Gold complexes with tridentate cyclometalating and NHC ligands: A search for new photoluminescent gold(III) compounds

Article abstract of DOI:10.1021/om301226b

Many square-planar Pt(II) complexes are strongly photoluminescent, particularly when they contain cyclometalating and/or NHC ligands which produce strong ligand fields. In this work we investigated the possibility of obtaining isoelectronic Au(III) complexes with favorable luminescence properties. Toward this end, the coordination chemistry of gold with three different (potentially) tridentate ligands was explored: 1,3-bis(1-hexyl-2′-benzimidazoyl)benzene (L¹H), 2,6-bis(3-butylimidazol-1-ium)pyridine (L²H ₂²⁺), and 2,6-bis(3-hexylbenzimidazol-1-ium)pyridine (L³H₂²⁺). Pt(II) or Pd(II) complexes are known for all of these ligands or closely related analogues, and hence we anticipated that similar Au(III) complexes would be synthetically accessible as well. This turned out to be the case only for L¹, despite exploration of different synthetic routes including (i) direct complexation of Au(III), (ii) transmetalation from Ag(I) precursor complexes, and (iii) transmetalation from suitable Hg(II) precursors. Only the mercury procedure was successful (at least in the case of L¹); transmetalation from silver or direct complexation yields other reaction products containing Au(I) in most cases. Likewise, with ligands L² and L³ mainly complexes of Au(I) were obtained: i.e., the propensity of gold for low oxidation states is a major obstacle to obtaining the desired Au(III) compounds. Several new complexes of Au(I) and Au(III) were characterized crystallographically. Our results provide insight into the differences between the coordination chemistry of isoelectronic Pt(II) and Au(III) with tridentate cyclometalating and NHC ligands.

Full text of DOI:10.1021/om301226b

Article
pubs.acs.org/Organometallics
Gold Complexes with Tridentate Cyclometalating and NHC Ligands:
A Search for New Photoluminescent Gold(III) Compounds
Annika Herbst,† Catherine Bronner,†,‡ Pierre Dechambenoit,§ and Oliver S. Wenger*,†,‡
†Institut fur Anorganische Chemie, Georg-August Universitat, Tammannstrasse 4, D-37077 Gottingen, Germany
̈
̈
̈
‡Departement fur Chemie, Universitat Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland
̈
̈
§Centre de Recherche Paul Pascal, Universite
France
́
de Bordeaux & CNRS, UPR 8641, 115 avenue du Dr. A. Schweitzer, F-33600 Pessac,
S
* Supporting Information
ABSTRACT: Many square-planar Pt(II) complexes are
strongly photoluminescent, particularly when they contain
cyclometalating and/or NHC ligands which produce strong
ligand fields. In this work we investigated the possibility of
obtaining isoelectronic Au(III) complexes with favorable
luminescence properties. Toward this end, the coordination
chemistry of gold with three different (potentially) tridentate
ligands was explored: 1,3-bis(1-hexyl-2′-benzimidazoyl)-
benzene (L1H), 2,6-bis(3-butylimidazol-1-ium)pyridine
(L2H22+), and 2,6-bis(3-hexylbenzimidazol-1-ium)pyridine
(L3H22+). Pt(II) or Pd(II) complexes are known for all of these ligands or closely related analogues, and hence we anticipated
that similar Au(III) complexes would be synthetically accessible as well. This turned out to be the case only for L1, despite
exploration of different synthetic routes including (i) direct complexation of Au(III), (ii) transmetalation from Ag(I) precursor
complexes, and (iii) transmetalation from suitable Hg(II) precursors. Only the mercury procedure was successful (at least in the
case of L1); transmetalation from silver or direct complexation yields other reaction products containing Au(I) in most cases.
Likewise, with ligands L2 and L3 mainly complexes of Au(I) were obtained: i.e., the propensity of gold for low oxidation states is a
major obstacle to obtaining the desired Au(III) compounds. Several new complexes of Au(I) and Au(III) were characterized
crystallographically. Our results provide insight into the differences between the coordination chemistry of isoelectronic Pt(II)
and Au(III) with tridentate cyclometalating and NHC ligands.
luminescent materials.6,11 Several of these previously explored
complexes contained nearly identical tridentate ligands, and
1. INTRODUCTION
In purely organic light-emitting diodes (OLEDs) one is
chemical variation mostly occurred at the fourth coordination
confronted with the problem that electrogenerated triplet
site of the Au(III) center. Here, we report our findings from a
excited states dissipate their energy to a large extent
nonradiatively, leading to electroluminescence quantum yields
lower than what is possible with transition-metal-doped
OLEDs. Iridium(III) and platinum(II) complexes have received
study in which we explored the coordination chemistry of gold
with three different (potentially) tridentate ligands (Scheme 1).
While the emphasis of the work reported herein is on exploring
possible synthetic pathways to such compounds, the question
much attention as so-called triplet harvesters in OLEDs,
whether cyclometalated Au(III) complexes can exhibit similarly
because many of them emit from excited states that have mixed
3MLCT/3IL character (MLCT = metal-to-ligand charge
high luminescence quantum yields in comparison to isoelec-
tronic Pt(II) complexes, possibly at even higher emission
transfer; IL = intraligand), exhibiting high luminescence
energies (band maxima shifted further toward the blue), is of
quantum yields and good color tunability combined with
good (photo)chemical stability.1−5 Complexes with the most
fundamental interest.
Ligand L1H is charge neutral and its analogue with butyl
favorable properties often contain cyclometalating ligands
which induce strong ligand fields, making nonradiative
relaxation from d−d excited states inefficient. While numerous
groups instead of hexyl chains has been previously used as a
tridentate cyclometalating ligand offering N,C,N coordination
sites for Pt(II) (Scheme 1).33−35 Ligands L2H22+ and L3H22+ are
Pt(II) complexes of this type exist, there has yet been a limited
cationic but lose their acidic carbene H atoms upon
amount of work on isoelectronic Au(III) complexes, as we
coordination to Pd(II) or Pt(II). L2 was previously found to
act as a tridentate C,N,C ligand to Pd(II) or Pt(II); a
already noted in a recent review.6 Over the past few years the
groups of Yam,7−15 Che,16−21 Venkatesan,22,23 and others24−32
reported on emissive Au(III) complexes containing cyclo-
metalating, N-heterocyclic carbene (NHC), or alkynyl ligands,
demonstrating the potential of this new class of compounds for
Received: December 19, 2012
Published: February 26, 2013
© 2013 American Chemical Society
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Scheme 1. The Three Potentially Tridentate Ligands Used in This Work
Scheme 2. Complexes Obtained with L1
palladium(II) complex of a modified version of L3 (with butyl
groups instead of hexyl chains) is known as well.36−38 Our goal
was to synthesize analogous Au(III) complexes in which L1−L3
are tridentate and to use phenylethynyl ligands at the fourth
coordination site of the expected square-planar complexes,
because comparable Pt(II) complexes are highly emissive.1,34
We wondered to what extent the luminescence properties of
these Au(III) compounds would differ from those of the
respective Pt(II) complexes. We found that the propensity of
gold for low oxidation states leads to a variety of new Au(I)
complexes, some of which could be characterized crystallo-
graphically. The desired square-planar complex of Au(III) could
only be obtained with L1, but only under carefully selected
reaction conditions. Direct cyclometalation of Au(III) by L1−L3
turned out to be impossible under the conditions used.
Transmetalation from Ag(I) NHC complexes gave Au(I)
compounds, while transmetalation from Hg(II) gave the
desired Au(III) complex of L1. Thus, the coordination
chemistry of Au(III) with L1−L3 is significantly different from
that for Pt(II) or Pd(II), for which direct cyclometalation or
transmetalation from Ag(I) precursors is feasible.
with 1-iodohexane.36 Detailed synthetic protocols and ligand
characterization data are given in the Supporting Information.
Three different strategies were explored for complexation of
Au(III) by L1−L3: (i) direct complexation of Au(III) using the
free ligand and commercially available gold(III) salts such as
KAuCl4 and Au(OAc)3, (ii) synthesis and isolation of a silver(I)
precursor complex which is then reacted with one of the
aforementioned gold(III) sources with the expectation of a
transmetalation reaction, and (iii) synthesis and isolation of a
mercury(II) precursor complex and subsequent transmetalation
to Au(III). The following sections report our findings with
these three strategies for L1−L3.
2.2. Complexation Attempts with 1,3-Bis(1-hexyl-2′-
benzimidazoyl)benzene (L1H). For direct cyclometalation of
Pt(II) using K2PtCl4 as a starting material acetonitrile/water
mixtures are a common choice as a solvent.1,41,42 Our attempts
to form a complex of Au(III) with L1 under analogous
conditions using KAuCl4 failed; similar attempts had been
made earlier with NaAuCl4/HAuCl4 and 2-phenylpyridine.43
We also explored the possibility of enforcing the desired
cyclometalation by heating the neat precipitate obtained after
acetonitrile removal from the aforementioned CH3CN/H2O
mixtures to 150 °C. In two independent attempts we were able
to isolate in ∼20% yield a product whose elemental analysis is
compatible with the formulation C64H76N8Au4Cl6, implying
2. RESULTS AND DISCUSSION
2.1. Ligand Syntheses and Strategies for Complex-
ation. Ligands L1−L3 were synthesized by following previously
published protocols. Briefly, L1H was obtained by reacting
isophthalic acid and o-phenylenediamine in polyphosphoric
acid,39 followed by alkylation with 1-iodohexane.40 The
1
two molecules of L1H per formula unit. H/13C NMR and
high-resolution mass spectroscopy data of this material are
consistent with a gold(I) dimer cation ([Au2(L1H)2]2+), as
shown in Scheme 2; from the NMR data it is obvious that
cyclometalation has not occurred. To account for the elemental
analysis data, one has to invoke one [AuCl2]− and one
[AuCl4]− counteranion, which seems to make chemical sense.
Given the preference of Au(I) for linear coordination, we
2+
bromide salt of L2H2 is available in one step from the
reaction of 2,6-dibromopyridine with 1-butylimidazole.38
L3H2 was obtained as an iodide salt from reaction of 2,6-
2+
dibromopyridine with benzimidazole followed by alkylation
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assume that each gold(I) center is ligated to two N atoms of
different ligands, giving a dimeric structure, as has been
reported previously for dinuclear Ag(I) or Au(I) complexes
with comparable ligands.36,44−46
chains).34 One noticeable difference is that the AuIII−Cl bond
distance in our three structures is shorter (2.350(3)−2.359(2)
Å) than the PtII−Cl distance (2.4046(11) Å). In contrast, the
AuIII−C distance (1.972(13)−2.005(10) Å) is longer than the
PtII−C distance (1.932(4) Å) in the aforementioned Pt(II)
complex. In [Au(L1)Cl]2[HgCl4] parts of the hexyl chains were
found to be disordered over two positions with equal
occupancy. More interesting are the differences in packing
between the three different salts of the [Au(L1)Cl]+ complex,
particularly in view of the possibility of d8−d8 interactions, as
observed for many square-planar Pt(II) complexes.49−51 In the
tetrachloromercurate(II) and dichloroaurate(I) salts, the
cations form linear chains along the crystallographic a axis
with individual complexes oriented in a head-to-tail fashion
(Figures S2 and S3 in the Supporting Information). These
chains form as a result of π-stacking between benzimidazole
rings of the cationic complexes ,with interplanar distances
ranging from ca. 3.2 to 3.6 Å.52 Within the chains, in the
tetrachloromercurate salt, there are alternatively short−long−
short−medium intermetallic distances (dAu−Au = 3.920(1)/
4.417(1)/3.920(1)/4.009(1) Å), whereas in the dichloroaurate
salt the intermetallic distances (dAu−Au) alternate between
4.198(2) and 4.389(2) Å. These AuIII−AuIII contacts are clearly
too long to speak of significant metal−metal interactions. For
reference, a recent study reported an AuIII−AuIII separation as
short as 3.495 Å,16 and a distance of 3.846 Å was found for
another material with square-planar gold(III).14 The cationic
chains along the a axis are separated from each other by the
counteranions and by space taken up by the hexyl chains
(Figures S2 and S3). These chains stack in a parallel fashion
with interchain distances of 15.6412(15) and 16.3321(14) Å in
the tetrachloromercurate salt and 15.2847(11) and
15.1948(15) Å in the dichloroaurate(I) salt.
Transmetalation from Hg(II) precursor complexes has
previously been identified as an efficient method for complex-
ation of Au(III) and other d8 metals;6,43,47,48 hence, in a first
step it seemed promising to react L1H with Hg(OAc)2 in
ethanol in the presence of LiCl. The reaction product, obtained
in 27% yield, is unequivocally the expected Hg(L1)Cl complex
(Scheme 2). Subsequent reaction of Hg(L1)Cl with HAuCl4 in
ethanol in the presence of NaHCO3 gave the desired
[Au(L1)Cl]+ complex (Scheme 2) in good yields (73−84%).
When Hg(L1)Cl and HAuCl4 are reacted in a 1:1 molar ratio,
the [Au(L1)Cl]+ complex is obtained as a tetrachloromercurate-
(II) salt ([Au(L1)Cl]2[HgCl4]), whereas a molar ratio of 1:2
between Hg(L1)Cl and HAuCl4 yields the tetrachloroaurate salt
([Au(L1)Cl][AuCl4]). Both salts were fully characterized (see
the Experimental Section), and we obtained X-ray diffraction
data from single crystals for both salts. The cation of
[Au(L1)Cl][AuCl4] is shown in Figure 1.
In the tetrachloroaurate(III) salt the crystal packing is very
different, with cations oriented both along the a and c axes
(Figure S1, Supporting Information). Here, too, the cationic
complexes are π stacked (interplane distance of ca. 3.5 Å) and
oriented in a head-to-tail fashion to form pairs with short AuIII−
AuIII distances of 3.622(1) Å. Each [Au(L1)Cl]+ cation pair is
Figure 1. Crystal structure of the [Au(L1)Cl]+ cation in [Au(L1)Cl]-
[AuCl4]. Hydrogen atoms are omitted for clarity.
−
A third crystal structure with AuCl2 as a counteranion
([Au(L1)Cl][AuCl2]) was also accidently obtained (see the
Supporting Information). There are no unusual features in the
[Au(L1)Cl]+ cation structures, as most of the bond lengths and
angles around the metal center are similar to those previously
reported for an analogous chloroplatinum(II) complex with a
modified version of tridentate L1 (butyl groups instead of hexyl
−
surrounded by two AuCl4 anions to form a charge-neutral
tetranuclear unit with AuIII−AuIII distances of 4.016(1) Å
between cationic and anionic units. The [Au(L1)Cl][AuCl4]
and [Au(L1)Cl]2[HgCl4] compounds both emit in the solid
state with λmax at 427 nm at room temperature, and they
Figure 2. Excitation (dashed lines) and emission (solid lines) spectra of [Au(L1)Cl][AuCl4] and [Au(L1)Cl]2[HgCl4] in frozen 2-
methyltetrahydrofuran at 77 K. For the excitation spectra detection occurred at 463 nm, and for the emission spectra excitation was at 345 nm.
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−
luminesce in frozen 2-methyltetrahydrofuran at 77 K (Figure
2). It thus appears that the counteranion has little influence on
the luminescence properties of these two materials. This
observation is noteworthy because many square-planar d8
complexes exhibit strongly counterion dependent emission
properties,53 sometimes even in dilute solution.54,55 In room-
temperature solution the [Au(L1)Cl][AuCl4] and [Au(L1)-
Cl]2[HgCl4] compounds are nonemissive.
There is a fairly large shift between absorption and emission
maxima in Figure 2, which we attribute to the fact that in
absorption singlet−singlet transitions are observed, while the
emission likely occurs from a triplet excited state.
Given the prior observation that alkynylplatinum(II) and
alkynylgold(III) compounds exhibit enhanced luminescence
properties with respect to chloroplatinum(II) and chlorogold-
(III) complexes, we were interested in replacing the chloro
ligand of [Au(L1)Cl]+ by a 4-ethynyltoluene ligand. A common
method for introducing alkynyl ligands to Pt(II) and Au(III)
complexes is the use of Sonogashira coupling conditions,14,56
but our attempts to perform ligand exchange in dichloro-
methane in the presence of CuI and triethylamine or
diisopropylamine were unsuccessful. A method previously
used for introduction of an ethynyl ligand to a gold(III) center
seemed to yield the desired [Au(L1)(CCC6H4CH3)]+
complex in very modest yields.15 This method makes use of
n-butyllithium in THF at −78 °C to deprotonate 4-
ethynyltoluene before exposing it to [Au(L1)Cl]+. However,
while we were able to detect the [Au(L1)(CCC6H4CH3)]+
cation in high-resolution mass spectrometry, we were unable to
obtain satisfactory elemental analysis data: i.e., the compound
could not be properly characterized. It seems interesting to
note that acetonitrile solutions of this compound are emissive
at room temperature (Figure S4, Supporting Information), but
more detailed investigations of this compound are not
appropriate under these circumstances. The key point is here
that the synthesis of the [Au(L1)(CCC6H4CH3)]+ complex
seems to be significantly more delicate than the synthesis of
analogous Pt(II) alkynyls.
ligands, but Br−/Cl− ligand exchange reactions on the AuCl4
complex are known.57 In our case the source of Br− must be the
L2H2Br2 starting material. We note that full exchange of Cl− by
Br− is only complete in the small fraction (∼16%) of the
reaction mixture which crystallized; mass spectrometry of the
−
supernatant provides evidence for AuCl2 , AuClBr−, and
−
AuCl4 anions (see the Supporting Information). The second
observation is that one of the two involved gold centers has
been reduced to the monovalent state. The Au−Br distances in
the tetrabromoaurate(III) anion range from 2.3500(12) to
2.4143(10) Å, while in the dibromoaurate(I) anion they are
2.3688(15) and 2.3700(13) Å. The two imidazolium rings of
the uncoordinated organic ligand are almost perfectly coplanar
with the central pyridine ring, whereas the n-butyl chains are
bent with maximum angles of ca. 104 and 138° with respect to
the average plane of the aromatic core. One of the two butyl
chains was found to be disordered over two positions in a 3:1
ratio. The uncoordinated organic ligand interacts with the
tetrabromoaurate anions through weak C−H···Br hydrogen
bonds (dC−Br = 3.620(1) and 3.777(1) Å).58
For the synthesis of NHC complexes the use of trans-
metalation reactions from silver(I) precursor complexes is
common practice, at least when aiming at gold(I) com-
plexes.59,60 We explored whether this would also be a viable
procedure for obtaining a [Au(L2)Cl] complex in which the L2
ligand is tridentate to Au(III). Reaction of L2H2Br2 with Ag2O
in dry methanol at room temperature and subsequent
treatment with KPF6 afforded the [Ag2(L2)2](PF6)2 complex,
which has a formula similar to that of a previously characterized
dinuclear silver(I) complex;36 probably its structure is similar,
but we have no crystallographic data to prove this. [Ag2(L2)2]-
(PF6)2 was then reacted with Au(OAc)3 in 2-methoxyethanol at
110 °C, yielding a structurally analogous dinuclear Au(I)
complex, similar to a recently published gold(I) dimer.59
[Au2(L2)2](PF6)2 could be crystallized from acetone solution,
and X-ray diffraction gave the structure shown in Figure 4.
2.3. Complexation Attempts with 2,6-Bis(3-butylimi-
dazol-1-ium)pyridine (L2H22+) and 2,6-Bis(3-hexylbenzi-
midazol-1-ium)pyridine (L3H22+). Reaction of KAuCl4 with
2+
2+
L2H2 or L3H2 in CH3CN/H2O mixtures does not lead to
any complexation of the organic ligands. From the reaction
with L2H2Br2 a material with the stoichiometry [L2H2][AuBr2]-
[AuBr4] crystallized (Figure 3). The first observation is that
−
chloro ligands of AuCl4 have been exchanged by bromo
Figure 4. Crystal structure of the cation of [Au2(L2)2](PF6)2.
Hydrogen atoms are omitted for clarity.
The bis-NHC ligands are arranged in a helical fashion,
yielding a C−Au−C angle of 173.9(2)°. Due to this helicity,
[Au2(L2)2][PF6]2 was found to crystallize in a chiral space
group (P6522). The Flack parameter was found to be
0.011(11), indicating that the measured crystal is enantiopure.
We did not try to isolate crystals of the other enantiomeric
form.
The intramolecular Au(I)−Au(I) distance is 3.3000(4) Å:
i.e., close to what may be called an aurophilic interaction.61 The
distances between gold(I) centers of two related dimers are
similar (3.2971(4) and 3.2797(9) Å, respectively).44,59 Given
the relatively short distance between metal centers, we were
Figure 3. Crystal structure of [L2H2][AuBr4][AuBr2]. Note that only
one of the two positions of the disordered n-butyl chains is shown.
Anisotropic displacement parameters are depicted at the 50%
probability level. Hydrogen atoms are omitted for clarity.
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interested in the emission properties of the [Au2(L2)2]2+
complex but found evidence that it might not be stable in
solution, at least not in CH3CN. From DOSY NMR
experiments a diffusion coefficient of 8.5 × 10−10 m2/s was
determined, which translates to a molecular radius of 6.96 Å
using the Stokes−Einstein relation for spherical particles. For
gold(I) complex with the formulation [Au2(L3)2]2+ (∼42%
yield) in which each Au(I) center is coordinated by an NHC
moiety from two different molecules of L3; slow evaporation of
CH3CN afforded single crystals suitable for X-ray diffraction,
and the obtained structure of the cation is shown in Figure 6
2+
reference, for the free L2H2 ligand we found a diffusion
coefficient of 1.01 × 10−9 m2/s, translating to a molecular
radius of 5.86 Å. The small increase (∼19%) in molecular
radius between free ligand and complex does not appear to be
compatible with a dimeric structure in CH3CN. Whether or not
the [Au2(L2)2]2+ complex is stable in noncoordinating solvents
is a separate question that we did not explore further. Under a
hand-held UV lamp the solid [Au2(L2)2](PF6)2 material did not
exhibit any emission that was readily visible by the naked eye.
Given the result of Au(I) coordination with L2 via the
silver(I) transmetalation procedure and our interest in Au(III)
complexes, with ligand L3 we decided to explore trans-
metalation from mercury(II) complexes. In a first step,
L3H2I2 was reacted with Hg(OAc)2 in ethanol at reflux, and
this resulted in a material (in ∼55% yield) whose elemental
analysis, NMR, and mass spectrometry data are consistent with
formulation as [Hg2(L3)2][HgI4]2.
Figure 6. Crystal structure of the cation from [Au2(L3)2][Hg2I6].
Hydrogen atoms are omitted for clarity.
Reaction of the mercury transmetalation product with
KAuCl4 in refluxing acetonitrile gives in 25% yield a dinuclear
Au(III) complex with the formulation [(AuI2Cl)2(L3)]. In this
complex the two NHC functions of L3 ligate to two different
Au(III) centers, each of which is additionally coordinated by
one chloro and two iodo ligands; an X-ray crystal structure of
this compound is shown in Figure 5. Evidently square-planar
(the counteranion is Hg2I62−). The pyridine moieties of two
different ligands L3 point to opposite sides of the cationic
complex, and they are tilted relative to the benzimidazole rings
by 49−77°. The metal centers are well separated with an Au−
Au distance of 6.562(2) Å. The Au−C bond distances range
from 2.007(9) to 2.027(7) Å and are consistent with an Au(I)
oxidation state; one of the two gold(I) coordination geometries
deviates significantly from linearity with a C−Au−C angle of
2−
168.8(3)°, due to a weak Au−I interaction with the Hg2I6
anion (dAu−I = 3.372(7) Å). The counteranion contains two
Hg(II) centers in distorted-tetrahedral environments with two
bridging iodine atoms.
3. SUMMARY AND CONCLUSIONS
The desired square-planar complexation of Au(III) by a
tridentate ligand backbone could only be achieved with L1, a
transmetalation reaction from a mercury(II) precursor being
the only viable synthetic route. The obtained [Au(L1)(C
CC6H4−CH3)]+ complex exhibits promising emission proper-
ties, and in the future it may be interesting to perform a
comparative photophysical study of such complexes with
variable alkynyl ligands. With ligands L2 and L3 mostly Au(I)
complexes were obtained, irrespective of whether trans-
metalation occurred from Ag(I) or Hg(II). Thus, we have
found no experimental evidence that L2 and L3 can indeed act
as tridentate ligands to Au(III), despite the fact that closely
related analogues are known to ligate to isoelectronic Pt(II) in a
tridentate fashion.36−38 In future work it might be worthwhile
to explore the use of gold sources other than KAuCl4 or
Figure 5. Crystal structure of the [(AuI2Cl)2(L3)] complex as found in
[(AuI2Cl)2(L3)]·Et2O. Note that only one of the two positions of the
disordered n-hexyl chains is shown. Hydrogen atoms are omitted for
clarity.
Au(III) is present, and the AuIII−C(carbene) bond lengths are
somewhat shorter (1.995(6) and 2.000(7) Å, respectively) than
what was observed above for the AuI−C(carbene) bond lengths
of [Au2(L2)2]2+ (2.008(7)−2.021(6) Å). In the structure shown
in Figure 5, ligand L3 seems to be distorted in such a way as to
maximize the distance between the two AuI2Cl moieties. The
extremity of one of the two hexyl chains was found to be
disordered over two positions with equal occupancy.
−
Au(OAc)3. The tetrabutylammonium salt of AuCl4 would
Clearly, this is not the product we intended to make, but at
least in this case the transmetalation occurred to Au(III) rather
than Au(I). Therefore, we decided to react the [(AuI2Cl)2(L3)]
compound with 1 equiv of the [Hg2(L3)2]4+ precursor material
from above. The idea was to use the [(AuI2Cl)2(L3)]
compound as an alternative gold source (instead of KAuCl4),
in which the two Au(III) centers are already ligated to a
carbene, and it was hoped that the iodo and chloro ligands of
each AuI2Cl entity would be replaced by tridentate L3.
However, reaction in refluxing CH3CN produced a dinuclear
represent an interesting choice for organic solvents. For Pt(II)
chemistry the [Pt(CH3CN)4]2+ complex is a highly useful
starting material, and similar gold(III) complexes would be
promising.
4. EXPERIMENTAL SECTION
Thin-layer chromatography was performed using Polygram SIL G/
UV254 plates from Machery-Nagel, and for column chromatography
silica gel 60 from the same company was employed. Reaction products
1
were characterized by H NMR spectroscopy on a Bruker Avance
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DRX 300 spectrometer, by mass spectrometry using a Finnigan MAT
8200 (electron ionization, EI) and an Applied Biosystems API 2000
(electrospray ionization, ESI) instrument, and by elemental analysis
(Vario EL III CHNS analyzer from Elementar). Optical absorption
spectroscopy was performed using an Agilent Cary 300 spectropho-
tometer, and steady-state luminescence spectra were measured on a
Fluorolog-3 instrument (FL322) from Horiba Jobin-Yvon.
yellow precipitate was collected and washed with Et2O. [Au(L1)Cl]-
[AuCl4] was obtained as a yellow solid (437 mg, 0.42 mmol, 84%).
Single crystals suitable for X-ray diffraction were grown by slow
diffusion of diethyl ether vapor into an acetonitrile solution of the
1
compound. H NMR (300 MHz, DMSO-d6): δ 0.84 (t, J = 6.9 Hz, 6
H, 2 × CH3), 1.22−1.32 (m, 8 H, 4 × CH2), 1.39−1.49 (m, 4 H, 2 ×
CH2), 1.87−1.96 (m, 4 H, 2 × CH2), 4.89 (t, J = 7.2 Hz, 4 H, 2 ×
NCH2), 7.58−7.65 (m, 4 H, CHAr), 7.90 (t, J = 7.9 Hz, 1 H, CHAr),
8.08 (dd, J = 6.4, 3.1 Hz, 2 H, CHAr), 8.13 (d, J = 8.0 Hz, 2 H, CHAr),
8.65−8.71 (m, 2 H, CHAr) ppm. 13C NMR (75 MHz, DMSO-d6): δ
13.8, 21.9, 25.4, 29.4, 30.8, 45.2, 112.8, 115.7, 125.5, 126.6, 128.2,
128.9, 132.9, 137.3, 158.1 ppm. ESI-HRMS: m/z 709.2365 [M]+
(calcd for [C32H37N4AuCl]+ 709.2368). Anal. Calcd for
C32H37N4Au2Cl5·H2O: C, 36.09; H, 3.69; N, 5.26. Found: C, 35.93;
H, 3.37; N, 5.26.
4.1. Synthesis of [Au2(L1H)2](AuCl4)(AuCl2). A mixture of
K[AuCl4] (0.079 g, 0.21 mmol, 1.0 equiv) in H2O (4 mL) and 1,3-
bis(1-hexyl-2′-benzimidazoyl)benzene (0.10 g, 0.21 mmol, 1.0 equiv)
in CH3CN (4 mL) was stirred at room temperature overnight. Then
the CH3CN was evaporated and the precipitate was collected. The
solid was heated to 150 °C under nitrogen atmosphere (without any
solvent) overnight. Then the solid was cooled to room temperature.
The crude product was purified by column chromatography (silica,
ethyl acetate + 1% NEt3, Rf = 0.82). After drying in air
C64H76Au4Cl6N8 was obtained as a red solid (58.5 mg, 0.04 mmol,
20%). 1H NMR (300 MHz, CDCl3): δ 0.82 (s, 12 H, 4 × CH3), 1.21−
1.25 (m, 24 H, 12 × CH2), 1.85−1.96 (m, 8 H, 4 × CH2), 4.46 (t, J =
7.3 Hz, 8 H, 4 × NCH2), 7.50−7.54 (m, 8 H, CHAr), 7.57−7.62 (m, 4
H, CHAr), 7.85−7.92 (m, 2 H, CHAr), 7.98−8.06 (m, 8 H, CHAr), 8.18
(d, J = 1.8 Hz, 2 H, CHAr) ppm. 13C NMR (75 MHz, CDCl3): δ 14.3,
22.5, 26.4, 31.2, 46.8, 60.5, 111.7, 119.1, 130.5, 140.0 ppm. ESI-
HRMS: m/z 675.2762 [M]2+ (calcd for [C64H76Au2N8]2+ 675.2756).
Anal. Calcd for C64H76N8Au4Cl6: C, 39.30; H, 3.92; N, 5.73. Found: C
39.41; H, 3.96; N, 5.44.
4.5. Synthesis of [Au(L1)(CCC6H4CH3)]+. To a solution of p-
tolylacetylene (0.05 mL, 0.39 mmol, 2.0 equiv) in dry THF (20 mL)
was added n-butyllithium (2.5 M in hexane, 0.19 mL, 0.46 mmol, 2.3
equiv) under nitrogen in a dropwise manner at −78 °C. The resulting
mixture was stirred for 5 min at −78 °C and transferred subsequently
to a suspension of [Au(L1)Cl][AuCl4] (202.1 mg, 0.19 mmol, 1.0
equiv) in THF (20 mL). The reaction mixture was stirred for 3 h at
room temperature in the dark, and then the mixture was quenched by
addition of a saturated aqueous ammonium chloride solution (0.7
mL). The crude product, which was obtained after solvent removal,
was washed with dichloromethane and diethyl ether, followed by
extraction with acetonitrile. The acetonitrile fraction was concentrated
and placed in a flask with diethyl ether overnight. A white solid
precipitated from the mixture. [Au(L1)(CCC6H4−CH3)]+ was
obtained by drying the filtrate in vacuo (9.2 mg, 0.008 mmol, 4.2%).
ESI-HRMS: m/z 789.3226 [M]+ (calcd for [C41H44N4Au]+ 789.3226).
4.6. Synthesis of [L2H2][AuBr2][AuBr4]. To a stirred solution of
L2H2Br2 (64.2 mg, 0.132 mmol) in acetonitrile (1.0 mL) was added an
aqueous solution (7.0 mL) of K[AuCl4] (50.0 mg, 0.132 mmol). The
resulting suspension was stirred at reflux under N2 and in the absence
of light for 1 day. The solvent was evaporated until the product
precipitated as a red solid. Single crystals, suitable for X-ray diffraction
studies, were grown by slow diffusion of diethyl ether vapor into an
acetone solution of the compound (25.3 mg, 0.02 mmol, 16%). When
the same reaction mixture was refluxed for 3 days, the same product
4.2. Synthesis of Hg[L1]Cl. 1,3-Bis(1-hexyl-2′-benzimidazoyl)-
benzene (200 mg, 0.418 mmol, 1.0 equiv) and Hg(OAc)2 (146.6 mg,
0.460 mmol, 1.1 equiv) were dissolved in ethanol (7 mL) and then
heated to 88 °C for 3 days. The reaction mixture was cooled to room
temperature, and LiCl (39 mg, 0.92 mmol, 2.2 equiv) in methanol (6
mL) was added. Then the reaction mixture was heated to reflux for 20
min and cooled back to room temperature again. After pouring the
solution in water, the aqueous mixture was extracted with ethyl acetate,
dried over Na2SO4, and evaporated to dryness. The crude product was
purified by column chromatography (silica gel, ethyl acetate/pentane/
CH2Cl2 4/4/2). After drying under vacuum, Hg[L1]Cl was obtained as
a white solid (80.1 mg, 0.11 mmol, 27%). 1H NMR (300 MHz,
DMSO-d6): δ 0.75−0.83 (m, 6 H, 2 × CH3), 1.18 (d, J = 3.1 Hz, 12 H,
4 × CH2), 1.75 (t, J = 7.2 Hz, 4 H, 2 × CH2), 4.39 (t, J = 7.6 Hz, 4 H,
2 × NCH2), 7.26−7.38 (m, 4 H, CHAr), 7.67−7.74 (m, 5 H, CHAr),
8.02 (d, J = 7.7 Hz, 2 H, CHAr) ppm. 13C NMR (75 MHz, DMSO-d6):
δ 13.8, 21.9, 25.7, 29.0, 30.5, 44.5, 111.2, 119.1, 122.3, 122.8, 128.1,
129.4, 135.8, 136.1, 142.0, 156.5 ppm. ESI-HRMS: m/z 715.2489 [M
+ H]+ (calcd for C32H38ClHgN4]+ 715.2480). Anal. Calcd for
C32H37N4ClHg·0.5H2O: C, 53.09; H, 5.30; N, 7.74. Found: C,
53.15; H, 5.20; N, 7.51.
1
was obtained. H NMR (300 MHz, CD3CN): δ 1.02 (t, J = 7.3 Hz, 6
H, 2 × CH3), 1.26−1.36 (m, 8 H, CH2), 4.32 (t, J = 7.3, 4 H, NCH2),
7.69 (t, J = 2.0 Hz, 2 H, CHAr), 7.92 (d, J = 8.1 Hz, 2 H, CHAr), 8.24
(t, J = 2.0 Hz, 2 H, CHAr), 8.45 (t, J = 8.1 Hz, 1 H, CHAr), 9.49 (s, 2 H,
CHAr) ppm. 13C NMR (75 MHz, CD3CN): δ 12.4, 18.8, 31.0, 50.1,
114.6, 119.4, 123.6, 144.6. FD-MS: m/z 592.1 [M + AuCl2]+, 638.0
[M + AuClBr]+, 664.0 [M + AuCl4]+, 682.0 [M + AuBr2]+. Anal. Calcd
for C19H27N5Au2Br6: C, 19.12; H, 2.28; N, 5.87. Found: C, 19.23; H,
2.28; N, 5.83.
4.3. Synthesis of [Au(L1)Cl]2[HgCl4]. A mixture of Hg[L1]Cl
(73.0 mg, 0.10 mmol, 1.0 equiv), HAuCl4 (34.7 mg, 0.10 mmol, 1.0
equiv), and NaHCO3 (8.4 mg, 0.10 mmol, 1.0 equiv) in ethanol (14
mL) was stirred in the absence of light at room temperature overnight.
The white precipitate was collected and washed with Et2O.
[Au(L1)Cl]2[HgCl4] was obtained as a white solid (77.3 mg, 0.073
mmol, 73%). Single crystals of [Au(L1)Cl]2[HgCl4]·CH3CN suitable
for X-ray diffraction measurements were grown by slow evaporation of
4.7. Synthesis of [Ag2(L2)2](PF6)2. A mixture of Ag2O (0.72 g,
3.12 mmol) and L2H2Br2 (0.60 g, 1.2 mmol) in anhydrous methanol
(54 mL) was stirred in the dark at room temperature under N2 for 2
days. Then the mixture was filtered through Celite. Subsequently a
solution of KPF6 in anhydrous methanol (21.5 mL) was added to the
filtrate. The resulting white precipitate was collected and washed with
hot methanol to afford colorless crystals of [Ag2(L2)2](PF6)2 (0.40 g,
1
acetonitrile. H NMR (300 MHz, DMSO-d6): δ 0.84 (t, J = 6.8 Hz, 6
1
H, 2 × CH3), 1.21−1.34 (m, 8 H, 4 × CH2), 1.40−1.49 (m, 4 H, 2 ×
CH2), 1.91 (t, J = 7.8 Hz, 4 H, 2 × CH2), 4.88 (t, J = 7.1 Hz, 4 H, 2 ×
NCH2), 7.57−7.64 (m, 4 H, CHAr), 7.90 (t, J = 7.9 Hz, 1 H, CHAr),
8.06 (dd, J = 6.6, 2.8 Hz, 2 H, CHAr), 8.13 (d, J = 8.0 Hz, 2 H, CHAr),
8.64 (dd, J = 6.5, 3.1 Hz, 2 H, CHAr) ppm. 13C NMR (75 MHz,
CD3CN): δ 14.2, 23.1, 26.9, 30.4, 32.0, 46.9, 113.2, 117.1, 118.8, 126.7,
127.8, 128.9, 130.6, 134.1, 138.8 ppm. ESI-HRMS: m/z 709.2361
[M]+ (calcd for [C32H37N4AuCl]+ 709.2368). Anal. Calcd for
C32H37N4AuCl5Hg: C, 36.53; H, 3.55; N, 5.33. Found: C, 36.66; H,
3.57; N, 5.19.
0.35 mmol, 30%). H NMR (300 MHz, CD3CN): δ 0.67 (t, J = 7.3
Hz, 12 H, 4 × CH3), 1.03 (h, J = 7.3, 7.3 Hz, 8 H, CH2), 1.22−1.39
(m, 4 H, CH2), 3.79 (t, J = 7.6 Hz, 8 H, NCH2), 7.36 (t, J = 1.8 Hz, 4
H, CHAr), 7.78 (d, J = 8.0 Hz, 4 H, CHAr), 7.88 (t, J = 1.7 Hz, 4 H,
CHAr), 8.32 (t, J = 8.0 Hz, 2 H, CHAr) ppm. 13C NMR (75 MHz,
CD3CN): δ 12.3, 18.7, 32.4, 51.7, 113.6, 123.0, 123.1, 143.4, 148.8
−
ppm. 31P NMR (162 MHz, acetone-d6): δ −144.2 (septuplet for PF6
anion). Positive-ion ESI-MS: m/z 432.0 [M]2+.
4.8. Synthesis of [Au2(L2)2](PF6)2. A solution of gold(III) acetate
(80.0 mg, 0.21 mmol) in 2-methoxyethanol (8.0 mL) was added to a
solution of [Ag2(L2)2](PF6) (112 mg, 0.09 mmol) in 2-methoxy-
ethanol (15 mL). The mixture was stirred at 110 °C in the dark under
N2 for 12 h. After it was cooled to room temperature, the reaction
mixture was filtered through Celite and the filtrate was concentrated
4.4. Synthesis of [Au(L1)Cl][AuCl4. ]A mixture of Hg[L1]Cl (353
mg, 0.49 mmol, 1.0 equiv), HAuCl4 (335.6 mg, 0.98 mmol, 2.0 equiv),
and NaHCO3 (41.5 mg, 0.49 mmol, 1.0 equiv) in ethanol (60 mL)
was stirred in the absence of light at room temperature overnight. The
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Organometallics
Article
under reduced pressure. The residue was dissolved in hot acetone (30
mL) and filtered through Celite. Slow evaporation of acetone afforded
colorless crystals of [Au2(L2)2](PF6)2 which were suitable for X-ray
diffraction (23.2 mg, 0.017 mmol, 20%). 1H NMR (300 MHz,
CD3CN): δ 0.63 (t, J = 7.3 Hz, 12 H, 4 × CH3), 1.00 (q, J = 7.3 Hz, 8
H, CH2), 1.23−1.35 (m, 8 H, CH2), 3.85−3.99 (m, 8 H, NCH2), 7.35
(d, J = 2.1 Hz, 4 H, CHAr), 7.80 (d, J = 8.1 H, 4 H, CHAr), 7.88 (d, J =
2.1 Hz, 4 H, CHAr), 8.32 (t, J = 8.1 Hz, 2 H, CHAr) ppm. 13C NMR
(75 MHz, CD3CN): δ 13.5, 19.9, 33.4, 52.7, 114.9, 120.1, 124.3 ppm.
using SADABS.62 All structures were solved by direct methods and
refined by a full-matrix least-squares method on F2 using SHELXL-
97.63 All non-hydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were placed at calculated
positions using suitable riding models. Their positions were con-
strained relative to their parent atom using the appropriate HFIX
command in SHELXL-97. Some parts of the hexyl chains in
[Au(L1)Cl]2[HgCl4]·MeCN, [Au(L1)Cl][AuCl4], [L2H2][AuBr2]-
[AuBr4], [(AuI2Cl)2(L3)]·Et2O, and [Au2(L3)2][Hg2I6] were refined
using DFIX, DANG, and SIMU contraints/restraints. Parts of some of
the alkyl chains were found to have further positional disorders. In
[Au(L1)Cl]2[HgCl4]·MeCN, C26 was refined on two positions
(named C26A and C26B) with identical anisotropic displacement
parameters. For atoms C29−C32 and C56−C58 we proceeded in the
same manner. The relative occupancies between the two positions of
each atom were refined with 1:1 ratios. In the structure of
[L2H2][AuBr2][AuBr4], the C2 and C3 atoms were refined on two
positions (named C2A/C2B and C3A/C3B) with identical anisotropic
displacement parameters. The relative occupancies between the A and
B positions were found to be ca. 3:1. In the structure of
[(AuI2Cl)2(L3)]·Et2O, the C31 atom was refined on two positions
(C31A/C31B) with identical anisotropic displacement parameters and
relative occupancies. In the structure of [Au2(L3)2][Hg2I6], small
channels occupying 4.8% of the volume of the crystal are located along
the b crystallographic axis. The highest residual electronic density in
these channels was found to be 1.35 e/Å3, which does not give clear
evidence for the presence of any solvent molecules in this void space.
Further details about the crystal structure refinements can be found
directly in the CIF files (Supporting Information).
E S I - M S : m / z 5 2 0 . 1 [ M ] 2 +
.
A n a l . C a l c d f o r
C38H50N10Au2P2F12·2H2O·C3H8O2: C, 34.11; H, 4.33; N, 9.71.
Found: C, 33.89; H, 4.44; N, 9.55.
4.9. Synthesis of [Hg2(L3)2][HgI4]2. A mixture of L3H2I2 (600 mg,
0.82 mmol, 1.0 equiv) and Hg(OAc)2 (260 mg, 0.82 mmol, 1.0 equiv)
was dissolved in ethanol (20 mL) and heated to reflux overnight. Then
the reaction mixture was cooled to room temperature. The white
precipitate was collected and washed with H2O. After drying in vacuo
[Hg2(L3)2][HgI4]2 was obtained as a white solid (629 mg, 0.23
mmol). 1H NMR (300 MHz, DMSO-d6): δ 0.89 (t, J = 6.7 Hz, 6 H, 2
× CH3), 1.12−1.43 (m, 16 H, 8 × CH2), 1.62 (s, 2 H, CH2), 4.21 (s, 2
H, NCH2), 7.60 (d, J = 8.3 Hz, 2 H, CHAr), 7.70 (t, J = 7.8 Hz, 2 H,
CHAr), 7.80 (t, J = 7.8 Hz, 2 H, CHAr), 8.05 (d, J = 8.3 Hz, 2 H, CHAr),
8.49 (d, J = 7.9 Hz, 2 H, CHAr), 8.80 (t, J = 8.0 Hz, 1 H, CHAr) ppm.
ESI-MS: m/z 808.13 [M]+. Anal. Calcd for C62H76N10Hg4I8: C, 26.82;
H, 2.69; N, 5.04. Found: C, 26.94; H, 2.77; N, 5.04.
4.10. Synthesis of [(AuI2Cl)2(L3)]. A suspension of [Hg2(L3)2]-
[HgI4]2 (150 mg, 0.05 mmol, 2.0 equiv) and K[AuCl4] (44.9 mg, 0.12
mmol, 1.1 equiv) in CH3CN (7 mL) was heated to reflux in the dark
for 24 h. During the heating process the mixture changed from yellow
to deep red. Then the mixture was cooled to room temperature and a
solid precipitated. [(AuI2Cl)2(L3)] was obtained as a red solid (39.9
mg, 0.027 mmol, 25%). Single crystals of [(AuI2Cl)2(L3)]·Et2O
suitable for X-ray diffraction were grown by slow diffusion of diethyl
ASSOCIATED CONTENT
* Supporting Information
■
S
Tables, figures, text, and CIF files giving X-ray diffraction data,
crystal packing diagrams, synthesis protocols, and product
characterization data for the organic ligands. This material is
available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre. CCDC 911958, 911959, 911960, 911961, 911962,
911963, and 911964 contain supplementary crystallographic
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
1
ether vapor into a dichloromethane solution of the compound. H
NMR (300 MHz, DMSO-d6): δ 0.92 (t, J = 6.7 Hz, 6 H, 2 × CH3),
1.31−1.51 (m, 12 H, 6 × CH2), 2.05 (t, J = 7.2 Hz, 4 H, 2 × CH2),
4.71 (t, J = 7.1 Hz, 4 H, 2 × NCH2), 7.52−7.68 (m, 4 H, CHAr), 8.05
(dd, J = 8.2, 3.6 Hz, 4 H, CHAr), 8.50 (d, J = 7.9 Hz, 2 H, CHAr), 8.70
(dd, J = 8.5, 7.4 Hz, 1 H, CHAr) ppm. 13C NMR (75 MHz, DMDO-
d6): δ 13.1, 21.2, 24.8, 28.5, 29.9, 40.1, 99.1, 100.9, 111.8, 112.7, 121.4,
124.6, 124.8, 131.6, 131.8, 148.5, 176.1 ppm. ESI-MS: m/z 908.2 [M −
I4Cl]+, 1000.14 [M − I3Cl2]+.
4.11. Synthesis of [Au2(L3)2][Hg2I6].
A solution of
[(AuI2Cl)2(L3)] (65.0 mg, 0.06 mmol, 1.0 equiv) in CH2Cl2 (8 mL)
was added to a solution of [Hg2(L3)2][HgI4]2 (183.3 mg, 0.07 mmol,
2.2 equiv of [Hg(L3)]2+) in CH3CN (8 mL). Then the mixture was
heated to reflux in the dark overnight. During the reaction the mixture
changed from red to colorless. Finally, the reaction mixture was cooled
to room temperature and concentrated to a small volume (∼4 mL).
The greenish solid was collected and washed with CH3CN, methanol,
acetone, H2O, and CH2Cl2 to yield [Au2(L3)2][Hg2I6] as a pale green
solid (49.7 mg, 0.025 mmol, 42%). Single crystals suitable for X-ray
AUTHOR INFORMATION
Corresponding Author
*E-mail: oliver.wenger@unibas.ch.
■
Notes
The authors declare no competing financial interest.
1
diffraction were grown by slow evaporation of acetonitrile. H NMR
ACKNOWLEDGMENTS
Funding from the Deutsche Forschungsgemeinschaft (DFG)
through Grant No. WE4815/2-1 is gratefully acknowledged.
(300 MHz, DMSO-d6): δ 0.72−0.79 (m, 12 H, CH3), 1.16 (d, J = 3.7
Hz, 12 H, 6xCH2), 1.21−1.33 (m, 12 H, 6 × CH2), 1.73−1.84 (m, 8
H, 4 × CH2), 4.60 (t, J = 7.3 Hz, 8 H, 4 × NCH2), 7.53−7.66 (m, 8 H,
CHAr), 7.79 (d, J = 7.9 Hz, 4 H, CHAr), 7.99 (d, J = 7.8 Hz, 4 H,
CHAr), 8.19 (d, J = 7.9 Hz, 4 H, CHAr), 8.46 (t, J = 7.9 Hz, 2 H, CHAr)
ppm. 13C NMR (75 MHz, DMSO-d6): δ 13.8, 21.9, 25.8, 29.7, 30.66,
48.7, 112.8, 113.2, 121.4, 125.8, 125.9, 132.4, 132.7, 148.6, 188.6 ppm.
ESI-HRMS: m/z 676.2709 [M]2+ (calcd for [C62H74N10Au2]2+
676.2712). Anal. Calcd for C62H74Au2N10I6Hg2: C, 29.60; H, 2.96;
N, 5.57. Found: C, 29.94; H, 3.04; N, 5.57.
4.12. X-ray Crystal Structure Studies. The crystallographic data
were collected with a Bruker APEX II diffractometer (in Bordeaux),
equipped with a graphite monochromator centered on the path of Mo
Kα radiation. Single crystals were coated with Paratone N oil and
mounted on a fiber loop, followed by data collection at 120 K (except
for [Au2(L2)2](PF6)2, which was measured at 100 K). The program
SAINT was used to integrate the data, which was thereafter corrected
■
́
The FEDER and Region Aquitaine are thanked for funding the
X-ray diffractometer.
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