Synthesis and thermal, fluorescence and structural studies of mixed-ligand lead(II) complexes with 2,2'-diamino-5,5'-dimethyl-4,4'-bithiazole

Article abstract of DOI:10.1080/00958972.2010.533763

The synthesized ligand (DADMBTZ = 2,2'-diamino-5,5'-dimethyl-4,4'- bithiazole) is used for preparing these two new 1: 2 adducts of [Pb(DADMBTZ)₂(NO₃)X] X = CH₃COO (1) and CLO₄ (2) complexes. Characterization was done by IR, ¹H-and ¹³C-NMR spectroscopy, elemental analysis, and single crystal X-ray determination. UV-Vis and fluorescence spectra were studied. Thermal stabilities of 1 and 2 were studied by thermal gravimetric (TG) and differential thermal analysis (DTA). The coordination number of Pb in 1 is seven (four by the chelating DADMBTZ, two oxygens of acetate and one oxygen of nitrate), whereas in 2 it is five (four by the chelating DADMBTZ and one oxygen of nitrate). Coordination geometries of 1 and 2 show a possible vacant site around Pb(II), occupied possibly by a stereoactive lone pair of electrons on lead(II); coordination around lead is hemidirected with a significant gap trans to chelating DADMBTZ, nitrate, and acetate. Both 1 and 2 make 3-D networks via N-H O and N-H N hydrogen bonds; O-H O hydrogen bonds are found in the network for 1.

Full text of DOI:10.1080/00958972.2010.533763

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Synthesis and thermal, fluorescence
and structural studies of mixed-
ligand lead(II) complexes with 2,2′-
diamino-5,5′-dimethyl-4,4′-bithiazole
Akram Hosseinian a & Ali Reza Mahjoub b
a Department of Engineering Science, University College of
Engineering, University of Tehran, P.O. Box 11365-4563, Tehran,
Islamic Republic of Iran
b Department of Chemistry, Tarbiat Modares University, P.O. Box
14115-175, Tehran, Islamic Republic of Iran
Version of record first published: 20 Nov 2010
To cite this article: Akram Hosseinian & Ali Reza Mahjoub (2010): Synthesis and thermal,
fluorescence and structural studies of mixed-ligand lead(II) complexes with 2,2′-diamino-5,5′-
dimethyl-4,4′-bithiazole, Journal of Coordination Chemistry, 63:24, 4245-4258
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Journal of Coordination Chemistry
Vol. 63, No. 24, 20 December 2010, 4245–4258
Synthesis and thermal, fluorescence and structural
studies of mixed-ligand lead(II) complexes with
2,29-diamino-5,59-dimethyl-4,49-bithiazole
AKRAM HOSSEINIAN*y and ALI REZA MAHJOUBz
yDepartment of Engineering Science, University College of Engineering, University of
Tehran, P.O. Box 11365-4563, Tehran, Islamic Republic of Iran
zDepartment of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran,
Islamic Republic of Iran
(Received 30 May 2010; in final form 13 September 2010)
The synthesized ligand (DADMBTZ ¼ 2,20-diamino-5,50-dimethyl-4,40-bithiazole) is used for
preparing these two new 1 : 2 adducts of [Pb(DADMBTZ)2(NO3)X] X ¼ CH3COOꢀ (1) and
X ¼ ClOꢀ4 (2) complexes. Characterization was done by IR, 1H- and 13C-NMR spectroscopy,
elemental analysis, and single crystal X-ray determination. UV-Vis and fluorescence spectra
were studied. Thermal stabilities of 1 and 2 were studied by thermal gravimetric (TG) and
differential thermal analysis (DTA). The coordination number of Pb in 1 is seven (four by the
chelating DADMBTZ, two oxygens of acetate and one oxygen of nitrate), whereas in 2 it is five
(four by the chelating DADMBTZ and one oxygen of nitrate). Coordination geometries of 1
and 2 show a possible vacant site around Pb(II), occupied possibly by a stereoactive lone pair of
electrons on lead(II); coordination around lead is hemidirected with a significant gap trans to
chelating DADMBTZ, nitrate, and acetate. Both 1 and 2 make 3-D networks via N–H ꢁ ꢁ ꢁ O
and N–H ꢁ ꢁ ꢁ N hydrogen bonds; O–H ꢁ ꢁ ꢁ O hydrogen bonds are found in the network for 1.
Keywords: X-ray; Fluorescence; Thermal; Coordination; Bithiazole; Hemidirected
1. Introduction
Coordination chemistry of Pb(II) has long been of interest for many reasons, including
understanding of toxicity of lead compounds [1–3], though there are certainly more
positive features [4, 5]. A fundamental aspect that has attracted considerable attention is
whether or not the coordination geometry about Pb(II) reflects repulsive effects due to a
‘stereochemistry active’ lone pair [6], usually considered to be the 6s2 electrons [7, 8].
Recent structural studies on PbII compounds [9, 10] have provided a detailed analysis
of coordination-sphere distortions as a consequence of the presence of such lone pairs.
Stereochemical activity of the lone pair in divalent Pb compounds has been discussed by
Shimoni-Livny et al. based on a thorough review of crystal data available from the
*Corresponding author. Email: hoseinian@ut.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.533763

4246
A. Hosseinian and A.R. Mahjoub
Cambridge Structural Database (CSD) and by means of ab initio calculations. These
authors classified lead coordination as ‘holodirected’ when the bonds to ligands are
directed throughout the surface of an encompassing sphere, and as ‘hemidirected’ in
cases where the bonds are directed throughout only part of the coordination sphere,
leaving a gap in the distribution of bonds to ligands. The latter case, present in all PbII
complexes with coordination numbers 2–5, is also quite common in PbII complexes with
coordination numbers 6, 7, and 8, but has not been found in those with higher
coordination numbers, where holodirected geometry is the rule. The lone-pair activity
can also depend on: (1) hard or soft ligands, (2) attractive or repulsive interactions
among ligands, (3) the p character of lone pairs, and (4) the number of electrons
(charge) transferred from the ligands to the metal [10, 11].
Mixed ligand complexes whose difference is only in one part of the coordination
sphere are interesting. The importance of this type of lead(II) complex is due to the
influence of different ligands on the structure and lone pair activity of the complexes.
Reports of the crystal structures of mixed ligand 1 : 1 adducts [Pb(phen)(O2CCH3)X]
X ¼ NCSꢀ, NOꢀ3 , ClO4ꢀ [12] and [Pb(bpy)(O2CCH3)X] X ¼ Iꢀ, NO3ꢀ, ClOꢀ4 and 1 : 2
adducts of [Pb(phen)2(O2CCH3)X] X ¼ NCSꢀ, NO3ꢀ, ClO4ꢀ complexes described the
presence of bridging acetate and its influence on the coordination stereochemistry of
lead(II) and also on their structures. The coordination chemistry of lead(II) with N- and
O-donors has been frequently discussed in regard to the coordination and stereoactivity
of the valence shell lone electron pairs [13–17].
Aromatic heterocyclic polymers containing bithiazole rings are good ligands because
two nitrogens in the bithiazole rings are able to chelate metal ions to form stable five-
membered rings. In addition, transition metal complexes of bithiazole ligands have
found increasing applications. For instance, Ni and Co complexes of 2,20-diamino-4,
40-bithiazole are effective inhibitors of DNA synthesis in tumor cells [18–25] and
Fe(II), Fe(III), and Cu(II) complexes have found application in soft magnetic
materials [26–30].
Following our previous study on bithiazole derivatives and their complexes, the
crystal structure of 2,20-diamino-5,50-dimethyl-4,40-bithiazolium dibromide mono
hydrate was reported [31–33]. In this article, we report the synthesis and characteriza-
tion of two new lead(II) complexes containing nitrate [Pb(DADMBTZ)2(NO3)X]
(X ¼ CH3COOꢀ, ClO4ꢀ).
2. Experimental
2.1. Preparation of 2,20-diamino-5,50-dimethyl-4,40-bithiazole
In this study, 2,20-diamino-5,50-dimethyl-4,40-bithiazolium dibromide mono hydrate
was neutralized with NaOH solution (1 mol Lꢀ1) giving 2,20-diamino-5,50-dimethyl-4,
40-bithiazole which was then recrystallized from CHCl3; 2,20-diamino-5,50-dimethyl-4,40-
bithiazole was prepared by the procedure described previously. Reaction of 2,
5-dibromo-3,4-hexadione and thiourea leads to 2,20-diamino-5,50-dimethyl-4,40-bithia-
zolium dibromide mono hydrate. Neutralization with NaOH solution (1 mol Lꢀ1
produces a bright yellow solid which was characterized as DADMBTZ (scheme 1).
)

Lead(II) complexes
4247
CHCl3
H3C
CH2
C
O
C
O
CH2
Br2
CH3
+
C
O
H3C CH
Br
C
O
CH
Br
CH3
CH3CH2OH
C
NH2
2
H3C CH
Br
C
O
CH
Br
CH3
C
S
NH2
+
O
CH3
CH3
S
S
2HBr
+
+
2H2O
N
N
NH2
H2N
CH3
CH3
S
S
CH3OH
Pb(NO3)2
+
NH2
+
Complex 1
NH4CH3COO
N
N
H2N
CH3
CH3
N
S
CH3OH
S
Pb(NO3)2
NaClO4
+
NH2
+
Complex 2
N
H2N
Scheme 1. Synthesis of complexes 1 and 2.
Analysis for C8H10N4S2 (226): C, 42.50 (Calcd C, 42.47); H, 4.25 (4.42); and N, 24.70
(24.77)%. IR (KBr, cmꢀ1): ꢀ(N–H) 3305 (s), 3420 (m), ꢀ(C–H)al 2905 (m), ꢀ(C¼C) 1683
1
(m), ꢀ(C¼N) 1523 (vs), ꢀ(C–S–C) 753 (m), ꢀ(C¼S) 627 (w). H-NMR ([D6]DMSO,
25ꢂC, TMS) ꢁ: 6.5 (4H, 2NH2), 2.2 (6H, 2CH3). 13C-NMR ([D6]DMSO, 25ꢂC, TMS) ꢁ:
164.1, 117.6, 114.1, and 11.83. UV-Vis in DMSO (ꢂmax, nm): 229.5, 229
(" ¼ 25,500 mol Lꢀ1 cmꢀ1).
.
2.2. Preparation of [Pb(DADMBTZ)2(NO3)(CH3COO)] H2O (1)
In this study, 1 was prepared by reaction of a methanolic solution of Pb(NO3)2
(0.1656 g, 0.5 mmol) with a methanolic solution of 2,20-diamino-5,50-dimethyl-4,
40-bithiazole (0.226 g, 1 mmol) and excess of [NH4][CH3COO]. After standing for 12
days at room temperature, colorless crystals were obtained, filtered, washed with
methanol and cold ether, and dried invacuum. The complex is soluble in DMSO and
insoluble in water, methanol, and CHCl3 (0.519 g, Yield: 65%).
Analysis for C18H25N9O6PbS4 (798.90): C, 27.00 (Calcd 27.03), H, 3.14 (3.12), and
N, 15.71 (15.77)%. IR data (KBr, cmꢀ1): ꢀ(N–H) 3355 (s) – 3170 (s), ꢀ(C–H)al 2965 (w),
ꢀ(C¼C) 1623 (m), ꢀ(C¼N) 1509 (s), ꢀ(Skeletal vibration) 1379 (w) and 1343 (s),
ꢀas(COOꢀ) 1509 (s), ꢀs(COOꢀ) 1379 (w), ꢀ(NOꢀ3 ) 1379, 1343, and 1108, ꢀ(C–S–C) 746
1
(w), ꢀ(C¼S) 655 (m), ꢀ(Pb–N) 501 (m). H-NMR ([D6]DMSO, 25ꢂC, TMS) ꢁ: 7.0

4248
A. Hosseinian and A.R. Mahjoub
(4H, 2NH2), 2.2 (6H, 2CH3), and 1.8 (6H, 2CH3). 13C-NMR ([D6]DMSO, 25ꢂC, TMS)
ꢁ: 179.28, 166.33, 140.55, 117.47, 27.18, and 12.38. UV-Vis in DMSO (ꢂmax, nm): 232.5.
232 (" ¼ 24,670 mol Lꢀ1 cmꢀ1).
2.3. Preparation of [Pb(DADMBTZ)2(NO3)(ClO4)] (2)
In this study, 2 was prepared by reacting a methanolic solution of Pb(NO3)2 (0.1656 g,
0.5 mmol) with a methanolic solution of 2,20-diamino-5,50-dimethyl-4,40-bithiazole
(0.226 g, 1 mmol) and excess of NaClO4. After standing 15 days at room temperature,
yellow crystals were obtained, filtered, washed with methanol and cold ether, and dried
in vacuum. The complex is soluble in DMSO and insoluble in water, methanol, and
CHCl3 (0.55 g, Yield: 67%).
Analysis for C16H20ClN9O7PbS4 (821.29): C, 23.32 (Calcd C, 23.37); H, 2.45 (2.43);
and N, 15.29 (15.34)%. IR data (cmꢀ1): ꢀ(N–H) 3425 (s) – 3195 (s), ꢀ(C–H)al 2940 (m),
ꢀ(C¼C) 1615 (s), ꢀ(C¼N) 1507 (s), ꢀ(Skeletal vibration) 1420 (s) and 1339 (w), ꢀ(Cl–O)
1153 (w), 1103 (s), and 1029 (w), ꢀ(NO3ꢀ) 1383, 1339, and 1029, ꢀ(C–S–C) 757 (w),
ꢀ(C¼S) 616 (m), ꢀ(Pb–N) 459 (w). 1H-NMR ([D6]DMSO, 25ꢂC, TMS) ꢁ ppm: 7.0 (4H,
13
2NH2), 2.4 (6H, 2CH3). C-NMR ([D6]DMSO, 25ꢂC, TMS) ꢁ ppm: 170.9, 117.1,
114.0, and 12.6. UV-Vis in DMSO (ꢂmax, nm): 276 (" ¼ 25,700 mol Lꢀ1 cmꢀ1).
2.4. Instrumental procedures
Carbon, hydrogen, and nitrogen analyses were performed by microanalytical methods
1
using a Heraeus CHN–O–RAPID apparatus. H-NMR spectra were recorded on a
1
Bruker Avance DRS 500 spectrometer. H chemical shifts were determined relative to
internal TMS. Infrared (IR) spectra were recorded on a Shimadzu model IR-60
spectrometer from KBr pellets (4000–370 cmꢀ1). Electronic absorption spectra were
recorded on a Shimadzu UV-Vis 2100 recording spectrophotometer. Emission and
excitation spectra of complexes were determined in DMSO using a Shimadzu RS-5000
fluorescence spectrophotometer at room temperature. The measurements were
performed using a PL-STA 1500 Thermal/Sciences in static air, in a ceramic crucible
with ꢃ-Al2O3 as the reference compound, at a heating rate of 5 K minꢀ1; 200-mg
samples were used.
2.5. Crystal structure determinations
Crystallographic data of [Pb(DADMBTZ)2(NO3)(CH3COO)] ꢁ H2O (1) and
[Pb(DADMBTZ)2(NO3)(ClO4)] (2) are given in table 1. X-ray diffraction measurements
were performed at 120 K using a CAD4 Enraf-Nonius diffractometer (1) and Bruker
APEX2 CCD area detector diffractometer (2), equipped with graphite monochromated
˚
Mo-Ka radiation (ꢂ ¼ 0.71073 A) using the ’–! scan technique. Empirical absorption
corrections were applied using SADABS.
The structures were solved by direct methods and subsequent Fourier difference
maps and refined with anisotropic displacement parameters. Hydrogens attached to
carbon and nitrogen were positioned geometrically, with Uiso values derived from the

Lead(II) complexes
4249
Table 1. Crystallographic data and structure refinement for [Pb(DADMBTZ)2(NO3)(CH3COO)] ꢁ H2O (1)
and [Pb(DADMBTZ)2(NO3)(ClO4)] (2).
Empirical formula
Formula weight
Temperature (K)
C18H25N9O6S4Pb (1)
798.90
566(2)
0.71073
Monoclinic
C2/c
C16H20ClN9O7PbS4 (2)
821.29
100(2)
0.71073
Orthorhombic
Pbca
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions (A, )
ꢂ
˚
a
b
c
ꢃ
ꢄ
ꢅ
21.541(4)
15.357(3)
19.109(4)
90
118.51(3)
90
5554.7(19), 8
1.911
6.427
13.392(2)
15.922(2)
25.227(4)
90
90
90
5379.1(14), 8
2.028
6.738
3
˚
Volume (A ), Z
Calculated density (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
3120
3184
Crystal size (mm3)
ꢆ range for data collection (ꢂ)
Limiting indices
0.19 ꢃ 0.17 ꢃ 0.14
1.71–25.99
ꢀ26ꢄhꢄ0;
ꢀ18ꢄkꢄ0;
ꢀ20ꢄlꢄ23
5546
0.45 ꢃ 0.35 ꢃ 0.22
2.22–29.00
ꢀ18ꢄhꢄ18;
ꢀ21ꢄkꢄ21;
ꢀ34ꢄlꢄ34
60494
Reflections collected
Independence reflection
Completeness to ꢆ (%)
Absorption correction
Max. and min. transmission
Refinement method
5405 [R(int) ¼ 0.0619]
70,000 [R(int) ¼ 0.1017]
99.0
Pci-scan
97.8
Semi-empirical from equivalents
0.3187 and 0.1514
Full-matrix
least-squares on F2
7000/52/424
1.075
0.403 and 0.308
Full-matrix
least-squares on F2
5405/0/347
1.063
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I42ꢇ(I)]
R1 ¼ 0.0350,
wR2 ¼ 0.0814
R1 ¼ 0.0678,
wR2 ¼ 0.0896
1.151 and ꢀ1.160
R1 ¼ 0.0534,
wR2 ¼ 0.0881
R1 ¼ 0.1163,
wR2 ¼ 0.1097
1.556 and ꢀ0.858
ꢀ3
˚
Largest difference peak and hole (e A
)
corresponding carbon and nitrogen. The structures of the title compounds were refined
with SHELXL-97 [34–36].
3. Results and discussion
3.1. Synthesis
Reaction of Pb(NO3)2 with DADMBTZ in 1 : 2 ratio in the presence of an excess of
ammonium acetate or sodium perchlorate leads to 1 and 2, respectively (scheme 1).
The IR spectrum of 1 shows bands at 1379 and 1343 cmꢀ1 for skeletal vibrations of
bithiazole ring suggesting that coordination occurred through the ring nitrogen
of bithiazole. Complex 2 similarly shows bands at 1339 and 1420 cmꢀ1. Comparison of
skeletal vibrations between complexes and free ligand provides evidence of coordination
through the bithiazole ring nitrogens.

4250
A. Hosseinian and A.R. Mahjoub
Table 2. Absorption (ꢂabs), emission (ꢂem) band maximaa of 1–4.
ꢀ1
ꢀ1
em nm
Compound
ꢂ
ꢂ
(298 K)
abs nm
[(C4H6N2S)2]
[Pb(DADMBTZ)2(NO3)(CH3COO)] (1)
[Pb(DADMBTZ)2(NO3)(ClO4)] (2)
229.5
232.5
276
360
363.2
363.2
aSolvent: DMSO.
The carboxylato is a multifunction ligand with a number of binding geometries:
monodentate and bidentate either by chelating, or by forming a bridge. Many
complexes containing carboxylates play a key role in biochemical systems containing
mono- or polymetallic sites [37]. The nature of carboxylate coordination can be
determined by IR spectroscopy [38]. The Dꢀ value (ꢀas–ꢀsym) in 1 is 130 cmꢀ1, indicating
that the carboxylate coordinates bidentate [39–41]. This is confirmed by the crystal
structure.
Nitrate could be mono and bidentate chelated and also could be bridged. One oxygen
of this anion is linked to two different hydrogens. In IR spectra of all nitrate complexes,
the region associated with the NO stretches shows many bands, the most intense at
1379, 1343, and 1108 cmꢀ1 in 1 and 1383, 1339, and 1029, which clearly identify these
species as containing coordinate nitrate [42, 43]. Complexity of these bands suggests the
presence of mono and bidentate nitrate, confirmed by X-ray diffraction studies of 1
and 2. The strong absorption bands at 1153, 1103, and 1029 cmꢀ1 are assigned to
ꢀ(ClOꢀ4 ) in 2. The IR spectra of 1 and 2 are in agreement with the X-ray structural data.
1
Comparison of H-NMR spectra in free ligand with the complexes shows a shift for
the amine from 6.5 for the ligand to 7.0 for 1 and 2.
13C-NMR spectrum shows two singlets with chemical shifts at 27.18 and 179.28 ppm
for methyl and carbonyl groups of acetate in 1.
Comparison of 13C-NMR spectra of 1, 2 and the free ligand shows carbon in the
thiazole rings, the donor nitrogen, sulfur, and amine group shifts downfield from
164.1 ppm in free ligand to 166.33 ppm in 1 and 170.9 ppm in 2.
UV-Vis spectra in DMSO display intense absorption bands at 229 for free ligand, 232
and 276 nm for 1 and 2, respectively (table 2), ascribed to the bithiazole ꢈ–ꢈ* and n–ꢈ*
transitions [44, 45] (figure 1).
3.2. Structural descriptions
Complex 1 contains [Pb(DADMBTZ)2]2þ (figure 2), two NO3ꢀ and CH3COOꢀ. The Pb
has an unsymmetrical seven-coordinate geometry, surrounded by four nitrogens of two
DADMBTZ and three oxygens of nitrate and acetate in a N4O3 coordination sphere.
Two ligands in 1 are bidentate in five-membered chelate rings, with internal angles
63.88(2)ꢂ and 66.15(2)ꢂ for N(1)–Pb(1)–N(3), N(5)–Pb(1)–N(7) (table 3). The Pb–N
˚
bond lengths are in the range 2.447(5)–2.767(5) A and the Pb–O bond lengths are in the
˚
range 2.596(5)–2.919(5) A.
Arrangement of DADMBTZ, acetate, and nitrate suggests a gap or hole in the
coordination geometry around lead (the N(5)–Pb–N(3) angle is 151.41ꢂ), occupied
probably by a stereoactive lone pair of electrons on lead(II). The observed shortening of

Lead(II) complexes
4251
Figure 1. Electronic absorption of ligand DADMBTZ (a), Electronic absorption of complex
1(b), Electronic absorption of complex 2 (c); Absorption: c ¼ 1.36 ꢃ 10ꢀ4 mol Lꢀ1, DMSO, d ¼ 1 cm for
ligand and complexes 1 and 2. The fluorescence spectra of ligand (d) and both complexes (e) in DMSO
solution. Room temperature, ꢂexc ¼ 250.
Figure 2. ORTEP drawing of 1 showing the atom-labeling scheme and 50% probability level displacement
ellipsoids.
˚
˚
the Pb–N bonds opposite to the putative lone pair 2.447 A compared with 2.767 A
for the adjacent bond supports the presence of this feature. Hence, the geometry of
the nearest coordination environment of every lead atom is likely to be caused
by the geometrical constraints of DADMBTZ, acetate, and nitrate and by the
influence of a stereochemically active lone pair. There is no additional interaction
between oxygens of acetate and neighboring leads in 2 : 1 adducts of
[Pb(DADMBTZ)2(NO3)(CH3COO)] ꢁ H2O, and 1 is a monomer.
There are eight types of N–H ꢁ ꢁ ꢁ O, O–H ꢁ ꢁ ꢁ O, and N–H ꢁ ꢁ ꢁ N intermolecular
hydrogen bonds in the 3-D network between [Pb(DADMBTZ)2]2þ, two different
anions, and an uncoordinated water. Unit cell packing of 1 is given in figure 3.

4252
A. Hosseinian and A.R. Mahjoub
Table 3. Selected bond lengths (A) and angles (ꢂ) for [Pb(DADMBTZ)2(NO3)
˚
(CH3COO)] ꢁ H2O (1).
Pb(1)–N(1)
Pb(1)–N(3)
Pb(1)–N(5)
Pb(1)–N(7)
Pb(1)–O(1)
Pb(1)–O(2)
Pb(1)–O(3A)
C(2)–C(4)
N(2)–C(1)
2.604(5)
2.767(5)
2.649(5)
2.447(5)
2.648(6)
2.596(5)
2.919(5)
1.362(8)
1.354(7)
1.305(7)
1.237(7)
1.236(7)
121.9(7)
91.81(2)
75.82(2)
66.16(2)
92.09(2)
63.89(2)
91.81(2)
151.42(2)
N(3)–C(8)
N(6)–C(9)
N(3)–C(5)
N(5)–C(9)
N(4)–C(8)
N(8)–C(16)
N(5)–C(12)
N(7)–C(16)
N(7)–C(13)
N(1)–C(4)
1.313(7)
1.349(9)
1.408(7)
1.305(7)
1.341(8)
1.347(7)
1.408(8)
1.307(7)
1.414(8)
1.386(7)
1.216(8)
119.2(7)
118.8(6)
78.54(2)
129.01(2)
84.83(2)
160.09(2)
48.95(2)
75.93(2)
122.34(2)
N(1)–C(1)
N(1A)–O(1A)
N(1A)–O(3A)
O(3A)–N(1A)–O(2A)
N(1)–Pb(1)–N(5)
N(1)–Pb(1)–N(7)
N(7)–Pb(1)–N(5)
N(7)–Pb(1)–N(3)
N(1)–Pb(1)–N(3)
N(1)–Pb(1)–N(5)
N(3)–Pb(1)–N(5)
N(1A)–O(2A)
O(1A)–N(1A)–O(2A)
O(1A)–N(1A)–O(3A)
N(7)–Pb(1)–O(2)
N(1)–Pb(1)–O(2)
N(7)–Pb(1)–O(1)
N(1)–Pb(1)–O(1)
O(2)–Pb(1)–O(1)
N(5)–Pb(1)–O(1)
N(3)–Pb(1)–O(1)
Figure 3. The unit cell of 1 showing intermolecular hydrogen bonding.
Complex 2 with its metal geometry (being bound to four nitrogens of two bidentate
bithiazole ligands and one oxygen of nitrate) is five coordinate (figure 4). In each ligand,
the two nitrogens coordinated to Pb(II) have different bond lengths (2.455(6)–
˚
2.593(6) A). The two DADMBTZ ligands in 2 are bidentate in five-membered chelate
rings, with different internal angles 67.67(2)ꢂ and 68.78(2) for N(1)–Pb(1)–N(3),

Lead(II) complexes
4253
Figure 4. ORTEP drawing of 2 showing the atom-labeling scheme and 50% probability level displacement
ellipsoids.
˚
N(5)–Pb(1)–N(7), respectively. The Pb–O (NO3) bond length is 2.822(5) A. The most
relevant bond lengths and angles are given in table 4. Unit cell packing of 2 is shown
in figure 5.
There are 19 types of N–H ꢁ ꢁ ꢁ O and N–H ꢁ ꢁ ꢁ N inter- and intramolecular hydrogen
bonds in a 3-D network between [Pb(DADMBTZ)2]2þ and two different anions
(figure 6).
The arrangement of the DADMBTZ ligands and nitrates suggests a gap or hole in
the coordination geometry around lead [the N(7)–Pb–N(3) angle is 156.5ꢂ], occupied
probably by a stereoactive lone pair of electrons on lead(II). The observed shortening of
˚
˚
the Pb–N bonds opposite to the putative lone pair (2.455 A compared with 2.593 A for
the adjacent bond) supports the presence of this feature. For the structures described
here, coordination around lead is hemidirected with a significant gap trans to
DADMBTZ. The ꢈ–ꢈ stacking interactions are not found in 1 and 2 because ꢈ–ꢈ
stacking interactions are rarely observed in complexes with a ligand–metal ratio of 2 : 1.
˚
Interestingly, if a limit of 2.83 A were to be placed upon Pb(II)-donor separations
regarded as involving coordinate bonding, only one oxygen of nitrate would be
considered bound and perchlorate would be considered uncoordinated. If, however, the

4254
A. Hosseinian and A.R. Mahjoub
ꢂ
˚
Table 4. Selected bond lengths (A) and angles ( ) for [Pb(DADMBTZ)2
(NO3)(ClO4)] (2).
Pb(1)–N(1)
Pb(1)–N(3)
Pb(1)–N(5)
Pb(1)–N(7)
Pb(1)–O(1A)
C(2)–C(1)
C(1)–C(5)
C(2)–C(3)
N(2)–C(4)
N(1)–C(1)
N(1S)–O(1)
N(1S)–O(3)
O(3)–N(1S)–O(2)
N(7)–Pb(1)–N(5)
N(7)–Pb(1)–N(3)
N(1)–Pb(1)–N(3)
2.455(6)
2.564(6)
2.466(6)
2.593(6)
2.73(3)
1.350(2)
1.470(9)
1.508(2)
1.338(9)
1.400(8)
1.218(7)
1.210(7)
129(3)
N(3)–C(8)
N(6)–C(12)
N(3)–C(5)
N(5)–C(9)
N(4)–C(8)
N(8)–C(16)
N(5)–C(12)
N(7)–C(16)
N(7)–C(13)
1.313(9)
1.361(9)
1.405(9)
1.392(8)
1.332(9)
1.327(2)
1.312(8)
1.337(9)
1.400(2)
1.302(9)
1.206(8)
120(3)
N(1)–C(4)
N(1S)–O(2)
O(1)–N(1S)–O(2)
O(1)–N(1S)–O(3)
N(1)–Pb(1)–O(1A)
N(1)–Pb(1)–N(5)
N(1)–Pb(1)–N(7)
110(3)
73.0(7)
75.3(2)
92.24(2)
68.78(2)
156.5(2)
67.66(2)
Figure 5. A view of unit cell of 2 showing intermolecular hydrogen bonding.
˚
bonding limit is extended to 3 A, the nitrate and perchlorate attached to Pb all become
(asymmetric) chelating entities, leading to seven-coordinate Pb in a very strongly
‘hemidirected’ array, evidently consistent with the presence of a lone pair in the
apparent coordination-sphere vacancy remote from the bound atoms. Such an
environment leaves space for Pb ꢁ ꢁ ꢁ O bond with the oxygen atoms of perchlorate.
˚
Each Pb atom in this structure forms two ‘weak’ Pb ꢁ ꢁ ꢁ O bonds (2.913 and 2.987 A).
The presence of a lone pair on lead is apparently the reason that bridging interactions
cannot occur in the two structures and the large space not occupied by ligand. If the

Lead(II) complexes
4255
Figure 6. Intramolecular hydrogen bonding of 2.
stereochemically active lone pair is not present, it might create more interactions
between bridging atoms of lead(II) with oxygens of counter-ions. Consequently,
this phenomenon could lead to inability of the complex to adopt higher symmetry
in 1 and 2.
Three N–O bond lengths and also three ONO bond angles of nitrate in 1
˚
[N–O ¼ 1.216(8), 1.236(7), and 1.237(7) A and ONO angle ¼ 118.8(6), 119.2 (7), and
ꢂ
˚
121.9(7) ] and 2 are different [N–O ¼ 1.206(8), 1.210(7), and 1.218(7) A and ONO
angle ¼ 110(3), 120(3), and 129(3)ꢂ], and consequently the O–O distances are different.
This point shows that the nitrate anion is highly distorted by the bridging.
Comparison of free ligand with that in two complexes represents the effect of
˚
coordination, for example the range of C–N distances in 1 is 1.305(7)–1.414(8) A, and in
˚
2, 1.302(8)–1.405(9) A, shorter than those in free ligand (1.393(4)–1.399(4) A); also
˚
˚
˚
C(4)–C(5) ¼ 1.472(8)–1.474(8) A in 1 and C(1)–C(5) ¼ 1.469(2)–1.470 A in 2 are shorter
˚
than those of free ligand (1.481(4)–1.485(4) A).
˚
The distances between the two bithiazole nitrogens in free ligands is almost 3.079 A
(two nitrogens are trans with each other), whereas in 1 these distances are about
˚
˚
2.788–2.845 A and in 2, 2.797–2.859 A in two DADMBTZ ligands (two nitrogens are cis).
The torsion angle of DADMBTZ in free ligand, ffN(3)–C(4)–C(40)–N(30), is about
59.6(4)ꢂ, and in 1, ffN(1)–C(4)–C(5)–N(3) ¼ ꢀ43.5(7), ffN(5)–C(12)–C(13)–N(7) ¼
ꢀ36.3(7) and in 2, ffN(1)–C(1)–C(5)–N(3) ¼ 36.2(2), ffN(5)–C(9)–C(13)–N(7) ¼ 40.6(2),
which shows that a deviation from planarity is formed by the two thiazole rings of
bithiazoles.
The C–N bond length in the bithiazole rings in free ligand are at the range
˚
1.393(4)–1.399(4) A, and the title complexes 1.302(3)–1.474(3) A, which are shorter than
˚
˚
˚
the single bond length of 1.48 A and longer than the typical C¼N distances of 1.28 A,
indicating partial double-bond character. This can be interpreted in terms of conjugation
in the heterocycle.
˚
On the other hand, the bond length range of N(2)–C(4) ¼ 1.338(9) A,
˚
˚
˚
N(4)–C(8) ¼ 1.332(9) A, N(8)–C(16) ¼ 1.326(9) A, and N(6)–C(12) ¼ 1.361(9) A in 1
˚
˚
and N(2)–C(1) ¼ 1.354(7) A, N(4)–C(8) ¼ 1.341(8), N(8)–C(16) ¼ 1.347(7) A, and

4256
A. Hosseinian and A.R. Mahjoub
˚
N(6)–C(9) ¼ 1.349(9) A in 2 are shorter than that of normal C–N single bond, which
confirms that the nitrogen of amido is involved in the delocalization system.
3.3. Luminescence properties
Luminescence spectra of 1 and 2 in DMSO exhibit an emission at 298 K upon excitation
at 250 nm (figure 1). The intense emission bands observed (table 4), 360 for free ligand
and 363 nm for 1 and 2, are tentatively assigned to the bithiazole ꢈ–ꢈ* and n–ꢈ*
transitions [44, 45].
3.4. Thermal studies
The
thermal
stabilities
of
[Pb(DADMBTZ)2(NO3)(CH3COO) ꢁ H2O
and
[Pb(DADMBTZ)2(NO3)(ClO4)] were investigated in static air from ambient to 700ꢂC
and studied by thermal gravimetric (TG) and differential thermal analysis (DTA)
(Supplementary material). Compound 1 does not melt and it is stable up to 176ꢂC. The
TG curve of 1 indicates release of one water up to 177.8ꢂC with an endothermic effect
to give water-free [Pb(DADMBTZ)2(NO3)(CH3COO)], which is stable to 270ꢂC.
Decomposing of acetate and nitrate takes place at 274ꢂC with an exothermic effect
(observed 14.25%, Calcd 15.14%). The weight loss of 55% is equivalent to loss of two
coordinated ligands DADMBTZ (Calcd 56.57%) with one exothermic effect at
530.17ꢂC. The solid residue formed at 615ꢂC is suggested to be PbO (observed 27.75%,
Calcd 27.93%).
Compound 2 begins to decompose at 267ꢂC. Decomposing of perchlorate takes place
at 283.6ꢂC with mass loss of 9.8% consistent with the calculated value 10% for
elimination of one Cl and three oxygens with one exothermic effect (observed 27.75%,
Calcd 27.93%). The release of nitrate takes place at 302ꢂC with a slightly exothermic
effect to give PbL2 at 470ꢂC (observed 6.9%, Calcd 7.54%).
The weight loss of 53.5% from 250ꢂC to 650ꢂCis equivalent to the loss of two
coordinated DADMBTZ molecules (Calcd 55%) with one exothermic effect at 511ꢂC.
The solid residue formed at 614ꢂC is suggested to be PbO.
4. Conclusion
Two different coordination complexes arise from reaction of bithiazole with Pb(II).
The coordination geometries of the complexes show a possible vacant site around
Pb(II), occupied possibly by a stereoactive lone pair of electrons making coordination
around lead hemidirected. This study demonstrates lead is capable to form compounds
with different coordination numbers deeply influenced by the counter-ions. We
anticipate that this property of lead(II) will result in a variety of new coordination
polymers and supramolecular complexes with novel patterns and interesting physical
properties.

Lead(II) complexes
4257
Supplementary material
Complete bond lengths and angles, coordinates, and displacement parameters have
been deposited with the Cambridge Crystallographic Data Centre, CCDC nos. 289427
for [Pb(DADMBTZ)2(NO3)(CH3COO)] ꢁ H2O (1) and 629103 for [Pb(DADMBTZ)2
(NO3)(ClO4)] (2). Copies of this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 IEZ, UK (Fax: þ44-1223-336033;
Email: deposit@cdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgments
The University of Tehran and Tarbiat Modares University Research Council supported
this study. We thank the Institute of Organoelement Compounds of the Russian
Academy of Science for determining the crystal structure by X-ray crystallography.
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