Structures and luminescent properties of polynuclear gold(I) halides containing bridging phosphine ligands

Article abstract of DOI:10.1039/a605911b

The complexes [AuI(PPh₃)] 1, [Au₂(μ-dppm)Cl₂] 2 [dppm = bis(diphenylphosphine)methane], [Au₂(μ-dppm)I₂] 3, [Au₃(μ-tppm)Cl₃] 4 [tppm = tris(diphenylphosphino)methane], [Au₃(μ-dpmp)I₃] 5, [Au₃(μ-dpmp)₂Cl₂]Cl 6 [dpmp = bis(diphenylphosphinomethyl)phenylphosphine] and [Au₃(μ-dpmp)₂I₂]I 7 were prepared. The crystal structures of 5-7 have been established by X-ray crystal analysis. The measured intramolecular Au-Au distances are 3.136(1) A in 5, 2.946(3) and 2.963(3) A in 6 and 2.952(1) and 3.020(1) A in 7. Extended-Hueckel molecular orbital calculations revealed that the 6p orbitals of iodide and 5d orbitals of gold(I) make a significant contribution to the highest occupied molecular orbitals of 5 and of 2 and 4 respectively. The lowest unoccupied molecular orbitals of these complexes mainly comprise π* orbitals of the phosphines. The photophysical properties of 1-6 have been studied. All show dual emissions. The low-energy emissions at around 660-680 nm have a small red shift in energy from chloro to iodo complexes, and a much higher intensity at room temperature than at 77 K. These are attributed to triplet states with mixed ³m.m.l.c.t. (metal-metal to ligand charge transfer, gold→phosphine) and ³l.l.c.t. (ligand to ligand charge transfer, halide to phosphine) characters. The high-energy emissions at around 460-530 nm are more prominent at 77 K and assigned to intraligand and or ³m.l.c.t. (metal to ligand charge transfer) transitions. The temperature effects on the luminescence lifetimes of these complexes have also been studied.

Full text of DOI:10.1039/a605911b

View Article Online / Journal Homepage / Table of Contents for this issue
Structures and luminescent properties of polynuclear gold(I) halides
containing bridging phosphine ligands
Hong Xiao,a Yu-Xiang Weng,a Wing-Tak Wong,a Thomas C. W. Mak b and Chi-Ming Che*,a
a
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
b Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong
The complexes [AuI(PPh3)] 1, [Au2(µ-dppm)Cl2] 2 [dppm = bis(diphenylphosphine)methane], [Au2(µ-dppm)I2] 3,
[Au3(µ-tppm)Cl3] 4 [tppm = tris(diphenylphosphino)methane], [Au3(µ-tppm)I3] 5, [Au3(µ-dpmp)2Cl2]Cl 6
[dpmp = bis(diphenylphosphinomethyl)phenylphosphine] and [Au3(µ-dpmp)2I2]I 7 were prepared. The crystal
structures of 5–7 have been established by X-ray crystal analysis. The measured intramolecular Au᎐Au distances
are 3.136(1) Å in 5, 2.946(3) and 2.963(3) Å in 6 and 2.952(1) and 3.020(1) Å in 7. Extended-Hückel molecular
orbital calculations revealed that the 6p orbitals of iodide and 5d orbitals of gold() make a significant
contribution to the highest occupied molecular orbitals of 5 and of 2 and 4 respectively. The lowest unoccupied
molecular orbitals of these complexes mainly comprise π* orbitals of the phosphines. The photophysical
properties of 1–6 have been studied. All show dual emissions. The low-energy emissions at around 660–680 nm
have a small red shift in energy from chloro to iodo complexes, and a much higher intensity at room temperature
3
than at 77 K. These are attributed to triplet states with mixed m.m.l.c.t. (metal–metal to ligand charge transfer,
3
gold→phosphine) and l.l.c.t. (ligand to ligand charge transfer, halide to phosphine) characters. The high-energy
emissions at around 460–530 nm are more prominent at 77 K and assigned to intraligand and or 3m.l.c.t. (metal to
ligand charge transfer) transitions. The temperature effects on the luminescence lifetimes of these complexes have
also been studied.
There is growing interest in the photophysical properties and
photochemistry of luminescent metal clusters, especially those
of d10 metal ions such as CuI,1 and AgI 2 and AuI.3–5 In most
reports on luminescent d10-metal clusters the effect of metal–
metal interaction on both the ground- and excited-state prop-
erties has been emphasized. Ford and Volger 1 revealed that
metal-cluster-centred excited states have been proposed in some
tetranuclear copper() clusters. In this laboratory much effort
has been directed to the synthesis and photophysical studies of
luminescent gold() complexes.3 By systematic variation of the
number of gold() atoms and the Au᎐Au separations, a signifi-
cant effect on the electronic absorption spectra of polynuclear
gold() complexes containing bridging phosphine ligands has
been observed. In most di- and tri-nuclear gold() phosphine
complexes studied the emitting states were suggested to arise
from metal-centred transitions.3a,c,f
[AuI(PPh3)]8 1 and [Au2(µ-dppm)Cl2]8 2 were prepared by pub-
lished procedures. All the solvents for photochemical measure-
ments were purified by repeated distillations. Acetonitrile
(Ajax, AR) was distilled from KMnO4 and CaH2 under
nitrogen.
Syntheses
[Au2(ì-dppm)I2] 3. The complex was synthesized by a modifi-
cation of the literature method.8 A mixture of [Au2(µ-dppm)Cl2]
(0.46 g, 0.59 mmol) and KI (0.8 g, 4.8 mmol) in acetone (150
cm3) was refluxed for 1 h and subsequently stirred for 24 h at
room temperature. Acetone was evaporated and the solid resi-
due washed with water. White crystals (yield 70%) were
obtained by diffusion of diethyl ether into a dichloromethane
solution. FAB mass spectrum: m/z = 905 (M+ Ϫ I). NMR
(CDCl3): 1H, δ 3.65, [t, 2 H, J(P᎐H) = 10.9 Hz, CH2] and 7.26–
7.76 (m, 20 H, Ph); 31P, δ 27.2 (s).
As part of our continuing program in the study of d10–d10
interactions, we here describe the structures and temperature-
dependent emission properties of several gold() halide clusters
with bridging phosphine ligands, [AuI(PPh3)] 1, [Au2(µ-
dppm)X2] [dppm = bis(diphenylphosphino)methane, X = Cl 2
or I 3], [Au3(µ-tppm)X3] [tppm = tris(diphenylphosphino)-
[Au3(ì-tppm)Cl3] 4. The complex was synthesized by a modi-
fication of the literature method.9 A solution of tppm (0.102 g,
0.18 mmol) in dichloromethane (10 cm3) was added dropwise to
a solution of chloro(dimethyl sulfide)gold() (0.16 g, 0.53
mmol) in the same solvent (20 cm3) at room temperature. Upon
stirring for 1 h a white precipitate was formed. The reaction
mixture was concentrated in vacuo to 20 cm3, and precipitation
of the product was completed by addition of pentane (50 cm3).
The crude product was recrystallized by diffusion of diethyl
ether into a dichloromethane solution (yield 60%). FAB mass
methane, X = Cl
4
or
I
5] and [Au3(µ-dpmp)2X2]X
[dpmp = bis(diphenylphosphinomethyl)phenylphosphine, X =
Cl 6 or I 7]. Luminescence thermochromism has been observed
in these complexes and the lowest emitting excited states are
suggested to have mixed 3m.m.l.c.t. (metal–metal to ligand
3
charge transfer) and l.l.c.t. (ligand to ligand charge transfer)
characters.
1
spectrum: m/z = 1230 (M+ Ϫ Cl). NMR (CDCl3: H, δ 7.13–
7.74 (m, 30 H, Ph) and 6.30 (s, 1 H, HCP3); 31P, δ 34.0 (s).
Experimental
[Au3(ì-tppm)I3] 5. The complex was synthesized by a modifi-
cation of the literature method.9 A suspension of KI (0.3 g, 1.8
mmol) and 4 (0.08 g, 0.1 mmol) in acetone (300 cm3) was
refluxed for 1 h and then stirred at room temperature for 24 h.
The mixture was evaporated to dryness and the solid residue
washed with water. The crude sample was recrystallized by dif-
Materials
The compounds K[AuCl4], dppm and tppm were obtained from
Strem Chemicals, dpmp was prepared by the literature method,6
triphenylphosphine (Merck) and 2,2Ј-thiodiethanol (Strem)
were used as received and chloro(dimethyl sulfide)gold(),7
J. Chem. Soc., Dalton Trans., 1997, Pages 221–226
221

View Article Online
(i)
(ii)
K[AuCl4] → [Au2(µ-dppm)Cl2] →[Au2(µ-dppm)I2]
fusion of diethyl ether into a dichloromethane solution (yield
68%). FAB mass spectrum: m/z 1413 (M+ Ϫ I). NMR (CDCl3):
1H, δ 7.80–7.26 (m, 30 H, Ph) and 6.41 (s, 1 H, HCP3); 31P,
δ 31.5 (s) [Found: C, 3.05; H, 2.40. Calc. for C37H31Au3I3P3ؒ
(CH3)2CO: C, 30.05; H, 2.35%].
(iii)
(ii)
[AuCl(SMe2)] →[Au3(µ-tppm)Cl3] →[Au3(µ-tppm)I3]
(iv)
(ii)
[AuCl(SMe2)] →[Au3(µ-dpmp)2Cl3] →[Au3(µ-dpmp)2I3]
Scheme 1 (i) 2,2Ј-Thiodiethanol, dppm, MeOH; (ii) KI, Me2CO; (iii)
tppm, CH2Cl2
[Au3(ì-dpmp)2Cl2]Cl 6. A dichloromethane (20 cm3) solution
of dpmp (0.2 g, 0.23 mmol) was dropwise added to a solution
of [AuCl(SMe2)] (0.68 mmol, 0.2 g) in the same solvent
(20 cm3) for 1 h. The solution was concentrated to 10 cm3.
Upon diffusion of diethyl ether, yellow crystals (yield 50%) of
[Au3(µ-dpmp)2Cl2]Cl were obtained. FAB mass spectrum: m/z
1675 (M+). NMR (CD2Cl2): 1H, δ 7.77–7.10 (m, 50 H, Ph) and
3.76–3.68 [q, 8 H, J(P᎐H) = 21.0 Hz, CH2]; 31P, δ 35.186 (s) and
30.600 (s) (Found: C, 43.9; H, 3.10; Cl, 5.90. Calc. for
C64H58Au3Cl3P6: C, 44.95; H, 3.40; Cl, 6.20%).
atomic scattering factors were employed, and anomalous dis-
persion corrections were incorporated.11 The weighting
2
2
2
schemes were w = 4Fo /[σ2(Fo ) + 0.04(Fo )2] for 6 and w =
[σ2|Fo| + 0.0002|Fo|2]Ϫ1 for 5 and 7.
Details of crystal parameters, data collection and structure
refinement are given in Table 1, selected bond distances and
angles in Table 2.
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/273.
[Au3(ì-dpmp)2I2]I 7. A suspension of [Au3(µ-dpmp)2Cl2]Cl
(0.2 g, 0.12 mmol) and KI (0.08 g, 1.5 mmol) in acetone
(150 cm3) was refluxed for 1 h, and then stirred for 24 h at
room temperature. The yellow solid obtained was recrystallized
from acetone to give yellow needle crystals (yield 70%). FAB
Molecular orbital calculations
1
mass spectrum: m/z 1855 (M+). NMR: H (CD3CN), δ 7.89–
Extended-Hückel molecular orbital (EHMO) calculations
were carried out by using the ARGUS program.12a The geom-
etry parameters were obtained from the X-ray diffraction
data. The parameters of the Au atom were taken from ref.
12(b).
7.26 (m, 50 H, Ph) and 3.71–3.61 [q, 8 H, J(P᎐H) = 24.6 Hz,
CH2]; 31P (CD2Cl2), δ 30.52 (s) and 27.98 (s) (Found: C, 37.8; H,
2.85; I, 18.9. Calc. for C64H58Au3I3P6: C, 38.75; H, 2.95; I,
19.2%).
Instrumentation
Results and Discussion
Proton and 31P NMR spectra were recorded on a Bruker DRX
500 (500 MHz) multinuclear FT-NMR spectrometer. Chemical
shifts (δ in ppm) are reported relative to tetramethylsilane (1H)
and external H3PO4 (31P), respectively. Mass spectra were
recorded on a Finnigan MAT 95 spectrometer, UV/VIS absorp-
tion spectra on a Milton Roy Spectronic 3000 diode-array spec-
trophometer and steady-state emission spectra on a SPEX
Fluorolog-2 spectrofluorometer. Lifetime measurements were
performed with a Quanta Ray DCR-3 Nd–YAG laser (pulse
output 355 nm, 8 ns). Solutions for photochemical experiments
were degassed by at least four freeze–pump–thaw cycles. Low-
temperature emission measurements were made with powder
samples clamped by two quartz plates in an ADP DE-202 cryo-
genic cooler. A resistance heater was used for temperature con-
trol between 10 and 300 K. The emitted light was collected at
right angles to the exciting light beam. Time-resolved emission
spectra were recorded on a Princeton Instrument CCD Spec-
troscopic Multichannel Analyzer (CSMA) system, operated in
the gated mode.
Synthesis
The syntheses of the gold() complexes studied are outlined in
Scheme 1. The complexes [Au2(µ-dppm)I2] 3, [Au3(µ-tppm)Cl3]
4 and [Au3(µ-tppm)I3] 5 have been reported previously.7–9 The
metathesis of [Au2(µ-dppm)2Cl2] and [Au3(µ-tppm)Cl3] with KI
in acetone readily gives 3 and 5 respectively. As expected, the 31
P
NMR spectra of 3–5 show a singlet with chemical shifts con-
sistent with the literature values.8,9
The reaction of [AuCl(SMe2)] with a stoichiometric amount
of dpmp in dichloromethane gave a clear yellow solution, from
which [Au3(µ-dpmp)2Cl2]Cl 6 was obtained. The complex
[Au3(µ-dpmp)2I2]I 7 was obtained by the reaction of 6 with KI.
The 31P NMR spectra show two singlets, at δ 35.19 and 30.60
for 6 and of δ 30.52 and 27.98 for 7.
Crystal structures
Fig. 1 shows a perspective view of the [Au3(µ-tppm)I3] mol-
ecule. The structure is similar to that of [Au3(µ-tppm)Cl3]
reported by Schmidbaur and co-workers.9 Three Au᎐I units are
held together by the tppm ligand and AuI–AuI interactions. The
three AuI form an equilateral triangular array with the
Au᎐Au᎐Au angle of 60.1(1)Њ. The Au–Au distances average
3.136(1) Å, slightly shorter than that in [Au3(µ-tppm)Cl3]
[3.201(1) Å]. This is in agreement with the recent work by
Pyykkö et al.13 that the AuI᎐AuI interaction would be enhanced
with co-ordinated iodide compared with chloride. Not surpris-
ingly, the AuI᎐AuI separations are larger than those in cationic
[Au3(µ-tppm)2Cl]2+ [2.9220(8) and 3.0889(8) Å].3e The I᎐Au᎐P
axis is close to linear with an angle of 168.3(1)Њ similar to that
of 172.5(1)Њ in [Au3(µ-tppm)Cl3].8
Crystallography
The
structures
of
[Au3(µ-tppm)I3]ؒH2O,
[Au3(µ-
dpmp)2Cl2]ClؒCH2Cl2 and [Au3(µ-dpmp)2I2]Iؒ0.5Me2CO were
determined. Raw intensity data were collected at 298 K on a
Rigaku AFC7R four-circle diffractometer (50 kV and 150 mA)
using graphite-monochromated Mo-Kα radiation (λ 0.710 73
Å) and the ω–2θ scan mode. Intensity data (5, 2θmax = 50Њ, h 0–
29, k 0–30, l Ϫ1 to 30; 6, 2θmax = 45Њ, h 0–14, k Ϫ19 to 18, l Ϫ12
to 12; and 7, 2θmax = 55Њ, h 0–17, k 0–13, l Ϫ25 to 24) were
corrected for absorption using ψ-scan data and also for
Lorentz-polarization effects. Patterson superposition yielded
the positions of all non-hydrogen atoms, which were subjected
to antisotropic refinement. All hydrogens except those of water
were generated geometrically (C᎐H fixed at 0.96 Å) and allowed
to ride on their respective parent C atoms; they were assigned
the same isotropic thermal parameters and included in the
structure-factor calculations. Computations were performed
using the SDP program 10a for 6 and the SHELTXL-PC
program package10b for 5 and 7. Analytic expressions of
A perspective view of the [Au3(µ-dpmp)Cl2]+ cation is shown
in Fig. 2. The three AuI are bridged by two dpmp ligands with
the Au᎐P distances ranging from 2.32(1) to 2.33(1) Å. These
values are comparable to those of 2.295(3)–2.315(3) Å in
[Au3(µ-dpmp)2]3+.3f Atom Au(2) is two-co-ordinated whereas
Au(1) and Au(3) are pseudo-three-co-ordinated. The
Au(3)᎐Cl(3) bond distance is longer than Au(1)᎐C(1), reflecting
a stronger gold–chloride interaction at Au(1) than at Au(3). This
222
J. Chem. Soc., Dalton Trans., 1997, Pages 221–226

View Article Online
Fig. 3 Perspective view of the [Au3(µ-dpmp)2I2]+ cation (phenyl rings
Fig. 1 Perspective view of [Au3(µ-tppm)I3]
omitted)
Spectroscopic properties
All the gold() complexes prepared in this work are light yellow
to yellow. Their UV/VIS spectral data are summarized in Table 3.
As representative examples, the absorption spectra of 6 and 7
are shown in Fig. 4. The mononuclear complex 1 displays no
appreciable absorption at 300–400 nm. However, the trinuclear
complexes which have Au᎐Au contacts less than 3.3 Å show
significant absorptions at wavelengths greater than 300 nm. For
example, 6 shows an intense absorption band at 356 nm and
a shoulder at 326 nm while 7 shows a maximum at 320 nm
with shoulders at 375 and 420 nm. We attribute this spectral
feature to weak gold()–gold() interactions in the trinuclear
gold() complexes, which cause the red-shift of the metal-
centred 5d → 6s/6p transitions. Previous studies on related
trinuclear gold() phosphine complexes [Au3(dmmp)2]3+ 3c and
[Au3(dpmp)2]3+ 3f revealed that the lowest-energy allowed transi-
tions are due to dσ* → pσ, where dσ* is the antisymmetric
2
combination of the 5dz orbitals and pσ is the symmetric com-
2
bination of the 6pz orbitals of the gold atoms.
Extended-Hückel molecular-orbital calculations on com-
plexes 2–5 have been undertaken. The energy and compositions
of the HOMO (highest occupied molecular orbital) and
LUMO (lowest unoccupied molecular orbital) are summarized
in Table 4. For 3 and 5 the HOMO has a large iodide contribu-
tion, whereas for 2 and 4 the Au 5d (96 and 95%, respectively)
orbital is predominant. Changing from chloride to iodide
causes a significant increase in the halide character of the
HOMO. In all the complexes studied, the LUMO is the phos-
phine π* orbital.
Except for [AuI(PPh3)] all the gold() complexes display
photoluminescence both in dichloromethane solution and in the
solid state. The photophysical data are summarized in Table 3.
At room temperature dichloromethane solutions of 2–7 give a
broad and featureless emission band with the emission maxima
ranging from 550 to 660 nm and emission lifetimes from 0.5 to
2.5 µs (Table 3). In the solid state the emissions of these gold()
complexes are strongly affected by temperature. In general, dual
emissions are observed at low temperature. The high-energy
emissions, if observable, are at 480–530 nm, whereas the low-
energy ones lie between 570 and 700 nm.
Fig. 2 Perspective view of the [Au3(µ-dpmp)2Cl2]+ cation
may explain the difference in the P᎐Au᎐P angles at Au(1) and
Au(3). Indeed the P(3)᎐Au(3)᎐P(4) angle of 173.9(5)Њ is
approximately linear. The Au(1)᎐Au(2)᎐Au(3) chain is bent
with an angle of 149.56(9)Њ. This is similar to the related value
of 136.26(4)Њ in [Au3(µ-dmmp)2]3+ [dmmp = bis(dimethyl-
phosphinomethyl)methylphosphine].3c The Au᎐Au distances of
2.946(3) and 2.963(3) Å are shorter than those of 3.0137(8) and
3.0049(8) Å in [Au3(µ-dpmp)2]3+.3f According to Schmidbaur,14
such intermetallic Au᎐Au contacts suggest the existence of
weak metal–metal interactions.
A perspective view of the [Au3(µ-dpmp)2I2]+ cation is depicted
in Fig. 3. All the gold atoms are three-co-ordinated: Au(2) and
Au(3) are bridged by one iodide whereas Au(1) has a terminal
iodide. The Au(2)᎐Au(1)᎐Au(3) angle of 103.5(1)Њ is much
smaller than that of 149.56(9)Њ in the chloride analogue, [Au3(µ-
dpmp)2Cl2]+. The much larger bending of the Au3 chain is
attributed to the stronger Au᎐Au bonding interaction, which is
enhanced by the soft IϪ ligand. In fact, the intramolecular
Au᎐Au distances of 2.952(1) and 3.020(1) Å are comparable to
the values of 3.0137(8) and 3.0049(8) Å in [Au3(µ-dpmp)2]3+,3f
2.981(1) and 2.962(1) Å in [Au3(µ-dmmp)2]3+ 3c and 2.946(3) and
2.963(3) Å [Au3(µ-dpmp)2Cl2]+.
The temperature effect on the solid-state emissions has been
studied. At room temperature the iodide complexes, 3, 5 and 7
display only the low-energy emission, while the chloride com-
plexes 2 and 6 show relatively weak visible emission. As repre-
sentative examples, the emission spectra of 3, 6 and 7 at various
temperatures are shown in Figs. 5–7 respectively. In the assign-
J. Chem. Soc., Dalton Trans., 1997, Pages 000–000
223

View Article Online
Table 1 Crystallographic data
[Au3(µ-tppm)I3]ؒH2O
C37H31Au3I3P3ؒH2O
[Au3(µ-dpmp)2Cl2]ClؒCH2Cl2
C64H58Au3Cl3P6ؒCH2Cl2
[Au3(µ-dpmp)2I2]ؒ0.5(Me2CO)
Formula
C64H68Au3I3P6ؒ0.5(CH3)2CO
M
1558.17
Cubic
I43d (no. 220)
0.15 × 0.15 × 0.15
25.274(3)
1795.20
Triclinic
P1 (no. 2)
2010.5
Monoclinic
P21/c
0.2 × 0.2 × 0.38
18.426(4)
14.459(3)
26.597(5)
Crystal system
Space group
Crystal size/mm
a/Å
b/Å
c/Å
α/Њ
β/Њ
¯
0.27 × 0.28 × 0.34
14.080(7)
19.798(4)
12.692(4)
94.26(3)
109.26(2)
103.86(4)
3196(2)
105.69(3)
γ/Њ
U/Å3
16 145(8)
16
6822(3)
4
Z
2
F(000)
11 264
133.2
2.564
1724
72.89
1.865
3764
µ/cmϪ1
Dc/g cmϪ3
1.958
No. of unique reflections
No. of data used in refinement
No. of variables
Maximum transmission factors
R,a RЈb
1284
8375
2756 [I > 2σ(I)]
372
0.417, 0.999
0.060, 0.057
6357
1113 [(Fo) > 4σ(Fo)]
143
0.642, 1.000
0.027, 0.028
5329 [(Fo) > 4σ(Fo)]
302
0.642, 1.000
0.034, 0.044
¹
2

a
2
R = ͚(|Fo| Ϫ |Fc|)/͚|Fo|. b RЈ = [͚w(|Fo| Ϫ |Fc|) /͚ |Fo| ] .
²
Table 2 Selected bond distances (Å) and angles (Њ) of complexes 5–7
Compound 5
Au(1)᎐I(1)
Au(1)᎐Au(1a)
2.568(1)
3.136(1)
Au(1)᎐P(1)
Au(1)᎐Au(1b)
2.275(3)
3.136(1)
I(1)᎐Au(1)᎐P(1)
P(1)᎐Au(1)᎐Au(1a)
P(1)᎐Au(1)᎐Au(1b)
168.3(1)
76.4(1)
94.2(1)
I(1)᎐Au(1)᎐Au(1a)
I(1)᎐Au(1)᎐Au(1b)
Au(1a)᎐Au(1)᎐Au(1b) 60.1(1)
114.71
88.6(1)
Compound 6
Au(1)᎐Au(2)
Au(1)᎐P(1)
Au(2)᎐Au(3)
Au(2)᎐P(5)
Au(3)᎐P(4)
2.946(3)
2.32(1)
2.963(3)
2.32(1)
2.32(1)
Au(1)᎐Cl(1)
Au(1)᎐P(6)
Au(2)᎐P(2)
Au(3)᎐P(3)
Au(3)᎐Cl(3)
2.77(1)
2.35(1)
2.33(1)
2.33(1)
2.84(1)
Au(2)᎐Au(1)᎐Cl(1)
Au(2)᎐Au(1)᎐P(6)
Au(1)᎐Au(2)᎐P(2)
Au(3)᎐Au(2)᎐P(2)
Au(2)᎐Au(3)᎐P(3)
78.9(3)
89.7(3)
88.1(3)
92.0(3)
86.4(3)
Au(2)᎐Au(1)᎐P(1)
Au(1)᎐Au(2)᎐Au(3)
P(1)᎐Au(1)᎐P(6)
P(2)᎐Au(2)᎐P(5)
P(3)᎐Au(3)᎐P(4)
93.3(3)
149.56(9)
147.9(5)
176.5(5)
173.9(5)
Fig. 4 The UV/VIS absorption spectra of (a) [Au3(µ-dpmp)2Cl2]Cl
(1.0 × 10Ϫ5 mol dmϪ3) and (b) [Au3(µ-dpmp)I2]I (2.4 × 10Ϫ5 mol dmϪ3) in
dichloromethane at room temperature
Compound 7
Au(1)᎐Au(2)
Au(1)᎐I(1)
Au(1)᎐P(2)
Au(2)᎐P(3)
Au(3)᎐I(2)
Au(3)᎐P(6)
2.952(1)
3.008(1)
2.316(3)
2.310(3)
3.191(1)
2.316(3)
Au(1)᎐Au(3)
Au(1)᎐P(1)
Au(2)᎐I(2)
Au(2)᎐P(4)
Au(3)᎐P(5)
3.020(1)
2.307(3)
3.036(1)
2.320(3)
2.313(4)
Au(2)᎐Au(1)᎐Au(3) 103.5(1)
Au(2)᎐Au(1)᎐I(1)
Au(2)᎐Au(1)᎐P(1)
Au(3)᎐Au(1)᎐P(2)
Au(1)᎐Au(2)᎐P(3)
P(1)᎐Au(1)᎐P(2)
P(3)᎐Au(2)᎐P(4)
P(5)᎐Au(3)᎐P(6)
85.0(1)
88.5(1)
86.6(1)
94.2(1)
173.0(1)
155.3(1)
170.5(1)
Au(3)᎐Au(1)᎐I(1)
Au(3)᎐Au(1)᎐P(1)
Au(2)᎐Au(1)᎐P(2)
Au(1)᎐Au(2)᎐I(2)
Au(1)᎐Au(3)᎐I(2)
Au(2)᎐I(2)᎐Au(3)
171.5(1)
86.9(1)
90.6(1)
77.6(1)
77.6(1)
97.7(1)
Symmetry transformations: a (z, x, y); b (y, z, x).
Fig. 5 Variable-temperature emission spectra of [Au2(µ-dppm)I2] in
the solid state at (a) 11.7, (b) 250 and (c) 292 K. Excitation at 355 nm
ment of the emission spectra the following points should be
noted: (a) the intensities of both the high- and low-energy emis-
sions are temperature dependent, with the latter favoured at
high temperature; (b) the low-energy emission shows a small
blue shift in energy on going from iodide to chloride; and (c) the
excitation spectra for both the high- and low-energy emissions
are the same and match the absorption spectra of the com-
plexes. We suggest that in the chloride complexes the low-
energy emission comes from the Au(d) → phosphine (π*)
transition, which is modified by the metal–metal interactions.
In the iodide complexes the low-energy emissions come from
224
J. Chem. Soc., Dalton Trans., 1997, Pages 221–226

View Article Online
Table 3 Photophysical data for gold() halide complexes in degassed dichloromethane at room temperature and in the solid state
λabs/nm
λem/nm
(τ0/µs)* [Φem]*
λem/nm
in the solid state
Compounds
Au᎐Au/Å
(ε/dm3 molϪ1 cmϪ1
)
1
2
275 (3.4 × 103)
3.351
268 (1.02 × 104)
585 (0.5)
300 (sh) (3.08 × 103)
[4.01 × 10Ϫ3
]
]
12 K: 500
270 K: 510, 680
12 K: 620 (sh), 530
298 K: 670
298 K: 510, 680
20 K: 500
3
4
268 (1.51 × 104)
615 (1.1)
300 (sh) (3.77 × 103)
275 (0.97 × 104)
[1.32 × 10Ϫ2
550 (1.1)
3.201
3.136
300 (sh) (0.51 × 104)
[8.5 × 10Ϫ3
]
298 K: 640
5
6
275 (1.39 × 104)
300 (sh) (0.80 × 104)
260 (3.37 × 104)
326 (sh)
590 (1.2)
12 K: 480, 680
298 K: 680
77 K: 485, 620
[1.75 × 10Ϫ2
650 (1.2)
]
]
2.946
2.963
[8.80 × 10Ϫ3
356 (1.49 × 104)
295 (2.94 × 104)
320 (2.05 × 104)
360 (1.03 × 104)
420 (sh) (4.78 × 103)
7
2.952
3.02
660 (2.5)
12 K: 575, 665
[2.4 × 10Ϫ2
]
* In dichloromethane solution at room temperature.
Table 4 Components of HOMO and LUMO for gold() halide complexes 2–5 calculated by the EHMO method
% Metal (d)
HOMO
% Halide (p)
HOMO
% Ligand
HOMO
Compound
LUMO
LUMO
LUMO
2
3
5
4
95.95
24.74
32.87
94.84
0.27
0.13
0.15
0.18
2.10
74.61
66.40
1.71
0.05
0.07
0.07
0.02
1.95
0.66
0.74
3.45
99.68
99.80
99.78
99.80
Fig. 7 Variable-temperature emission spectra of [Au3(µ-dpmp)2I2]I in
the solid state at (a) 12 and (b) 250 K. Excitation at 355 nm
tions, and the excited states are represented by i.l./3m.l.c.t. A
3
scheme for intersystem energy crossing between the 3i.l./3m.l.c.t.
and the 3m.m.l.c.t./3l.l.c.t. states can be constructed (Fig. 8). As
shown, when the temperature is raised, curve-crossing between
3i.l./3m.l.c.t. and 3m.m.l.c.t./3l.l.c.t. states might occur. We
Fig. 6 Emission spectrum of [Au3(µ-dpmp)2Cl2]Cl in the solid state at
77 K. Excitation at 355 nm
excited states which have substantial IϪ→phosphine (π*)
charge-transfer character. The EHMO calculations are also
consistent with this assignment. As mentioned in the previous
section, the HOMO of the gold() complexes have increased
halide contribution from chloride to iodide. We denote the
excited states for the low-energy emissions as 3m.m.l.c.t./3l.l.c.t.
Here, m.m.l.c.t. means metal–metal (dσ*) to ligand (phosphine)
charge transfer and l.l.c.t. ligand (halide) to ligand (phosphine)
charge transfer. Recently, Fackler and co-workers4d reported
the temperature-dependent photoluminescence of 1,3,5-triaza-
7-phosphaadamantane complexes of gold, which show
multiple-state emissions originating from thermally non-
equilibrated excited states. The excited states for the high-
energy emissions could have mixed character involving both
intraligand (i.l.) and m.l.c.t. [Au → π*(phosphine)] transi-
3
anticipate that the m.m.l.c.t./3l.l.c.t. state could be thermally
populated from the high-energy state by overcoming the cross-
ing barrier, and hence the low-energy emission is favoured at
high temperature. This may account for the observed lumi-
nescence thermochromism.
Study of the variable-temperature emission spectra reveals
that luminescence thermochromism is more pronounced in the
iodide complexes. The well resolved high- and low-energy emis-
sion bands of 3 guarantee independent measurement of the
emission lifetimes for the two excited states. It is expected that
these excited states would be coupled at high temperatures, at
which they will be thermally equilibrated and decay at the same
rate. The lifetimes for the two excited states plotted against
temperature are shown in Fig. 9. As shown, the lifetimes of the
J. Chem. Soc., Dalton Trans., 1997, Pages 221–226
225

View Article Online
with that for the appearance of the low-energy emission. The
observed rate constants were analysed by equation 16 (1) based
kp = (k1 + k2 eϪ∆E/RT)/(1 + eϪ∆E/RT
)
(1)
on the assumption that the emissions originate from two
thermally equilibrated levels with temperature-independent rate
constants. The fitting of the rate constants vs. temperature is
shown in Fig. 10, and the empirically derived parameters are
k1 = 2 × 104 sϪ1, k2 = 8 × 108 sϪ1 and ∆E = 945 ± 45 cmϪ1. The
energy gap can be interpreted as the energy barrier for curve-
crossing, as shown in Fig. 8. It is interesting that a similar acti-
vation energy (990 ± 370 cmϪ1) has previously been reported for
tetranuclear copper() bromide complexes.17
Fig. 8 Proposed model for the potential curve-crossing between
3m.l.c.t./3i.l. and 3m.m.l.c.t./3l.l.c.t., where state ∆E is the activation
energy for the crossing barrier
Acknowledgements
We acknowledge support from the University of Hong Kong
and The Hong Kong Research Grants Council.
References
1 P. C. Ford and A. Vogler, Acc. Chem. Res., 1993, 26, 220.
2 A. Vogler and H. Kunkley, Chem. Phys. Lett., 1989, 158, 74;
C. M. Che, H. K. Yip, D. Li, S. M. Peng, G. H. Lee, Y. M. Wang and
S. T. Liu, J. Chem. Soc., Chem. Commun., 1991, 1615; D. M. Knot-
ter, H. L. van Maanen, D. M. Grove, A. L. Spek and G. van Koten,
Inorg. Chem., 1991, 30, 3309.
3 (a) C. M. Che, H. L. Kwong, V. W. W. Yam and C. K. Cho, J. Chem.
Soc., Chem. Commun., 1989, 855; (b) C. M. Che, H. L. Kwong,
V. W. W. Yam and C. K. Poon, J. Chem. Soc., Dalton Trans., 1990,
3215; (c) V. W. W. Yam, T. F. Lai and C. M. Che, J. Chem. Soc.,
Dalton Trans., 1990, 3747; (d) C. M. Che, W. T. Wong, T. F. Lai,
H. L. Kwong, C. K. Poon and V. W. W. Yam, J. Chem. Soc., Dalton
Trans., 1992, 2445; (e) C. M. Che, H. K. Yip, V. W. W. Yam, P. Y.
Cheung, T. F. Lai, S. J. Shieh and S. M. Peng, J. Chem. Soc., Dalton
Trans., 1992, 427; (f) D. Li, C. M. Che, S. M. Peng, S. T. Liu, Z. Y.
Zhou and T. C. W. Mak, J. Chem. Soc., Dalton Trans., 1993, 189;
(g) H. Xiao, K. K. Cheung, C. X. Guo and C. M. Che, J. Chem.
Soc., Dalton Trans., 1994, 1867.
Fig. 9 Emission lifetimes recorded at various temperatures and moni-
tored at (a) 530 and (b) 680 nm for [Au2(µ-dppm)I2]
4 (a) C. King, J. C. Wang, S. Wang, M. N. I. Khan and
J. P. Fackler, jun., Inorg. Chem., 1988, 27, 1672; (b) C. King, M. N. I.
Khan, R. J. Staples and J. P. Fackler, jun., Inorg. Chem., 1992, 31,
3236; (c) J. P. Fackler, jun., B. Assmann, K. Angermaier and
H. Schmidbaur, Inorg. Chem., 1995, 34, 75; (d) Z. Assefa,
B. G. McBurnett, R. J. Staples and J. P. Fackler, jun., Inorg. Chem.,
1995, 34, 4965; (e) J. M. Forward, D. Bohmann, J. P. Fackler, jun.
and R. J. Staples, Inorg. Chem., 1995, 34, 6330.
5 H. K. Yip, A. Schier, J. Riede and H. Schmidbaur, J. Chem. Soc.,
Dalton Trans., 1994, 2333; T. M. McCleskey and H. B. Gray, Inorg.
Chem., 1992, 31, 1733.
6 R. Appel, K. Geisler and H. F. Schöler, Chem. Ber., 1979, 112, 648.
7 K. C. Dash and H. Schmidbaur, Chem. Ber., 1973, 106, 1221.
8 H. Schmidbaur, A. Wohlleben, F. Wagner, O. Orama and
G. Huttner, Chem. Ber., 1977, 110, 1748.
9 A. Stützer, P. Bissinger and H. Schmidbaur, Chem. Ber., 1992, 125,
367.
10 (a) SDP Structure Determination Package, Enraf-Nonius, Delft,
1985; (b) G. M. Sheldrick, in Crystallographic Computing 3,
eds. G. M. Sheldrick, C. Krüger and R. Goddard, Oxford Uni-
versity Press, New York, 1985, p. 175.
11 J. A. Ibers and W. C. Hamilton (Editors), International Tables for
X-Ray Crystallogaphy, Kynoch Press, Birmingham, 1974, vol. 4,
p. 55, 149.
12 (a) M. A. Thompson, ARGUS, A Quantum Chemical Electronic
Structure Program, Version 1.1 User Manual, Pacific Northwest
Laboratory, Richland, WA, 1992; (b) L. C. Porter, M. N. I. Khan, C.
King and J. P. Fackler, jun., Acta Crystallogr., Sect. C, 1989, 45, 947.
13 P. Pyykkö, J. Li and N. Runeberg, Chem. Phys. Lett., 1994, 218, 133.
14 H. Schmidbauer, Gold Bull., 1990, 23, 11.
15 K. R. Klye, W. E. Palke and P. C. Ford, Coord. Chem. Rev., 1990, 97,
35.
16 W. A. Fordyce, H. Rau, M. L. Stone and G. A. Crosby, Chem. Phys.
Lett., 1981, 77, 404.
Fig. 10 Variation in the decay of the high-energy emission of [Au2(µ-
dppm)I2] as a function of temperature between 10 and 200 K
two excited states are different at temperatures below 120 K and
become the same at above 140 K. This clearly demonstrates that
the two states responsible for the high- and low-energy emis-
sions poorly couple at low temperatures. A plot of emission
lifetimes vs. temperature for 3 measured at 530 nm is shown in
Fig. 10. When the temperature is below 110 K there is little
change in the lifetime with temperature. However, at tempera-
tures >110 K a dramatic decrease in lifetime is observed. The
temperature at which the dramatic change occurs coincides
17 C. K. Ryu, M. Vitale and P. C. Ford, Inorg. Chem., 1993, 32, 869.
Received 27th August 1996; Paper 6/05911B
226
J. Chem. Soc., Dalton Trans., 1997, Pages 221–226