Organized assemblies of lead(II) complexes of a tetraiminodiphenol macrocyclic ligand: Manifestation of weak metal-anion interactions and the directional influence of anions

Article abstract of DOI:10.1039/b201608g

The syntheses and crystal structures of the lead(II) complexes [Pb(LH₂)(ClO₄)][ClO₄], [Pb(LH₂)(NO₃)₂] and [Pb₂L(NO₃)₂] of the tetraiminodiphenol macrocyclic ligand (H₂L) derived from a [2+2] condensation reaction between 2,6-diformyl-4-methylphenol and 1,3-diaminopropane are reported. In the mononuclear complexes, the two uncoordinated imino nitrogens are protonated and are hydrogen bonded to the phenolate oxygens. A supramolecular assembly occurs for [Pb(LH₂)(ClO₄)][ClO₄], due to weak interactions between the metal and three oxygen atoms of three different symmetry-related perchlorates, thereby forming a hexameric species with a propeller structure. [Pb(LH₂)(NO₃)₂], however, is a monomer with normal bidentate binding modes for the nitrates. By contrast, [Pb₂L(NO₃)₂] exhibits a 2-D structural network comprising parallel chains from two independent [Pb₂L]²⁺ units, to which the nitrate anions are associated rather unconventionally: one oxygen is coordinated to two symmetry-related metal centres, another oxygen to a single lead, while the third oxygen remains free. The structural features of the complexes in solution have been investigated by ¹H NMR spectroscopy.

Full text of DOI:10.1039/b201608g

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Organized assemblies of lead(II) complexes of a tetraiminodiphenol
macrocyclic ligand: manifestation of weak metal–anion interactions
and the directional influence of anions
a
b
a
c
a
Bula Dutta, Bibhutosh Adhikary, Pradip Bag, Ulrich Flörke and Kamalaksha Nag*
a
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Jadavpur, Kolkata 700 032, India. E-mail: ickn@mahendra.iacs.res.in
Department of Chemistry, B. E. College (A Deemed University), Howrah 711 103, India
Anorganische und Analytische Chemie der Universität Gesamthochschule Paderborn, D-33098,
Paderborn, Germany
b
c
Received 12th February 2002, Accepted 1st May 2002
First published as an Advance Article on the web 28th May 2002
The syntheses and crystal structures of the lead() complexes [Pb(LH )(ClO )][ClO ], [Pb(LH )(NO ) ] and
2
4
4
2
3 2
[
Pb L(NO ) ] of the tetraiminodiphenol macrocyclic ligand (H L) derived from a [2ϩ2] condensation reaction
2
3
2
2
between 2,6-diformyl-4-methylphenol and 1,3-diaminopropane are reported. In the mononuclear complexes, the two
uncoordinated imino nitrogens are protonated and are hydrogen bonded to the phenolate oxygens. A supramolecular
assembly occurs for [Pb(LH )(ClO )][ClO ], due to weak interactions between the metal and three oxygen atoms
2
4
4
of three different symmetry-related perchlorates, thereby forming a hexameric species with a propeller structure.
[
[
Pb(LH )(NO ) ], however, is a monomer with normal bidentate binding modes for the nitrates. By contrast,
2 3 2
ϩ
2
Pb L(NO ) ] exhibits a 2-D structural network comprising parallel chains from two independent [Pb L] units, to
2
3
2
2
which the nitrate anions are associated rather unconventionally: one oxygen is coordinated to two symmetry-related
metal centres, another oxygen to a single lead, while the third oxygen remains free. The structural features of the
1
complexes in solution have been investigated by H NMR spectroscopy.
Introduction
Over the past three decades extensive studies have been made
on the chemistry of phenolate-bridged metal complexes derived
1–6
from Schiff base-type dinucleating macrocyclic ligands I. The
symmetric ligand II has been of particular interest because it
provides an ideal platform for the investigation of cooperative
interactions between two metal centres (the same or different)
under identical stereochemical environments. The focus of
interest in complexes of this sort has been the probing of
7–14
3,6,15–21
magneto-structural relations,
selective activation of substrates.
redox activities
and
Although a large number
6,22
of these macrocyclic complexes have been structurally charac-
terized, they are virtually all derived from divalent metal ions.
Significantly, there remains, however, wider scope to study
M()M(), M()MЈ(), M()M() or M()MЈ() types of
systems. This is especially relevant in the context of modelling
the active sites of non-heme iron proteins such as hemery-
Experimental
Materials
Reagent grade chemicals obtained from commercial sources
were used as received. 2,6-Diformyl-4-methylphenol was pre-
pared according to the literature method.
23
24
25
16b,28
thrine, methane monooxygenase, purple acid phosphatase,
26
27
ribonucleotide reductase and calcineurin.
In our efforts to develop systematically the chemistry of
mixed-valent M()M(), mixed-metal M()MЈ() and iso-
Preparation of the complexes
CAUTION: all the perchlorate salts reported in this study are
potentially explosive and therefore should be handled with care.
valent M()M() complexes of II (H L), we introduce here a
2
2ϩ
core complex cation, [Pb(LH )] (III), which serves as a useful
2
2ϩ
precursor for the generation of other mononuclear [M(LH )]
and [M(LH )] species. The present study is concerned with
2
3ϩ
[Pb(LH )(ClO )][ClO ] (1). To a boiling methanol solution
2
2
4
4
3
the eleboration of the structural features of three lead()
(100 cm ) of 2,6-diformyl-4-methylphenol (3.28 g, 20 mmol)
3
complexes, [Pb(LH )(ClO )] [ClO ] , [Pb(LH (NO ) ] and [Pb -
was added a methanol solution (20 cm ) of Pb(ClO ) ؒ3H O
2
4
6
4 6
2
3
2
2
4
2
2
3
L(NO ) ] , in the solid state and in solution. It is demonstrated
(4.6 g, 10 mmol) and 1.5 cm of acetic acid. The solution was
kept stirred and 1,3-diaminopropane (1.48 g, 20 mmol) diluted
3
2 ∞
that the influences of weak metal–anion interactions, anion-
imposed directionality and crystallographic symmetry require-
ments all combine together to set out the structural paradigm.
3
with methanol (20 cm ) was added. The color of the solution
changed from light yellow to orange and, eventually, a yellow
2
760
J. Chem. Soc., Dalton Trans., 2002, 2760–2767
DOI: 10.1039/b201608g
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3
polycrystalline product began to separate out. Refluxing of the
mixture was continued for 3 h, after which it was kept at room
temperature for another 3 h. The product was collected by
filtration and washed with methanol and diethyl ether; yield
1064s, 803m, 620m, 501w. UV-vis data in DMF [λmax/nm (ε/dm
Ϫ1 Ϫ1
mol cm )]: 392 (32 000).
Although single crystals of 4 were obtained as before, they
spontaneously lose a solvent molecule on removal from the
mother liquor.
6
.4 g (80%). Found: C, 35.6; H, 3.4; N, 6.8; C H N O Pb-
24 28 4 2
(
ClO ) requires: C, 35.5; H, 3.5; N, 6.9%. Selected IR data
4 2
Ϫ1
on KBr (ν/cm ): 3440br, 3040br, 1647s, 1546s, 1460m, 1353m,
1
4
[Cd(LH
2
)][ClO
] (5). To a boiling acetonitrile solution
4 2
3
273m, 1235m, 1092s, 1057sh, 991m, 871w, 807w, 623m,
(50 cm ) of 1 (0.81 g, 1 mmol) was added a solution of CdCl
2
ؒ
3
Ϫ1
Ϫ1
3
91w. UV-vis data in DMF [λmax/nm (ε/dm mol cm )]: 408
2.5H
2
O (0.23 g, 1 mmol) in acetonitrile (10 cm ). After 0.5 h, the
(
24 000).
precipitated PbCl
2
was removed by filtration and 0.5 g NaClO
4
Crystals of 1 for structure determination were obtained in
was added to the filtrate. On concentration of the solution to
3
the following way. A multiple-necked round bottomed flask was
fitted with three graduated pressure-equilized addition funnels,
a reflux condenser and a thermometer. The flask was charged
with 200 cm methanol, 5 cm N,N-dimethylformamide (DMF)
and 0.5 cm acetic acid. The reaction temperature of the bath
was set to 55 ЊC and from the addition funnels three solutions
of 0.66 g 2,6-diformyl-4-methylphenol, 0.9 g Pb(ClO ) ؒ3H O
and 0.3 g 1,3-diaminopropane each dissolved in 30 cm metha-
nol were added simultaneously at the rate of 1 cm min . The
solution was kept at 55 ЊC for 4 h and then brought to room
temperature over a period of 8 h. The crystals that deposited on
the wall of the flask were collected after 24 h.
ca. 20 cm , a bright yellow crystalline product was obtained,
which was filtered and washed with 1 : 1 acetonitrile–methanol
mixture; yield 0.43 g (60%). Found: C, 40.05; H, 4.05; N, 7.9;
3
3
C H N O Cd(ClO ) requires: C, 40.25; H, 3.9; N, 7.85%.
24 28 4 2 4 2
Ϫ1
3
Selected IR data on KBr (ν/cm ): 3025br, 1645s, 1542s, 1455m,
1360m, 1273m, 1235m, 1091s, 1055sh, 996m, 917w, 877w, 811w,
3
Ϫ1
625m, 566w, 497w. UV-vis data in DMF [λmax/nm (ε/dm mol
4
3
2
2
Ϫ1
cm )]: 406 (21 600).
3
Ϫ1
[
Cd L(NO ) ] (6), [Zn L(NO ) ] (7). To a boiling methanol
2 3 2 2 3 2
3
solution (50 cm ) containing 2,6-diformyl-4-methylphenol
0.33 g, 2 mmol) and Cd(NO ) ؒ6H O (0.84 g, 2 mmol) or
(
3
2
2
3
Zn(NO ) ؒ6H O (0.60 g, 2 mmol), a methanol solution (5 cm )
3
2
2
3
of 1,3-diaminopropane (0.15 g, 2 mmol) was slowly added.
The resulting lime solution was refluxed for 4 h, during which
period the cadmium complex deposited as a greenish-yellow
polycrystalline material and was separated by filtration (60%).
The solution containing zinc was concentrated to ca. 20 cm
which, on standing, gave a canary-yellow crystalline product
[
Pb(LH )(NO ) ] (2). To a boiling methanol solution (60 cm )
2
3 2
containing 2,6-diformyl-4-methylphenol (1.64 g, 10 mmol) and
acetic acid (1 cm ), finely ground Pb(NO ) (1.65 g, 5 mmol)
dissolved in DMF (15 cm ) was added, followed by a methanol
solution (20 cm ) of 1,3-diaminopropane (0.74 g, 10 mmol).
After refluxing for 4 h, the product that deposited as yellow
microcrystals was filtered off and washed with methanol and
diethyl ether; yield 3.3 g (90%) Found: C, 39.25; H, 3.8; N, 11.2;
C H N O Pb(NO ) requires: C, 39.15; H, 3.8; N, 11.4%.
Selected IR data on KBr (ν/cm ): 3450br, 3030br, 1645s, 1541s,
1
8
3
3
2
3
3
3
and was collected by filtration (70%).
6
. (Found: C, 38.6; H, 3.6; N, 11.05. C H N O Cd (NO )
24 26 4 2 2 3 2
requires: C, 38.35; H, 3.45; N, 11.2%). Selected IR data on KBr
2
4
28
4
2
3 2
Ϫ1
Ϫ1
(
1
[
ν/cm ): 1633s, 1560s, 1464m, 1384s, 1328m, 1282m, 1235w,
123m, 1070m, 1023w, 818m, 778w, 506w. UV-vis data in DMF
387w, 1460m, 1384s, 1360sh, 1266m, 1229m, 1021w, 986w,
65w, 803w, 494w.
Single crystals of 2 were obtained in the same way as
3
Ϫ1
Ϫ1
λmax/nm (ε/dm mol cm )]: 380 (31 600).
. (Found: C, 43.7; H, 4.05; N, 12.65. C H N O Zn (NO )
3 2
7
24 26
4
2
2
requires: C, 43.85; H, 3.95; N, 12.8%). Selected IR data on
KBr (ν/cm ): 1636s, 1563s, 1450m, 1384s, 1328m, 1282m,
235m, 1123m, 1070w, 818m, 771w, 512w. UV-vis data in DMF
λmax/nm (ε/dm mol cm )]: 370 (17 200).
described for 1. However, in this case, the reaction flask
contained 100 cm methanol and 0.5 cm acetic acid, while
the addition funnels contained 0.66 g Pb(NO ) dissolved in
a mixture of 10 cm DMF and 20 cm methanol, 0.66 g
2
1
Ϫ1
3
3
1
[
3
2
3 Ϫ1 Ϫ1
3
3
3
,6-diformyl-4-methylphenol in 30 cm methanol and 0.3 g
3
,3-diaminopropane in 30 cm methanol.
Measurements
Elemental C, H and N analyses were performed in-house on a
Perkin–Elmer 2400II elemental analyzer. Infrared spectra were
recorded on a FT-IR Nexus Nicolet spectrometer using KBr
discs. Electronic spectra were measured in DMF on a Shimadzu
UV-2100 spectrophotometer. The H, { H– H} COSY and
variable temperature NMR spectroscopic measurements were
performed on a Bruker Avance DPX-300 spectrometer in
[
Pb L(NO ) ] (3). To a vigorously stirred boiling methanol
2 3 2
3
solution (80 cm ) of 2,6-diformyl-4-methylphenol (1.64 g,
0 mmol) were added successively a DMF solution (25 cm ) of
Pb(NO ) (3.31 g, 10 mmol) and a methanol solution (20 cm )
of 1,3-diaminopropane (0.74 g, 10 mmol). In a few minutes,
a canary-yellow compound began to deposit. Refluxing of the
mixture was continued for 5 h, after which the product was
filtered off and washed with methanol; yield 4.2 g (90%) Found:
C, 30.85; H, 2.8; N, 8.85; C H N O Pb (NO ) requires:
3
1
3
3
2
1
1
1
(
CD ) SO solutions.
3 2
24
26
4
2
2
3 2
X-Ray crystallography
Ϫ1
C, 30.6; H, 2.75; N, 8.95%. Selected IR data on KBr (ν/cm ):
1
8
635s, 1561m, 1447m, 1384s, 1299m, 1256m, 1123m, 1064m,
06m, 501w, 468w.
To obtain single crystals of 3, the following changes were
Single crystals of 1, 2 and 3 were mounted on glass fibres and
coated with epoxy resin. Intensity data were collected with a
Siemens R3m/V diffractometer at 203 K using graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å). The cell
parameters were obtained by least-squares refinement of
twenty automatically centred reflections. The standard reflec-
tions were measured after every 150 observations during data
collection and no significant variations in intensities were
observed. Crystal data and details of structure determinations
are summarized in Table 1. The intensity data were corrected
for Lorentz-polarization effects and semi-empirical absorption
corrections were made from Ψ-scans. The structures were
solved by direct and Fourier methods and refined by full-matrix
made to the procedure adopted for 2. The reaction flask con-
tained 100 cm methanol but no acetic acid and the addition
funnels contained (i) 0.66 g Pb(NO ) dissolved in a mixture
of 15 cm DMF and 15 cm methanol, (ii) 0.33 g 2,6-diformyl-
3
3
2
3
3
3
4
-methylphenol in 30 cm methanol and (iii) 0.15 g 1,3-di-
3
aminopropane in 30 cm methanol.
[
Pb L(ClO ) ]1.5H O (4). This compound was prepared in
2
4
2
2
the same way as 3, with the difference that a methanol solution
of Pb(ClO ) ؒ3H O was used (yield 86%). Found: C, 27.6;
H, 2.9; N, 5.3; C H N O Pb (ClO ) ؒ1.5H O requires: C, 27.9;
4
2
2
2
least-squares based on F using the programs SHELXTL-
24
26
4
2
2
4
2
2
Ϫ1
29
30
H, 2.7; N, 5.4%. Selected IR data on KBr (ν/cm ): 3460br,
630s, 1561m, 1446m, 1395w, 1315m, 1256w, 1122s, 1086sh,
PLUS and SHELXL-93. Neutral atom scattering factors
31
1
were taken from Cromer and Waber. The non-hydrogen atoms
J. Chem. Soc., Dalton Trans., 2002, 2760–2767 2761

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Table 1 Crystallographic data for [Pb(LH )(ClO )][ClO ] (1), [Pb(LH )(NO ) ] (2) and [Pb L(NO ) ] (3)
2
4
4
2
3
2
2
3 2
1
2
3
Formula
M
C H Cl N O Pb
810.59
C H N O Pb
735.71
C H N O Pb
2
940.89
2
4
28
2
4
10
24 28
6
8
24 26
6
8
Crystal size/mm
Crystal system
Space group
0.20 × 0.17 × 0.15
Hexagonal
R3
0.20 × 0.40 × 0.22
Monoclinic
P2 /n
1
0.58 × 0.32 × 0.28
Triclinic
¯
P1
a/Å
b/Å
c/Å
α/Њ
β/Њ
γ/Њ
U/Å
Z
D/g cm
35.124(5)
35.124(5)
12.095(4)
—
—
120
12922(4)
18
1.875
10.277(1)
17.922(3)
14.368(3)
—
92.08(1)
—
2644.6(8)
4
1.848
7.582(1)
9.531(1)
18.285(2)
95.30(1)
91.00(1)
92.69(1)
1313.9(3)
2
3
Ϫ3
2.378
T /K
µ/mm
203(2)
6.122
203(2)
6.439
203(2)
12.858
Ϫ1
No. measured, observed reflections
Parameters refined
6919, 5831
371
0.0748, 0.1429
0.2748, 0.2227
0.866
7520, 6082
353
0.0385, 0.0619
0.0703, 0.0693
0.973
7234, 6010
362
0.0450, 0.1060
0.0653, 0.1150
1.028
a
b
Final R1, wR2 [I > 2σ(I )]
R1, wR2 (all data):
c
S
a
b
2
2
2
2
2
o
2
1/2
c
2
2
c
2
1/2
R1(F) = Σ||F | Ϫ |F ||/Σ|F |. wR2(F ) = [Σw(F Ϫ F ) /Σw(F ) ]
.
S = [Σw(Fo Ϫ F ) /(N Ϫ P)] where N is the number of data and P the total
o
c
o
o
c
number of parameters refined.
were refined anisotropically, while the hydrogen atoms were
placed at the geometrically calculated positions with fixed
isotropic thermal parameters.
CCDC reference numbers 179593–179595.
See http://www.rsc.org/suppdata/dt/b2/b201608g/ for crystal-
lographic data in CIF or other electronic format.
several days. Moreover, the proportion of the metal-free macro-
cycle was found to increase with time. Furthermore, imine-
protonated mononuclear cryptates of several di- and trivalent
metal ions derived from [2 ϩ 3] condensation reaction between
tris(2-aminoethyl)amine and 2,6-diformyl-4-methylphenol have
33
been reported by others using a different synthetic protocol.
Preliminary studies have shown that complexes 1 and 2 are
convenient precursors for the preparation of mononuclear
complexes of other metal ions which are kinetically either inert
or labile in the oxidation states ϩ2 and ϩ3. For example, the
inert complexes [Pt(LH )][ClO ] and [Rh(LH )Cl(H O)]-
Results and discussion
Syntheses
2
4 2
2
2
The condensation reactions involving one equivalent each of
[
[
ClO ] , and the labile complexes [Ga(LH )Cl(H O][ClO ] and
4 2 2 2 4 2
2
,6-diformyl-4-methylphenol, 1,3-diaminopropane and lead
Ln(LH )Cl (H O) ][ClO ] can be obtained by the metathetical
2
2
2
2
4
nitrate or lead perchlorate produce the corresponding dinuclear
reaction between 1 and the chloride salt of the required metal
lead complexes [Pb L(NO ) ] (3) and [Pb L(ClO ) ] (4) in
2
3
2
2
4 2
ion in acetonitrile. The precipitation of PbCl acts as a driving
2
near quantitative yield. When these reactions are carried out
with half an equivalent of the metal salts, complexes 3 and 4
are again obtained, but the yields of the products are less than
half those of the previous reactions. The lack of formation of
the neutral lead complex [PbL] coupled with the absence of
force for the replacement reaction. The transmetallation
reaction can also be carried out by using a relatively harder
metal ion without recourse to precipitation of PbCl . For
2
instance, complex 2 on treatment with an equivalent amount of
the nitrate salt of a lanthanide in methanol affords the complex
II
any reported [M L] compound indicate the thermodynamic
[
Ln(LH )(NO ) ][NO ].
2 3 2 3
instability of such species, arising from the propensity to hydro-
lytic cleavage of the non-coordinated imine groups of the macro-
cycle. A useful approach to circumvent nucleophilic attack on
A characteristic feature in the IR spectra of the mononuclear
Ϫ1
complexes is the occurrence of a weak band at about 3030 cm
due to the νN–H ؒ ؒ ؒ O vibration. Moreover, the ν stretching
C᎐N
᎐
the CH᎐N groups and, hence, to stabilize the mononuclear
᎐
vibration for the mononuclear compounds is observed at a
complex species would be to protonate the imine nitrogens
so that they become intramolecularly hydrogen bonded with
the phenolate oxygens (as shown in III). We have found that
this can be readily achieved by carrying out the condensation
reaction in the presence of a weak acid. Thus, when one equiva-
lent of lead perchlorate or lead nitrate is reacted with two
equivalents each of 2,6-diformyl-4-methylphenol and 1,3-di-
aminopropane, and 2–3 equivalents of acetic acid, the imine-
protonated mononuclear complexes [Pb(LH )(ClO )][ClO ] (1)
Ϫ1
somewhat higher energy (ca. 1645 cm ) relative to that for the
Ϫ1
dinuclear compounds (ca. 1635 cm ).
Crystal structures
[Pb(LH )(ClO )][ClO ] (1). The structural analysis of com-
2
4
4
2ϩ
plex 1 has revealed the presence of the core cation [Pb(LH )]
2
and two perchlorate anions. An ORTEP representation of the
2ϩ
[Pb(LH )] cation is shown in Fig. 1 and selected interatomic
2
4
4
2
and [Pb(LH )(NO ) ] (2) are obtained in high yield (>80%).
distances and angles are listed in Table 2.
2
3 2
We note that in a study involving the reaction of equivalent
amounts of 1,3-diamine-2-hydroxypropane, 2,6-diformyl-4-
methylphenol and lead perchlorate in methanol, the formation
of three products and their structural characterization as
the dinuclear macrocyclic lead complex [Pb (H LЈ)][ClO ] , the
The lead atom occupying one of the compartments of the
macrocyclic ligand is bonded to the phenolate oxygens [Pb(1)–
O(1) = 2.388(14), Pb(1)–O(2) = 2.356(13) Å] and to the imine
nitrogens N(1) and N(2) [Pb(1)–N(1) = 2.539(18), Pb(1)–N(2) =
2.488(17) Å]. The non-coordinated imine nitrogens N(3) and
N(4) are separated from O(2) and O(1) by 2.63 and 2.57 Å,
respectively. Although the hydrogen atoms connected to these
two protonated imine nitrogens could not be seen, they appear
to be strongly hydrogen bonded to the phenolate oxygens, with
the N–H ؒ ؒ ؒ O angles being 131.9 and 131.3Њ. The angles
2
2
4 2
nononuclear protonated complex [Pb(H LЈ)][ClO ] and
4
4 2
the metal-free protonated macrocyclic ligand salt [(H LЈ)-
6
32
(
H O) [ClO ] has been reported. The dilead complex was
2 2 4 2
obtained as the initial reaction product, while the other two
compounds were obtained on keeping the reaction mixture for
2
762
J. Chem. Soc., Dalton Trans., 2002, 2760–2767

View Article Online
Table 2 Selected bond lengths (Å) and angles (Њ) for [Pb(LH )(ClO )][ClO ] (1) and [Pb(LH )(NO ) ] (2)
2
4
4
2
3 2
1
2
Pb(1)–O(1)
Pb(1)–O(2)
Pb(1)–N(1)
Pb(1)–N(2)
Pb(1)–O(21A)
Pb(1)–O(24B)
Pb(1)–O(23)
N(3) ؒ ؒ ؒ O(2)
N(4) ؒ ؒ ؒ O(1)
2.388(14)
2.356(13)
2.539(18)
2.488(17)
2.767(17)
2.972(17)
3.004(17)
2.63(2)
Pb(1)–O(1)
Pb(1)–O(2)
Pb(1)–N(1)
Pb(1)–N(2)
Pb(1)–O(11)
Pb(1)–O(13)
Pb(1)–O(21)
Pb(1)–O(23)
N(3) ؒ ؒ ؒ O(2)
N(4) ؒ ؒ ؒ O(1)
2.373(4)
2.363(4)
2.580(5)
2.559(4)
2.831(4)
3.027(4)
2.960(5)
2.855(5)
2.61(2)
2.57(2)
2.60(2)
O(1)–Pb(1)–O(2)
O(2)–Pb(1)–N(2)
N(2)–Pb(1)–N(1)
N(1)–Pb(1)–O(1)
O(1)–Pb(1)–N(2)
O(2)–Pb(1)–N(1)
N(3)–H(3A) ؒ ؒ ؒ O(2)
N(4)–H(4A) ؒ ؒ ؒ O(1)
76.3(5)
74.1(6)
70.4(6)
73.5(5)
111.2(5)
119.8(5)
132.5(2)
131.7(2)
O(1)–Pb(1)–O(2)
O(2)–Pb(1)–N(2)
N(2)–Pb(1)–N(1)
N(1)–Pb(1)–O(1)
O(1)–Pb(1)–N(2)
O(2)–Pb(1)–N(1)
O(11)–Pb(1)–O(13)
O(21)–Pb(1)–O(23)
78.70(13)
71.51(13)
67.98(13)
71.17(13)
107.81(14)
117.52(13)
43.18(11)
42.53(12)
Fig. 2 The mode of linkage of the Cl(20) perchlorate ion and two
other symmetry-related perchlorate ions, Cl(2A) and Cl(2B), with the
2
ϩ
2ϩ
Fig. 1 ORTEP representation of the [Pb(LH )] cation of complex 1
core [Pb(LH )] cation of 1.
2
2
at the 50% probability level.
involving the metal centre all deviate considerably from 90Њ;
the angles O(1)Pb(1)O(2), N(1)Pb(1)N(2), O(1)Pb(1)N(1) and
O(2)Pb(1)N(2) lie between 70.4(6) and 76.3(5)Њ, while the angles
O(1)Pb(1)N(2) and O(2)Pb(1)N(1) are 111.2(5) and 119.8(5)Њ,
respectively. The atoms O(1), O(2), N(1) and N(2), forming
a trapezoid, are deviated from the mean plane by not more
than ± 0.07 Å, while the displacement of the metal centre is
1
.298(3) Å.
Of the two perchlorate ions, the one related to Cl(10) remains
free. On the other hand, the oxygen atoms O(21), O(23) and
O(24), but not O(22), belonging to the second perchlorate with
Cl(20), weakly interact with the metal centre. The mode of
binding is rather subtle in nature. Each of the three oxygen
atoms are coordinated to three different but symmetrically
equivalent lead units and each lead, in turn, is connected to
three oxygen atoms from three different (but symmetrically
equivalent) perchlorate groups, as shown in Fig. 2. The metal–
anion connectivity leads to self-assembly, the course of which
is governed by symmetry relationships. The process finally
Fig. 3 A view of the self-assembled hexameric species [{Pb(LH )-
2
2ϩ
6ϩ
(
ClO )} ] formed for complex 1.
gives rise to supramolecular association of six [Pb(LH )]
4 6
2
Ϫ
cations and six ClO4 anions. Fig. 3 shows the structure of the
hexameric species [{Pb(LH )(µ-O ClO)} ] thus produced. The
6ϩ
[2.767(23) Å] is shorter relative to Pb(1)–O(23) [3.004(15) Å]
and Pb(4)–O(24) [2.972(18) Å]. Another important con-
sequence of this interaction is the adoption by the macrocyclic
unit of a folded configuration, as is evident from the dihedral
angle between the two phenyl rings of 69.3(5)Њ.
2
3
6
novel propeller-like architecture is built around a hexagonal
frame provided by the lead atoms. As a result of interaction
with perchlorate oxygen, the lead centre obtains a seven-fold
coordination geometry in which the Pb(1)–O(21) distance
J. Chem. Soc., Dalton Trans., 2002, 2760–2767
2763

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a
Table 3 Selected bond lengths (Å) and angles (Њ) for [Pb L(NO ) ] (3)
2
3 2
Pb(1)–O(1)
Pb(1)–O(1A)
Pb(1A)–O(1)
Pb(1)–N(1)
Pb(1)–N(2)
Pb(1)–O(12)
Pb(1)–O(13)
2.350(6)
2.366(6)
2.366(6)
2.485(7)
2.567(7)
2.900(7)
2.962(7)
3.009(7)
3.903(1)
Pb(2)–O(2)
Pb(2)–O(2A)
Pb(2)–O(2)
Pb(2)–N(3)
Pb(2)–N(4)
Pb(2)–O(22)
Pb(2)–O(23)
2.355(5)
2.357(6)
2.357(6)
2.513(8)
2.496(8)
3.010(7)
3.002(7)
3.060(7)
3.891(1)
b
b
Pb(1)* –O(13)
Pb(1) ؒ ؒ ؒ Pb(1A)
Pb(2)* –O(23)
Pb(2) ؒ ؒ ؒ Pb(2A)
O(1)–Pb(1)–O(1A)
O(1)–Pb(1)–N(1)
O(1A)–Pb(1)–N(2)
N(1)–Pb(1)–N(2)
O(1)–Pb(1)–N(2)
O(1A)–Pb(1)–N(1)
68.3(2)
72.9(2)
71.7(2)
79.4(2)
115.4(2)
113.4(2)
O(2)–Pb(2)–O(2A)
O(2)–Pb(2)–N(4)
O(2A)–Pb(2)–N(3)
N(3)–Pb(2)–N(4)
O(2)–Pb(2)–N(3)
O(2A)–Pb(2)–N(4) 112.4(2)
Pb(2)–O(2)–Pb(2A) 111.3(2)
68.7(2)
73.5(2)
72.2(2)
79.0(2)
117.5(2)
Pb(1)–O(1)–Pb(1A) 111.7(2)
O(12)–Pb(1)–O(13)
43.5(2)
O(23)–Pb(2)–O(23)
41.7(2)
a
b
There are two independent molecules in the unit cell. Metal centre
belongs to another molecule related by symmetry.
Fig. 4 ORTEP representation of [Pb(LH )(NO ) ] (2) at the 50%
2
3 2
probability level.
from the least-squares planes. The metal centres are displaced
from the basal plane in opposite direction by 1.316 Å [Pb(1)/
Pb(1A)] and 1.301(1) Å [Pb(2)/Pb(2A)]. The N(10) nitrate
coordinates to Pb(1)/Pb(1A) and the N(20) nitrate to Pb(2)/
Pb(2A) in the same pattern, albeit the binding mode is rather
uncommon. The metal centre obtains a seven-coordinate
geometry due to three-fold coordination by the nitrate ions, two
oxygen atoms stem from one nitrate group and the third oxygen
atom stems from a second but symmetry-related nitrate group.
This latter oxygen bridges two lead atoms from two different
[
Pb(LH )(NO ) ] (2). The ORTEP representation of 2 (Fig. 4)
2 3 2
shows that the macrocyclic ligand is bound to the metal centre
in the same way as in 1. The lead atom is additionally bound
to two bidentate nitrate anions and, thus, acquires an eight-
coordinate [PbN O ] distorted dodecahedral geometry. Table 2
lists selected bond distances and angles for 2.
The Pb–O(phenolate) distances [av. 2.368(5) Å] and Pb–N-
imine) distances [av. 2.569(9) Å] in 2 are similar to those
observed in 1. The two Pb–O distances in each of the bidentate
nitrates are not identical [Pb(1)–O(11) = 2.831(4), Pb(1)–O(13)
2
6
(
2ϩ
(but symmetry-related) [Pb L] units. Thus, one oxygen atom
2
=
3.027(4); Pb(1)–O(21) = 2.960(5), Pb(1)–O(23) = 2.855 Å].
from each nitrate is bound to two lead atoms, another oxygen
atom to one lead, while the third oxygen atom is not involved in
O ؒ ؒ ؒ Pb interaction (Fig. 6). As shown in Fig. 7, the whole
No supramolecular association occurs in 2, presumably because
of the attainment of eight-coordinate geometry by the lead.
Similar to complex 1, the protonated imines are hydrogen
bonded to the adjacent phenolate oxygens [N(3) ؒ ؒ ؒ O(2) =
structure then consists of parallel ؒ ؒ ؒ (NO
) ؒ ؒ ؒ [Pb L] ؒ ؒ ؒ
3 2 2
(NO ؒ ؒ ؒ [Pb L] ؒ ؒ ؒ (NO ؒ ؒ ؒ chains along [010], one
)
)
3 2
3
2
2
2
1
.61(2), N(4) ؒ ؒ ؒ O(1) = 2.60(2) Å; N(3)–H(3A) ؒ ؒ ؒ O(2) =
32.5(2), N(4)–N(4A) ؒ ؒ ؒ O(1) = 131.7(2)Њ].
chain includes the crystallographic Pb(1)/Pb(1A) atoms and
the other chain the Pb(2)/Pb(2A) atoms, which, viewed along
[010], give rise to a two-dimensional self-assembled network.
The average Pb–O(phenolate) distance [2.357(7) Å] in 3 is
[
Pb L(NO ) ] (3). From the structural analysis of 3 it became
2 3 2
very similar to that in 2 [2.368(5) Å], however, the correspond-
ing Pb–N(imine) distances [2.52(4) Å for 3 and 2.57(1) Å for 2]
are not so close. The Pb–O(nitrate) distances in the two sets of
[Pb L(NO ) ] are not exactly identical. The distances involving
evident that there are two halves of two independent cations per
asymmetric unit and the centres of the complete [Pb L(NO ) ]
molecules each lie on crystallographic inversion centres. An
2
3 2
2ϩ
ORTEP representation for the [Pb L] cation and a projection
2
3 2
2
Pb(1)–O(12), Pb(1)–O(13) and the symmetry-related Pb(1)*–
O(13) bond are 2.900(7), 2.962(7) and 3.009(8) Å, respectively,
and may be compared with the corresponding distances
involving Pb(2)–O(22) [3.017(7) Å], Pb(2)–O(23) [3.022(7) Å]
and Pb(2)*–O(23) [3.060(9) Å]. The non-bonded metal–metal
distance is 3.903(1) Å for Pb(1A) ؒ ؒ ؒ Pb(1A) and 3.891(1) Å for
Pb(2) ؒ ؒ ؒ Pb(2A). On the other hand, the separations between
the planes of the macrocycles [Pb L] ؒ ؒ ؒ [Pb L] are 4.106(2) Å
of [Pb L(NO ) ] along [100] are shown in Fig. 5 and 6, respec-
2
3 2
tively. Selected internuclear distances are listed in Table 3.
The macrocyclic ligand is flat in this case, the deviations of
the constituent donor atoms [N O ] do not exceed ±0.025(5) Å
2
2
2
2
[involving Pb(1)/Pb(1A)] and 4.139(2) Å [involving Pb(2)/
Pb(2A)].
1
H NMR spectroscopy
Proton NMR spectroscopic studies were carried out for com-
plexes 1–7 in dimethyl sulfoxide and the observed chemical
shifts are listed in Table 4. The spectral assignments (Table 4)
1
1
were facilitated by H– H correlation spectroscopy (COSY).
The mononuclear lead complexes 1 and 2 exhibit identical spec-
tra, as do the dinuclear complexes 3 and 4, indicating that, in
dimethyl sulfoxide, solvation of the core complex cation leads
to complete dissociation of the anions.
The spectral features exhibited by the mononuclear lead
(1, 2) and cadmium (5) complexes are quite similar in the lower
field region. For example, the hydrogen-bonded protonated
2
ϩ
Fig. 5 ORTEP representation of the [Pb(1)LPb(1A)] cation of
2
ϩ
complex 3 at the 50% probability level. The second [Pb(2)LPb(2A)]
cationic species of 3 has a similar appearence.
ϩ
imine N–H ؒ ؒ ؒ O (a, proton labelling scheme is shown in
2
764
J. Chem. Soc., Dalton Trans., 2002, 2760–2767

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Fig. 6 The binding mode of the nitrate ions in [Pb(2)LPb(2A)(NO ) ] (3). The self-assembled chain is viewed along [100]. Similar chain is also
3
2
formed in [Pb(1)LPb(1A)(NO ) ].
3
2
4
.24 (g) and 3.77 (h) ppm, they are isochronous on the metal-
free side (i = j, 3.94 ppm). The CH CH CH protons on both the
2
2
2
sides, however, are isotropic, and the one in the vicinity of Pb is
more shielded. In complex 5, no anisotropic effect is observed
and the equivalence of the CH CH CH and CH CH CH
2
2
2
2
2
2
protons on both the sides appears to be accidental.
The effect of variation of temperature (25 to 70 ЊC) on the
resonances of complex 1 is shown in Fig. 8. As can be seen, the
doublet (b) and the singlet (c) due to the imino CH approach
Fig. 7 A view of the 2D network along [010] for complex 3. The
alternating parallel chains consist of crystallographic Pb(1)/Pb(1A) and
Pb(2)/Pb(2b) atoms.
Table 4) is observed as a broad singlet at 13.21 ppm for 1 and
1
3.37 ppm for 5. Similar to complex 1, which exhibits a doublet
at 8.65 ppm (J = 13.7 Hz) and three singlets at 8.44, 7.47 and
.36 ppm (all integrating to two protons each), complex 5
7
exhibits these bands at 8.63 (J = 13.2 Hz), 8.24, 7.47 and 7.30
ppm. The COSY spectra showed correlation between the
ϩ
doublet (c) and N–H ؒ ؒ ؒ O (a), indicating that trans coupling
between the NH and CH protons at the metal-free compart-
ment causes splitting of the CH resonance to a doublet. The
complimentary CH resonance (b) at the metal-containing part
is associated with weak satellites due to S = 1/2 metal isotopes.
Thus, the singlet at 8.44 ppm for complex 1 has satellite peaks
207
due to Pb (J = 25 Hz), while for complex 5, the peak at 8.24
111,113
ppm shows satellites due to
Cd (J = 30 Hz). Of the two
aromatic protons (d and e), the less shielded resonance seems to
be due to the one closer to the protonated imine. In the aliphatic
region, although the chemical shift due to CH (f ) is almost
3
identical for 1 (2.16 ppm) and 5 (2.17 ppm), significant differ-
ences are observed in the two cases for the CH resonances.
2
Thus, while for complex 1 five signals at 4.24 (2), 3.94 (4),
3
.77 (2), 2.39 (2) and 1.48 (2) ppm are observed (values in
parentheses indicate the number of protons), only two signals
at 3.93 (8) and 2.23 (4) are observed for complex 5. The COSY
spectrum of 1 showed correlation between the following pairs:
3
.94 and 13.21, 3.94 and 2.39, and 4.24 and 1.58. Taken
1
2ϩ
Fig. 8 H NMR spectra at different temperatures for the [Pb(LH )]
2
together, it may be concluded that while the CH CH CH
protons on the Pb side are anisochronous and are observed at
2
2
2
cation of 1 in (CD ) SO. The peaks due to the solvent and HOD are
marked with asterisks.
3 2
J. Chem. Soc., Dalton Trans., 2002, 2760–2767
2765

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a
Table 4 Proton NMR spectra of complexes 1–7
2
ϩ
2ϩ
2ϩ
2ϩ
2ϩ
Assignment
[Pb(LH )]
[Cd(LH )]
[Pb L]
[Cd L]
[Zn L]
2
2
2
2
2
1
, 2
5
3, 4
6
7
ϩ
N –H ؒ ؒ ؒ O
a
b
c
d
e
f
g
h
i
13.21 (s, 2)b
13.37 (s, 2)c
ϩ
d
e
HN ᎐CH
8.44 (s, 2)
8.24 (s, 2)
8.43 (s, 4)
7.36 (s, 4)
8.36 (s, 4)
7.34 (s, 4)
2.24 (s, 6)
8.49 (s, 4)
7.52 (s, 4)
8.65 (d, 2)
7.36 (s, 2)
7.47 (s, 2)
2.16 (s, 6)
4.24 (t, 2)
3.77 (d, 2)
3.94 (d, 4)
—
8.63 (d,2 )
7.30 (s, 2)
7.47 (s, 2)
2.17 (s, 6)
3.93 (m, 8)
Aromatic
CH3
CH2
2.29 (s, 6)
4.37 (t, 4)
2.28 (s, 6)
3.97 (m, 8)
3.92 (m, 8)
3.86 (dd, 4)
j
k
l
—
—
—
—
1.58 (q, 2)
—
2.23 (m, 4)
—
1.66 (q, 4)
1.99 (m, 4)
1.94 (m, 4)
—
—
—
m
n
2.39 (m, 2)
—
—
—
—
—
a
b 207
c 111,113
d 207
Spin multiplicity and the number of protons are given in parenthesis.
Pb satellites, J = 25 Hz.
Cd satellites, J = 30 Hz.
Pb satellites,
e 111,113
J = 22 Hz.
Cd satellites, J = 20 Hz.
each other and coalesce at 50 ЊC, while the chemical shifts due
to the aromatic singlets (d and e) get averaged at 40 ЊC. Signifi-
A second point of interest in this context would be to com-
pare the magnitude of the satellite coupling to Pb or Cd iso-
topes in the mononuclear vis-à-vis dinuclear complexes. In the
case of the mononuclear cadmium complex 5, J = 30 Hz, while
for the dinuclear cadmium compound 6, the J value (20 Hz) is
considerably less. Such a difference in J values, however, is not
so conspicuous between the mononuclear and dinuclear lead
complexes 1 (25 Hz) and 3 (22 Hz).
cant changes occur for the signals due to the CH protons, with
2
increasing temperature, the rotational barriers for the g and h
protons decrease, and they collapse at ca. 60 ЊC. Variation of
the temperature produces little effect on the chemical shifts due
to the CH (f ) and N–H ؒ ؒ ؒ O (a) moieties. Over the increasing
3
temperature range (25 to 70 ЊC, the chemical shift of f changes
from 2.16 to 2.18 ppm, while for a, the change from 13.21 to
1
3.17 ppm is accompanied by a considerable increase in line
Conclusion
broadening.
The dinuclear lead (3, 4) and cadmium(6) complexes display
A convenient synthetic route to obtain the mononuclear
macrocyclic lead complexes [Pb(LH )(ClO )][ClO ] and [Pb-
207
well-resolved satellite peaks due to the coupling of Pb–CH
2
4
4
111,113
(
b) [J = 22 Hz] and
Cd–CH(b) [J = 20 Hz]. Similar to their
(LH )(NO ) ] of the type III has been developed. These com-
2
3 2
nϩ
mononuclear analogues, complexes 4 and 6 differ with regard to
pounds can be readily converted to other [M(LH )] (n = 2, 3)
2
the CH resonances. Complex 4 exhibits three signals at 4.37,
complex species, which, in turn, could be used as precursors for
synthesizing various heterometallic and heterovalent complexes
of the symmetrical tetraiminodiphenol macrocyclic ligand II.
It has been observed that the solid state architectures obtained
for [Pb(LH )(ClO )][ClO ] and [Pb L(NO ) ] owe their origin
2
3
.86 and 1.66 ppm, each arising from four protons. Complex 6,
as well as the dizinc complex 7, however, show only two reson-
ances, from eight and four protons [6: 3.92(8) and 1.99(4);
7
: 3.97(8) and 1.94(4) ppm], due to the CH CH CH and
2 2 2
2
4
4
2
3 2
CH CH CH protons, respectively. The COSY spectrum
to weak interactions between the metal cation and the anions,
the dentacity and directionality of the anions and crystallo-
graphic symmetry requirements. Thus, [Pb(LH )(ClO )][ClO ]
2
2
2
of 4 showed that the resonance at 4.37 ppm is correlated
with the resonances at 3.86 and 1.66 ppm, indicating aniso-
chronous behaviour of these CH CH CH protons. Clearly, free
2
4
4
assembles to a hexameric species through three-fold coordin-
ation of the perchlorate ion, in which the metal atoms of the
macrocyclic units are arranged around a hexagonal frame like
butterflies. A different type of chain structure develops for
[Pb L(NO ) ] via an uncommon bridging binding mode of
2
2
2
2ϩ
rotation of CHHЈ in the vicinity of the larger Pb ion (vdW r =
2ϩ
2
ϩ
1
(
.19 Å) is more restricted relative to Cd (0.95 Å) and Zn
0.74 Å).
It would be of interest to compare such parameters as the
2
3 2
ϩ
1
chemical shift due to N–H ؒ ؒ ؒ O and the trans coupling
between N–H and C–H for the mononuclear lead (1, 2) and
the nitrate ions. In solution, the H NMR spectra show con-
siderable differences in the number and patterns of resonances
due to the methylene protons for both mononuclear and
dinuclear lead complexes as compared to their cadmium
and zinc analogues. In the lead complexes, the CHHЈ protons in
the vicinity of the metal atoms are anisochronous, while they
are isochronous in the cadmium and zinc complexes, thereby
showing the considerable influence of the size of the metal ions
ϩ
cadmium (5) complexes with similar mononuclear metal
33
cryptates. For the divalent metal ion cryptates, the following
33
2ϩ
δ and J values for these parametrs have been reported: Pb
2
ϩ
2ϩ
(
13.59 ppm,13.5 Hz), Cd (13.84 ppm, 13.6 Hz), Zn (13.86
2ϩ
ppm, 13.6 Hz) and Ca (13.53 ppm, 14.1 Hz). The correspond-
ing values observed for 1 (13.21 ppm, 13.7 Hz) and 5 (13.37
ppm, 13.2 Hz) are quite similar.
on the rotational barrier of the CH groups.
2
2
766
J. Chem. Soc., Dalton Trans., 2002, 2760–2767

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