Self-assembly of lamellar and expanded lamellar coordination networks

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sense,[7] probably due to the relatively poor metal-complexing
ability of nonchelating thioethers.[8] Herein, we introduce a
family of layered coordination networks, structurally remi-
niscent of anionic clays,[9] generated by the self-assembly of a
novel dithia ligand with AgBF4. Single-crystal data on two
lamellar arrays are presented which illustrate the formation
and expansion of the layers. Differential scanning calorimetry
(DSC) results reveal thermal stability to over 1808C, which is
attributed to a ªlamellar chelate effect.º
[2] a) H. C. Aspinall, M. R. Tillotson, Inorg. Chem. 1996, 35, 5; b) G. A.
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Commun. 1995, 47; c) M. Andrianarison, D. Stalke, U. Klingebiel,
Chem. Ber. 1990, 123, 71; d) M. Driess, H. Pritzkow, M. Skipinski, U.
Winkler, Organometallics 1997, 16, 5108.
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[4] G. W. Rabe, H. Heise, G. P. A. Yap, L. M. Liable-Sands, I. A. Guzei,
A. L. Rheingold, Inorg. Chem., in press.
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Kirchner, M. Schmidt, Inorg. Synth. 1990, 27, 235.
[6] G. W. Rabe, S. Kheradmandan, H. Heise, L. M. Liable-Sands, I. A.
Guzei, A. L. Rheingold, Main Group Chem., in press.
[7] K. Ruhlandt-Senge, J. E. Ellison, R. J. Wehmschulte, F. Pauer, P. P.
Power, J. Am. Chem. Soc. 1993, 115, 11353.
[8] X.-W. Li, W. T. Pennington, G. H. Robinson, Organometallics 1995,
14, 2109, and references therein.
[9] R. J. Wehmschulte, W. J. Grigsby, B. Schiemenz, R. A. Bartlett, P. P.
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hammer, Chem. Eur. J. 1997, 3, 1418, and references therein.
The dithia ligand 1 contains two
sulfurs linked by a rigid durene
unit, which prohibits chelation of
both donors to a single metal
center. The ligand 1 was synthe-
sized in excellent yield by the
reaction of tetrabromodurene
with sodium sulfide. An equimolar mixture of 1 and AgBF4
was stirred for three hours in MeCN, and then benzene was
diffused into this solution to afford colorless platelike crystals
of [{Ag(1)(MeCN)2}1][BF4]1 (2), suitable for X-ray diffrac-
tion analysis. An infinite two-dimensional layered structure is
formed by the cationic {Ag(1)(MeCN)2} building blocks while
the BF4 anions reside between the parallel layers (Figure 1).
Self-Assembly of Lamellar and Expanded
Lamellar Coordination Networks**
George K. H. Shimizu,* Gary D. Enright,
Chris I. Ratcliffe, John A. Ripmeester, and
Danial D. M. Wayner
The construction of infinite solid-state arrays by employing
coordinate covalent bonding and the principles of self-
assembly has resulted in numerous metal ± ligand networks
with fascinating structural topologies.[1] Among the frame-
work types that have resulted are PtS analogues,[1a] honey-
comb structures,[1b] a-Po analogues,[1c] diamondoid net-
works,[1f, j] and SrSi2 analogues.[1g] With these metallo-organic
networks, one hopes to realize the wealth of applications
known for solely inorganic frameworks, which range from
separations[2] to catalysis[3] to devices.[4] The preponderance of
infinite arrays formed by metal coordination chemistry
employ either aromatic N-donor ligands[1a, d, i, j, 5] or cyano-
derived ligands[1b, e, 6] as the metal-chelating point of contact.
Thioethers have been largely neglected as ligands in this
Figure 1. Structure of 2 in the crystal, showing the lamellar network with
interlayer BF4 ions and MeCN molecules that point into the interlayer
region. Hydrogen atoms are omitted for clarity.
[*] Dr. G. K. H. Shimizu, Dr. G. D. Enright, Dr. C. I. Ratcliffe,
Dr. J. A. Ripmeester, Dr. D. D. M. Wayner
Steacie Institute for Molecular Sciences
National Research Council of Canada
The coordination geometry about the AgI ions is a trigonal
bipyramid comprising three equatorial sulfur donors and two
axially bound MeCN molecules. Remarkably, in order to
achieve such a structure, it is necessary for the highly
symmetrical 1 to be asymmetrically coordinated to three
AgI ions. Figure 2 clearly shows that one thioether group of 1
coordinates a single AgI center, while the sulfur atom on the
100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada)
Fax: (‡1)613-991-4278
E-mail: shimizu@ned1.sims.nrc.ca
[**] The NRC Institute for Biological Sciences is acknowledged for the use
of their NMR, MS, and EA facilities. Dr. Chris Tulk and Rudi
Branderhorst are acknowledged for their assistance with the DSC
measurements. NRCC publication 40870.
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Figure 2. View down onto a single lamella of the structure of 2. BF4 ions
and hydrogen atoms are omitted for clarity.
Figure 3. The ªswelledº interlayer region in the structure of 3. The p-
stacked PhCN pseudo-pillars and the PhCN guest molecules[15] are clearly
visible.
opposite side of the ligand employs both lone pairs to
coordinate to two different AgI centers.
The cationic layers lie perpendicular to the crystallographic
c axis with an interlayer separation of 10.085(1) Š.[10] The
axial MeCN molecules are ligated in a linear fashion and
protrude directly into the interlayer region. The ligand 1 may
adopt either a syn or anti conformation with respect to the
orientation of the sulfur donors, owing to inversion at the
benzylic carbon atoms, but 1 is observed exclusively in the syn
conformation. Throughout the structure, the syn sulfur atoms
are oriented towards the same crystal face. Adjacent layers
are offset by 3.672(2) Š along the b axis. The calculated
surface area of the layered structure (St ˆ 1160 m2 g 1 [11]) and
C11 ˆ 141.3(4)8). Furthermore, the phenyl moiety of each
coordinated PhCN molecule participates in a p-stacking
interaction with another PhCN molecule from an adjacent
layer to form a ªpseudo-pillarº. This results in a swelling of
the interlayer region and an increase in the d spacing from
10.085(1) Š to 13.890(1) Š.[10, 15] The void space generated by
this interlamellar expansion is occupied by a single PhCN
molecule per repeat unit.[16] An additional effect of the
pseudo-pillar is to align adjacent layers in the crystal structure.
The lamellae are offset by only 0.624(2) Š, primarily in the a
direction, which is considerably different from the 3.672(2) Š
offset observed in 2. Interestingly, all molecules of 1 are again
in a syn conformation, but the ligands in adjacent layers are
oriented in opposite directions.
The individual cationic lamellae formed by AgBF4 and 1
are quite robust in nature. DSC and thermogravimetric (TG)
measurements reveal the loss of the nitrile molecules for both
2 and 3 below 1008C; however, the desolvated complexes do
not undergo any further phase changes until an endothermic
transition with an onset temperature of 1888C is observed in
both complexes.[17]
Monodentate thioethers are notoriously poor ligands for
transition metal ions.[8] In fact, homoleptic transition metal
complexes of Me2S are quoted as ªvirtually impossible to
prepareº.[18] Thus, it is interesting to note that 1, which can be
pictured as two molecules of Me2S linked by a benzene ring,
forms complexes stable to over 1808C with the air- and light-
sensitive AgBF4 salt. As this stability stems from the
regimented coordination environment about the Ag1 center
enforced by the layered structure, we refer to this as a
ªlamellar chelate effectº. Work in progress has shown that
these complexes undergo anion exchange reactions and that
some of these anions serve to pillar the interlayer region.[19]
This observation further extends the analogy of these lamellar
networks to claylike solids.
the fixed charge density ((fcd) ˆ 5.58  1013
e
1 cm 2 [12]) are
both comparable to other classes of layered compounds.[13]
As with any layered material, the prospect of ªswellingº the
structure to afford greater access to the interlayer region is
highly appealing.[14] The presence of labile coordination sites
on the metal directed into the interlamellar region makes the
use of a larger coordinating ligand, such as PhCN, a logical
choice. Therefore, a dried sample of 2 was dissolved in PhCN,
and then benzene was diffused into this solution to give
colorless, needlelike crystals of [{Ag(1)(PhCN)}1][BF4]1 ´1
PhCN (3), where one molecule of PhCN is coordinated to the
silver ion and the second is present as a guest molecule. The
structure of 3 (Figure 3) is a remarkable illustration of a
swelled lamellar solid. It is noteworthy that only a single
molecule of PhCN is coordinated to each AgI ion, necessitat-
ing a shift in metal ion geometry from a five-coordinate
trigonal bipyramid to a severely distorted four-coordinate
tetrahedron (N1-Ag-S1 ˆ 93.9(1)8, N1-Ag-S2 ˆ 102.2(1)8, N1-
Ag-S2' ˆ 79.8(1)8). The individual {Ag(1)} lamellae of 3,
however, are completely planar and identical to the individual
layers observed in 2. Therefore, despite the strained geometry
at the metal and the change in metal coordination number, an
analogous lamellar structure is retained. The coordinated
PhCN molecules, which serve to swell the layers, are
coordinated to the metal in a bent orientation (Ag-N1-
1408
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[6] a) T. Iwamoto, J. Inclusion Phenom. Mol. Recognit. Chem. 1996, 24,
61 ± 132; b) H. Zhao, R. A. Heintz, K. B. Dunbar, R. D. Rogers, J. Am.
Chem. Soc. 1996, 118, 12844 ± 12845; c) D. Venkataraman, G. B.
Gardner, S. Lee, J. S. Moore, ibid. 1995, 117, 11600 ± 11601.
[7] A few examples employing thioethers have recently appeared in the
literature, in addition to ref. [1h], a) J. R. Black, N. R. Champness, W.
Levason, G. Reid, Inorg. Chem. 1997, 36, 4432 ± 4438; b) ibid. 1996, 35,
1820 ± 1824.
Experimental Section
1:[20] Tetrabromodurene (1.99 g, 4.44 mmol) was added to a solution of
Na2S ´ 9H2O (2.14 g, 8.88 mmol) in ethanol (100 mL) and refluxed for 6 h.
Removal of solvent resulted in an off-white residue that was partitioned
between CH2Cl2 (100 mL) and H2O (50 mL). The aqueous layer was
separated and further extracted with CH2Cl2 (2 Â 100 mL). The organic
fractions were combined and dried (MgSO4). Yield: 0.84 g (4.34 mmol,
97%), >95% purity by 1H NMR; m.p. 220 ± 2238C; 1H NMR (200 MHz,
CDCl3): d ˆ 7.08 (s, 2H, arom.), 4.19 (s, 8H, CH2S); 13C{1H}: d ˆ 139.66,
120.50 (arom.), 37.31 (CH2S); CPMAS SS 13C NMR (75 MHz): d ˆ 140.6,
[8] S. G. Murray, F. R. Hartley, Chem. Rev. 1981, 81, 365 ± 414.
Á
[9] F. Cavani, F. Trifero, A. Vaccari, Catal. Today 1991, 11, 173 ± 301.
[10] In both crystal structures, the interlayer separation was defined as the
perpendicular distance between planes of silver ions since the metals
are on special positions.
‡
120.7 (arom.), 39.1 (CH2S); FAB-MS: m/z: 194.2 [M ]; C, H analysis: calcd:
[11] Calculated from the expression (1);
C 61.81, H 5.19; found: C 61.59, H 5.14.
1
St ˆ Nab  10 18 nMc
(1)
2: A solution of 1 (48.3mg, 0.249 mmol) in MeCN (40 mL) was added to a
solution of AgBF4 (48.3 mg, 0.249 mmol) in MeCN (10 mL). The solution
was stirred for 12 h and then concentrated to about 10 mL. Diffusion of
benzene into this solution resulted in the growth of platelike crystals
suitable for an X-ray analysis. C, H analyses:[21] calcd: C 35.70, H 3.42;
found: C 32.97, H 2.99. Crystal data:[22] C7H8Ag0.5B0.5F2NS, Mr ˆ 235.54,
[11] where N is the Avogadro constant, a and b are the surface area of one
side of the unit cell, n is the number of such exposed sides in the
interlayer region, and Mc is the formula weight of the unit cell: G.
Alberti, U. Costantino in Comprehensive Supramolecular Chemistry,
Vol. 7 (Eds.: J. L. Atwood, J. E. D. Davies, D. D. MacNicol, F. Vögtle),
Elsevier, New York, 1996, pp. 1 ± 24.
colorless plates, orthorhombic, space group I2cm, a ˆ 7.6520(2), b ˆ
3
11.7135(4), c ˆ 20.1711(7), Vˆ 1808.0(1) Š3, Z ˆ 8, 1calcd ˆ 1.731 gcm
,
[12] Calculated as n'(abn) 1, where n' is the number of charges, a, b and n
are defined as in ref. [11].
R ˆ 0.033, Rw ˆ 0.041 and GOF ˆ 3.14 for 113 parameters, 1287 reflections
with Fo > 2.5s(Fo).
[13] For comparison, typical values of St and fcd for a Zr(HPO4)2 structure
3: Benzene was diffused into a saturated, filtered solution of 2 in PhCN.
This resulted in the growth of colorless needles suitable for X-ray analysis.
C, H analyses:[21] calcd: C 48.43, H 3.39, found: C 45.82, H 3.15. Crystal
data:[22] C24H20AgBF4N2S2, Mr ˆ 595.23, colorless needles, monoclinic,
are 965 m2 g and 4.1 Â 1014
e
1 cm 2, respectively, and for a smectite
1
clay, 759 m2 g and 47.4 Â 1013 e cm 2, respectively.[11]
[14] a) M. A. Occelli, H. Robson, Expanded Clays and Other Microporous
Solids, Academic Press, New York, 1992; b) A. Clearfield, M.
Kuchenmeister in Supramolecular Architecture: Synthetic Control in
Thin Films and Solids (Ed.: T. Bein), ACS Symp. Ser. 499, American
Chemical Society, Washington, DC, 1992, pp. 128 ± 144.
1
space group P21/c, a ˆ 10.1909(5), b ˆ 27.780(1), c ˆ 8.6870(5), b ˆ
3
94.96(1), Vˆ 2450.1(2) Š3, Z ˆ 4, 1calcd ˆ 1.600 gcm
,
R ˆ 0.051, Rw ˆ
0.038 and GOF ˆ 2.11 for 387 parameters, 4032 reflections with Fo >
2.5s(Fo).
[15] In both structures 2 and 3, the interlayer spacing corresponds to
exactly half the length of one of the principal axes: the c axis for 2 and
the b axis for 3.
[16] Upon loss of solvent or attempts to exchange the PhCN for benzene,
the crystals become opaque and no longer diffract.
Received: October 24, 1997 [Z11080IE]
German version: Angew. Chem. 1998, 110, 1510 ± 1513
[17] For 2, a steady loss of MeCN is observed between room temperature
and 958C. For 3, loss of PhCN occurs, as expected, in two stages. The
first, steady loss from room temperature to 528C corresponds to the
unbound PhCN, followed by a second mass change from 62 ± 978C for
the Ag-bound PhCN. No further changes in the DSC or TG are
observed for both 2 and 3 until a transition with an onset temperature
of 188 Æ 18C occurs. All mass changes are within reasonable limits
(5%) of the expected values given that the room temperature
desolvation of 2 and 3 made an accurate determination of the initial
mass impossible. The value of 1888C is comparable to other Ag
coordination arrays with ligands generally accepted to be better
donors than thioethers. See: F.-Q. Liu, T. D. Tilley, Inorg. Chem. 1997,
36, 5090 ± 5096.
[18] S. R. Cooper, Acc. Chem. Res. 1988, 21, 141 ± 146.
[19] G. K. H. Shimizu, G. D. Enright, C. I. Ratcliffe, J. A. Ripmeester,
D. D. M. Wayner, unpublished results.
[20] Compound 1 has twice been observed as a synthesis by-product: a) S. J.
Loeb, G. K. H. Shimizu, Synlett 1992, 823 ± 825; b) F. Vögtle, B.
Kleiser, Angew. Chem. Suppl. 1982, 1392 ± 1397.
[21] Elemental analyses were performed on single crystals of both 2 and 3
as expeditiously as possible. However, some loss of the nitrile solvent
was unavoidable resulting in the slightly low observed C, H values.
Keywords: coordination modes ´ layered compounds ´ self-
assembly ´ silver ´ S ligands
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1
0.71073 Š), m(MoKa) ˆ 1.04 mm
.
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