Anhydrous lead(II) heptanoate

Article abstract of DOI:10.1107/S0108270101001615

The title compound, catena-poly[[(heptanoato-O,O')lead(II)]μ-heptanoato-O,O':O:O'], [Pb(C₇H₁₃O₂)₂], is a metallic soap which can be used as a corrosion inhibitor since it forms a passive film at the Pb surface. Its structure is characterized by two-dimensional layers parallel to the bc plane. The layers are packed through van der Waals interactions along the a direction and form blocks parallel to (001). The 6s² lone pair of electrons on Pb^II is stereochemically active in this compound, which leads to a hemidirected octahedral geometry for the O-environment around the Pb atoms.

Full text of DOI:10.1107/S0108270101001615

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
Crystallographic structures for two short linear-chain
carboxylates are known, namely lead formate, [Pb(CHO2)2],
and lead acetate trihydrate, [Pb(C2H3O2)2]Á3H2O (Harrison &
Steel, 1982). The former has a three-dimensional polymeric
structure, while the latter is built up of parallel sheets and so
adopts a two-dimensional character. The structure of the title
compound, (I), is characterized by a lamellar building of
sheets, formed by PbÐO bonds, parallel to the bc plane. The
sheets are packed along the a direction by van der Waals
interactions and consequently form blocks parallel to (001), as
shown in Fig. 1. The Pb atoms are disposed on a zigzag chain
through the middle of the sheets, running along the b direc-
tion.
ISSN 0108-2701
Anhydrous lead(II) heptanoate
FrancËoise Lacouture,a* Michel FrancËois,a Claude
Didierjean,b Jean-Pierre Rivera,c Emmanuel Roccaa
and Jean Steinmetza
a
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Laboratoire de Chimie du Solide Mineral, UMR 7555, Universite Henri Poincare
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Nancy I, Faculte des Sciences, BP 239, 54506 Vandoeuvre les Nancy CEDEX,
b
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France, Laboratoire de Cristallographie et de Modelisation des Materiaux Mineraux
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et Biologiques, UPRESA 7036, Universite Henri Poincare Nancy I, Faculte des
c
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Sciences, BP 239, 54506 Vandoeuvre les Nancy CEDEX, France, and Departement
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de Chimie Minerale, Analytique et Appliquee, Universite de Geneve, 30 quai Ernest
Á
Ansermet, CH-1211 Geneve 4, Switzerland
Correspondence e-mail: francoise.lacouture@lcsm.uhp-nancy.fr
Received 6 October 2000
Accepted 25 January 2001
Fig. 2 shows the environment around Pb. Each Pb atom is
surrounded by six O atoms, which form a very distorted
polyhedron. The six O atoms belong to four different biden-
tate carboxylate groups. Carboxylate O11/O12 is chelating
The title compound, catena-poly[[(heptanoato-O,O0)lead(II)]-
ꢀ-heptanoato-O,O0:O:O0], [Pb(C7H13O2)2], is a metallic soap
which can be used as a corrosion inhibitor since it forms a
passive ®lm at the Pb surface. Its structure is characterized by
two-dimensional layers parallel to the bc plane. The layers are
packed through van der Waals interactions along the a
direction and form blocks parallel to (001). The 6s2 lone pair
of electrons on PbII is stereochemically active in this
compound, which leads to a hemidirected octahedral
geometry for the O-environment around the Pb atoms.
i
i
Ê
[PbÐO11 2.583 (8) and PbÐO12 2.735 (8) A; symmetry
code: (i) x, y, z] and also bridges the adjacent Pb atoms
along the b direction [PbÐO11 2.567 (7) and PbÐO12ii
ii
ꢁ
Ê
2.620 (7) A, and O11ÐPbÐO12 166.6 (3) ; symmetry code:
(ii) x, 1 + y, z]. Carboxylate O21/O22 is only chelating and
leads to the shortest PbÐO distances in the structure [PbÐ
Ê
O21 2.451 (8) and PbÐO22 2.410 (9) A]. The average PbÐO
Ê
distance is 2.56 A, which is slightly shorter than the sum of the
ionic radii (ionic radii: PbII = 1.19 A when the coordination
Ê
Ê
number is 6, and O = 1.40 A; Shannon, 1976). The six PbÐO
bonds are directed on the same side of a globe surrounding the
Pb atom, so that the coordination can be quali®ed as `hemi-
directed octahedral coordination' (Shimoni-Livny et al., 1998).
This type of coordination arises for PbII when the 6s2 lone pair
is stereochemically active. There are voids in the PbÐO
bonding distribution which make the lone-pair position iden-
ti®able; the lone pair is approximately situated in the direction
of the relatively short PbÐO21 bond.
Comment
Electrochemical studies have shown that aliphatic sodium
carboxylate inhibits the corrosion of lead in aqueous solution
(Rocca & Steinmetz, 2001). Particularly, the ef®ciency of this
inhibition by these compounds, with the general formula
CH3(CH2)n 2COONa (n = 7±11), was found to depend on the
chain length of the aliphatic group. The passivation of the
metal was attributed to the growth of passive layers containing
metallic soap, [Pb(CnH2n 1O2)2]. Metals such as Cu, Zn, Mg
and Fe, the corrosion/passivation behaviour of which is under
study in our laboratory, can be protected by their corre-
sponding metallic soaps. The general aim of these studies
concerns new protective treatments, which would be less
polluting than the phosphatation or chromatation often
currently used in metal protection. To optimize the treatments,
for example by varying the chain length of the aliphatic
carboxylate group, it is necessary to understand better the
interactions between the surface of the metal, oxidized or not,
and the metallic soap, which requires knowledge of the crys-
tallographic structure formed by the hydrophobic and
protecting metallic soap.
The absence of structural water, contrary to the case of the
equivalent acetate compound, which is the trihydrate, was
con®rmed by thermogravimetric analysis measurements (no
Figure 1
Projection of the structure of (I) along [100]. Displacement ellipsoids are
drawn at the 70% probability level and H atoms have been omitted for
clarity.
ꢀ
530 # 2001 International Union of Crystallography
Printed in Great Britain ± all rights reserved
Acta Cryst. (2001). C57, 530±531

metal-organic compounds
Table 1
Selected geometric parameters (A, ).
weight loss was observed between room temperature and
448 K) and micro-Raman spectroscopy (no signal due to
water-molecule vibration was recorded in the wave-number
range 3100±3500 cm 1). The structures of both (I) and lead
acetate have a two-dimensional character. The building of the
sheets is similar, but the main differences in lead acetate are
the existence of hydrogen bonds formed by water molecules
and the coordination number for the Pb atoms, which is
increased to eight by the O atoms of the water molecules.
ꢁ
Ê
PbÐO22
PbÐO21
PbÐO11
PbÐO11i
2.410 (9)
2.451 (8)
2.567 (7)
2.583 (8)
PbÐO12ii
PbÐO12i
O11ÐC11
O12ÐC11
2.620 (7)
2.735 (8)
1.270 (12)
1.239 (12)
O22ÐPbÐO21
O22ÐPbÐO11
O21ÐPbÐO11
O22ÐPbÐO11i
O21ÐPbÐO11i
O11ÐPbÐO11i
O22ÐPbÐO12ii
O21ÐPbÐO12ii
52.4 (3)
81.3 (3)
91.1 (3)
118.7 (3)
77.6 (3)
65.2 (3)
86.4 (3)
77.2 (3)
O11ÐPbÐO12ii
O11iÐPbÐO12ii
O22ÐPbÐO12i
O21ÐPbÐO12i
O11ÐPbÐO12i
O11iÐPbÐO12i
O12iiÐPbÐO12i
166.6 (3)
117.4 (3)
129.2 (3)
78.1 (3)
113.4 (2)
48.3 (2)
70.9 (3)
Symmetry codes: (i) x; y; z; (ii) x; 1 ‡ y; z.
Re®nement
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.042
wR(F2) = 0.132
S = 1.034
2820 re¯ections
172 parameters
H-atom parameters constrained
w = 1/[ꢅ2(Fo2) + (0.0852P)2]
where P = (Fo2 + 2Fc2)/3
(Á/ꢅ)max < 0.001
3
Ê
Áꢆmax = 1.12 e A
3
Ê
2.15 e A
Áꢆmin
=
Figure 2
The environment of the PbII ion in (I) showing the orientation of the
linear heptanoate chains. Displacement ellipsoids are drawn at the 70%
probability level and H atoms have been omitted for clarity (symmetry
codes are as in Table 1).
Ê
H atoms were placed geometrically (CÐH = 0.95±0.97 A) but their
parameters were not re®ned and their individual isotropic displace-
ment parameters were ®xed at Uiso = 1.2Ueq(C).
Data collection: COLLECT (Nonius, 1998); cell re®nement:
SCALEPACK in HKL (Otwinowski & Minor, 1997); data reduction:
SCALEPACK and DENZO in HKL; program(s) used to solve
structure: SHELXS97 (Sheldrick, 1990); program(s) used to re®ne
structure: SIR97 (Altomare et al., 1998); molecular graphics: ATOMS
(Dowty, 1995).
Experimental
Crystals of the title compound were prepared by the reaction of a
solution of lead nitrate with sodium heptanoate. The precipitates
obtained were washed with distilled water and dried. A small quan-
tity of the product was recrystallized from ethanol for one month at
room temperature. The colourless crystals were small plates with the
(001) face well developed.
The authors are grateful to the Services Communs de
Â
Diffractometrie Automatique of the Universite Henri Poin-
care, and to Edward McRae for correcting the manuscript.
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Crystal data
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: OS1131). Services for accessing these data are
described at the back of the journal.
[Pb(C7H13O2)2]
Mr = 465.2
Triclinic, P1
a = 4.8574 (10) A
Ê
b = 7.3046 (10) A
c = 23.1846 (10) A
ꢁ = 91.61 (1)ꢁ
ꢂ = 95.66 (1)ꢁ
ꢃ = 90.99 (1)ꢁ
Z = 2
Dx = 1.890 Mg m
Mo Kꢁ radiation
3
Ê
Cell parameters from 41 187
re¯ections
ꢄ = 1±31ꢁ
ꢀ = 10.318 mm
T = 293 (2) K
Ê
References
1
Altomare, A., Burla, M. C., Camalli, M., Cascarano, G., Giacovazzo, C.,
Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1998). J.
Appl. Cryst. 32, 115±119.
Blessing, R. H. (1995). Acta Cryst. A51, 33±38.
Dowty, E. (1995). ATOMS for Windows. Version 3.1. Shape Software, 521
Hidden Valley Road, Kingsport, TN 37663, USA.
Plate, colourless
0.15 Â 0.13 Â 0.01 mm
3
Ê
V = 818.1 (2) A
Data collection
Nonius KappaCCD area-detector
diffractometer
CCD scans
Absorption correction: empirical,
®tted by spherical harmonic
functions (SORTAV; Blessing,
1995)
16 127 measured re¯ections
2820 independent re¯ections
2419 re¯ections with I > 2ꢅ(I)
Rint = 0.078
Harrison, P. & Steel, A. (1982). J. Organomet. Chem. 239, 105±113.
Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.
Otwinowski, Z. & Minor, W. (1997). Methods Enzymol. 276, 307±326.
Rocca, E. & Steinmetz, J. (2001). Corros. Sci. 43, 891±899.
Shannon, R. D. (1976). Acta Cryst. A32, 751±767.
Sheldrick, G. M. (1990). Acta Cryst. A46, 467±473.
Shimoni-Livny, L., Glusker, J. P. & Bock, C. W. (1998). Inorg. Chem. 37, 1853±
1867.
ꢄ
max = 24.84ꢁ
h = 5 ! 5
k = 8 ! 8
l = 0 ! 27
Tmin = 0.22, Tmax = 0.90
ꢀ
Acta Cryst. (2001). C57, 530±531
FranËcoise Lacouture et al. [Pb(C7H13O2)2] 531