Formation and structure of the novel heptanuclear lead(II) oxo cluster [Pb7(μ3-O)(μ4-O) (μ3-OMe)4(μ2-I)4] I2: With an unprecedented cage structure

Article abstract of DOI:10.1002/1099-0682(200212)2002:12<3210::AID-EJIC3210>3.0.CO;2-7

A novel lead(II) cluster [Pb₇(μ₃-O)(μ₄-O) (μ₃-OMe)₄(μ₂-I)₄] I₂ (1) has been isolated from the reaction mixture of PbI₂ and pyrazine in DMF/MeOH solvent with a reasonable yield (46%). The X-ray crystallography shows that 1 exhibits a novel unprecedented cage structure with centered μ₃-O and μ₄-O atoms and four different coordination environments of lead atoms. It is the first structurally characterized example of a lead compound containing bridging oxo, methoxide and iodide ligands. Compound 1 crystallizes in the tetragonal space group P42₁m, a = b = 11.7768(13), c = 9.8606(16) A, Z = 2, V = 1367.6(3) A³. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200212)2002:12<3210::AID-EJIC3210>3.0.CO;2-7

FULL PAPER
Formation and Structure of the Novel Heptanuclear Lead(II) Oxo Cluster
[Pb7(µ3-O)(µ4-O)(µ3-OMe)4(µ2-I)4]I2 with an Unprecedented Cage Structure
Yu-Jun Shi,[a] Yan Xu,[a] Xue-Tai Chen,*[a] Ziling Xue,[b] and Xiao-Zeng You*[a]
Keywords: Lead / Cluster compounds / Alkoxides / Oxo ligands / Crystal structure
A novel lead(II) cluster [Pb7(µ3-O)(µ4-O)(µ3-OMe)4(µ2-I)4]I2 (1)
lead compound containing bridging oxo, methoxide and iod-
has been isolated from the reaction mixture of PbI2 and pyra- ide ligands. Compound 1 crystallizes in the tetragonal space
˚
zine in DMF/MeOH solvent with a reasonable yield (46%).
The X-ray crystallography shows that 1 exhibits a novel un-
precedented cage structure with centered µ3-O and µ4-O
atoms and four different coordination environments of lead
atoms. It is the first structurally characterized example of a
group P421m, a = b = 11.7768(13), c = 9.8606(16) A, Z = 2,
V = 1367.6(3) A .
3
˚
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
O)(µ4-O)(µ3-OMe)4(µ2-I)4]I2 (1) reproducibly in 46% isol-
ated yield, which contains bridging oxo, methoxide and iod-
ide ligands. Lead() dimethoxide has been reported previ-
ously, although it was only poorly characterized due to its
low solubility and air- and moisture-sensitivity.[8] To the
best of our knowledge, there have been no lead oxomethox-
ide complexes reported in the literature. Herein we report
the preparation of the unusual heptanuclear lead oxo clus-
ter 1 and its unprecedented cage structure.
Lead() alkoxides and oxo alkoxides have been extens-
ively studied for their uses as molecular precursors to lead-
containing metal oxide materials via chemical routes such
as MOCVD and sol-gel processes.[1] There has been much
research interest focused on the synthesis and spectroscopic
characterization of lead alkoxide and oxoalkoxide com-
plexes. However, only a limited number of crystal structures
have been reported for lead alkoxides and oxoalkoxides.
These include oxygen-free, monomeric, trimeric, and one-
Results and Discussion
dimensional Pb(OR)2 (R
ϭ 2,6-di-tert-butyl-4-methyl-
phenyl,[2] tBu,[3] iPr,[3] and CH2CH2OMe[3]), and two oxy-
gen-centered, regular polyhedral clusters [Pb4(µ4-O)-
(OSiPh3)6][4] and [Pb6(µ3-O)4(µ3-OiPr)4].[5] Sita and co-
workers[6] recently reported a novel lead() oxoalkoxide
cluster [Pb7(µ3-O)(µ4-O)(µ2-OSiMe3)10] containing Pb4(µ4-
O) and Pb3(µ3-O) units. Obviously the structures of lead
alkoxides are highly dependent on the R groups and the
method of preparation.
We have recently become interested in the construction
of supramolecular structures using PbX2 as the building
blocks and have reported a novel 2-D coordination polymer
[PbI2(4,4Ј-bpy)] from the reaction of 4,4-bipyridine and
PbI2 in DMF/MeOH.[7] We intended to extend this chem-
istry from 4,4-bipyridine to pyrazine with the expectation
of preparing a similar PbI2 complex containing pyrazine
ligands. We were surprised that the mixture of PbI2 and
pyrazine in MeOH/DMF gave a cluster complex [Pb7(µ3-
The syntheses of 1 and our previously reported cluster
are summarized in Scheme 1, indicating how different prod-
ucts can be isolated by varying the ligand from 4,4-bipyrid-
ine to pyrazine. The formation of 1 can be rationalized as
follows. As the basicity of pyrazine is greater than that of
4,4Ј-bipyridine, pyrazine could act as a stronger proton ac-
ceptor than 4,4-bipyridine in abstracting the proton of
MeOH and H2O and enhance coordination between lead()
and the oxo and methoxide ligands. The low solubility of
1 might also favor its isolation from solution. A nitrogen-
containing heterocyclic ligand plays a similar role in the
preparation of transition metal clusters, for example
[Fe13O4F24(OMe)12]5Ϫ [9]
,
which was isolated from
FeF3·3H2O and pyridine in MeOH.
[a]
State Key Laboratory of Coordination Chemistry,
Coordination Chemistry Institute, Nanjing University,
Nanjing 210093, China
E-mail: xtchen@netra.nju.edu.cn
[b]
Department of Chemistry, The University of Tennessee,
Knoxville, Tennessee 37996-1600, USA
Scheme 1
3210  2002 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/02/1212Ϫ3210 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2002, 3210Ϫ3213

Formation and Structure of a Lead(II) Oxo Cluster
FULL PAPER
Compound 1 is insoluble in common organic solvents,
which prevents its characterization in solution. The crystal
structure of 1 was determined by X-ray crystallography. A
labeled ORTEP diagram of the cluster cation of 1 is shown
in Figure 1 and bond lengths and bond angles are listed in
Table 1. The structure of the cluster 1 exhibits C2v sym-
metry with a C2 axis through Pb(3), O(3) and O(1). There Unit cell dimensions
are four symmetrically different sets of lead atoms which
vary in the type and number of coordinated ligands. The
pyramidal Pb(2) and Pb(2A) are three-coordinate with one
Table 1. Crystal data and structure refinement for 1
Empirical formula
Formula mass
C4H12I6O6Pb7
2367.94
293(2)
Temperature (K)
˚
Wavelength (A)
0.71073
Crystal system, space group
Tetragonal, P421m
˚
˚
a ϭ 11.7768(13) A, α ϭ90°
b ϭ 11.7768(13) A, β ϭ 90°
˚
c ϭ 9.8606(16) A, γ ϭ 90°
3
˚
Volume (A )
1367.6(3)
Z
2
Calculated density (Mg/m3)
Absorption coefficient (mmϪ1
F(000)
5.750
49.712
1952
µ4-O and two µ3-OMe ligands, while Pb(1) and Pb(1A) are
in an inverted square-pyramidal configuration surrounded
by one µ4-O, one µ3-O, and two µ3-OMe ligands. More in-
teresting is the mixed coordination environment around
Pb(4) and Pb(4A), and Pb(3). Pb(4) and Pb(4A) are coord-
inated by two µ3-OMe and two iodide ligands, and the
unique Pb(3) is in an inverted square pyramidal I4O envir-
onment. The coordination spheres of all four Pb atoms in
1 are strongly distorted as a result of the presence of the
stereochemically active 6s2 lone-pair electrons on the PbII
cations. The PbϪO bond lengths fall into three different
categories depending on the environments of the O atoms.
The mean bond lengths of Pb-(µ3-O), Pb-(µ4-O), and
)
Crystal size (mm)
θ range for data collection (°)
Limiting indices
0.011 ϫ 0.009 ϫ 0.009
2.07 to 26.02
-14 Յ h Յ 7, -14 Յ k Ͻ 14,
-12 Յ l Յ 12
9808
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
837 (Rint ϭ 0.0684)
Empirical
0.639 and 0.590
Full-matrix
least-squares on F2
837/24/65
Data/restraints/parameters
Goodness-of-fit on F2
1.062
Final R indices [I Ͼ 2σ(I)]
Largest diff. peak and hole (e·A
R1 ϭ 0.0420, wR2 ϭ0.1008
2.824 and Ϫ2.724
˚
Ϫ3
˚
PbϪOMe are 2.20(3), 2.28(2), 2.439(17) A, respectively. The
)
˚
PbϪI bond lengths of 3.198(2)Ϫ3.302(3)
A
are
normal.[10Ϫ12] *The cage structure of 1 can also be viewed
as being built-up from a Pb4(µ4-O) unit bonded to Pb(4),
Pb(4A) and Pb(3) through four µ3-OMe groups, a µ3-O and
four iodide atoms. The µ4-O(1) atom tetrahedrally bridges
Pb(2), Pb(2A), Pb(1), and Pb(1A). The planar µ3-O is sur-
rounded by Pb(1), Pb(1A) and Pb(3). A similar three-
coordinate planar configuration has been observed in the
lead() thiolate cluster [Pb5O(SRF)8]·2C7H8 [RF ϭ 2,4,6-
trsi(trifluromethylphenyl)].[13]
x Ϫ 1, 1 Ϫ z), 3.63(2); I(1)···Pb(2), 3.68(2); I(1)···Pb(2a) (y,
1 Ϫ x, 1 Ϫ z), 3.49(2); I(1)···Pb(2b) (1 Ϫ y, Ϫ1 ϩ x, 1 Ϫ z),
3.49(2); I(1)···Pb(3a) (y, 1 Ϫ x, 1 Ϫ z), 4.01(2) and
˚
I(1)···Pb(4), 3.48(2) A].
Figure 2. The cell packing of the crystal structure of 1 showing the
weak interactions
Figure 1. The ORTEP diagram of cluster cation of 1
The PbII atoms of the cluster cation are involved in weak
interactions with the anion IϪ as shown in Figure 2, where
each IϪ anion links three cationic clusters to form an
extensive three-dimensional supramolecular assembly
Conclusions
In summary, a novel heptanuclear lead() cluster 1 has
through the six weak interactions [I(1)···Pb(1a)(1 Ϫ y, been isolated and characterized by X-ray crystallography.
Eur. J. Inorg. Chem. 2002, 3210Ϫ3213
3211

Y.-J. Shi, Y. Xu, X.-T. Chen, Z. Xue, X.-Z. You
FULL PAPER
˚
Table 2. Bond lengths [A] and angles [ °] for 1 (symmetry transformations used to generate equivalent atoms: A: Ϫx ϩ 2, Ϫy ϩ 1, z; B:
y ϩ 1/2, x Ϫ 1/2, z; C: Ϫy ϩ 3/2, Ϫx ϩ 3/2, z)
Pb(1)ϪO(3)
Pb(1)ϪO(1)
Pb(1)ϪO(2A)
Pb(1)ϪO(2B)
Pb(1)ϪPb(1A)
Pb(2)ϪO(1)
Pb(2)ϪO(2)
Pb(2)ϪO(2B)
2.22(2)
2.34(2)
Pb(3)ϪI(2)
Pb(3)ϪI(2B)
Pb(4)ϪO(2B)
Pb(4)ϪO(2)
Pb(4)ϪI(2B)
Pb(4)ϪI(2)
O(1)ϪPb(2A)
O(1)ϪPb(1A)
3.198(2)
3.198(2)
2.417(18)
2.417(18)
3.302(3)
3.302(3)
2.240(16)
2.34(2)
2.565(17)
2.565(17)
3.632(3)
2.240(16)
2.336(17)
2.336(16)
2.16(4)
Pb(3)ϪO(3)
O(2)ϪC(1)
1.48(3)
Pb(3)ϪI(2C)
Pb(3)ϪI(2A)
3.198(2)
3.198(2)
74.2(10)
93.2(5)
71.7(4)
93.2(5)
71.7(4)
139.4(7)
77.9(7)
77.9(7)
75.4(9)
80.78(5)
80.78(5)
85.75(8)
80.78(5)
91.31(9)
161.57(10)
80.78(5)
161.57(10)
91.31(9)
85.75(8)
72.4(8)
O(2)ϪPb(1A)
O(3)ϪPb(1A)
2.565(17)
2.22(2)
81.7(4)
O(3)ϪPb(1)ϪO(1)
O(3)ϪPb(1)ϪO(2A)
O(1)ϪPb(1)ϪO(2A)
O(3)ϪPb(1)ϪO(2B)
O(1)ϪPb(1)ϪO(2B)
O(2A)ϪPb(1)ϪO(2B)
O(1)ϪPb(2)ϪO(2)
O(1)ϪPb(2)ϪO(2B)
O(2)ϪPb(2)ϪO(2B)
O(3)ϪPb(3)ϪI(2C)
O(3)ϪPb(3)ϪI(2A)
I(2C)ϪPb(3)ϪI(2A)
O(3)ϪPb(3)ϪI(2)
I(2C)ϪPb(3)ϪI(2)
I(2A)ϪPb(3)ϪI(2)
O(3)ϪPb(3)ϪI(2B)
I(2C)ϪPb(3)ϪI(2B)
I(2A)ϪPb(3)ϪI(2B)
I(2)ϪPb(3)ϪI(2B)
O(2B)ϪPb(4)ϪO(2)
O(2B)ϪPb(4)ϪI(2B)
O(2)ϪPb(4)ϪI(2B)
O(2B)ϪPb(4)ϪI(2)
O(2)ϪPb(4)ϪI(2)
I(2B)ϪPb(4)ϪI(2)
Pb(3)ϪI(2)ϪPb(4)
Pb(2)ϪO(1)ϪPb(2A)
Pb(2)ϪO(1)ϪPb(1A)
Pb(2A)ϪO(1)ϪPb(1A)
Pb(2A)ϪO(1)ϪPb(1)
Pb(2)ϪO(1)ϪPb(1)
Pb(1A)ϪO(1)ϪPb(1)
C(1)ϪO(2)ϪPb(2)
Pb(2)ϪO(2)ϪPb(4)
C(1)ϪO(2)ϪPb(1A)
Pb(2)ϪO(2)ϪPb(1A)
Pb(4)ϪO(2)ϪPb(1A)
C(1)ϪO(2)ϪPb(4)
Pb(3)ϪO(3)ϪPb(1)
Pb(3)ϪO(3)ϪPb(1A)
Pb(1)ϪO(3)ϪPb(1A)
81.7(4)
129.3(4)
82.44(9)
85.90(7)
120.3(14)
108.28(16)
108.28(16)
108.28(16)
108.28(16)
101.8(12)
122.9(15)
103.5(7)
107.1(15)
98.4(6)
109.1(6)
114.2(15)
125.1(7)
125.1(7)
109.8(15)
129.3(4)
scan mode. An empirical absorption correction was applied to the
data, and structure solution and refinement on F2 were done. The
structures were solved by direct methods by using SHELXS 97[14]
and refined by full-matrix least-squares calculation on F2 with
SHELXL 97.[15] All non-hydrogen atoms were refined aniso-
tropically, whereas the hydrogen atoms were generated geometric-
ally. Crystal data, data collection parameters, and refinement
statistics for 1 are listed in Table 1. Relevant bond lengths and bond
angles for 1 are collected in Table 2.
The isolation of 1 implies that a suitable choice of base and
alkoxide ligand could lead to the formation of novel mixed-
coordinate lead clusters.
Experimental Section
Materials and Methods: All chemicals are commercially available
and were used without further purification, except PbI2, which was
prepared by the reaction of PbO with HI 35%. C, H and N analyses
were carried on a PerkinϪElmer 240C elemental analyzer. IR spec-
tra were recorded on a Bruker Optik Gmbh spectrophotometer
(range: 400Ϫ4000 cmϪ1) as KBr pellets.
CCDC-184695 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Center, 12, Union Road, Cambridge
CB2 1EZ, UK; fax: (internat.) ϩ44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
Preparation of 1: Single crystals of 1 were grown at room temper-
ature by using a layered solution approach. The bottom solution
layer, contained within a long straight tube, consisted of PbI2
(0.239 g, 0.5 mmol) dissolved in DMF. A mixed-solvent layer of
methanol/DMF (1:1) was carefully placed on top of the PbI2 solu-
tion using a syringe. Finally, pyrazine (a stoichiometric quantity
relative to the PbI2) dissolved in methanol was added to the top of
the buffer. As the layers slowly mixed, well-formed crystals of 1
appeared that were suitable for X-ray single-crystal analysis. Yield
77.8 mg, 46% (based on PbI2). C4H12I6O6Pb7 (2368.0): calcd. C,
2.03, H 0.51; found C 2.22, H 0.63. IR (KBr): ν˜ ϭ 603.86 cmϪ1
(vs), 682.04 (m), 750.83 (w), 838.09 (w), 1401.10 (s), 1608.43 (m).
Acknowledgments
This work was supported by Major State Basic Research Develop-
ment Program (Grant No. G2000077500), Overseas Outstanding
Young Scholar Fund from the National Natural Science Founda-
tion of China (No. 20028101) and Natural Science Grant of
Jiangsu Province (BK, 99032).
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Formation and Structure of a Lead(II) Oxo Cluster
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