Assembly of Heterometallic Silver(I)-Copper(I) Alkyl-1,3-diynyl Clusters via Inner-Core Expansion

Article abstract of DOI:10.1021/jacs.6b08674

New tetranuclear supramolecular precursors [(R - C≡C - C≡C)Ag]₄ (R = ⁱPr, ^tBu, and chx) are employed to construct a series of heterometallic silver(I)-copper(I) alkyl-1,3-diynyl cluster complexes (1-9) that bear a common CuAg₃ core (normally trigonal-planar, but can be distorted to pyramidal) consolidated by cupro-argentophilic interaction under 3.12 ?, as found in 1 and 2. The photophysical properties of the multinuclear supramolecular precursors and selected complexes have been investigated. The present results strongly suggest that the assembly of medium-nuclearity clusters 3 to 9 is initiated by accretion of additional Ag(I) ions by the ubiquitous CuAg₃ template through argentophilic (<3.4 ?) interaction, with cooperative cuprophilic enhancement (<2.76 ?) in the case of compound 9. To our knowledge, the present study provides the first report of conversion of a Group 11 homonuclear cluster into a heteronuclear one of higher nuclearity via inner-core expansion.

Full text of DOI:10.1021/jacs.6b08674

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Article
Assembly of Heterometallic Silver(I)-Copper(I) Alkyl-1,3-
diynyl Cluster Complexes via Inner-Core Expansion
Sam C. K. Hau, Margaret C. L. Yeung, Vivian Wing-Wah Yam, and Thomas C. W. Mak
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b08674 • Publication Date (Web): 27 Sep 2016
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Assembly of Heterometallic Silver(I)-Copper(I) Alkyl-1,3-diynyl Clusters
via Inner-Core Expansion
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Sam C. K. Hau,a,b, Margaret C.ꢀL. Yeung,c Vivian W.ꢀW. Yam,c Thomas C. W. Maka*
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aDepartment 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
bDepartment of Chemistry, Hong Kong Baptist University, Kowloon, Hong Kong SAR,
People’s Republic of China
c Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants
Committee, Hong Kong) and Department of Chemistry, The University of Hong Kong,
Pokfulam Road, Hong Kong, People’s Republic of China
ABSTRACT
New tetranuclear supramolecular precursors [(R−C≡C−C≡C)Ag]4 (R = iPr, tBu and chx)
are employed to construct a series of heterometallic silver(I)ꢀcopper(I) alkylꢀ1,3ꢀdiynyl
cluster complexes (1−9) that bear a common CuAg3 core (normally trigonalꢀplanar, but can
be distorted to pyramidal) consolidated by cuproꢀargentophilic interaction under 3.12 Å, as
found in 1 and 2. The photophysical properties of the multinuclear supramolecular precursors
and selected complexes have been investigated. The present results strongly suggest that the
assembly of mediumꢀnuclearity clusters 3 to 9 is initiated by accretion of additional Ag(I)
ions by the ubiquitous CuAg3 template through argentophilic (< 3.4 Å) interaction, with
cooperative cuprophilic enhancement (< 2.76 Å) in the case of compound 9. To our
knowledge, the present study provides the first report of conversion of a Group 11
homonuclear cluster into a heteronuclear one of higher nuclearity via innerꢀcore expansion.
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INTRODUCTION
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Monovalent group 11 metal alkynyl complexes have been actively investigated over the past
decade owing to their ubiquitous metallophilic interactions and variable metalꢀcarbon
interactions,1ꢀ4 which account for their rich structural diversity and remarkable photophysical
and photochemical properties.5ꢀ6 In particular, tetranuclear cuboidal complexes of d10
electronic configuration are wellꢀknown and a number of their analogs have been shown to
exhibit desirable luminescence properties.7 In addition, extension of studies on the alkynyl
ligands to homologous diynyl systems showed significant effect on the luminescence
behavior of their corresponding complexes.7b,8ꢀ9 On the contrary, heteronuclear alkynyl
complexes have been much less explored because of the difficulty in controlling assembly of
heterometallic systems, in contrast to the relative strong tendency to form homonuclear
arrays.10ꢀ17
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In a previous study, we employed the multinuclear supramolecular synthon R−C≡C⊃Agn
t
(R = Bu and chx) to construct two Ag38 highꢀnuclearity silver ethynide cluster complexes
which bear the same novel Cl6Ag8 central core.18 The formation of these clusters is suggested
to involve transformation of the encapsulated chloride template within a Ag14 cage into a
Cl6Ag8 central core within a much expanded Ag38 cluster, which provided the first example of
conversion of a silver cluster into one of high nuclearity via innerꢀcore transformation.
Herein, we describe the synthesis, structural characterization and photophysical
properties of a series of novel heteronuclear Ag(I)···Cu(I) molecular cluster complexes
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t
obtained from the reaction between designed [(RC≡C−C≡C)Ag]4(PPh3)4 (R = Pr, Bu and
chx) precursors and [Cu(MeCN)4]X (X = PF6 and ClO4) via CuAg3 core expansion,
stabilization of the products being provided by peripheral alkylꢀ1,3ꢀdiynyl and
triphenylphosphine ligands.
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RESULTS and DISCUSSION
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General procedure to prepare synthetic precursors [(RC≡C
and chx)
−C≡C)Ag]4(PPh3)4 (R = Pr, Bu
CAUTION. Silver ethynides are potentially explosive and should be handled in small
amounts with extreme care!
Polymeric silver ethynides [(RC≡C−C≡C)Ag]n (0.1 mmol)18 was first dissolved in a
mixed solution of dichloromethane (3.0 mL) and methanol (0.5 mL); triphenylphosphine (0.1
mmol) was then added with vigorous stirring to achieve complete dissolution. The resulting
solution was filtered and left to stand in the dark at room temperature. After two days,
colorless
blockꢀlike
crystals
of
[(iPrC≡C−C≡C)Ag]4(PPh3)4,
[(tBuC≡C−C≡C)Ag]4(PPh3)4·2MeCN and [(chxC≡C−C≡C)Ag]4(PPh3)4·2MeOH were each
deposited in ca. 80 % yield.
Description of Crystal and Molecular Structure
[(chxC≡C−C≡C)Ag]4(PPh3)4·2MeOH
There are two independent and isostructural [(chxC≡C−C≡C)Ag]4(PPh3)4 molecular
clusters each occupying an inversion center in its crystalline methanol solvate. The core of
each molecule consists of two nearly isosceles Ag3 triangles sharing a common edge, with the
resulting parallelogramꢀlike Ag4 array consolidated by two pairs of bridging chxC≡C−C≡C¯
groups, whereas the PPh3 ligands are attached only to the outer Ag1 centers (Figure 1). In the
two independent cluster molecules, the observed argentophilic Ag···Ag distances range from
2.962(5) to 3.008(5) Å, and the Ag1ꢀAg2ꢀAg1A and Ag2ꢀAg1ꢀAg2A angles are 120.3(1)˚ and
59.5(1)˚, respectively. The two methanol molecules are linked together by a weak hydrogen
bond of length 2.67 Å.
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Figure 1. Coordination environment of the silver(I) atoms in the discrete molecule [(chxC≡C−C≡C)Ag]4(PPh3)4.
The C≡C triple bonds in the alkylꢀ1,3ꢀdiynyl ligands are shown as thick rods. Silver atoms are drawn as thermal
ellipsoids (50% probability level) with atom labeling. (Color scheme: purple, silver atoms; broken lines, Ag−C
bonds) The argentophilic Ag···Ag distances lie in the range 2.70−3.40 Å. Symmetry code: A: 0.5−x, 1.5−y, z.
As expected, singleꢀcrystal Xꢀray analysis established that the tetranuclear molecular
clusters [(RC≡C−C≡C)Ag]4(PPh3)4 (R = iPr and tBu) are structural analogs of
[(chxC≡C−C≡C)Ag]4(PPh3)4, with each iꢀpropyl or tertꢀbutyl group replacing the
corresponding peripheral cyclohexyl group, the only difference between them is that
crystalline [(iPrC≡C−C≡C)Ag]4(PPh3)4 is solventꢀfree, and there are two coꢀcrystallized
acetonitrile molecules in [(tBuC≡C−C≡C)Ag]4(PPh3)4·2MeCN.
[CuAg3(chxC≡C− −C≡C)3(PPh3)6]PF6 (2)
C≡C)3(PPh3)6]PF6ꢁ2Et2O (1) and [CuAg3(iPrC≡C
The reaction between 1.0 equiv. of [(chxC≡C−C≡C)Ag]4(PPh3)4 and 0.7 equiv. of
[Cu(MeCN)4]PF6 in CH2Cl2 gave complex 1 in ca. 50% yield. In the crystal structure of 1,
the Cu(I) ion is bound by three Ag(I) atoms through cuproꢀargentophilic interactions
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(2.684(1)−2.739(3) Å) to yield a trigonalꢀplanar CuAg3 core (Figure 2a), which is stabilized
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by three ꢂ3−coordinated chxC≡C−C≡C¯ groups on one side and
a
pair of
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η1−triphenylphosphine ligands on the other. As expected, singleꢀcrystal Xꢀray analysis
established that 2 is a structural analog of 1, with each isoꢀpropyl group replacing the
corresponding peripheral cyclohexyl group (Figure 2b), the only difference between them
being the incorporation of two coꢀcrystallized diethyl ether molecules in 1.
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Figure 2. a) Coordination environment of the silver(I) and copper(I) atoms in the discrete molecule
[CuAg3(chxC≡C−C≡C)3(PPh3)6]PF6 in (1). b) Perspective view of the analogous cluster structure of
[CuAg3(iPrC≡C−C≡C)3(PPh3)6]PF6 (2). The hexafluorophosphate ions, diethyl ether solvate molecules and
hydrogen atoms are omitted for clarity. Silver and copper atoms are drawn as thermal ellipsoids (50%
probability level) with atom labeling. (Color scheme: purple, silver atoms; turquoise, copper atoms; broken lines,
Ag−C and Cu−C bonds; the same color scheme for atoms and bonds applies to all other figures.) The
argentophilic Ag(I)···Ag(I) distances lie in the range 2.70−3.40 Å, and the cupro−argentophilic Cu(I)···Ag(I)
distances lie in the range 2.40−3.12 Å.
[{CuAg3}Ag4(chxC≡C
[{CuAg3}Ag4(tBuC≡C
−
C≡C)7(PPh3)5]PF6ꢁ1.5Et2O (3),
−
C≡C)7(PPh3)5]ClO4 (4) and
[{CuAg3}Ag3(iPrC≡C
−
C≡C)6(PPh3)5]PF6 (5)
was prepared by the reaction of
Yellow complex
3
2
equiv. of
[(chxC≡C−C≡C)Ag]4(PPh3)4 and 1.5 equiv. of [Cu(MeCN)4]PF6 in CH2Cl2 (3 mL) at room
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temperature. Recrystallization by layering diethyl ether afforded yellow crystals in 25% yield.
As illustrated in Figure 3a, seven Ag(I) and Cu(I) ions are aggregated to form a distorted
augmented triangular prism through argentophilic interaction with Ag(I)ꢁꢁꢁAg(I) bond
distances in the range 2.844(1)−3.343(1) Å, which are comparable to those observed in a
wide variety of silver double and multiple salts.19 Silver atoms Ag1, Ag2 and Ag3 are bound
to the Cu1 atom (Ag(I)ꢁꢁꢁCu(I) bond distances: 2.641(1)−2.932(1) Å) in trigonalꢀplanar
fashion, and also to the nonꢀplanar tetragon formed by the remaining four silver atoms Ag4 to
Ag7 on one side. The seven chxC≡C−C≡C¯ ligands can be divided into four groups based on
their different ligation behavior: two each in ꢂ4−η1,η1,η2,η2, ꢂ3−η1,η1,η2 and ꢂ3−η1,η1,η1, and
one in ꢂ2−η1,η1 mode (Figure 3b). Silver atoms Ag1, Ag2, Ag3, Ag5 and Ag7 are each
stabilized by a peripheral η1−triphenylphosphine ligand. Of the two solvated diethyl ether
molecules, one was found to have 50% site occupancy.
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Notably, addition of a polar protic solvent like methanol (0.5 mL) to the reaction mixture
is detrimental to the formation of complex 3.
Figure 3. a) Thermal ellipsoid plot (50% probability level) of the {CuAg3}Ag4 core in
[{CuAg3}Ag4(chxC≡C−C≡C)7(PPh3)5]PF6ꢁ1.5Et2O (3) with atom labeling. b) Perspective view of the cluster
structure including all peripheral ligands.
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The reaction between [(tBuC≡C−C≡C)Ag]4(PPh3)4 and [Cu(MeCN)4]ClO4 was
conducted in CH2Cl2 to obtain crystalline complex 4, which is isostructural with 3. In its
CuAg7 core, the argentophilic Ag(I)ꢁꢁꢁAg(I) distances lie in the range of 2.876(1)−3.368(1) Å
and the cuproꢀargentophilic interactions ranging from 2.650(1)−2.989(1) Å (Figure S1a in
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t
Supporting Information). The seven peripheral BuC≡C−C≡C¯ ligands in 4 can be divided
into five groups based on their different ligation behavior: two each in ꢂ4−η1,η1,η2,η2 and
ꢂ3−η1,η1,η1; one each in ꢂ3−η1,η2,η2, ꢂ3−η1,η1,η2 and ꢂ2−η1,η1 mode (Figure S1b in Supporting
Information).
i
Using a less bulky PrC≡C−C≡C¯ ligand to react with [Cu(MeCN)4]PF6 in CH2Cl2
i
yielded a smaller heterometallic CuAg6 core (Figure 4a). The six peripheral PrC≡C−C≡C¯
ligands in 5 can be divided into four groups based on their different ligation behavior: one
ꢂ4−η1,η1,η1,η2, one ꢂ4−η1,η1,η1,η1, two ꢂ3−η1,η1,η1 and two ꢂ3−η1,η1,η2 (Figure 4b).
Figure 4. a) Thermal ellipsoid plot (50% probability level) of the {CuAg3}Ag3 core with atom labeling. b)
Perspective view of the cluster structure of [{CuAg3}Ag3(iPrC≡C−C≡C)6(PPh3)5]PF6 (5).
[{CuAg3}Ag4{CuAg3}(chxC≡C
[{CuAg3}Ag4{CuAg3}(iPrC≡C
−
C≡C)10(PPh3)6](PF6)2 (6) and
−
C≡C)10(PPh3)6](PF6)2 (7)
Yellow blockꢀlike crystals of complex 6 were obtained in 15% yield from crystallization
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by layering diethyl ether over the reaction between 1.0 equiv. of [(chxC≡C−C≡C)Ag]4(PPh3)4
and 0.9 equiv. of [Cu(MeCN)4]PF6 in CH2Cl2. Copper(I) atom Cu1 is surrounded by silver(I)
atoms Ag3, Ag4 and Ag5 in trigonalꢀplanar fashion with Cu(I)ꢁꢁꢁAg(I) interactions in the
range 2.680(1)–2.837(7) Å (Figure 5a). Atoms Ag1 and Ag2 and their inversionꢀrelated
counterparts constitute a Ag4 rhombus, which unsymmetrically bridge a pair of CuAg3
aggregates through argentophilic interaction to engender a {CuAg3}Ag4{CuAg3} core
structure. The different cyclohexylꢀ1,3ꢀdiynyl ligand coordination modes that stabilize the
heterometallic core can be divided into three groups: four ꢂ4−η1,η1,η1,η2, two ꢂ4−η1,η1,η1,η1
and four ꢂ3−η1,η1,η2 (Figure 5b). The six symmetryꢀrelated triphenylphosphine ligands are
each attached to one silver atom in the normal µ1−P ligation mode.
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Figure 5. a) Thermal ellipsoid plot (50% probability level) of the centrosymmetric {CuAg3}Ag4{CuAg3} core
of [{CuAg3}Ag4{CuAg3}(chxC≡C−C≡C)10(PPh3)6](PF6)2 (6) with atom labeling. b) Perspective view of the
cluster structure showing all peripheral ligands. Symmetry code: A: −x, 1−y, 1−z.
Similar reaction using an analogous [(iPrC≡C−C≡C)Ag]4(PPh3)4 precursor produced
isoꢀstructural complex 7 in 15% yield. In its {CuAg3}Ag4{CuAg3} core, the Cu(I)⋅⋅⋅Ag(I)
interaction distances lie in the range of 2.639(1)–2.679(1) Å, and argentophilic Ag(I)⋅⋅⋅Ag(I)
distances between shell silver atoms range from 2.871(1) to 3.396(1) Å (Figure S2a in
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Supporting Information). The ten peripheral isoꢀpropylꢀ1,3ꢀdiynyl ligands can be divided into
three groups based on their different ligation behavior: two ꢂ4−η1,η1,η1,η2, two ꢂ3−η1,η1,η2,
and six ꢂ3−η1,η1,η1 (Figure S2b in Supporting Information).
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[Cu2Ag10(tBuC≡C
−C≡C)12(PPh3)2] (8)
When the reaction between 1.0 equiv. of [(tBuC≡C−C≡C)Ag]4(PPh3)4 and 0.8 equiv. of
[Cu(MeCN)4]ClO4 was carried out in a more concentrated condition (2 mL CH2Cl2), wellꢀ
formed yellow rhombusꢀlike crystals of 8 were obtained in 30% yield. Two inversionꢀrelated
pyramidal CuAg3 segments, in which the central Cu1 atom is displaced from the leastꢀsquares
plane of atoms Ag1, Ag1A and Ag4A by 0.435(6) Å, coalesce through argentophilic
interaction to generate a heterometallic {CuAg3}Ag2Ag2{CuAg3} core through vertex (Ag5
and Ag5A) and segment (Ag2−Ag3 and Ag2A−Ag3A) sharing (Figure 6a). The twelve
peripheral tBuC≡C−C≡C¯ ligands exhibit three kinds of coordination modes: two
ꢂ4−η1,η1,η1,η2, four ꢂ3−η1,η1,η1, and six ꢂ2−η1,η1 (Figure 6b). Silver atoms Ag5 and Ag5A are
each further protected by a η1−triphenylphosphine ligand.
Figure 6. a) Thermal ellipsoid plot (50% probability level) of the {CuAg3}Ag6{CuAg3} core with atom labeling.
b) Perspective view of the cluster structure of [Cu2Ag10(tBuC≡C−C≡C)12(PPh3)2] (8). Symmetry code: A: 2−x,
2−y, 2−z.
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[{CuAg3}CuAg6{CuAg3}(tBuC≡C
(tBuC≡C
−C≡C)12(PPh3)6] [{CuAg3}Cu2Ag2{CuAg3}
−
C≡C)10(PPh3)6] (PF6)4ꢁ(OH)ꢁ3Et2O (9)
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Orange blockꢀlike crystals of 9 were obtained in 10% yield by layering diethyl ether
over a mixed solution of dichloromethane (3 mL) and methanol (0.5 mL) used in the reaction
between 1.0 equiv. of [(tBuC≡C−C≡C)Ag]4(PPh3)4 and 1.0 equiv. of Cu(MeCN)4PF6. It is
notable that only a yellowish oily substance was obtained when [Cu(MeCN)4]ClO4 replaced
[Cu(MeCN)4]PF6 in the reaction.
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Figure
7.
Perspective
view
of
the
structure
of
(left)
cationic
clusters
and
[{CuAg3}CuAg6{CuAg3}(tBuC≡C−C≡C)12(PPh3)6]3+
[{CuAg3}Cu2Ag2{CuAg3}(tBuC≡C−C≡C)10(PPh3)6]3+ (right) in complex 9. Symmetry code: A: −x, 2−y, 2−z; B:
1−x, 1−y, 1−z.
There are two discrete centrosymmetric heterometallic molecular cations in the crystal
structure, and charge balance is provided by four hexafluorophosphate anions and one
hydroxide anion. In the larger cation [{CuAg3}CuAg6{CuAg3}(tBuC≡C−C≡C)12(PPh3)6]3+
(Figure 7, left side), a central Cu3 rodꢀshaped segment (Cu(I)···Cu(I) distance = 2.752(8)Å,
which indicates the presence of significant cuprophilic interaction in the range 2.46−3.42 Å.20)
is surrounded by
a
quasiꢀcuboctahedral shell of twelve Ag(I) ions through
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cuproꢀargentophilic Cu(I)···Ag(I) interactions in the range 2.682(1)−2.898(7) Å and
argentophilic Ag(I)···Ag(I) interactions ranging from 2.909(1) to 3.327(1) Å. The six
symmetryꢀrelated pairs of peripheral tBuC≡C−C≡C¯ ligands are bound to such heterometallic
core via different coordination modes, which can be divided into three groups: two
ꢂ4−η1,η1,η1,η2, four ꢂ3−η1,η1,η2 and six ꢂ3−η1,η1,η1. The six triphenylphosphine ligands are
each chelated on one silver atom via the µ1−P ligation mode (Figure 8a).
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Figure 8. a) Thermal ellipsoid plot (50% probability level) of the core structure in the
[{CuAg3}CuAg6{CuAg3}(tBuC≡C−C≡C)12(PPh3)6]3+ cationic cluster molecule. b) Thermal ellipsoid plot (50%
probability level) of the core structure in [{CuAg3}Cu2Ag2{CuAg3}(tBuC≡C−C≡C)10(PPh3)6]2+ cationic cluster
molecule. Symmetry code: A: −x, 2−y, 2−z; B: 1−x, 1−y, 1−z.
In
the
smaller
heterometallic
cation
[{CuAg3}Cu2Ag2{CuAg3}(tBuC≡C−C≡C)10(PPh3)6]2+ (Figure 7, right side), a central Cu2Ag2
zigzag segment is linked by a pair of trigonalꢀplanar CuAg3 aggregates through Cu(I)ꢁꢁꢁCu(I)
(2.861(1) Å) and Ag(I)ꢁꢁꢁAg(I) interactions to engender a Cu4Ag8 heterometallic core. The ten
t
peripheral symmetryꢀrelated pairs of BuC≡C−C≡C¯ ligands are each bonded to either three
or four Ag(I) centers in different ligation modes: four in ꢂ4−η1,η1,η1,η1 and six in ꢂ3−η1,η1,η2
mode, and the three independent triphenylphosphine groups are each chelated on one silver
atom (Figure 8b).
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Complex 9 is unique as it is the only one in the series that contains two different cationic
5
6
silver(I)ꢀcopper(I) clusters that are consolidated by cuprophilic Cu(I)···Cu(I) interactions.
7
8
9
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Photophysical Properties
The photophysical data for the three synthetic precursors and complexes 1–3 and 5–8
are summarized in Table 1. Figure 9 illustrates the electronic absorption spectra of the
[(chxC≡C−C≡C)Ag]4(PPh3)4 precursor and 1 in CH2Cl2 at room temperature, while Figure 10
depicts the emission spectra of 7 in the solid state at room temperature and 77 K.
The electronic absorption spectra of the three precursors and complexes 1–3 and 5–8
show an intense highꢀenergy absorption band at ca. 240–295 nm, while 1–3 and 5–8 show an
additional lowerꢀenergy absorption shoulder at ca. 320 nm. The highꢀenergy absorption band
can be assigned as the intraꢀligand transition of the triphenylphosphine and diynyl ligands
while the lowerꢀenergy absorption shoulder can be tentatively assigned as the metalꢀperturbed
intraligand [π→π*(RC≡C−C≡C−)] transition.7,22,23
Excitation of the three precursors and complexes 1–3 and 5–8 in ethanolꢀmethanol glass
and in the solid state at 77 K, the solid samples of [(chxC≡C−C≡C)Ag]4(PPh3)4, 1 and 6–8,
and the fluid solutions of 2, 5–7 at room temperature at λ > 320 nm results in longꢀlived
emission. Their emission lifetimes in the microsecond range suggest the triplet parentage of
the emission origins.
Highly structured emission bands are obtained for all the complexes in ethanolꢀmethanol
glass at 77 K with vibrational progressional spacings of ca. 1350–1450 cm–1 and 1800–2100
cm–1, which are typical of the
ν(C–H) and ν(C≡C) stretching modes in the ground state.
Similar vibronicꢀstructured emission bands have also been observed for the solid samples of
the three synthetic precursors, 1–3, 5 and 8 at 77 K, [(chxC≡C−C≡C)Ag]4(PPh3)4 precursor
and 1 at room temperature, and the fluid solution of 2, 5–7 at room temperature. These
observations are suggestive of the involvement of the diynyl unit in the emissive excited
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state.7,22,23 Structureꢀless emission bands have been obtained for the solid samples of 6 and 7
at room temperature and 77 K, which can be tentatively assigned as the metal centered d→s
state, mixing with the ligandꢀtoꢀmetal chargeꢀtransfer (LMCT) character modified by the
Ag(I)⋅⋅⋅Ag(I) and/or Ag(I)⋅⋅⋅Cu(I) interactions.7,22,23 These findings are in line with the crystal
structures obtained for 6 and 7, which consist of more compact {CuAg3}Ag4{CuAg3}cores
with more extended Ag(I)⋅⋅⋅Ag(I) and Ag(I)⋅⋅⋅Cu(I) interactions, and are different from the
relatively open CuAg3 cores of 3 and 5 and {CuAg3}Ag2Ag2{CuAg3} core of 8 that mainly
lead to vibronicꢀstructured ligandꢀcentered emission bands.
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Table 1. Photophysical data for the synthetic precursors and selected complexes.
Absorption
/ nm (
/ dm3
mol–1 cm–1)a
Emission λem
Medium (T /
Complex
/
λ
ε
K)
nm (τ / ꢀs)
e
248 sh (99,120),
274 sh (39,680),
295 sh (12,710)
CH2Cl2 (298)
Solid (298)b
Solid (77)b
–
[(chxC≡C−C≡C)Ag]4(PPh3)4
485 (258)
483 (495)
472 (107)
Glass (77)b–d
e
[(iPrC≡C−C≡C)Ag]4(PPh3)4
246 sh (90,950),
276 sh (35,230),
291 sh (13,780)
CH2Cl2 (298)
Solid (298)
Solid (77)b,c
Glass (77)b–d
–
e
–
476 (380)
468 (109)
e
[(tBuC≡C−C≡C)Ag]4(PPh3)4
247 sh (102,340),
276 sh (38,610),
CH2Cl2 (298)
Solid (298)
–
e
–
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294 sh (13,720)
Solid (77)b,c
465 (503)
473 (118)
Glass (77)b–d
7
8
9
e
10
11
12
13
14
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247 (134,910), 256
sh (107,690), 276
sh (73,740), 321 sh
(10,210)
CH2Cl2 (298)
Solid (298)b,c
Solid (77)b,c
Glass (77)b–d
–
[CuAg3(chxC≡C−C≡C)3(PPh3)6]PF6ꢁ2Et2O
(1)
464 (10.6)
468 (51.6)
465 (38.7)
Absorption
/ nm (
/ dm3
mol–1 cm–1)a
Emission
Medium
λ
ε
λem
/
Complex
(T / K)
nm (
τ
/
ꢀs)
[CuAg3(iPrC≡C−C≡C)3(PPh3)6]PF6 (2)
244 (125,000),
256 sh
CH2Cl2
(298)b,c
Solid
506 (9.37)
e
–
(104,520), 276
sh (74,190), 319
(12,070)
486 (71.9)
466 (45.5)
(298)
Solid
(77)b,c
Glass
(77)b–d
CH2Cl2
(298)
Solid
e
244
(170,820), 254
sh (143,860),
sh
–
[{CuAg3}Ag4(chxC≡C−C≡C)7(PPh3)5]PF6ꢁ1.5Et2O (3)
e
–
462
276 sh (94,470),
322 sh (16,060)
(298)
Solid
(17.9)
484
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(77)b,c
Glass
(31.4)
7
8
9
(77)b–d
CH2Cl2
(298)b,c
Solid
[{CuAg3}Ag3(iPrC≡C−C≡C)6(PPh3)5]PF6 (5)
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11
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243 (125,130),
501
253
sh
(10.1)
e
(109,520), 277
sh (69,140), 318
(13,020)
–
(298)
484
Solid
(64.0)
465
(77)b,c
Glass
(39.2)
(77)b–d
245
sh
CH2Cl2
(298)b,c
Solid
501
[{CuAg3}Ag4{CuAg3}(chxC≡C−C≡C)10(PPh3)6](PF6)2
(6)
(189,500), 264
(10.2)
705
sh
(141,300),
sh
278
(298)
Solid
(1.05)
725
(104,310), 318
sh (19,360)
(77)
(7.81)
483
Glass
(77)b–d
(28.8)
Emission
Absorption
Medium
λem
/
λ
/ nm (
mol–1 cm–1)a
ε
/ dm3
Complex
(T / K)
nm (
τ
/
ꢀs)
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[{CuAg3}Ag4{CuAg3}(iPrC≡C−C≡C)10(PPh3)6](PF6)2
244 (229,010),
CH2Cl2
(298)b,c
505 (10.4)
634 (5.16)
(7)
252
(199,270), 278
sh (125,170),
sh
Solid (298) 650 (35.5)
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Solid (77)
Glass
458 (10.9)
318 (25700)
(77)b–d
CH2Cl2
(298)
e
[Cu2Ag10(tBuC≡C−C≡C)12(PPh3)2] (8)
242
sh
–
(236,160), 254
498
sh
(164,220),
sh
Solid (298)
Solid
(0.98)
474
263
(131,450), 277
sh (95,900), 293
sh (54,800), 318
sh (22,160)
(77)b,c
(12.4)
478
Glass
(77)b–d
(26.0)
a Measured in CH2Cl2
b Vibrational progressional spacing of ca. 2100 cm–1
c Vibrational progressional spacing of ca. 1350 cm–1
d Measured in ethanolꢀmethanolꢀdichloromethane (4:1:0.1, v/v) glass
e Nonꢀemissive
15
10
5
ε
0
300
400
Wavelength /nm
Figure 9. Electronic absorption spectra of [(chxC≡C−C≡C)Ag]4(PPh3)4 (solid line) and 1 (dashed line) in
CH2Cl2 at 298 K.
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*
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9
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60
500
600
700
800
900
Wavelength /nm
Figure 10. Emission spectra of 7 in the solid state at 298 K (solid line) and 77 K (dashed line) (* denotes
instrumental artefact).
Assembly Mechanism
Design of the three synthetic precursors was based on the anticipation that bulky alkyl
1,3ꢀdiynꢀ1ꢀide and triphenylphosphine could play complementary roles in serving as
peripheral protective ligands for the generation and stabilization of heteropolynuclear
Cu(I)ꢀAg(I) clusters. In either [Cu(MeCN)4]PF6 or [Cu(MeCN)4]ClO4, the Cu(I) ion is
isolated by four linear acetonitrile ligands from poorlyꢀcoordinating PF6¯ and ClO4¯ groups.
i
The argentophilic Ag4 aggregate of all three precursors [(RC≡C−C≡C)Ag]4(PPh3)4 (R = Pr,
tBu and chx) may be envisaged to partially degrade upon dissolution in CH2Cl2 in the
presence of Cu(I) ions, thereby freeing it for condensation with the abundant supply of Cu(I)
ions. As a result, the central Cu(I) ion is encapsulated by three Ag(I) alkyl diynyls through
cuproꢀargentophilic interaction to yield 1 and 2, which serve as a core structural element in
the formation of complexes 3–9. Attempts to isolate the structural analog of 1 using
[(tBuC≡C−C≡C)Ag]4(PPh3)4 as a synthetic precursor were unsuccessful, but existence of
complexes 4, 8 and 9 indicated the inꢀsitu formation of Cu[Ag(tBuC≡C−C≡C)]3 during
synthesis.
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Generation of heteronuclear cluster complexes 3–9 presumably materializes from the
choice of, and proper stoichiometric balance between, silver(I) alkylꢀ1,3ꢀdiynyl and
acetonitrileꢀcoordinated copper(I) salts in CH2Cl2. A plausible assembly mechanism for the
series of cluster complexes 3−9 is illustrated in Figure 11. It is proposed that each assembly is
first initiated by the formation of a CuAg3(C≡C−C≡CR)3 central core from the reaction
between [(RC≡C−C≡C)Ag]4 and [Cu(MeCN)4]X (X = PF6 or ClO4). For complex 3 and 4, the
{CuAg3}Ag4 core is assembled through argentophilic interaction between inꢀsitu generated
CuAg3(C≡C−C≡CR)3 and remaining neighbor [(RC≡C−C≡C)Ag]4 clusters. The decreased
bulkiness of the isoꢀpropyl group with respect to the tertꢀbutyl or cyclohexyl group accounts
for the fact that only a smaller {CuAg3}Ag3 core exists in 5.
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58
59
60
Figure 11. Proposed assembly mechanism for complexes 1−9, showing only the connection between
monovalent Group 11 cations.
As the concentration of Cu(I) ions in the reaction mixture increases, the corresponding
CuAg3(C≡C−C≡CR)3 complex is expected to be generated in a relatively higher content, in
which case the ratio of CuAg3 complex and unreacted [(RC≡C−C≡C)Ag]4 clusters reaches
2:1. For both the isoꢀpropyl and cyclohexyl groups, which are considered to be less sterically
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hindered, two CuAg3 units sandwich a Ag4 aggregate through argentophilic interaction to
yield a {CuAg3}Ag4{CuAg3} structural core (complexes 6 and 7). When either the isoꢀpropyl
or cyclohexyl peripheral group is replaced by the more bulky tertꢀbutyl group in 8, two
pyramidal CuAg3 units are connected by a pair of Ag2 rods to yielded a
{CuAg3}Ag2Ag2{CuAg3} cluster core. In the synthesis of 9, the reaction mechanism
presumably involves multiple steps when molar ratio of the precursor and Cu(I) salt becomes
1:1. There are two discrete molecules in one asymmetric unit, in which
CuAg3(tBuC≡C−C≡C)3 is found to be their common structural unit.
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Among the seven heterometallic clusters, the peripheral triphenylphosphine ligands play
a key role to stabilize each core structure. Complexes 1–7 are slightly soluble in
dichloromethane, while complexes 8 and 9 are insoluble in different polar organic solvents.
The solution properties of 1−7 were investigated using ESIꢀMS and NMR spectroscopy.
Unfortunately, attempts to record the molecular weight signals of all complexes were
unsuccessful, as the highly charged cluster cation was labile during the ESI process, in which
the molecular ions of the corresponding clusters or fragments generated could not be detected.
It is worthy of note that although the reꢀassembly process that results in the synthesis of 1–9
takes a long time to accomplish at room temperature, it is nonetheless energetically feasible
and reproducible.
CONCLUSION
In summary, we have employed designed tetranuclear precursors [(R−C≡C−C≡C)Ag]4
i
t
(R = Pr, Bu and chx) to construct a series of heteropolynuclear silver(I)ꢀcopper(I) diynyl
complexes (1−9) that bear a common trigonalꢀplanar CuAg3 cluster core. The tetranuclear
precursors and selected complexes are found to exhibit longꢀlived emission upon
photoꢀexcitation in various media at room temperature and 77 K.
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The present study strongly suggests that the formation of mediumꢀnuclearity Group 11
heterometallic clusters 3–9 is initiated by accretion of additional Ag(I) ions by the ubiquitous
trigonalꢀplanar CuAg3 template through argentophilic interaction, with cooperative
cuprophilic enhancement in the case of compound 9. To our knowledge, the synthesis and
structural characterization of clusters 3ꢀ9 provides the first example of conversion of a
homonuclear coinageꢀmetal cluster into a heteronuclear one of higher nuclearity via
innerꢀcore transformation.
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ASSOCIATED CONTENT
Supporting Information
Experimental details, additional figures, NMR spectra, and Xꢀray crystallographic data in CIF
format. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
tcwmak@cuhk.edu.hk
Notes
The authors declare no competing financial interest.
ACKNOWLEDGEMENTS
We gratefully acknowledge financial support by the Wei Lun Foundation and the
award of a Postdoctoral Research Fellowship to S. C. K. Hau by The Chinese University of
Hong Kong. V.W.ꢀW.Y. acknowledges the support from The University of Hong Kong under
the University Grants Committee Areas of Excellence Scheme (AoE/Pꢀ03/08) from the
Research Grants Council of Hong Kong Special Administrative Region, China.
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6
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New tetranuclear supramolecular precursors [(R−C≡C−C≡C)Ag]4 (R = iPr, tBu and chx) are employed to construct
a series of heterometallic silver(I)-copper(I) alkyl-1,3-diynyl cluster complexes (1-9) that bear a common CuAg3
core (normally trigonal-planar, but can be distorted to pyramidal) consolidated by cupro-argentophilic interaction.
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