New lead(II) complexes with N,S-ligands, including a lead pyrazolonate with unusual packing flexibility

Article abstract of DOI:10.1016/j.poly.2007.05.016

The reaction of lead(II) acetate in methanol with thiosemicarbazones derived from β-keto esters and β-keto amides (HTSCs) afforded two lead(II) thiosemicarbazonates and numerous homoleptic ([PbL₂]) and/or heteroleptic ([Pb(OAc)L]) complexes containing deprotonated pyrazolones L^- formed by metal-induced cyclization of the starting HTSC ligands. All the complexes isolated were characterized by IR spectroscopy in the solid state and by ¹H and ¹³C NMR spectroscopy in DMSO solution; in addition, crystals containing [Pb(L⁶)₂] and [Pb(L⁷)₂] were examined by X-ray crystallography. [Pb(L⁶)₂] · 0.5H₂O · 0.3MeOH (HL⁶ = 4-ethyl-2,5-dihydro-3-methyl-5-oxo-1H-pyrazole-1-carbothiamide) showed three types of molecule with significant structural differences that appear to be determined by packing interactions. In all three molecules the Pb?Pb distances are very short [3.6096(8)-3.7562(8) A?], but density-functional-theoretic calculations at the B3LYP level do not support the existence of Pb-Pb bonds. In [Pb(L⁷)₂] (HL⁷ = N-ethyl-2,5-dihydro-3-methyl-5-oxo-1H-pyrazole-1-carbothiamide) all the molecules are of a single type, and they are linked in a three-dimensional network by weak intermolecular Pb?O bonds.

Full text of DOI:10.1016/j.poly.2007.05.016

Polyhedron 26 (2007) 4228–4238
www.elsevier.com/locate/poly
New lead(II) complexes with N,S-ligands, including a lead
pyrazolonate with unusual packing flexibility
a,
b
b
a
*
´
´
´
Jose S. Casas , Eduardo E. Castellano , Javier Ellena , Marıa S. Garcıa-Tasende ,
a
a
a
c
´
´
´
´
´
´
Agustın Sanchez , Jose Sordo , Angeles Touceda , Saulo Vazquez Rodrıguez
a
Departamento de Quı´mica Inorga´nica, Facultade de Farmacia, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain
b
Instituto de Fı´sica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, CEP 13560, Sao Carlos, SP, Brazil
Departamento de Quı´mica Fı´sica, Facultade de Quı´mica, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain
c
Received 24 April 2007; accepted 11 May 2007
Available online 24 May 2007
Dedicated to Professor Alfonso Castineiras on the occasion of his 65th birthday.
˜
Abstract
The reaction of lead(II) acetate in methanol with thiosemicarbazones derived from b-keto esters and b-keto amides (HTSCs) afforded
two lead(II) thiosemicarbazonates and numerous homoleptic ([PbL2]) and/or heteroleptic ([Pb(OAc)L]) complexes containing deproto-
nated pyrazolones LÀ formed by metal-induced cyclization of the starting HTSC ligands. All the complexes isolated were characterized
by IR spectroscopy in the solid state and by 1H and 13C NMR spectroscopy in DMSO solution; in addition, crystals containing [Pb(L6)2]
and [Pb(L7)2] were examined by X-ray crystallography. [Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH (HL6 = 4-ethyl-2,5-dihydro-3-methyl-5-oxo-1H-
pyrazole-1-carbothiamide) showed three types of molecule with significant structural differences that appear to be determined by packing
˚
interactions. In all three molecules the PbÁ Á ÁPb distances are very short [3.6096(8)–3.7562(8) A], but density-functional-theoretic calcu-
lations at the B3LYP level do not support the existence of Pb–Pb bonds. In [Pb(L7)2] (HL7 = N-ethyl-2,5-dihydro-3-methyl-5-oxo-1H-
pyrazole-1-carbothiamide) all the molecules are of a single type, and they are linked in a three-dimensional network by weak intermo-
lecular PbÁ Á ÁO bonds.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Lead(II) complexes; Thiosemicarbazone ligands; Pyrazolone ligands; X-ray diffraction
1. Introduction
The coordination chemistry of Pb(II) is mainly deter-
mined by two factors: (i) its large size (ionic radius
˚
˚
Lead is a widespread environmental pollutant and its
neurotoxicity constitutes a health problem of global magni-
tude [1]. Recent research connects lead(II) toxicity with its
coordination preferences, which because of their significant
differences from those of important biometals such as
zinc(II) are probably responsible for lead interfering in
the normal functioning of certain proteins, such as those
containing thiol-rich zinc-binding sites [2]. These findings
are focusing attention on the coordination chemistry of
the Pb(II) ion [3].
1.32 A [4], covalent radius 1.54 A [4], van der Waals radius
˚
2.00 A [5]), which permits coordination numbers that range
from quasi-one [6] to twelve [3b]; and (ii) its 6s electron
pair, which may or may not play a role in the stereochem-
istry of lead(II) complexes [3a]. When the 6s electrons con-
stitute a stereochemically active lone pair (SALP), they
occupy a significant proportion of the coordination sphere
of the metal [3a], with the result that bonds with ligand
donor atoms tend either to be placed only in the opposite
hemisphere or to be shorter in that direction than around
the SALP (‘‘hemidirected coordination’’) [3c]. By contrast,
Pb(II) complexes in which the lone pair is not stereochem-
ically active have ‘‘holodirected coordination’’, with a more
*
Corresponding author. Fax: +34 981 54 71 02.
E-mail address: qiscasas@usc.es (J.S. Casas).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.05.016

J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
4229
symmetrical spatial distribution of ligand-metal bonds. The
greater length of Pb–donor distances on the SALP side of
hemidirected Pb(II) centres, which is usually attributed to
repulsion between the SALP and the electron pairs of the
donor atoms, is sometimes so marked that the existence
of a real bonding interaction is questionable [7].
Pb(II) complexes, with ligands derived from b-keto esters
and b-keto amides (Scheme 1).
2. Experimental
2.1. Physical measurements
An interesting aspect of lead(II) SALPs is the possibility
of their enabling the metal centre to act as a Lewis base, as
tin(II) does in some of its complexes [8]. Interactions of this
kind could be considered as non-conventional bonds [9].
Their existence has been hypothesized in the case of some
short PbÁ Á ÁH [10], PbÁ Á Áaromatic ring [11] and PbÁ Á ÁPb
[12] contacts, but the evidence has mostly been incon-
clusive.
New light is thrown on the above issues by the structures
of certain complexes of Pb(II) with 5-pyrazolones resulting
from metal-induced cyclization of thiosemicarbazones [13].
In this paper we report the synthesis of these and other
Elemental analyses were performed on a Fisons Instru-
ments EA1108CHNS-O microanalyser. Melting points
(mp) were determined with a Buchi apparatus. The electro-
¨
spray mass spectra of the complexes were recorded on a
Hewlett–Packard model LC-MSD 1100 instrument (posi-
tive ion mode, 98:2 MeOH/HCOOH as mobile phase,
20–100 V). IR spectra were recorded from KBr discs on a
Bruker IFS66V FT-IR spectrometer and are reported in
1
cmÀ1. The H and 13C NMR spectra of DMSO solutions
were recorded on Bruker WM-250, AMX-300 or AMX-
500 instruments; chemical shifts are expressed on the d
R2
3
R2
R1
R1
R3
2
4
3
2
H
3
4
3
N
O
2
HN
HN
O
2
N
1
1
1
1
H
S
N
S
N H
R
R
I (HTSCn)
R1
II (HLn)
I/II
HTSC1/HL1
R
R2
R3
5
6
-H
-H
-CH3
-OCH3
6
7
9
11 12
-OCH2CH3
5
HTSC2/HL2
8
-H
-H
-H
10
5
6
7
HTSC3/HL3
HTSC4/HL4
-H
-H
-CH2OCH3
-OCH3
5
6
7
-H
-CH2CH3
-OCH3
5
6
8
7
HTSC5/HL5
-H
-CH3
-CH3
-OCH2CH3
5
6
7
8
9
HTSC6/HL6
HTSC7/HL7
-H
5
-CH2CH3
-CH3
-CH2CH3
-OCH2CH3
6
7
8
-H
-CH3
-OCH3
7
8
4
6
5
HTSC8/HL1
9
9
-H
-H
-H
HN
-CH3
11 10
12
CH3O
8
7
5
HTSC9
4
6
-H
-H
-CH3
HN
11 10
8
7
12
OCH3
4
HN
6
9
5
HTSC10
-H
-CH3
11 10
Scheme 1.

4230
J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
Table 1
scale (downfield shifts positive) relative to tetramethylsi-
lane. All physical measurements were carried out in the
RIAIDT services of the University of Santiago de
Compostela.
Reactions of Pb(OAc)2 with HTSCs in MeOH: conditions and complexes
obtained
Ligand
M:L (mol ratio)
T
Complex
HTSC1 1:2
HTSC1 1:1
HTSC2 1:2
HTSC2 1:1
HTSC3 1:2
HTSC3 1:1
HTSC4 1:2
HTSC4 1:1
HTSC5 1:2
HTSC6d 1:2
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
[Pb(L1)2]a
[Pb(OAc)(L1)]a
[Pb(L2)2)]b
2.2. Materials
[Pb(OAc)(L2)]
Thiosemicarbazide (Merck), N1-ethylthiosemicarbazide
(Merck), methyl acetoacetate (Aldrich), ethyl benzoylace-
tate (Aldrich), methyl 4-methoxyacetoacetate (Aldrich),
methyl propionoylacetate (Aldrich), ethyl 2-methylacetoac-
etate (Aldrich), ethyl 2-ethylacetoacetate (Aldrich),
acetoacetanilide (Merck), o-acetoacetanisidide (Aldrich),
p-acetoacetanisidide (Aldrich) and lead(II) acetate trihy-
drate (Probus) were used as received.
[Pb(L3)2]b
[Pb(OAc)(L3)]
[Pb(L4)2]a
[Pb(OAc)(L4)] Æ H2Oa
[Pb(OAc)(L5)]c
1st fraction, [Pb(OAc)(L6)]e
2nd fraction,
[Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH
HTSC7 1:2
r.t.
1st fraction, Pb(OAc)(L7)]f
2nd fraction, [Pb(L7)2]g
2.3. Synthesis of ligands
HTSC8 1:2
HTSC8 1:1
HTSC9h 1:1
HTSC10 1:2
a
r.t.
r.t.
r.t.
r.t.
[Pb(L1)2]a
[Pb(OAc)(L1)]a
[Pb(TSC9)2]
[Pb(TSC10)2]c
The thiosemicarbazones derived from b-ketoesters and
b-ketoamides (HTSCn, n = 1–10; see Scheme 1) were pre-
pared as per Jayasree and Aravindakshan [14]. Their phys-
ical and analytical properties, and those of the
pyrazolonates HLn that were derived from them by cycliza-
tion, have been reported elsewhere [13]. Crystals of HTSC6,
HTSC7, HL6 and HL7 that were suitable for X-ray studies
were obtained from the mother liquors.
Also obtained when the reaction mixture was refluxed for 6 h.
b
Also obtained when the reaction mixture was refluxed for 6 h, for both
1:1 and 1:2 M:L ratios.
c
Obtained under all M:L and temperature conditions.
The same results were obtained refluxing a 1:1 M:L mixture for 6 h.
Also obtained with a 1:1 M:L ratio at room temperature and a 1:2
d
e
ratio under reflux.
f
Also obtained with a 1:1 M:L ratio, both at room temperature and
under reflux.
2.4. Syntheses of complexes
g
Also obtained with a 1:2 M:L ratio under reflux.
h
With a 1:1 M:L ratio under reflux, and with a 1:2 M:L ratio under
General procedure. A solution of Pb(OAc)2 in methanol
was mixed in 1:2 or 1:1 mole ratio with a solution or sus-
pension of the thiosemicarbazone ligand in the same
solvent. The mixture was stirred for 6 h at room tempera-
ture or under reflux. The experimental conditions and the
complexes obtained are summarized in Table 1. All these
reactions are described in detail in the supporting
information.
reflux or at r.t., unidentified products were obtained.
742 m m(C@S). 1H NMR (300 MHz, DMSO-d6, d in
ppm) 11.80, 9.70 (2H, s, N(1)H2), 4.71 (s, 2H, C(3)H), 2.10
(s, 3H, CH3COO), 1.78 (s, 3H, C(5)H3); 13C NMR
(75.48 MHz, DMSO-d6, d in ppm) 178.2 (CH3COO),
176.1 (C(1)), 168.1 (C(4)), 158.9 (C(2)), 85.4 (C(3)), 27.0
(CH3COO), 15.2 (C(5)).
Analytical, physical and spectroscopic data of the com-
plexes isolated are as follows.
[Pb(L2)2)]. Colour beige. Yield: 52 mg (58%). M.p.:
193 °C (d). Anal. Calc. for C20H16N6O2S2Pb (643.71): C,
37.32; H, 2.51; N, 13.06; S, 9.96. Found: C, 36.95; H,
2.45; N, 12.67; S, 9.41%. MS (ESI+): m/z 645 [M+H],
426 [M+HÀ(L2)], 331 [MÀ{(L2) + Ph + NH3}]. IR (KBr,
cmÀ1): 3358 m br, 3300 m br m(N–H); 1598 s m(C@O);
1592 s m(ring); 742 m m(C@S). 1H NMR (300 MHz,
DMSO-d6, d in ppm) 11.82, 9.79 (s, 2H, N(1)H2), 5.08 (s,
1H, C(3)H), 7.53 (m, 2H, C(6,10)H), 7.28 (m, 3H, C(7À9)H);
13C NMR (75.48 MHz, DMSO-d6, d in ppm) 175.9 (C(1)),
167.7 (C(4)), 58.4 (C(2)), 32.9 (C(5)), 129.0 (C(6,10)), 128.6
(C(7,9)), 126.0 (C(8)), 82.8 (C(3)).
[Pb(L1)2]. Colour yellow. Yield: 80 mg (64%). M.p.:
171 °C. Anal. Calc. for C10H12N6O2S2Pb (519.56): C,
23.12; H, 2.33; N, 16.18; S, 12.34%. Found: C, 22.98; H,
2.38; N, 17.08; S, 11.83%. MS (ESI+): m/z 332
[MÀ{(L1)+CH3+NH3}], 304 [MÀ{(L1)+(C(S)NH2)}]. IR
(KBr, cmÀ1): 3425 m br, 3110 w m(N–H); 1636 s m(C@O);
1597 s m(ring); 748 m m(C@S). 1H NMR (300 MHz,
DMSO-d6, d in ppm) 11.76, 9.69 (s, 2H, N(1)H2), 4.67 (s,
1H, C(3)H), 1.97 (s, 3H, C(5)H3); 13C NMR (75.48 MHz,
DMSO-d6, d in ppm) 175.9 (C(1)); 168.1 (C(4)); 158.8
(C(2)); 85.4 (C(3)), 15.2 (C(5)).
[Pb(OAc)(L1)]. Colour yellow. Yield: 88 mg (40%).
M.p.: 165 °C. Anal. Calc. for C7H9N3O3SPb (422.43): C,
19.90; H, 2.15; N, 9.95; S, 7.59. Found: C, 19.98; H, 2.78;
N, 10.09; S, 7.95%. MS (ESI+): m/z 332
[MÀ{(OAc)+NH3+CH3}], 304 [MÀ{(OAc)+(C(S)NH2)}].
IR (KBr, cmÀ1): 3420, m br, 3126, s br, m(N–H); 1613 s
m(C@O); 1550 s, 1379 s m(CH3COO); 1598 sh m m(ring);
[Pb(OAc)(L2)]. Colour beige. Yield: 126 mg (53%).
M.p.: 205 °C (d). Anal. Calc. for C12H11N3O3SPb
(484.50): C, 29.75; H, 2.29; N, 8.67; S, 6.62. Found: C,
29.77; H, 2.01; N, 10.18; S 6.46%. MS (ESI+): m/z 425
[MÀ(OAc)], 67 [M+HÀ{(C(S)NH2)+(OAc)}]. IR (KBr,
cmÀ1): 3409, 3358, 3300 m br m(N–H); 1599 s br m(C@O);
1573 s, 1400 sh m(CH3COO); 742 m m(C@S). 1H NMR

J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
4231
(300 MHz, DMSO-d6, d in ppm) 11.84, 9.87 (s, 2H,
N(1)H2), 7.53 (m, 2H, C(6,10)H), 7.28 (m, 3H, C(7À9)H),
5.08 (s, 1H, C(3)H), 1.69 (s, 3H, CH3COO); 13C NMR
(75.48 MHz, DMSO-d6, d in ppm) 177.6 (CH3COO),
176.3 (C(1)), 167.5 (C(4)), 158.4 (C(2)), 133.1 (C(5)), 128.7
(C(6,10)), 128.5 (C(7)), 125.9 (C(9)), 124.5 (C(8)), 82.4 (C(3)),
26.8 (CH3COO).
in ppm) 177.5 (CH3COO), 175.5 (C(1)), 167.8 (C(4)), 164.3
(C(2)), 83.3 (C(3)), 26.3 (CH3COO), 22.4 (C(5)), 13.1 (C(6)).
[Pb(OAc)(L5)]. Colour yellow. Yield: 78 mg (78%).
M.p.: 182 °C (d). Anal. Calc. for C8H12N3O3SPb
(437.46): C, 21.96; H, 2.78; N, 9.61; S, 7.33. Found: C,
21.60; H, 2.59; N, 9.36; S, 7.17%. MS (ESI+): m/z 378
[M+HÀ(C(S)NH2)], 319 [M+HÀ{(OAc)+(C(S)NH2)}].
IR (KBr, cmÀ1): 3386, 3127 m m(N–H); 1623 s m(C@O);
1542, 1388 s m(CH3COO); 747 m m(C@S). 1H NMR
(300 MHz, DMSO-d6, d in ppm) 11.82, 9.61 (s, 2H,
[Pb(L3)2]. Colour beige. Yield: 72 mg (54%). M.p.:
192 °C (d). Anal. Calc. for C12H16N6O4S2Pb (579.62): C,
24.87; H, 2.78; N, 14.50; S, 11.06. Found: C, 24.52; H,
2.98; N, 13.73; S, 10.70%. MS (ESI+): m/z 394
[M+HÀ(L3)], 303 [MÀ{(L3)+(C(S)NH2)+(CH3O)}]. IR
(KBr, cmÀ1): 3423 m br, 3281 m m(N–H); 1606 s br
m(C@O); 1606 s br m(ring); 747 m m(C@S). 1H NMR
(300 MHz, DMSO-d6, d in ppm) 11.61, 9.64 (s, 2H,
N
(1)H2), 2.07 (s, 3H, CH3COO), 1.67 (s, 2H, C(5)H2), 1.16
(s, 3H, C(6)H3); 13C NMR (75.48 MHz, DMSO-d6, d in
ppm) 177.7 (CH3COO); 175.3 (C(1)), 165.9 (C(4)), 157.4
(C(2)), 90.9 (C(3)), 26.5 (CH3COO), 13.1 (C(5)), 6.4 (C(6)).
[Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH. Colour yellow. M.p.:
146 °C (d). Anal. Calc. for C14.6H22.2N6O2.8S2Pb (594.35):
C, 28.90; H, 3.73; N, 14.15; S, 10.78. Found: C, 28.87; H,
3.81; N, 14.34; S, 10.93%. MS (ESI+): m/z 392 [M–(L6)]
(M = [Pb(L6)2]), 331 [M+HÀ{(L6)+(C(S)NH2)}]. IR (KBr,
cmÀ1): 3405, 3240 m br m(N–H); 1613 s m(C@O); 1598 sh
N
(1)H2), 4.59 (s, 1H, C(3)H), 3.16 (s, 2H, C(5)H2), 4.39 (s,
3H, C(6)H3); 13C NMR (75.48 MHz, DMSO-d6, d in
ppm) 177.2 (C(1)), 168.5 (C(4)), 158.5 (C(2)), 82.5 (C(3)),
69.2 (C(5)) and 59.3 (C(6)).
[Pb(OAc)(L3)]. Colour beige. Yield: 92 mg (44%).
M.p.: 153 °C (d). Anal. Calc. for C8H12N3O4SPb
(453.46): C, 21.19; H, 2.67; N, 9.27; S, 7.07. Found: C,
20.55; H, 2.44; N, 8.91; S, 7.00%. MS (ESI+): m/z 394
[MÀ(OAc)], 331 [MÀ{(OAc)+(CH3OCH2)+NH2+H}].
IR (KBr, cmÀ1): 3390 m br, 3123 m m(N–H); 1608 s
1
m(ring); 745 m m(C@S). H NMR (300 MHz, DMSO-d6, d
in ppm) 11.67, 9.46 (s, 2H, N(1)H2), 2.07 (c, 2H, C(6)H2),
2.03 (s, 3H, C(5)H3), 0.84 (t, 3H, C(7)H3); 13C NMR
(75.48 MHz, DMSO-d6, d in ppm) 175.0 (C(1)), 165.4
(C(4)), 156.4 (C(2)), 97.8 (C(3)), 14.9 (C(6)), 14.7 (C(7)), 13.1
(C(5)).
1
m(C@O); 1576 s, 1400 s m(CH3COO); 759 m m(C@S). H
NMR (300 MHz, DMSO-d6, d in ppm) 11.61, 9.73 (s,
2H, N(1)H2), 4.60 (s, 1H, C(3)H), 4.40 (s, 3H, C(6)H3),
3.21 (s, 2H, C(5)H2), 1.68 (s, 3H, CH3COO); 13C NMR
(75.48 MHz, DMSO-d6, d in ppm) 178.0 (CH3COO),
176.3 (C(1)), 167.8 (C(4)), 158.4 (C(2)), 82.3 (C(3)), 68.0
(C(5)), 58.8 (C(6)), 27.0 (CH3COO).
[Pb(OAc)(L6)]. Colour yellow. Yield: 64 mg (68%).
M.p.: 185 °C (d). Anal. Calc. for C9H13N3O3SPb
(450.48): C, 24.00; H, 2.91; N, 9.33; S, 7.12%. Found: C,
23.98; H, 2.74; N, 9.21; S, 7.33%. MS (ESI+): m/z 392
[MÀ(OAc)], 331 [MÀ{(OAc)+(C(S)NH2)+H}], 287
[MÀ{(OAc)+(C(S)NH2)+(CH3)+(CH2CH3)}]. IR (KBr,
cmÀ1): 3418 s br m(N–H); 1614 s m(C@O); 1597 sh m
m(ring); 1553 s, 1394 m m(CH3COO); 745 m m(C@S). 1H
NMR (300 MHz, DMSO-d6, d in ppm) 11.82, 9.62 (s,
2H, N(1)H2), 2.08 (c, 2H, C(6)H2), 2.07 (s, 3H, C(5)H3),
1.86 (s, 3H, CH3COO), 0.93 (t, 3H, C(7)H3); 13C NMR
(75.48 MHz, DMSO-d6, d in ppm) 177.7 (CH3COO),
175.3 (C(1)), 165.7 (C(4)), 156.9 (C(2)), 97.8 (C(3)), 26.5
(CH3COO), 14.8 (C(6)), 14.7 (C(7)), 13.0 (C(5)).
[Pb(L4)2]. Colour light yellow. Yield: 40 mg (31%).
M.p.: 178 °C (d). Anal. Calc. for C12H16N6O2S2Pb
(547.62): C, 26.32; H, 2.94; N, 15.35; S, 11.71. Found: C,
26.00; H, 2.81; N, 14.87; S, 11.61%. MS (ESI+): m/z 548
[M], 532 [MÀ(CH3+H)], 448 [MÀ(NCNC(S)NH2)], 378
[MÀ(L4)], 331 [MÀ{(L4)+(CH3CH2)+NH2+H}], 287
[MÀ{(L4)+(C(S)NH2)+(CH3CH2)+H}]. IR (KBr, cmÀ1):
3426 m br, 3278 , 3132 w m(N–H); 1624 s m(C@O); 1598
sh m m(ring).1H NMR (300 MHz, DMSO-d6, d in ppm)
11.71, 9.63 (s, 2H, N(1)H2), 4.60 (s, 1H, (C(3)H), 2.40 (c,
2H, C(5)H2), 1.08 (t, 3H, C(6)H3); 13C NMR (75.48 MHz,
DMSO-d6, d in ppm) 174.9 (C(1)), 167.4 (C(4)), 163.6
(C(2)), 82.7 (C(3)), 22.0 (C(5)), 12.7 (C(6)).
[Pb(L7)2]. Colour white. M.p.: 232 °C (d). Anal. Calc.
for C14H20N6O2S2Pb (575.67): C, 29.21; H, 3.50; N, 14.60;
S, 11.14. Found: C, 29.16; H, 3.33; N, 14.30; S, 11.33%. MS
(ESI+): m/z 378 [M+HÀ{(L7)+(CH3)}]. IR (KBr, cmÀ1):
3118 m m(N–H); 1619 s m(C@O); 1568 m br m(ring); 751 m
[Pb(OAc)(L4)] Æ H2O. Colour beige. Yield: 87 mg
(41%). M.p.: 173 °C (d). Anal. Calc. for C8H14N3O4SPb
(455.48): C, 21.10; H, 3.10; N, 9.23; S, 7.04. Found: C,
21.50; H, 2.51; N, 8.74; S, 6.88%. MS (ESI+): m/z 378
[MÀ(OAc)] (M = [Pb(OAc)(L4)]), 331 [MÀ{(OAc)+
(CH3CH2)+NH2+H}], 287 [MÀ{(OAc)+(C(S)NH2)}]. IR
(KBr, cmÀ1): 3453 m m(OH); 3400 sh, 3260 m br, 3121 w
m(N–H); 1606 s m(C@O); 1552 s, 1400 sh m(CH3COO);
m(C@S). H NMR (300 MHz, DMSO-d6, d in ppm) 12.85
1
(s, 1H, N(1)H), 4.57 (s, 1H, C(3)H), 3.54 (m, 2H, C(5)H2),
2.05 (t, 3H, C(6)H3), 1.17 (s, 3H, C(7)H3); 13C NMR
(75.48 MHz, DMSO-d6, d in ppm) 175.0 (C(1)), 167.3
(C(4)), 156.8 (C(2)), 85.3 (C(3)), 79.1 (C(5)), 14.8 (C(6)), 13.8
(C(7)).
[Pb(OAc)(L7)]. Colour pale yellow. Yield: 40 mg
(44%). M.p.: 217 °C (d). Anal. Calc. for C9H13N3O3SPb
(450.48): C, 24.00; H, 2.91; N, 9.33; S, 7.13. Found: C,
24.76; H, 2.97; N, 10.06; S, 7.69%. MS (ESI+): m/z 392
[MÀ(OAc)], 331 [MÀ{(OAc)+(NHCH2CH3)+H+CH3}],
305 [MÀ{(OAc)+(C(S)NHCH2CH3)}]. IR (KBr, cmÀ1):
1
1597 sh m m(ring); 757 m m(C@S). H NMR (300 MHz,
DMSO-d6, d in ppm) 11.72, 9.65 (s, 2H, N(1)H2), 4.58 (s,
1H, C(3)H), 2.42 (c, 2H, C(5)H2), 1.69 (s, 3H, CH3COO),
1.08 (t, 3H, C(6)H3). 13C NMR (75.48 MHz, DMSO-d6, d

4232
J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
3120 m m(N–H); 1612s m(C@O); 1568 s br m(ring); 1568 s,
1400 m m(CH3COO); 748 m m(C@S). H NMR (300 MHz,
(C(2)), 132.1–113.7 (C(Ph)), 55.1 (C(12)), 46.5 (C(3)), 25.0
(C(5)), C(1) is not observed.
1
DMSO-d6, d in ppm) 12.85 (s, 1H, N(1)H), 4.56 (s, 1H,
The compounds for which crystals suitable for X-ray
diffractometry were obtained were [Pb(L6)2] Æ 0.5H2O Æ
0.3MeOH, isolated as the second harvest of crystals from
the mother liquor of the reaction of Pb(OAc)2 with HTSC6
in 1:1 mole ratio under reflux; and [Pb(L7)2], obtained as a
second crystal harvest from the mother liquor of the reac-
tion of Pb(OAc)2 with HTSC7 in 1:2 mole ratio at room
temperature.
C
(3)H), 3.56 (m, 2H, C(5)H2), 2.08 (t, 3H, C(6)H3), 1.66 (s,
3H, CH3COO), 1.18 (s, 3H, C(7)H3); 13C NMR
(75.48 MHz, DMSO-d6, d in ppm) 177.8 (CH3COO),
175.1 (C(1)), 167.3 (C(4)), 157.0 (C(2)), 85.2 (C(3)), 79.1
(C(5)), 26.9 (CH3COO), 14.7 (C(6)), 13.9 (C(7)).
[Pb(TSC9)2]. Colour white. Yield: 40 mg (41%). M.p.:
190 °C (d). Anal. Calc. for C24H30N8O4S2Pb (765.87): C,
37.64; H, 3.95; N, 14.63; S, 8.37. Found: C, 37.57; H,
3.92; N, 14.40; S, 8.00%. MS (ESI+): m/z 767 [M+H],
487 [MÀ(TSC9)], 429 [M+HÀ{(HTSC9)+(C(S)NH2)}],
303 [HTSC9+Na]. IR (KBr, cmÀ1): 3462 s, 3347 s m(N–
H); 1677 s m(C@O); 1609 s m(C@N); 1544 s, 1249 m
m(NH–Ph); 1435 w d(OCH3); 789 w m(C@S).
2.5. X-ray crystallography
Crystal data were collected at room temperature
(HL6) or low temperature (all others) on an Enraf–Non-
ius CAD-4 (RIAIDT, University of Santiago de Com-
postela) or an Enraf–Nonius Kappa CCD (Sao Carlos
Institute of Physics, University of Sao Paulo). The data
were corrected for absorption by multi-scan [15] or psi-
scan [16]. Structures were solved using direct methods
for the ligands and the Patterson method for the com-
plexes, followed by normal difference Fourier techniques.
All hydrogen atoms were included at ideal geometrical
positions. The program used was SHELX97 [17]. Molecu-
lar graphics were obtained with ORTEP [18], PLATON [19]
and MERCURY [20]. Crystal and refinement data are listed
in Table 2. Selected bond lengths and angles are listed
in Table 3 (for HTSC6, HTSC7, HL6and HL7) and
[Pb(TSC10)2]. Colour pale pink. Yield: 60 mg (44%).
M.p.: 184 °C (d). Anal. Calc. for C24H30N8O4S2Pb
(765.87): C, 37.64; H, 3.95; N, 14.63; S, 8.37. Found: C,
36.58; H, 3.86; N, 14.16; S, 8.10%. MS (ESI+): m/z 767
[M+H], 525 [M+HÀ{2(C(S)NH2)+(NPhOCH3)}], 487
[MÀ(TSC10)], 429 [M+HÀ{(HTSC10)+(C(S)NH2)}], 364
[MÀ{(TSC10)+(OCH3Ph)+(CH3)}], 303 [HTSC10+Na].
IR (KBr, cmÀ1): 3456, 3330 s m(N–H); 1656 s m(C@O);
1609 s m(C@N); 1244 m m(NH–Ph); 1448 w d(OCH3); 825,
791 m m(C@S). 1H NMR (300 MHz, DMSO-d6; d in
ppm) 10.11, 10.08, 9.99, 9.86 (s, 1H, N(2)H), 7.48 (d, 2H,
C
N
C
(7,11)H), 6.87 (d, 2H, C(8,10)H), 6.68, 6.48 (s, 2H,
(1)H2), 3.71 (s, 3H, C(12)H3), 3.57, 3.51, 3.24 (s, 2H,
(3)H2), 2.15, 2.08, 1.96, 1.93 (s, 3H, C(5)H3); 13C NMR
Table 4
(for [Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH and [Pb-
(L7)2]). Hydrogen bond lengths and angles are listed in
Table S1.
(75.48 MHz, DMSO-d6, d in ppm) 165.8 (C(4)), 155.1
Table 2
Crystallographic data for ligands and complexes
HTSC6
HTSC7
HL6
HL7
[Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH
[Pb(L7)2]
Empirical formula
Molecular weight
T (K)
k (A)
Crystal system
C
462.63
120(2)
0.71073
triclinic
18H34N6O4S2
C8H15N3O2S
217.29
120(2)
0.71073
monoclinic
P21/n
6.45400(10)
21.6896(4)
7.7124(2)
90
95.1340(10)
90
C7H11N3OS
185.25
140(2)
1.54184
monoclinic
P21/c
11.9461(10)
6.7921(3)
12.0336(8)
90
111.140(5)
90
C7H11N3OS
185.25
140(2)
0.71073
monoclinic
P21/c
6.7805(2)
6.1803(2)
21.0593(8)
90
90.3242(13)
90
882.49(5)
4
1.394
0.322
C14.3H22.2N6O2.8PbS2
594.29
120(2)
0.71073
monoclinic
C2/c
27.9900(5)
7.2980(2)
37.8920(8)
90
90.2560(10)
90
7740.2(3)
16
2.040
8.961
C14H20N6O2S2Pb
575.67
120(2)
0.71073
tetragonal
I41/a
14.5213(3)
14.5213(3)
17.7219(5)
90
˚
ꢀ
Space group
P1
˚
a (A)
9.2260(3)
11.5870(3)
13.3900(5)
65.106(2)
80.0350(10)
72.359(2)
1235.65(7)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
90
90
3
˚
V (A )
1075.29(4)
4
1.348
910.69(11)
4
1.351
3736.99(15)
8
2.046
Z
Dcalc. (Mg/m3)
1.243
0.249
l (mmÀ1
)
0.282
2.824
9.274
Measured reflections
Unique reflections
R(int)
20213
4337
0.1258
0.0437
0.1070
1.037
6430
1884
0.0349
0.0332
0.1082
1.122
3655
1822
0.0262
0.0318
0.0886
1.071
5239
1545
0.0436
0.0364
0.0882
1.069
16846
8406
0.1056
0.0580
0.1036
1.084
10697
2135
0.0399
0.0259
0.0579
1.083
R1 (I > 2rI)
wR2 (I > 2rI)
Goodness-of-fit

J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
4233
Table 3
˚
Bond lengths (A) and angles (°) in thiosemicarbazone and pyrazolone ligands
HTSC6
HTSC7
HL6
HL7
S(1)–C(1)
O(1)–C(4)
N(1)–C(1)
N(2)–C(1)
N(2)–N(3)
N(3)–C(2)
N(2)–C(4)
1.688(2)
1.206(2)
1.322(3)
1.356(3)
1.398(2)
1.285(3)
1.6951(19)
1.215(2)
1.318(3)
1.358(3)
1.402(2)
1.288(2)
1.6863(17)
1.212(2)
1.329(2)
1.367(2)
1.386(2)
1.277(2)
1.6701(15)
1.2493(18)
1.317(2)
1.390(2)
1.3725(17)
1.342(2)
1.673(2)
1.251(2)
1.323(3)
1.398(3)
1.379(2)
1.338(3)
1.414(2)
1.4151(17)
C(1)–N(2)–N(3)
C(2)–N(3)–N(2)
N(1)–C(1)–N(2)
N(1)–C(1)–S(1)
N(2)–C(1)–S(1)
N(3)–C(2)–C(3)
C(2)–C(3)–C(4)
O(1)–C(4)–C(3)
N(3)–N(2)–C(4)
C(1)–N(2)–C(4)
O(1)–C(4)–N(2)
N(2)–C(4)–C(3)
116.97(17)
116.37(18)
116.57(18)
123.83(16)
119.57(16)
114.54(19)
111.45(18)
125.1(2)
117.10(16)
116.72(17)
117.33(17)
122.83(15)
119.83(15)
115.26(18)
110.62(17)
124.18(19)
118.32(14)
117.72(14)
116.10(15)
125.04(13)
118.83(12)
115.69(14)
113.05(14)
125.11(15)
121.51(11)
108.60(11)
113.95(13)
124.94(13)
121.10(11)
110.23(13)
107.17(13)
132.39(14)
108.11(12)
129.62(12)
121.71(14)
105.89(12)
121.61(15)
108.69(16)
113.31(16)
126.02(15)
120.67(14)
109.61(17)
108.15(18)
133.23(18)
108.44(15)
129.79(16)
121.74(18)
105.03(16)
Table 4
˚
Selected bond lengths (A) and angles (°) in pyrazolonate complexes
Molecule 1
Molecule 2
Molecule 3
[Pb(L6)2] Æ 0.5H2O Æ 0.3MeOHa
Pb(1)–N(13)
Pb(1)–N(16)
Pb(1)–S(12)
Pb(1)–S(11)
Pb(1)–N(16)i
Pb(1)–S(11)ii
Pb(1)–S(12)i
Pb(1)–N(13)ii
Pb(1)Á Á ÁPb(1)i
Pb(1)Á Á ÁPb(1)ii
S(11)–C(11)
S(12)–C(18)
O(11)–C(14)
O(12)–C(111)
2.555(8)
Pb(2)–N(23)
Pb(2)–S(21)
Pb(2)–N(33)
Pb(2)–S(31)
Pb(2)Á Á ÁPb(3)iii
Pb(2)Á Á ÁPb(3)
S(21)–C(21)
O(21)–C(24)
2.599(9)
2.905(3)
3.092(9)
3.274(3)
3.6096(8)
3.6884(8)
1.708(11)
1.250(14)
Pb(3)–N(33)
Pb(3)–S(31)
Pb(3)–N(23)v
Pb(3)–S(21)v
Pb(3)Á Á ÁPb(2)vi
Pb(3)Á Á ÁPb(2)
S(31)–C(31)
O(31)–C(34)
2.637(9)
2.922(3)
3.002(8)
3.201(3)
3.6096(8)
3.6884(8)
1.723(11)
1.289(12)
2.691(9)
2.838(3)
2.920(3)
3.003(8)
3.180(3)
3.317(3)
3.371(8)
3.6234(8)
3.7562(8)
1.718(11)
1.736(11)
1.239(14)
1.264(11)
N(13)–Pb(1)–N(16)
N(13)–Pb(1)–S(12)
N(16)–Pb(1)–S(12)
N(13)–Pb(1)–S(11)
N(16)–Pb(1)–S(11)
S(12)–Pb(1)–S(11)
90.6(3)
82.6(2)
66.6(2)
66.5(2)
142.6(2)
80.93(9)
N(23)–Pb(2)–N(23)iv
N(23)–Pb(2)–S(21)iv
N(23)–Pb(2)–S(21)
S(21)iv–Pb(2)–S(21)
109.9(4)
78.0(2)
66.0(2)
N(33)iv–Pb(3)–N(33)
N(33)iv–Pb(3)–S(31)
N(33)–Pb(3)–S(31)
S(31)–Pb(3)–S(31)iv
111.1(4)
79.26(17)
65.62(17)
116.00(11)
115.31(12)
[Pb(L7)2]b
Pb–N(3)
Pb–Oii
Pb–S
2.532(3)
2.727(3)
2.8142(11)
1.691(4)
1.261(5)
N(3)i–Pb–N(3)
N(3)–Pb–Oii
N(3)–Pb–Oiii
N(3)i–Pb–S
N(3)–Pb–S
140.15(16)
96.28(10)
101.32(10)
81.96(8)
Oii–Pb–Oiii
Oii–Pb–S
Oiii–Pb–S
Si–Pb–S
126.73(13)
75.52(7)
157.26(7)
82.87(5)
S–C(1)
O–C(4)
a
68.21(8)
i: Àx + 1/2, Ày + 1/2, Àz + 2; ii: Àx + 1/2, Ày À 1/2, Àz + 2; iii: x, y À 1, z; iv: Àx + 1, y, Àz + 1/2; v: Àx + 1, y + 1, Àz + 1/2; vi: x, y + 1,z.
b
i: Àx + 1, Ày + 1/2, z; ii: y + 1/4, Àx + 1/4, z + 1/4; iii: Ày + 3/4, x + 1/4, z + 1/4.
2.6. Computational details
on three structures modelling fragments of [Pb(L6)2] Æ
0.5H2O Æ 0.3MeOH. Structure A consisted of three type 1
molecules arranged as depicted in Fig. 4a; structure B
of one type 2 molecule sandwiched between two type 3
Single-point density functional theory (DFT) calcula-
tions were performed using the Gaussian 03 package [21]

4234
J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
molecules; and structure C of one type 3 molecule between
two type 2 molecules, as shown in Fig. 4b. All the geome-
tries were taken from the crystallographic data. The
exchange/correlation functional was B3LYP, which com-
bines Becke’s three-parameter nonlocal hybrid exchange
potential [22] with the nonlocal correlation functional of
Lee, Yang, and Parr [23]. The standard 6-31+G(d,p) basis
set was employed for all atoms except Pb, for which the
LanL2DZ effective core potential basis function [24] was
used. In addition, the program AIMPAC [25] was used
to analyse the DFT electron densities by means of quantum
theory of atoms in molecules (QTAIM) [26] in order to
assess the strength of Pb–N, Pb–S and possible Pb–Pb
bonds. QTAIM identifies the critical point of minimum
electron density on the bond path between mutually
bonded atoms. The use of effective core potentials instead
of all-electron basis sets for this purpose has been reported
to afford acceptable results [27].
soluble in DMSO and DMF but only poorly soluble in
the other solvents, and [Pb(TSC9)2] is insoluble in all the
above solvents, among others.
3.2. X-ray studies
3.2.1. Ligands
Fig. 1 shows the molecular structures of HTSC6 and
HTSC7 together with the numbering schemes used. The
asymmetric unit of HTSC6 comprises two independent mol-
ecules, 1 and 2. Both ligands adopt E configuration around
the C(2)–N(3) bond and place the sulphur atom trans to
N(3), so allowing the formation of the intramolecular
hydrogen bond N(1)–H(1)Á Á ÁN(3) (see Table S1, and Fig-
ures S1 and S2). Bond lengths and angles (Table 3) are sim-
ilar to those previously found in other thiosemicarbazones
[28]. Both ligands are basically arranged so as to form
two planes at dihedral angles of 71.57(0.07)° [HTSC6, mol-
ecule 1: C(11)S(1)N(11)N(12)N(13)C(12), rms = 0.0803°
and C(14)O(11)O(12)C(13)C(16)C(17)C(18), rms = 0.0934],
87.31(0.06)° [HTSC6, molecule 2: C(21)S(2)N(21)N(22)N-
(23)C(22)C(23)C(25), rms = 0.1403 and C(23)C(24)O(21)-
O(22)C(28), rms = 0.0103] and 63.51(0.05)° [HTSC7,
SC(1)N(1)N(2)N(3)C(2)C(3)C(5)C(7), rms = 0.0663 and
C(3)C(4)O(1)O(2)C(8), rms = 0.0108].
3. Results and discussion
3.1. Synthesis and physical properties of the complexes
All the ligands reacted with lead(II) acetate in methanol,
the products being in some cases thiosemicarbazonates and
in others complexes with a deprotonated pyrazolone deriv-
ative formed in situ by cyclization of the starting ligand.
Also, the acetate was in some cases fully displaced from
the coordination sphere of the metal, and in others only
partially. Usually, but not always, complete displacement
occurred in reactions with 1:2 M:L mole ratio, which some-
times allowed sequential isolation of both heteroleptic and
homoleptic complexes (see Table 1). Thus the stoichiome-
try of the complexes isolated was influenced not only by
the metal:ligand mole ratio used in the synthesis, but also
by some more elusive factor, possibly solubility differences
between the complexes.
In HTSC6 each molecule of type 1 interacts with a sec-
ond via an N(11)–H(11B)Á Á ÁO(11)i hydrogen bond, giving
rise to infinite chains parallel to the a-axis, and N(12)–
H(12)Á Á ÁS(1)ii hydrogen bonds connect these chains in pairs
(see Table S1 and Figure S1). Type 2 molecules are con-
HTSCs derived from b-ketoesters afforded hetero- or
homoleptic pyrazolonates, both at room temperature and
under reflux (Scheme 2). By contrast, two of the HTSCs
derived from b-ketoamides, HTSC9 and HTSC10, gave thi-
osemicarbazonates, suggesting that this kind of thiosemi-
carbazone is less prone to cyclization.
Most of the complexes obtained in this work are col-
oured solids that are stable in air and decompose at tem-
peratures of 146–232 °C. The [Pb(Ln)2] and [Pb(OAc)(Ln)]
complexes are soluble in methanol, ethanol, acetone,
DMSO and DMF, but insoluble in water. [Pb(TSC10)2] is
R2
R1
O
H
N
R1
Mn+
+
R3
N
C(S)NHR
N
O
HR3
H+
N
H
R2
M(n-1)+
RHNCS
Fig. 1. Molecular structures and numbering schemes of the ligands
HTSC6 (a) and HTSC7 (b).
Scheme 2.

J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
4235
nected by similar interactions, and also by an N(21)–
H(21A)Á Á ÁO(21)iii hydrogen bond, resulting in a two-
dimensional network parallel to the ab-plane (Table S1
and Figure S1).
that associates the molecules in chains. In HL6, an addi-
tional hydrogen bond [N(1)–H(1B)Á Á ÁSi] links the chains
in sheets parallel to the bc-plane.
The ethyl group on N(1) in HTSC7 makes it less capable
of hydrogen bond formation than HTSC6. In fact, its only
intermolecular bond is N(2)–H(2)Á Á ÁO(1)i, which associates
the molecules in dimers (Table S1 and Figure S2).
The molecular structures of HL6 and HL7 are shown in
Fig. 2, together with the numbering schemes used. Both
ligands have bond lengths and angles (Table 3) comparable
to those found in the previously studied similar molecules
HL1 [13a], HL2 [13c], HL4 [13c], and HL5 [29]. In the solid
state, both adopt the ketothione form and can be consid-
ered as almost planar if the terminal methyls of ethyl sub-
stituents are ignored (rms 0.063 and 0.030, respectively).
Both have two intramolecular hydrogen bonds [N(1)–
H(1A)Á Á ÁO and N(3)–H(3)Á Á ÁS (see Table S1, and Figures
S3 and S4)] and an intermolecular bond [N(3)–H(3)Á Á ÁOx]
3.2.2. Complexes
Crystals of [Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH contain
[Pb(L6)2] molecules with the three crystallographically
independent geometries shown, together with the number-
ing scheme used, in Fig. 3. Selected bond lengths and
angles are listed in Table 4. The asymmetric unit comprises
one complete molecule of type 1, half a molecule of type 2,
half a molecule of type 3, a water molecule, and 0.6 mole-
cules of MeOH. In all the ligands, the usual evolution to
the thiol form upon coordination [13] is reflected in the
˚
lengthening of the C–S bond from 1.6703(15) A in the free
ligand (Table 3) to 1.708(11)–1.736(11) A in molecules 1–3
(Table 4).
˚
In all three independent molecules the metal forms four
strong primary bonds with two N,S-dentate pyrazolonates.
In molecule 1 both the two Pb–N distances and the two
Pb–S distances differ, and the fact that all these bonds lie
on one side of the metal atom suggests the existence of a
SALP on the other side, which would make the coordina-
tion polyhedron a distorted trigonal bipyramid with the
hypothesized SALP in one of the equatorial positions.
Molecules 2 and 3, in both of which the two ligands are
mutually symmetrical, resemble each other quite closely,
although the Pb–N and Pb–S bonds are a little shorter in
2 than in 3; in both 2 and 3, as in 1, there seems likely to
be a SALP on one side of the metal atom, but in these cases
the coordination polyhedron is a slightly distorted square
pyramid in which the hypothesized SALP occupies the
apex and the donor atoms come close to defining a perfect
plane (rms = 0.0308 in 2, 0.0286 in 3). In all three mole-
cules the chelate rings are bent around the line S–N so that
the two ligands are almost parallel, but whereas in mole-
cules 2 and 3 this results in the ligands also being quasi-
coplanar, in molecule 1 they are bent the other way so that
they face each other (Fig. 4).
Fig. 2. Molecular structures and numbering schemes of the ligands HL6
(a) and HL7 (b).
Fig. 3. Molecular structures of the three independent molecules of [Pb(L6)2] in [Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH.

4236
J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
Fig. 4. Primary and secondary interactions of Pb(1) (a) and Pb(2) and Pb(3) (b) in [Pb(L6)2] Æ 0.5H2O Æ 0.3MeOH.
Table 5
The structural differences between molecule 1 and mole-
cules 2 and 3 regarding their primary coordination spheres
and the arrangement of their ligands are accompanied by
significant differences in their intermolecular interactions,
notably as regards the weak secondary bonds that, as is
usual in Pb(II) complexes with hemidirected coordination
[3c], appear to border the volume presumably occupied
by the SALP (Fig. 4). Comparison with the sums of van
Electron charge densities (qc, in atomic units) at the critical points of
bonds with Pb(1), Pb(2) and Pb(3) in the model compounds A, B and Ca,
˚
together with the corresponding bonds lengths (A)
Bond length
qc
Pb(1)–N(13)
Pb(1)–N(16)
Pb(1)–S(12)
Pb(1)–S(11)
Pb(1)–N(16)i
Pb(1)–N(13)ii
Pb(1)–S(12)ii
Pb(1)–S(12)i
Pb(2)–N(23)
Pb(2)–S(21)
Pb(2)–N(33)
Pb(2)–S(31)
Pb(3)–N(33)
Pb(3)–S(31)
Pb(3)–N(23)v
Pb(3)–S(21)v
2.556(8)
2.691(9)
2.838(3)
2.920(3)
3.003(8)
3.371(8)
3.180(3)
3.317(3)
2.599(9)
2.905(3)
3.092(9)
3.274(3)
2.637(9)
2.922(3)
3.002(8)
3.201(3)
0.0326
0.0275
0.0317
0.0281
0.0178
0.0102
0.0196
0.0161
0.0311
0.0295
0.0160
0.0169
0.0293
0.0285
0.0183
0.0185
˚
˚
der Waals radii (3.55 A for PbÁ Á ÁN, 3.80 A for PbÁ Á ÁS) sug-
gests that Pb(1) has secondary bonds with the chelating N
and S atoms of the nearest ligands of two neighbouring
i
˚
˚
type
1
molecules [Pb(1)–N(16) = 3.003(8) A, Pb(1)–
i
ii
˚
S(12) = 3.317(3) A, Pb(1)–N(13) = 3.371(8) A, Pb(1)–
ii
˚
S(11) = 3.180(3) A; (i): Àx + 1/2, Ày + 1/2, Àz + 2; (ii):
Àx + 1/2, Ày À 1/2, Àz + 2]. These bonds, which link the
type 1 molecules in slightly zig-zag chains along the b-axis
(Pb–Pb–Pb = 163°; see Fig. 4), are similar to those
observed in other Pb(II) complexes with PbÁ Á ÁN and
PbÁ Á ÁS secondary interactions [30,31]. In molecules 2 and
3, which alternate in stacks (likewise along the b-axis),
the Pb atoms have secondary bonds with all four primary
donor atoms of one of their type 3 or type 2 neighbours
(see Fig. 4 and Table 4 for bond lengths). The existence
of all these secondary bonds is supported by the detection
of the corresponding critical points by the QTAIM calcula-
tions, which among both primary and secondary bonds
showed the expected negative correlation between bond
length and charge density at the critical point (Table 5).
In both the chains of molecules 1 and the stacks of type
i: Àx + 1/2, Ày + 1/2, Àz + 2; ii: Àx + 1/2, Ày À 1/2, Àz + 2; v: Àx + 1,
y + 1, Àz + 1/2.
a
See Section 2.
bonds, so the short PbÁ Á ÁPb distances in the present com-
plex seem likely to be due simply to the secondary Pb–L6
donor bonds.
Each type 1 molecule is linked to molecule 3 of its near-
est type 2/3 unit by a direct N(11)–H(11B)Á Á ÁO(31)ix bond,
and to molecule 2 by a chain of hydrogen bonds that starts
at N(14) and proceeds via the methanol and water mole-
cules to N(21) (see Table S1, and Figs. S6 and S7, for these
and other hydrogen bonds).
˚
2/3 units, the PbÁ Á ÁPb distances [3.6096(8)–3.7562(8) A]
(see Fig. 5) are shorter than in [PbII(XS2)2] complexes,
where (XS2)À is a monoanionic didentate ligand [12], and
are close to the upper limit for Pb–Pb bonds in diplumbene
In [Pb(L7)2], in which the two LÀ ligands are mutually
symmetrical (Fig. 6), the presence of the four primary
bonds within quite a small solid angle suggests that, like
the preceding complex, it has a SALP (see Table 4 for bond
lengths and angles). In fact, it seems that it may be only ste-
ric hindrance between their N(1) ethyl groups that prevents
the two ligands from drawing even closer together (which
may be why the primary coordination polyhedron is not
˚
dimers, 3.527 A [32]. As in the case of bis(pyrrolidinecar-
bodithioato)lead(II), the molecules of which are stacked
˚
with a PbÁ Á ÁPb distance of 3.886(1) A [12], the possibility
of weak SALP-mediated Pb–Pb bonds therefore arises.
However, our QTAIM calculations failed to detect critical
points of electron density supporting the existence of such

J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
4237
plexes (see Section 2), since the spectra of pyrazolones dif-
fer clearly from those of thiosemicarbazones [13].
In the spectra of the [Pb(Ln)2] compounds the m(ring)
band shifts to higher frequencies upon metallation while
the m(C@S) band shifts to lower frequencies or becomes
weaker, which is in keeping with the observation of N,S-
coordination in the L6 and L7 derivatives and in previously
studied pyrazolonates [13].
To judge by the positions of m(ring) and m(C@S), the LÀ
ligand of the [Pb(OAc)(Ln)] complexes is also N,S-coordi-
nated. The value of Dm = mas(COOÀ) À msym(COOÀ) ranges
from 151 to 173 cmÀ1, which suggests that the carboxylate
group acts as a bismonodentate bridging ligand [33].
Upon coordination, the spectra of the thiosemicarba-
zone ligands HTSC9 and HTSC10 undergo significant
modification in the 3000–3500 cmÀ1 region due to deproto-
nation of N(2) and concomitant alteration of the hydrogen
bond network. By contrast, the position of the strong
m(C@O) band at 1650–1670 cmÀ1 is unchanged, suggesting
that this group is not involved in coordination. The slight
shift of m(C@N), the weakening, and slight shift to lower
wavenumbers, of the m(C@S) band at 800 cmÀ1, and the
vanishing of the m(C@S) band at 1100 cmÀ1, are all sugges-
tive of N,S-coordination [13b].
Fig. 5. Assembly of the chains of molecules 1 and the stacks of molecules
2 and 3, together with PbÁ Á ÁPb distances (view perpendicular to the
b-axis).
1
3.4. H and 13C NMR spectroscopy
1
For assignments of the H and 13C NMR signals of all
the complexes except [Pb(TSC9)2] (which is insoluble in
DMSO-d6), see Section 2.
In the proton spectra of [Pb(Ln)2] and [Pb(OAc)(Ln)],
the non-appearance of the HTSCn signals corresponding
to the R3 group and one C(3) proton is in keeping with
the release of HR3 (methanol, ethanol or an aniline) during
cyclization. Similarly, the R3 signals are missing from the
13C NMR spectra of the complexes, and C(3) is deshielded
ca. 40 ppm with respect to HTSCn.
Fig. 6. Molecular structure of [Pb(L7)2].
a square pyramid but a trigonal bipyramid with the
hypothesized SALP equatorial and the N atoms apical).
However, this complex has just a single type of molecule,
and the chelate rings are, as usual, flat (and almost copla-
nar with the corresponding pyrazolonate ring), with a dihe-
dral angle of about 70° between them. It is perhaps this,
with the concomitant orientation of the C(2) methyl
groups, that prevents secondary bonding to the N and S
atoms of neighbouring molecules. The secondary bonds
that do exist, with the O atoms of two neighbouring mole-
The differences between the spectra of the complexes
and those of the free HLn ligands are similar to those found
for the pyrazolonate derivatives of Zn(II) [13], Cd(II)[13]
and Re(I) [13], and can be summarized as follows: (i)
absence of the N(3)H signal due to deprotonation; (ii)
deshielding of the protons on N(1); and (iii) deshielding
of C(2) and C(4) by 5–13 ppm and 3–5 ppm, respectively,
and shielding of C(3) by 5–8 ppm. These modifications sug-
gest that the solid state coordination mode of [Pb(L6)2] and
[Pb(L7)2] (see crystallographic results) persists in DMSO
and is probably that of all the complexes of this type.
ii
ii
iii
˚
cules [PbÁ Á ÁO = 2.727(3) A, O –Pb–O = 126.7°], link the
molecules in a three-dimensional network (Figs. S8–S10).
Thus in this complex the molecular and packing geometry
appears to be determined largely by steric effects; because
of the partial substitution of N(1) and the absence of sol-
vent molecules, hydrogen bonding is limited to the intra-
molecular N(1)–HÁ Á ÁO bond (Table S1).
1
In the H NMR spectrum of [Pb(TSC10)2] the signals
assigned to N(2)H disappear, confirming deprotonation,
and those belonging to N(4)H are split into four. The sig-
nals corresponding to the two N(1)H2 groups are shifted
upfield and lie closer to each other than in the free ligands,
probably due to deprotonation and coordination via the S
atom. In the 13C spectrum, there is no C(1) signal and C(2)
is deshielded ca. 6 ppm, suggesting the involvement of N(3)
in coordination to the metal.
3.3. IR spectroscopy
Whether or not the thiosemicarbazone ligands had
undergone cyclization upon coordination was easily
detected by examination of the main IR bands of the com-

4238
J.S. Casas et al. / Polyhedron 26 (2007) 4228–4238
[10] R.D. Hancock, J.H. Reibenspies, H. Maumela, Inorg. Chem. 43
Acknowledgements
(2004) 2981.
[11] J.M. Harrowfield, S. Maghaminia, A.A. Soudi, Inorg. Chem. 43
(2004) 1810.
[12] F. Caruso, M.L. Chan, M. Rossi, Inorg. Chem. 36 (1997) 3609.
We thank the Secretariat General for Research and
Development of the Xunta de Galicia (Spain) and the
Spanish Ministry of Science and Technology for financial
support under Projects PGIDIT03PXIC20306PN and
CTQ2006-11805-BQU.
´
[13] (a) J.S. Casas, M.V. Castano, E.E. Castellano, M.S. Garcıa-Tasende,
˜
´
´
A. Sanchez, M.L. Sanjuan, J. Sordo, Eur. J. Inorg. Chem. (2000) 83;
(b) J.S. Casas, M.V. Castano, E.E. Castellano, J. Ellena, M.S. Garc´ıa-
˜
´
´
Tasende, A. Gato, A. Sanchez, L.M. Sanjuan, J. Sordo, Inorg. Chem.
41 (2002) 1550;
´
´
(c) J.S. Casas, M.V. Castano, M.S. Garcıa-Tasende, E. Rodrıguez
˜
Appendix A. Supplementary material
´
´
´
Castellon, A. Sanchez, L.M. Sanjuan, J. Sordo, Dalton Trans. (2004)
2019;
CCDC 622367, 622368, 622369, 622370, 622371 and
622372 contain the supplementary crystallographic data
for HTSC6, HTSC7, HL6, HL7, [Pb(L6)2] Æ 0.5H2O Æ 0.3-
MeOH and [Pb(L7)2]. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.poly.2007.
05.016.
´
´
(d) J.S. Casas, M.V. Castano, M.S. Garcıa-Tasende, A. Sanchez, J.
˜
Sordo, A. Touceda, Polyhedron 24 (2005) 3057;
(e) R. Carballo, J.S. Casas, E. Garcıa-Martınez, G. Pereiras-Gabian,
´
´
´
´
´
´
A. Sanchez, J. Sordo, E.M. Vazquez-Lopez, Inorg. Chem. 42 (2003)
6395.
[14] S. Jayasree, K.K. Aravindakshan, Polyhedron 12 (1993) 1187.
[15] R.H. Blessing, Acta Crystallogr. A 51 (1995) 33.
[16] A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr. Sect. A
24 (1968) 351.
[17] G.M. Sheldrick, in: SHELX-97, An Integrated System for Solving and
Refining Crystal Structures from Diffraction Data, University of
Go¨ttingen, Go¨ttingen, Germany, 1997.
[18] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[19] A.L. Spek, PLATON 99,
A Multipurpose Crystallographic Tool,
University of Utrecht, Utrecht, The Netherlands, 1999.
[20] I.J. Bruno, J.C. Cole, P.R. Edgington, M.K. Kessler, C.F. Macrae, P.
McCabe, J. Pearson, R. Taylor, Acta Crystallogr. B58 (2002) 389.
[21] M.J. Frisch et al., GAUSSIAN 03, Revision A.1, Gaussian Inc.,
Pittsburgh, PA, 2003.
References
[1] C.D. Toscano, T.R. Guilarte, Brain Res. Rev 49 (2005) 529.
[2] J.S. Magyar, T.C. Weng, C.M. Stern, D.F. Dye, B.W. Rous, J.C.
Payne, B.M. Bridgewater, A. Mijovilovich, G. Parkin, J.M. Zaleski,
J.E. Penner-Hahn, H.A. Godwin, J. Am. Chem. Soc. 127 (2005)
9495.
[3] (a) R.D. Hancock, in: A.F. Williams, C. Floriani, A.E. Merbach
(Eds.), Perspectives in Coordination Chemistry, VCHA:VCH, Basel,
1992, p. 129;
[22] (a) A.D. Becke, J. Chem. Phys. 98 (1993) 5648;
(b) A.D. Becke, J. Chem. Phys. 96 (1992) 2155.
[23] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[24] W.R. Wadt, P.J. Hay, J. Chem. Phys. 82 (1985) 284.
[25] R.F.W. Bader, in: AIMPAC, A Suite of Programs for the Theory of
Atoms in Molecules, McMaster University, Hamilton, Ontario,
Canada, 1994.
(b) C.E. Holloway, M. Melnik, Main Group. Met. Chem. 20 (1997)
399;
[26] (a) R.F.W. Bader, Chem. Rev. 91 (1991) 893;
(c) L. Shimoni-Livny, J.P. Gluske, C.W. Bock, Inorg. Chem. 37
(1998) 1853;
(b) R.F.W. Bader, in: Atoms in Molecules-A Quantum Theory,
Oxford University Press, Oxford, UK, 1990.
(d) E.S. Claudio, H.A. Godwin, J.S. Magyar, Prog. Inorg. Chem. 51
(2003) 1;
[27] A. Sierraalta, F. Ruette, Int. J. Quantum Chem. 60 (1996) 1015.
´
[28] J.S. Casas, M.S. Garcıa-Tasende, J. Sordo, Coord. Chem. Rev. 209
(e) J.S. Casas, J. Sordo, M.J. Vidarte, in: J.S. Casas, J. Sordo (Eds.),
Lead: Chemistry, Analytical aspects, Environmental Impact and
Health Effects, Elsevier, Amsterdam, 2006.
(2000) 197.
´
´
´
[29] R. Carballo, S. Casas, E. Garcıa-Martınez, G. Pereiras-Gabian, A.
´
´
´
Sanchez, J. Sordo, E.M. Vazquez-Lopez, Acta Crystallogr. E 58
[4] J. Emsley, in: The Elements, Oxford Univ. Press, NY, 1998.
[5] J.E. Huheey, E.A. Keiter, R.L. Keiter, in: Inorganic Chemistry, 4th
ed., HarperCollins College Publishers, New York, 1993.
[6] S. Hino, M. Brynda, A.D. Phillips, P.P. Power, Angew. Chem. Int.
Ed. 43 (2004) 2655.
(2002) o787.
[30] S. Hino, M. Olmstead, A.D. Phillips, R.J. Wright, P.P. Power, Inorg.
Chem. 43 (2004) 7346.
[31] Y.Z. Yuan, J. Zhou, X. Liu, L.H. Liu, K.B. Yu, Inorg. Chem.
Commun. 10 (2007) 475.
[7] J. Harrowfield, Helv. Chim. Acta 88 (2005) 2430.
[8] P.J. Smith (Ed.), Chemistry of Tin, 2nd ed., Blackie Academic &
Professional, London, 1998.
[32] A. Morsali, A.R. Mahjoub, Solid State Sci. 7 (2005) 1429.
[33] K. Nakamoto, in: Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 5th ed., John Wiley & Sons, Inc., NY,
1997.
[9] J.S. Miller, J.J. Novoa, Acc. Chem. Res. 40 (2007) 189.