Formation of a novel luminescent form of gold(I) phenylthiolate via self-assembly and decomposition of isonitrilegold(I) phenylthiolate complexes

Full text of DOI:10.1021/ja000973z

7146
J. Am. Chem. Soc. 2000, 122, 7146-7147
complete structural characterization difficult, elemental analysis
data agree with an empirical formula of [C6H5SAu]n (1).7
Irradiation of 1 with UV light (TLC lamp, λex ) 254/366 nm)
results in the emission of an orange-red light that is easily visible
to the naked eye in an undarkened room. Measurement of the
solid-state fluorescence spectrum (Figure 1) of 1 revealed two
emission bands at 465 and 643 nm, with the longer wavelength
emission being considerably more intense. The excitation spec-
trum consists of a broad featureless band centered at ap-
proximately 355 nm. Preliminary lifetime data for both emission
bands were fit with single-exponential decay curves to yield
lifetimes of 5.0 ns (465 nm) and 1.1 µs (643 nm), respectively.
The relatively long lifetime of the 643 nm emission is consistent
with its assignment to a triplet metal-centered state, while the
behavior of the 465 nm band indicates that it arises from a ligand-
to-metal charge-transfer-derived state.3
Formation of a Novel Luminescent Form of Gold(I)
Phenylthiolate via Self-Assembly and Decomposition
of Isonitrilegold(I) Phenylthiolate Complexes
Robert E. Bachman,*,† Sheri A. Bodolosky-Bettis,†
Shana C. Glennon,† and Scott A. Sirchio‡
Department of Chemistry, Georgetown UniVersity
Box 571227, Washington, D.C. 20057-1227
Department of Chemistry and Biochemistry
UniVersity of Maryland, College Park, Maryland 20742
ReceiVed March 20, 2000
The tendency of gold(I) centers to form relatively strong
noncovalent interactions with each other has been well established
over the past two decades.1 These “aurophilic” interactions have
been shown to play a critical role in determining both molecular
and supramolecular structure in gold-containing compounds.2
They have also been suggested to produce and/or modify the
luminescent behavior observed for many gold-containing com-
pounds, particularly the gold(I) thiolates.2d,3
Gold(I) thiolates have attracted significant attention over the
past half-century because of their importance in the pharmacology
of gold.1c,4 More recently, the unique properties of the gold-
sulfur bond have been extensively exploited for the development
of thin-film technologies.5 At the molecular level, it has been
suggested that the presence of thiolate ligands should strengthen
the interactions between gold centers relative to those seen for
systems with other anionic ligands, such as the halides.6 As part
of our investigation into the use of aurophilic interactions for the
assembly of well-defined supramolecular architectures, we decided
to examine the behavior of systems with the general formula
RNCAuSPh (R ) n-alkyl). To our surprise, these compounds were
unstable with respect to the loss of the isonitrile ligand and
decomposed to produce a novel, intensely luminescent modifica-
tion of the polymeric species [PhSAu]n. Interestingly, this new
modification of gold(I) phenylthiolate appears to form exclusively
via the self-assembly and decomposition of the isonitrilegold(I)
phenylthiolate complexes that were our intended target.
Figure 1. Emission spectrum for 1 with λex ) 360 nm. Inset A:
Magnification of the emission spectrum in the region around 450 nm
(λex ) 275 nm for this spectrum). Inset B: excitation spectrum for 1
with λem ) 660 nm.
The formation of 1 was surprising to us in light of the relative
stability of the C-Au bond in isonitrile gold(I) complexes1c and
a recent report detailing the structures of two isonitrilegold(I)
thiolate complexes.2c Consequently, we were interested in deter-
mining how 1 is formed in the above process. Replacing the
isonitrile ligand of EtNCAuCl with a longer alkyl chain homolog
suppresses but does not halt the formation of 1. Upon mixing of
C5H11NCAuCl with PhSNa in methanol, there is a several minute
induction period before the formation of 1 is first observed, and
after 30 min the formation of 1 is still incomplete. Separation of
the solution from 1 followed by rapid evaporation of the solvent
yielded a small quantity of C5H11NCAuSPh (2a)8a as colorless
crystals, along with additional amounts of 1. The luminescence
behavior of 1 produced from this reaction is identical to that
produced from EtNCAuCl. By further increasing the length of
the alkyl chain of the isonitrile ligand, the formation of 1 may be
completely halted during the initial reaction. Mixing C7H15-
NCAuCl with methanolic solutions of phenylthiolate produced
Addition of PhSNa to methanolic solutions of EtNCAuCl
results in the almost instantaneous formation of a white micro-
crystalline precipitate that is completely insoluble in all common
solvents. While the insoluble nature of this material makes its
† Georgetown University.
‡ University of Maryland.
(1) For reviews see: (a) Schmidbaur, H. Chem. Soc. ReV. 1995, 391. (b)
Schmidbaur, H. Gold Bull. 1990, 23, 11. (c) Gold: Progress in Chemistry,
Biochemistry and Technology; Schmidbaur, H., Ed.; Wiley: Chichester, 1999.
(2) For recent representative examples see: (a) Bachman, R. E.; Schmid-
baur, H. Inorg. Chem. 1996, 35, 1399. (b) Harwell, D. E.; Mortimer, M. D.;
Knobler, C. B.; Anet, F. A. L.; Hawthorne, M. F. J. Am. Chem. Soc. 1996,
118, 2679. (c) Schneider, W.; Bauer, A.; Schmidbaur, H. Organometallics
1996, 15, 5445. (d) Vickery, J. C.; Olmstead, M. M.; Fung, E. Y.; Balch, A.
L. Angew. Chem., Int. Ed. Engl. 1997, 36, 1179. (e) Hollatz, C.; Schier, A.;
Schmidbaur, H. J. Am. Chem. Soc. 1997, 119, 8115. (f) Hunks, W. J.; Jennings,
M. C.; Puddephatt, R. J. Inorg. Chem. 1999, 38, 5930.
(3) (a) Assefa, Z.; McBurrnett, B. G.; Staples, R. J.; Fackler, J. P., Jr.;
Assmann, B.; Angermair, K.; Schmidbaur, H. Inorg. Chem. 1995, 34, 75. (b)
Assefa, Z.; McBurrnett, B. G.; Staples, R. J.; Fackler, J. P., Jr. Inorg. Chem.
1995, 34, 4965. (c) Jones, W. B.; Yuan, J.; Narayanaswany, R.; Young, M.
A.; Elder, R. C.; Bruce, A. E.; Bruce, M. R. M. Inorg. Chem. 1995, 34, 1996.
(d) Forward, J. M.; Bohmann, D.; Fackler, J. P., Jr.; Staples, R. J. Inorg.
Chem. 1995, 34, 6330. (e) King, C.; Wang, J.-C.; Khan, Md. N. I.; Fackler,
J. P., Jr. Inorg. Chem. 1989, 28, 2145.
(4) (a) Shaw, C. F. Inorg. Perspect. Biol. Med. 1979, 2, 287. (b) Brown,
D. H.; Smith, W. E. Chem. Soc. ReV. 1980, 9, 217.
(5) Bain, C. D.; Whitesides, G. M. Angew. Chem., Int. Ed. Engl. 1989, 28,
506.
(7) Spectral and analytical data for 1: IR (KBr, cm-1) 3065, 1586, 1484,
1450, 1032, 739, 720. Anal. Calcd for [C6H5SAu]n: C, 23.54; H, 1.65; Au,
64.34. Found: C, 23.67; H, 1.57; Au, 64.14.
(8) (a) Spectral data for 2a: IR (KBr, cm-1) 3058, 2954, 2930, 2870, 2248,
1
1580, 1476, 1089, 1030, 741, 720; H NMR (CDCl3, ppm) 7.53 (2H, d, J )
8.1 Hz), 7.10 (2H, t, J ) 7.8 Hz), 6.99 (1H, t, J ) 7.8 Hz), 3.61 (2H, tt, JH-H
) 7.9 Hz, JN-H ) 1.2 Hz), 1.83 (2H, m), 1.42 (4H, m) 0.95 (3H, t, J ) 7.2
Hz). (b) Spectral data for 2b: IR (KBr, cm-1) 3051, 2592, 2932, 2868, 2253,
1
1584, 1471, 1085, 1030, 736, 715; H NMR (CDCl3, ppm) 7.52 (2H, d, J )
(6) (a) Pyykko¨, P.; Li, J.; Runeberg, N. Chem. Phys. Lett. 1994, 218, 133.
(b) Van Calcar, P. M.; Olmstead, M. M.; Balch, A. L. J. Chem. Soc., Chem.
Commun. 1995, 1773.
8.1 Hz), 7.10 (2H, t, J ) 7.9 Hz), 6.99 (1H, t, J ) 7.9 Hz), 3.60 (2H, t, JH-H
) 7.2 Hz), 1.83 (2H, m), 1.42 (2H, m), 1.32 (6H, m), 0.95 (3H, t, J ) 6.9
Hz).
10.1021/ja000973z CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/07/2000

Communications to the Editor
J. Am. Chem. Soc., Vol. 122, No. 29, 2000 7147
no noticeable precipitate after 30 min, and evaporation of the
solvent yielded the isonitrile gold(I) thiolate complex, C7H15-
NCAuSPh (2b), as the only product in good yield.8b However,
crystalline samples of 2b left to stand for several days become
progressively more insoluble and begin to display luminescence
behavior identical to that of samples of 1 prepared in solution
from either EtNCAuCl or C5H11NCAuCl. This process can be
accelerated considerably by gently heating 2 in vacuo; however,
samples of 1 produced in this manner have a slight gold tint,
indicating that a small amount of decomposition occurred as well.
stack together in an antiparallel fashion via van der Waals contacts
between alkyl chains and phenyl rings on adjacent tapes.
This supramolecular motif, combined with the observed solid-
state transformation of 2b, suggests a structure for 1 such as that
shown in Scheme 1. Preliminary attempts to index the powder
XRD pattern of 1 have yielded a unit cell consistent with the
proposed structure. Additionally, the structural results combined
with the catalytic ability of the isonitriles to produce 1 allude to
a possible mechanism for its formation involving the comple-
mentary self-recognition and self-assembly of the isonitrile
complexes, either in solution or as crystallization occurs, followed
by loss of the isonitrile ligand. We are currently working to
confirm the structure of 1 as well as the proposed mechanism
for its formation. Studies are also underway that explore how
the identity of the thiolate influences the physical properties of
related gold(I) thiolate polymers.
The isolation of the isonitrile complexes 2a and 2b, as well as
the solid-state conversion of 2b to 1, provides convincing evidence
that the initial product formed in all of the above reactions is the
isonitrilegold(I) thiolate complex. Furthermore, the rate at which
1 forms is directly correlated with the chain length, and by
extension the volatility, of the isonitrile ligand. An additional
interesting aspect of these results is that the luminescent behavior
of 1 appears to depend on its formation via decomposition of the
isonitrile complexes. Preparation of samples of [PhSAu]n via the
previously reported procedures,9 such as the reaction of Me2SAuCl
with PhSNa or the reaction of PhSH with HAuCl4, produces
materials with the correct elemental composition but that show
no luminescence and are amorphous (as judged by XRD).
However, this amorphous material may be transformed into 1 by
reaction with a catalytic amount (∼5 mol %) of an isonitrile in
hot MeOH. Interestingly, DSC measurements show a difference
in the thermal behaviors of 1 and amorphous [PhSAu]n. The
amorphous material displays a strong exothermic process, which
is absent for 1, just before the onset of decomposition at 255 °C.
The origin of this extra peak is currently unclear, as visual
observation shows only the same decomposition observed for 1
occurring.
Scheme 1. Proposed “Mechanism” for the Self-Recognition
and Assembly of RNCAuSPh Molecules and the Subsequent
Formation of 1 from the Resulting Supramolecular Polymer
To better understand the role that the isonitrile ligands play in
the formation of 1, we undertook structural studies of 2a and
2b.10 At the molecular level, these two complexes differ only in
the length of the alkyl chain and all bonding parameters agree
with expectations. At the supramolecular level, both 2a and 2b
aggregate in an antiparallel fashion into dimeric units via Au-S
(2a, 3.663(2) Å; 2b, 3.6858(15) Å) and weak aurophilic interac-
tions (2a, 3.7858(6) Å; 2b 3.6105(5) Å). The dimer units in turn
come together in a parallel manner via additional weak Au-S
interactions (2a, 4.060(2) Å; 2b, 40224(16) Å), resulting in a motif
that can be described as a “crinkled tape” (Figure 2). The tapes
Acknowledgment. This work was supported by Georgetown Uni-
versity and the donors of the Petroleum Research Fund, administered by
the ACS (No. 31945-G3). Funding for the X-ray diffractometer was
provided by the National Science Foundation (CHE-9115394) and
Georgetown University. The authors thank Prof. Gerry Meyer at The Johns
Hopkins University for assistance in acquiring the lifetime data.
Supporting Information Available: Displacement ellipsoid plots,
tables of crystal data, structure refinement details, atomic coordinates,
bond lengths and angles, and anisotropic parameters for 2a and 2b (PDF).
An X-ray crystallographic file (CIF). This material is available free of
charge via the Internet at http://pubs.acs.org.
JA000973Z
(9) Al-Sa’ady, A. K. H.; Moss, K.; McAuliffe, C. A.; Parish, R. V. J. Chem.
Soc., Dalton Trans. 1984, 1609.
(10) Crystallographic data for 2a: C12H16AuNS, FW 403.28, triclinic space
group P1h (No. 2), a ) 5.5295(4) Å, b ) 7.6073(5) Å, c ) 16.6967(12) Å, R
) 89.0530(10)°, â ) 80.5330(10)°, γ ) 69.0710(10)°, V ) 646.39(8) Å3, Z
) 2, Bruker SMART CCD diffractometer, Mo KR radiation (λ ) 0.71069
Å), T ) -50 °C, 7402 reflections measured, 3095 unique (Rint ) 0.0393).
wR2 ) 0.1055 (all data), R1 ) 0.0433 (2466 data with I > 2σ(I)), GOF )
1.035. Crystallographic data for 2b: C14H20AuNS, FW 431.34, triclinic space
group P1h (No. 2), a ) 5.4405(4) Å, b ) 7.5603(5) Å, c ) 18.7189(12) Å, R
) 87.6570(10)°, â ) 87.1010(10)°, γ ) 70.4210(10)°, V ) 724.26(9) Å3, Z
) 2, Siemens SMART CCD diffractometer, Mo KR radiation (λ ) 0.71069
Å), T ) -100 °C, 8259 reflections measured, 3440 unique (Rint ) 0.0417).
wR2 ) 0.0686 (all data), R1 ) 0.0324 (2715 data with I > 2σ(I)), GOF )
0.865.
Figure 2. Packing diagram for 2a showing the “crinkled tape” motif
formed by the Au-S and Au-Au interactions. The dotted lines indicate
the Au-S and Au-Au interactions.