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Molecular Machines Molecular Structure of [(p-Tol3P)10Au13Ag12Cl8](PF7)Чa Cluster with a Biicosahedral Rotorlike Metal Core and an Unusual Arrangement of Bridging Ligands.

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Molecular Machines: Molecular Structure of
[ (p-Tol,P), oAu,,Ag, ,CI,](PF,)--a
Cluster with
a Biicosahedral Rotorlike Metal Core and an
Unusual Arrangement of Bridging Ligands **
(interpenetrating) bicapped pentagonal prisms (as in the ses
configuration), instead of (interpenetrating) icosahedra (as
in the sss conformation).[8s9*loci Clusters based on other
building blocks and different modes of construction can be
found in the literat~re.[’~-’~I
By Boon K . Teo* and Hong Zhang
Further miniaturization poses a major challenge in the
development of microelectronics.[’] Progress must rely on
the fabrication of components on the nanometer scale (“nanotechnology”, molecular machines, molecular computers,
etc.[’. 31). Two approaches for building such devices can be
The PFT-salt of cluster cation 3 was prepared by the redistinguished: the “scaling down” of state-of-the-art miduction of a mixture of (p-Tol),P, HAuCI, and AgNO,,
croelectronics technology (“top-down’’ method)[‘] and the
(Au:Ag = 1 : 1 ) with NaBH, in absolute ethanol, followed by
construction of molecular or supramolecular assemblies
the addition of excess NH,PF, in ethanol. The dark red
with specific functions and properties from smaller building
precipitate was filtered and purified by recrystallization from
blocks (“bottom-up’’ m e t h ~ d ) . [ ~ -These
~I
organized and
ethanol/hexane. Crystals suitable for X-ray diffraction study
functional supramolecules and -c~mplexes,[”~
constructed eiwere obtained by evaporation of an ethanol/hexane solution
ther by direct synthesis or by self-assembly, are prototypes of
of the recrystallized product.[’’, 21]
more sophisticated molecular devices.[51In this regard, the
In Figure l a and b the metal core and the
“cluster of clusters” concept proposed by usr8- ‘‘I for build[P,,,Au,,Ag,,CI,] framework of 3 are depicted. The cluster
ing large cluster aggregates from smaller clusters is also usehas ten tri(p-toly1)phosphine and eight chloride ligands. The
ful in the design and synthesis of “supraclusters” which may
ten phosphine ligands coordinate to ten peripheral Au atoms
ultimately serve as models for molecular machines of welldefined structures. The driving force for such spontaneous
cluster assemblage is the “self-organization self-similarity”
a)
Ael I
principle (fractal) often observed in nature.“. ‘‘I”I In this
paper, we report a new 25-metal-atom cluster which, along
with two recently reported clusters of the series, can be visualized as a molecular rotor with two metal icosahedra sharing
a vertex. Hence, this supracluster assemblage may also be
termed a “biicosahedral rotor”. The ellipsoidal (prolate)
metal core measures approximately 1 x 1 x 1.5 nm3, suggesting that this series of clusters can be envisaged as a prototype
for nanomechanical rotary devices.
Our recent work in the synthesis and structural characterization of a series of phosphine Au-Ag halide clusters gave
rise to a new sequence of cluster structures which can be
described as vertex-sharing polyicosahedra.[8-’01 In these
structures, the basic building block is an icosahedron composed of 13 metal atoms (Au,Ag,), and the design rule
(mode of construction) is vertex-sharing.“, 91 The first member of this series is the cationic 25-metal-atom cluster 1 (isoAgl2
lated as the PF; salt), which can be considered as two Au-centered Au,Ag, icosahedra sharing one Au atom (nuclearity =
C)
c13
2 x 13 - 1 = 25).[’0b1The adjacent metal pentagons in 1 are
@?
C14
staggered (s) with respect to one another, giving rise to three
icosahedral (or bicapped pentagonal antiprismatic) cages
(sss conformation). More recently, the SbF; salt of the cluster cation 2 was shown to have a novel staggered/eclipsed/
staggered (ses) conformation.[’0c1Here, the two middle Ags
c12
pentagons are eclipsed (e), resulting in a central bicapped
US
pentagonal prismatic cage. The title cluster cation [(pTOI,P),~AU,,A~,,C~,]+
(3), has a new conformation nearly
halfway between those observed in 1 and 2, and an unusual
arrangement of the bridging ligands which is distinct from
c11
C16
that of 1 or 2. Larger clusters in this series include the 37Fig. 1 . Crystal structure of 3 (PF, salt). a) Biicosahedral framework of the
metal-atom dication [(p-Tol,P),,Au,,Ag,,Br,
and
Au,,Ag,, core; b) metal-ligand framework (P,,Au,,Ag,,CI,); c) projection of
the 38-metal atom cluster [(p-To13P),,Au,,Ag,oCl~4]~’of~~1
the two Ag, pentagons onto the approximate plane of the six doubly bridging
and the 46-metal atom cluster [ (Ph3P),,Au,4Ag22C1,,].[’oh1 chloride ligands. The cluster has an idealized C, axis passing through A g l l ,
Aull,Au13,Au12,andAg12.Importantdistances[~]:(n= l - 5 , m = 6 - 1 0 ) :
In these latter structures, the icosahedral units are linked by
+
[*] Prof. B. K. Teo, H . Zhang
Department of Chemistry, University of Illinois at Chicago
Chicago. IL 60680 (USA)
[**I
This work was supported by a grant from the U S . National Science Foundation (CHE 9115278). We would also like to thank Prof. P. Pyykko,
Helsinki, for pointing out the importance of relativistic effects.
Angew. Chm. Ini Ed. Engl. 31 11992) N o . 4
0 VCH
Aull-Au(n) 2.718(av), Aull-Ag(n) 2.804(av), A u l l - A g l l 2.86(1), Aull-Aul3
2.791(9), AulZ-An(m) 2.719(av), Aul2-Ag(m) 2.874(av), Au12-Ag12 2.69(1),
Au12-Au13 2.847(9), Aul3-Ag(n) 2.91(av), Aul3-Ag(m) 2.86(av), Au-P
2.32(av), Agl 1-C111 2.33(5), Ag12-Cl12, 2.36(5), doubly bridging chloride ligands C12-CI5, CI-Ag 2.47(av), triply bridging chloride ligands, CII-Agl 2.62(6),
CII-Ag2 2.93(5), CII-Ag6 2.51(5), C16-Agl 2.48(4), C16-Ag6 3.07(5), C16-AglO
2.78(5). The six chloride ligands form a distorted hexagon with “nonbonding”
. C15
(crystallographically independent) distances of C16. . . Cl1 3.66,
3.78, CI1 . . . C12 4.01, C12...C13 4.93, C13’.“J4 5.03, C14...C15 4.31.
Verlagsgesell.whafi mbH. W-6940 Wernheim, 1992
0570-0833/92/0404-0445 3 3.50+.25j0
445
in a radial fashion. As for the eight chloride ligands, two are
terminal (Clll and CllZ), while the remaining six are bridging (Cll-C16) (Fig. 1 c).
The most interesting feature of the structure of 3 is that the
metal framework has neither an ses nor an sss conformation
(cf. Fig. 1c). In fact, it is nearly halfway between these two
extremes. As a result, the metal framework has an idealized
D, symmetry (instead of D,,for sss as in 1, or D,,for ses as
in 2). The projection of the four pentagons of metal atoms
(two outer Au, rings and two inner Ag, rings) onto the plane
of the bridging ligands gives rise to a ring of 20 metal atoms
more or less evenly distributed around the circle (Fig. 2). It
is conceivable that in solution, the two metal icosahedra are
relatively free to rotate about the shared vertex (Aul3),[*’]
and that the observed solid-state structure is a snapshot of
one of many energy minima.
Fig. 2. The projection of the four pentagons of metal atoms in 3 (see Fig. 1 a)
onto the plane of the bridging ligands.
The arrangement of the six bridging chloride ligands
(Cll -C16) which connect the two Ag, pentagons (Agl -Ag5
and Ag6-AglO) is also rather unusual. Since pentagonal symmetry is incommensurate with the hexagonal net, we expect
significant distortions in the arrangement of the bridging
ligands. Indeed, as shown in Figure 1 c the six bridging ligands can be categorized into two groups: four doubly bridging (C12-Cl5) and two triply bridging (Cll, C16) ligands. The
coordination of the doubly bridging ligands is more or less
symmetrical whereas that of the triply bridging ligands is highly asymmetrical. For example, C11 has one long (2.93(5) A)
and two short (2.51(5) and 2.62(6) A) C1-Ag distances. The
opposite is true for C16, which has one short (2.48(4) A) and
two long (2.78(5) and 3.07(5) A) CI-Ag distances.
There are several empirical rules for the Au-Ag supraclusters that we have structurally characterized : 1. The interstitial or “bulk” atoms in the icosahedral cages are gold
atoms; 2. The shared vertices (bicapped pentagonal prismatic cages) are also gold atoms; 3. The phosphine ligands are
attached to surface gold atoms; 4. The halide ligands are
bonded to silver atoms. These observations can be explained
by the fact that gold is substantially more electronegative
than silver (2.54 for Au, 1.93 for Ag). This disparity in electronegativity is related to relativistic effects.r231The more
electronegative gold atoms tend to prefer sites of high electron density, including the centers of the icosahedra or the
shared vertices (which are centers of the bicapped pentagonal prisms). The more electron-donating phosphine ligands
prefer more electronegative Au atoms, whereas the more
electron-withdrawing halide ligands prefer the more electropositive Ag atoms.
This metal framework with a conformation halfway between ses and sss provides strong evidence for the concept of
a “cluster of clusters” as applied to this series of vertexsharing icosahedral Au-Ag supraclusters. Further structural
446
0 VCH
Verlagsgeseilschaft mhH, W-6940 Weinheim. 1992
evidence comes from the separations between the pentagons :
the intraicosahedra Au(1-SFAg(1-5) and Au(6-10)-Ag(610) interplanar distances of 2.40 A and 2.52 8, are 0.5 A
shorter than the intericosahedra (inner) Ag(1- 5)-Ag(6- 10)
interplanar distance of 2.91 A. Moreover, the average intraicosahedral metal-metal distances of 2.772 A (Aul l-centered) and of 2.792 A (Aul2-centered) in 3 are significantly
shorter (ca. 0.1 A) than the average intericosahedral distances of 2.872 A (Aul3-centered). These observations suggest that intraicosahedral bondings are stronger than
intericosahedral bonding, thereby reinforcing the cluster of
clusters concept in which the individual icosahedron serves
as a building block.
Received: October 2, 1991 [Z 4951 IE]
German version: Angew. Chem. 1992, 104,447
111 Physics and Technology of Submicron Structures (Eds.: H. Heinrich, G.
Bauer, F. Kuchar), Springer, Berlin, 1988.
121 a) H. I. Smith, H. G. Craighead, Phys. Todav 1990, 43(2), 24; b) J. N.
Randall, M. A. Reed, G. A. Frazier, J. Yac. Sci. Technol. B 1989, 7, 1398.
[3l a) G. D. Stucky, N.Herron, Y Wang, M. Eddy, D. Cox, K. Moller, T.
Bein, J. Am. Chem. SOC.1989, 111, 530; b) G . D. Stucky, J. E. MacDougall, H. Eckert, N. Herron, Y. Wang, K. Moller. T. Bein, &id. 1989, Iff,
8006.
[41 a) J.-M. Lehn, Angew. Chem. 1990,102,1347; Angew. Chem. Int. Ed. Engl.
1990,29,1304; b) Pure Appl. Chem. 1978,50,871; c) Angetv. Chem. 1988,
100, 91; Angew. Chem. Int. Ed. Engl. 1988, 27, 89.
[51 a) F. H. Kohnke, J. P. Mathias, J. F. Stoddart Angetv. Chem. Adv. Mater.
1989, 10f.1129; Angew. Chem. In!. Ed. Engl. Adv. Muter. 1989,28, 1103;
b)P. L. Anelli, N. Spencer, J. F. Stoddart J. Am. Chem. Soc. 1991, 113,
5131; R. R. Ashton, C. L. Brown, E. J. T. Crystal, K. P. Parry, M. Pietraskiewicz, N. Spencer, J. F. Stoddart, Angew. Chem. 1991, 102, 1058;
Angen. Chem. l n t . Ed. Engl. 1991, 30, 1042.
161 J. S. Lindsey, New J. Chem. 1991, 15, 153.
171 M. P. Byrn, C. J. Curtis, I. Goldberg, Y Hsiou. S. I. Khan, P. A. Sawin.
S. K. Tendick, C. E. Strouse, J. Am. Chem. Soc. 1991, 113, 6549.
[XI B. K. Teo, H. Zhang, Proc. Narl. Acad. Sci. USA 1991, 88. 5067, and
references cited therein.
191 Reviews: a) B. K. Teo, H. Zhang, J. Cluster Sci.1990, I, 223; b) ibid. 1990,
I, 155; c) Polyhedron. 1990, 9, 1985; d) B. K. Teo, ibid. 1988, 7, 2317.
[lo] a) B. K. Teo, K. Keating, 1 Am. Chem. Soc. 1984,106,2224;b) B. K. Teo,
H. Zhang, X. Shi, Inorg. Chem. 1990, 29, 2083: c) B. K. Teo, X. Shi, H.
Zhang, J. Am. Chem. Soc. 1991, f 13,4329; d) B. K. Teo, H. Zhang, Inorg.
Chrm. 1991, 30, 3115; e)B. K. Teo, M. Hong, H. Zhang, D. Huang,
Angew. Chem. 1987,99,943; Angew. Chem. Inr. Ed. Engl. 1987,26,897;
f) B. K. Teo, M. Hong, H. Zhang, D. Huang, X. Shi .
I
Chem. Soi. Chem.
Commun. 1988, 204; g) B. K. Teo, H. Zhang, X. Shi J. Am. Chem. SOC.
1990,112,8552;h) B. K. Teo, H. Zhang Inorg. Chim. Acra 1988,144,173;
i) Inorg. Chem. 1988, 27, 414.
1111 B. B. Mandelbrot The Fractal Geomerry qf Nature, Freeman, New York,
1983.
1121 H. 0. Peitgen, P. Richter, The Beuuty of Fractals, Springer, Heidelberg,
1986.
I131 A. J. Whoolery, L. F. Dahl. J. Am. Chem. SOC.
1991, 13, 6683.
1141 J.-E You, B. S. Snyder. R. H. Holm J. Am. Chem. SOC.1988, 110,6589.
[15] a) R. D. Adams. 2. Dawoodi, D. F, Forest, B. E. Segmuller, J. Am. Chem.
Soc. 1983,105.831; b) P. D. Williams, M. D. Curtis, D. N. Duffey, W. M.
Butler, Organornetalhcs 1983,2,165: c) B. F. G. Johnson, Philos. i7ans. R.
SOC.London, Ser. A 1982, 308, 5 .
(161 a) C. M. T. Hayward, J. R. Shapley, M. R. Churchill, C. Bueno, A. L.
Rheingold, J. Am. Chem. Soc. 1982, 104, 7347; b) S. Martinengo, A. Fumagalli, R. Bonfichi, G. Ciani, A. Sironi J. Chem. SOC.,Chem. Commun.
1982, 825; c) V. G. Albano, P. L. Bellon J. Organornet. Chem. 1969, 19,
405; d) R. D. Pergola, F. Demartin, L. Garlascbelli, M. Manassero, S.
Martinengo, M. Sansoni, Inorg. Chem. 1987,26,3487;e) A. Fumagalli, S.
Martinengo, G. Ciani, A. Sironi, J. Chem. Soc.; Chrm. Commun. 1983,
453.
[17] S. R. Drake, K. Henrick, B. F. G. Johnson, 3. Lewis, M. McPartlin, J.
Morris J. Chem. SOC.,Chem. Commun 1986,928.
[18] a) E. G . Mednikov, N. K. Eremenko, J. Orgunomef. Chem. 1986, C35C37, 301 ; b) E. G. Mednikov, N. K. Eremenko. Yu. L. Slovokhotov,
Yu. T. Struchkov, J. Mendeleev Chem. SOC. (Russian), cited in [4a];
c) E. G. Mednikov, N. K. Eremenko. Yu. L. Slovokhotov, Y u . T. Struchkov, S. P. Gubin, J. Organomet. Chem. 1983, 258, 247.
1191 For reviews on metal clusters see, for example, a) K. Kharas, L. Dahl Adv.
Chem. Phys. 1988, 70, 1 ; h) P. Chini GQZ. Chim. rial. 1979.109, 225: c) J.
Organomet. Chem. 1980,200, 37; d) P. Chini, G. Longoni, V. G. Albano
OS70-~833192IO404-0446
$3.50+ ,2510
Angetv. Chem. In!. Ed. Engl. 31 (1992) No. 4
Adu. Organomel. Chem. 1976. 14, 285; e) Transition Metal Clusters (Ed.:
B . F. G .Johnson), Wiley-Interscience. Chichester, England, 1980;f) B. F.G.
Johnson. R. E. Benfield Top. Inorg. Organomel. Stereocheni. (Ed.: G.
Geoffroy), 1981, g) D. Fenske, J. Ohmer. J. Hachgenei, K . Merzweiler
Angew. Chem. 1988, 100. 1300; Angew. Chem. Int. Ed. Engl. 1988, 27,
1277; h) G. Schmid Siruct. Bonding (Berlin) 1985, 62, 51.
[20] Single crystal X-ray diffraction data were collected with an Enraf-Nonius
diffractometer (Mo,, radiation). [@-Tol,P),,Au, ,Ag,,CI,](PF,)~ nEtOH:
monoclinic P2,, a = 20.410(1), b = 20.767(3), c = 28.182(3) A, y =
91.71(4): V =11939.9(4)A3, Z = 2 . The tolyl groups and the PF; anion
were refined as rigid bodies (see [log] for details). Anisotropic (heavy
atoms)-isotropic (carbon atoms) refinement gave R , = 0.112 for 6706 independent reflections (20 < 46") with I > 3 6.
[21] Further details of the crystal structure are available on request from the
Fachinfonnationszentrum Karlsruhe, Gesellschaft fur wissenschaftlichtechnische Information mbH in D-W-7514 Eggenstein-Leopoldshafen 2,
on quoting the following number CSD-56021. the names of the authors,
and the journal citation.
[22] It is interesting to note that the isotropic thermal parameters of all the gold
atoms (Aul -Au12) fall within the narrow range of B = 2-3 A', with the
exception of the shared vertex (Au13) which has a B value of 6.6(2) A'.
This latter value may signify a greater thermal motion and/or site disorder
(split peaks) of the shared vertex. For comparation, the B values of the
silver atoms fall within the range of 3-5 A'.
[23] a) P. Pyykko. J. Desclaux. Acc. Chem. Rrs. 1979, 12, 276; b) K . S . Pitzer
ihid. 1979, 12, 271.
products is an ester which has the composition [HVO,(OR)]and a formation constant of K = 0.13(2) M - ' . [ ~ ]
In nonaqueous systems in which the competitive condensation reaction of monovanadate to form oligovanadates
does not take place, the formation tendency for vanadate
esters is clearly more pronounced than that of the analogous
phosphate esters. The ester 1 formed from VOCI, and cycluC,H,OH['o] shows one signal in the " V NMR spectrum at
concentrations over 1 0 0 m (6
~ = - 616); at lower concentra-
tions a second signal appears (6 = - 6231, which increases in
intensity as the total concentration decreases (Fig. 1). We
Tris(cyclopentanolato)oxovanadium(v) :
a Model for the Transition State of Enzymatic
Phosphoester Cleavage**
By Frank Hillerns, Falk Olbrich, Ulrich Behrens,
and Dieter Rehder*
-6
Dedicated to Professor Reinhard Nast
on the occasion of his 80th birthday
(A1koxo)oxovanadium complexes ("vanadate esters") have
come under general scrutiny lately, on one hand because of
their potential in generating thin metal-oxide and -carbide
layers by gas-phase deposition,"' and on the other because
of the biological importance of vanadium ester compounds.
The ester-like bond in vanadate(v) ( H Z V 0 4 )is discussed, for
example, in connection with the vanadate-dependent haloperoxidases from brown marine algaef2]and with the interaction of vanadate with phosphate-metabolizing enzymes
and their
Some of these enzymes are inhibited
by vanadium-the inhibition of ribonuclease A[41and T, ,[51
for example, have been well studied. The cleavage (or formation) of the phosphoester bond in RNA proceeds via a pentavalent, trigonal-bipyramidal intermediate.@]Enzymes take
up vanadate esters as substrate in competition to phosphate
esters,13]and their function is thereby blocked. Such vanadate-enzyme complexes, which are stable analogues of the
transition state of the phosphorylation reaction, were detected in systematic "V NMR investigations,['' but could not be
isolated. We have thus conducted model studies with cyclopentanol"] in order to characterize them better. We show
that vanadate esters, unlike phosphate esters, can be pentacoordinate.
In aqueous medium vanadate(v) forms esters with cyclopentanol (ROH) that can be identified by "V NMR spectroscopy. At physiological pH, the major component of the
[*] Prof. Dr. D. Rehder, Dip1.-Chem. F. Hillerns, Dipl.-Chem. F, Olbrich,
Prof. Dr. U. Behrens
Institut fur Anorganische und Angewandte Chemie der Universitat
Martin-Luther-King-Platz 6, D-W-2000 Hamburg 13 (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschdft and
the Fonds der Chemischen Industrie.
Angew. Chem. Int. Ed. Engl. 31 (1992) No. 4
0 VCH
Fig. 1. ''V NMR spectra (94.7 MHz) of [VO(cyclo-C,H,O),] (1) in CDCI,.
showing the position of the equilibrium described in Equation (a) for four
concentrations c. The signal at high magnetic field (6(5'V = -623, hatched)
corresponds to the monomer, that at 6 = -616 to the dimer. A 2D EXSY
(exchange spectroscopy) experiment shows that the chemical exchange formulated in Equation (a) actually takes place.
have already observed concentration and temperature dependence of 6(5'V) for other vanadyl esters and concluded
that at least two species participate in an exchange equilibrium [Eq. (a)].[8b3 When R = cyclo-C,H, the exchange is so
slow even at room temperature that monomer and oligomer
can be detected simultaneously.[' 'I In the concentration
range c of 0.001 to 0 . 0 8 ~for the vanadyl ester 1, n x 2
[Eq. (a)], and the dimerization constant K = [dimer]/
[monomerI2 = 870(50) M-'. An X-ray structure analysis of
the dimer of 1 showed how the dimerization took place.
[fVO(cycl0-C,H,0),),][~I' comprises two monomeric units
bridged by two alkoxide oxygen atoms (Fig. 2). In each of
these units vanadium is in the center of a distorted trigonal
bipyramid. The 0x0 ligand and the bridging alkoxo oxygen
atom of the adjacent unit form the apexes. The vanadium
atom lies 35 pm above the plane spanned by the three oxygen
atoms of the alkoxo ligands (all-cis configuration). The distance from the V atom to the bridging 0 atom ( 0 2 ) of
183.5(4) pm is distinctly longer than the distances to 0 3 and
0 4 1176.213) and 176.3(6) pm]. Even longer [229.6(3) pm] is
the distance from 0 2 to the symmetry-related VA of the
second monomeric unit of the dimer, which is only a little
shorter than these bond lengths in multinuclear oxo-vanadi-
YerlagsgeseNschaft m b H , W-6940 Weinheim, 1992
0570-0833/92/0404-0447 S 3.50+ .25/0
447
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corel, molecular, bridging, arrangement, ligand, machine, 10au13ag12cl8, rotorlike, structure, clusters, biicosahedral, metali, tol3p, unusual, pf7
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