A layered silver sulfonate incorporating nine-coordinate Ag(I) in a hexagonal grid

Article abstract of DOI:10.1039/a904445k

Silver benzenesulfonate is an example of a layered 'inorgano-organic' solid where the inorganic component is comprised of sulfonate-bridged silver(I) centers and the organic moiety is a phenyl group; the resulting network of silver ions forms a planar hexagonal array incorporating a previously unobserved six-fold metal-bridging mode for the sulfonate ion.

Full text of DOI:10.1039/a904445k

A layered silver sulfonate incorporating nine-coordinate AgI in a hexagonal
grid
George K. H. Shimizu,*† Gary D. Enright, Chris I. Ratcliffe, Keith F. Preston, Jennifer L. Reid and John A.
Ripmeester
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, K1A 0R6, Canada.
E-mail: gshimizu@ucalgary.ca
Received (in Columbia, MO, USA) 3rd June 1999, Accepted 30th June 1999
Silver benzenesulfonate is an example of a layered ‘in-
organo–organic’ solid where the inorganic component is
comprised of sulfonate-bridged silver(i) centers and the
organic moiety is a phenyl group; the resulting network of
silver ions forms a planar hexagonal array incorporating a
previously unobserved six-fold metal-bridging mode for the
sulfonate ion.
disordered between two positions situated 81° apart about the
major axis of the ring. NMR shows that at room temperature this
disorder is dynamic.7 The nearest distance between phenyl
groups is 5.20(1) Å.8 The structure is representative of the bulk
phase as PXRD data was indexed to the same unit cell.9
The structure of 1 is extremely unusual both with respect to
the coordination of the AgI ions and the mode of coordination of
the sulfonate groups to the metals. Each AgI ion is nine-
coordinate (Fig. 2) with a coordination sphere comprised of six
sulfonate oxygen atoms [from six different sulfonate groups,
Ag–O distances range from 2.42(1)–2.56(1) Å] and three bonds
to other Ag ions [Ag–Ag 2.915(1) Å].10 The geometry at each
AgI may be considered as a distorted octahedron of oxygen
donors, with three silver donors approaching in a trigonal plane
bisecting the octahedron.11 Congruently, the SO3 groups must
form bonds to six different Ag ions, each oxygen coordinating
to two silver centres.12 The six Ag–O distances span a smaller
range than observed for the five Ag–O interactions in AgOTs
[2.391(6)–2.700(3) Å].4 Interestingly, the network of Ag–Ag
Currently, there are numerous well studied examples of
‘inorgano–organic’ lamellar solids.1 This term is used to
describe layered solids containing a planar backbone, com-
prised solely of inorganic elements, which also incorporate
organic moieties as covalently bound pendant groups. Organic
derivatization of inorganic layers couples the skeletal rigidity of
the inorganic lamellae with the structural diversity inherent to
organic functionalization. The result can be a new compound
with markedly different properties (solubility, intercalation,
exfoliation) from the parent inorganic backbone. The principal
sub-groups of complexes in this class include metal phospho-
nates,2 and perovskite halides.3 Whereas examples of lamellar
networks with phosphonate groups abound,2 lamellar ‘in-
organo–organic’ systems employing sulfonates are virtually
unknown.4,5 Silver benzenesulfonate is a two-dimensional
network from which the phenyl groups protrude from both
sides. The resulting phenyl–silver(sulfonate)–phenyl trilayer
then assembles by dispersive forces between the phenyl groups.
The network of Ag–Ag bonds forms a nearly perfect hexagonal
grid. Each AgI in the structure has nine atoms at less than van
der Waals contact distances and each SO3 group caps six
6
different AgI centers. The observed h -coordination mode of the
sulfonate group to metals is unprecedented.
Silver benzenesulfonate 1 may be generated by the addition
of aqueous sodium benzenesulfonate to a solution of AgNO3 in
water. Concentration of this solution results in the precipitation
of 1, in very good yields, as a light gray solid.‡ Elemental
analyses confirmed a 1+1 stoichiometry of AgI to benzenesulfo-
nate. Diffusion of isopropyl ether into a MeOH solution of 1
resulted in the growth of extremely thin plate-like crystals
suitable for an X-ray diffraction analysis.§
Silver benzenesulfonate forms a two-dimensional infinite
array wherein the AgI centers are bridged by SO3 groups to form
layers and the phenyl moieties of the sulfonates protrude into
the interlayer region (Fig. 1).6 The asymmetric unit contains a
single disordered silver benzenesulfonate unit. The interlayer
distance, defined as the perpendicular distance between the
layers of AgI ions, is 15.23(2) Å. The thickness of an individual
lamella, defined as the region containing solely the Ag, S and O
atoms, is 3.87(2) Å. The difference between these two values,
11.36(2) Å, constitutes the gallery height in the complex.
Adjacent layers in the complex are slightly offset by 1.32(2) Å
in a direction between the a and b axes. The benzenesulfonate
has its major axis oriented ca. 14° off the normal to the plane
containing the silver atoms. The interlayer phenyl group is
Fig. 1 Structure of 1 showing the overall lamellar network with phenyl
groups protruding into the interlayer region. Disorder has been removed for
clarity.
† Current address: Department of Chemistry, University of Calgary, 2500
University Drive N.W., Calgary, Alberta, T2N 1N4, Canada.
Chem. Commun., 1999, 1485–1486
1485

disorder) in P1 to a residual R1(Rw) of 0.045 (0.063). However, under P1,
strong correlations between parameters, non-positive definite thermal
parameters, unacceptable C–C bond distances, higher residuals and an
inconsistency with the NMR dynamics studies convinced us to accept the
¯
50+50 disordered P1 structure. The O and C atoms are all 50% occupied.
The hydrogens were all placed in calculated positions. The partially
occupied atoms in close contact (C1, C1a and C4, C4a) were refined
2
isotropically. This structure was corroborated by CP MAS 13C and H SS
NMR studies to be reported in detail elsewhere. CCDC 182/1311.
1 G. Alberti and U. Costantiono, in Comprehensive Supramolecular
Chemistry, ed. J. L. Atwood, J. E. D. Davies, D. D. MacNicol and F.
Vo¨gtle, Elsevier Science, New York, 1996, vol. 7, ch. 1, pp. 1–24.
2 For a- and g-Zr phosphonates, see: G. Alberti and U. Costantino, in
Inclusion Compounds, ed. J. L. Atwood, J. E. Davies and D. D.
MacNicol, Oxford University Press, New York, 1991, vol. 5, ch. 5, pp.
136–176; for a review to 1997, see, A. Clearfield, Prog. Inorg. Chem.,
1998, 47, 371.
3 C. Bellito and P. Day, in Comprehensive Supramolecular Chemistry, ed.
J. L. Atwood, J. E. D. Davies, D. D. MacNicol and F. Vo¨gtle, Elsevier
Science, New York, 1996, vol. 7, ch. 9, pp. 293–313.
4 G. K. H. Shimizu, G. D. Enright, C. I. Ratcliffe, G. S. Rego, J. L. Reid
and J. A. Ripmeester, Chem. Mater., 1998, 10, 3282.
5 Sulfonates have been employed as H-bond acceptors in the generation
of layered guanidinium sulfonates. Interestingly, in these complexes the
sulfonate group forms six H-bonds much like the sulfonates herein form
six-coordinate covalent bonds, see: V. A. Russell, C. C. Evans, W. Li
and M. D. Ward, Science, 1997, 276, 575; J. A. Swift, A. M. Pivovar,
A. M. Reynolds and M. D. Ward, J. Am. Chem. Soc., 1999, 121, 5887;
V. A. Russell, M. C. Etter and M. D. Ward, J. Am. Chem. Soc., 1994,
116, 1941.
6 Tetranuclear AgI clusters bridged by succinates have been previously
observed, A. Michaelides, V. Kiritis, S. Skoulika and A. Aubry, Angew.
Chem., Int. Ed. Engl., 1993, 32, 1495.
7 From CP MAS 13C and 2H solid state NMR, a model for the dynamics
about the twofold axis of the phenyl ring consistent with the disorder
was determined.
8 For a comparison with the structure of Zr(O3PPh)2, see: M. D. Poojary,
H.-L. Hu, F. L. Campbell III and A. Clearfield, Acta Crystallogr., Sect.
B, 1993, 49, 996.
9 PXRD data of a bulk sample of silver benzenesulfonate was indexed to
the following triclinic cell: a = 5.1564, b = 5.1956, c = 15.3099 Å, a
= 86.785, b = 84.582, g = 61.149°, V = 357.62 Å3.
10 Moore and coworkers have recently performed a comprehensive search
of the Cambridge Structural Database to quantify occurrences of metal
ion geometries, see: D. Venkataraman, Y. Du, S. R. Wilson, P. Zhang,
K. Hirsch and J. S. Moore, J. Chem. Educ., 1997, 74, 915. Their results,
which are available at http://sulfur.scs.uiuc.edu, indicate AgI primarily
occurs in linear, trigonal or tetrahedral coordination modes. No
examples of nine-coordinate AgI are known. The Ag–Ag distances
reported here are all significantly less than the van der Waals contact
distance for Ag–Ag of 3.40 Å.
11 The most common geometry for nine-coordinate species, primarily
observed for nonahydrated lanthanide complexes, is a tricapped trigonal
prism, see F. A. Cotton and G. Wilkinson, Advanced Inorganic
Chemistry, John Wiley, Toronto, 5th edn., 1988, p. 17. The present
structure would fit this description if the two sulfonate groups bonded to
each silver(i) were in an eclipsed orientation.
Fig. 2 View down onto a single lamella of the structure of 1 with phenyl
rings and disordered oxygen atoms removed for clarity. Silver atoms: large
circles, sulfur atoms: medium shaded circles, oxygen atoms: small circles.
Note the hexagonal arrangement of the silver(i) centers and the nonavalent
coordination mode, and the m6-sulfonate groups.
interactions forms a nearly perfect hexagonal grid reminiscent
of graphite.13,14 The hexagons are completely planar with the
observed angles around the Ag periphery averaging to 120.0(1)°
[the three different angles are 114.83(3), 116.12(3) and
128.79(3)°]. Each Ag hexagon is capped by an SO3 group and
the mean distance across a hexagon is 6.01(30) Å. The solely
inorganic component of this structure, the AgSO3 lamellae,
possess almost hexagonal symmetry. The phenyl groups,
however, cannot adopt this high symmetry necessitating a
distortion in the overall structure to a triclinic, albeit pseudo-
hexagonal, space group.15 DSC–TGA analyses of a sample of
silver benzenesulfonate revealed the sample to be completely
stable to 139.7 °C at which point a reversible endothermic
transition was observed in the DSC. A second non-reversible
endothermic transition was observed at 198.2 °C followed by an
exothermic transition with an onset temperature of 253.4 °C
corresponding to loss of 43.9% of sample weight.
Silver(i) is a notoriously pliant ion with respect to its
coordination sphere. Coordination numbers ranging from two to
four are common10 but examples of five- and six-coordinate AgI
have also been observed.16 Even in this light, the structure of 1
is remarkable. Silver benzenesulfonate possesses a fascinating
structure both from the macroscopic viewpoint, the lamellar
motif, and from the microscopic perspective, the highly unusual
nine-coordinate AgI as well as a novel six-fold bridging mode
for a coordinating sulfonate.The question of structure-directing
effects (Ag–O versus Ag–Ag) in the silver sulfonate family will
be resolved upon consideration of other derivatives.
12 In a review of triflate binding, a listing of observed coordination modes
of R–SO3 to metals does not include the six-fold bridging mode
observed here. See: G. A. Lawrance, Chem. Rev., 1986, 86, 17.
13 H. Zabel and S. A. Solin, Graphite Intercalation Compounds I, Springer
Series in Material Science 14, Springer, Berlin, 1990.
14 Based upon the structural similarity to graphite, the prospect that the
network may be a conductor was entertained. However, EPR spectra
revealed a noiseless signal to 77 K, indicative that all the electrons were
highly localized and the material is not a conductor.
15 For a hexagonal unit cell, the symmetry requirements are: a = b, a =
b = 90, g = 120°. The observed unit cell parameters, with doubling of
g, are slight distortions from these conditions.
16 For examples of other penta- and hexa-coordinate AgI, see: K. A.
Hirsch, S. R. Wilson and J. S. Moore, Inorg. Chem., 1997, 36, 2960; L.
Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, Angew. Chem., Int.
Ed. Engl., 1995, 34, 1895; G. K. H. Shimizu, G. D. Enright, C. I.
Ratcliffe, J. A. Ripmeester and D. D. M. Wayner, Angew. Chem. Int.
Ed., 1998, 37, 1407.
Notes and references
‡ 1: To a solution of AgNO3 (1.44 g, 8.50 mmol) in H2O (20 mL) was added
a solution of sodium benzenesulfonate (1.53 g, 8.50 mmol) in H2O (50 mL).
A clear solution resulted which was concentrated to ca. 10 mL. A gray solid
precipitated which was vacuum filtered, washed with cold water (2 mL) and
dried. Yield: 1.78 g (6.72 mmol, 79%) CP MAS SS 13C NMR (75 MHz) d
144.1 (quat. arom), 127.5 (tert. arom). C, H analyses: calc. C, 27.19, H, 1.90:
obs. C, 26.82, H, 1.84%. Diffusion of isopropyl ether into a MeOH solution
of 1 gave plate-like crystals suitable for an X-ray analysis.
§ Crystal data for 1: C12H10Ag2S2O6, M
= 530.06, colorless plates,
¯
triclinic, space group P1, a = 5.1596(8), b = 5.1979(8), c = 15.296(2) Å,
a = 86.75(2), b = 84.56(2), g = 61.00(2)°, V = 357.2(1) Å3, Z = 2, Dc
2.464 g cm23, R = 0.037, Rw = 0.043 and GOF = 1.27 for 161 parameters
using 1540 [Fo > 2.5s(Fo)] reflections. Mo-Ka radiation (l = 0.71073 Å),
m(Mo-Ka) 3.05 mm21. Data collection temp. 2100 °C. The data was
collected on a Siemens SMART CCD diffractometer using the w scan mode
(3 < 2q < 57.3°) and solved using the NRCVAX suite of programs.17 An
17 E. J. Gabe, Y. LePage, J.-P. Charland, F. L. Lee and P. S. White, J. Appl.
Crystallogr., 1989, 32, 384.
¯
initial refinement was attempted in P1. The discovery from this of the
PhSO3 molecule disordered over two equally occupied positions then led us
to consider the P1 space group. We were able to refine the structure (without
Communication 9/04445K
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Chem. Commun., 1999, 1485–1486