Triangular and tetrahedral array of silver(I) ions by a novel disk-shaped tridentate ligand: Dynamic control of coordination equilibrium of the silver(I) complexes

Article abstract of DOI:10.1021/ja028659n

A disk-shaped tridentate ligand 1 arranges silver(I) ions in a two-dimensional triangular and a three-dimensional tetrahedral fashion in the metal-ligand ratios, 3:2 and 1:1, respectively. The resulting sandwich-type (Ag₃1₂) and tetrahedral (Ag₄1₄) architectures are in a dynamic equilibrium in solution. Copyright

Full text of DOI:10.1021/ja028659n

Published on Web 11/15/2002
Triangular and Tetrahedral Array of Silver(I) Ions by a Novel Disk-Shaped
Tridentate Ligand: Dynamic Control of Coordination Equilibrium of the
Silver(I) Complexes
Shuichi Hiraoka,† Tao Yi,† Motoo Shiro,‡ and Mitsuhiko Shionoya*,†
Department of Chemistry, Graduate School of Science, The UniVersity of Tokyo, Hongo, Bunkyo-ku, Tokyo
113-0033, Japan, and Rigaku Corporation, 3-9-12 Matsubaracho, Akishima, Tokyo 196-8666, Japan
Received September 24, 2002
The multimetal array, controlled by predesigned multidentate
ligands, has received increasing attention with respect not only to
supramolecular architecturing but also to equilibrium control of a
prototypical dynamic library.1,2 This strategy has opened ways to
create novel functions that have not previously been achieved by
the ligands or the metal ions only. With an interest in finding new
multidentate ligand frameworks, we set out to synthesize a novel
disk-shaped tridentate ligand 1,3 which is capable of arranging to
metal centers in a variety of fashions (Figure 1). This ligand was
designed so that three methyl groups could force the neighboring
benzimidazolyl groups out of the plane of the central aromatic ring.
As a consequence, metal ions should be arrayed on the disk plane
with metal-metal distances of several angstroms. Herein we
describe the potential ability of 1 to arrange Ag+ ions reversibly in
a two-dimensional (2-D) triangular and a three-dimensional (3-D)
tetrahedral fashion. The Ag+ complexes of 1 were proven to assume
both sandwich-shaped Ag312 and tetrahedral Ag414 structures which
are in a controllable dynamic equilibrium in solution, depending
on the ratio of 1 to Ag+ ions. The structure of the latter tetrahedral
complex was also confirmed by its single-crystal X-ray analysis.
1
Figure 1. Schematic representation of the reversible conversion between
tetrahedral Ag414 and sandwich-shaped Ag312 complexes.
The solution behavior of 1 with AgOTf was studied by the H
NMR titration experiment. Upon addition of equimolar AgOTf to
1
1 ([AgOTf]/[1] ) 1.0) in a 1:1 CDCl3-CD3OD solution, the H
NMR spectrum of the mixture displayed only one set of new highly
symmetrical signals (Figure 2b). When 0.5 equiv of AgOTf was
further added to the mixture ([AgOTf]/[1] ) 1.5), the other set of
signals completely replaced those before addition with downfield
shift (Figure 2d). Further addition of AgOTf (up to 2 equiv) did
not change the spectrum at all. Electrospray ionization-time-of-
flight (ESI-TOF) mass spectra of these complexes showed the
signals corresponding to Ag414 and Ag312 complexes when
[AgOTf]:[1] ) 1:1 and 3:2, respectively.4 The ESI mass spectrum
of a mixture of [AgOTf]:[1] ) 1:1 contains peaks for multiply
charged cationic species missing two or three triflate counteranions.
The two main peaks at m/z 1302.2 and 818.4 are assignable to the
cationic species, [Ag414‚(OTf)2]2+ and [Ag414‚(OTf)]3+, respec-
tively, verifying the presence of Ag414 complex in solution. In
contrast, the ESI mass spectrum of a mixture of [AgOTf]:[1] )
3:2 displayed only three main peaks at m/z 1559.0, 648.0, and 419.6,
corresponding to the species [Ag312‚(OTf)2]+, [Ag312‚(OTf)]2+, and
[Ag312]3+, respectively. These results indicate the formation of both
Ag312 and Ag414 complexes in solution depending on the ratio
[AgOTf]/[1]. Plot of [Ag414]/([Ag414]+[Ag312]) and [Ag312]/
([Ag414]+[Ag312]) as a function of [AgOTf]/[1] (Figure 3) based
Figure 2. 1H NMR spectra of the mixture of 1 and AgOTf (500 MHz, [1]
) 21.3 mM, CDCl3:CD3OD ) 1:1 (v/v)): (a) [AgOTf] ) 0 mM, (b)
[AgOTf] ) 21.3 mM, (c) [AgOTf] ) 24.0 mM, and (d) [AgOTf] ) 32.0
mM.
on these 1H NMR spectral changes shows that the sum of [Ag414]
and [Ag312] is constant and that these two species are complemen-
tary to each other in the concentration. In addition, the conversion
between the two products is quantitative and completed within a
few minutes.
19F NMR study of 1 suggested the presence of an encapsulated
triflate anion inside the Ag414 complex. 19F NMR spectrum of Ag414
(see Supporting Information) displayed two separate signals as two
singlets, δ 92 ppm (3F) and 85 ppm (9F), whereas in the cases of
Ag312 and AgOTf only one signal (δ 85 ppm) was observed for
each.5 These results suggest that one triflate anion is encapsulated
in the Ag414 complex and that the exchange of the triflate anions
* To whom correspondence should be addressed. E-mail: shionoya@
chem.s.u-tokyo.ac.jp.
† The University of Tokyo.
‡ Rigaku Corporation.
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J. AM. CHEM. SOC. 2002, 124, 14510-14511
10.1021/ja028659n CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
four tridentate ligands 1 resulting in a tetrahedral Ag414 structure
including a methanesulfonate anion in the cavity. Each Ag+ ion
binds to three imidazole nitrogen atoms of different ligands, and
three of the four Ag+ ions, Ag1 to Ag3, display a distorted tetrahedral
geometry having a Ag-O (methanesulfonate) bond, whereas Ag4
assumes a distorted trigonal planar coordination without a Ag-O
bond (Figure 4c). Thus, four Ag+ ions are not equivalent; the Ag-
Ag distances between Ag1, Ag2, and Ag3 are shorter (5.86 Å in
average) than those of Ag4-Agn (n ) 1-3) distances (6.53 Å in
average).9
In summary, a disk-shaped tridentate ligand 1 allows 2-D
triangular and 3-D tetrahedral arrays of Ag+ ions, highly dependent
on the metal-ligand ratio. In addition, the dynamic equilibrium is
accompanied by the encapsulation and the release of a triflate
anion: in other words, the tetrahedral Ag414 complex encapsulates
one triflate or one methanesulfonate anion in the cavity, whereas
the sandwich-type Ag312 complex has no space for guest molecules.
Such a controllable dynamic system will be potentially applicable
to specific anion recognition and transport based on predesigned
molecular motion.
Figure 3. Plot of [Ag414]/([Ag414]+[Ag312]) (filled circles) and [Ag312]/
([Ag414]+[Ag312]) (open circles) versus [AgOTf]/[1].
Acknowledgment. This work was partly supported by a Grant-
in-Aid for Encouragement of Young Scientists (B) to S.H. (No.
14740361) from the Ministry of Education, Culture, Sports, Science,
and Technology of Japan.
Supporting Information Available: Synthetic procedures for 1,
ESI-TOF mass data for Ag414 and Ag312, 19F NMR spectra of Ag414‚
(OTf)4 and Ag312‚(OTf)3 (PDF), and an X-ray crystallographic file for
Ag414‚(OTf)4 (in CIF format). This material is available free of charge
via the Internet at http://pubs.acs.org.
References
(1) For recent articles on metal alignment, see: (a) Kamiyama, A.; Noguchi,
T.; Kajiwara, T.; Ito, T. Inorg. Chem. 2002, 41, 507-512. (b) Baxter, P.
N. W.; Lehn, J-.M.; Baum, G.; Fenske, D. Chem. Eur. J. 2000, 6, 4510-
4517 and references therein. (c) Shimizu, G. K. H.; Enright, G. D.;
Ratcliffe, C. I.; Preston, K. F.; Reid, J. L.; Ripmeester, J. A. Chem.
Commun. 1999, 16, 1485-1486. (d) Mann, K. L. V.; Psillakis, E.; Jeffery,
J. C.; Rees, L. H.; Harden, N. M.; McCleverty, J. A.; Ward, M. D.;
Gatteschi, D.; Totti, F.; Mabbs, F. E.; McInnes, E. J. L.; Riedi, P. C.;
Smith, G. M. J. Chem. Soc., Dalton Trans. 1999, 3, 339-348.
(2) For studies focusing on dynamic combinatorial library, see: (a) Otto, S.;
Furlan, R. L. E.; Sanders, J. K. M. Science 2002, 297, 590-593. (b)
Kubota, Y.; Sakamoto, S.; Yamaguchi, K.; Fujita, M. Proc. Natl. Acad.
Sci. U.S.A. 2002, 99, 4854-4856. (c) Furlan, R. L. E.; Ng, Y. F.; Otto,
S.; Sanders, J. K. M. J. Am. Chem. Soc. 2001, 123, 8876-8877. (d)
Ziegler, M.; Miranda, J. J.; Andersen, U. N.; Johnson, D. W.; Leary, J.
A.; Raymond, K. N. Angew. Chem., Int. Ed. 2001, 40, 733-736. (e) Hof,
F.; Nuckolls, C.; Rebek, J., Jr. J. Am. Chem. Soc. 2000, 122, 4251-4252.
(f) Calama, M. C.; Timmerman, P.; Reinhoudt, D. N. Angew. Chem., Int.
Ed. 2000, 39, 755-758. (g) Hiraoka, S.; Fujita, M. J. Am. Chem. Soc.
1999, 121, 10239-10240.
Figure 4. (a) Molecular structure of Ag414 complex, (b) a view of the
cavity in which one ligand is omitted, and (c) Ag+ ions arranged in a
tetrahedral fashion and a CH3SO3 anion coordinating to three of the four
Ag+ ions (Ag1, Ag2, and Ag3) from the inside.
between the inner and outer cavity is rather slow compared with
the NMR time scale. The significant downfield shift observed with
the encapsulated triflate anion is probably due to desolvation effect
or coordination effect of anion to Ag+ ions.
The formation of Ag414 complex highly depends on the size and
shape of counteranions employed. Upon additon of equimolar
AgPF6 to a solution of 1 in a 1:1 CDCl3-CD3OD, Ag312 complex
and free ligand 1 mainly formed, whereas Ag414 complex was
(3) For preparation of 1, see Supporting Information.
(4) ESI-TOF mass spectra of Ag414 and Ag312 are reported in the Supporting
Information.
(5) The chemical shifts were determined using C6F6 as the internal standard.
(6) The tetrahedral structure was preliminarily obtained for the core Ag414
portion.
1
generated only slightly as was observed in their H NMR spectra.
Further addition of AgPF6 completed the formation of Ag312
complex. These results indicate that the stability of the Ag414
complex is gained by a template triflate anion in the core, leading
to the exclusive formation of the Ag312 complex even when the
ratio of Ag+ to 1 is 1:1.
We first tried the X-ray analysis of crystals obtained from a
mixture of 1 and AgOTf, but due to the disorder of solvent and
anion molecules no sufficient data were obtained.6 The structure
of Ag414 complex was finally determined when AgCH3SO3 was
used in place of AgOTf as the Ag+ source (Figure 4).7,8 The crystal
structure revealed that four Ag+ ions are tetrahedrally arranged by
(7) Crystal data for Ag414‚(CH3SO3)4: C124H120Ag4N24O18S4, M ) 2794.17.
Trigonal, space group R-3, a ) b ) 40.805(3) Å, c ) 60.529(0) Å, R )
â ) 90°, γ ) 120°, V ) 87282.4 Å3, Z ) 24. Final R indicates (I >
2σ(I)): R1 ) 0.0887, wR2 ) 0.1280. GOF on F2 ) 1.118.
(8) The crystal of Ag414‚CH3SO3 was obtained from a mixture of AgCH3-
SO3 and 1 in the ratio of 3:2 where Ag312 complex is predominantly
formed in the solution. This is due to the equilibrium shift from Ag312 to
of Ag414‚CH3SO3 through the crystallization process.
(9) 1H NMR spectrum of Ag414‚CH3SO3 was highly symmetrical at room
-
temperature, and these signals did not show any changes even at low
-
temperature (193 K). These results indicate that the encapsulated CH3SO3
is rotating in the Ag414 capsule above 193 K.
JA028659N
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