Luminescence studies of dinuclear gold(I) phosphor-1,1-dithiolate complexes

Article abstract of DOI:10.1016/S0022-2860(99)00231-8

Luminescence properties of several structurally characterized dinuclear gold(I) complexes with phosphor-1,1-dithiolato type ligands were investigated. Among these complexes, single crystal X-ray analyses revealed structural types, where weak intermolecular Au···Au interactions (~ 2.90- 3.20 A?) were present in some cases and absent in others. This interaction showed a profound influence on the observed emission spectra for the title complexes. A clear correlation between the emission profiles of these gold- sulfur complexes and the presence of intermolecular Au···Au interactions in the solid state has been established.

Full text of DOI:10.1016/S0022-2860(99)00231-8

Journal of Molecular Structure 516 (2000) 99–106
www.elsevier.nl/locate/molstruc
Luminescence studies of dinuclear gold(I) phosphor-1,1-dithiolate
complexes
a
b
a*
W.E. van Zyl , J.M. L o´ pez-de-Luzuriaga , J.P. Fackler Jr.
a
Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University, P.O. Box 30012,
College Station, TX 77842-3012, USA
b
Departamento de Qu ´ı mica, Universidad de La Rioja, Obispo Bustamante 3, E-26001 Logro n˜ o, Spain
Received 20 April 1999; accepted 23 April 1999
Abstract
Luminescence properties of several structurally characterized dinuclear gold(I) complexes with phosphor-1,1-dithiolato type
ligands were investigated. Among these complexes, single crystal X-ray analyses revealed structural types, where weak
…
˚
intermolecular Au Au interactions (ϳ2.90–3.20 A) were present in some cases and absent in others. This interaction showed
a profound influence on the observed emission spectra for the title complexes. A clear correlation between the emission profiles
…
of these gold–sulfur complexes and the presence of intermolecular Au Au interactions in the solid state has been established.
2000 Elsevier Science B.V. All rights reserved.
᭧
Keywords: Dinuclear gold–sulfur complexes; Luminescence properties; Phosphor-1,1-dithiolates
1
. Introduction
X-ray crystallographic study have been frustrated.
The problem is further compounded where growth
of single crystals is not readily achieved where, for
example, the products are amorphous solids such as
the anti-arthritic gold–sulfur drugs Myochrysine and
Solganol [8]. Indeed, although the crystal structure of
Myochrysine have recently been reported, suitable
crystals could only be obtained in an unconventional
manner after numerous other strategies failed [9]. The
solid state structure of Solganol is still uncertain.
A method that could qualitatively detect the
Presence of weak intermolecular metal–metal
interactions has been implicated in the design of elec-
tronic and sensor devices [1–4]. Gold–sulfur
complexes often show weak intermolecular bonding
Ϫ1
interactions (5–15 kcal mol ) between the closed
10
shell d gold atoms. This phenomenon is termed
aurophilicity’, with an origin best described by rela-
‘
tivistic and correlation effects [5–7]. Energies asso-
ciated with crystal packing effects often dominate the
aurophilicity, however, and thus dictate whether weak
interactions will be present or absent in the crystalline
solid. For this reason, attempts to determine the
presence of such interactions by means other than
…
presence of intermolecular Au Au interactions in
the bulk solid sample would have clear benefits, one
of which may provide information about the biolo-
gical function of the aforementioned gold–sulfur
drugs. Investigations to find a relationship between
the observation of emission and the presence of
weak intermolecular bonding interactions between
neighboring gold atoms have been addressed
*
Corresponding author. Tel.: ϩ 1-409-845-0648; fax: ϩ 1-409-
8
45-3154.
E-mail address: fackler@mail.chem.tamu.edu (J.P. Fackler Jr.)
0
022-2860/00/$ - see front matter ᭧ 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(99)00231-8

1
00
W.E. van Zyl et al. / Journal of Molecular Structure 516 (2000) 99–106
previously [10–12], but a conclusive answer has not
been obtained. Here we report the luminescence prop-
erties of several closely related dinuclear gold–sulfur
complexes and show how their emission profile
relates to the solid state structure in each case. In
in vacuo. The complex was extracted with CH Cl
2 2
(25 ml) and filtered through anhydrous MgSO to
4
remove NH Cl. The filtrate was evaporated under
4
reduced pressure, which afforded a pale yellow
powder. The crude material was washed with three
10 ml portions of ether, and dried under vacuum
…
particular, the presence or absence of Au Au inter-
Ϫ2
actions was found to be accurately predicted for all
complexes investigated, based solely on the
complex’s emission profile. The synthesis and single
crystal X-ray structure of [AuS PPh(OCH
(10 Torr) for 1 h; mp: 144ЊC. ϩFAB/DIP MS
ϩ
ϩ
(NBA/CHCl , m/z): 853 ([Mϩ1] ), 655 ([M-Au] ),
3
ϩ
1
427 ([M-AuL] ). H NMR data for cis and trans
isomers (chloroform-d , 300 MHz, 20ЊC, d): 8.11–
2
2-
1
CHyCH )] 1 is included in the present study as a
8.01 (m, 4H, Ph), 7.61–7.44 (m, 6H, Ph), 6.10–5.90
2
2
representative example of the title compounds.
Since this study is aimed at the luminescence proper-
ties of the title complexes, a detailed account of the
synthesis, structure and reactivity of these complexes
will be published elsewhere.
(m-br, 2H, CHyCH ), 5.46 (d, 4H, OCH ), 5.30 (d,
2
2
3
1
1
4H, OCH ), 4.88 (s-br, 4H, CyCH ). P{ H} NMR
2
2
data for cis and trans isomers (chloroform-d1,
200 MHz, 19ЊC, d): 106.18 (s), 103.37(s).
2
.3. Luminescence studies
2. Experimental
Excitation and emission spectra were obtained on a
SLM/AMINCO, Model 8100 spectrofluorometer
2.1. General
Table 1
1
The H NMR spectrum of 1 was obtained on a
Crystal data and structure refinement for [AuS PPh(OCH
2
2-
Varian XL-200 spectrometer operating at 200 MHz,
and is expressed in parts per million (ppm) downfield
shift referenced internally to the residual proton
impurity in the deuterated solvent, and is reported
2 2
CHyCH )] 1
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
18 2 2 2 4
C H20Au O P S
852.45
293(2) K
0.71073 A
˚
as: chemical shift position (d ); multiplicity (s ˆ
H
Triclinic
P1¯
singlet, d ˆ doublet, m ˆ multiplet, br ˆ broad);
3
1
1
relative integral; and assignment. The P{ H} NMR
spectrum of 1 was obtained on a Varian XL 200 MHz
broadband spectrometer operating at 81 MHz, with
chemical shifts reported relative to a 85% H PO in
˚
Unit cell dimensions
a ˆ 9.559(2) A, a ˆ 103.21(3)Њ
˚
b ˆ 12.283(3) A, b ˆ
110.42(3)Њ
˚
c ˆ 12.547(3) A, g ˆ
3
4
105.16(3)Њ
D O external standard solution. The positive fast atom
2
3
˚
Volume, Z
1246.5(4) A , 2
2.271 mg m
12.231 mm
bombardment (ϩFAB/DIP (direct insertion probe))
mass spectrum was acquired on a VG Analytical
Ϫ3
Density (calculated)
Absorption coefficient
F(000)
Crystal size
u range for data collection
Limiting indices
Ϫ1
(Manchester, UK) 70S high resolution, double
792
3
focusing mass spectrometer.
0.08 × 0.08 × 0.28 mm
2.10–22.49Њ
Ϫ10 Յ h Յ 9, Ϫ13 Յ k Յ 12,
Յ l Յ 13
2
.2. Preparation of [AuS PPh(OCH CHyCH )] 1
2 2 2 2
0
Reflections collected
Independent reflections
Refinement method
3258
A
50 ml Schlenk tube was charged with
3258 [R(int) ˆ 0.0000]
Full-matrix least-squares on F
3258/62/254
[
NH ][S PPh(OCH CHyCH )] (79 mg, 0.32 mmol)
2
4
2
2
2
and placed under vacuum for 30 min. The salt was
dissolved in 20 ml THF, and upon dissolution
ClAuTHT (100 mg, 0.31 mmol) was added in one
portion at room temperature. An immediate white
precipitate (NH Cl) was observed. The mixture was
stirred for 40 min followed by removal of the solvent
Data/restraints/parameters
2
Goodness-of-fit on F
1.038
Final R indices [I Ͼ 2s(I)]
R indices (all data)
Extinction coefficient
R1 ˆ 0.0408, wR2 ˆ 0.0896
R1 ˆ 0.0575, wR2 ˆ 0.0955
0.0329(9)
4
˚
Ϫ3
Largest difference peak and hole 0.776 and Ϫ0.971 e A

W.E. van Zyl et al. / Journal of Molecular Structure 516 (2000) 99–106
101
Table 2
Selected bond lengths (A) and angles (Њ) for [AuS
CHyCH )] 1 (symmetry transformations used to generate equiva-
lent atoms: #1: Ϫxϩ1, Ϫyϩ1, Ϫzϩ1; #2: Ϫxϩ1, Ϫy, Ϫzϩ1)
Table 2 (continued)
˚
2
PPh(OCH2-
2
2
S(4)#2–Au(2)–Au(2)#2
S(3)–Au(2)–Au(2)#2
Au(1)–Au(2)–Au(2)#2
O(2)–P(2)–C(21)
O(2)–P(2)–S(3)
C(21)–P(2)–S(3)
O(2)–P(2)–S(4)
C(21)–P(2)–S(4)
S(3)–P(2)–S(4)
P(2)–S(3)–Au(2)
P(2)–S(4)–Au(2)#2
C(12)–C(11)–C(16)
C(12)–C(11)–P(1)
C(16)–C(11)–P(1)
C(11)–C(12)–C(13)
C(14)–C(13)–C(12)
C(15)–C(14)–C(13)
C(14)–C(15)–C(16)
C(11)–C(16)–C(15)
C(26)–C(21)–C(22)
C(26)–C(21)–P(2)
C(22)–C(21)–P(2)
C(21)–C(22)–C(23)
C(24)–C(23)–C(22)
C(25)–C(24)–C(23)
C(24)–C(25)–C(26)
C(21)–C(26)–C(25)
C(1)–O(1)–P(1)
92.10(9)
95.47(9)
170.84(3)
102.3(8)
112.6(6)
106.6(5)
110.4(6)
106.3(5)
117.3(2)
101.7(2)
104.1(2)
116.8(13)
122.1(10)
121.1(9)
121.3(14)
Au(1)–S(1)
2.299(3)
2.310(3)
3.0963(9)
3.1231(11)
1.576(10)
1.792(12)
2.006(5)
2.008(4)
2.310(3)
2.290(4)
2.301(4)
3.1171(10)
1.588(14)
1.73(2)
Au(1)–S(2)#1
Au(1)–Au(2)
Au(1)–Au(1)#1
P(1)–O(1)
P(1)–C(11)
P(1)–S(2)
P(1)–S(1)
S(2)–Au(1)#1
Au(2)–S(4)#2
Au(2)–S(3)
Au(2)–Au(2)#2
P(2)–O(2)
121(2)
117(2)
122(2)
121.2(14)
108(2)
128(2)
P(2)–C(21)
P(2)–S(3)
P(2)–S(4)
S(4)–Au(2)#2
C(11)–C(12)
C(11)–C(16)
C(12)–C(13)
C(13)–C(14)
C(14)–C(15)
C(15)–C(16)
C(21)–C(26)
C(21)–C(22)
C(22)–C(23)
C(23)–C(24)
1.993(5)
2.013(5)
2.290(4)
1.376(12)
1.382(12)
1.380(12)
1.366(13)
1.366(13)
1.383(12)
1.296(13)
1.323(14)
1.333(14)
1.31(2)
123.7(13)
127(2)
125(2)
108(2)
128(2)
125(2)
126.6(10)
116(2)
99(2)
O(1)–C(1)–C(2)
C(3)–C(2)–C(1)
C(4)–O(2)–P(2)
O(2)–C(4)–C(5)
C(24)–C(25)
1.31(2)
132(2)
123(3)
94(3)
C(25)–C(26)
O(1)–C(1)
C(1)–C(2)
1.329(14)
1.427(12)
1.45(2)
C(6)–C(5)–C(4)
C(2)–C(3)
1.35(2)
O(2)–C(4)
1.36(3)
C(4)–C(5)
C(5)–C(6)
1.44(3)
1.40(3)
using a xenon lamp. The radiation was filtered
through a 0.10 M KNO solution to reduce the amount
2
S(1)–Au(1)–S(2)#1
S(1)–Au(1)–Au(2)
S(2)#1–Au(1)–Au(2)
S(1)–Au(1)–Au(1)#1
S(2)#1–Au(1)–Au(1)#1
Au(2)–Au(1)–Au(1)#1
O(1)–P(1)–C(11)
O(1)–P(1)–S(2)
C(11)–P(1)–S(2)
O(1)–P(1)–S(1)
C(11)–P(1)–S(1)
S(2)–P(1)–S(1)
P(1)–S(1)–Au(1)
P(1)–S(2)–Au(1)#1
S(4)#2–Au(2)–S(3)
S(4)#2–Au(2)–Au(1)
S(3)–Au(2)–Au(1)
172.38(11)
84.68(8)
88.26(S(1)
93.33(8)
94.29(8)
160.33(3)
107.1(5)
114.4(4)
107.7(4)
104.8(4)
104.7(4)
117.4(2)
102.9(2)
101.6(2)
172.31(11)
90.17(9)
82.55(9)
of scattered light. Low-temperature measurements
were made in a cryogenic device of local design.
Collodion was used to attach the powder samples to
the holder. The collodion was scanned for a baseline
subtraction. Liquid nitrogen was used to obtain the
7
7 K measurements.
2
.4. Crystallography
A single crystal of 1 suitable for X-ray crystallo-
graphic studies was obtained as a pale yellow needle
from a CH Cl solution layered with hexane. The
2
2
crystal was mounted on the tip of a quartz fiber with
fast-adhesive glue. Single crystal diffraction analysis

1
02
W.E. van Zyl et al. / Journal of Molecular Structure 516 (2000) 99–106
Table 3
4
Atomic coordinates ( × 10 ) and equivalent isotropic displacement
2
3
˚
parameters (A × 10 ) for the complex [AuS
2
PPh(OCH
2
CHyCH
2
)]
2
1. U(eq) is defined as one-third of the trace of the orthogonalized Uij
tensor
Atom
x
y
z
U(eq)
Au(1)
P(1)
S(1)
S(2)
Au(2)
P(2)
5384(1)
7014(4)
6246(5)
5392(5)
4981(1)
7240(4)
7238(5)
7313(5)
7713(14)
6741(21)
7229(23)
8759(21)
9747(20)
9246(16)
8955(20)
10371(20)
11730(27)
11892(27)
10520(25)
9149(25)
8539(11)
9177(21)
10512(34)
9760(33)
5846(19)
4436(41)
3497(65)
3405(78)
3913(1)
5132(3)
3516(3)
5895(3)
1289(1)
923(3)
5292(1)
3646(3)
3802(3)
3147(3)
5140(1)
7640(3)
6971(3)
6639(3)
2494(10)
1291(11)
396(15)
676(15)
1871(14)
2771(14)
9003(12)
9172(19)
10196(20)
11197(20)
10974(19)
9965(13)
4887(8)
5423(15)
5218(38)
4482(24)
8058(12)
7773(40)
8450(58)
8329(30)
62(1)
63(1)
79(1)
83(1)
65(1)
72(1)
91(1)
89(1)
67(3)
116(6)
136(7)
120(6)
110(5)
95(4)
S(3)
S(4)
2246(3)
Ϫ578(3)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
O(1)
C(1)
4874(10)
4620(16)
4282(18)
4316(15)
4596(14)
4877(13)
1507(13)
2230(22)
2709(27)
2489(21)
1686(23)
1225(17)
5932(8)
7216(12)
7856(29)
8378(27)
583(14)
772(45)
620(46)
97(5)
Fig. 1. A perspective view of the molecular structure of 1 showing
the atom labeling scheme. Only the atoms in the metallocycle are
shown as thermal ellipsoids at the 50% probability level. All other
atoms are of arbitrary size.
176(9)
236(13)
185(11)
210(11)
156(8)
93(3)
120(6)
336(32)
269(20)
148(5)
377(32)
430(36)
659(75)
shelxtl plus (Micro Vax II) [13]. The systematic
absences were consistent with the assigned space
group. The crystal structure was solved using direct
methods to determine the gold atom position, while all
other atoms were located with difference Fourier
maps. Structure refinement was carried out using
shelx-93. The position of the hydrogen atoms were
calculated by assuming idealized geometries, C–H ˆ
C(2)
C(3)
O(2)
C(4)
C(5)
C(6)
Ϫ562(32)
˚
.93 A. The relevant crystal data and structure refine-
0
was carried out on an automated Nicolet R3 four-
circle diffractometer utilizing the Wyckoff scanning
ment for 1 are shown in Table 1. The selected bond
˚
lengths (A) and angles (Њ) for 1 are shown in Table 2.
4
technique with graphite monochromated Mo-Ka
Atomic coordinates ( × 10 ) and equivalent isotropic
2
3
ꢀ
ꢀ
(
l ˆ 0:71073 A) radiation. Refined cell parameters
displacement parameters (A × 10 ) for 1 are shown
were determined from setting angles of 25 reflections
with 20 Ͻ 2u Ͻ 30Њ. The unit cell was determined
using the search, center, index, and least squares
refinement routine. The Laue class and lattice dimen-
sions were verified by axial oscillation photography.
The intensity data were corrected for absorption,
Lorentz and polarization effects. An empirical absorp-
tion correction was performed based on c scans of five
strong reflections spanning a range of 2u values. All
data processing were performed on a Data General
Eclipse S140 minicomputer using the shelxtl crys-
tallographic package (version 5.1) and Siemens
in Table 3.
3. Results and discussion
The luminescence properties of a number of struc-
turally characterized gold–sulfur complexes were
investigated. Some of these compounds show inter-
…
molecular Au Au bonding. All the complexes in this
study luminesce at 77 K in the solid state. The
complex [AuS PPh(OCH CHyCH )] 1 contains
2
2
2
2
…
intermolecular Au Au interactions, and its

W.E. van Zyl et al. / Journal of Molecular Structure 516 (2000) 99–106
103
Table 4
Solid state luminescence data for dinuclear gold(I)–sulfur compounds
Complex
298 (K)
77 (K)
Excitation (nm)
Emission (nm)
Excitation (nm)
Emission (nm)
a
[
[
[
[
[
[
[
[
AuS
AuS
AuS
AuS
AuS
AuS
AuS
AuS
2
2
2
2
2
2
2
2
PPh(OC
3
H
5
)]
2
1
400
400
398
392
398
400
443
461
447
467
487
440
400
380
400
395
396
400
319
320
445, 491
451, 495
453, 496
453, 494
491, 530
435, 610
417
a
PPh
PPh(OEt)]
P(4-C OMe)(OEt)]
PPh(OC
2 2
]
a
2
b
6
H
4
2
c
5
9 2
H )]
i
c
2 2
P(O Pr) ]
c
P(4-C
6
H
H
4
OMe)(OSiPh
OMe)(O-
3 2
)] 2
P(4-C
6
4
447
c
menthyl)]
2
c
[
[
[
AuS
2
PEt
PMe
[Au
CyC(CN)
2
]
338
327
388
423
421
495, 527
553
c
AuS
2
2
]
2
c
NBu
4
]
2
2
{S
2
CyC(CN)
2
]
K
2
[S
2
2
]
468 (fine)
a
…
˚
Complexes with intermolecular Au Au ( ϳ 3.1 A) interactions.
b
c
Structure not determined.
…
Complexes with no intermolecular Au Au interactions.
molecular structure is shown in Fig. 1. The structure is
a neutral eight membered metallocycle in an elon-
gated chair conformation with short transannular
intermolecular interactions. It was previously reported
by two of us [14]. The luminescence spectra of 2 is
shown in Fig. 3. All other compounds examined (see
Table 4) show a similar excitation and emission
profile as obtained for 1 and 2. The observation that
the emission wavelength is different for 1 and 2
suggests that the excitation is from the sulfur orbital
of the ligand, and not from a p orbital associated with
˚
gold–gold (ϳ3.1 A) interactions. The selected bond
˚
lengths (A) and angles (Њ) for 1 are shown in Table 2.
The luminescence spectrum of 1 is shown in Fig. 2.
The complex [AuS P(4-C H OCH )(OSiPh )] 2 is a
2
6
4
3
3
2
representative example of a complex with no
Fig. 2. Excitation (— - —) at room temperature, emission at room temperature (- - -), and emission at 77 K (—) spectra for 1.

1
04
W.E. van Zyl et al. / Journal of Molecular Structure 516 (2000) 99–106
Fig. 3. Excitation and emission spectra of 2 at 77 K.
a phenyl group, since a large change in energy differ-
ence would not be anticipated in the latter case. Thus,
these emissions can be assigned as ligand-to-metal
charge-transfer (LMCT), similar to other dinuclear
gold(I) complexes bonded to sulfur, with the excita-
tion associated with a sulfur-to-metal based orbital in
the excited state.
The blue shift observed in the emission bands with
increasing temperature is consistent with an increase
in Au–Au separation as a result of thermal expansion.
This fact seems to indicate that the Au–Au distance
has a significant influence on the HOMO–LUMO
gap, which increases with increasing Au–Au separa-
tion distance. Correlations of emission energies with
the Au–Au distance do exist [15] showing that the
emission energy is sensitive to this variable. In the
series of dithiophosphonates reported here, the donor
properties of the different substituents on the phos-
phorus centers are virtually the same, and are not
considered responsible for the shifts.
placed at ϳ400 nm which is assigned to the transition
observed in emission. Concentration dependent UV–
vis spectra in gold(I) compounds were reported as an
evidence of molecular association [16], but to our
knowledge no study have previously shown a clear
correlation between emission and structure at a vari-
able temperature in the solid state. All of these facts
seem to indicate that although the emission is assigned
…
to a LMCT transition, the Au Au interactions have a
systematic influence on the energies of the frontier
orbitals responsible for the emission. In fact, as
…
previously reported [10], the effect of Au Au inter-
actions produce a destabilization of the dz orbital
2
(where the z-axis is along the direction of the
metal–metal interaction), while the empty 6p orbital
z
is stabilized. This would have the net effect of
lowering the energy of the transition producing a
red shift of the emission energy. As the number of
…
Au Au interactions increases, the HOMO–LUMO
gap is reduced.
When a spectral measurement for 1 is carried out in
The high energy band in 1 appears to result from
fluorescence (due to the small Stokes shift) and lower
energy band from phosphorescence. The latter band
presumably is related to the close proximity of the
gold centers, because it disappears when there are
no interaction between two adjacent molecules. In
order to determine if there is a general trend
emanating from these luminescence studies, we inves-
tigated the previously reported complexes
Ϫ4
dilute CHCl solutions (ϳ 10 M), the yellow color
3
disappears and the emission is quenched, but it keeps
the color and optical properties in concentrated solu-
tions ( Ͼ 0.1 M) where the molecules must be closely
associated. The absorption spectra of 1 measured at
0
.1, 0.03 and 0.01 M concentrations show a progres-
sive blue shift of the charge transfer absorption, and
the disappearance of a very low intensity broad band

W.E. van Zyl et al. / Journal of Molecular Structure 516 (2000) 99–106
105
i
[
AuS P(O Pr) ] , which shows intra- and intermole-
one band. The ability to predict the presence of weak
intermolecular Au Au interactions with a different
gold–sulfur system was tested for the complex
2
2 2
…
…
cular Au Au interactions [17], and [AuS PMe ]
2
2 2
…
which shows only intramolecular Au Au interac-
tions [18]. The luminescence properties of all these
complexes are consistent with results obtained in the
present study. In the former complex, the room
temperature emission spectrum shows one band,
while at 77 K, it shows two (see Table 4). The latter
complex is non-emissive at room temperature and
shows one emission band at 77 K at 421 nm and at a
maximum excitation energy of 327 nm.
[NBu ] [Au {S CyC(CN)} ], of which the structure
4
2
2
2
2
…
is known [19] and shows no intermolecular Au Au
interactions. The complex is also dinuclear, but has a
S–C–S bridging moiety as opposed to the S–P–S
moiety presented throughout this paper. Interestingly,
the complex showed two emission bands (495,
527 nm) at 77 K, which apparently contradict the
theory presented in the present study. Subsequent
studies proved, however, that the yellow potassium
salt as a free ligand luminesce at 77 K with an emis-
sion at 553 nm. The 527 nm emission of the complex
was thus attributed to the ligand since it had the same
emission profile. This phenomenon was not seen for
any of the other complexes investigated which all had
colorless free ligands.
This study revealed that the presence or absence of
intermolecular Au Au interactions in the solid state
…
have a profound influence on the nature of the lumi-
nescence the compounds exhibit. Specifically, a lower
energy emission had been observed only at a low
temperature (77 K), which became faint and “disap-
peared” as the temperature was increased. The first
possible explanation to account for the origin of this
unusual fact is that the excited state that gives rise to
the emission only connects with the higher energy
state as the temperature increases (thus populating
higher vibrational levels). As the temperature is
lowered, the molecules remain in the excited energy
level for a longer period, eventually crossing over into
a different state which gives rise to a second emission
band. A second possible explanation considered is a
second-order phase transition in the structure, which
traps the low energy excited state. Subsequent experi-
ments have ruled this out, however, based on X-ray
crystallographic studies performed on a single crystal
of the complex [AuS PPh ] . Data were collected at
In conclusion, study of the series of complexes
reported here suggests that the emission profile
alone is a useful predictor of the presence of intermo-
…
lecular linear chain Au Au interactions for the
dinuclear gold(I)–sulfur compounds. We expect the
results to be extended to other dinuclear gold–sulfur
systems and possibly even other gold(I)–sulfur
…
compounds wherein Au Au interactions influence
the LUMO and hence the emission spectra.
Acknowledgements
The authors acknowledge the Robert A. Welch
Foundation. J.M.L-de-L. acknowledges the financial
support from the University of La Rioja. We thank Mr
R. Theron Stubbs for assistance with the structure
refinement of 1.
2
2 2
2
13 and 293 K and the structure solved, but the results
˚
…
indicated only a small change (0.02 A) in the Au Au
interactions, not significant enough to consider a
second-order phase transition.
Recently, Eisenberg and co-workers reported [1]
two forms of a dinuclear gold(I) dithiocarbamate
complex. The one form contains intermolecular inter-
actions (solvated) and the other form contains no
intermolecular interactions (not solvated). The lumi-
nescence properties of both forms are in accordance
with our results. The former shows one emission
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