Homoleptic copper(I), silver(I), and gold(I) bisphosphine complexes

Article abstract of DOI:10.1002/ejic.201301349

A series of homoleptic copper(I), silver(I), and gold(I) complexes of two bisphosphine ligands {1,2-bis(diphenylphosphino)benzene, dppb; bis[2-(diphenylphosphino)phenyl]ether, POP} have been prepared. Whilst all three [M(dppb)₂]BF₄ complexes are tetracoordinate, this geometry is found only for the silver(I) complex with POP. Instead, [Cu(POP)₂]⁺ and [Au(POP)₂]⁺ adopt a trigonal coordination geometry with an uncoordinated phosphorus atom. A close inspection of the P-M bond lengths reveals an interesting trend. From the copper to silver and gold complexes, a substantial elongation is found. On the other hand, from the silver to gold compounds, a decrease in the M-P bond length is found. Indeed, gold(I) has a smaller van der Waals radius than silver(I) as a result of its peculiar relativistic effects. Electrochemical investigations revealed two oxidation processes for all of the [M(dppb)₂]BF ₄ and [M(POP)₂]BF₄ complexes. The first oxidation is likely metal-centered, whereas the second one corresponds to ligand-centered processes in all cases. The emission properties of these compounds in solution, in frozen rigid matrices at 77 K, and in the solid state at room temperature have been systematically investigated. Although all of them are weak emitters in solution, remarkably high emission quantum yields were found in the solid state, in particular for [Cu(dppb)₂]BF₄ and [Ag(dppb)₂]BF₄. Finally, these two compounds were used for the fabrication of light-emitting devices. Interestingly, both the copper(I) and the silver(I) complex afford quite broad electroluminescence spectra with white light emission. Copper(I), silver(I), and gold(I) [M(PP) ₂]BF₄ complexes have been prepared from two bisphosphine ligands, namely, 1,2-bis(diphenylphosphino)benzene (dppb) and bis[2-(diphenylphosphino)phenyl]ether (POP). Their electronic properties have been systematically investigated and rationalized as a combination of steric and electronic effects as well as by differences in their coordination geometries.

Full text of DOI:10.1002/ejic.201301349

FULL PAPER
DOI:10.1002/ejic.201301349
Homoleptic Copper(I), Silver(I), and Gold(I) Bisphosphine
Complexes
Adrien Kaeser,[a,b] Omar Moudam,[a,b] Gianluca Accorsi,[c]
Isabelle Séguy,*[d,e] Jose Navarro,[d] Abdelhalim Belbakra,[c]
Carine Duhayon,[b] Nicola Armaroli,*[c] Béatrice Delavaux-Nicot,*[b]
and Jean-François Nierengarten*[a,b]
Dedicated to Bruno Chaudret on the occasion of his 60th birthday
Keywords: Phosphine ligands / Copper / Silver / Gold / Emission
A series of homoleptic copper(I), silver(I), and gold(I) com-
plexes of two bisphosphine ligands {1,2-bis(diphenylphos-
vestigations revealed two oxidation processes for all of the
[M(dppb)2]BF4 and [M(POP)2]BF4 complexes. The first oxi-
phino)benzene, dppb; bis[2-(diphenylphosphino)phenyl]- dation is likely metal-centered, whereas the second one cor-
ether, POP} have been prepared. Whilst all three [M(dppb)2]-
BF4 complexes are tetracoordinate, this geometry is found
only for the silver(I) complex with POP. Instead, [Cu(POP)2]+
and [Au(POP)2]+ adopt a trigonal coordination geometry with
an uncoordinated phosphorus atom. A close inspection of the
P–M bond lengths reveals an interesting trend. From the cop-
per to silver and gold complexes, a substantial elongation is
found. On the other hand, from the silver to gold compounds,
a decrease in the M–P bond length is found. Indeed, gold(I)
has a smaller van der Waals radius than silver(I) as a
result of its peculiar relativistic effects. Electrochemical in-
responds to ligand-centered processes in all cases. The emis-
sion properties of these compounds in solution, in frozen ri-
gid matrices at 77 K, and in the solid state at room tempera-
ture have been systematically investigated. Although all of
them are weak emitters in solution, remarkably high emis-
sion quantum yields were found in the solid state, in particu-
lar for [Cu(dppb)2]BF4 and [Ag(dppb)2]BF4. Finally, these two
compounds were used for the fabrication of light-emitting
devices. Interestingly, both the copper(I) and the silver(I)
complex afford quite broad electroluminescence spectra with
white light emission.
bisphosphine derivatives have been systematically investi-
gated with virtually all of the metallic elements.[1] In the
particular case of the group 11 elements, a strong driving
force for structural investigations of bisphosphine com-
plexes is related to their relevance in the field of catalysis.[2]
In contrast, their electronic properties have attracted atten-
tion only in recent years. The discovery of strongly lumines-
cent copper(I) complexes incorporating bisphosphine li-
gands in their coordination sphere has been the starting
point of this research. In particular, McMillin and co-
workers have reported heteroleptic CuI complexes prepared
from 1,10-phenanthroline derivatives and bis[2-(diphenyl-
phosphino)phenyl]ether (POP),[3,4] which are characterized
by remarkably high emission quantum yields from their
long lived metal-to-ligand charge-transfer (MLCT) excited
states. Following this key finding, numerous examples of
related heteroleptic CuI complexes have been prepared from
bisphosphine and aromatic diimine ligands.[5–7] Eventually,
copper(I) compounds prepared exclusively from bisphos-
phine ligands were also reported.[8,9] Some of these com-
pounds exhibit excellent emission properties, which have
been exploited to fabricate efficient electroluminescent de-
vices; therefore, inexpensive and earth-abundant copper(I)
Introduction
Bisphosphines are widely used chelating ligands, and the
coordination properties of many commercially available
[a] Laboratoire de Chimie des Matériaux Moléculaires, Université
de Strasbourg et CNRS (UMR 7509),
25 rue Becquerel, 67087 Strasbourg Cedex 2, France
E-mail: nierengarten@unistra.fr
http://www-ecpm.u-strasbg.fr/umr7509/
WebLaboNierengarten.htm
[b] Laboratoire de Chimie de Coordination du CNRS (UPR 8241),
Université de Toulouse (UPS, INPT),
205 Route de Narbonne, 31077 Toulouse, France
E-mail: beatrice.delavaux-nicot@lcc-toulouse.fr
http://www.lcc-toulouse.fr/lcc/spip.php?article25
[c] Istituto per la Sintesi Organica e la Fotoreattività,
Consiglio Nazionale delle Ricerche,
Via Gobetti 101, 40129 Bologna, Italy
E-mail: nicola.armaroli@isof.cnr.it
http://www.isof.cnr.it/?q=content/armaroli-nicola
[d] Laboratoire Plasma et Conversion d’Energie (LAPLACE),
UPS-CNRS (UMR 5213),
118 route de Narbonne, 31062 Toulouse Cedex 9, France
[e] CNRS, LAAS,
7 avenue du colonel Roche, 31400 Toulouse, France
E-mail: iseguy@laas.fr
http://www.laas.fr/MICA/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301349.
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FULL PAPER
is an attractive alternative to noble metal ions for such ap-
plications.[9–11] Investigations on luminescent bisphosphine
copper(I) complexes have also been extended to analogous
silver(I) and gold(I) derivatives.[12–17] Interesting vapo-
chromic and mechanochromic properties have been re-
ported for these silver(I) and gold(I) derivatives.[13,14] Lumi-
nescent gold(I) bisphosphine complexes have also been
tested in light-emitting devices.[15a]
In the frame of this expanding research field, we pre-
pared [Cu(PP)2]+ complexes with various bisphosphine li-
gands and systematically investigated their electronic prop-
erties.[9] The emission properties of the copper(I) complex
with 1,2-bis(diphenylphosphino)benzene (dppb) were par-
ticularly interesting. Although the emission quantum yield
of this compound is quite low in solution, it exhibits bright
luminescence in the solid state at room temperature as well
as in rigid frozen CH2Cl2 solutions at 77 K. Indeed, under
these conditions, geometric distortions that prompt nonra-
diative deactivation of the MLCT excited states are pre-
vented, as is often observed for copper(I) complexes.[18,19]
The [Cu(dppb)2]+ complex has also been used for the fabri-
cation of an electroluminescent device.[9]
Following these earlier studies on copper(I) compounds,
we became naturally interested in extending our investi-
gations to analogous silver(I) and gold(I) complexes. In this
paper, we now report homoleptic copper(I), silver(I), and
gold(I) complexes prepared from two bisphosphine ligands,
namely, dppb and POP. Although the three complexes ob-
tained from dppb are tetracoordinate, this geometry is
found only for the silver(I) compound with POP. Indeed,
both [Cu(POP)2]+ and [Au(POP)2]+ adopt a trigonal coor-
dination geometry with an uncoordinated phosphorus
atom. The electrochemical and photophysical properties of
the six compounds have been investigated and rationalized
Scheme 1. Preparation of [M(dppb)2]BF4 and [M(POP)2]BF4 (M =
Cu, Ag, or Au); all of the compounds were isolated in pure form
by recrystallization in either CH2Cl2/Et2O or CH2Cl2/hexane. Rea-
gents and conditions: (i) [Cu(CH3CN)4]BF4, CH2Cl2 {[Cu(dppb)2]-
BF4: 68%; [Cu(POP)2]BF4: 83%}; (ii) AgBF4, CH2Cl2/MeOH (5:1)
{[Ag(dppb)2]BF4: 93%; [Ag(POP)2]BF4: 70%}; (iii) [Au(SMe2)]Cl,
CH2Cl2 then NaBF4, CH2Cl2/H2O {[Au(dppb)2]BF4: 97%;
[Au(POP)2]BF4: 91%}.
on the basis of their different coordination geometries. Fi- [Ag(dppb)2]+ and [Ag(POP)2]+ have been reported pre-
nally, the potential for electroluminescence applications has viously as their hexafluorophosphate[12] and triflate[23] salts,
been evaluated for the most promising compounds.
respectively.
Finally, the corresponding gold complexes were obtained
by addition of the appropriate bisphosphine ligand (dppb
or POP) to a suspension of [Au(SMe2)]Cl in CH2Cl2. After
1 h, the resulting [Ag(PP)2]Cl complexes[13,15c] were sub-
jected to an anion-exchange reaction. Aqueous NaBF4
Results and Discussion
Synthesis and Characterization
As shown in Scheme 1, the copper(I) complexes solutions (1 m) were added to the reaction mixtures. After
[Cu(dppb)2]BF4 and [Cu(POP)2]BF4 were obtained by 1 h of vigorous stirring, the organic layers were evaporated,
treatment of the corresponding bisphosphine ligand and the gold complexes were isolated as their tetrafluoro-
(2 equiv.) with [Cu(CH3CN)4]BF4 (1 equiv.) in CH2Cl2. borate salts by recrystallization.
Both compounds were then isolated in pure form by
X-ray quality crystals were obtained for the six com-
recrystallization in CH2Cl2/Et2O. [Cu(dppb)2]+ has been re- plexes, and X-ray crystal structure analyses were performed
–
–
ported previously as its PF6 or CnF2n+2CO2 (n = 2, 4, 6, for the whole series. The structures are depicted in Figures 1
8 or 9) salts.[20,21] The homoleptic copper(I) complex ob- and 2; selected bond lengths and angles are summarized in
tained from POP has been reported previously by Balak- Tables 1 and 2. Whatever the metal, the [M(dppb)2]+ cat-
rishna[22] and some of us[7] in independent studies.
ions are all tetracoordinate and both dppb ligands chelate
The reaction of AgBF4 with two equivalents of the ap- the metal center. The relative orientations of the two dppb
propriate bisphosphine ligand in CH2Cl2/MeOH (5:1) gave ligands are very similar for the three [M(dppb)2]+ cations.
the corresponding homoleptic silver(I) complexes. However, in contrast to that of [Cu(dppb)2]BF4, the struc-
[Ag(dppb)2]BF4 was isolated in 93% yield by recrystalli- tures of [Ag(dppb)2]BF4 and [Au(dppb)2]BF4 are not cen-
zation in CH2Cl2/Et2O, and [Ag(POP)2]BF4 was obtained trosymmetric. In these two cases, the two cocrystallized
in 70% yield by recrystallization in CH2Cl2/hexane. Both CH2Cl2 molecules change substantially the packing of the
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[M(dppb)2]+ cations (M = Ag or Au) when compared to the
packing of the corresponding copper complex, for which no
cocrystallized solvent molecules are present. For this
reason, the environment around the metal center cannot re-
main centrosymmetric for the silver and gold complexes. A
close inspection of the P–M bond lengths reveals an inter-
esting trend. From copper to silver or gold, a substantial
increase is observed [Cu–P 2.291(1)–2.309(1) Å; Ag–P
2.478(4)–2.510(3) Å, Au–P 2.388(1)–2.432(1); see Table 1].
This is line with the larger size of silver or gold ions when
compared with copper ions. In contrast, a comparison of
the silver and gold complexes revealed a decrease in the M–
P bond lengths when going down the column of the group
11 elements. Indeed, gold(I) has a smaller van der Waals
radius than that of silver(I) as a result of its peculiar relativ-
istic effects.[24] This size feature is also responsible for sig-
nificant differences in the electrochemical properties of
[Au(dppb)2]BF4 when compared with those of the copper
and silver analogues (vide infra).
Figure 2. Structure of the [M(POP)2]+ cations in the X-ray crystal
structures of (A) [Cu(POP)2]BF4, (B) [Ag(POP)2]BF4·1.5(CH2Cl2)·
2.5(H2O), and (C) [Au(POP)2]BF4. Thermal ellipsoids drawn at the
50% probability level, H atoms omitted for clarity. C: pale gray, P:
gray, O: black, Cu: dark gray, Ag: dark gray, Au: dark gray.
Table 1. Bond lengths [Å] and angles [°] within the coordination
spheres of [Cu(dppb)2]+, [Ag(dppb)2]+, and [Au(dppb)2]+ (see Fig-
ure 1 for the numbering).
[Cu(dppb)2]+[a] [Ag(dppb)2]+ [Au(dppb)2]+
M(1)–P(1)
M(1)–P(2)
M(1)–P(3)
M(1)–P(4)
P(1)–M(1)–P(2)
P(1)–M(1)–P(3)
P(1)–M(1)–P(4)
P(2)–M(1)–P(3)
P(2)–M(1)–P(4)
P(3)–M(1)–P(4)
P(1)–M(1)–P(1Ј)
P(1)–M(1)–P(2Ј)
P(2)–M(1)–P(2Ј)
2.309(1)
2.291(1)
2.510(3)
2.478(4)
2.508(3)
2.495(4)
82.27(11)
80.05(11)
122.96(11)
123.10(12)
121.26(12)
130.93(12)
2.432(1)
2.3931(1)
2.388(1)
2.414(1)
83.60(2)
84.25(2)
120.30(2)
121.70(2)
130.17(2)
121.84(2)
84.72(3)
122.59(5)
120.94(3)
127.85(5)
Figure 1. Structure of the [M(dppb)2]+ cations in the X-ray crystal
structures of (A) [Cu(dppb)2]BF4, (B) [Ag(dppb)2]BF4·2(CH2Cl2),
and (C) [Au(dppb)2]BF4·2(CH2Cl2). Thermal ellipsoids drawn at
the 50% probability level, H atoms omitted for clarity. C: pale gray,
P: gray, Cu: dark gray, Ag: dark gray, Au: dark gray.
[a] From ref.[9]
Table 2. Bond lengths [Å] and angles [°] within the coordination
spheres of [Cu(POP)2]+, [Ag(POP)2]+, and [Au(POP)2]+ (see Fig-
ure 2 for the numbering).
As shown in Figure 2, both POP ligands chelate the sil-
ver(I) cation, which is in a distorted tetrahedral AgP4 coor-
dination environment. In contrast, for both copper and
gold, one POP ligand behaves as a chelating unit, but only
one P atom of the second POP ligand coordinates effec-
tively to the metal center. The other P atom of the latter
ligand is clearly located at a nonbonding distance from the
metal center [Cu(1)–P(4) 3.958(2) Å and Au(1)–P(4)
3.9788(8) Å]. As a result, both the copper(I) and the gold(I)
center adopt a trigonal coordination geometry with P–M–
P bond angles close to 120° (see Table 2). In both cases, the
metal ions lie almost in the center of the P(1)–P(2)–P(3)
[Cu(POP)2]+[a] [Ag(POP)2]+ [Au(POP)2]+
M(1)–P(1)
M(1)–P(2)
M(1)–P(3)
M(1)–P(4)
P(1)–M(1)–P(2)
P(1)–M(1)–P(3)
P(1)–M(1)–P(4)
P(2)–M(1)–P(3)
P(2)–M(1)–P(4)
P(3)–M(1)–P(4)
2.273(2)
2.261(2)
2.263(2)
3.958(2)
114.03(6)
121.49(5)
2.610(2)
2.611(2)
2.539(2)
2.524(2)
111.46(6)
104.48(6)
111.94(6)
108.16(6)
111.75(6)
108.71(6)
2.3748(6)
2.3849(7)
2.3419(6)
3.9788(8)
111.78(2)
123.34(2)
121.90(5)
123.49(2)
[a] From ref.[7]
plane (deviation of 0.21 Å for the copper complex and O atoms of the POP ligands are always at a nonbonding
0.16 Å for the gold complex). Whatever the metal, the ether distance from the metal centers (Ͼ3.2 Å). In the case of the
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smallest cations, that is, copper and gold, it appears that the timescale, and the four P atoms appear as equivalent in the
metal center is unable to accommodate two POP chelating room-temperature 31P{1H} NMR spectra. To confirm this
ligands. This is most probably the result of steric crowding, hypothesis, the 31P{1H} NMR spectra of [Cu(POP)2]BF4,
which forces one of the four P atoms out of the coordina- [Ag(POP)2]BF4, and [Au(POP)2]BF4 were recorded at dif-
tion sphere and results in tricoordinate complexes. In con- ferent temperatures. As shown in Figure 3, as the solution
trast, the silver cation is larger than the copper and gold is cooled, the exchange between the different conformers
cations; therefore, the M–P bonds are longer (Table 2) and becomes slower on the NMR timescale, as attested by the
allow the system to accommodate a tetrahedral geometry broadening of the 31P NMR resonances for both [Cu-
with two chelating POP ligands.
(POP)2]BF4 and [Au(POP)2]BF4. In contrast, no changes
The compounds [M(dppb)2]BF4 and [M(POP)2]BF4 (M were observed for [Ag(POP)2]BF4. These observations are
= Cu, Ag, or Au) were also characterized in solution by in perfect agreement with the difference in the coordination
NMR spectroscopy. Their structures were further con- environments observed in their X-ray crystal structures, that
firmed by mass spectrometry. The NMR spectra for all of is, tetrahedral for [Ag(POP)2]BF4 and trigonal for
the dppb derivatives in CD2Cl2 are fully consistent with [Cu(POP)2]BF4 and [Au(POP)2]BF4.
their X-ray crystal structures. Their 31P{1H} NMR spectra
(CD2Cl2) revealed that the four P atoms are equivalent for
all of the [M(dppb)2]BF4 derivatives. Effectively, a single Electrochemistry
resonance is observed at δ = 8.12 and 21.43 ppm for
The electrochemical properties of [M(dppb)2]BF4 and
[Cu(dppb)2]BF4 and [Au(dppb)2]BF4, respectively. For
[M(POP)2]BF4 (M = Cu, Ag or Au) were determined by
[Ag(dppb)2]BF4, the 31P{1H} NMR spectrum displays two
cyclic voltammetry (CV) and Osteryoung square wave vol-
tammetry (OSWV). For comparison, the ligands dppb and
POP were also investigated under the same experimental
conditions. All of the experiments were performed at room
temperature in CH2Cl2 solutions containing tetra-n-butyl-
ammonium tetrafluoroborate (0.1 m) as the supporting elec-
trolyte, a Pt wire as the working electrode, and a saturated
doublets centered at δ = 0.28 ppm because of the coupling
of the equivalent phosphorus atoms with both the 107Ag (1J
= 230 Hz) and 109Ag (1J = 265 Hz) nuclei (for 107Ag and
109Ag, the natural abundances are 48.2 and 51.8%, respec-
tively).[12,25] Similarly, the 31P{1H} NMR spectra of
[Cu(POP)2]BF4, [Ag(POP)2]BF4, and [Au(POP)2]BF4 in
CD2Cl2 at room temperature show single resonances, which
calomel electrode (SCE) as the reference electrode. The po-
suggests that the four P atoms of the POP ligands are also
tential data for all of the compounds are collected in
equivalent for all of the complexes (Figure 3). This is in
Table 3, and typical examples of the OSVW voltammog-
perfect agreement with the solid-state structure of
[Ag(POP)2]BF4. However, the apparent equivalence of the
rams are depicted in Figure 4.
four P atoms contradicts the solid-state structures of
Table 3. Electrochemical data of dppb, POP, [M(dppb)2]BF4, and
[Cu(POP)2]BF4 and [Au(POP)2]BF4, for which three reso-
nances are expected for the different P atoms. Indeed, the
P atoms of the two POP ligands may exchange their posi-
tion inside and outside the coordination sphere in solution.
In other words, this dynamic exchange is fast on the NMR
[M(POP)2]BF4 (M = Cu, Ag or Au) determined by OSWV with
a Pt working electrode in CH2Cl2 and 0.1 m nBu4NBF4 at room
temperature.[a]
Oxidation
Eox1
Reduction
Ered1
[b]
[b]
[b]
Eox2
[d]
dppb
+1.04
+1.19[c]
+0.99[c]
+0.70
+1.31
+1.46
+1.68
+1.42
+1.69
+1.66
broad
broad
+1.54
+1.70
broad
+1.60
[Cu(dppb)2]BF4
[Ag(dppb)2]BF4
[Au(dppb)2]BF4
POP
[Cu(POP)2]BF4
[Ag(POP)2]BF4
[Au(POP)2]BF4
–2.20
–2.14
[d]
[d]
[d]
[d]
[d]
[a] The OSWV data were obtained with a sweep width of 20 mV, a
frequency of 10 Hz, and a step potential of 5 mV. [b] Values in V
vs. SCE. [c] Quasi-reversible process in CV. [d] No signals observed
in the available potential windows (Ͼ –2.20 V vs. SCE) under our
experimental conditions.
In the cathodic region, no reduction process could be
observed for most of the studied compounds under our ex-
perimental conditions. In contrast, two main oxidation pro-
cesses are observed for the six complexes. In all of the cases,
the first oxidation is likely metal-centered, whereas the sec-
ond one corresponds to ligand-centered processes.[6] In the
particular cases of [Cu(dppb)2]BF4 and [Ag(dppb)2]BF4,
the first one-electron oxidation process is quasi-reversible
and is assigned to the M2+/M+ redox couple. In both cases,
Figure 3. 31P{1H} NMR (202 MHz, CD2Cl2) spectra of [Cu-
(POP)2]BF4, [Ag(POP)2]BF4, and [Au(POP)2]BF4 at 298 and
198 K.
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zation of the gold(III) complex.[26] Under our conditions,
such stabilization is not possible, and the new signals ob-
served could be partly due to AuIII chlorine adducts formed
in CH2Cl2, in agreement with the previous studies.[26]
For the POP complexes, the metal-centered oxidation
process is more difficult than those of their dppb analogues.
This results from a combination of effects, one of which is
the difference in the electronic properties of the two bis-
phosphine ligands as deduced from the difference in the
first oxidation potentials of POP and dppb (Table 3). For
[Ag(POP)2]BF4, the metal center adopts a tetrahedral coor-
dination geometry, and the larger P–Ag–P bite angle, com-
pared to that of dppb, hinders the formation of a flatter
structure (i.e., square planar), which would be more appro-
priate for the silver(II) oxidation state. As a result,
[Ag(POP)2]2+ is destabilized, and oxidation of the silver(I)
complex is more difficult. For both [Cu(POP)2]BF4 and
[Au(POP)2]BF4, the situation is more complex. As shown
by CV, their first oxidation process is also irreversible. How-
ever, the metal centers are now in a trigonal environment,
and their oxidation potential is probably closer to that of
the mono-coordinated diphosphine. Upon oxidation, the
three P ligands are not sufficient to stabilize the higher oxi-
dation states and, simultaneously, rearrangement and de-
coordination process may easily occur. Finally, it is note-
worthy that substitution of the dppb ligand by the POP
Figure 4. OSWV voltammograms (anodic scan) of [Cu(dppb)2]BF4,
[Ag(dppb)2]BF4, and [Au(dppb)2]BF4 with a Pt electrode in CH2Cl2
and 0.1 m nBu4NBF4 at room temperature.
the second oxidation is chemically irreversible and, as al- ligand has a dramatic effect for the gold compound, as the
ready reported for analogous phosphine-containing com- first oxidation potential is shifted by 720 mV toward anodic
plexes,[6] chemical reactions occur with ligand-centered oxi- potential.
dations. For [Au(dppb)2]BF4, the first oxidation is observed
at a lower potential than those of its copper and silver ana-
logues. This oxidation is indeed a two-electron process that
leads to the formation of a gold(III) complex. As already
Photophysical Properties
mentioned, gold exhibits a large relativistic effect, and
The absorption spectra of [M(dppb)2]BF4 and
higher oxidation states are more accessible in gold than in [M(POP)2]BF4 (M = Cu, Ag or Au) as well as those of
silver. Indeed, the gold s electrons are more strongly bound, dppb and POP have been recorded in both tetrahydrofuran
and their orbitals are smaller as a consequence of the rela- (THF) and CH2Cl2 (see Supporting Information). As a typ-
tivistic effect; simultaneously, the d and f electrons are more ical example, the absorption spectrum of [Ag(dppb)2]-
loosely bound owing to an increased shielding of the nu- BF4 in THF is depicted in Figure 5. For the free ligands,
clear charge. As a result, oxidation to gold(III) is energeti- several photostability tests have been made by exciting them
cally less disfavored when compared to oxidation of the re- at 300 nm in both solvents because of the well-known pho-
lated Cu or Ag complexes.[24] It can be added that the elec- toreactivity of phosphine molecules.[27] All of the samples
trochemistry of [Au(dppb)2]+ has already been investigated were unstable in solution under light irradiation, especially
in detail by McArdle and Bossard.[26] On the basis of spec- in CH2Cl2;[12] changes in the absorption spectra were sys-
troelectrochemical investigations performed in CH3CN, tematically observed after a couple of hours. To minimize
they have proposed a change from a tetrahedral coordina- irreversible photochemical degradation, solutions of all of
tion geometry for [Au(dppb)2]+ to a square-planar structure the compounds were always kept in the dark and investi-
for the [Au(dppb)2]3+ complex obtained upon oxidation. gated immediately after dissolution. The electronic absorp-
Under their conditions (CH3CN), the oxidation process is tion of the complexes is mainly localized in the UV region
perfectly reversible. In contrast, we used a non-coordinating down to ca. 350 and 400 nm for [M(POP)2]BF4 and
solvent (CH2Cl2), and this oxidation is irreversible. More- [M(dppb)2]BF4, respectively. For the latter family of com-
over, in the CV experiments, additional reduction waves ap- plexes, a comparison with the absorption spectrum of dppb
pear when scanning back towards cathodic potentials (see reveals an additional absorption tail above 350 nm that is
Supporting Information). The intensity of these new signals likely due to charge-transfer transitions, which, for CuI and
is scan-rate dependent, which suggests that they result from AgI, are attributed to metal-to-ligand charge-transfer
a chemical reaction of the [Au(dppb)2]3+ complex. Indeed, (MLCT) states (vide infra), in line with previous re-
the high stability of [Au(dppb)2]3+ in CH3CN suggests that ports.[9,12] By contrast, absorption tails above 350 nm are
the coordinating solvent may also contribute to the stabili- not observed for the [M(POP)2]BF4 complexes; this sug-
Eur. J. Inorg. Chem. 2014, 1345–1355
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gests that the lowest electronic transitions are ligand-cen- mer in the MLCT excited state when MII ions are formally
tered. This interpretation is supported by the electrochemi- generated. This hypothesis is in line with the lower oxi-
cal data. Metal-centered oxidations of [M(POP)2]BF4 com- dation potential of [Ag(dppb)2]BF4 compared with that of
pounds occur at higher potentials than those of the analo- [Cu(dppb)2]BF4 (Table 3).
gous dppb derivatives, therefore the MLCT transitions oc-
Table 4. Luminescence data in air-equilibrated and air-free THF
cur at higher energy.
solutions at room temperature.
λmax [nm][a] Φem [%][b]
τ [ns][c]
[d]
[d]
[d]
dppb
[Cu(dppb)2]BF4
[Ag(dppb)2]BF4
[Au(dppb)2]BF4
POP
[Cu(POP)2]BF4
[Ag(POP)2]BF4
[Au(POP)2]BF4
560
Ͻ0.01 (0.04)
[d] (26)
608
Ͻ0.01 (0.5)
[d] (8400)
[d]
[d]
[d]
430
423
462
490
0.03 (0.8)
0.05 (0.1)
0.04 (0.04)
0.2 (1.5)
[d] (1.5)
1.4 (2.0)
[d]
126 (2200)
[a] Emission maxima from uncorrected spectra, λexc = 300 (com-
plexes) and 280 nm (free ligands). [b] Emission quantum yields in
air-equilibrated and air-purged solutions (in brackets). [c] Excited-
state lifetimes in air-equilibrated and air-purged solutions (in
brackets). [d] Weak signal. In particular, for lifetime measurements,
hours of accumulation are required with the time-correlated single
photon counting (TCSPC) spectrometer; hence, the signal-to-noise
ratios are too low for a reliable appraisal.
Figure 5. Left: electronic absorption spectra of [Ag(dppb)2]BF4 in
CH2Cl2 (black) and THF (grey) at room temperature. Right: nor-
malized emission spectra (λexc = 300 nm) of [Ag(dppb)2]BF4 in
CH2Cl2 (full squares) and THF (empty circles) at room temp., as
powder (10% in KBr) at room temp. (empty squares), and in rigid
THF matrix at 77 K (full circles).
Table 5. Luminescence data in a frozen THF rigid matrix (77 K)
and in the solid state (KBr disks, room temperature).
Rigid matrix 77 K
Solid state (KBr disk, 298 K)
The photoluminescence properties of the whole series of
compounds were investigated in THF and CH2Cl2 (see Sup-
porting Information). They were further investigated in ri-
gid THF matrices at 77 K and in the solid state at room
temperature (KBr disks). The data in THF are summarized
in Tables 4 and 5. On the basis of the large Stokes shift and
the sensitivity of the excited-state lifetime towards oxygen,
λmax
τ
[ms]
λmax
Φem
[%]
τ
[μs]
[nm][a]
[nm][a]
[b]
[b]
[b]
dppb
500
17.6
1.9
3.4
[Cu(dppb)2]BF4 455
[Ag(dppb)2]BF4 448
[Au(dppb)2]BF4 503
497
505
56
22
28
4
2
1
2.5
6.8
0.14, 12.5 529
2.9
[b]
POP
[Cu(POP)2]BF4
480
401
405
445
16.5
2.3
9.0
445
469
458
494
[b]
[b]
the weak emission of [Ag(dppb)2]BF4 in THF is assigned [Ag(POP)2]BF4
to a triplet MLCT excited state.[12] The compound is sub-
[Au(POP)2]BF4
1.3, 8.4
5
6.9
stantially influenced by conformational changes from a
pseudotetrahedral coordination geometry (ground state) to
a flattened structure in the excited state, which leads to a
stabilized excited state exhibiting a formally silver(II) cen-
ter. This is in line with the results obtained by Osawa and
Hoshino with [Ag(dppb)2]PF6.[12] The same rationale can
[a] Emission maxima from uncorrected spectra, λexc = 325 (com-
plexes) and 280 nm (free ligands). [b] Weak signal. In particular,
for lifetime measurements, hours of accumulation are required with
the TCSPC spectrometer; hence, the signal-to-noise ratio results are
too low for a reliable appraisal.
Whereasthe emissionquantumyieldsof both[Cu(dppb)2]-
be applied to the emission behavior of [Cu(dppb)2]BF4 in BF4 and [Ag(dppb)2]BF4 are very low in solution, they both
solution, though its excited-state lifetime in oxygen-free exhibit a bright luminescence in the solid state at room tem-
THF (26 ns) is much shorter than that of the AgI analogue perature as well as in rigid frozen THF matrices at 77 K.
(8400 ns). THF is a coordinating solvent, and the flattened Under these conditions, geometric distortions that prompt
square-planar structure of the MLCT excited state may fa- nonradiative deactivation of the MLCT excited states are
cilitate the formation of a pentacoordinate exciplex with an prevented.[12,13] This is further confirmed by the large blue-
incoming solvent molecule, as is often observed for cop- shifted emission maxima when going from room tempera-
per(I) complexes, which may exhibit triplet lifetimes as ture to 77 K in THF for both [Cu(dppb)2]BF4 and
short as a few ns.[18,19] This view is supported by the ex- [Ag(dppb)2]BF4 (Tables 4 and 5).[12,13]
cited-state lifetimes recorded in non-coordinating CH2Cl2,
Although emission was detected for [Cu(dppb)2]BF4 and
for which τ = 1.5 ns was found in air-equilibrated solution, [Ag(dppb)2]BF4 in solution, the corresponding gold(I) de-
whereas τ = 244 ns was measured in oxygen-free solution. rivative is nonemissive under these conditions (Table 4).
Accordingly, it appears that copper complexes are more However, as reported by Osawa,[13] a strong emission is ob-
prone to form pentacoordinate exciplexes than their silver served for this compound at 77 K in a frozen THF rigid
analogues. Interestingly, the emission of the AgI complex matrix or at room temperature in the solid state (Table 5).
occurs at lower energy than that of the CuI analogue. This It must be highlighted that the excited state is rather dif-
is attributed to a stronger excited-state distortion of the for- ferent in this case when compared to those of the analogous
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copper and silver complexes. Indeed, as deduced from DFT versible metal-centered oxidation process and a high emis-
calculations on [Au(PP)2]+ systems,[13,15,28] the lowest emit- sion quantum yield in the solid state. Poly(vinyl carbazole)
ting state is mainly a charge-transfer state from a P atom (PVK) was chosen as the host material because of its good
to the phenylene or phenyl groups of the dppb ligand. The hole-transport ability, broad band-gap, and the overlap of
nature of the lowest excited state in AuI bisphosphine com- its emission spectra with the absorption spectra of
plexes is highly sensitive to small conformational changes, [Cu(dppb)2]BF4 and [Ag(dppb)2]BF4. The light-emitting
that is, symmetry reduction caused by change of the devices were prepared by spin coating a thin film of a
counteranion and the occurrence of intramolecular CH–π [Cu(dppb)2]BF4:PVK[9] or a [Ag(dppb)2]BF4:PVK blend
interactions in one conformation, which affects the localiza- (ca. 120 nm) on an indium tin oxide (ITO) substrate. The
tion of the lowest unoccupied molecular orbital (LUMO) concentration of [Cu(dppb)2]BF4 and [Ag(dppb)2]BF4 in
level.[13] Thus, emission maxima are observed over quite a the PVK matrix was 12.5 wt.-%. After the film had been
large spectral window (478–596 nm) depending on the sym- dried under vacuum at room temperature for 2 h, the cath-
metry of the [Au(PP)2]+ cation.[13]
ode was fabricated by thermal evaporation of an Al layer
For the POP-based complexes, the situation appears to (100 nm). A typical example electroluminescence (EL) spec-
be rather different. As already mentioned, in this case, the trum of [Ag(dppb)2]BF4 in PVK films is displayed in Fig-
lowest electronic transitions are likely to be ligand-centered. ure 6.
This has already been discussed by McCleskey and Gray
for a three-coordinate monomeric AuP3 complex.[17] The
electronic transition involves the promotion of an electron
from the lone pair of a phosphorus atom to an empty anti-
bonding π* orbital of a phenyl subunit attached to the P
atom. Depopulation of the lone pair of one P atom should
in principle strengthen the Au–P bonds by a retrodonation
mechanism. As a result, a substantial contraction of the
AuP3 core may explain the rather large Stokes shift ob-
served for [Au(POP)2]BF4. As for the AuP3 complex re-
ported by McCleskey and Gray,[17] the AuP3 monomeric
unit in [Au(POP)2]BF4 is also sterically protected, which
seems to be a key prerequisite for the observation of emis-
sion in solution for AuP3 units that retain their integrity in
solution. It is likely that similar excited states are involved
in the emission of [(CuPOP)2]BF4 and [Ag(POP)2]BF4.
Along the series, the Stokes shift increases from copper to
Figure 6. I–V–B characteristics of the device obtained from
[Ag(dppb)2]BF4. Inset: EL spectra of [Ag(dppb)2]BF4 at a concen-
tration of 12.5 wt.-% in a PVK matrix.
silver and finally to gold. The retrodonation, which can
strengthen the M–P bonds leading to a deformation of the
coordination sphere around the metal center, is expected to
be increasingly pronounced as group 11 is descended. In-
deed, the excited-state properties of [(CuPOP)2]BF4 in solu-
tion are almost identical to those of the uncoordinated POP
The electroluminescence spectrum of [Ag(dppb)2]BF4 is
ligand. For the three [M(POP)2]BF4 complexes, significant significantly broader when compared to the photolumines-
blueshifts are observed for the emission spectra recorded in cence spectrum recorded in THF solution. As a result, al-
the frozen THF matrices at 77 K relative to those recorded most white light was produced by the device. Similar results
at room temperature in solution. Indeed, changes in the co- were obtained with [Cu(dppb)2]BF4.[9] The current–volt-
ordination sphere are more limited under such conditions. age–brightness (I–V–B) characteristics (Figure 6) of the de-
However, the differences observed between the emission vice prepared from [Ag(dppb)2]BF4 indicate that it has a
maxima at 298 and 77 K are less pronounced for the POP- turn-on voltage of ca. 15 V and maximum brightness of
based complexes (ca. 20–60 nm) when compared to those 365 cdm–2 at 20 V (measured with a Minolta LS 110 lumi-
for the dppb derivatives (ca. 100–160 nm). This is in agree- nance meter). To the best of our knowledge, this is the first
ment with the different nature of the excited states involved example of a light-emitting device that incorporates a sil-
in the emission of the different compounds.
ver(I) complex as a triplet emitter in its active layer. The I–
V–B characteristics obtained with the corresponding cop-
per(I) complex are similar[9] (turn-on voltage of ca. 15 V
and a maximum brightness of 490 cdm–2 at 20 V); there-
fore, silver(I) complexes are also attractive candidates for
Light-Emitting Devices
On the basis of their electrochemical properties and the light-emitting applications. However, it is clear that the de-
photoluminescence data, [Cu(dppb)2]BF4 and [Ag(dppb)2]- vice efficiencies have not been yet optimized. They should
BF4 were selected for the fabrication of light-emitting de- be improved through the use of appropriate hole-blocking
vices. Indeed, these two compounds combine a quasi-re- and electron-transfer layers in the device configuration.
Eur. J. Inorg. Chem. 2014, 1345–1355
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by using a water aspirator and drying in vacuo at 10–2 Torr. NMR
spectra were recorded with Bruker ARX 250, Bruker DPX 300,
Conclusions
We have prepared homoleptic copper(I), silver(I), and Avance 300, and Avance 500 spectrometers equipped with a 5 mm
triple-resonance inverse probe with a dedicated 31P channel op-
gold(I) complexes with two bisphosphine ligands, namely,
dppb and POP. Whereas the three complexes obtained from
erating at 500.33 for 1H NMR spectroscopy. Chemical shifts (δ) are
in ppm relative to an external tetramethylsilane reference for 1H
dppb are tetracoordinate, in the case of POP, only the sil-
and 13C, 85 % H3PO4 for 31P, and AgNO3 for 109Ag; coupling con-
ver(I) complex exhibits such a geometry. Indeed, both
stants (J) are in Hz. The temperature was calibrated by using a
[Cu(POP)2]+ and [Au(POP)2]+ adopt a trigonal coordina-
methanol chemical shift thermometer. 109Ag NMR resonances
tion geometry with an uncoordinated phosphorus atom
both in the solid state and in solution. Owing to steric hin-
drance caused by the large bite angle of the POP ligand,
the CuI and AuI cations are unable to accommodate two
were obtained by using 2D 31P–109Ag proton-decoupled heteronuc-
lear multiple quantum correlation (HMQC-{1H}). Elemental
analyses were performed with a Perkin–Elmer 2400 B analyzer
(flash combustion and detection by catharometry) at the Microana-
chelating POP moieties in a tetrahedral complex. This is lytical Laboratory (LCC, Toulouse, France). Mass spectra were ob-
only possible for the largest AgI cation. The electrochemical
tained at the Service Commun de Spectrométrie de Masse (Uni-
versité Paul Sabatier and CNRS, Toulouse, France). Spectra were
properties of the six complexes have been investigated, and
recorded with a triple quadrupole mass spectrometer (Perkin–
ElmerSciex API 365) by using electrospray ionization.
two oxidation processes have been observed in all cases. The
first one is likely metal-centered, and the second one is li-
gand-centered. However, major differences have been ob-
served for both series of compounds. The POP-based deriv-
[Cu(dppb)2]BF4: A mixture of Cu(CNCH3)BF4 (80 mg, 0.18 mmol)
and dppb (170 mg, 0.37 mmol) in CH2Cl2 (20 mL) was stirred for
atives are more difficult to oxidize than their dppb ana- 1 h under Ar at room temperature. The resulting solution was con-
centrated to ca. 5 mL. Crystals of [Cu(dppb)2]BF4 were obtained
by vapor diffusion of Et2O into this CH2Cl2 solution. Compound
[Cu(dppb)2]BF4 was thus isolated as colorless crystals in 68% yield.
1H NMR (300 MHz, CDCl3): δ = 6.98 (m, 16 H), 7.09 (m, 16 H),
7.34 (m, 8 H), 7.54 (m, 8 H) ppm. 31P{1H} NMR (121 MHz,
CDCl3): δ = 8.12 ppm. 13C{31P}{1H} NMR (62 MHz, CDCl3): δ
= 129.0, 130.2, 131.2, 131.7, 132.4, 134.0, 141.6 ppm. ES-MS: m/z
logues. This observation is explained by a combination of
steric and electronic effects as well as by the difference in
their coordination geometries. For similar reasons, the pho-
tophysical properties of [M(dppb)2]BF4 and [M(POP)2]BF4
complexes are rather different. Whereas the emissions of
[Cu(dppb)2]BF4 and [Ag(dppb)2]BF4 are attributed to trip-
let MLCT excited states, their POP analogues are charac-
terized by ligand-centered triplet excited states. The gold
complexes [Au(dppb)2]BF4 and [Au(POP)2]BF4 have similar
excited states that result from the promotion of an electron
from the lone pair of a phosphorus atom to an empty anti-
bonding π* orbital of a phenyl subunit attached to the P
atom; however, their behavior is substantially different as a
result of their particular coordination geometries (i.e., AuP3
vs. AuP4). Finally, the two compounds that combine revers-
ible metal-centered oxidation processes with high emission
– +
= 955.2 [M – BF4 ] . C60H48BCuF4P4·H2O: C 67.90, H 4.75; found
C 67.85, H 4.40.
[Cu(POP)2]BF4: As described for [Cu(dppb)2]BF4 from
Cu(CNCH3)BF4 (50 mg, 0.16 mmol) and POP (171 mg,
0.32 mmol). Recrystallization (CH2Cl2/Et2O) gave [Cu(POP)2]BF4
as colorless crystals in 83% yield. 1H NMR (500 MHz, CD2Cl2): δ
= 6.49 (dd, J = 8 and 1 Hz, 4 H), 6.79 (m, 20 H), 7.00 (m, 20 H),
7.16 (m, 4 H), 7.26 (t, J = 7 Hz, 8 H) ppm. 31P{1H} NMR
(202 MHz, CD2Cl2):
(63 MHz, CD2Cl2): δ = 119.6, 125.0, 125.05, 129.0, 130.5, 131.5,
δ =
–13.57 ppm. 13C{31P}{1H} NMR
– +
quantum yields in the solid state, namely, [Cu(dppb)2]BF4 132.4, 134.1, 134.7, 158.5 ppm. ES-MS: m/z = 1139.7 [M – BF4 ] .
C72H56P4O2CuBF4: C 70.46, H 4.60; found C 70.57, H 4.74.
and [Ag(dppb)2]BF4, have been selected for the fabrication
of light-emitting devices. Interesting electroluminescence
properties have been observed for both compounds, which
highlights the potential of the group 11 ions for such appli-
cations.
[Ag(dppb)2]BF4: A mixture of AgBF4 (22 mg, 0.11 mmol) and dppb
(100 mg, 0.22 mmol) in CH2Cl2/MeOH (5:1, 20 mL) was stirred for
1 h under Ar at room temperature. The resulting solution was evap-
orated. Recrystallization (CH2Cl2/Et2O) gave [Ag(dppb)2]BF4 as
1
This work paves the way towards the design of new cop-
colorless crystals in 93% yield. H NMR (300 MHz, CD2Cl2): δ =
per, silver, and gold complexes with improved emission 7.11 (m, 32 H), 7.34 (m, 8 H), 7.54 (m, 8 H) ppm. 31P{1H} NMR
(202 MHz, CD2Cl2): δ = 0.28 (2d, 1J
= 265 Hz, 1J
31P,107Ag
31P,109Ag
properties. This will require the design of PP ligands with
appropriate chelate bite angles, optimized donating abilities,
and suitable steric hindrance to isolate the metallic center
without compromising the tetrahedral coordination geome-
try. Work in this direction is under way in our laboratories.
230 Hz) ppm. 109Ag NMR (23 MHz, CD2Cl2): δ = 1052 ppm. ES-
– +
MS: m/z = 999.4 [M – BF4 ] . C60H48P4AgBF4·(CH2Cl2)2/3: C
63.68, H 4.35; found C 67.47, H 4.32.
[Ag(POP)2]BF4: As described for [Ag(dppb)2]BF4 from AgBF4
(50 mg, 0.26 mmol) and POP (277 mg, 0.51 mmol). Recrystalli-
zation (CH2Cl2/hexane) gave [Ag(POP)2]BF4 as colorless crystals
in 70% yield. 1H NMR (500 MHz, CD2Cl2): δ = 6.71 (m, 4 H),
6.85 (m, 16 H), 6.94 (m, 20 H), 7.04 (m, 4 H), 7.19 (m, 12 H) ppm.
Experimental Section
31P,109Ag
=
General Procedures: Reagents were purchased as reagent grade and
used without further purification. Et2O was distilled from Na/
benzophenone under Ar. Dichloromethane was distilled from
CaH2 under Ar. All reactions were performed in standard glass-
ware under an argon atmosphere by using Schlenk and vacuum-
line techniques. Evaporations and concentrations were performed
31P{1H} NMR (202 MHz, CD2Cl2): δ = –9.58 (2d, 1J
268 Hz, 1J
234 Hz) ppm. 13C{31P}{1H} NMR (63 MHz,
31P,107Ag
CD2Cl2): δ = 119.2, 124.7, 125.0, 128.9, 130.4, 131.8, 132.4, 134.2,
134.6, 157.5. 109Ag NMR (23 MHz, CD2Cl2): δ = 1192 ppm. ES-
– +
MS: m/z = 1183.7 [M – BF4 ] . C72H56AgBF4O2P4 (1271.80):
calcd. C 68.00, H 4.44; found C 67.89, H 4.56.
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[Au(dppb)2]BF4: A mixture of [Au(SMe2)]Cl (100 mg, 0.34 mmol)
and dppb (303 mg, 0.68 mmol) in CH2Cl2 (20 mL) was stirred for
1 h under Ar at room temperature. A 1 m aqueous NaBF4 solution
atoms were refined anisotropically. Solvent molecules and
counteranions were refined isotropically for [Ag(POP)2]BF4 and
[Au(POP)2]BF4. For [Ag(dppb)2]BF4, only the heaviest atoms were
(10 mL) was then added, and the resulting mixture was vigorously refined anisotropically owing to the lack of data. Hydrogen atoms
stirred for 1 h. The organic layer was decanted, and the aqueous
layer was extracted with CH2Cl2 (2ϫ). The combined organic lay-
ers were dried (MgSO4) and filtered, and the solvent was evapo-
rated. Recrystallization (CH2Cl2/Et2O) gave [Au(dppb)2]BF4 as col-
orless crystals in 97% yield. 1H NMR (500 MHz, CD2Cl2): δ =
were refined by using a riding model. Absorption corrections were
introduced by using the MULTISCAN program.[32] The X-ray
[9]
crystal structures of [Cu(dppb)2]BF4
(CCDC-645318) and
[7]
[Cu(POP)2]BF4 (CCDC-952429) have been reported previously.
The colorless crystal used for the diffraction studies were produced
7.05 (m, 32 H), 7.33 (m, 8 H), 7.46 (m, 8 H) ppm. 31P{1H} NMR by either slow diffusion of Et2O into a CH2Cl2 solution of the
(202 MHz, CD2Cl2): δ = 21.43 ppm. ES-MS: m/z = 1089.6 [M –
BF4 ] . C60H48AuBF4P4 (1176.70): calcd. C 61.24, H 4.11; found
C 61.05, H 3.65.
appropriate complex {[Ag(dppb)2]BF4 and [Au(dppb)2]BF4} or
slow diffusion of hexane into a CH2Cl2 solution of the appropriate
complex {[Ag(POP)2]BF4 and [Au(POP)2]BF4}. The crystallo-
graphic data are reported in Table 6.
– +
[Au(POP)2]BF4: As described for [Au(dppb)2]BF4 from [Au-
(SMe2)]Cl (100 mg, 0.34 mmol) and POP (366 mg, 0.68 mmol). Electrochemistry: The cyclic voltammetric measurements were per-
Recrystallization (CH2Cl2/Et2O) gave [Au(POP)2]BF4 as colorless formed with an Autolab PGSTAT100 potentiostat. The experi-
crystals in 83% yield. H NMR (500 MHz, CD2Cl2): δ = 6.36 (d, ments were performed at room temperature in a homemade airtight
1
J = 8 Hz, 4 H), 6.72 (d, J = 7 Hz, 4 H), 6.96 (m, 20 H), 7.09 (m,
three-electrode cell connected to a vacuum/argon line. The refer-
20 H), 7.32 (t, J = 7 Hz, 8 H) ppm. 31P{1H} NMR (121 MHz, ence electrode consisted of a saturated calomel electrode (SCE) sep-
CD2Cl2): δ = 17.00 ppm. 13C{31P}{1H} NMR (63 MHz, CD2Cl2): arated from the solution by a bridge compartment. The counter
δ
=
119.6, 124.7, 125.2, 129.1, 130.8, 132.4, 134.1, 134.8, electrode was a platinum wire of ca 1 cm2 apparent surface area.
– +
158.4 ppm. ES-MS: m/z = 1273.4 [M – BF4 ] . C72H56AuBF4O2P4
The working electrode was a Pt microdisk (0.5 mm diameter). The
supporting electrolyte [nBu4N][BF4] (Fluka, 99% electrochemical
grade) was used as received and simply degassed under argon.
Dichloromethane was freshly distilled from CaH2 prior to use. The
concentrations of the solutions used during the electrochemical
studies were typically 10–3 m in complex and 0.1 m in supporting
electrolyte. Before each measurement, the solutions were degassed
by bubbling Ar through them, and the working electrode was pol-
ished with a polishing machine (Presi P230).
(1360.90): calcd. C 63.55, H 4.15; found C 63.41, H 3.89.
X-ray Crystal Structures: The data were collected at low tempera-
ture with an Oxford Xcalibur, STOE IPDS, or Bruker APEX2 dif-
fractometer by using graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å) and an Oxford Cryosystems Cryostream cooling de-
vice. The structures were solved by direct methods by using
SIR92[29] and refined by full-matrix least-squares procedures by
using the programs of the PC version of CRYSTALS.[30] Atomic
scattering factors were taken from the International Tables for X-
ray Crystallography.[31] For [Au(dppb)2]BF4, all non-hydrogen
Photophysical Measurements: The absorption spectra were re-
corded with a Perkin–Elmer λ9 spectrophotometer. For lumines-
Table 6. Crystallographic and structure refinement data for [Ag(dppb)2]BF4, [Au(POP)2]BF4, [Au(dppb)2]BF4, and [Ag(POP)2]BF4.
[Ag(dppb)2]BF4 [Au(POP)2]BF4 [Au(dppb)2]BF4 [Ag(POP)2]BF4
C60H48AgBF4P4·2(CH2Cl2) C72H56AuBF4O2P4 C60H48AuBF4P4·2(CH2Cl2) C72H56AgBF4O2P4·1.5(CH2Cl2)· 2.5(H2O)
Chemical formula
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
1257.47
monoclinic
P21/n
16.7320(10)
19.407(2)
18.601(2)
90
1360.90
orthorhombic
Pbcn
20.2099(5)
24.6442(6)
24.7354(6)
90
1346.57
monoclinic
P21/n
16.6179(8)
19.3178(9)
18.5362(9)
90
1444.24
monoclinic
P21/c
12.8583(5)
16.5170(7)
33.6578(13)
90
β [°]
107.656(9)
90
5755.6(10)
4
90
90
107.502(2)
90
5675.0(5)
4
90.193(4)
90
7148.2(5)
4
γ [°]
V [Å]3
12319.6(5)
8
Z
Density
1.451
0.700
2560
1.467
2.551
5472
1.576
2.947
2688
1.342
0.542
2940
μ (Mo-Kα) [mm–1
F(000)
]
T [K]
180
180
180
180
Reflections collected 57391
244744
21485
0.041
181443
19515
0.046
76241
18996
0.109
Unique reflections
Rint
11135
0. 125
Reflections used
in the calculations
[I Ͼnσ(I)]
3377, n = 1.6
11970, n = 3
12289, n = 3
7687, n = 1.2
Parameters
330
731
685
764
Goodness- of-fit on F 1.001
1.029
0.0306
0.0328
1.130
0.0202
0.0241
1.078
0.0787
0.0808
R
0.0605
0.0672
wR
Eur. J. Inorg. Chem. 2014, 1345–1355
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
cence experiments, the samples (with optical densities between 0.1
Acknowledgments
and 0.4) were placed in 1 cm path fluorimetric cuvettes and, when
necessary, purged of oxygen by bubbling argon through them. Un-
corrected emission spectra were obtained with an Edinburgh
FLS920 spectrometer equipped with a Peltier-cooled Hamamatsu
R928 photomultiplayer tube (PMT; 185–850 nm). An Edinburgh
Xe900 450 W Xenon arc lamp was used as the excitation light
source. Corrected spectra were obtained by using a calibration
curve supplied with the instrument. The luminescence quantum
yields (Φem) in solution were obtained from spectra corrected for
the instrumental response on a wavelength scale [nm] and were de-
termined according to the approach described by Demas and
This research was supported by the French Centre National de la
Recherche Scientifique (CNRS), by the European Commission
(EC) (contract PITN-GA-2008-215399 - FINELUMEN), by the
Italian Ministero dell’Università e della Ricerca (MIUR) (PRIN
2010 INFOCHEM, contract number CX2TLM; FIRB Futuro in
Ricerca SUPRACARBON, contract number RBFR10DAK6) and
by the Consiglio Nazionale delle Ricerche (CNR) (MACOL
PM.P04.010; Progetto Bandiera N-CHEM). The authors gratefully
thank Dr. P. Braunstein for helpful discussions about the relativistic
effects and Dr. P. Destruel for his support. F. Lacassin is thanked
for NMR measurements, A. Saquet for her help with the electro-
chemical measurements, and C. Claparols for the mass spectra.
Crosby[33] by using air-equilibrated [Ru(bpy)3]Cl2 in water [Φem
=
0.028][34] as the standard.
The emission lifetimes were determined by the single-photon
counting technique with the same Edinburgh FLS920 spectrometer
by using a laser diode as the excitation source (1 MHz, λexc
=
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time determinations, 20% for emission quantum yields, and 2 and
5 nm for the absorption and emission peaks, respectively.
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Received: October 16, 2013
Published Online: February 6, 2014
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim