Assembly of a tri-silver metallo-capsule incorporating a tripodal tris-pyridyl ligand

Article abstract of DOI:10.1039/b505365j

A trinuclear metallo-capsule has been assembled from a new tripodal pyridyl ligand and three silver(I) ions; the X-ray structure shows the presence of a Ag-Ag interaction in the solid state giving rise to a non-symmetric capsule arrangement while NMR evid

Full text of DOI:10.1039/b505365j

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C O M M U N I C A T I O N
Assembly of a tri-silver metallo-capsule incorporating a tripodal
tris-pyridyl ligand
David J. Bray,a Li-Ling Liao,b Bianca Antonioli,c Karsten Gloe,c Leonard F. Lindoy,*a
John C. McMurtrie,a Gang Wei*d and Xiao-Yi Zhang*b
a Centre for Heavy Metals Research, School of Chemistry, University of Sydney, NSW 2006,
Australia. E-mail: Lindoy@chem.usyd.edu.au; Fax: +61 2 9351 3329; Tel: +61 2 9351 4400
b School of Physics and Chemistry, Guizhou Normal University, Guiyang, Guizhou 550001,
P. R. China
c Institut fu¨r Anorganische Chemie der TU Dresden, D-01062 Dresden, Germany
d CSIRO, Industrial Physics, PO Box 218, Lindfield, NSW 2070, Australia
Received 15th April 2005, Accepted 3rd May 2005
First published as an Advance Article on the web 13th May 2005
A trinuclear metallo-capsule has been assembled from a
new tripodal pyridyl ligand and three silver(I) ions; the X-
ray structure shows the presence of a Ag–Ag interaction
in the solid state giving rise to a non-symmetric capsule ar-
rangement while NMR evidence indicates that the structure
in solution is symmetrical.
A frequent objective of metallo-supramolecular chemistry over
the past few decades has been the design of ligands which
can be directed, with the aid of a suitable metal ion, to form
pre-determined architectures.1 Prior research in this area has
focussed on the use of a range of metal ions largely displaying
four or six coordination geometries. In contrast, the use of two
or three coordinate metal ions as structural components has
been less exploited.2
Fig. 1 (a) Predicted mass spectral distribution for [(C21H24N3S3)2Ag3-
(NO3)2]+ (b) Observed isotopic distribution for this ion in the ESI mass
spectrum of 2.
Fig. 2 The molecular structure of [Ag3(1)2(NO3)2](NO3). Two of the
We now report the synthesis of a molecular capsule which
assembles from two flexible, potentially tripodal pyridyl lig-
ands of type 1 and three silver ions to yield a colourless
complex of stoichiometry Ag3L2(NO3)3 (L = 1). Ligand 1 was
synthesised in 90% yield via a nucleophilic reaction between
4-mercaptopyridine and 1,3,5-tris(bromomethyl)benzene† that
was based on a literature synthesis for related compounds.3
Addition of a methanol/acetonitrile solution of silver nitrate to a
solution of 1 in methanol resulted in immediate precipitation of a
white solid whose microanalysis showed it to be of stoichiometry
Ag3L2(NO3)3.‡ The positive ion mass spectrum (HR-ESI) of this
complex yielded a peak corresponding to [Ag3L3(NO3)2]+ with
a 107Ag, 109Ag isotopic pattern that matched that calculated for
this ion (Fig. 1); other peaks corresponding to [Ag2L2(NO3)]+,
[AgL2]+ and [AgL]+ were also present. The 1H NMR spectrum
of the product indicated that it had a highly symmetric structure
in CD3CN, indicative of the presence of equivalent silver sites in
this solvent.
˚
silver atoms are involved in a direct contact (distance 3.1621(4) A). These
two silver atoms are connected to the third via bridging nitrato oxygen
atoms. The third nitrate counter ion does not coordinate to the metal
complex.
ions are equivalent and interact via a Ag–Ag contact at 3.1621(4)
˚
A; the latter separation is considerably less than the van der
4
˚
Waals diameter for silver (3.44 A). Related Ag–Ag contacts in
other systems have now been well documented.5 In the present
structure, the two interacting silver centres are connected to the
third centre by means of bridging nitrato groups
Inspection of molecular (CPK) models suggested that the
binding of silver to the pyridyl rings of 1 rather than to its softer
sulfur groups appears largely as a consequence of steric factors
inhibiting the formation of a reasonable coordination geometry
that involves the participation of all three sulfur donors of each
ligand. In any case, a number of pyridyl-containing ligands have
been documented previously7,8 to exhibit strong affinities for
silver(I).
The X-ray structure of 2 (Fig. 2), recrystallised from ace-
tonitrile, shows that each of the silver ions acts as a bridge
between pairs of pyridyl groups on different ligands to produce
the capsule-like structure illustrated in Fig. 2.§ Two of the silver
In an extension of the above study, competitive mixed metal,
bulk membrane transport experiments (water/chloroform/
water) were also undertaken using 1 as the ionophore at
2 0 8 2
D a l t o n T r a n s . , 2 0 0 5 , 2 0 8 2 – 2 0 8 3
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
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10−3 mol dm−3 in the chloroform phase. Details of the experimen-
tal arrangement and conditions employed have been described
in more detail elsewhere.6 The aqueous source phase contained
an equimolar mixture of cobalt(II), nickel(II), copper(II), zinc(II),
cadmium(II), silver(I) and lead(II) nitrate (each at 10−2 mol dm−3).
The source and receiving phases were buffered at pH 4.9 and
3.0, respectively, and the metal concentration in the aqueous
receiving phase was determined on termination of each experi-
ment after 24 h. Under the conditions employed, clear transport
selectivity for silver(I) occurred. Namely, silver was transported
at a rate (J) of 178 × 10−7 mol per 24 h while no transport of any
of the other six metals present in the source phase was observed
within the detection limits of the experiments.¶
positions and refined using a riding model. The refinement residuals
are defined as R1 = RꢀFo| − |Fcꢀ/R|Fo| for Fo > 2r(Fo) and wR2 =
2
1/2
{R[w(Fo − Fc2)2]/R[w(Fc2)2]} where w = 1/[r2(Fo2) + (0.0362P)2 +
2.2743P], P = (Fo + 2Fc2)/3. Crystal data: [Ag3(1)2(NO3)2]NO3;
2
Formula C48H42Ag3N9O9S6, M = 1404.88, monoclinic, space group
˚
˚
˚
P21/n (#14), ◦a = 14.4759(14) A, b = 16.4153(16) A, c = 22.157(2) A,
b = 90.879(2) , V = 5264.5(9) A , Dc = 1.773 g cm−3, Z = 4, crystal size
3
˚
0.28 × 0.23 × 0.17 mm, colourless, habit columnar, temperature 150(2)
K, k(Mo-Ka) = 0.71073, l(Mo-Ka) 1.407 mm−1, T(Empirical)min,max
=
0.713, 0.787, 2hmax = 56.62, hkl range −18 to 18, −20 to 21, −29 to
28, N = 51185, Nind = 12583 (Rmerge = 0.0461), Nobs = 9153 (I >
2r(I)), Nvar = 676, residuals R1(F, 2r) = 0.0364, wR2(F2, all) = 0.0822,
GoF(all) = 1.011, Dqmin,max = −0.516, 1.024 e A−3. CCDC reference
˚
number 265029. See http://www.rsc.org/suppdata/dt/b5/b505365j/
for crystallographic data in CIF or other electronic format.
¶ A J value of 20 × 10−7 mol per 24 h corresponds to the detection limit
for the transport runs and any apparently smaller values were treated as
zero.
In conclusion, the interaction of silver(I) with the tripodal
ligand 1 provides a facile means of generating a new trinuclear
metallo-capsule. While the latter adopts a symmetrical structure
in solution, a less symmetrical arrangement incorporating a AgI–
AgI interaction between two of its three silver centres, is obtained
in the crystalline state.
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Speed and R. M. Town, J. Chem. Soc., Dalton Trans., 2001, 3641;
R.-F. Song, Y.-B. Xie, J.-R. Li and X.-H. Bu, Dalton Trans., 2003,
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Acknowledgements
We thank Guizhou Normal University, the Deutsche
Forschungsgemeinschaft and the Australian Research Council
for financial support.
Notes and references
† Preparation of 1,3,5-tris((pyridin-4-ylthio)methyl)benzene (1).
A
suspension of 4-mercaptopyridine (15 mmol, 1.67 g), 1,3,5-
tris(bromomethyl)benzene9 (5 mmol, 1.78 g) and triethylamine
(20 mmol, 2.0 g) in acetonitrile (30 ml) was stirred at 0 ◦C for 18 h.
The resulting solid was filtered, washed with water, and recrystallised
1
from methanol/water resulting in a pale yellow solid (2.0 g, 90%). H
NMR (CDCl3, 200 MHz, 300 K), d: 4.17 (s, 6H, CH2), 7.07 (d, 6H, py),
7.33 (s, 3H, C6H3), 8.36 (d, 6H, py). 13C NMR (CDCl3, 75 MHz, 300 K),
35.77, 121.35, 128.78, 137.48, 149.02, 149.53. MS (ESI) m/z = 448.1
(M + H)+. Found: C, 64.15; H, 5.02; N, 9.08. C24H21N3S3 requires: C,
64.42; H, 4.73; N, 9.40%.
‡ Preparation of [Ag3L2(NO3)2]NO3 (L = 1). A solution of AgNO3
(0.09 g, 0.5 mmol) in 15 ml methanol/acetonitrile (2 : 1) was added to
a warm solution of 1,3,5-tris((pyridin-4-ylthio)methyl)benzene (0.22 g,
0.5 mmol) in MeOH (10 ml). This resulted in formation of the complex
(0.15 g, 65%) as a white precipitate. Found: C, 41.39; H, 3.04; N,
8.99. C48H42Ag3N9O9S6 requires: C, 41.11; H, 3.02; N, 9.00%. HRMS-
ESI (methanol) found 1342.8721. C48H42Ag3N8O6S6 requires 1342.8700,
[Ag3L2(NO3)2]+. 1H NMR (acetonitrile-d3, 200 MHz, 300 K), d: 4.29 (s,
6H, CH2), 7.19 (d, 6H, py), 7.46 (s, 3H, C6H3), 8.32 (d, 6H, py). This
product was recrystallised from acetonitrile to yield crystals suitable
for X-ray structure analysis. The complex is stable under ambient light
conditions for months, with no noticeable coloration of the bulk sample
when exposed to direct sunlight.
§ Full sphere data were collected at 150(2) K with x scans to approxi-
mately 56◦ 2h using a Bruker SMART 1000 diffractometer employing
graphite-monochromated Mo-Ka radiation generated from a sealed
˚
tube (0.71073 A). Data integration and reduction were undertaken with
SAINT and XPREP10 and subsequent computations were carried out
using the WinGX-3211 graphical user interface. Multi-scan empirical
absorption correction12 was applied to the data using the program
SADABS.13 The structure was solved by direct methods using SIR9714
then refined and extended with SHELXL-97.15 Non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were included in idealised
D a l t o n T r a n s . , 2 0 0 5 , 2 0 8 2 – 2 0 8 3
2 0 8 3