coordinated and free pyridine rings of Py[6], respectively,
while a singlet peak at 8.15 ppm can be ascribed to the phenyl
protons of [1,3,5-(CRC)3-C6H3] (Fig. in the ESIz). In contrast
to the only one set of NMR signals of the neat Py[6]9 at room
temperature arising from its fluxional conformation, these NMR
observations demonstrate a rigid skeleton of Py[6] in 1 upon its
coordination with a well-matched silver cluster aggregate.
A synthetic procedure similar to that of 1 with Py[7] in place
of Py[6] was then applied to yield complex 2. X-ray crystallo-
graphy revealed the formula of 2 as [Ag20.5{1,3,5-(CRC)3-
C6H3}2(Py[7])6(CF3SO3)4](CF3SO3)10.5 (2) (solvent molecules
are not included), which involves two almost identical
[Ag10{1,3,5-(CRC)3-C6H3}(Py[7])3(CF3SO3)2]
ensembles
and a half external triflate-bonded silver atom (Fig. S1, ESIz).
In every ensemble, each acetylide is joined to a Ag3 aggregate,
which is encircled by a different conformational Py[7] through
both Ag–N coordination and silver–aromatic p interactions
similar as in 1 (Fig. S2, ESIz). In contrast to the sharp proton
NMR peaks of 1, the peaks of 2 become broader (Fig. S7,
ESIz), suggesting the existence of multiform conformations
of Py[7] in 2. This can be rationalized by incompatible
coordination between the large Py[7] macrocycle and the small
Ag3 cluster aggregate.
Fig. 1 Crystal structure of [Ag9{1,3,5-(CRC)3-C6H3}(Py[6])3](CF3SO3)6
(1). (a) Coordination environments of the central Ag3 aggregate. Other
groups are omitted for clarity. Symmetry code: A x, y, 112 ꢁ z. Selected
bond lengths and distances (A): C20–C21 1.222(12); C20–Ag1 2.044(8);
C20–Ag2 2.176(5); C21–Ag2 2.321(7); Ag1–N1 2.163(7); Ag2–N5 2.180(5);
Ag2ꢀꢀꢀAg2A 3.370(3). (b) Top view of the trefoil structure in complex 1
with the silver-phenylacetylide aggregate shown in the space-filling model.
(c) Side view and (d) top view of the trefoil structure with two triflate
groups filling in the cavities. Color scheme for atoms: Ag, purple; C, black;
H, gray; O, red; N, blue; F, cyan; S, yellow.
Along with the size expansion from Py[7] to Py[8], a metal
cluster-pillared triangular prism architecture that includes two
[1,3,5-(CRC)3-Ph] trianions is found in complex 3. X-ray
crystallographic analysis explored the formula of complex 3 as
[Ag15{1,3,5-(CRC)3-C6H3}2(Py[8])3(CF3SO3)3](CF3SO3)6 (solvent
%
molecules are not included in the formula), which has a R3c space
group. The asymmetrical unit of 3 consists of a {Ag5CPy[8]}
adduct (C represents encirclement), two one-third segments of
[1,3,5-(CRC)3-Ph] and three triflate groups at variable disordered
positions. Each acetylide moiety of the [1,3,5-(CRC)3-Ph]
trianion bonds to a Ag3 aggregate in a m3-Z1,Z1,Z1 or
m3-Z1,Z2,Z2 mode. A silver atom-sharing between two Ag3
aggregates leads to the formation of a five-membered silver
chain (Fig. 2a). Such a chain-like Ag5 aggregate is coordinated
by a triflate group and four alternate pyridyl nitrogen atoms of
a Py[8] ligand. Silver–aromatic p interactions are observed as
well between this Ag5 aggregate and Py[8]. In this way, a
coordination self-assembled triangular prism with the formula
of [Ag15{1,3,5-(CRC)3-C6H3}2(Py[8])3(CF3SO3)3]6+ is finally
achieved, wherein two [1,3,5-(CRC)3-Ph] groups and three
Py[8]-protected Ag5 aggregates act as the panels and pillars
of the triangular prism, respectively (Fig. 2b). No significant
p–p stacking is observed between the two completely
parallel phenyl rings of the [1,3,5-(CRC)3-Ph] panels. The
coordination of three triflate groups at the bottom of the prism
engenders the nether opening 1.7 A wider than the upper one.
A cavity at the top of the prism built by three methyl
groups and three pyridine rings also accommodates a triflate
anion in a similar way as in 1 (Fig. 2c). Meanwhile, the
three Py[8] ligands pinch a triflate anion by three-fold
C6–H6Cꢀ ꢀ ꢀO5 interactions with the trifluoromethane group
of this triflate protruding into the nether cavity. The proton
NMR of complex 3 showed a series of sharp doublet and
triplet peaks in the range of 6.09–8.16 ppm corresponding
to the uneven pyridine rings of the fixed Py[8] ligand in 3
(Fig. S8, ESIz).
[1,3,5-(CRC)3-Ph] trianion through the encirclement of three
Py[6] ligands was successfully solved by X-ray crystallography
(Fig. 1). Complex 1 crystallizes in the hexagonal space group
of P63/m. A C3 axis perpendicularly passes through the center
of the benzene ring of 1,3,5-(CRC)3-Ph, which is located on a
mirror plane. The asymmetrical unit of 1 consists of one and
a half independent silver atoms, half Py[6] ligand, one-sixth of
a [1,3,5-(CRC)3-Ph]n trianion, and a triflate group at several
disordered positions. The formula of 1 can be expressed as
[Ag9{1,3,5-(CRC)3-C6H3}(Py[6])3](CF3SO3)6 (solvent mole-
cules are not included). As shown in Fig. 1a, the acetylide
moiety C20RC21 is bonded to three silver atoms (Ag1, Ag2
and Ag2A) by both s- and p-bonding in a m3-Z1,Z2,Z2 mode.
This trigonal silver aggregate is located at the center of a Py[6]
macrocycle and is coordinated by three alternate pyridyl
nitrogen atoms (N1, N5, and N5A). The remaining three
uncoordinated pyridine rings laterally encompass the Ag3
aggregate by six-fold Z2 silver–aromatic p interactions which
are in the range of 2.77–2.96 A, being well below the sum of
the van der Waals radii of the silver atom (1.72 A) and the
carbon atom (1.70 A).12 In this way, the resulting [1,3,5-
(Ag3CRC)3-Ph]6+ ionic species is encircled by three Py[6]
macrocycles to form a trefoil structure as shown in Fig. 1b. It
is noticeable that two cavities are formed in such a trefoil
structure, each of which is occupied by a triflate anion (Fig. 1c
and d). This finding spotlights a potential application of this
kind of supramolecules in anion recognition.
The 1H NMR spectrum of 1 exhibited two sets of resonances
at 8.08/7.62 and 7.12/6.65 ppm for the g- and b-protons of
c
10878 Chem. Commun., 2012, 48, 10877–10879
This journal is The Royal Society of Chemistry 2012
He, Xin
