5)
2.674(5)
2.730(4)
2.789(5)
2.672(5)
130.4
173.5
178.6
169.7
165.9
97.7
Figure 3. The molecular structure of [PbPh2(OAc)(N2-L1)]·
MeOH·EtOH.
[a] Symmetry operators, i: –x + 2, –y + 1, –z + 1; ii: x, y, z + 1;
iii: –x + 1, –y + 1, –z + 1; iv: –x + 1, –y + 2, –z + 1.
The molecular structure of [PbPh2(OAc)(N3-L2)]·H2O
and the numbering scheme used are shown in Figure 4; the
most relevant bond lengths and angles are given in Table 5.
Table 3. Selected bond lengths [Å] and angles [°] in [PbPh2-
(OAc)(N2-L1)]·MeOH·EtOH.
Pb–C(20)
Pb–C(30)
Pb–O(2)
Pb–N(2)
Pb–O(1)
2.161(4)
2.172(4)
2.406(3)
2.433(4)
2.606(3)
2.6434(11)
2.803(3)
1.724(5)
1.229(5)
1.282(5)
1.247(5)
1.317(6)
1.339(5)
1.363(5)
1.330(5)
N(4)–C(3)
N(4)–C(9)
C(2)–C(8)
C(2)–C(3)
C(4)–C(9)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(10)–C(11)
O(1S)–C(1S)
O(2S)–C(2S)
C(2S)–C(3S)
1.361(5)
1.395(5)
1.456(6)
1.504(6)
1.381(6)
1.386(6)
1.373(7)
1.375(6)
1.391(6)
1.403(6)
1.506(6)
1.440(6)
1.414(6)
1.441(7)
2+
As in the (L1)– complex, the PbPh2 unit is bound to an
anisobidentate acetate and a tridentate thiosemicarb-
azonate, both located on the equatorial plane of a distorted
pentagonal bipyramid in which the Ph groups are the api-
ces. Unlike the coordination mode exhibited by (L1)– in
[PbPh2(OAc)(N2-L1)]·MeOH·EtOH, (L2)– is O,N3,S-coor-
dinated and forms two five-membered chelate rings with the
metal. To achieve this, the configuration of HL2 must be
strongly modified after deprotonation (see Figures 1 and
4). Specifically, the configuration around the C(1)–N(2)
bond must change from E to Z and that around C(2)=N(3)
from Z to E, both by rotating 180° about the respective
bonds. The former change implies, in addition to overcom-
ing the rotational barrier due to the partial multiplicity of
the bond, the breaking of the N(1)–H···N(3) intramolecular
Pb–S(1)
Pb···O(3)
S(1)–C(1)
O(1)–C(3)
O(2)–C(10)
O(3)–C(10)
N(1)–C(1)
N(2)–N(3)
N(2)–C(1)
N(3)–C(2)
C(20)–Pb–C(30) 156.58(16)
N(2)–Pb–O(1)
O(1)–Pb–O(3)
O(2)–Pb–O(3)
70.54(11)
103.90(9)
49.49(9)
O(2)–Pb–S(1)
N(2)–Pb–S(1)
75.70(7)
60.24(9)
Eur. J. Inorg. Chem. 2010, 4992–5004
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J. S. Casas et al.
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hydrogen bond. The change around the C(2)=N(3) bond is
not affected by the other intramolecular hydrogen bond
[N(2)–H···O(1)] because it disappears when HL2 is depro-
tonated. The molecules of the complex and those of the
water interact in the lattice through hydrogen bonds that
involve the oxygen atoms of the acetate and the water mole-
cule and the N(1)–H, N(4)–H and O(1 W)–H groups (see
Table 6). The N(4)–H(4)···O(3)ii bond links the
[PbPh2(OAc)(N3-L2)] molecules to give dimers that, in turn,
interact through the water molecules to form chains packed
as shown in Figure 5. The π-π stacking interactions between
the phenyl groups of the organometal moiety (distance be-
tween centroids (C30–35) is 3.875 Å) assemble these chains
into a 2D-network (Figure 5).
Figure 5. The distribution of the chains formed by hydrogen bond-
ing interactions in the lattice of [PbPh2(OAc)(N3-L2)]·H2O, and the
π-π stacking interactions.
[Pb(OAc)(N2-L1)] and [Pb(OAc)(N3-L1)]·3H2O
The structures of these complexes are presented in Fig-
ure 6 and the relevant bond lengths and angles are listed in
Table 7. Both derivatives were obtained from the mother
liquor of the same reaction after slow evaporation of the
solvent at room temperature. The complex [Pb(OAc)(N2-
L1)] evolved as abundant but very small prismatic yellow
crystals, whereas [Pb(OAc)(N3-L1)]·3H2O crystallized as a
small number of octahedral bright-orange crystals.
Figure 4. The molecular structure of [PbPh2(OAc)(N3-L2)]·H2O.
Table 5. Selected bond lengths [Å] and angles [°] in
[PbPh2(OAc)(N3-L2)]·H2O.
Pb–C(20)
Pb–C(30)
Pb–O(2)
Pb–N(3)
Pb–S(1)
Pb–O(1)
Pb–O(3)
S(1)–C(1)
O(1)–C(3)
O(2)–C(11)
O(3)–C(11)
N(1)–C(1)
N(1)–C(10)
N(2)–C(1)
2.212(15)
2.205(16)
2.431(12)
2.523(15)
2.596(4)
2.686(12)
2.743(12)
1.757(18)
1.232(19)
1.26(2)
1.24(2)
1.33(2)
1.45(2)
1.36(2)
N(2)–N(3)
N(3)–C(2)
N(4)–C(3)
N(4)–C(9)
C(3)–C(2)
C(2)–C(8)
C(4)–C(9)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(11)–C(12)
1.35(2)
1.29(2)
1.33(2)
1.41(2)
1.47(2)
1.47(2)
1.37(3)
1.38(3)
1.42(3)
1.39(3)
1.39(2)
1.43(2)
1.54(3)
As shown in Figure 7, [Pb(OAc)(N2-L1)] and [Pb(OAc)-
(N3-L1)] are linkage isomers with the thiosemicarbazonate
ligand O,N2,S-coordinated in the former and O,N3,S-coor-
dinated in the latter. The coordination sphere of lead(II) in
both complexes is rather irregular. The void in the distribu-
tion of the bonds around the metal suggests the presence
of a stereochemically active lone electron pair (hemidirected
coordination[16]). In [Pb(OAc)(N2-L1)], if the very weak
bonding interactions are ignored, the coordination sphere
can be roughly described as a square pyramid with a vacant
basal position and the two O atoms of the acetate sharing
the apical position due to the narrow bite of this ligand
(Figure 7, a). In [Pb(OAc)(N3-L1)]·3H2O, again only taking
into account the most significant bonds, the stereochemical
arrangement around the metal (Figure 7, b) is also a square
pyramid with a vacant basal position but, in this case, only
one O atom occupies the apex because the acetate is practi-
cally monodentate. As with the diphenyllead(IV) derivatives
(see Tables 3 and 5), there are clear differences between the
Pb–N bond lengths of the two isomers, this distance being
shorter in the N2-bound than in the N3-bound complex. In
the latter case, the relaxation of this bond is accompanied
C(20)–Pb–C(30) 154.1(7)
N(3)–Pb–O(1)
O(1)–Pb–O(3)
O(2)–Pb–O(3)
65.2(4)
94.6(4)
49.8(4)
O(2)–Pb–S(1)
N(3)–Pb–S(1)
78.9(3)
71.7(4)
Table 6. Hydrogen bonding parameters (Å, °) in [PbPh2(OAc)(N3-
L2)]·H2O.
D–H···A[a]
N(1)–H(1)···O(1W)i
d(D–H)
d(H···A) d(D···A)
1.96 2.81(2)
Ͻ(DHA)
0.86
174.4
O(1W)–H(1W)···O(2) 0.858(15)
1.952(12) 2.750(19) 154.2(12)
1.88 2.741(18) 176.6
N(4)–H(4)···O(3)ii
0.86
[a] Symmetry operators, i: –x, –y + 1, –z + 1; ii: –x, –y, –z.
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Back to the Coordination Modes of the Thiosemicarbazonate Chain
Table 7. Selected bond lengths [Å] and angles [°] in [Pb(OAc)(N2-
L1)] and [Pb(OAc)(N3-L1)]·3H2O.
[Pb(OAc)(N2-L1)][a]
[Pb(OAc)(N3-L1)]·3H2O[a]
Pb–O(1)
Pb–O(2)
Pb–O(3)
Pb–N(2)
Pb–N(3)
Pb–S
2.560(5)
2.444(5)
2.697(5)
2.385(6)
2.700(6)
2.382(5)
2.946(11)
2.535(7)
2.665(3)
3.343(2)
2.860(2)
Pb···Si
Pb···O3ii
Pb···O1iii
S–C(1)
3.038(5)
3.196(4)
1.701(8)
1.245(8)
1.270(8)
1.241(9)
1.330(9)
1.344(8)
1.365(9)
1.310(9)
1.378(9)
1.395(8)
1.691(9)
O(1)–C(3)
O(2)–C(10)
O(3)–C(10)
N(1)–C(1)
N(2)–N(3)
N(2)–C(1)
N(3)–C(2)
N(4)–C(3)
N(4)–C(9)
1.241(10)
1.282(11)
1.229(10)
1.325(10)
1.344(9)
1.364(10)
1.340(10)
1.367(11)
1.398(11)
N(2)–Pb–O(1)
N(2)–Pb–S
72.97(16)
58.60(14)
N(3)–Pb–S
68.27(16)
78.31(18)
66.0(2)
47.66(19)
123.6(11)
O(2)–Pb–O(1)
N(3)–Pb–O(1)
O(2)–Pb–O(3)
O(3)–C(10)–O(2)
50.39(15)
122.5(7)
[a] Symmetry operators, i: 0.25 + y, 0.75 – x, 0.75 – z; ii: –x + 2,
–y, –z; iii: –x + 1, –y, –z.
Figure 6. The molecular structures of (a) [Pb(OAc)(N2-L1)] and (b)
[Pb(OAc)(N3-L1)]·3H2O.
by a reinforcement of the Pb–S bond and, as the sulfur
displaces toward the PbII atom, the isatin oxygen atom
moves away from the metal, thus increasing the Pb···O(1)
distance. Therefore, the bonding system in [Pb(OAc)(N3-
L1)]·3H2O is quite similar to that in the homoleptic com-
plex [Pb(Ishewim)2] [HIshewim = isatin-3-(hexamethyl-
eneiminyl-thiosemicarbazone)],[11] although the bond
lengths are slightly shorter.
In [Pb(OAc)(N2-L1)], each molecule forms two weak
Pb···O interactions with neighbouring molecules to form
chains along the a axis. These chains are associated into a
3D-lattice through intermolecular N(1)–H(1B)···O(2)i and
N(4)–H(4)···O(3)ii hydrogen bonds (see Table 8 and Figure
S4).
Figure 7. The coordination spheres of lead(II) in (a) [Pb(OAc)(N2-
L1)] and (b) [Pb(OAc)(N3-L1)]·3H2O.
interact through the N(1)–H(1A)··O(2)i hydrogen bond to
The lattice of [Pb(OAc)(N3-L1)]·3H2O is more complex. form the 3D arrangement shown in Figure S6. The water
The weak intermolecular Pb···S bond (see Figure 7, b) and molecules are placed in the void spaces of this arrangement
the N(1)–H(1B)···O(3)ii hydrogen bond (Table 8) assemble and, as it was not possible to locate their hydrogen atoms,
the molecules into tetramers (Figure S5). These tetramers the association of these molecules must be described on the
Eur. J. Inorg. Chem. 2010, 4992–5004
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J. S. Casas et al.
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Table 8. Hydrogen bonding parameters (Å, °) in [Pb(OAc)(N2-L1)]
and [Pb(OAc)(N3-L1)]·3H2O.
D–H···A
d(D–H) d(H···A) d(D···A) Ͻ(DHA)
[Pb(OAc)(N2-L1)][a]
N(1)–H(1A)···N(3)
N(1)–H(1B)···O(2)i
N(4)–H(4)···O(3)ii
0.86
0.86
0.86
2.30
2.02
2.00
2.610(9) 101.4
2.858(8) 163.7
2.845(7) 167.3
[Pb(OAc)(N3-L1)]·3H2O[b]
N(1)–H(1A)···O(2)i
N(1)–H(1B)···O(3)ii
O(1 W)···O(1 W)iii
O(2 W)···O(1 W)
O(2 W)···O(2)iii
O(3 W)···O(2 W)
N(4)–H(4)···O(3 W)iv
O(3 W)···O(1 W)iii
O(3 W)···O(3 W)v
0.86
0.86
2.15
1.97
2.941(9) 153.5
2.823(9) 173.3
2.778(9)
2.853(9)
2.797(8)
2.739(9)
2.865(9) 172.9
2.792(8)
0.86
2.01
2.788(12)
[a] i: x, –y + 1/2, z – 1/2, ii: x – 1, y, z. [b] i: –x + 1/2, –y + 1/2,
–z + 1/2; ii: –y + 3/4, x – 1/4, –z + 3/4; iii: y – 1/4, –x + 5/4, –z +
1/4; iv = –x + 1, –y + 3/2, z + 0,
v = –x + 1, –y + 2, –z.
basis of the O···O distances (see Table 8). The water mole-
cules arrange to form a dodecameric (H2O)12 cluster; this
type of cluster has previously been observed[17] but, as far
as we know, the saddle-shaped form detected in the present
case (Figure 8, a) is new. The distances between the oxygen
atoms range from 2.739 to 2.853 Å, with the shorter dis-
tances associated with the four O(2 W)···O(3 W) bonds of
the saddle. The lower limit of the range is close to that of
hexagonal ice (2.75 Å[18]) and, in general, these O···O dis-
tances are a little shorter than in other dodecameric clus-
ters.[17] This structure can be considered to be a modifica-
tion of the fused-cube structure[19] in which the faces of
the two cubes opposite to those fused are partially opened,
possibly to allow additional interactions of the cluster with
the molecules of the complex and with the neighbouring
clusters. The first interactions (Table 8 and Figure 8, b) con-
nect O(3 W) with the N(4)–H(4) group from the isatin pen-
tagonal ring and O(2 W) with the oxygen from the acetate
[O(2)] bound to the metal in the complex. Additionally, the
interaction of the cluster with neighbouring (H2O)12 entities
through O(3 W)···O(3 W)v interactions (2.788 Å) links the
water molecules in a 3D sub-lattice (Figure 8, c).
Figure 8. The (H2O)12 cluster in the crystal of [Pb(OAc)(N3-L1)]·
3H2O showing: (a) the saddle-shaped form; (b) the hydrogen bonds
with the molecules of complex and the connections with neigh-
bouring clusters through O(3 W)···O(3 W) interactions (x); and (c)
the final 3D-arrangement of the water molecules.
NMR Spectroscopy
that we used to prepare the complexes in the solid state.
The results discussed above do not shed much light on The appropriateness of this approach is supported by the
1
the factors that determine the N2- and N3-coordination fact that both solvents afford similar H NMR spectra for
modes. In fact, the study of the diphenyllead(IV) complexes selected samples. The NMR spectroscopic data are given in
seems to suggest that small modifications in the N(1) sub- the Experimental Section.
1
stituents in the thiosemicarbazonate ligand could determine
In the H NMR spectra of HL1 and HL2, the most rel-
the adopted mode, whereas the behaviour of the PbII/HL1 evant signals from the coordination point of view are that
system indicates that both coordination modes coexist in of N(2)–H (δ ≈ 12.5 ppm) and C(7)–H (δ ≈ 7.6 ppm) (see
the synthetic reaction. Therefore, to further clarify this mat- the numbering scheme in Figure 1). The former signal dis-
ter, we decided to perform 1H and 13C NMR spectroscopic appeared on formation of the complexes in accordance with
solution studies. For solubility reasons, the spectra were deprotonation of the ligand, and the second signal was very
measured in [D6]DMSO instead of methanol, the solvent sensitive to the coordination mode of the ligands (see be-
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Back to the Coordination Modes of the Thiosemicarbazonate Chain
low). Deprotonation and metallation also affect the reso- ther clarify the findings in the solid state. The evolution of
nances of C(1), C(2), C(3) and C(7), which occur at δ ≈ 178, the spectrum of [Pb(OAc)(N2-L1)] with time is shown in
132, 163 and 121 ppm, respectively, in the 13C NMR spectra Figure 9 and is particularly illustrative of the point outlined
of the free ligands.
above. The first plot (t = 0) is of the solid isolated by con-
The spectra of the complexes usually contain a higher centrating the reaction solution after only 3 h under reflux.
number of signals than expected, suggesting the presence of Although the presence of a small quantity of the N3,S iso-
more than one species in solution – presumably isomeric mer cannot be ruled out because its signal may be masked
derivatives. Thus, in the 1H and 13C NMR spectra of by the strong broad signal associated with the N(1)H2
[Pb(OAc)(L1)], two doublets associated with the C(7)–H group, it is evident that the N2 isomer predominates in this
proton and two signals for some of the carbons from the first solution. This situation is reasonable considering the
ligand, including the C(7) carbon were observed. The isola- short reaction time and the slow structural evolution of this
tion and full characterization in solid state of the two iso- type of ligand on deprotonation.[14] When the spectrum of
mers in the case of complex [Pb(OAc)(L1)] allowed, using the same solution was recorded after two days, the signals
freshly prepared solutions, the identification of the signals of both isomers were observed with the predominance of
of both isomers and the subsequent analysis of the influ- the N3-coordinated complex. It is worth noting that after
ence of the two coordination modes on the ligand spectra.
one week some N2 isomer still remains, but most of the
The best “fingerprint” in the 1H NMR spectrum to complex is the N3 isomer. After one week, no further sig-
identify the N2 and the N3 isomer is the doublet associated nificant evolution occurs (Figure 9).
with the proton bound to C(7). This signal appears at δ =
7.65 ppm in HL1 but is displaced to δ = 7.72 ppm in the N2-
bound isomer and to δ = 8.27 ppm in the N3-coordinated
complex. The different deshielding of C(7)–H in the two
isomers is probably due to a nonequivalent influence of the
magnetic anisotropy associated with the π-charge of the hy-
drazinic bond. Although this bond is formally represented
as a single bond (Schemes 1 and 2), thiosemicarbazones
have an extensively delocalized system[20] so the N(2)–N(3)
bond possesses a partial double bond character, as con-
firmed by our DFT study (see below). Unlike the N2 iso-
mer, in the N3 isomer this bond is situated close to C(7)–H
and therefore causes deshielding of this proton.
In the 13C NMR spectra, besides the differences in the
position of the C(7) signal, some other carbon signals are
also modified on changing the coordination mode of the
ligand. For example C(1), which is always deshielded with
Figure 9. The evolution of the 1H NMR spectrum of the
[Pb(OAc)(L1)] complex with time (see text for details).
respect to the corresponding carbon in the free ligand (δ ≈
178 ppm), is at lower field in the N3 isomer than in the
N2 isomer {δ = 183.0 ppm in [Pb(OAc)(N2-L1)] and δ =
187.0 ppm in [Pb(OAc)(N3-L1)]}. In addition, the C(3) nu-
Therefore, as the solid state study also suggested, the
cleus, the signal of which is at δ ≈163 ppm in the free ligand, evolution of these complexes in solution is as follows: i) if
is shielded in the N2,S isomer {δ = 158.6 ppm in the reaction time is short or the initially formed complex is
[Pb(OAc)(N2-L1)]} and deshielded in the N3,S isomer {δ = insoluble, the N2 isomer is isolated; and ii) when the reac-
168.1 ppm in [Pb(OAc)(N3-L1)]}. The behaviour of the C(1) tion time increases or the complex is kept in solution for a
resonance can be rationalized by considering that the induc- long period, the solid formed is mostly the N3 derivative,
tive influence of the metal should be more important in the which is probably the thermodynamically controlled prod-
N3 isomer, because the shorter S–metal bond distance in uct.
this isomer suggests a stronger interaction. The more com-
This conclusion is also supported by the behaviour of
plex behaviour of C(3) may be due to the confluence of the [PbPh2(OAc)(L1)]. When the solution obtained in the syn-
induction provoked by the O(3)-metal interaction and the thesis of this complex was immediately concentrated, the
loss of the strong intramolecular N(2)–H···O(3) hydrogen isolated solid mainly corresponded to the N2 isomer (see
bond.
the 1H NMR spectroscopic data, Experimental Section).
Taking into account the behaviour of the C(7)–H signal When the solution was concentrated one week after the syn-
1
in the H NMR spectrum of a freshly prepared solution of thetic reaction, the spectral fingerprints of the product,
[Pb(OAc)(L2)], this complex, which was not studied by X- however, mainly corresponded to the N3 derivative.
ray diffraction, is isolated as the [Pb(OAc)(N2-L2)] isomer.
The spectra of the (L2)– compounds are more complex
Once the N2- and N3 isomers were identified from the than those of (L1)–, suggesting the presence of more than
NMR spectra, it was possible to analyze the evolution of two non-equivalent species from the spectroscopic view-
these systems with time. This type of analysis helped to fur- point. In an effort to explain this finding, one can speculate
Eur. J. Inorg. Chem. 2010, 4992–5004
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J. S. Casas et al.
FULL PAPER
that the changes in the configuration of the ligand may not
be simultaneous in the (L2)– complexes when it evolves from
the N2 isomer to the N3 isomer [rotation about the C(1)–
N(1) and C(2)–N(3) bonds], thus leading to intermediate
stages (such as that shown in Scheme 5) that are stable
enough to be detected. This proposal is plausible because
the methyl group on N(1) probably influences the strength
of the N(1)–H···N(3) hydrogen bond, which must be broken
to allow rotation around C(1)–N(2), however, the idea was
not explored further.
Scheme 5.
Figure 10. The gas-phase optimized conformations for (a)
[Pb(OAc)(N2-L1)] and (b) [Pb(OAc)(N3-L1)]. Bond lengths involv-
ing the Pb atom are given in Å (numbers in bold). Bond orders for
the bonds of the thiosemicarbazone chain are in italic.
DFT Calculations
The gas-phase structures of [Pb(OAc)(N2-L1)] and
[Pb(OAc)(N3-L1)] optimized in this study by DFT calcula-
tions are depicted in Figure 10. The Figure shows the in-
teratomic distances between the Pb ion and the ligand
atoms, as well as the bond orders of the bonds associated
with the thiosemicarbazone chain. As can be seen, the gas-
phase conformations retain the most relevant geometrical
features observed in the X-ray structures (see below). Thus,
the Pb–S distance in [Pb(OAc)(N2-L1)] (2.923 Å) is substan-
tially longer than that calculated for [Pb(OAc)(N3-L1)]
(2.783 Å), as also observed in the solid state. In addition,
the Pb–O(1) and Pb–N [N(2) or N(3)] distances in
[Pb(OAc)(N2-L1)] (2.532 Å and 2.445 Å, respectively) are
significantly shorter than those in [Pb(OAc)(N3-L1)]
(2.642 Å and 2.572 Å, respectively). In both complexes, the
calculated Pb–O(2) lengths are markedly shorter that the
Pb–O(3) ones, showing a more pronounced anisobidentate
character of the acetate ligand than that found in the solid
state. Note that, despite all these differences, the agreement
between experimental and theoretical studies are rather
good considering that the latter do not take into account
the presence of the intermolecular hydrogen bonds and
packing forces in the crystal structures.
The DFT calculations predict that, in the gas phase,
the energies of the two complexes are very similar to each
other, although [Pb(OAc)(N3-L1)] is more stable than
[Pb(OAc)(N2-L1)] by 0.6 kcal/mol. This is a rather small dif-
ference when compared with the results of similar DFT cal-
culations on some benzaldehyde thiosemicarbazone com-
plexes of ruthenium(II)[6] and explains the simultaneous
isolation of both isomers in the present study.
The free energies of the two complexes in the gas phase
at 298.15 K were also evaluated. The difference between ∆G
values of [Pb(OAc)(N3-L1)] and [Pb(OAc)(N2-L1)] is calcu-
lated to be 0.8 kcal/mol, which gives an isomeric equi-
librium constant of 3.79, favouring the formation of
[Pb(OAc)(N3-L1)]. In dimethylsulfoxide, the DFT calcula-
tions with the PCM model predict that the difference be-
tween the ∆G values is 2.0 kcal/mol, suggesting that the for-
mation of [Pb(OAc)(N3-L1)] is also favoured in this solvent.
Conclusion
The calculations show that electron delocalization along
the thiosemicarbazone chain is substantial (see bond orders
In summary, in the complexes of isatin-3-thiosemicarb-
2+
in Figure 10). It is also noteworthy that the bond order pre- azones with PbPh2 and Pb2+ metal cations, although the
dicted for the C–S bond in [Pb(OAc)(N2-L1)] (1.36) is N3-chelated complex is thermodynamically more stable, the
higher than that in [Pb(OAc)(N3-L1)] (1.28). This suggests difference in stability with the N2-chelated isomer is proba-
that the sulfur atom in the latter structure has more thiol bly small. Additionally, the initial configuration of the isatin
character, which correlates with a stronger interaction with 3-thiosemicarbazone ligand, and its slow evolution from the
the Pb metal (i.e., shorter S–Pb bond length). Also of inter- E,Z to Z,E configuration with respect to the C(1)–N(2) and
est is the fact that the N(2)–C(1) bond order in the C(2)=N(3) bonds in solution, favoured the initial formation
[Pb(OAc)(N2-L1)] complex (1.24) is lower than the corre- of the N2 isomer as the kinetically controlled product. In
sponding bond order in [Pb(OAc)(N3-L1)] (1.31).
accordance with this type of control, if the N2 isomer does
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Back to the Coordination Modes of the Thiosemicarbazonate Chain
Complexes: The complexes were prepared by reacting the thiosemi-
carbazone with diphenyllead(IV) acetate or lead(II) acetate tri-
hydrate in 1:1 and 1:2 molar ratios. The results were similar in both
cases so only the 1:1 reactions are described.
not precipitate and remains in solution, it evolves with
time – albeit not completely – to the more stable N3 isomer
(the thermodynamically controlled product). This incom-
plete transformation of the initial product and the slow iso-
meric transition allow the presence of both complexes in
[PbPh2(OAc)(L1)]: A solution of diphenyllead(IV) acetate (0.435 g,
solution. This situation also permits the isolation of pure 0.90 mmol) in methanol (50 mL) was slowly added to a solution of
HL1 (0.200 g, 0.90 mmol) in ethanol (20 mL). The yellow solution
or mixed solids depending on the reaction time and the sol-
was stirred and heated under reflux for 3 h. The mixture was cooled
ubility of the complexes.
to r.t. and the volume of the solution was partially reduced until
It seems plausible that all N,S-bonded thiosemicarb-
an orange crystalline solid appeared. The solid was removed by
azones react with the metal ions as the isatin-3-thiosemi-
filtration; yield 31%, m.p. 203 °C (dec.). C25H26N4O4PbS
carbazone does. In most cases, however, the kinetically con-
{[PbPh2(OAc)(L1)]·EtOH} (685.77): calcd. C 43.79, H 3.82, N 8.17,
trolled N2 isomer probably evolves to form the N3 isomer
S 4.68; found C 42.30, H 3.56, N 8.15, S 4.69. 1H NMR ([D6]-
so quickly that only the second is detected. The N2 isomer
DMSO): δ = 11.06 [br. s, 1 H, N(4)H], 9.00, 8.90, 8.60 [br. s, 2 H,
N(1)H2], 8.30, 7.71 [d, 1 H, C(7)H], 7.85 [d, 3J(1H-207Pb) = 194 Hz,
4 H, Ho-Ph)], 7.52, 7.48 (t, 4 H, Hm-Ph), 7.35, 7.34 (t, 2 H, Hp-Ph),
7.26, 7.24 [t, 1 H, C(5)H], 7.02, 7.01 [t, 1 H, C(6)H], 6.85, 6.81 [d,
1 H, C(4)H], 4.34 (s, 1 H, OHEtOH), 3.22 (q, 2 H, CH2, EtOH),
1.78 (s, 3 H,CH3, OAc), 1.06 (t, 3 H, CH3, EtOH) ppm. 13C NMR
([D6]DMSO): δ = 182.5, 178.8 (C1), 179.5 (COO), 166.8 (Ci-Ph),
166.4, 159.6 (C3), 141.0, 140.5 (C9), 136.6, 136.2 (C2), 132.6
[2J(13C-207Pb) = 119 Hz, Co-Ph], 130.9, 128.9 (C5), 130.1, 130.0
[3J(13C-207Pb) = 193 Hz, Cm-Ph], 129.4 (Cp-Ph), 126.2, 120.3 (C7),
122.2 (C6), 121.9, 117.1 (C8), 110.8, 110.5 (C4), 56.1 (CH2, EtOH),
23.5 (CH3, OAc), 18.6 (CH3, EtOH) ppm. Here and hereafter the
italicized signals correspond to a minor product. A monocrystal
composed of [PbPh2(OAc)(N2-L1)]·MeOH·EtOH suitable for an
X-ray diffraction study was selected from the isolated crystalline
solid. This solid easily lost the alcohol molecules justifying the
slightly low value for the experimental C percentage.
is identified only when the electronic and steric influences
of the R1–R4 substituents (see Scheme 1) slow down the
conformational changes in the thiosemicarbazone chain.
Experimental Section
General: Thiosemicarbazide (Merck), 4-methyl-3-thiosemicarbaz-
ide (Aldrich), 2,3-indolinedione (isatin; Aldrich), silver acetate
(Fluka), lead(II) acetate trihydrate (Probus), diphenyllead(IV) di-
chloride (ABCR), all of reagent grade, were used without further
purification. Diphenyllead(IV) diacetate was prepared by reacting
diphenyllead(IV) dichloride and silver acetate in methanol. The
AgCl was removed by filtration and the solution containing
organolead(IV) acetate was used immediately in the preparation of
the complexes.
Elemental analyses for C,H,N and S were performed with a Fisons
1108 microanalyser. Melting points were determined with a Büchi
melting point apparatus. NMR spectra were recorded in [D6]-
DMSO using Varian Mercury 300 and Varian Inova 500 spectrom-
eters. The 1H NMR spectra (at 300.14 or 500.14 MHz) and 13C
NMR spectra (75.4 or 125.76 MHz) are referenced to TMS by
using the solvent signals: 1H, 2.50 ppm; 13C, 39.50 ppm. HMQC
and HMBC experiments were also carried to confirm the assign-
ments. Elemental analyses, spectroscopic measurements and X-ray
data collection were carried out in the RIAIDT services of the Uni-
versity of Santiago de Compostela.
Ligands: The isatin 3-thiosemicarbazones HL1 and HL2 were pre-
pared according to the previously described method for HL1 [12] by
reacting isatin and the corresponding thiosemicarbazide, in a 1:1
molar ratio, in an ethanol/water solvent mixture.
HL1: Yellow solid; yield 55%. C9H8N4OS (220.25): calcd. C 49.08,
H 3.66, N 25.44, S 14.56; found C 49.64, H 3.89, N 25.92, S 15.19.
1H NMR ([D6]DMSO): δ = 12.47 [s, 1 H, N(2)H], 11.19 [s, 1 H,
N(4)H], 9.04, 8.67 [s, 2 H, N(1)H2], 7.65 [d, 1 H, C(7)H], 7.35 [t, 1
H, C(5)H], 7.08 [t, 1 H, C(6)H], 6.92 [d, 1 H, C(4)H] ppm. 13C
NMR ([D6]DMSO): δ = 178.6 (C1), 162.6 (C3), 143.3 (C9), 132.0
(C2), 131.2 (C5), 122.3 (C6), 120.9 (C7), 119.9 (C8), 111.0 (C4)
ppm.
A second reaction was carried out under similar conditions and
the resulting solution was not concentrated immediately but one
week later. An orange solid formed and was removed by filtration,
vacuum dried and subjected to elemental analysis and 1H NMR
spectroscopy. C24H20N4O3PbS ([PbPh2(OAc)(L1)]) (651.71): calcd.
C 44.23, H 3.09, N 8.60, S 4.92; found C 43.75, H 3.08, N 8.85, S
1
5.15. H NMR ([D6]DMSO): δ = 11.06 [br. s, 1 H, N(4)H], 8.95,
3
8.87 [br. s, 2 H, N(1)H2], 8.23 [d, 1 H, C(7)H], 7.82 [d, J(1H-207Pb
= 193 Hz, 4 H), Ho-Ph], 7.48 (t, 4 H, Hm-Ph), 7.34 (t, 2 H, Hp-Ph),
7.26 (t, 1 H, C5 H), 7.01 [t, 1 H, C(6)H], 6.84 [d, 1 H, C(4)H] ppm.
[PbPh2(OAc)(L2)]: A methanolic solution (35 mL) of freshly pre-
pared diphenyllead(IV) acetate (0.400 g, 0.85 mmol) was added to
a hot solution of the ligand HL2 (0.200 g, 0.85 mmol) in the same
solvent. The orange solution was heated under reflux for 3 h and
allowed to cool. The solution was filtered to remove a slight cloudi-
ness. The clear solution was then concentrated to half its initial
volume until an orange solid formed. This solid was filtered off
and vacuum dried; yield 30%, m.p. 228 °C (dec.). C24H22N4O3PbS
{[PbPh2(OAc)(L2)]} (653.72): calcd. C 44.10, H 3.39, N 8.57, S
4.90; found C 43.63, H 3.55, N 8.54, S 4.06. 1H NMR ([D6]-
DMSO): δ = 11.02 [br. s, 1 H, N(4)H], 9.61, 9.19, 9.3 [br. s, 1 H,
N(1)H], 8.23, 8.03, 7.68 [d, 1 H, C(7)H], 7.83, 7.81 [d, 3J(1H-207Pb)
≈ 198 Hz, 4 H, Ho-Ph], 7.52, 7.48 (t, 4 H, Hm-Ph), 7.36, 7.33 (t, 2 H,
HL2: Yellow solid; yield 60%. C10H10N4OS (234.28): calcd. C
Hp-Ph), 7.28, 7.24 [t, 1 H, C(5)H], 7.06, 7.02 [t, 1 H, C(6)H], 6.86,
51.27, H 4.30, N 23.91, S 13.68; found C 51.04, H 4.31, N 23.70,
S 13.40. H NMR ([D6]DMSO): δ = 12.59 [s, 1 H, N(2)H], 11.20
6.82 [d, 1 H, C(4)H], 3.20, 3.11, 3.05 [s, 3 H, C(10)H3], 1.72 (s, 3
1
H, CH3, OAc) ppm. 13C NMR ([D6]DMSO): δ = 185.2, 178.9 (C1),
[s, 1 H, N(4)H], 9.24 [q, 1 H, N(1)H], 7.63 [d, 1 H, C(7)H], 7.35 [t, 178.7 (COO), 167.2, 166.7 (C3), 166.6, 166.4 [1J(13C-Pb207) =
1 H, C(5)H], 7.08 [t, 1 H, C(6)H], 6.93 [d, 1 H, C(4)H], 3.08 [d, 3 1574 Hz, Ci-Ph], 141.5, 140.4 (C9), 136.7, 135.2 (C2), 132.7, 132.5
H, C(10)H3] ppm. 13C NMR ([D6]DMSO): δ = 177.5 (C1), 162.5
[2J (13C-Pb207) = 119.7 Hz, Co-Ph], 131.1 (C5), 130.1, 130.0 [3J(13C-
(C3), 142.1 (C9), 131.5 (C2), 131.0 (C5), 122.2 (C6), 120.5 (C7), Pb207) = 194 Hz, Cm-Ph], 129.4 (Cp-Ph), 126.4, 125.6, 119.9 (C7),
119.9 (C8), 111.0 (C4), 31.2 (C10) ppm. Monocrystals of HL2·H2O 122.8, 122.3 (C6), 117.3, 116.9 (C8), 111, 110.8 (C4), 31.8, 31.0
suitable for X-ray diffraction were isolated from the mother liquor.
(C10), 23.2 (CH3.OAc) ppm. One week later, a small amount of
Eur. J. Inorg. Chem. 2010, 4992–5004
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5001

J. S. Casas et al.
FULL PAPER
[PbPh2(OAc)(N3-L2)]·H2O monocrystals, suitable for X-ray diffrac-
tion, were isolated from the mother liquor.
H], 7.30 [t, 1 H, C(5)H], 7.06 [t, 1 H, C(6)H], 6.91 [d, 1 H, C(4)H],
1.87 (s, 3 H, CH3, OAc) ppm. (b) t = 1 week. 1H NMR ([D6]-
DMSO): δ = 10.90 [br. s, 1 H, N(4)H], 8.55, 8.30, 8.20 [br. s, 2 H,
N(1)H2], 8.36, 7.73 [d, 1 H,C(7)H], 7.23 [t, 1 H, C(5)H], 7.00 [t, 1
H, C(6)H], 6.87 [d, 1 H, C(4)H], 1.63 (s, 3 H, CH3, OAc) ppm.
Similar spectra (in terms of signal positions and integrations) were
[Pb(OAc)(L1)]: A solution of lead(II) acetate trihydrate (0.340 g,
0.91 mmol) in methanol (20 mL) was slowly added to a solution of
HL1 (0.200 g, 0.91 mmol) in the same solvent (20 mL). An orange
solid formed immediately and the mixture was stirred and heated
under reflux for 3 h. The mixture was cooled to r.t. and the solid
was removed by filtration and dried under vacuum; yield 40%, m.p.
237 °C (dec.). C11H10N4O3PbS {[Pb(OAc)(L1)]} (485.49): calcd. C
27.21, H 2.08, N 11.54, S 6.60; found C 27.28, H 1.94, N 11.32, S
1
obtained two weeks and one month later. H NMR ([D4]MeOH):
δ = 8.40, 7.71 [d, 1 H, C(7)H], 7.32, 7.30 [t, 1 H, C(5)H], 7.09, 7.06
[t, 1 H, C(6)H], 6.95, 6.91 [d, 1 H, C(4)H], 1.87 (s, 3 H, CH3, OAc)
ppm.
[Pb(OAc)(L2)]: A solution of lead(II) acetate trihydrate (0.160 g,
1
6.56. H NMR ([D6]DMSO): δ = 11.05 [br. s, 1 H, N(4)H], 8.36,
7.73 [d, 1 H, C(7)H], 8.30 [br. s, 2 H, N(1)H2], 7.26, 7.24 [t, 1 H,
0.43 mmol) in methanol (10 mL) was slowly added to a solution of
C(5)H], 7.02, 7.01 [t, 1 H, C(6)H], 6.91, 6.88 [d, 1 H, C(4)H], 1.63 HL2 (0.100 g, 0.43 mmol) in the same solvent (25 mL). After a few
(s, 3 H, CH3, OAc) ppm. 13C NMR ([D6]DMSO): δ = 187.1, 183.0 minutes, an orange solid precipitated from the yellow solution and
(C1), 177.5 (COO), 168.2, 158.6 (C3), 140.9, 140.3 (C9), 137.2, the resulting suspension was heated under reflux for 3 h. The
136.1 (C2), 129.9, 129.0 (C5), 126.4, 119.9 (C7), 122.8, 118.2 mixture was cooled to r.t. and the solid was removed by filtration
(C8),121.9 (C6), 110.3 (C4), 26.6 (CH3, OAc) ppm.
and dried under vacuum; yield 38%, m.p. 232 °C (dec.).
C12H12N4O3PbS ([Pb(OAc)(L2)]) (499.51): calcd. C 28.80, H 2.42,
A crystalline solid formed on the slow evaporation of the mother
liquor. Examination of this solid by stereoscopic microscopy
showed a mixture of two types of crystals, mainly yellow prisms
and a few orange octahedrons, both of which were suitable for X-
ray analyses and had the compositions: [Pb(OAc)(N2-L1)] and
[Pb(OAc)(N3-L1)]·3H2O, respectively. A small sample of the yellow
crystals ([Pb(OAc)(N2-L1)]) was selected by hand and characterized
by 1H and 13C NMR spectroscopy in [D6]DMSO and 1H NMR
spectroscopy in [D4]MeOH. The evolution of the complex in both
solvents was followed by 1H NMR spectroscopy and spectra of the
sample recorded at different time intervals. The results (see also
Figure 10) are as follows: (a) t = 0. 1H NMR ([D6]DMSO): δ =
11.03 [br. s, 1 H, N(4)H], 8.30 [br. s, 2 H, N(1)H2], 7.73 [d, 1 H,
C(7)H], 7.23 [t, 1 H, C(5)H], 7.00 [t, 1 H, C(6)H], 6.87 [d, 1 H,
1
N 11.20, S 6.39; found C 29.12, H 2.36, N 11.11, S 6.80. H NMR
([D6]DMSO): δ = 10.96 [br. s, 1 H, N(4)H], 9.14, 8.75, 8.37 [br. s,
1 H, N(1)H], 8.33, 8.11, 7.71 [d, 1 H, C(7)H], 7.29, 7.22 [t, 1 H,C(5)
H], 7.07, 7.01, 7.00 [t, 1 H,C(6)H], 6.93, 6.90, 6.87 [d, 1 H, C(4)H],
3.04, 2.97, 2.95 [d, 3 H, C(10)H3], 1.63 (s, 3 H, CH3, OAc) ppm.
13C NMR ([D6]DMSO): δ = 190.1, 184.3, 183.5 (C1), 177.4 (COO),
168.5, 168.0, 158.7 (C3), 141.4, 140.1, 139.8, 139.0 (C9), 135.1,
134.7 (C2), 130.2, 129.0, 128.5 (C5), 126.3, 125.6, 119.4 (C7), 122.3,
118.3, 117.9 (C8), 123.9, 121.7 (C6), 110.4, 110.3 (C4), 32.4, 32.1,
30.5 (C10), 26.6 (CH3, OAc) ppm.
X-ray Structure Determination: Crystal data were collected on a
Bruker Smart CCD-1000 diffractometer for HL2 and on a Bruker
x8 Kappa APEX II instrument for all the complexes, at 110 K.
C(4)H], 1.63 (s, 3 H, CH3, OAc) ppm. 13C NMR ([D6]DMSO): δ Data were corrected for absorption by multi-scan (SADABS).[21]
= 183.1 (C1), 177.4 (COO), 158.6 (C3), 140.3 (C9), 136.2 (C2), The data for [PbPh2(OAc)(N3-L2)]·H2O (twinned) were processed
129.0 (C5), 122.9 (C8), 121.9 (C6), 119.9 (C7), 110.3 (C4), 26.6 with GEMENI and SAINT.[22] Structures were solved by direct
(CH3, OAc) ppm. 1H NMR ([D4]MeOH): δ = 7.70 [d, 1 H, C(7) methods for the ligand and the Patterson method for the com-
Table 9. Crystal data, data collection and refinement details for the ligand and complexes.
HL2·
H2O
[PbPh2(OAc)(N2-L1)]· [PbPh2(OAc)(N3-L2)]· [Pb(OAc)(N3-L1)]·
[Pb(OAc)(N2-L1)]
MeOH·EtOH
H2O
3H2O
Empirical formula
M
C10H12N4O2S
252.30
C26H30N4O5PbS
717.79
C24H24N4O4PbS
671.72
C11H16N4O6PbS
539.53
C11H10N4O3PbS
485.48
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P21/c
8.8290(3)
12.9946(4)
10.1211(3)
90
93.953(2)
90
1158.42(6)
4
triclinic
P1
triclinic
P1
tetragonal
I41/a
15.5805(8)
15.5805(8)
26.4015(12)
90
90
90
6409.0(5)
16
2.237
monoclinic
P21/c
8.278 (5)
15.412(5)
11.702(5)
90
115.707(5)
90
1345.2(11)
4
¯
¯
11.1922(5)
11.6052(4)
12.2181(6)
84.638(2)
74.790(3)
64.979(2)
1387.40(10)
2
10.1933(12)
11.4755(15)
13.0474(18)
95.216(8)
112.206(7)
113.602(7)
1240.9(3)
2
α [°]
β [°]
γ [°]
V [Å3]
Z
Dc [Mgm–3]
µ [mm–1]
F(000)
1.447
0.276
528
1.718
6.197
704
1.798
6.919
652
2.397
12.709
904
10.695
4096
Crystal size [mm]
θ range for
data collection [°]
Index ranges h,k,l
0.53ϫ0.45ϫ0.21
0.23ϫ0.18ϫ0.07
0.27ϫ0.12ϫ0.06
0.25ϫ0.14ϫ0.07
0.05ϫ0.04ϫ0.03
2.31–29.57
–12, 12; 0, 18; 0, 14
1.73–25.68
1.76–25.35
1.52–26.01
2.34–26.47
–12, 13; –13, 14; 0, 14 –12, 11; –13, 13; 0, 15 –19, 19; –19, 19; –32, 32 –10, 9; 0, 19; 0, 14
Reflections collected 26295
Unique reflections, R 3238 [Rint = 0.0225]
Final R1, wR2
40617
5227 [Rint = 0.0461]
37687
4527 [Rint = 0.1331]
20985
3153 [Rint = 0.0579]
14244
2765 [Rint = 0.0817]
[IϾ2σ(I)]
(all data)
0.0280, 0.0731
0.0307, 0.0749
0.0258, 0.0523
0.0329, 0.0544
0.0933, 0.2231
0.1236, 0.2561
0.0410, 0.0729
0.0648, 0.0800
0.0374, 0. 0685
0.0553, 0.0731
5002
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 4992–5004

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plexes, followed by normal difference Fourier techniques, and re-
fined using SHELXS-97.[23] All hydrogen atoms were introduced
into calculated positions, except those of the ligand HL2, which
were located, and those of the water molecules in [Pb(OAc)-
(N3-L1)]·3H2O, which were neither located nor included in the re-
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crystal and refinement data are listed in Table 9.
CCDC-765721 (for HL2), 765722 {for [PbPh2(OAc)(N2-L1)]·
MeOH·EtOH}, 765723 {for [PbPh2(OAc)(N3-L2)]·H2O}, 765724
{for [Pb(OAc)(N3-L1)]·3H2O} and 765725 {for [Pb(OAc)(N2-L1)]}
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Computational Details: DFT calculations were carried out to inves-
tigate the relative structural stability of [Pb(OAc)(N2-L1)] and
[Pb(OAc)(N3-L1)]. Specifically, we employed the B3LYP method,
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in the gas phase using, as starting points, geometries taken from
the corresponding X-ray crystallographic structures. Frequency cal-
culations were subsequently performed to ensure that the optimized
structures correspond to minima on the potential energy surface
and to compute zero-point vibrational energies (ZPE). Finally, sol-
vent effects were considered by single-point B3LYP calculations
with the polarizable continuum model (PCM),[30–33] using dimethyl
sulfoxide as solvent. All the calculations were performed with the
Gaussian 03 package.[34]
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Supporting Information (see also the footnote on the first page of
this article): Figures S1 and S2 show association by hydrogen bond-
ing forming chains in the lattice of HL2 and [PbPh2(OAc)(N2-L1)]·
MeOH·EtOH, respectively. Figures S3 and S4 show the packing in
the lattice of [PbPh2(OAc)(N2-L1)]·MeOH·EtOH and [Pb(OAc)-
(N2-L1)], respectively. Figure S5 shows the tetrameric association
by hydrogen bonding in [Pb(OAc)(N3-L1)]. Figure S6 represents a
parallel view along the b axis of the [Pb(OAc)(N3-L1)]·3H2O lattice.
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Acknowledgments
We thank the Spanish Ministry of Education and Science (MEC)
(Project CTQ2006-11805) and the Spanish Ministry of Science and
Innovation (MICINN) (Project CTQ2009-10738) for financial sup-
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Received: June 18, 2010
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