Self-Assembly of a Au16 ring via metal-metal bonding interactions

Article abstract of DOI:10.1002/asia.201403448

Metal-metal bonding interactions have been employed as an efficient strategy to generate a number of unique gold(I) metallo-macrocycles with fascinating functions. The self-assembly, crystal structure and emission property of novel nest-like tetramer 1

Full text of DOI:10.1002/asia.201403448

CHEMISTRY
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Accepted Article
Title: Self-assembly of Au16 Ring via Metal-Metal Bonding Interactions
Authors: ShuYan Yu; Yaqing Wang; XuanFeng Jiang; Hao Li
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Chemistry - An Asian Journal
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Self-assembly of Au16 Ring via Metal-Metal Bonding Interactions
Ya-Qing Wang,[a] Xuan-Feng Jiang*,[b] and Shu-Yan Yu*[a],[b]
Abstract: Metal-metal bonding interactions have been employed as an
efficient strategy to generate a numerous of unique gold(I) metallo-
macrocycles with fascinating functions. The self-assembly, crystal
structure and emission property of novel nest-like tetramer 14, namely,
phenyl (PPh3)-H and methylene-H, respectively. For complex
1•2BF4– , the featured broad peaks ranged from 3.83 to 4.25 ppm
were assigned to methylene-H from dctp2- ligands and dppm di-gold
motifs, while the upfield chemical shift at 6.65-6.78 ppm were
corresponded to aromatic protons from dctp2- ligand. The proton
resonances of the triphenylphosphine appear as a set of overlap
signal at δ 7.90-7.02 ppm. The formation of the monomer 1 was also
supported by CSI-MS showing the mass to charge ratio (m / z) peak
971.8 for [(dppm)2Au4(dpt2-)]2+ (Fig. S6).
{[Au4(μ-dppm)2(μ-dctp2-)](BF4)2}4•(CH3CN)2
(dppm
=
bis(diphenylphosphino)methane, dctp2- = N,N’-bis(dicarbodithioate)-2,11-
diaza[3.3]paracyclophane) was reported. The complex has been
characterized by single-crystal X-ray diffraction analysis, 1H NMR, 13C
NMR, CSI-MS spectrometry. The aggregate demonstrates the sixteen
gold(I) atoms array in the ring with the circumference of 50.011(68)Å
generated by AuI∙∙∙AuI attractions. UV–visible and luminescence
spectroscopies revealed that such novel AuI∙∙∙AuI bonding metallo-
macrocycle exhibited yellow phosphorescence.
The study of polynuclear Au(I) complexes has attracted
a
considerable current interest because of their unusual structures and
catalytic, optical, photochemical and electronic properties [1−9]. The
Au(I)···Au(I) bonding interactions, which are similar in strengths with
hydrogen bonds, have emerged as structural motifs in the design
and construction of metal-organic supramolecular aggregates. Such
gold-containing assembles received particular attention because of
not only their diverse structures, such as polynuclear metallo-
macrocycles[10], cages[11] and clusters[12], but also owing to their
intriguing spectroscopic properties[2d,3a,13−16]. Until now, there are
some reported small rings with Au(I)···Au(I) bonding interactions like
Au3 (triangle)[17], Au4 (square)[2e,3a], Au5 (pentagon)[18], however, the
self-assembly of well-defined large-ring aggregates containing
continuous metal–metal bonds (M–M type) or bonding interactions
(M···M type) remains a challenge. Very recently, our group has
increased the number of Au(I) to construct the chiral giant gold rings
from Au12 to Au16 and Au36, the largest member of the gold ring
family to date, which using the unique Au(I)···Au(I) bonding
Scheme 1. Synthetic route for gold(I) tetramer 14. The yellow bands represent the
[(dppm)Au2]48+ half-rings, and the blue arch-bridges represent the dctp2- ligands.
interactions-directed stepwise macrocyclization strategy[10]
.
Based on previous work, we designed a new ligand to self-assembly
a large size of crown-like Au16 ring in this communication. Such large
gold ring exhibited yellow phosphorescence and may serve as
potential luminescent materials for chemical sensors and OLEDs.
A solution of the dicarbodithioate ligand (dctp) in methanol was
added dropwise to a white suspending solution of (dppm)Au2Cl2 in
methanol for 24 hrs at room temperature. Recrystallization by
diffusion of diethyl ether into a MeCN solution afforded light yellow
crystals. As shown in Figure S4, the 1H-NMR spectrum of 1•2BF4¯ in
CD3CN exhibited broad signals in comparing with free organic ligand
in the metal-organic macrocyclic architecture. All of signals in the
spectra could be ascribed to four kinds of protons, phenyl (dctp2-)-H,
¯
Figure 1. The perspective view of 14. The eight BF4 anions located
outside the cationic macrocycle, all the H atoms and Benzene rings are
omitted for clarity (gold-Au, yellow-S, purple-P, gray-C).
Single-crystal X-ray analysis has revealed that the molecular
structure of the cation of tetramer 14 (see Fig. 1) consists of sixteen
gold(I) atoms arranged in a slightly distorted ring including the half-
ring 1 (Au1, Au2, Au3, Au4, Au4(A), Au3(A), Au2(A) and Au1(A))
and the half-ring 2 (Au8, Au7, Au6, Au5, Au5(A), Au6(A),Au7(A) and
Au8(A)). Figure 1 shows the perspective view of the cation of 14,
with each monomer combined by two {(dppm)Au2} units orientedly
linked by a bridging dctp2- ligand but two gaps because of the larger
inducing group, phenyl. The average distance between
intermolecular Au(I)···Au(I) bonding is 2.949Å (monomer to
monomer) and the gap is 4.404Å (between eight-member half rings).
The tetramer can be viewed as making up of two halves a dimer-to-
dimer coupling. The two monomers, [(dppm)Au1…Au2-dctp-Au5…
Au6(dppm)] and [(dppm)Au3…Au4-dctp-Au7-Au8-(dppm)] are linked
[a] Ya-qing Wang and Dr. Prof. Shu-yan Yu
Laboratory for Self-Assembly Chemistry, Department of Chemistry,
Renmin University of China, Beijing 100872, P.R. China.
E-mail: yusy@ruc.edu.cn
[b] Dr. Xuan-feng Jiang
Beijing Key Laboratory for Green Catalysis and Separation, Department
of Chemistry and Chemical Industry, College of Environmental and
Energy Engineering, Beijing University of Technology, Beijing 100124,
P.R. China.
Supporting information for this article is given via a link at the end of the
document.

Chemistry - An Asian Journal
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together by two intermolecular Au(I)…Au(I) interactions (Au2…Au3
and Au6 … Au7), affording a dimer. Similarly, the other two
monomers formed another dimer. The two dimers were coupled by
two intermolecular Au(I)…Au(I) interactions(Au4…Au4(A)) and Au5
…Au5(A)) to form a ring-like framework of 16 Au(I) centers. The
average intramolecular Au(I)…Au(I) separation is 2.86 Å, which was
about 0.18Å shorter than the intermolecular ones. It has proved that
Au(I)…Au(I) interactions exist in the molecule for both are shorter
than the sum of van der Waals radii for gold (3.32Å)[19]. In addition,
the 16 Au(I) centers are not in the same plane. The perimeter of the
gold ring is about 50.011(68) Å. Inside of the gold ring are four
cross-shaped dithiocarbamate linkers; outside of the ring are eight
dppm units which are arranged in a distorted array.
Figure 2 shows the UV-visible absorption spectrum of solutions of 1
in MeCN at 298K. The electronic absorption spectra of 1(Figure 2a)
in MeCN at 298 K are dominated by high-energy absorption bands
at 272 nm (εmax = 149,207 M−1 cm−1), which is assigned as metal-
perturbed intraligand transitions of the dppm and/or thiocarbamate
ligands with reference to the previous studies on Au(I) thiolate
complexes[2,10]. There are additional low-energy shoulders at around
408 nm (εmax = 6231 M−1 cm−1) that become more apparent with
increasing concentration. The low-energy shoulders are tentatively
assigned as ligand-to-metal charge transfer LMCT (thiocarbamate-
to-gold) transitions.
Upon excited at 390nm, 1 emit at 500nm in deoxygenated
acetonitrile solution at 298 K. With reference to the previous reports
[2,10]
on the luminescence studies of Au(I) thiolate complexes,
the
Absorbtion(UV-Vis) and luminescence properties
emission bands are tentatively assigned to be derived from triplet
excited states of metal-centered (ds/dp) and ligand-to-metal charge
transfer character that has been modified by AuI···AuI interactions.
In summary, we present a novel Au16 ring with continuous
Au(I)···Au(I)
interactions
self-assembled
from
bridging
dithiocarbamate linkers and dinuclear terminal blocks. The
Au(I)···Au(I) bonding interactions have provided the driving force to
induce the self-assembly of
a
unique gold(I)-containing
supramolecular metallo-macrocycle. NMR, CSI-TOF-MS, single-
crystal X-ray diffraction analysis, UV-Vis and luminescence
spectroscopies were used to characterize the metallo-macrocycle.
Such nest-like tetrameric gold (I) ring exhibit triplet yellow
phosphorescence in solution, which could be exploited as potential
phosphorescent sensor materials via host-guest and metal-metal
bonding
interaction.
Experimental Section
N,N’-bis(dicarbodithioate)-2,11-diaza[3.3]paracyclophane To
a
stirred
suspension of NaH (60%, 3.8g, 95.0mmol) in DMF (180ml) was added a
mixture of 1,4-bis(bromomethyl)benzene (11.9g, 45.2mmol) and p-
toluenesulfonamide (7.6g, 45.2mmol) in DMF (180ml) over a period of 5hrs
under nitrogen atmosphere, the temperature being kept at 50oC. After
additional stirring and heating for 5hrs, the still hot yellow filtrate to give 10.8 g
of a pale yellow precipitate. Separation by column chromatography (Wako-gel
C-300, CH2Cl2/CH3COOC2H5 = 40:1) afforded Ts2N2[32]PC (660.8mg). The
removal of the tosyl groups was achieved by treatment with a large excess of
LiAlH4 under mild conditions (40-50oC, THF, 18hrs) to yield the 2,11-
diaza[3.3]paracyclophane (H2N2[32]PC) in 88% yield. Carbon disufide reacted
with the aqueous solution of H2N2[32]PC easily produced the ligand dctp,
N,N’-bis(dicarbodithioate)-2,11-diaza[3.3]paracyclophane.
Au16(μ-dppm)8(μ- dctp2-)4](BF4)8(CH3CN)2 A solution of ligand (9.4 mg, 0.02
mmol) in methanol (3ml) was added dropwise to a white suspending solution
of (dppm)Au2Cl2 (34 mg, 0.04mmol) in methanol (2ml) over 10 minutes. The
reaction mixture turned yellow immediately and remained clear. After being
stirred at room temperature for 24 hrs, an excess of NaBF4 in methanol (2ml)
was added to separate the product as light yellow powder. Upon removal of
the solvent, the product was washed with methanol and dried in vacuum-
desiccator, yield 49.0mg, 83.8%. Recrystallization by diffusion of diethyl ether
into a MeCN solution afforded light yellow crystals.
Figure. 2 UV-vis spectral traces of 14 in MeCN solution. The insert shows the
dimerization plot for a monomer-dimer equilibrium at various concentrations, top;
Fluorescence emission spectrum (right) of 14 in MeCN solution, down.
Empirical formula [C272H240N8P16S16Au16][BF4]8[CH3CN]2, formula weight
8557.58, temperature 293(2)K, crystal system: monoclinic, space group C 2/c,
a = 31.5257(66)Å, b = 44.6773(74)Å, c = 26.3487(41)Å, β = 101.164(9)°, V =
36409.43(6564)Å3, and Z = 8. Data collections were performed at 293(2)K on
a Bruker-AXS Smart CCD diffractometer (graphite-monochromated Mo Kα

Chemistry - An Asian Journal
10.1002/asia.201403448
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radiation, λ = 0.71073Å). The raw frame data for 14 was integrated into
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Acknowledgements
This project was supported by the National Natural Science
Foundation of China (no. 91127039, 21471011) and the Research
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Importation and Development of High-Caliber Talents Project of
Beijing Municipal Institution. We also acknowledge the support from
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Ya-qing Wang, Xuan-feng Jiang* and
Shu-yan Yu*
Gold ring: A novel metallo-macrocyle
composing of 16 gold(I) atoms self-
assembled via strong AuI…AuI
Page No. – Page No.
Title
bonding interaction in the solid state
Self-assembly of Au16 Ring via Metal-
Metal Bonding Interactions