Ligand-induced assembly of coordination chains and columns containing high-nuclearity silver(I) ethynide cluster units

Article abstract of DOI:10.1021/om5003733

The multinuclear metal-ligand supramolecular synthon RC₆H ₄C≡C?Ag_n (R = Me, F; n = 3-5) has been employed to construct the two high-nuclearity silver ethynide cluster compounds [(NO ₃)₂@Ag₂₆

Full text of DOI:10.1021/om5003733

Communication
pubs.acs.org/Organometallics
Ligand-Induced Assembly of Coordination Chains and Columns
Containing High-Nuclearity Silver(I) Ethynide Cluster Units
Sam C. K. Hau, Ping-Shing Cheng, and Thomas C. W. Mak*
Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, New
Territories, Hong Kong SAR, People’s Republic of China
S
* Supporting Information
ABSTRACT: The multinuclear metal−ligand supramolecular
synthon RC6H4CC⊃Agn (R = Me, F; n = 3−5) has been
employed to construct the two high-nuclearity silver ethynide
cluster compounds [(NO3)2@Ag26(o-MeC6H4CC)16]-
(NO3)8·5H2O (1) and [NO3@Ag15(o-FC6H4CC)10]-
(NO3)4 (2), which bear the same nitrate central core. The
synthesis of [CrO4@Ag18(iPrCC)12](ClO4)4 (3) and
[ClO4@Ag18(iPrCC)12](ClO4)5 (4) demonstrated the
effect of variation of central anionic core size and charge on
the construction of multidimensional organosilver(I) net-
works. The bulkiness of the peripheral ligands and the
orientation of substituents with respect to the ethynide group proved to be dominant factors that direct the formation of high-
nuclearity clusters and the assembly of coordination networks. To our knowledge, 1 and 2 are the first examples using the nitrate
anion for templated cluster synthesis.
norganic anions are often employed as templates in
coordination network assembly, owing to their relatively
nitrate templates, which is surrounded by 16 peripheral o-
MeC6H4CC¯ groups, and charge balance is provided by eight
exterior nitrate ions (Figure 1a). The Ag···Ag distances lying in
the range of 2.902(3)−3.367(1) Å are comparable to those
observed in a wide variety of silver double and multiple salts
reported by our group and are attributed to argentophilic
interactions.8 The eight independent peripheral ethynide ligands
are each bound to either three or four silver(I) centers in different
ligation modes: μ4-η2,η2,η2,η1, μ4-η2,η2,η1,η1, two μ3-η2,η2,η1, three
μ3-η2,η1,η1, and μ3-η1,η1,η1 (Figure 1b). The four independent
peripheral nitrate ligands are each attached to either two or three
silver(I) atoms in different ligation modes: μ2-η1,η2 and three μ3-
η1,η2. The crystal structure is also consolidated by a μ2-
coordinated aqua ligand (O1W) and two lattice water molecules
(O2W and O3W), each having 0.75 site occupancy (Figure S1a in
the Supporting Information).
Such Ag26 clusters are interconnected through argentophilic
interaction between Ag4 and Ag4Atogenerate an infinite chainof
linked clusters along the a axis (Figure S1b in the Supporting
Information). Bridged by a pair of symmetry-related nitrate
ligands (labeled by N3 and N3B), adjacent silver chains are
interassociated, yieldingatwo-dimensional coordinationlayer. As
illustrated in Figure 2a, the coordination layer is further stabilized
by hydrogen bonds in the range of 2.59(2)−2.94(3) Å involving
nitrate groups, aqua ligands, and lattice water molecules.
Furthermore, adjacent metal−organic layers are interconnected
through C−H···O interactions between methyl substituents of
I
strong and directional bonding interactions with metal centers.1
Facile anionic templates inducing self-assembly is a well-
established route to construct high-nuclearity silver ethynide2
clusters. Various anionic templates, such as halides,3 carbonate,4
chromate,5 and polyoxometalates (POMs)6 have been utilized in
the synthesis of giant silver ethynide clusters, with nuclearities
rangingfrom 14to70. However, thenitrate ionisrarely employed
for such purposes, owing to its dominant capacity for planar
coordination, which plays a major role in directing a two-
dimensional argentophilic assembly. Recently, we synthesized a
new series of silver(I) nitrate complexes containing new ligands,
each composed of a functionalized phenyl nucleus bearing a
terminal ethynyl substituent.7
Hereinwereportthetwohigh-nuclearity silverethynide cluster
compounds [(NO3)2@Ag26(o-MeC6H4CC)16](NO3)8·5H2O
(1) and [NO3@Ag15(o-FC6H4CC)10](NO3)4 (2), assembled
by nitrate templation with the multinuclear supramolecular
synthon RCC⊃Agn (n = 3−5), which has been demonstrated
to be useful in the designed synthesis of discrete molecules as well
as one-, two-, and three-dimensional coordination networks. The
complexes [CrO4@Ag18(iPrCC)12](ClO4)4 (3) and [ClO4@
Ag18(iPrCC)12](ClO4)5 (4) have also been synthesized to
investigate the effect of varying the bulkiness of the peripheral
ligands and the central anionic template on crystal packing.
Details of the synthesis of compounds 1−4 are given in the
Supporting Information.
Single-crystal X-ray analysis revealed that [(NO3)2@Ag26(o-
MeC6H4CC)16](NO3)8·5H2O (1) features a centrosymmetric
peanut-shaped Ag26 face-sharing double cage enclosing two
Received: April 29, 2014
Published: June 26, 2014
© 2014 American Chemical Society
3231
dx.doi.org/10.1021/om5003733 | Organometallics 2014, 33, 3231−3234

Organometallics
Communication
Figure 3. (a) Perspective view of the nitrate-encapsulating cluster lying
on a crystallographic 2-axis in [NO3@Ag15(o-FC6H4CC)10](NO3)4
(2). The argentophilic Ag···Ag distances, shown as thick rods, lie in the
range 2.70−3.50 Å. Labeled silver(I) atoms are drawn as thermal
ellipsoids at the 50% probability level. (b) Coordination mode of exo-
polyhedral nitrate groups. Symmetry codes: (A) 1 − x, y, 0.5 − z; (B) x,
−1 + y, z; (C) 1 − x, −1 + y, 0.5 − z.
Figure 1. (a) Perspective view of the centrosymmetric Ag26 cluster in
[(NO3)2@Ag26(o-MeC6H4CC)16](NO3)8·5H2O (1). The argento-
philicAg···Agdistances, shownasthickrods, lieintherange2.70−3.40 Å.
Silver atoms are drawn as thermal ellipsoids (50% probability level) with
atom labeling. (b) Perspective view of the coordination modes of the
eight independent o-MeC6H4CC¯ peripheral ligands in 1. Symmetry
code:(A)2−x, 1−y, 1−z.Inthisandallotherfigures, thehydrogenand
fluorine atoms are omitted for clarity.
Figure 4. (a) Perspective view of interassociation between neighboring
chains in 2, showing all notable weak C−H···O and C−H···F
interactions. (b) Perspective view of crystal packing in 2, showing all
notable weak C−H···O and C−H···F interactions. Symmetry codes: (A)
1 − x, y, 0.5 − z; (B) x, −1 − y, 0.5 + z; (C) 1.5 − x, −0.5 + y, 0.5 − z.
polyhedra, each silver(I) cage having a 2-fold axis passing through
atoms Ag1, N1, and O2, also the midpoint of the Ag6−Ag6A edge
(Figure 3a). Such an Ag15 cage is consolidated by 10 o-FC6H4C
C¯ groups, which are each bound to three silver(I) atoms in either
the μ3-η2,η2,η1 or μ3-η2,η1,η1 mode (Figures S2 and S3a in the
Supporting Information). One independent exo-polyhedral
nitrate ligand is attached to a silver(I) atom via the μ2-O,O′
chelating mode and the other to two silver(I) atoms via the μ2-
O,O,O′,O″ mode (Figure S3b in the Supporting Information).
Adjacent Ag15 polyhedra are interassociated through argento-
philic interactions between Ag1B and the symmetry-related atom
pairs of Ag6 and Ag7 together with bridging nitrate groups (N3
and N3A) to yield an infinite chain of corner-to-face-linked Ag15
polyhedra along the b axis (Figure 3b).
Figure 2. (a) Perspective view of the coordination layer in 1, with all
notable hydrogen bonding interactions shown by broken lines. (b)
Perspective view of the 3D supramolecular framework formed by weak
C−H···O interactions between methyl groups and nitrate ligands.
Symmetrycodes:(A)−1+x, y,−1+z;(B)1−x,1−y,1−z;(C)1−x, 1
− y, −z; (D) 2 − x, 1 − y, 1 − z; (E) x, y, −1 + z; (F) x, −1 + y, z.
ethynide groups and nearby nitrate ligands (C42D−H···O5F,
2.576(3) Å) to produce a 3D supramolecular network (Figure
2b).
The crystal structure of [NO3@Ag15(o-FC6H4CC)10]-
(NO3)4 (2) is composed of infinite chains of linked Ag15
3232
dx.doi.org/10.1021/om5003733 | Organometallics 2014, 33, 3231−3234

Organometallics
Communication
Figure 5. (a) Perspective view of the Ag18 cluster in [CrO4@
Ag18(iPrCC)12](ClO4)4 (3) with atom labeling. The argentophilic
Ag···Agdistances, shownasthickrods,lieintherange2.70−3.50Å. Silver
atoms are drawn as thermal ellipsoids (50% probability level). (b)
Perspective view of the linkage between adjacent silver(I) polyhedra.
Symmetry codes: (A) −x, y, 0.5 − z; (B) x, −1 + y, z.
Figure 7. (a) Perspective view of the perchlorate-centered Ag18 cluster in
[ClO4@Ag18(iPrCC)12](ClO4)5 (4) with atom labeling. The
argentophilic Ag···Ag distances, shown as thick rods, lie in the range
2.70−3.50 Å. Silver atoms are drawn as thermal ellipsoids (50%
probability level). (b) Perspective view of the linkage between adjacent
silver(I) polyhedra in 4.
Figure 6. (a) Perspective view of interassociation between neighboring
chains in 3, showing all notable weak C−H···O interactions. (b)
Perspective view of crystal packing in 3, showing all notable weak C−H···
Ointeractions. Symmetry codes: (A) −x, 1 − y, 1 −z;(B) 0.5 − x, −0.5 +
y, 0.5 − z.
Figure 8. (a) Perspective view of interassociation between neighboring
chains in 4, showing all notable weak C−H···O interactions. (b)
Perspective view of crystal packing in 4, showing all notable weak C−H···
O interactions. Symmetry codes: (A) −0.5 − x, y, 1.5 − z; (B) −1 − x, −1
−y, 1−z;(C)−0.5+x, −1−y, −0.5+z;(D)−1−x, −y, 1−z;(E)−0.5
+ x, −y, −0.5 + z.
The coordination chains are further associated by weak C−H···
O(C22A−H···O8B, 2.587(6) Å)and C−H···F(C21A−H···F3B,
2.667(5) Å) interactions between fluorophenyl and nitrate
groups to form a supramolecular layer (Figure 4a). Neighboring
layers are interconnected by additional C−H···O (C5C−H···O5,
2.674(7) Å) and C−H···F (C6C−H···F1, 2.539(6) Å)
interactions, leading to generation of a supramolecular network
(Figure 4b).
As illustrated in Figure 5a, [(CrO4)@Ag18(iPrCC)12]-
(ClO4)4 (3) contains an olive-shaped Ag18 polyhedron with a
crystallographic 2-fold axis passing through the Ag1, Ag10, and
Cr1 atoms. Three independent peripheral iPrCC¯ groups are
attached to silver(I) centers in μ3-η2,η2,η1, μ3-η2,η2,η1, and μ3-
η1,η1,η1 modes (Figures S4 and S5a in the Supporting
Information), along with two symmetry-related pairs of μ1-
coordinated Cl1 and μ2-coordinated Cl2 perchlorate ligands
(Figure S5b in the Supporting Information). Such Ag16 cages are
interconnected through a corner-to-corner argentophilic linkage
between Ag1 and Ag10B to yield an infinite silver(I) chain along
the b axis (Figure 5b).
2.473(5) and 2.560(4) Å) to produce a supramolecular layer
(Figure 6a). Such layers are further associated by additional
hydrogen bonding (C18A−H···O10, 2.832(6) Å) to yield a 3D
supramolecular network (Figure 6b).
Single-crystal X-ray analysis established that [ClO4@
Ag18(iPrCC)12](ClO4)5 (4) is a structural analogue of 3,
with a perchlorate anion replacing the corresponding chromate
template in the Ag18 cage held by argentophilic Ag···Ag distances
ranging from2.923(1) to3.467(1) Å(Figure 7a intheSupporting
Information). The four exo-polyhedral perchlorate ions in 4 are
divided into three groups on the basis of their different ligation
behaviors: Cl2 and Cl5 in μ1-η1, Cl3 in μ3-η2,η1, and Cl4 in μ3-
η1,η1,η1 modes (Figure S6a in the Supporting Information). In
addition, the charge balance is provided by two more lattice
perchlorate ligands (Cl6 and Cl7), which exhibit half-site
occupancy. Twelve iPrCC¯ ligands are connected to the olive
Ag18 cluster via two ligation modes: 11 μ3-η2,η1,η1 and 1 μ3-
η2,η2,η1 (Figure S7 in Supporting Information). Two adjacent
Ag18 cages are fused to form a distorted peanut-shaped dimeric
Ag36 cluster through face-to-face argentophilic interactions
As illustrated in Figure 6a, adjacent silver chains are linked
through weak hydrogen bonds between perchlorate ligands and
terminal methyl groups of ethynide ligands (C25−H···O5A,
3233
dx.doi.org/10.1021/om5003733 | Organometallics 2014, 33, 3231−3234

Organometallics
Communication
between four symmetry-related atom pairs of Ag12, Ag13, Ag14,
and Ag15 (Figure 7b in the Supporting Information).
the central anionic template on the construction of multidimen-
sionalsilver(I)ethynidenetworks. Thebulkinessoftheperipheral
ligands and the orientation of substituents with respect to the
ethynide group proved to be dominant factors in directing the
assembly of high-nuclearity clusters.
With an inversion center located at the midpoint of peripheral
chloride atoms Cl6 and Cl6A, which both have half-site
occupancy (Figure S6b in the Supporting Information), such a
dinuclear perchlorate species is bridging two neighboring Ag26
clusters through weak C−H···O interactions (C5A−H···O21,
2.415(3) Å; C5A−H···O22A, 2.455(5) Å) and generates an
infinite wavy metal−organic supramolecular chain along the c axis
(Figure S8 in the Supporting Information). Cross-linkage of
adjacent silver-organic supramolecular chains through weak C−
H···O interactions (C59B−H···O15, 2.807(3) Å; C30−H···
O18C, 2.819(3) Å; C29−H···O19C, 2.976(3) Å) yields a
supramolecular layer (Figure 8a). Such layers are linked by
additional hydrogen bonding between terminal methyl groups of
ethynide ligands and perchlorate ligands (C45−H···O24,
2.712(2) Å; C13E−H···O5, 2.566(2) Å; C15E−H···O6,
2.209(5) Å), in which Cl7 and O24 exhibit half-site occupancy,
leadingtotheformationofasupramolecularnetwork(Figure8b).
The central nitrate template in both 1 and 2 reaffirms its
dominant coordination capacity up to μ4-η1,η1,η1,η1. The methyl
and fluoro substituents, in 1 and 2, respectively, at the ortho
position of the phenylethynide nucleus are about the same size.
However, the more hydrophilic fluoro group leads to the
formation of an infinite silver(I) column composed of smaller
Ag15 cluster units, and it also forms a weak C−H···F acceptor
hydrogen bond to link adjacent columns to generate a three-
dimensional supramolecular network in 2. On the other hand, the
Ag26 cluster in 1 is enveloped by eight nitrate groups and two aqua
ligands, and symmetry-related clusters are bridged by a single
argentophilic interaction to give a dimeric building unit. The
presence of peripheral nitrate groups facilitates the formation of a
coordination layer structure in 1, and neighboring layers are
connected through weak C−H···O interactions to yield a
supramolecular network. In accordance with our previously
reported results,7 the ortho position of the substituent with
respect to the ethynide moiety on the phenyl nucleus is crucial for
the formation of a high-nuclearity cluster. When the methyl
substituent is located at the para position in 12Ag(C
CC6H4Me-p)·7AgNO3,7 an argentophilic silver(I) layer is
obtained instead.
Complex 4 can be regarded as a structural analogue of 3 with a
lesssymmetricalAg18 cage. Sincebotharepreparedfromthesame
AgCCiPr as a synthetic precursor, such distortion of the cage in
4 is accounted for by the relatively bulky and less negatively
charged perchlorate center (Figure S9 in the Supporting
Information), leading to the fusion of two adjacent Ag18 clusters
through argentophilic interactions. The surrounding perchlorate
anions play a significant role in bridging adjacent chains to form a
supramolecular network through weak C−H···O interactions. In
comparison to the high-nuclearity silver(I) cluster [Ag22(C
CtBu)18(CrO4)](BF4)2 synthesized by Wang et al.,5 the infinite
chain of clusters generated by AgCCiPr in 3 implies that the
bulkiness of ethynide ligands plays a significant role in influencing
the packing between cluster units.
In summary, we have employed the multinuclear supra-
molecular synthon RC6H4CC⊃Agn (R = Me, F; n = 3−5) to
construct the two high-nuclearity silver ethynide cluster
compounds [(NO3)2@Ag26(o-MeC6H4CC)16](NO3)8·5H2O
(1) and [NO3@Ag15(o-FC6H4CC)10](NO3)4 (2), which bear
the same nitrate central template. The synthesis of [CrO4@
Ag18(iPrCC)12](ClO4)4 (3) and [ClO4@Ag18(iPrCC)12]-
(ClO4)5 (4) demonstrated the influence of the size and charge of
ASSOCIATED CONTENT
* Supporting Information
■
S
Text, figures, a table, and CIF files giving additional structures,
experimental details, X-ray crystallographic data, and structure
refinement parameters for 1−4. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail for T.C.W.M.: tcwmak@cuhk.edu.hk.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support by the Hong Kong
ResearchGrantsCouncil(GRFCUHK402710)andtheWeiLun
Foundation, and the award of a Studentship to P.-C.C. and a
Postdoctoral Research Fellowship to S.C.K.H., respectively, by
The Chinese University of Hong Kong.
REFERENCES
■
(1) Gimeno, N.; Vilar, R. Coord. Chem. Rev. 2006, 250, 3161−3189.
(2)Forreviews oftheestablishment ofthemultinuclear supramolecular
synthon RCC⊃Agn (R = alkyl, aryl; n = 3−5) and its utility in
supramolecular assembly, see: (a) Mak, T. C. W.; Zhao, X.-L.; Wang, Q.-
M.; Guo, G.-C. Coord. Chem. Rev. 2007, 251, 2311−2333. (b) Mak, T. C.
W.; Zhao, L. Chem. Asian J. 2007, 2, 456−467. (c) Mak, T. C. W.; Zhao,
L.; Zhao, X.-L. Supramolecular Assembly of Silver(I) Complexes with
Argentophilic and Silver···Carbon Interactions. In The Importance of Pi-
Interactions in Crystal Engineering-Frontiers in Crystal Engineering III;
Tiekink, E. R. T., Zukerman Schpector, J., Eds.; Wiley: Chichester, U.K.,
2012; Chapter 13, pp 323−366. The term “silver ethynide” is preferred
to “silver ethynyl” because the silver−carbon bonding interaction is
considered to be mainly ionic with minor covalent σ and π components;
the negative charge residing mainly on the terminal C atom draws
neighboring Ag(I) atoms close to one another to facilitate the onset of
argentophilic Ag···Ag interactions.
(3) Rais, D.; Yau, J.; Mingos, D. M. P.; Vilar, R.; White, A. J. P.; Willams,
D. J. Angew. Chem., Int. Ed. 2001, 40, 3464−3467. (b) Bian, S.-D.; Wang,
Q.-M. Chem. Commun. 2008, 5586−5588.
(4) Bian, S.-D.; Jia, J.-H.; Wang, Q.-M. J. Am. Chem. Soc. 2009, 131,
3422−3423. (b) Gruber, F.; Jansen, M. Angew. Chem., Int. Ed. 2010, 49,
4924−4926.
(5)Bian, S.-D.; Wu, H.-B.; Wang, Q.-M. Angew. Chem., Int. Ed. 2009, 48,
5363−5365.
(6) (a) Gao, G.-G.; Cheng, P.-S.; Mak, T. C. W. J. Am. Chem. Soc. 2009,
131, 18257−18259. (b) Qiao, J.; Shi, K.; Wang, Q.-M. Angew. Chem., Int.
Ed. 2010, 49, 1765−1767. (c) Xie, Y.-P.; Mak, T. C. W. J. Am. Chem. Soc.
2011, 133, 3760−3763. (d) Xie, Y.-P.; Mak, T. C. W. Angew. Chem., Int.
Ed. 2012, 51, 8783−8786. (e) Jiang, Z.-G.; Shi, K.; Lin, Y.-M.; Wang, Q.-
M. Chem. Commun. 2014, 50, 2353−2355.
(7) Cheng, P.-S.; Hau, S. C. K.; Mak, T. C. W. Inorg. Chim. Acta 2013,
403, 110−119.
(8) (a) Guo, G.-C.; Zhou, G.-D.; Mak, T. C. W. J. Am. Chem. Soc. 1999,
121, 3136−3141. (b) Guo, G.-C.; Zhou, G.-D.; Wang, Q.-G.; Mak, T. C.
W. Angew. Chem., Int. Ed. 1998, 37, 630−632. (c) Wang, Q.-G.; Mak, T.
C. W. J. Am. Chem. Soc. 2001,123, 1501−1502. (d)Wang,Q.-M.;Mak, T.
C. W. Angew. Chem., Int. Ed. 2001, 40, 1130−1133. (e) Wang, Q.-M.;
Mak, T. C. W. Chem. Commun. 2001, 37, 807−808.
3234
dx.doi.org/10.1021/om5003733 | Organometallics 2014, 33, 3231−3234