Strong intra- and intermolecular aurophilic interactions in a new series of brilliantly luminescent dinuclear cationic and neutral Au(I) benzimidazolethiolate complexes

Article abstract of DOI:10.1021/ic701763x

The structural and photophysical properties of a new series of cationic and neutral Au(I) dinuclear compounds (1 and 2, respectively) bridged by bis(diphenylphosphino)methane (dppm) and substituted benzimidazolethiolate (X-BIT) ligands, where X = H (a), Me (b), OMe (c), and Cl (d), have been studied. Monocationic complexes, [Au₂-(M-X-BIT)(μ-dppm)](CF ₃CO₂), were prepared by the reaction of [Au ₂(μ-dppm)](CF₃CO₂)₂ with 1 equiv of X-BIT in excellent yields. The cations 1a-1d possess similar molecular structures, each with a linear coordination geometry around the Au(I) nuclei, as well as relatively short intramolecular Au(I)...Au(I) separations ranging between 2.88907-(6) A for 1d and 2.90607(16) A for 1a indicative of strong aurophilic interactions. The cations are violet luminescent in CH ₂Cl₂ solution with a λ_em^max of ca. 365 nm, assigned as ligand-based or metal-centered (MC) transitions. Three of the cationic complexes, 1a, 1b, and 1d, exhibit unusual luminescence tribochromism in the solid-state, in which the photoemission is shifted significantly to higher energy upon gentle grinding of microcrystalline samples with ΔE = 1130 cm^-1 for 1a, 670 cm^-1 (1b), and 870 cm^-1 (1d). The neutral dinuclear complexes, [Au₂(μ-X- BIT)(μ-dppm)] (2a-2d) were formed in good yields by the treatment of a CH₂Cl₂ solution of cationic compounds (1) with NEt ₃. 2a-2d aggregate to form dimers having substantial intra- and intermolecular aurophilic interactions with unsupported Au(I)...Au(I) intermolecular distances in the range of 2.8793(4)-2.9822(8) A, compared with intramolecular bridge-supported separations of 2.8597(3)-2.9162(3) A. 2a-2d exhibit brilliant luminescence in the solid-state and in DMSO solution with red-shifted λ_em^max energies in the range of 485-545 nm that are dependent on X-BIT and assigned as ligand-to-metal-metal charge transfer (LMMCT) states based in part on the extended Au...Au...Au...Au interactions.

Full text of DOI:10.1021/ic701763x

Inorg. Chem. 2008, 47, 957−968
Strong Intra- and Intermolecular Aurophilic Interactions in a New Series
of Brilliantly Luminescent Dinuclear Cationic and Neutral Au(I)
Benzimidazolethiolate Complexes
Jacob Schneider, Young-A Lee, Javier Pe´rez, William W. Brennessel, Christine Flaschenriem, and
Richard Eisenberg*
Department of Chemistry, UniVersity of Rochester, Rochester, New York 14627
Received September 7, 2007
The structural and photophysical properties of a new series of cationic and neutral Au(I) dinuclear compounds (1
and 2, respectively) bridged by bis(diphenylphosphino)methane (dppm) and substituted benzimidazolethiolate (X
BIT) ligands, where X H (a), Me (b), OMe (c), and Cl (d), have been studied. Monocationic complexes, [Au2-
-X BIT)( -dppm)](CF3CO2), were prepared by the reaction of [Au2( -dppm)](CF3CO2)2 with 1 equiv of X BIT in
excellent yields. The cations 1a 1d possess similar molecular structures, each with a linear coordination geometry
−
)
(
µ
−
µ
µ
−
−
around the Au(I) nuclei, as well as relatively short intramolecular Au(I)‚‚‚Au(I) separations ranging between 2.88907-
(6) Å for 1d and 2.90607(16) Å for 1a indicative of strong aurophilic interactions. The cations are violet luminescent
max
in CH2Cl2 solution with a λem of ca. 365 nm, assigned as ligand-based or metal-centered (MC) transitions. Three
of the cationic complexes, 1a, 1b, and 1d, exhibit unusual luminescence tribochromism in the solid-state, in which
the photoemission is shifted significantly to higher energy upon gentle grinding of microcrystalline samples with
∆E
1
1
1
)
1130 cm- for 1a, 670 cm- (1b), and 870 cm- (1d). The neutral dinuclear complexes, [Au2(
µ −BIT)(µ-
-X
−2d) were formed in good yields by the treatment of a CH2Cl2 solution of cationic compounds (1) with
dppm)] (2a
NEt3. 2a
−
2d aggregate to form dimers having substantial intra- and intermolecular aurophilic interactions with
2.9822(8) Å, compared with
2.9162(3) Å. 2a-2d exhibit brilliant luminescence in the
545 nm that are dependent
unsupported Au(I)‚‚‚Au(I) intermolecular distances in the range of 2.8793(4)
intramolecular bridge-supported separations of 2.8597(3)
solid-state and in DMSO solution with red-shifted λem energies in the range of 485
−
−
max
−
on X
−BIT and assigned as ligand-to-metal−metal charge transfer (LMMCT) states based in part on the extended
Au‚‚‚Au‚‚‚Au‚‚‚Au interactions.
Introduction
aggregate through closed-shell “aurophilic” interactions6-8
plays a key role in their luminescence properties and in
In recent years, there has been a developing interest in
luminescent metal complexes because of their possible
application as dopant emitters in organic light emitting device
technology.1,2 In this context, Au(I) complexes represent
potential targets of opportunity, owing to their intense, long-
lived luminescence in the solid-state with a wide range of
emission energies.3-5 The tendency of Au(I) complexes to
determining their consequent solid-state structures.9-13 Ad-
ditionally, these types of closed-shell aggregates may also
be influenced by hydrogen-bonding interactions between Au-
(I) complexes.11,14-17 A number of different emitting states
have been proposed for Au(I) complexes including metal-
(4) Wang, Q.-M.; Lee, Y.-A.; Crespo, O.; Deaton, J.; Tang, C.; Gysling,
H. J.; Gimeno, M. C.; Larraz, C.; Villacampa, M. D.; Laguna, A.;
Eisenberg, R. J. Am. Chem. Soc. 2004, 126 (31), 9488-9489.
(5) Ma, Y.; Zhou, X.; Shen, J.; Chao, H.-Y.; Che, C.-M. Appl. Phys. Lett.
1999, 74 (10), 1361-1363.
* To whom correspondence should be addressed. Email: eisenberg@
chem.rochester.edu.
(1) Holder, E.; Langeveld, B. M. W.; Schubert, U. S. AdV. Mater.
(Weinheim, Germany) 2005, 17 (9), 1109-1121.
(2) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord. Chem. ReV. 2006,
250 (15+16), 2093-2126.
(3) Ramamurthy, V.; Schanze, K. S. Mol. Supramol. Photochem. 1999,
4, 345.
(6) Schmidbaur, H.; Graf, W.; Mu¨ller, G. Angew. Chem., Int. Ed. Engl.
1988, 27 (3), 417-419.
(7) Scherbaum, F.; Huber, B.; Mu¨ller, G.; Schmidbaur, H. Angew. Chem.,
Int. Ed. Engl. 1988, 27 (11), 1542-1544.
(8) Scherbaum, F.; Grohmann, A.; Huber, B.; Kru¨ger, C.; Schmidbaur,
H. Angew. Chem., Int. Ed. Engl. 1988, 27 (11), 1544-1546.
10.1021/ic701763x CCC: $40.75
Published on Web 01/11/2008
© 2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 3, 2008 957

Schneider et al.
Scheme 1
sion was turned on upon the gentle crushing of colorless,
nonemissive crystals of the complexes.28 In the present study,
three of the cationic complexes exhibit luminescence tribo-
chromism, but the behavior differs from that reported earlier.
From the structural characterization of the new complexes,
we are able to assess the extent and magnitude of aurophilic
interactions in these complexes and compare them with those
found in the previously reported systems. Like the X-TU
complexes, the cationic X-BIT complexes 1 exhibit sig-
nificant intramolecular Au‚‚‚Au interactions but significantly
different intermolecular contacts, whereas the neutral com-
plexes 2 show evidence of strong inter- as well as intramo-
lecular Au‚‚‚Au interactions, as was seen for the correspond-
ing X-TU systems.28
centered or cluster-based (MC), ligand-to-metal charge
transfer (LMCT), ligand-to-metal-metal charge transfer
(LMMCT), and intraligand (IL), and often a combination of
two or more of them has been assigned to explain the
observed luminescence behavior.12,18-27
Experimental Section
The present study describes the structural and photophysi-
cal properties of new dinuclear cationic and neutral Au(I)
complexes bridged by bis(diphenylphosphino)methane (dppm)
and a series of benzimidazolethiolate ligands (X-BIT)
(Scheme 1). The study of these systems was undertaken
because an unusual behavior, termed luminescence tribo-
chromism, and was seen in a closely related set of complexes
in which the bridging N, S ligand was a derivative of
thiouracil (X-TU). In luminescence tribochromism, a change
in photoemission energy (as well as intensity) occurs in solid-
state samples upon the application of mild pressure. For the
X-TU complexes reported earlier, a bright cyan photoemis-
Characterization and Instrumentation. All of the NMR spectra
were recorded on either Bruker Avance 400 or 500 MHz spec-
trometers. 1H NMR chemical shifts (in ppm) are relative to SiMe4
and referenced using the chemical shift of DMSO-d6. 31P NMR
chemical shifts (in ppm) are relative to an external 85% solution
of H3PO4 in the appropriate solvent. For cationic complexes, mass
determinations were carried out by electrospray ionization mass
spectrometry (ESI-MS) using a Hewlett-Packard Series 1100 mass
spectrometer (Model A) equipped with a quadrupole mass filter.
For neutral complexes, mass spectra were measured using a
Hewlett-Packard 1100 series mass selective detector operated with
an electrospray source and the detection of positive and negative
ions. The samples were dissolved in CH2Cl2 for 1a-1d or CH2-
Cl2/CH3OH (1:1 v/v) for 2a-2d and pumped into the spray chamber
using 100% CH3OH. Absorption spectra were recorded using a
Hitachi U2000 scanning spectrophotometer (200-1100 nm). Steady-
state emission spectra were obtained using a Spex Fluoromax-P
fluorimeter corrected for instrument response with monochromators
positioned with a 2 nm band-pass. The free X-BIT ligand
concentration of solution samples was 1.0 × 10-5 M in CH2Cl2/
MeOH (1:1, v/v) and each sample was degassed by at least two
freeze-pump-thaw cycles. The metal complex concentration of
solution samples was 1.0 × 10-5 M in CH2Cl2 for cationic
complexes or DMSO for neutral complexes, and each sample was
degassed by at least three freeze-pump-thaw cycles. Solid-state
emission samples were prepared as a 10% (w/w) mixture of the
complex in a matrix of finely ground KBr. Elemental analyses were
performed by Quantitative Technologies Inc..
Crystallographic Structure Determinations. Crystals were
attached to glass fibers and mounted under a stream of N2,
maintained at either 100.0(1) K or 193(2) K for 1b, on a Bruker
SMART platform diffractometer equipped with an APEX II CCD
detector, positioned at -33° in 2θ and 5.0 cm from the samples.
The X-ray source, powered at 50 kV and 30 mA, provided Mo KR
radiation (λ ) 0.71073 Å, graphite monochromator). Preliminary
random samplings of reflections were used to determine unit cells
and orientation matrices.29 Complete data collections were obtained
by ω scans of 183° (0.5° steps) at four different æ settings. Final
cell constants were calculated from the xyz centroids of ap-
proximately 4000 strong reflections from the actual data collection
after integration.30 The data were additionally scaled and corrected
for absorption.31 Space groups were determined based on systematic
(9) King, C.; Wang, J.-C.; Khan, M. N. I.; Fackler, J. P., Jr. Inorg. Chem.
1989, 28 (11), 2145-2149.
(10) Forward, J. M.; Fackler, J. P., Jr.; Assefa, Z. Optoelectronic Properties
of Inorganic Compounds, Roundhill, D. M., Fackler, J. P., Jr., Eds.;
Plenum Press: New York, 1999; pp 195-229.
(11) Hao, L.; Mansour, M. A.; Lachicotte, R. J.; Gysling, H. J.; Eisenberg,
R. Inorg. Chem. 2000, 39, 5520-5529.
(12) Lee, Y.-A.; McGarrah, J. E.; Lachicotte, R. J.; Eisenberg, R. J. Am.
Chem. Soc. 2002, 124, 10662-10663.
(13) White-Morris, R. L.; Stender, M.; Tinti, D. S.; Balch, A. L.; Rios, D.;
Attar, S. Inorg. Chem. 2003, 42 (10), 3237-3244.
(14) Tzeng, B.-C.; Schier, A.; Schmidbaur, H. Crystal Engineering of Gold-
(I) Thiolate Based Compounds via Cooperative Aurophilic and
Hydrogen-Bonding Interactions. Inorg. Chem. 1999, 38, 3978-3984.
(15) Hao, L.; Lachicotte, R. J.; Gysling, H. J.; Eisenberg, R. Inorg. Chem.
1999, 99 (21), 4616-4617.
(16) Hunks, W. J.; Jennings, M. E.; Puddephatt, R. J. Inorg. Chem. 2002,
41, 4590-4598.
(17) Wilton-Ely, J. D. E. T.; Schier, A.; Mitzel, N. W.; Nogai, S.;
Schmidbaur, H. J. Organomet. Chem. 2002, 643-644, 313-323.
(18) Tzeng, B.-C.; Liao, J.-H.; Lee, G.-H.; Peng, S.-M. Inorg. Chim. Acta
2004, 357 (5), 1405-1410.
(19) Tzeng, B.-C.; Chan, C.-K.; Cheung, K.-K.; Che, C.-M.; Peng, S.-M.
Chem. Commun. 1997, 135-136.
(20) Li, D.; Che, C.-M.; Peng, S.-M.; Liu, S.-T.; Zhou, Z.-Y.; Mak, T. C.
W. J. Chem. Soc., Dalton Trans. 1993, 189-194.
(21) Bardaj´ı, M.; Calhorda, M. J.; Costa, P. J.; Jones, P. G.; Laguna, A.;
Pe´rez, M. R.; Villacampa, M. D. Inorg. Chem. 2006, 45 (3), 1059-
1068.
(22) Forward, J. M.; Boohmann, D.; Fackler, J. P.; Staples, R. J. Inorg.
Chem. 1995, 34, 6330-6336.
(23) Yam, V. W. W.; Chan, C.-L.; Li, C.-K.; Wong, K. M.-C. Molecular
Coord. Chem. ReV. 2001, 216-217, 173-194.
(24) Ho, S. Y.; Cheng, E. C.-C.; Tiekink, E. R. T.; Yam, V. W.-W. Inorg.
Chem. 2006, 45 (20), 8165-8174.
(25) Chen, J.; Mohamed, A. A.; Abdou, H. E.; Bauer, J. A. K.; Fackler, J.
P., Jr.; Bruce, A. E.; Bruce, M. R. M. Chem. Commun. 2005, (12),
1575-1577.
(26) Tzeng, B.-C.; Yeh, H.-T.; Huang, Y.-C.; Chao, H.-Y.; Lee, G.-H.;
Peng, S.-M. Inorg. Chem. 2003, 42 (19), 6008-6014.
(27) Yam, V. W. W.; Cheng, E. C. C.; Cheung, K. K. Angew. Chem., Int.
Ed. 1999, 38 (1-2), 197-199.
(28) Lee, Y.-A.; Eisenberg, R. J. Am. Chem. Soc. 2003, 125, 7778-7779.
(29) APEX2 V2.1-0, Bruker AXS: Madison, WI, 2006.
(30) SAINT V7.34A, Bruker AXS: Madison, WI, 2006.
958 Inorganic Chemistry, Vol. 47, No. 3, 2008

Strong Intra- and Intermolecular Aurophilic Interactions
absences, intensity statistics, and space group frequencies. Structures
were solved by direct or Patterson methods.32,33 Non-hydrogen
atoms were located by difference Fourier syntheses, and their
positions were refined with anisotropic displacement parameters
by full-matrix least-squares cycles on F 2.33 All of the hydrogen
atoms, unless otherwise noted, were placed geometrically and
refined as riding atoms with relative isotropic displacement
parameters. For 1b, 1d, and 2d, reflection contributions from highly
disordered solvent molecules that include dichloromethane, diethyl
ether, or both, could not be modeled and were removed using the
program PLATON, function SQUEEZE.34,35 The final set of
refinement cycles, run to convergence, provided the reported quality
assessment parameters.
Materials. Potassium tetrachloroaurate(III) (Aldrich), silver
trifluoroacetate (Aldrich), bis(diphenylphosphino)methane (dppm)
(Strem), 2-mercaptobenzimidazole (H-BIT) (Aldrich), 2-mercapto-
5-methylbenzimidazole (Me-BIT) (Aldrich), 5-methoxy-2-benz-
imidazolethiol (OMe-BIT) (Aldrich), 5-chlorobenzimidazole-2-
thiol (Cl-BIT) (Avocado), and DMSO-d6 (Cambridge Isotope
Laboratories) were purchased commercially and used without
further purification. [Au2(µ-dppm)Cl2] was prepared according to
the literature procedure.5,36 All of the other solvents and reagents
were purchased commercially and used without further purification.
Synthesis and Characterization of New Au(I) Complexes.
[Au2(µ-H-BIT)(µ-dppm)](CF3CO2) (1a). To a solution of [Au2-
(µ-dppm)Cl2] (0.30 g, 0.353 mmol) in CH2Cl2 (15 mL) was added
AgCF3CO2 (0.156 g, 0.706 mmol), and the white mixture was
stirred at room temperature (RT) for 30 min while covered in foil.
The suspension was filtered through a pad of celite, to remove the
AgCl precipitate, and into a suspension of H-BIT (53 mg, 0.353
mmol) in CH2Cl2 (15 mL). The reaction mixture was stirred
overnight at RT. The resulting solution was concentrated to ∼5
mL, and the addition of Et2O (75 mL) gave an off-white precipitate.
The precipitate was collected by filtration and washed with
Et2O. Recrystallization by slow diffusion of Et2O into a CH2Cl2
solution gave a white colored product. Yield 71%. Mp 215 °C (dec).
ESMS (m/z): 927.0, [M-(CF3CO2)]. 1H NMR (DMSO-d6, 400
MHz): δ 13.61 (br s, 1H, N-H), 7.91-7.72 (m, 9H, dppm phenyl
and H-BIT aryl), 7.54-7.35 (br m, 13H, dppm phenyl and H-BIT
aryl), 7.35-7.24 (m, 2H, H-BIT aryl), 4.92 (t, JHP ) 13.7 Hz,
2H, dppm). 31P{1H} NMR (DMSO-d6, 162 MHz): δ 33.7 (d, JPP
) 51 Hz), 28.0 (d, JPP ) 51 Hz). Anal. Calcd for C34H27-
Au2F3N2O2P2S: C, 39.24; H, 2.62; N, 2.69. Found: C, 39.63; H,
2.65; N, 2.71.
BIT aryl), 7.25 (s, 1/2H, Me-BIT aryl), 7.10 (br t, 1H, Me-BIT
aryl), 4.92 (t, JHP ) 13.7 Hz, 2H, dppm), 2.42 (s, 3H, Me-BIT).
31P{1H} NMR (DMSO-d6, 162 MHz): δ 33.6 (d, JPP ) 51 Hz),
27.9 (d, JPP ) 51 Hz), 27.8 (d, JPP ) 52 Hz). Anal. Calcd for C35H29-
Au2F3N2O2P2S: C, 39.86; H, 2.77; N, 2.66. Found: C, 39.58; H,
2.82; N, 2.60.
[Au2(µ-OMe-BIT)(µ-dppm)](CF3CO2) (1c). This compound
was prepared by the same method as for 1a, using OMe-BIT (63
mg, 0.353 mmol) in place of H-BIT. Recrystallization by slow
diffusion of Et2O or hexane into a CH2Cl2 solution of the complex
gave a white colored product. Yield 78%. Mp 206 °C (dec). ESMS
1
(m/z): 957.0, [M-(CF3CO2)]. H NMR (DMSO-d6, 400 MHz): δ
13.45 (br s, 1H, N-H), 7.92-7.71 (m, 8H, dppm phenyl), 7.70 (d,
JHH ) 8.8 Hz, 1/2H, OMe-BIT aryl), 7.51-7.37 (br m, 12H, dppm
phenyl), 7.34 (d, JHH ) 8.8 Hz, 1/2H, OMe-BIT aryl), 7.30 (s,
1/2H, OMe-BIT aryl), 6.93 (br s, 1H, OMe-BIT aryl), 6.88 (d,
JHH ) 8.8 Hz, 1/2H, OMe-BIT aryl), 4.91 (t, JHP ) 13.7 Hz, 2H,
dppm), 3.80 (s, 3H, OMe-BIT). 31P{1H} NMR (DMSO-d6, 162
MHz): δ 33.7 (d, JPP ) 52 Hz), 33.6 (d, JPP ) 51 Hz), 28.1 (d, JPP
) 51 Hz), 27.8 (d, JPP ) 51 Hz). Anal. Calcd for C35H29-
Au2F3N2O3P2S: C, 39.26; H, 2.73; N, 2.62. Found: C, 39.77; H,
2.60; N, 2.34.
[Au2(µ-Cl-BIT)(µ-dppm)](CF3CO2) (1d). This compound was
prepared by the same method as for 1a, using Cl-BIT (65 mg,
0.353 mmol) in place of H-BIT. Recrystallization by slow diffusion
of Et2O into a CH2Cl2 solution of the complex gave a pale yellow
colored product. Yield 70%. Mp 188 °C (dec). ESMS (m/z): 961.0,
1
[M-(CF3CO2)]. H NMR (DMSO-d6, 500 MHz): δ 13.79 (br s,
1H, N-H), 8.01 (s, 1/2H, Cl-BIT aryl), 7.95-7.70 (m, 8 1/2 H,
dppm phenyl and Cl-BIT aryl), 7.59-7.32 (br m, 13H, dppm
phenyl and Cl-BIT aryl), 7.31 (br t, 1H, Cl-BIT aryl), 4.99-
4.82 (m, 2H, dppm). 31P{1H} NMR (DMSO-d6, 202 MHz): δ 33.1
(br d, JPP ) 52 Hz), 27.1 (br t). Anal. Calcd for C34H26Au2-
ClF3N2O2P2S: C, 37.99; H, 2.44; N, 2.61. Found: C, 37.77; H,
2.25; N, 2.28.
[Au2(µ-H-BIT)(µ-dppm)] (2a). To a solution of 1a (75 mg,
0.072 mmol) in CH2Cl2 (20 mL) was added NEt3 dropwise until a
bright green suspension began to form. After stirring overnight at
RT, the light green suspension was collected by filtration, washing
with H2O (3 × 5 mL), cold MeOH (3 × 5 mL) and Et2O. Yield
76%. Mp > 250 °C. ESMS (m/z): 926.8, [M]. 1H NMR (DMSO-
d6, 500 MHz): δ 7.92-7.70 (m, 8H, dppm phenyl), 7.58-7.31
(br m, 13H, dppm phenyl and H-BIT aryl), 7.24 (d, JHH ) 7.7
Hz, 1H, H-BIT aryl), 6.89-6.81 (m, 2H, H-BIT aryl), 4.78 (t,
JHP ) 13.3 Hz, 2H, dppm). 31P{1H} NMR (DMSO-d6, 202 MHz):
δ 33.6 (d, JPP ) 56 Hz), 28.1 (d, JPP ) 56 Hz). Anal. Calcd for
C32H26Au2N2P2S: C, 41.48; H, 2.83; N, 3.02. Found: C, 40.68;
H, 2.63; N, 2.86.
[Au2(µ-Me-BIT)(µ-dppm)] (2b). The method to prepare this
compound was analogous to that for 2a beginning with 1b (75 mg,
0.071 mmol). Yield 73%. Mp > 250 °C. ESMS (m/z): 940.8, [M].
1H NMR (DMSO-d6, 400 MHz): δ 7.88-7.70 (m, 8H, dppm
phenyl), 7.51-7.33 (br m, 12H, dppm phenyl), 7.32 (d, JHH ) 7.7
Hz, 1/2H, Me-BIT aryl), 7.24 (s, 1/2H, Me-BIT aryl), 7.11 (d,
JHH ) 7.8 Hz, 1/2H, Me-BIT aryl), 7.04 (s, 1/2H, Me-BIT aryl),
6.67 (br t, 1H, Me-BIT aryl), 4.76 (t, JHP ) 13.4 Hz, 2H, dppm),
2.32 (s, 3H, Me-BIT). 31P{1H} NMR (DMSO-d6, 162 MHz): δ
34.1 (d, JPP ) 56 Hz), 28.6 (d, JPP ) 56 Hz), 28.5 (d, JPP ) 56
Hz). Anal. Calcd for C33H28Au2N2P2S: C, 42.14; H, 3.00; N, 2.98.
Found: C, 41.57; H, 3.00; N, 3.03.
[Au2(µ-Me-BIT)(µ-dppm)](CF3CO2) (1b). This compound
was prepared by the same method as for 1a, using Me-BIT (58
mg, 0.353 mmol) in place of H-BIT. Recrystallization by slow
diffusion of Et2O into a CH2Cl2 solution of the complex gave a
white colored product. Yield 73%. Mp 199 °C (dec). ESMS (m/z):
1
941.0, [M-(CF3CO2)]. H NMR (DMSO-d6, 400 MHz): δ 13.48
(br s, 1H, N-H), 7.91-7.71 (m, 8H, dppm phenyl), 7.68 (d, JHH
)
8.2 Hz, 1/2H, Me-BIT aryl), 7.61 (s, 1/2H, Me-BIT aryl), 7.55-
7.35 (br m, 12H, dppm phenyl), 7.33 (d, JHH ) 8.1 Hz, 1/2H, Me-
(31) Sheldrick, G. M. SADABS V2004/1, University of Go¨ttingen: Go¨t-
tingen, Germany, 2004.
(32) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. SIR97: A New Program for SolVing and Refining Crystal
Structures; Istituto di Cristallografia, CNR: Bari, Italy, 1999.
(33) SHELXTL V6.14, Bruker AXS: Madison, WI, 2000.
(34) Spek, A. L. PLATON V300106, Utrecht University: Utrecht, The
Netherlands, 2006.
(35) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7-13.
(36) Schmidbaur, H.; Wohlleben, A.; Wagner, F.; Orama, O.; Huttner, G.
Chem. Ber. 1977, 110, 1748-1754.
[Au2(µ-OMe-BIT)(µ-dppm)] (2c). The method to prepare this
compound was analogous to that for 2a beginning with 1c (75 mg,
0.071 mmol). Yield 70%. Mp > 250 °C. ESMS (m/z): 956.9, [M].
Inorganic Chemistry, Vol. 47, No. 3, 2008 959

Schneider et al.
Scheme 2
Scheme 3
1H NMR (DMSO-d6, 400 MHz): δ 7.90-7.69 (m, 8H, dppm
phenyl), 7.50-7.33 (br m, 12H, dppm phenyl), 7.32 (d, JHH ) 7.1
Hz, 1/2H, OMe-BIT aryl), 7.12 (d, JHH ) 7.4 Hz, 1/2H, OMe-
BIT aryl), 7.00 (s, 1/2H, OMe-BIT aryl), 6.81 (s, 1/2H, OMe-
BIT aryl), 6.50 (br m, 1H, OMe-BIT aryl), 4.77 (t, JHP ) 13.3
Hz, 2H, dppm), 3.71 (s, 3H, OMe-BIT). 31P{1H} NMR (DMSO-
d6, 162 MHz): δ 34.2 (d, JPP ) 58 Hz), 34.1 (d, JPP ) 56 Hz),
28.7 (d, JPP ) 56 Hz), 28.6 (d, JPP ) 55 Hz). Anal. Calcd for C33H28-
Au2N2OP2S: C, 41.43; H, 2.95; N, 2.93. Found: C, 40.65; H, 2.78;
N, 2.82.
[Au2(µ-Cl-BIT)(µ-dppm)] (2d). The method to prepare this
compound was analogous to that for 2a beginning with 1d (75 mg,
0.071 mmol). Yield 78%. Mp > 250 °C. ESMS (m/z): 960.9, [M].
1H NMR (DMSO-d6, 400 MHz): δ 7.90-7.70 (m, 8H, dppm
phenyl), 7.52-7.33 (br m, 13H, dppm phenyl and Cl-BIT aryl),
7.23 (br s, 1/2H, Cl-BIT aryl), 7.20 (s, 1/2H, Cl-BIT aryl), 6.84
(br t, 1H, Cl-BIT aryl), 4.80-4.72 (m, 2H, dppm). 31P{1H} NMR
(DMSO-d6, 162 MHz): δ 34.2 (d, JPP ) 55 Hz), 34.1 (d, JPP ) 56
Hz), 28.6 (d, JPP ) 55 Hz), 28.4 (d, JPP ) 55 Hz). Anal. Calcd for
C32H25Au2ClN2P2S: C, 39.99; H, 2.62; N, 2.92. Found: C, 39.82;
H, 2.32; N, 2.92.
CO2)2 with 1 equiv of X-BIT for X ) Me, OMe, and Cl,
giving six rather than three aromatic resonances, some of
which overlap with one another, that correspond to the
substituted BIT ligand, plus a broad resonance from the
uncoordinated N-H imidazole proton at ca. 13.5 ppm. As
an example, the 1H NMR spectra of 1a and 1c are shown in
Figure 1.
The 31P{1H} NMR data are also of interest for cationic
complexes 1a-1d. Whereas 1a shows two doublets (JPP
)
Results and Discussion
51 Hz) that correspond to the two inequivalent phosphorus
nuclei, in which one Au-P is trans to the benzimidazole
nitrogen atom and the other Au-P is trans to the thiolate,
complexes 1b-1d each exhibit two sets of doublets corre-
sponding to the two isomers present in a 1:1 ratio with the
same JPP of 51-52 Hz. Figure 2 illustrates the spectra of 1a
and 1c, with two doublets observed for 1a and two sets of
doublets observed for 1c. Upon heating 1b-1d to 60 °C in
DMSO-d6, no coalescence is observed, indicating that rapid
interconversion between the m- and p-isomers that would
involve Au-N bond cleavage and free rotation about the
C-S bond of the BIT ligand does not occur on the NMR
time scale. This observation contrasts with that observed for
Synthesis and Characterization. The monocationic com-
plexes, [Au2(µ-X-BIT)(µ-dppm)](CF3CO2), were prepared
for X ) H (1a), Me (1b), OMe (1c), and Cl (1d), by the
reaction of [Au2(µ-dppm)](CF3CO2)2, generated in situ from
the reaction of [Au2(µ-dppm)Cl2] with 2 equiv of AgCF3-
CO2, with 1 equiv of X-BIT in excellent yields (Scheme
2). 1a-1d were characterized by both 1H and 31P{1H} NMR
spectroscopies, mass spectrometry, elemental analyses, and
1
single-crystal X-ray diffraction. The H NMR data of 1b-
1d reveal the presence of two geometric isomers, described
as m- and p-isomers in Scheme 3, in a 1:1 ratio that forms
upon the reaction of the in situ-generated [Au2(µ-dppm)](CF3-
960 Inorganic Chemistry, Vol. 47, No. 3, 2008

Strong Intra- and Intermolecular Aurophilic Interactions
Figure 1. 1H NMR spectra of 1a (bottom) and 1c (top) in DMSO-d6. Notice the isomers that have formed in 1c for both the OMe-BIT aryl resonances
and also the N-H imidazole proton; DCM ) dichloromethane.
Figure 2. 31P{1H} NMR spectra of 1a (bottom) and 1c (top) in DMSO-d6. Notice the two isomers that have formed in 1c.
a similar system, [Au(4,6-Me2pym-2-S]2, in which coales-
cence in the 1H NMR spectrum was seen at only 30 °C, via
the mechanism proposed to involve Au-N bond cleavage.15
Dissolution of the monocationic complexes, 1a-1d, in
CH2Cl2 followed by the slow addition of NEt3 leads to the
formation of a bright yellow-green precipitate corresponding
to [Au2(µ-X-BIT)(µ-dppm)], with X ) H, Me, OMe, and
Cl, for 2a-2d, respectively, in good yields (Scheme 2).
Similar spectroscopic behavior is observed for each of these
complexes. Like 1b-1d, the 1H NMR data of 2b-2d exhibit
two sets of aromatic resonances, some overlapping, resulting
from the substituted BIT ligand, as seen in Figure 3 for 2b
complexes (1) to give the neutral complexes (2), a change
in JPP is observed, from 51-52 Hz in the former to a slightly
larger JPP of 55-58 Hz in the latter.
Crystal Structure Determinations. Crystals of 1a-1d,
suitable for single-crystal X-ray diffraction, were grown by
slow diffusion and/or layering of a nonpolar solvent such as
diethylether or hexane into a dichloromethane solution
containing the cationic complex as the trifluoroacetate salt.
The unit cell, data collection and refinement parameters are
summarized for 1a-1d in Table 1 with selected bond lengths
and angles given in Table 2. Structurally, 1a-1d are very
similar, with a linear coordination geometry at each Au(I)
ion, and a close intramolecular Au‚‚‚Au separation ranging
from 2.8807(6) to 2.90607(16) Å (Table 2). The intramo-
lecular Au‚‚‚Au distances found for 1a-1d are comparable
to those found in analogous Au(I) complexes reported
previously for N,S-bridged Au2 systems: 2.8797(4) Å in
[Au2(µ-TU)(µ-dppm)](CF3CO2), and 2.8617(7) and 2.8864-
(6) Å in [Au2(µ-Me-TU)(µ-dppm)](CF3CO2).28 In compari-
son with the dinuclear N,S-bridged complex, [Au2(µ-
SC4H2N2O2)(µ-dppe)] where dppe ) bis(diphenylphoshino)-
ethane, the intramolecular Au‚‚‚Au distances for 1a-1d are
1
and 2d. The one notable difference between the H NMR
spectra of the cationic and neutral complexes is the absence
of the N-H resonance in the neutral complexes that is the
result of deprotonation of the cationic complexes by NEt3.
A similar pattern exists for the 31P{1H} NMR spectra of the
neutral complexes to that seen for the respective cationic
systems 1a-1d. Specifically, two doublets are seen for 2a,
and two sets of doublets are found for 2b-2d with
monosubstituted BIT ligands. An example is shown for 2c
and 2d in Figure 4. Upon deprotonation of the cationic
Inorganic Chemistry, Vol. 47, No. 3, 2008 961

Schneider et al.
Figure 3. 1H NMR spectra of 2b (bottom) and 2d (top) in DMSO-d6; both show isomers, whereas the X-BIT aryl resonances for 2d overlap, and those
of 2b do not.
1
Figure 4. 31P{1H} NMR spectra of 2b (bottom) and 2d (top) in DMSO-d6. Contrary to their respective H NMR spectra, the isomeric resonances in 2b
are overlapping (doublet on the left), whereas those of 2d are not.
slightly shorter than in the former complex, 2.9536(5) Å,
which is not unexpected when increasing the bite angle of
the bridging phosphine from dppm to dppe.16
3.39, 3.46, and 3.49 Å for 1a-1d, respectively, and angles
between the ring planes ranging from 3.73(7) to 12.05(23)°,
as shown for 1a in Figure 6. In accordance with NMR
spectroscopic data, the crystal structures reveal a disorder
in the position of the X-substituent in 1b-1d for two
geometric isomers.
Whereas the intramolecular Au‚‚‚Au separations for 1a-
1d indicate strong aurophilic interactions, there are no
significant intermolecular Au‚‚‚Au interactions. This stands
in sharp contrast with what was found for the analogous
cationic X-TU complexes, in which unbridged Au‚‚‚Au
intermolecular separations of 3.2363(6)-3.3538(7) Å sug-
gested extended aurophilic interactions, leading to a helical
arrangement of Au(I) ions in the crystal for those systems.
The absence of similar intermolecular Au‚‚‚Au interactions
for 1a-1d may be the result of the more sterically demand-
ing X-BIT ligands. The CF3COO- anion refines satisfac-
torily in 1a-1d, but with large anisotropic thermal param-
eters, and is hydrogen bonded to the X-BIT ligands through
the protonated and uncoordinated benzimidazole nitrogen
atom, with N-H‚‚‚O distances of ca. 2.7 Å (Table 2, Figure
5). The crystal structure for each cationic complex also
reveals π stacking of one pair of the phenyl rings of the
bridging dppm ligand with short interplanar distances of 3.39,
The neutral complexes 2a, 2b, and 2d were also character-
ized crystallographically (Table 3), and show much different
structural characteristics than their cationic counterparts.
Whereas the coordination geometry around each Au(I) ion
remains linear, the neutral dinuclear complexes actually
crystallize as dimers, held together by an unbridged inter-
molecular distance that ranges between 2.8793(4) and
2.9822(8) Å. These separations are similar in magnitude to
the intramolecular distances in the dinuclear complexes that
span the values 2.8597(3)-2.9162(3) Å (for selected bond
distances and angles see Table 4). These distances provide
evidence of substantial aurophilicity and for the unsupported
intermolecular separations are similar in strength to the
intramolecular interactions in their cationic precursors. The
intermolecular Au‚‚‚Au distances in 2a-2b and 2d compare
962 Inorganic Chemistry, Vol. 47, No. 3, 2008

Strong Intra- and Intermolecular Aurophilic Interactions
Table 1. Cystallographic Data and Structure Refinement for 1a-1d
1a
1b
1c
1d
formula
fw
T (K)
C34H27Au2F3N2O2P2S‚CH2Cl2 C35H29Au2F3N2O2P2S‚x Solvent C35H29Au2F3N2O3P2S‚C6H14 C34H26Au2ClF3N2O2P2S‚x Solvent
1125.44
100.0(1)
0.71073
monoclinic
C2/c
1054.55
193(2)
0.71073
monoclinic
C2/c
1113.62
100.0(1)
0.71073
monoclinic
C2/c
1074.75
100.0(1)
0.71073
monoclinic
C2/c
λ (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
18.1091(7)
21.2668(8)
19.7968(7)
90
16.810(3)
22.339(4)
20.605(4)
90
16.4687(11)
21.6745(15)
21.3525(15)
90
16.793(3)
22.211(4)
20.428(4)
90
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
107.260(1)
90
102.613(3)
90
100.990(1)
90
103.059(3)
90
7280.9(5)
8
7551(2)
8
7482.0(9)
8
7422(2)
8
F
calcd (mg/m3)
µ (mm-1
2.053
1.855
1.977
1.924
)
8.393
7.950
8.030
8.159
cryst color
colorless block
0.32 × 0.24 × 0.24
1.65-30.03
10 575
colorless block
0.30 × 0.20 × 0.20
1.54-27.88
8920
pale yellow-green block
0.21 × 0.20 × 0.12
1.57-28.31
9271
colorless plate
0.28 × 0.21 × 0.15
1.55-28.49
9341
cryst size (mm3)
θ range (deg)
no. of data
no. of params
458
1.030
425
1.073
0.0583, 0.1350
0.1023, 0.1457
501
1.049
0.0338, 0.0929
0.0433, 0.0984
434
1.050
0.0510, 0.1317
0.0773, 0.1416
GOFa
R1, wR2 (F 2, I > 2σ(I))b 0.0199, 0.0457
R1, wR2 (F2, all data)b
0.0239, 0.0466
a GOF ) S ) [∑w(Fo - Fc )2/(m - n)]1/2, where m ) number of reflections and n ) number of parameters. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 )
2
2
[∑w(Fo - Fc )2/∑w(Fo )2]1/2, where w ) 1/[σ2(Fo)2 + (aP) + bP] and P ) /3 max(0, Fo ) + [2/3] Fc .
2
2
2
1
2
2
(C5H11)2)]2‚DMSO37 and are in fact shorter than those found
Table 2. Selected Bond Lengths (Angstroms) and Angles (Degrees) for
1a-1d
for the analogous complexes of [Au2(µ-NH2-TU)(µ-dppm)]2‚
2CH3OH‚H2O and [Au2(µ-NH2-TU)(µ-dppm)]2‚8CH3OH‚
2H2O, which have intermolecular distances of 3.011 and
3.051 Å, respectively.38 For 2a-b, there are two unique half
molecules per asymmetric unit, thus giving two independent
intra- and intermolecular Au‚‚‚Au distances (Table 4, Figure
7), whereas for 2d, only one set of values for intra- and
intermolecular Au‚‚‚Au distances is obtained. The inter-
molecular aggregation in these neutral complexes might be
due to the absence of the N-H imidazole proton, removing
the possibility of hydrogen bonding with CF3COO- and/or
polar solvent molecules. Whereas no additional Au‚‚‚Au
interactions beyond the dimer exist, it is important to note
the short intermolecular distances within the dimers and the
Au‚‚‚Au‚‚‚Au‚‚‚Au configuration with dihedral angles span-
ning 105.12-140.12 ° in these complexes.
1a
1b
1c
1d
Au‚‚‚Au
2.90607(16) 2.8861(8) 2.8955(4)
Au-P, trans to N 2.2416(6)
Au-P, trans to S 2.2624(6)
2.8807(6)
2.2376(14) 2.236(2)
2.2636(13) 2.259(2)
2.053(4)
2.3138(13) 2.313(2)
2.691(10)
177.85(15) 178.12(16)
2.245(3)
2.264(3)
2.073(8)
2.319(3)
2.700(13) 2.64(3)
178.1(2)
176.51(9) 177.82(5)
93.92(7)
90.30(7)
84.9(2)
Au-N
Au-S
2.050(2)
2.3157(6)
2.718(3)
179.07(6)
175.48(2)
93.192(16)
91.566(16)
86.00(6)
2.070(7)
N-H‚‚‚OOCF3
N-Au-P
S-Au-P
176.85(7)
94.01(5)
90.25(6)
85.54(19)
91.09(6)
P-Au‚‚‚Au (N)
P-Au‚‚‚Au (S)
N-Au‚‚‚Au
S-Au‚‚‚Au
92.61(4)
91.24(4)
85.49(15)
90.94(4)
90.204(16)
91.08(8)
Absorption, Excitation, and Emission. The photophysi-
cal data for 1a-1d and 2a-2d are summarized in Tables
5-7. The solution absorption and emission data for 1a-1d
and 2a-2d under steady-state conditions are shown in
Figures 8 and 9, respectively. Both sets of complexes, 1 and
2, exhibit intense ligand-centered absorptions at λ < 270
nm, whereas the near-UV transitions between 270 and 340
nm have molar absorptivities (ꢀ) on the order of 10 000 dm3
mol-1 cm-1. These absorptions resemble those of the free
X-BIT ligands, which are shown as Figure S7 in the
Supporting Information. The higher-energy absorption maxima
at ca. 279 nm are assigned to an intraligand transition of the
bridging dppm moieties,27 whereas the lower energy maxima
at ca. 316 nm are tentatively assigned as a mixture of a
Figure 5. Perspective view of cationic 1a interacting with CF3COO-
anion; phenyl rings of dppm moiety omitted for clarity.
(37) Mansour, M. A.; Connick, W. B.; Lachicotte, R. J.; Gysling, H. J.;
Eisenberg, R. J. Am. Chem. Soc. 1998, 120, 1329-1330.
(38) These structures were obtained by Young-A Lee and will be reported
separately.
well with other unbridged Au‚‚‚Au separations in neutral
Au2 complexes including 2.9235(4) Å in [Au2(µ-Me-TU)-
(µ-dppm)]2‚3CH3OH28 and 2.9617(7) Å in [Au(S2CN-
Inorganic Chemistry, Vol. 47, No. 3, 2008 963

Schneider et al.
Figure 6. Perspective views of cationic 1a showing π stacking in two of the phenyl rings of the bridging dppm ligand.
Table 3. Crystallographic Data and Structure Refinement for 2a, 2b, and 2d
2a
2b
2d
formula
fw
T (K)
(C32H26Au2N2P2S)2‚2.5DMF
2035.70
100.0(1)
0.71073
monoclinic
C2/c
32.4834(17)
17.0904(9)
25.3173(13)
90
102.887(1)
90
13701.0(12)
8
1.974
(C33H28Au2N2P2S)2‚4CH3OH‚H2O
(C32H25Au2ClN2P2S)2‚x solvent
2027.20
100.0(1)
0.71073
monoclinic
C2/c
34.066(6)
17.125(3)
29.566(5)
90
124.571(2)
90
14203(4)
8
1921.85
100.0(1)
0.71073
orthorhombic
Pccn
29.764(4)
12.0886(17)
17.881(3)
90
λ (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
90
90
6433.5(16)
4
1.984
F
calcd (mg/m3)
1.896
8.437
pale yellow plate
0.38 × 0.16 × 0.04
1.39-30.51
21 658
µ (mm-1
)
8.746
9.382
cryst color
yellow needle
0.38 × 0.05 × 0.05
1.29-30.51
20 525
colorless needle
0.38 × 0.06 × 0.01
1.37-28.28
7980
cryst size (mm3)
θ range (deg)
no. of data
no. of params
836
1.062
0.0335, 0.0794
0.0556, 0.0902
757
1.056
0.0596, 0.1312
0.1433, 0.1725
378
1.066
0.0599, 0.1184
0.1121, 0.1347
GOFa
R1, wR2 (F 2, I > 2σ(I))b
R1, wR2 (F 2, all data)b
2
2
a GOF ) S ) [∑w(Fo - Fc )2/(m - n)]1/2, where m ) number of reflections and n ) number of parameters. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 )
2
2
2
1
2
2
[∑w(Fo - Fc )2/∑w(Fo )2]1/2, where w ) 1/[σ2(Fo)2 + (aP) + bP] and P ) /3 max(0, Fo ) + [2/3] Fc .
benzimidazolethiolate IL transition and an LMCT transition
from the BIT thiolate donor to the Au(I) ion (S f Au).18,39
For neutral complexes 2a-2d in DMSO solution, similar
absorption maxima are observed around 283 nm and 314
nm, corresponding to the same IL and IL/LMCT transitions
as for the cationic complexes. For 2a-2d, the lowest-energy
absorption maxima corresponding to the mixed IL/LMCT
transitions, decrease in the order X ) H > Me ∼ OMe >
Cl. For 1, the analogous lowest-energy absorption maxima
decrease in the order X ) H > Me > Cl > OMe.
The emission spectra for 1a-1d in CH2Cl2 solution
(Figure 8) differ from those of the corresponding free X-BIT
ligands in CH3OH/CH2Cl2 solution (Figure S8 in the Sup-
porting Information). The emission maxima for 1a-1d lie
in the UV region at ca. 365 nm, with 1c having an additional
maximum at 465 nm. The lower energy emission maximum
for 1c is highly concentration dependent. While absent at a
concentration of 10-7 M, the emission increases relative to
that at 364 nm, reaching a maximum ratio at 10-4 M. At an
even higher concentration of 10-3 M, the emission at 465
nm is no longer observed, possibly as a consequence of self-
quenching (Figure S9 in the Supporting Information). Room-
temperature excitation spectra of 1c with λem ) 370 nm and
470 nm show no exceptional difference (Figure S10 in the
Supporting Information). The λemmax of complexes 1 do not
show a significant change on going from 1a to 1d, an
indication that the emission is either purely ligand-based (in
which case the X substituent affects the HOMO and LUMO
energies in similar ways) or MC.
Contrary to the cationic complexes, the emission spectra
for the neutral series 2 in DMSO solution (Figure 9) show
that λemmax changes substantially on going from 2a-2d. The
max
change in λem
clearly indicates the involvement of the
(39) Narayanaswamy, R.; Young, M. A.; Parkhurst, E.; Ouellette, M.; Kerr,
M. E.; Ho, D. M.; Elder, R. C.; Bruce, A. E.; Bruce, M. R. M. Inorg.
Chem. 1993, 32, 2506-2517.
X-BIT ligand in the excited-state. Considering the absence
of this characteristic shift in cationic series 1, the assignment
964 Inorganic Chemistry, Vol. 47, No. 3, 2008

Strong Intra- and Intermolecular Aurophilic Interactions
Table 4. Selected Bond Lengths (Angstroms) and Angles (Degrees) for 2a, 2b, and 2da
2a
2b
2db
intra Au‚‚‚Au
inter Au‚‚‚Au
Au-P, trans to N
Au-P, trans to S
Au-N
2.8597(3)
2.8793(4)
2.2281(13)
2.2827(12)
2.023(4)
2.9162(3)
2.9457(4)
2.2471(13)
2.2728(12)
2.047(4)
2.8930(7)
2.9019(8)
2.246(3)
2.277(3)
2.066(10)
2.302(3)
2.8984(7)
2.9457(9)
2.244(3)
2.270(3)
2.058(9)
2.303(3)
2.9080(6)
2.9822(8)
2.235(3)
2.266(3)
2.15b
Au-S
2.3237(12)
2.3151(12)
2.34b
Intramolecular
N-Au-P
175.70(13)
176.88(4)
95.88(3)
88.17(3)
86.13(11)
89.93(3)
178.75(11)
178.17(5)
93.56(3)
90.44(3)
86.49(11)
89.46(3)
178.3(3)
176.26(14)
93.07(8)
91.86(7)
87.6(3)
178.3(3)
175.23(12)
93.53(7)
90.85(7)
87.4(3)
176b
S-Au-P
175.3b
92.54(7)
91.86(7)
87b
P-Au‚‚‚Au (N)
P-Au‚‚‚Au (S)
N-Au‚‚‚Au
S-Au‚‚‚Au
89.36(8)
89.24(9)
88.7b
Intermolecular
P-Au‚‚‚Au (S)
S-Au‚‚‚Au
Au‚‚‚Au‚‚‚Au
Au‚‚‚Au‚‚‚Au‚‚‚Au
94.75(3)
87.94(3)
158.085(9)
105.12
94.78(3)
86.16(3)
152.014(9)
114.20
96.85(8)
84.17(8)
144.36(3)
122.95
95.89(7)
86.61(9)
146.83(3)
116.54
101.15(7)
81.2b
136.60(3)
140.12
b
a For complexes 2a and 2b, there were two unique half-molecules per asymmetric unit; for 2d, only one unique half-molecule per asymmetric unit. 2d
showed severe disorder, and therefore these parameters are taken as the averages of a modeled disorder (CIF for more information).
Figure 7. Perspective view of the two unique dimers of neutral 2a, having intra and intermolecular Au‚‚‚Au interactions; phenyl rings of the dppm moiety
were omitted for clarity.
Table 5. Photophysical Data for 1a-1d
solid-state λemmax/nmc
a
λ
abs/nm (ꢀ/dm3 mol-1 cm-1
)
soln λem/nma,b
1a
1b
1c
1d
278 (21 400), 310 (9100)
280 (21 760), 314 (9790)
280 (25 890), 322 (10 350)
279 (22 430), 317 (14 320)
355 (sh), 364 (max), 380 (sh)
355 (sh), 364 (max), 380 (sh)
355 (sh), 364 (max), 380 (sh), 465
355 (sh), 365 (max), 380 (sh)
469
472
476
475
b
a 1.0 × 10-5 M in CH2Cl2. λex ) 320 nm. c 10% (w/w) mixture with KBr, λex ) 395 nm.
Table 6. Photophysical Data for 2a-2d
Table 7. Luminescence Tribochromism Data for 1a, 1b, and 1d
soln
solid-state
solid-state
solid-state
λemmax/nma,b
λemmax/nmc
crystals λemmax/nma
crushed λemmax/nmb
∆E/cm-1 c
a
λ
abs/nm (ꢀ/dm3 mol-1 cm-1
)
2a
2b
2c
2d
281 sh (25 720), 312 sh (14 450)
284 sh (18 720), 313 sh (10 840)
285 sh (26 330), 313 sh (11 760)
283 sh (29 340), 316 sh (13 860)
499
514
543
486
523
534
533
512
1a
1b
1d
484
481
478
459
466
459
1130
670
870
a λex ) 365 nm. b Measured as a solid-state mixture with KBr, λex
365 nm. c ∆E ) Ecrushed - Ecrystals
)
a 1.0 × 10-5 M in DMSO. λex ) 290 nm. c 10% (w/w) mixture with
KBr, λex ) 440 nm.
.
b
the para- (σp) or meta- (σm) position41 relative to the Au-N
imidazole nitrogen on the ligands (Scheme 3). For σp
Hammett constant values, the data correlate very well; the
most electron-donating OMe-BIT ligand (2c) has the lowest
for the emission of the neutral series 2 is most likely that of
an LMMCT, due in part to the extended Au‚‚‚Au interac-
tions.4,40 We can also correlate the emission energies of 2
with Hammett constant values for the substituent X in either
λemmax, whereas 2d has the highest λem due to the more
max
(40) Yam, V. W.-W.; Lo, K. K.-W. Chem. Soc. ReV. 1999, 28 (5), 323-
(41) Smith, M. B.; March, J. March’s AdVanced Organic Chemistry:
Reactions, Mechanisms, and Structure, 5th Ed.; 2000; p 1824.
334.
Inorganic Chemistry, Vol. 47, No. 3, 2008 965

Schneider et al.
Figure 8. Room-temperature absorption and emission (λex ) 320 nm)
spectra for 1a-1d in 1.0 × 10-5 M CH2Cl2 solution.
Figure 11. Solid-state excitation (λem ) 465 nm) and emission (λex
)
395 nm) spectra for 1a-1d in a 10% (w/w) mixture with KBr at room
temperature.
Figure 9. Room temperature absorption and emission (λex ) 290 nm)
spectra for 2a-2d in 1.0 × 10-5 M DMSO solution.
Figure 12. Solid-state excitation and emission (λex ) 440 nm) spectra
for 2a-2d in a 10% (w/w) mixture with KBr at room temperature.
following effects: (1) configuration mixing due in part to
the extended Au‚‚‚Au‚‚‚Au‚‚‚Au intermolecular interactions
found in the structures of the neutral complexes,40,42
a
property not observed for the cations; and (2) change in the
overall charge of the complex, from monocationic to neutral.
The solid-state emission spectra of 1 and 2 were done in
a matrix of KBr at room temperature and are summarized
in Tables 5-7. For the series of cationic complexes 1, the
excitation spectra mirror the emission spectra, with emission
maxima of 469, 472, 476, and 475 nm for 1a-1d, respec-
tively, when λex ) 395 nm (Figure 11). Like the emission
spectra in the CH2Cl2 solution, the small change in λemmax in
the solid-state indicates the X-BIT ligands are having little
to no effect on the excited-state of the complexes, indicating
that the emission is either ligand-based or MC in nature.
Figure 10. Correlation between σp and σm Hammett constants41 versus
emission energy for 2a-2d in 1.0 × 10-5 M DMSO solution.
electron-withdrawing Cl-BIT ligand (Figure 10). The σm
Hammett constants for 2a, 2b, and 2d also correlate in a
similar fashion with the emission energies, but the correlation
does not hold for the -OMe substituent.
Like their cationic counterparts, the excitation spectra of
2a-2d mirror their respective emission spectra, but the
corresponding solid-state emission spectra of the neutral
complexes 2a-2d show red-shifted maxima of 523, 534,
533, and 512, respectively, when λex ) 440 nm (Figure 12).
As in DMSO solution, the solid-state emission spectra of
When comparing the λemmax for solution emission spectra
between the cationic series 1 and the neutral series 2, there
is a significant shift from higher to lower energy, respec-
tively. This shift may result from either or both of the
(42) Balch, A. L. Gold Bulletin 2004, 37 (1-2), 45-50.
966 Inorganic Chemistry, Vol. 47, No. 3, 2008

Strong Intra- and Intermolecular Aurophilic Interactions
similar behavior was described by Assefa et al., who reported
that the 1D chain compound, [(TPA)2Au][Au(CN)2] (TPA
) 1,3,5-triaza-7-phosphaadamantane), that was not lumi-
nescent in the visible region in crystalline form, became
brightly emissive when ground to a fine powder.45 However,
these authors proposed a different basis for the observation
in terms of localized lattice defects in the emissive powder
that encompass dimeric or oligomeric units. Both reports
differ from the present study in that solid samples of the
cationic complexes 1a, 1b, and 1d reported here are green
emissive prior to crushing, shifting to higher energy after
grinding.
In contrast with the earlier report involving [Au2(µ-X-
TU)(µ-dppm)]Y complexes,28 the cationic complexes 1a, 1b,
and 1d exhibit no evolution of volatile CF3CO2H after gentle
heating or sonication. Furthermore, there is no correlation
between the solid-state emission maxima of the crushed form
of 1a, 1b, and 1d and those of the neutral complexes 2a,
2b, and 2d, which is in contrast with what was observed for
the cationic and neutral [Au2(µ-X-TU)(µ-dppm)]+/0 com-
plexes.
The origin of the luminescence tribochromism observed
in the present study thus differs from the earlier reports.28,45
One difference may lie in the bulkiness of the X-BIT ligands
that prevents extended or chainlike intermolecular Au‚‚‚Au
interactions from occurring in the cationic complexes, 1a-
1d, which is not the case for the dinuclear cations bridged
by the less-bulky X-TU ligands in Lee’s study. At this point,
the basis of luminescence tribochromism in the complexes
described here, as well as in the previously reported systems,
can only be conjectured and will require unambiguous
assignments of the emissive states in these complexes.
Additional photophysical studies will be required, including
lifetime measurements and an analysis of systematic sub-
stituent effects on photophysical properties to accomplish
this goal.
Figure 13. Solid-state emission (λex ) 365 nm) spectra showing
luminescence tribochromism of 1a-1b and 1d in a finely ground matrix
of KBr at room temperature.
max
2a-2d show a correlation between λem
and the X
max
substituent of X-BIT. The energies for λem increase in
the order X ) Cl > H > OMe ≈ Me, a trend that follows
well with having a mixture of m- and p-isomers in the solid-
state samples. The excited-state transitions for solid samples
of 2a-2d are comparable to those in DMSO solution and
are tentatively assigned as LMMCT in nature. In fact, the
lifetime for a solid-state sample of 2c was measured to be
0.2 µs when λex ) 400 nm. Ma and Che reported similar
lifetime measurements for the dinuclear Au(I) complex, [Au2-
(dppm)Cl2], which had triplet excited lifetimes of 0.15, 0.3,
and 0.45 µs in CH3CN solution, solid-state, and in the poly-
(methyl methacrylate) (PMMA) matrix, respectively.5
Luminescence Tribochromism. A unique solid-state
emission property that is observed with 1a, 1b, and 1d is
that of luminescence tribochromism.43,44 When X-ray quality
crystals of 1a, 1b, and 1d are irradiated with 365 nm light,
they show emission maxima of 484, 481, and 478 nm,
respectively (Figure 13). Upon gentle crushing of the crystals
with a spatula, the emission maxima shift to higher ener-
gies: 459, 466, and 459 for 1a, 1b, and 1d, respectively; a
change in emission energies that ranges from 670 to 1130
cm-1 (Table 7). For 1c, this unique mechanical effect is not
observed to the extent of the other three cationic complexes;
the change in emission upon grinding crystals of 1c is within
the error of the instrument.
Conclusions
We have successfully synthesized a series of new cationic
and analogous neutral dinuclear Au(I) phosphine thiolate
complexes that exhibit interesting structural and lumines-
cence properties that include short intramolecular Au‚‚‚Au
interactions, with no extended aggregation observed and
luminescence tribochromism that occurs upon mechanical
grinding of microcrystalline samples of the cationic systems
to powder. The neutral complexes crystallize as dimers with
significant intra- and intermolecular Au‚‚‚Au interactions,
which causes the λemmax to shift substantially to the red region
when compared to the emission maxima of the cations. Both
sets of complexes possess a wide variety of structural and
photophysical properties that lead to excited-state assign-
ments that include LMCT, ligand-based, MC, and LMMCT
states.
Lee and Eisenberg previously reported a similar lumines-
cence phenomenon for the analogous cationic [Au2(µ-X-
TU)(µ-dppm)]Y complexes, where X ) H, Me, and Y- )
-
-
NO3 , ClO4 , and Au(CN)2-.28 In their study, solid samples
of the cationic complexes were either nonemissive or weakly
photoluminescent, and after gentle crushing the solid samples
exhibited bright blue or cyan photoluminescence. The effect
was attributed in part to (1) disruption of weak Au‚‚‚Au
intermolecular interactions accompanied by rearrangement
to dimers having stronger intermolecular contacts; and (2)
the evolution of volatile acid upon crushing. A somewhat
Acknowledgment. We thank the Eastman Kodak Com-
pany, the National Science Foundation (Grant CHE-
(43) Asiri, A. M. A.; Heller, H. G.; Hursthouse, M. B.; Karalulov, A., Chem.
Commun. 2000, 799-800.
(44) Bouas-Laurent, H.; Durr, H. Pure Appl. Chem. 2001, 73, 639-665.
(45) Assefa, Z.; Omary, M. A.; McBurnett, B. G.; Mohamed, A. A.;
Patterson, H. H.; Staples, R. J.; Fackler, J. P., Jr. Inorg. Chem. 2002,
41, 6274-6280.
Inorganic Chemistry, Vol. 47, No. 3, 2008 967

Schneider et al.
with CF3COO- anion and dimers of 2b and 2d, room temperature
absorption and emission spectra of free X-BIT ligands, room-
temperature emission spectra of 1c at varying concentrations, and
room-temperature excitation spectrum of 1c. Crystallographic data
is in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
0207018), and the donors of the Petroleum Research Fund
administered by the American Chemical Society (Grant PRF
# 36243-AC3) for support of this research. We also thank
Mr. Terry O’Connell for assisting with mass spectrometric
measurements and Dr. Paul Merkel for help with the lifetime
measurement of 2c.
Supporting Information Available: Perspective views of 1a
showing phenyl π stacking, cationic complexes 1b-1d interacting
IC701763X
968 Inorganic Chemistry, Vol. 47, No. 3, 2008