A functionalized Ag2S molecular architecture: Facile assembly of the atomically precise ferrocene-decorated nanocluster [Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18]

Article abstract of DOI:10.1002/anie.201411944

A ferrocene-based dithiol 1,1′-[fc(C{O}OCH₂CH₂SH)₂] has been prepared and treated with a Ag^I salt to form the stable dithiolate compound [fc(C{O}OCH₂CH₂SAg)₂]_n (fc=[Fe

Full text of DOI:10.1002/anie.201411944

Angewandte
Chemie
DOI: 10.1002/anie.201411944
Cluster Compounds
A Functionalized Ag2S Molecular Architecture: Facile Assembly of
the Atomically Precise Ferrocene-Decorated Nanocluster
[Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18]**
Yiyi Liu, Bahareh Khalili Najafabadi, Mahmood Azizpoor Fard, and John F. Corrigan*
Abstract:
A
ferrocene-based
dithiol
1,1’- photoemission from the two components in the materials.[4b,5]
[fc(C{O}OCH2CH2SH)2] has been prepared and treated with From a structural perspective, Fenske and co-workers have
a
AgI salt to form the stable dithiolate compound developed an extensive library of crystallographically char-
[fc(C{O}OCH2CH2SAg)2]n (fc = [Fe(h5-C5H4)2]). This is acterized Ag2S frameworks, including the molecular struc-
used as a reagent for the preparation of the nanocluster ture of the largest silver sulfide cluster reported to date,
[Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18] which was obtained [Ag490S188(SC5H11)114].[6]
in good yield (dppp = 1,3-bis(diphenylphosphino)propane).
At a more fundamental level, the structurally character-
ized nanocluster [Ag62S13(StBu)32]4+ [7] was reported as the first
T
he chemistry, materials, and biomaterials science of atomi- example of such a large, molecular system displaying lumi-
cally precise Ag2S nanoclusters is currently at the forefront of nescence both in solution and in the solid state. The photo-
research. Interest in these frameworks has continued to physics of the cluster were recently cemented by Zhu and co-
develop since the early preparation of Ag2S clusters and the workers[8] with an in-depth structure–property relationship
investigation of their photophysical properties when bound as study of it and the related framework [Ag62S12(StBu)32]2+
,
guest molecules in zeolitic hosts, a progression which has which contains a “metallic” core. These studies complement
mirrored the development of larger, nanoscopic frame- recent findings showing how silver–thiolate surfaces can
works.[1] Ag2S nanoparticles and nanoclusters continue to stabilize larger Ag cores in atomically precise nanoclusters.[9]
attract interest as a result of their optical properties, their
In addition to their optical properties, the stabilization of
structural diversity, and their potential applications. The the surfaces in these clusters with thiolate ligands offers an
exciton Bohr radius of Ag2S is approximately 2.2 nm and opportunity to incorporate specific chemical properties into
nanoscale assemblies of this material display photolumines- the frameworks.[10] With this in mind, the incorporation of
cence in the near-infrared region of the electromagnetic multiple ferrocenyl units onto nanoclusters of Ag2S was
spectrum.[2] This has led to several reports of Ag2S quantum reported in 2010.[11] The targeted synthesis of polyferrocenyl
dots as novel near-infrared photoluminescent materials for assemblies on inorganic supports is attracting significant
bioimaging in living systems.[3] This environmentally benign research focus because of the electrochemical properties of
material has also attracted interest for photovoltaic applica- the frameworks, which offer potential applications as redox-
tions[4] and because of the fact that silver(I)-based metal– active and/or luminescent sensors,[12] and as electrode materi-
sulfide heterostructures can also display interesting dual als.[13] In metal cluster chemistry, supports for such assemblies
include the aforementioned metal–chalcogen frame-
works,[11,14] gold nanoparticles,[12a,15] polyoxometalates[16]
[*] Y. Liu, B. Khalili Najafabadi, M. Azizpoor Fard,
and, recently, tin–chalcogenide clusters as developed by
Prof. Dr. J. F. Corrigan
Dehnen and co-workers.[17]
Department of Chemistry, The University of Western Ontario
London, Ontario, N6A 5B7 (Canada)
E-mail: corrigan@uwo.ca
We
had
previously
prepared
the
reagent
Fc(C{O}OCH2CH2SSiMe3) (Fc = [CpFe(C5H4)]), which,
when treated with silver acetate and S(SiMe3)2, yielded
surface functionalized, high-nuclearity Ag2S clusters with
ferrocene-rich surfaces.[18] Despite their apparent size mono-
dispersity single crystals proved elusive, however through the
combination of high-resolution TEM (HRTEM) and addi-
tional analytical methods, idealized molecular formulae
including [Ag36S9(SCH2CH2O{O}CFc)18(PPh3)3] could be
derived.[18] These formulations are in keeping with data
obtained for the crystallographically characterized
[Ag48S6(SCH2Fc)36] which contains a shorter tether between
the ferrocenyl units and the surface thiolate ligands.[11]
However, the retention of more functionalized ferrocenyl
units is important in the context of developing sensitivity
towards analytes[12,19] and using Ag2S as a monodisperse
support in this regard has tremendous potential. We specu-
lated that the preparation of bidentate ferrocenyl–chalcogen
Prof. Dr. J. F. Corrigan
Centre for Advanced Materials and Biomaterials Research
The University of Western Ontario
London, Ontario, N6A 5B7 (Canada)
[**] We thank the Natural Sciences and Engineering Research Council
(NSERC Canada) for financial support for this research. The Canada
Foundation for Innovation, NSERC, and the University of Western
Ontario are also acknowledged for equipment funding. The authors
thank Dr. M. Hessari for the help with cyclic voltammetry experi-
ments. Some research described in this paper was performed using
beamline 08B1-1 at the Canadian Light Source, which is supported
by the Canada Foundation for Innovation, NSERC, the National
Research Council Canada, the Canadian Institutes of Health
Research, the Government of Saskatchewan, Western Economic
Diversification Canada, and the University of Saskatchewan.
dppp=1,3-bis(diphenylphosphino)propane; fc=[Fe(h5-C5H4)2].
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201411944.
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reagents would limit surface flexibility and lead to an
increased stability/rigidity of the corresponding clusters,
thus permitting the formation of single crystals suitable
for X-ray diffraction analysis. Herein, we describe
a
surprisingly facile route to the nanoscale cluster
[Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18] (1) (dppp = 1,3-
bis(diphenylphosphino)propane; fc = Fe(h5-C5H4)2) which
was obtained in good yield. The structural characterization
of 1 by single-crystal X-ray diffraction is also reported.
One useful strategy to access to Ag/S/SR clusters involves
the addition of “S2ꢀ” to a preformed silver(I) thiolate
coordination polymer [AgSR]n. Convenient sources of the
sulfide ion include the use of CS2 and S(SiMe3)2.[6,20] The
development of tailored [AgSR]n polymers offers an avenue
through which a specific functional group might be readily
incorporated onto
a
Ag2S cluster. In this vein,
[fc(C{O}OCH2CH2SAg)2]n (2) was prepared from 1,1’-
[fc(C{O}OCH2CH2SH)2] upon reaction with two equivalents
of AgSO3CF3, which was then used as a precursor for cluster
1. The dithiol 1,1’-[fc(C{O}OCH2CH2SH)2] itself can be
conveniently prepared from 1,1’-[fc(C{O}Cl)2] (Scheme 1
and Supporting Information).
Scheme 1. Synthesis of [fc(C{O}OCH2CH2SAg)2]n 2.
Although insoluble in all common organic solvents,
[fc(C{O}OCH2CH2SAg)2]n (2) can be dissolved with excess
dppp (2 equiv) in CH2Cl2. Treatment of these solutions with
S(SiMe3)2 (0.3 equiv) at room temperature proceeds with
a color change from orange to dark red. Layering reaction
solutions with diethyl ether lead to the selective isolation of
the cluster [Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18] (1) in
high yield as dark red crystals with other side products left in
solution.
Figure 1. a) Ball-and-stick diagram of the molecular structure of
[Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18] (1). H atoms have been omit-
ted for clarity. b) Ball-and-stick diagram of the Ag74S55 core of 1.
c) Space-filling diagram of the Ag74S55 core with the C atoms of dppp
omitted to show the distribution of ferrocenyl ligands in 1. Atom
colors in (a–c): Ag=blue, S=yellow, P=green, O=red, Fe=orange,
C=gray.
Cluster 1 was analyzed by single-crystal X-ray diffraction
to elucidate its structural features (Figure 1). Single crystals of
1 are highly solvated and only weakly diffracting. Although
a structural model of the Ag2S core could be obtained from
diffraction data using a conventional, sealed-tube X-ray
source, data suitable to refine the entire structure and thus
the surface characteristics required a brighter source and
were collected using a synchrotron beam line at the Canadian
Light Source (18 keV; l = 0.68877 ꢀ). Cluster 1 was solved
C and O atoms were refined isotropically. One of the three
crystallographically independent ferrocenyl units (thus six of
the eighteen) displayed disorder. A two-site model for the
ferrocenyl dithiolate ligand “Fe1” was satisfactorily refined
with 50:50 occupancy. For clarity, the disorder is not shown in
Figure 1.
The rather symmetrical Ag74S55 core ( ꢁ 1.7 ꢁ 1.5 ꢁ
1.4 nm3) of cluster 1 consists of seventy-four silver centers
bonded to nineteen sulfide (S2ꢀ) and thirty-six thiolate ligands
(each 1,1’-[fc(C{O}OCH2CH2S)2]2ꢀ providing two). The over-
all dimensions of 1 (including the ferrocenyl shell) are
ꢀ
and refined in the space group R3; a central sulfide resides
ꢀ
about a crystallographic 3 site. All Ag, S, P, and (non-
disordered) Fe atoms were refined anisotropically whereas all
2
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approximately 3.1 ꢁ 3.0 ꢁ 3.0 nm3. The central sulfide adopts diffraction. The preparation and isolation of 1 complements
a m8-bridging coordination model whereas the other 18 the employed synthetic strategy which uses silver thiolate
sulfides form m6 bridges to Ag centers. Thirteen of the S2ꢀ polymers (AgSR) and S(SiMe3)2 as precursors for the
centers are arranged in a (non-bonded) centered icosahedral preparation of high-nuclearity Ag2S clusters.[6,20b] Use of this
arrangement in the cluster core whereas the six additional synthetic method offers potential to tune the R substituent in
S
2ꢀ centers are closer to the cluster surface. The surface the nanocluster molecular design. We are further developing
thiolates form m2, m3, or m4 bridges to Ag atoms. The the reaction chemistry of [fc(C{O}OCH2CH2SAg)2]n 2 and are
AgI centers in cluster 1 adopt three coordination geometries: investigating the preparation of other functionalized silver
distorted linear, trigonal planar, or distorted tetrahedral. The thiolates [AgSR]n for nanocluster formation.
arrangement of the six dppp ligands at the cluster surface can
be described as being at the corners of an octahedron if each
_
PP is considered as occupying one vertex position.
Experimental Section
Of the eighteen [fc(C{O}OCH2CH2S)2]2ꢀ ligands, the
twelve that were not disordered display a conformation with
the two substituents of the two cyclopentadienyl rings rotated
at angle of circa 31.58 with respect to each other along the
Synthesis of [fc(C{O}OCH2CH2SH)2]: [fc(C{O}OCH2CH2Br)2]
(0.41 g, 0.84 mmol) was dissolved in tetrahydrofuran (THF; 25 mL)
and the solution was cooled to ꢀ108C. S(SiMe3)2 (0.53 mL, 2.5 mmol)
was added, followed by tetrabutylammonium fluoride (TBAF; 0.48 g,
1.8 mmol) in THF (15 mL). The reaction was stirred for 10 min at
ꢀ108C and the mixture was subsequently stirred at RT for 3.5 h. The
solvent was removed under vacuum, and THF (35 mL) was used to
dissolve the residue. Heptane (35 mL) was added to the flask and the
majority of THF was then removed under vacuum. The orange
solution was filtered through dry Celite to remove the precipitated
salts and heptane was removed under vacuum to yield
[fc(C{O}OCH2CH2SH)2] as a dark orange solid. Separation by flash
chromatography on a silica gel column using ethyl acetate (EtOAc) as
eluent can be used to purify the product; however, it was of sufficient
purity to use for the preparation of 2 (below). Yield = 0.25 g (75%).
1H NMR (400 MHz, CDCl3, 238C): d = 4.85 (m, 4H, CH), 4.45 (m,
4H, CH), 4.35 (t, 3J = 6.4 Hz, 4H, CH2), 2.86 (dt, 3J = 6.4 Hz, 2J =
ꢀ
ꢀ
=
C5 Fe C5 axis (Figure 1). The two C O moieties of the
[fc(C{O}OCH2CH2S)2]2ꢀ are oriented in the same direction
and are essentially coplanar with their respective C5 rings to
which they are bonded. The two C5 rings themselves are close
to being parallel. The six disordered [fc(C{O}OCH2CH2S)2]2ꢀ
=
were satisfactorily refined with the C O oriented in opposite
directions on the two C5 rings.
Silver–sulfide bond lengths for 1 range between 2.381(7)–
2.968(7) ꢀ whereas those for silver–thiolate interactions
measure between 2.372(7)–2.800(7) ꢀ. Ag···Ag distances in
the cluster fall within the range 2.901(3)–3.374(3) ꢀ. Similar
distances/bond lengths are reported for the comparably sized
cluster [Ag70S16(SPh)34(PhCO2)4(triphos)4] (triphos = 1,1,1-
tris{(diphenylphosphino)methyl}ethane).[21] Ag···Ag distan-
8.0 Hz, 4H, CH2), 1.60 ppm (t, J = 8.0 Hz, 2H, SH); 13C{1H} NMR
(100.5 MHz, CDCl3): d = 169.8 (C(O)), 73.0 (CH), 72.4 (C), 71.7
(CH), 65.7 (CH2), 23.5 ppm (CH2); HRMS: m/z: calcd for
C16H18Fe1O4S2: 393.99961; found: 393.99860.
Synthesis of [fc(C{O}OCH2CH2SAg)2]n 2: To a solution of
fc(C{O}OCH2CH2SH)2 (0.23 g, 0.59 mmol) in CH3CN (20 mL) was
added a solution of AgSO3CF3 (0.38 g in 10 mL CH3CN, 1.5 mmol).
The mixture stirred rapidly for 5 min. NEt3 (0.19 mL, 1.4 mmol) was
added to the reaction mixture which resulted in the formation of an
orange precipitate of [fc(C{O}OCH2CH2SAg)2]n. The orange precip-
itate was collected by filtration and washed with CH3CN (4 ꢁ 10 mL).
The solid was dried under vacuum. Yield = 0.13 g (36%). Elemental
analysis calcd. (%) for C16H16O4S2Ag2Fe: C 31.62, H 2.65, S 10.52;
found: C 32.25, H 2.76, S 9.67; m.p.: 173–1778C.
3
ꢀ
ces for 1 confirmed that there is no significant Ag Ag
interaction,[22] consistent with the + 1 oxidation state assigned
for all silver centers. The space-filling model (see the
Supporting Information) clearly demonstrates how the
ligands effectively shield the Ag74S55 core and also shows
clearly how the 1,1’-[fc(C{O}O)2] units remain exposed at the
cluster surface.
Although crystals of 1 are poorly soluble in organic
solvents, they do dissolve in CH2Cl2 in sufficient concentra-
tions for analysis by cyclic voltammetry ( ꢁ 0.003 mm). One
quasi-reversible redox wave (ipa/ipc ꢁ 1.1; where ipa is the
anodic peak current and ipc is the cathodic peak current) is
detected with the E1/2 value (E1/2 = (Epa + Epc)/2) at 949 mV
and a DE value (DE =j EpaꢀEpc j) of 168 mV (vs. Ag/AgCl;
scan rate = 100 mVsꢀ1). The redox wave can be assigned to
the one-electron oxidation/reduction of the iron centers of the
ferrocenyl moieties and the peak potentials are similar to
those detected for [fc(C{O}OCH2CH2Br)2] (E1/2 = 980 mV;
see the Supporting Information).[12a,15] The shape and rever-
sibility of the redox wave for the solution of 1 suggest that the
molecular architecture remains intact upon oxidation of these
FeII centers and that there is limited absorption of the cluster
onto the electrode surface, unlike what was detected for
[Ag36S9(SCH2CH2O{O}CFc)18(PPh3)3].[18]
Synthesis
and
characterization
of
[Ag74S19(dppp)6-
(fc(C{O}OCH2CH2S)2)18] 1: The silver thiolate 2 (0.10 g, 0.16 mmol)
was dissolved in CH2Cl2 (20 mL) with dppp (0.14 g, 0.33 mmol) by
stirring for 1.5 h to yield an orange solution. S(SiMe3)2 (0.01 mL,
0.05 mmol) was then added and the reaction mixture was stirred for
two hours at room temperature. The resultant solution was dark red in
color. The mixture was layered with Et2O (20 mL) and stored in
subdued light for 3–4 days to yield dark-red single crystals of 1. The
structure was identified by X-ray crystallography to be [Ag74S19-
(dppp)6(fc(C{O}OCH2CH2S)2)18]. Yield: 30 mg (63%). Increasing the
relative amount of S(SiMe3)2 in reactions led to a decreased yield of 2
and the formation of dark amorphous materials. Elemental analysis
calcd. (%) for Ag74S55Fe18C450H444P12O72: C 29.83, H 2.47, S 9.70;
found: C 28.97, H 2.32, S 9.63.
The structure of 1 was solved with direct methods and refined
using the SHELX suite of crystallographic software.[23] Crystal data
ꢀ
for 1: C450H444Ag74Fe18O72P12S55, space group R3, a = 36.775(19), b =
36.775(19), c = 41.225(19) ꢀ, g = 1208, V= 48283(42) ꢀ3, Z = 3, R1 =
0.0916 for reflections with I > 2s(I), wR2 = 0.2639 for all data. CCDC-
1038495 (complex 1), 1038496 [fc(C{O}OCH2CH2Br)2], 1038497
[fc(C{O}OCH2CH2Br)COOH], and 1038498 [(fc(C{O}O{O}C))2]
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
The formation and characterization of 1 demonstrates
a straightforward approach for the surface modification of
Ag2S nanoclusters and shows that bidentate ferrocenyl
chalcogen reagents facilitate the structural characterization
of such decorated nanoclusters by single-crystal X-ray
Angew. Chem. Int. Ed. 2015, 54, 1 – 5
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Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
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Received: December 11, 2014
Revised: February 1, 2015
Published online: && &&, &&&&
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Keywords: cluster compounds · iron · metallocenes · silver ·
structure elucidation
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4
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 1 – 5
These are not the final page numbers!

Angewandte
Chemie
Communications
Cluster Compounds
All wrapped up! A ferrocenyl-based
dithiol reagent has been employed as
a precursor for the preparation of a sur-
face-functionalized Ag74S55 nanocluster
[Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18]
(dppp=1,3-bis(diphenylphosphino)-
propane, fc=[Fe(h5-C5H4)2]). The elec-
trochemical properties and single-crys-
talX-ray structure of the cluster are
reported (atom colors: Ag=blue, S=
yellow, P=green, O=red, Fe=orange,
C=gray).
Y. Liu, B. Khalili Najafabadi,
M. Azizpoor Fard,
J. F. Corrigan*
&&&& — &&&&
A Functionalized Ag2S Molecular
Architecture: Facile Assembly ofthe
Atomically Precise Ferrocene-Decorated
Nanocluster[Ag74S19-
(dppp)6(fc(C{O}OCH2CH2S)2)18]
Angew. Chem. Int. Ed. 2015, 54, 1 – 5
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!