Pb ? N interactions and π-stacking in lead(II) bis(hydrazone) compounds

Article abstract of DOI:10.1016/j.poly.2016.04.005

2,6-Diacetylpyridine-bis(benzoylhydrazone), H₂L^Ph, reacts with Pb(OAc)₂·3H₂O and NEt₃ as a supporting base forming a polymeric solid of the composition [Pb(L^Ph)]_n. A reaction wit

Full text of DOI:10.1016/j.poly.2016.04.005

Polyhedron 112 (2016) 96–103
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Pbꢀ ꢀ ꢀN interactions and
p-stacking in lead(II) bis(hydrazone) compounds
b
b
c
Vânia Denise Schwade a, , Tiago Bessega , Ernesto Schulz Lang , Ulrich Abram
⇑
a Faculdade de Ciências Exatas e Tecnologia, Universidade Federal da Grande Dourados, Rodovia Dourados-Itahum, km 12, 79804-970 Dourados, MS, Brazil
b Departamento de Química, Laboratório de Materiais Inorgânicos, Universidade Federal de Santa Maria, Av. Roraima, n.1000, 97105-900 Santa Maria, RS, Brazil
c Freie Universität Berlin, Institute of Chemistry and Biochemistry, Fabeckstr. 34-36, D-14195 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
2,6-Diacetylpyridine-bis(benzoylhydrazone), H2LPh, reacts with Pb(OAc)2ꢀ3H2O and NEt3 as a supporting
base forming a polymeric solid of the composition [Pb(LPh)]n. A reaction with pyridine results in cleavage
of the polymer and formation of the dimeric, crystalline compound [Pb(py)(LPh)]2.
Similar reactions with PbX2 salts (X = Cl, Br, I) also give almost insoluble solids of the tentative compo-
sition [Pb(H2LPh)X2]n. After ongoing reactions with DMSO, single deprotonation of the organic ligand and
the formation of pseudo-dimeric [Pb(HLPh)X]2 complexes was observed. Depending on the presence of
Article history:
Received 21 January 2016
Accepted 5 April 2016
Available online 9 April 2016
Keywords:
Lead complexes
Benzoylhydrazones
Self-assembly
X-ray structure
solvent molecules they form different supramolecular aggregates by p–p interactions.
The use of Pb(NO3)2 results in a dimeric structure with relatively short Pb–O bonds of 2.442(2) Å
between the monomeric sub-units. The formed dimers aggregate to a polymeric assembly by hydrogen
bonds.
p–p interactions
The products were studied by spectroscopic methods and X-ray diffraction.
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
clear and dinuclear structures involving the first row transition
metals have been prepared and structurally characterized. With
The structural coordination chemistry of 2,6-diacetylpyridine-
bis(hydrazones), -bis(semicarbazones) or -bis(thiosemi-car-
bazones) with lead(II) is hitherto restricted to syn close complexes
[1–5]. The compounds are formed by N3O2 or N3S2 coordination of
the pentadentate ligands as is shown in Chart 1. While there is only
each one structurally characterized example for hydrazone com-
plexes I and semicarbazone complexes II [1,4], a few thiosemicar-
bazone compounds of type III are reported [2,3,5]. The lead(II)
compounds are usually obtained by electrochemical syntheses
[1,2], conventional metathesis procedures [3,4] or by decomposi-
tion of methyllead(IV) compounds [5].
the p block metals, however, there are only a few examples with
Sn(II), Sb(III) and Bi(III) ions [1,8] in addition to the Pb(II) com-
pounds referred above and shown in Chart 1. The coordination
spheres of the metal ions are completed by anions such as halides
or nitrate, and by solvent molecules such as water, dimethyl sul-
foxide, dimethylformamide or pyridine. The coordination of two
ligand molecules to the same metal ion is found only in Ln3+ and
Th4+ complexes [7–11], for which large coordination numbers are
common.
Intermolecular Pbꢀ ꢀ ꢀS and
p
–
p
interactions as well as N–Hꢀ ꢀ ꢀS
or N–Hꢀ ꢀ ꢀN hydrogen bonds have been described for the lead(II)
thiosemicarbazonato complexes (type III) [2,3,5]. For the struc-
turally studied lead(II) hydrazonato and semicarbazone complexes
there are no related intermolecular interactions [1,4].
2,6-Diacetylpyridine-bis(benzoylhydrazone) can coordinate as a
neutral, monoanionic or dianionic ligand. The degree of deprotona-
tion in the products is influenced by the coordinated metal ion, the
reactions conditions and the availability of potential anionic co-
ligands or counter ions [6,7]. A considerable number of mononu-
In the present communication, we describe syntheses and crys-
tal structures of pseudo-dimeric and polymeric lead(II) complexes
with 2,6-diacetylpyridine-bis(benzoylhydrazone) (H2LPh) and the
influence of solvent molecules and anionic co-ligands in the struc-
tural chemistry of this class of componds.
⇑
Corresponding author.
E-mail address: vaniaschwade@ufgd.edu.br (V.D. Schwade).
http://dx.doi.org/10.1016/j.poly.2016.04.005
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

V.D. Schwade et al. / Polyhedron 112 (2016) 96–103
97
Chart 1. Benzoylhydrazone, semicarbazone and thiosemicarbazone complexes of Pb(II).
2. Results and discussion
2.1. [Pb(LPh)]n and [Pb(py)(LPh)]2
Equivalent amounts of lead(II) acetate and H2LPh react after
addition of triethylamine as supporting base in methanol with a
yellow solid being formed. The product precipitates directly from
the reaction mixture in a practically quantitative yield. It is only
very slightly soluble in dimethylformamide or dimethylsulfoxide,
even under gentle heating, but well soluble in pyridine. Thus,
recrystallization from a pyridine/methanol mixture gives yellow
crystals of [Pb(py)(LPh)]2 (Scheme 1).
The IR spectrum of [Pb(LPh)]n clearly supports the coordination
of the dianionic [LPh 2ꢁ
]
ligand by the observed bathochromic shift
of the
m
C@O frequency from 1663 cmꢁ1 in H2LPh to 1497 cmꢁ1 in the
product, while the mN–H vibrations disappeared in the spectrum of
the complex. Unfortunately, the compound was not sufficiently
soluble to obtain NMR spectra of reasonable quality. A polymeric
structure as is depicted in Scheme 1 is proposed for this compound
(i) by its low solubility, even in a number of coordinating solvents,
and (ii) by the assumption of a stereochemically active lone-pair in
the coordination plane of the chelating ligands, which would allow
polymerization perpendicular to this plane, e.g. by
p-stacking or
weak Pbꢀ ꢀ ꢀN interaction as they have been found in the pyridine
derivative, the structure of which will be discussed vide infra.
The IR spectrum of the pyridine adduct [Pb(py)(LPh)]2 shows the
presence of pyridine by the bands at 1450, 1216, 767 and
621 cmꢁ1, which additionally appear in comparison to the spec-
trum of the polymeric starting material [Pb(LPh)]n.
[Pb(py)(LPh)]2 crystallizes in the orthorhombic space group
Pbca. Fig. 1a depicts an ellipsoid plot of its molecular structure
and selected bond lengths and angles are summarized in Table 1.
The gap in the coordination sphere, which can be assigned to the
position of the stereochemically active lone-pair of the Pb(II) ion,
can best be seen in Fig. 1b. The corresponding O1–Pb1–O2 angle
of 104.21(6)° is clearly larger than the O–N and N–N angles inside
the plane, which range between 60.16(6)° and 63.57(7)°. The pyr-
idine ligand is coordinated in the apical position and completes the
Fig. 1. (a) Ellipsoid representation [33] of the monomeric unit of the molecular
structure of [Pb(py)(HLPh)]2. Thermal ellipsoids represent 50 per cent probability.
Hydrogen atoms have been omitted for clarity. (b) Representation of the pseudo-
dimeric structure formed by Pbꢀ ꢀ ꢀN interactions. Symmetry operator: (0) ꢁx, ꢁy + 1,
ꢁz + 1.
Scheme 1. Formation of [Pb(py)(LPh)]2 from [Pb(LPh)]n.

98
V.D. Schwade et al. / Polyhedron 112 (2016) 96–103
Table 1
Selected bond lengths (Å) and angles (°) in [Pb(py)(LPh)]2.
Pb1–O1
Pb1–O2
Pb1–N1
Pb1–N2
Pb1–N4
Pb1–N6
2.6174(19)
2.4794(19)
2.5545(19)
2.603(2)
2.514(2)
2.518(2)
O1–C8
N3–C8
N2–N3
O2–C17
N5–C17
N4–N5
1.245(3)
1.346(3)
1.377(3)
1.273(3)
1.331(3)
1.375(3)
Pb1ꢀ ꢀ ꢀN30
3.180(2)
O1–Pb1–N1
O1–Pb1–N2
O1–Pb1–N4
O1–Pb1–N6
O1–Pb1–O2
120.63(7)
60.16(6)
156.50(7)
78.41(7)
104.21(6)
O2–Pb1–N1
O2–Pb1–N2
O2–Pb1–N4
O2–Pb1–N6
N1–Pb1–N2
125.18(6)
158.67(7)
62.93(6)
80.64(7)
62.61(7)
N1–Pb1–N4
N1–Pb1–N6
N2–Pb1–N4
N2–Pb1–N6
N4–Pb1–N6
63.57(7)
79.37(7)
125.38(6)
81.83(7)
80.00(7)
Symmetry operator: (0) ꢁx, ꢁy + 1, ꢁz + 1.
Scheme 2. Formation of [Pb(HLPh)X]2.
pentagonal pyramidal coordination sphere of the lead(II) ion. The
pentagonal N3O2 plane shows only slight deviations from planarity
(a maximum deviation of 0.078(1) Å has been found for the atom
N2). The metal atom is situated 0.4432(9) Å below this plane, in
the opposite direction of the pyridine ligand.
[Pb(py)(LPh)]2 is the first neutral complex with a bis(hydra-
zonato) ligand having a neutral ligand in the apical position. In
the literature, we only have found one structurally related com-
pound with a cyanido ligand in the apical position [1].
The Pb–O bond lenghts are different, with the Pb1–O1 bond of
2.6174(19) Å being markedly longer than the Pb1–O2 one
(2.4794(19) Å). This effect may be caused by the intermolecular
Pb1ꢀ ꢀ ꢀN30 interactions.
Intermolecular interactions between the monomers originate a
pseudo-dimeric structure (Fig. 1b). The Pb1ꢀ ꢀ ꢀN30 distance of 3.180
(2) Å (symmetry code: ꢁx, ꢁy + 1, ꢁz + 1) is within the sum of the
van der Waals radii [12] of the corresponding atoms and is in the
average of Pbꢀ ꢀ ꢀN interactions found before for isonicotinoylhydra-
zone derivatives [13,14].
Finally, two points are remarkable: (i) only the excellent donor
pyridine was able to break the polymeric structure of [Pb(py)
(LPh)]2, while the compound did not react in the same way with
DMSO or DMF, and (ii) that the fragmentation of the polymer stops
in the reported pseudo-dimeric arrangement and does not give the
(more expected) bis pyridine adduct. The latter fact might be due
to the lone pair effect, which rules the coordination chemistry of
lead(II) compounds [15,16]. The coordination of a second molecule
of pyridine and the formation of pentagonal bipyramidal coordina-
tion spheres has been observed for corresponding Mn(II), Co(II) and
Cd(II) compounds [17,18].
Fig. 2. (a) Ellipsoid representation [33] of the molecular structure of [Pb(HLPh)Cl]2.
Thermal ellipsoids represent 50 per cent probability. Hydrogen atoms have been
omitted for clarity, with exception of NH. (b) View of the pseudo-dimeric structure
formed by
p
–p
and Pbꢀ ꢀ ꢀN interactions. Symmetry operator: (0) ꢁx + 1, ꢁy + 1, ꢁz + 1.
2.2. [Pb(H2LPh)X2]n and [Pb(HLPh)X]2 (X = Cl, Br, I)
sparingly soluble, yellow to orange-yellow solids (Scheme 2).
They can be assigned to
composition of [Pb(H2LPh)X2]n
(X = Cl, Br, I) by means of elemental analysis and their IR spectra.
The compounds are most probably polymers with infinite
a
Reactions of lead(II) halides with H2LPh in methanol, but without
the addition of a supporting base also result in the formation of

V.D. Schwade et al. / Polyhedron 112 (2016) 96–103
99
Table 2
Selected bond lengths (Å) and angles (deg) in [Pb(HLPh)X]2 complexes.
[Pb(HLPh)Cl]2
[Pb(HLPh)Br]2
[Pb(HLPh)I]2
[Pb(HLPh)I]2ꢀ2MeOHꢀH2O
Pb1–O1
Pb1–O2
Pb1–N1
Pb1–N2
Pb1–N4
Pb1–X1
Pb1ꢀ ꢀ ꢀN30
O1–C8
2.465(3)
2.924(4)
2.556(4)
2.460(4)
2.786(4)
2.6258(17)
3.156(4)
1.263(5)
1.331(6)
1.390(5)
1.188(6)
1.379(7)
1.379(5)
2.459(3)
2.919(4)
2.553(3)
2.448(3)
2.809(4)
2.7750(5)
3.170(3)
1.263(4)
1.339(5)
1.382(4)
1.211(5)
1.359(5)
1.383(4)
2.4503(19)
2.927(3)
2.566(2)
2.439(2)
2.820(2)
2.9950(3)
3.180(2)
1.266(3)
1.335(4)
1.381(3)
1.213(4)
1.360(4)
1.383(3)
2.512(6)
2.851(7)
2.590(7)
2.492(6)
2.738(7)
2.9879(7)
3.190(7)
1.272(10)
1.322(10)
1.372(9)
1.237(11)
1.315(11)
1.368(9)
N3–C8
N2–N3
O2–C17
N5–C17
N4–N5
O1–Pb1–N1
O1–Pb1–N2
O1–Pb1–N4
O1–Pb1–X1
O1–Pb1–O2
O2–Pb1–N1
O2–Pb1–N2
O2–Pb1–N4
O2–Pb1–X1
N1–Pb1–N2
N1–Pb1–N4
N1–Pb1–X1
N2–Pb1–N4
N2–Pb1–X1
N4–Pb1–X1
127.71(12)
64.39(12)
164.90(12)
82.43(10)
117.05(12)
114.94(13)
170.23(13)
55.50(12)
98.49(9)
65.39(13)
60.13(12)
85.04(10)
125.50(13)
91.26(10)
85.78(11)
128.29(9)
64.41(10)
165.25(9)
82.67(7)
116.86(10)
114.66(11)
170.15(11)
55.24(10)
100.73(8)
65.41(10)
60.16(10)
83.90(7)
129.06(7)
65.21(7)
165.04(6)
82.33(5)
115.97(7)
114.68(8)
171.92(8)
55.37(7)
101.92(6)
65.48(7)
59.85(7)
82.48(5)
125.32(7)
86.14(5)
87.65(5)
126.3(2)
62.9(2)
166.0(2)
87.05(16)
115.9(2)
117.1(2)
177.9(2)
57.3(2)
86.63(15)
64.4(2)
60.0(2)
87.95(15)
124.3(2)
94.95(16)
80.44(15)
125.55(10)
89.10(8)
86.70(7)
Symmetry operator: (0) ꢁx + 1, ꢁy + 1, ꢁz + 1 for [Pb(HLPh)Cl]2 and [Pb(HLPh)I]2; ꢁx + 2, ꢁy, ꢁz + 2 for [Pb(HLPh)Br]2.
Fig. 3. Polymeric structure of [Pb(HLPh)I]2ꢀ2MeOHꢀH2O formed by
p-stacking interactions between the pyridine and phenyl rings [33]. The solvent molecules have been
omitted.
ꢀ ꢀ ꢀCl–Pb(HLPh)–Cl–Pb(HLPh)–Clꢀ ꢀ ꢀ chains. The formation of
bis(chlorido)-bridged dimers as shown in parenthesis in Scheme 2
cannot be ruled out, but may be regarded as unlikely, since such a
benzoyl-hydrazones, where the corresponding IR bands are
bathochromically shifted by more than 100 cmꢁ1. Interestingly,
the spectroscopic results are not reflected by the bond lengths of
the C–O bonds in the dimeric units isolated from the polymers
[Pb(LPh)]n and [Pb(H2LPh)X2]n.
coordination would require
a holodirected, stereochemically
inactice 6s lone pair, while for all other compounds of this
study and in the previously reported lead(II) complexes with 2,6-
diacetylpyridine-bis(hydrazones) or -bis(semicarba-zones) hemidi-
rected lone pairs were observed.
Dissolution of [Pb(H2LPh)X2]n compounds in DMSO results in the
scission of the polymeric chains and the formation of pseudo-
dimeric complexes of the composition [Pb(HLPh)X]2 (X = Cl, Br, I).
Remarkably, these reactions go along with abstraction of one
equivalent of HX and the formation of single-deprotonated
Evidence for the coordination of H2LPh in protonated form is
clearly given by the IR spectra of the compounds. The mNH vibra-
tions appear at 3143, 3351 and 3367 cmꢁ1 for the compounds with
Cl, Br and I, respectively. More indicative is the detection of the
mC@O frequencies at 1641, 1654 and 1657 cmꢁ1 for these com-
pounds, which is a strong indicator, that almost no delocalization
of electron density is present in the corresponding chelate rings.
This contrasts the situation in complexes with deprotonated
[HLPh ꢁ ligands. Coordination of H2LPh and its derivatives as neutral
]
ligands to M2+ ions has been observed before for Mn, Fe, Co, Ni, Cu,
Zn and Cd in structurally well-characterized mononuclear
complexes [19–25]. For the deprotonation of coordinated
2,6-diacetylpyridine-bis(hydrazone) ligands, there is to the best
of our knowledge only one precedent. It has been observed for

100
V.D. Schwade et al. / Polyhedron 112 (2016) 96–103
structurally related [M(H2L)Cl2] complexes (M = Mn, Co) after the
addition of sodium tetraphenylborate [26].
of p–p -interactions organizing the dimers into a two-dimensional
network along the (001) plane. The centroid–centroid distances of
these weak interactions are 3.763 and 3.899 Å. The assembly of the
pseudo-dimers into a supramolecular 2D network is depicted in
Fig. 3.
The [Pb(HLPh)X]2 complexes are sufficiently soluble in DMSO to
record 1H NMR spectra of reasonable quality. The NH signals can be
detected at 10.87, 11.05 and 11.47 ppm for [Pb(HLPh)Cl]2, [Pb(HLPh
)
Br]2 and [Pb(HLPh)I]2, respectively. Monodeprotonation of the
organic ligands can also been derived from the IR spectra of the
complexes, where each pairs of signals are observed in the region
around 1670 and 1507 cmꢁ1. The mNH vibrations appear at 3242,
2.3. [Pb(HLPh)(NO3)]2
The reaction of H2LPh with lead(II) nitrate in methanol forms
without the adddition of a supporting base immediately a slightly
3262 and 3265 cmꢁ1 for [Pb(HLPh)Cl]2, [Pb(HLPh)Br]2 and [Pb(HLPh
I]2, respectively.
)
[Pb(HLPh)Cl]2, [Pb(HLPh)Br]2 and [Pb(HLPh)I]2 are isostructural
and crystallize in the monoclinic space group P21/c. Fig. 2a depicts
an ellipsoid plot of [Pb(HLPh)Cl]2 as a representative of the halide
compounds. The molecular structures of [Pb(HLPh)Br]2 and
[Pb(HLPh)I]2 are virtually identical. For this reason no extra figures
are given for them. Selected bond lengths and angles of all three
[Pb(HLPh)X]2 complexes are summarized in Table 2, the corre-
sponding labeling scheme has been adopted from Fig. 2a. By means
of the Pb–O distances (each one in the range of 2.4–2.5 Å and one
between 2.8 and 2.9 Å) it is possible to distinguish between the
‘‘protonated” and the ‘‘deprotonated arms” of the ligands indicating
a weaker bonding to the uncharged carbonyl oxygen atoms O2. The
Pb–Cl bond length in the chloride compound of 2.626(2) Å is
remarkably shorter than the distance of 2.707(4) Å, which has
been determined for the related semicarbazone complex reported
in Ref. [4]. There are no reference values available for the Pb–Br
and Pb–I bonds in [Pb(HLPh)Br]2 and [Pb(HLPh)I]2, since they
represent the first lead(II) hydrazone complexes with these halides
as co-ligands.
The pentagonal N3O2 coordination spheres of the halide com-
plexes are almost planar. Maximum deviations from planarity
was found for the atoms N2 or N4 for all complexes and are in
the range between 0.161(5) and 0.281(3) Å. The lead atoms are sit-
uated out of these mean least-square planes on the opposite sides
compared to the halide ligands with distances between 0.026(2)
and 0.119(3) Å.
Intermolecular interactions between the monomers produce
pseudo-dimeric structures, as can be seen in Fig. 2b. Since the main
structural features are identical for [Pb(HLPh)Cl]2, [Pb(HLPh)Br]2
and [Pb(HLPh)I]2, the situation in the chlorido compound shall be
described exemplarily. Weak Pb1ꢀ ꢀ ꢀN30 (symmetry code: ꢁx + 1,
ꢁy + 1, ꢁz + 1) interactions organize each two of the molecules
parallel to each other with Pb–N distances of 3.156(4) Å (3.170
(3) Å for the bromido complex and 3.180(2) Å for the iodido com-
plex). The Pbꢀ ꢀ ꢀN interactions are reinforced by
p–p interactions
between the pyridine rings and the phenyl rings of the adjacent
molecule. The ‘parallel offset’ aromatic stacking arrangement [27]
is identified in these complexes. The centroid–centroid distances
are 3.653, 3.651 and 3.654 Å for [Pb(HLPh)Cl]2, [Pb(HLPh)Br]2 and
[Pb(HLPh)I]2, respectively. To the best of our knowledge, there is
only one more report, which describes both interactions (Pbꢀ ꢀ ꢀN
and p–p) in a lead(II) compound with a monohydrazonato ligand,
and a copper(II) compound with 2-pyridylaldehyde isonicotinoyl-
hydrazone [28].
Since the solvated iodide derivative [Pb(HLPh)I]2ꢀ2MeOHꢀH2O
crystallizes with solvent molecule in the monoclinic space group
P21/n, the crystal packing features of this compound are different
from the not solvated halido complexes. Also here, relatively short
intermolecular Pbꢀ ꢀ ꢀN distance is observed. With 3.190(7) Å they
are slightly longer than for the previous halido compounds. Conse-
Fig. 4. (a) Ellipsoid representation [33] of the asymmetric unit of [Pb(HLPh)(NO3)]2.
Thermal ellipsoids represent 50 per cent probability. Hydrogen atoms have been
omitted for clarity, with exception of NH. (b) View of the dimeric molecular
structure. (c) Polymeric network formed by N–Hꢀ ꢀ ꢀO hydrogen bonds. Phenyl
groups have been omitted for clarity. Symmetry operators: (0) ꢁx, ꢁy + 1, ꢁz; (00) ꢁx
+ 0.5, y ꢁ 0.5, ꢁz + 0.5.
quently, the centroid–centroid distance of the
p-stacking interac-
tions is also bigger (3.744 Å). The pseudo-dimer formed due to
these interactions is shown in Fig. 3. In contrast to the situation
in [Pb(HLPh)X]2, the phenyl rings, which are not involved in
p-stacking to form the pseudo-dimers establish a second group

V.D. Schwade et al. / Polyhedron 112 (2016) 96–103
101
Table 3
Selected bond lengths (Å) and angles (°) in [Pb(HLPh)(NO3)]2.
Pb1–O1
Pb1–O2
Pb1–N1
Pb1–N2
Pb1–N4
Pb1–O3
2.7513(19)
2.7082(15)
2.5431(17)
2.6693(17)
2.4902(19)
2.701(2)
O1–C8
N3–C8
N2–N3
O2–C17
N5–C17
N4–N5
1.227(3)
1.359(3)
1.372(2)
1.299(3)
1.305(3)
1.387(3)
Pb1ꢀ ꢀ ꢀO20
Pb1ꢀ ꢀ ꢀO5
2.4420(16)
3.309(2)
O1–Pb1–N1
O1–Pb1–N2
O1–Pb1–N4
O1–Pb1–O3
O1–Pb1–O2
O2–Pb1–N1
O2–Pb1–N2
120.77(6)
59.01(5)
O2–Pb1–N4
O2–Pb1–O3
N1–Pb1–N2
N1–Pb1–N4
N1–Pb1–O3
N2–Pb1–N4
N2–Pb1–O3
60.17(6)
115.81(7)
61.83(6)
64.28(6)
71.89(7)
126.08(6)
87.24(8)
N4–Pb1–O3
N1–Pb1–O2’
N2–Pb1–O2’
N4–Pb1–O2’
O1–Pb1–O2’
O2–Pb1–O2’
O3–Pb1–O2’
78.02(7)
82.87(6)
82.14(5)
89.81(6)
86.65(7)
75.15(6)
154.71(7)
173.31(6)
107.38(7)
113.36(5)
119.54(5)
156.63(5)
Hydrogen bonds (N–H, Hꢀ ꢀ ꢀO, Nꢀ ꢀ ꢀO, \NHO)
N3–H3Aꢀ ꢀ ꢀO500
0.86
2.31
3.083(3)
149.4
Symmetry operators: (0) ꢁx, ꢁy + 1, ꢁz; (00) ꢁx + 1/2, y ꢁ 1/2, ꢁz + 1/2.
Table 4
X-ray structure data collection and refinement parameters.
[Pb(py)(LPh)]
[Pb(HLPh)Cl]
[Pb(HLPh)Br]
[Pb(HLPh)I]
[Pb(HLPh)I] ꢀMeOHꢀ0.5H2O
[Pb(HLPh)(NO3)]2
Formula
Mw
Crystal system
a (Å)
b (Å)
c (Å)
C28H24N6O2Pb
683.72
orthorhombic
20.8235(7)
11.4127(3)
21.4438(6)
90
C23H20ClN5O2Pb
641.08
monoclinic
8.4151(17)
12.981(3)
20.321(4)
90
C23H20BrN5O2Pb
685.54
C23H20IN5O2Pb
732.53
C24H25IN5O3.5Pb
773.58
C46H40N12O10Pb2
1335.28
monoclinic
27.4709(8)
8.5387(2)
23.5924(7)
90
monoclinic
8.4393(3)
13.0932(5)
20.4388(7)
90
monoclinic
8.4644(2)
13.2888(3)
20.6322(5)
90
monoclinic
15.8483(5)
11.5216(4)
16.2156(6)
90
a
(°)
b (°)
90
90
5096.2(3)
Pbca
8
94.50(3)
90
2213.0(8)
P21/c
92.979(2)
90
2255.38(14)
P21/c
90.7090(10)
90
2320.57(9)
P21/c
109.219(2)
90
2795.91(17)
P21/n
124.3640(10)
90
4568.1(2)
C2/c
c
(°)
V (Å3)
Space group
Z
4
4
4
4
4
Dcalc. (g cmꢁ3
)
1.782
6.659
1.924
7.776
2.019
9.283
2.097
8.631
1.827
7.171
1.942
7.435
l
(mmꢁ1
)
No. of refl.
No. of indep.
No. param.
R1/wR2
59595
7447
336
0.0222/0.0404
1.005
33935
6845
291
0.0425/0.0703
0.962
39342
6941
291
0.0333/0.0580
1.006
39599
6982
291
0.0260/0.0464
1.038
47684
8598
322
0.0508/0.1187
0.963
67956
6884
318
0.0205/0.0435
1.025
Goodness-of-fit (GOF) on F2
yellow solid, which can be assigned to a composition of [Pb(H2LPh
)
Fig. 3b. The nitrate ion is coordinated to the Pb atom through the
O3 atom with a distance of 2.701(2) Å, which is longer than the
Pb–O bond lengths found in other Pb/monohydrazone complexes
with coordinated nitrate [13,29]. As in the other two crystal struc-
tures with nitrato ligands [13,29], a second oxygen atom (O5 atom)
of the nitrate weakly interacts with Pb. In [Pb(HLPh)(NO3)]2, this
contact is relatively long (3.309(2) Å), since this oxygen atom
establishes an intermolecular hydrogen bond to the nitrogen atom
of the ‘‘non-deprotonated arm” of an adjacent complex molecule.
These N–Hꢀ ꢀ ꢀO hydrogen bonds arrange the dimeric complex
molecules to a two-dimensional network in the (10ꢁ1) plane as
is shown in Fig. 4c.
(NO3)2]2 or [Pb(H2LPh)(NO3)2]n as has been discussed in an analo-
gous manner before for the halido compounds. The IR spectrum
of the precipitated material clearly confirms the coordination of
the ligand without deprotonation. The mN–H vibration is detected
at 3228 cmꢁ1 and the mC@O frequency appears at 1648 cmꢁ1. The
coordination of nitrate is supported by the bands at 1440 and
1383 cmꢁ1
.
The solid readily dissolves in dimethylformamide or dimethyl
sulfoxide forming yellow solutions. From both solvents, single
crystals of the composition [Pb(HLPh)(NO3)]2 could be obtained.
Similar to the [Pb(HLPh)X]2 complexes (X = Cl, Br, I), dissolution in
coordinating solvents results in monodeprotonation of the ligand,
the elimination of HNO3 and the final formation of a well-defined
dimeric compound: [Pb(HLPh)(NO3)]2.
3. Conclusions
[Pb(HLPh)(NO3)]2 crystallizes in the monoclinic space group
C2/c. An ellipsoid representation of the asymmetric unit is shown
in Fig. 4a. Table 3 contains selected bond lengths and angles. The
Pb–O bonds inside the five-membered chelate rings of the pen-
tadentate ligand are 2.751(2) (Pb1–O1) and 2.708(2) Å (Pb1–O2).
This means, they are almost equal, which is in contrast to the
The coordination chemistry of 2,6-diacetylpyridine-bis(ben-
zoylhydrazone) with lead(II) goes beyond the simple formation
of complexes with pentadentate organic ligands. The use of differ-
ent Pb(II) salts in essentially similar reactions results in
supramolecular assemblies of different arrangements depending
on the starting materials and the reaction conditions. Weak inter-
halide complexes, which also possess monodeprotonated [LPh ꢁ
]
ligands. Surprisingly short Pb–O bonds of 2.442(2) Å, however,
are established between the lead(II) ions and the O20 donors of
the adjacent chelate (symmetry code: ꢁx, ꢁy + 1, ꢁz). They estab-
lish the coordination dimers of [Pb(HLPh)(NO3)]2 as is illustrated in
molecular Pbꢀ ꢀ ꢀN interactions,
p-stacking or hydrogen bonds orga-
nize the products in different dimeric arrangements ([Pb(py)
(LPh)]2, [Pb(HLPh)Cl]2, [Pb(HLPh)Br]2) or supramolecular assemblies
with dimeric sub-structures ([Pb(HLPh)I]2, [Pb(HLPh)(NO3)]2).

102
V.D. Schwade et al. / Polyhedron 112 (2016) 96–103
1379 (w), 1290 (w), 1264 (s), 1164 (m), 1155 (m), 1118 (w),
1071 (w), 999 (w), 897 (w), 801 (m), 709 (s), 683 (w), 658 (w),
478 (w).
4. Experimental
4.1. Materials
4.3.3.3. [Pb(H2LPh)I2]n. Yield: 92%. Anal. Calc. for C23H21I2N5O2Pb: C,
32.10; H, 2.46; N, 8.14. Found: C, 31.71; H, 2.49; N, 7.69%. IR (KBr,
mmax in cmꢁ1): 3367 (w), 3024 (w), 1657 (s), 1614 (m), 1597 (m),
1577 (m), 1517 (m), 1480 (m), 1447 (m), 1376 (w), 1290 (w),
1261 (s), 1165 (m), 1155 (m), 1118 (w), 1069 (w), 999 (w), 898
(w), 799 (m), 707 (m), 682 (w), 657 (w), 467 (w).
All reagents used were reagent grade and used without further
purification. H2LPh was prepared from equivalent amounts of 2,6-
diacetylpyridine and benzoylhydrazine in ethanol following litera-
ture procedures [30,31].
4.2. Physical measurements
4.3.4. [Pb(HLPh)X]2 (X = Cl, Br, I)
Infrared spectra were measured from KBr pellets on a Bruker
Tensor 27 FTIR instrument between 400 and 4000 cmꢁ1. Elemental
analysis of carbon, hydrogen and nitrogen were determined using a
Perkin Elmer CHN 2400 elemental analyzer. NMR-spectra were
Recrystallization of the [Pb(H2LPh)X2]2 (X = Cl, Br, I) complexes
from neat DMSO or DMSO/MeOH mixtures resulted in HX abstrac-
tion and the formation of yellow, block-shaped single crystals of
the [Pb(HLPh)X]2 complexes.
taken with
spectrometer.
a
Bruker DPX-NMR 400 MHz multinuclear
4.3.4.1. [Pb(HLPh)Cl]2. Yellow crystals. Yield: 60%. Anal. Calc. for C23
-
H20ClN5O2Pb: C, 43.09; H, 3.14; N, 10.92. Found: C, 41.65; H, 3.25;
N, 10.09%. IR (KBr, mmax in cmꢁ1): 3242 (w), 3050 (w), 1667 (s),
1581 (w), 1533 (w), 1505 (s), 1449 (w), 1417 (w), 1347 (s), 1315
(w), 1300 (w), 1265 (m), 1196 (w), 1175 9w), 1147 (m), 1067
(w), 1034 (m), 1022 (m), 936 (w), 895 (w), 804 (m), 735 (w), 711
(s), 689 (m), 677 (m), 664 (m), 500 (w). 1H NMR (DMSO-D6; d,
ppm): 2.52 (s, 6H, CH3), 7.51–7.62 (m, 6H, Ph), 7.91–7.93 (m, 5H,
py + Ph), 8.06 (br, 2H, py), 10.87 (s, 1H, NH).
4.3. Syntheses
4.3.1. [Pb(LPh)]n
A solution of Pb(OAc)2ꢀ3H2O (100 mg, 0.26 mmol) in 4 mL of
MeOH was added dropwise to a suspension of H2LPh (105 mg,
0.26 mmol) in 8 mL of MeOH. After the complete addition of the
ligand, 10 drops of Et3N were added and the reaction mixture
was stirred for additional 2 h. The formed solid was filtered off
and washed with MeOH. Yield: 99%. Anal. Calc. for C23H19N5O2Pb:
C, 45.69; H, 3.17; N, 11.58. Found: C, 45.54; H, 3.06; N, 11.35%. IR
(KBr, mmax in cmꢁ1): 3060 (w), 2909 (w), 1583 (w), 1538 (w),
1497 (m), 1474 (w), 1406 (w), 1350 (s), 1320 (m), 1295 (m),
1175 (m), 1159 (m), 1049 (w), 1001 (w), 898 (w), 798 (w), 732
(w), 707 (m), 685 (w), 672 (w), 500 (w).
4.3.4.2. [Pb(HLPh)Br]2. Yellow crystals. Yield: 75%. Anal. Calc. for C23
-
H
20BrN5O2Pb: C, 40.30; H, 2.94; N, 10.22. Found: C, 40.08; H, 3.01;
N, 9.99%. IR (KBr,
m
max in cmꢁ1): 3262 (w), 3050 (w), 1670 (s), 1581
(w), 1522 (w), 1507 (s), 1449 (w), 1417 (w), 1347 (s), 1316 (w),
1300 (w), 1265 (m), 1197 (w), 1175 (w), 1147 (m), 1067 (w),
1033 (m), 1022 (m), 937 (w), 895 (w), 804 (m), 734 (w), 712 (s),
689 (m), 677 (m), 664 (m), 499 (w). 1H NMR (DMSO-D6; d, ppm):
2.58 (s, 6H, CH3), 7.52–7.63 (m, 6H, Ph), 7.94–7.96 (m, 4H, Ph),
8.03 (br, 1H, py), 8.11 (br, 2H, py), 11.05 (s, 1H, NH).
4.3.2. [Pb(py)(LPh)]2
The solid of [Pb(LPh)]n (50 mg) was dissolved under stirring in
10 mL of neat pyridine, which resulted in an yellow solution. This
solution was mixed with 5 mL MeOH and kept for slow evapora-
tion at room temperature, which gave yellow, block-shaped single
crystals of [Pb(py)(LPh)]2. Yield: 90%. Anal. Calc. for C28H24N6O2Pb:
C, 49.19; H, 3.54; N, 12.29. Found: C, 49.17; H, 3.93; N, 12.10%. IR
(KBr, mmax in cmꢁ1): 3046 (w), 2920 (w), 1583 (w), 1536 (m),
1508 (m), 1479 (m), 1450 (m), 1405 (w), 1348 (s), 1312 (m),
1291 (m), 1216 (w), 1168 (m), 1150 (m), 1064 (w), 1031
(m), 1001 (m), 976 (w), 911 (w), 847 (w), 798 (m), 767 (m), 732
(w), 714 (s), 670 (m), 621 (m), 510 (w), 415 (w).
4.3.4.3. [Pb(HLPh)I]2. Yellow crystals. Yield: 70%. Anal. Calc. for C23
20IN5O2Pb: C, 37.71; H, 2.75; N, 9.56. Found: C, 37.77; H, 2.83; N,
-
H
9.32%. IR (KBr, mmax in cmꢁ1): 3265 (w), 3048 (w), 1673 (s), 1581
(w) 1550 (w), 1508 (s), 1450 (w), 1417 (w), 1347 (s), 1316 (w),
1299 (w), 1265 (m), 1199 (w), 1174 (w), 1148 (m), 1067 (w),
1033 (m), 999 (w), 936 (w), 896 (w), 804 (m), 791 (w), 733 (w),
714 (s), 689 (m), 678 (m), 664 (m), 497 (w). 1H NMR (DMSO-D6;
d, ppm): 2.65 (s, 6H, CH3), 7.55–7.67 (m, 6H, Ph), 7.99–8.01 (m,
4H, Ph), 8.21 (br, 3H, py), 11.47 (s, 1H, NH).
Yellow crystals of [Pb(HLPh)I]2ꢀ2MeOHꢀH2O were obtained as a
mixture when a small amount of the solution was let over a glass
plate during the night.
4.3.3. [Pb(H2LPh)X2]n (X = Cl, Br, I)
A suspension of H2LPh (48 mg, 0.12 mmol) in 4 mL of MeOH was
added dropwise to suspensions of PbX2 (0.1 mmol) in 2 mL of
MeOH. After the complete addition of the ligand, the yellow to
orange turbid reaction mixtures were stirred at room temperature
for 2 h. The resulting solids were filtered off and washed with
MeOH.
4.3.5. [Pb(H2LPh)(NO3)2]2 and [Pb(HLPh)(NO3)]2
4.3.5.1. [Pb(H2LPh)(NO3)2]2. A suspension of H2LPh (48 mg,
0.12 mmol) in 4 mL of MeOH was added dropwise to a suspension
of Pb(NO3)2 (33 mg, 0.1 mmol) in 2 mL of MeOH. The resulting yel-
low turbid solution was stirred at room temperature for 2 h. The
pale yellow solid was filtered off and washed with MeOH. Yield:
85%. Anal. Calc. for C23H21N7O8Pb: C, 37.81; H, 2.90; N, 13.42.
Found: C, 37.85; H, 2.93; N, 13.15%. IR (KBr, mmax in cmꢁ1): 3228
(w), 3047 (w), 1684 (s), 1618 (w), 1601 (w), 1579 (m), 1536 (m),
1491 (w), 1440 (m), 1383 (m), 1273 (s), 1166 (m), 1074 (w),
1027 (w), 898 (w), 805 (w), 735 (w), 711 (m), 686 (w), 663 (w),
529 (w).
4.3.3.1. [Pb(H2LPh)Cl2]n. Yield: 86%. Anal. Calc. for C23H21Cl2N5O2Pb:
C, 40.77; H, 3.12; N, 10.34. Found: C, 40.58; H, 3.16; N, 9.98%. IR
(KBr, mmax in cmꢁ1): 3143 (w), 2940 (w), 1641 (s), 1616 (m),
1600 (m), 1577 (m), 1531 (s), 1489 (m), 1452 (m), 1432 (m),
1372 (m), 1274 (s), 1156 (m), 1117 (w), 1074 (w), 1010 (w), 896
(w), 805 (m), 736 (m), 713 (s), 688 (m), 529 (w), 457 (w).
4.3.3.2. [Pb(H2LPh)Br2]n. Yield: 76%. Anal. Calc. for C23H21Br2N5O2Pb:
C, 36.04; H, 2.76; N, 9.14. Found: C, 35.72; H, 2.85; N, 8.76%. IR
(KBr, mmax in cmꢁ1): 3351 (w), 3027 (w), 1654 (s), 1616 (m),
1598 (m), 1578 (m), 1523 (m), 1483 (m), 1449 (m), 1427 (m),
4.3.5.2. [Pb(HLPh)(NO3)]2. Light-yellow, block-shaped crystals were
obtained by recrystallization from deutered DMSO or DMSO/MeOH
mixture. Yield: 52%. Anal. Calc. for C46H40N12O10Pb2: C, 41.38; H,

V.D. Schwade et al. / Polyhedron 112 (2016) 96–103
103
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cmꢁ1): 3214 (w), 3083 (w), 1658 (s), 1581 (w), 1530 (m), 1487 (m),
1385 (s), 1346 (s), 1310 (s), 1199 (w), 1148 (m), 1067 (w), 1035
(m), 933 (w), 897 (w), 806 (m), 717 (m), 693 (w), 677 (w), 533
(w). 1H NMR (DMSO-D6; d, ppm): 2.65 (s, 6H, CH3), 7.55–7.67 (m,
6H, Ph), 8.00–8.02 (m, 4H, Ph), 8.21 (br, 3H, py), 11.74 (s, 1H, NH).
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4.4. X-ray crystallography
The intensities for the X-ray determinations were collected on a
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were performed with SHELXS and SHELXL [32]. Hydrogen atom posi-
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‘riding model’ option of SHELXL. All crystals of [Pb(HLPh)Cl]2 were
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Acknowledgment
The authors thank the financial support from CNPq (Grant pro-
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Appendix A. Supplementary data
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CCDC 1448755, 1448756, 1448757, 1448758, 1448759 and
1448760 contains the supplementary crystallographic data for
[Pb(py)(LPh)]2, [Pb(HLPh)Cl]2, [Pb(HLPh)Br]2, [Pb(HLPh)I]2, [Pb(HLPh
)
I]2ꢀ2MeOHꢀH2O and [Pb(HLPh)(NO3)]2, respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
[32] G.M. Sheldrick, SHELXL-97, program for the refinement of crystal structures,
University of Göttingen, Göttingen, Germany, 1997.
[33] K. Brandenburg, H. Putz, DIAMOND – a program for the representation of crystal
structures, vers. 3.2, Crystal Impact, Bonn, Germany (2011).
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