Fine-tuning the luminescence and HOMO-LUMO energy levels in tetranuclear gold(I) fluorinated amidinate complexes

Article abstract of DOI:10.1021/ic2010634

Tetranuclear gold(I) fluorinated amidinate complexes have been synthesized and their photophysical properties and structures described. DFT calculations were carried out to illustrate how a minor change in the ligand resulted in a loss of emission in the

Full text of DOI:10.1021/ic2010634

Article
pubs.acs.org/IC
Fine-Tuning the Luminescence and HOMO−LUMO Energy Levels in
Tetranuclear Gold(I) Fluorinated Amidinate Complexes
Hanan E. Abdou,† Ahmed A. Mohamed,§ Jose M. Lopez-de-Luzuriaga,‡ Miguel Monge,‡
́
́
and John P. Fackler, Jr.*,†
†Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
‡Departamento de Química, Universidad de La Rioja, Grupo de Síntesis Química de La Rioja, UA-CSIC, Madre de Dios 51, E-26004
Logrono, Spain
̃
§Department of Chemistry, Delaware State University, Dover, Delaware 19901, United States
S
* Supporting Information
ABSTRACT: Tetranuclear gold(I) fluorinated amidinate complexes have been
synthesized and their photophysical properties and structures described. DFT
calculations were carried out to illustrate how a minor change in the ligand
resulted in a loss of emission in the perfluorophenyl amidinate complex
compared with nonfluorinated phenyl amidinate complexes reported previously.
The fluorinated complexes reported here [Au(ArN)2C(H)]4 (1, Ar = 4-FC6H4;
2, 3,5-F2C6H3; 3, 2,4,6-F3C6H2; 4, 2,3,5,6-F4C6H) emit in the blue-green region
at 470, 1, 478, 2, 508, 3, and 450 nm, 4, by excitation at ca. 375 nm at room
temperature with nanosecond lifetimes. The emissions observed at 77 K in the
solid state show structured emission for complexes 1 and 2, with a vibrational
spacing of ca. 1200 and 1500 cm−1, corresponding to the vibrational modes of the
amidinate ligand. The pentafluorophenyl derivative 5, Ar = C6F5, shows no
photoluminescence in the solid state nor in the solution. This result is different
from results in which the pentafluorophenyl group is attached to a phenylpyridine ligand in an Ir(III) complex and other
organics. This quenching appears to be related to a nonradiative de-excitation process caused by the ππ*−πσ* crossover in the
excited state of the pentafluorophenyl amidinate ligand. With increasing numbers of fluorine atoms, there is a progressive
decrease in the contribution of the amidinate ligands to the corresponding HOMO orbital. There also is a slight decrease in the
ligand contribution to the LUMO with increased numbers of fluorine atoms and an exchange of the character of the orbitals of
the gold centers.
our laboratory by the reaction of Au(THT)Cl with the
potassium or sodium salt of the amidinate ligand in THF.9a
Tetranuclear gold(I) amidinate complexes with groups on the
NCN carbon, NC(Me)N and NC(Ph)N, were also prepared.9b
Preliminary studies of the tetranuclear gold(I) amidinate
complexes show luminescence differences with changes in the
substituents on the phenyl rings. These differences likely are
caused by the influence of each substituent on the electron rich,
delocalized NCN linkage. The tetranuclear complexes [Au-
(ArN)2C(H)]4, Ar = 4-OMeC6H4, 3-CF3C6H4, 4-MeC6H4, and
3,5-Cl2C6H3, show bright blue-green fluorescence at room
temperature. The tetranuclear 1-naphthyl derivative [Au-
(C10H7N)2C(H)]4 is luminescent only at 77 K. Surprisingly,
the pentafluorophenyl derivative Ar = C6F5 did not show any
observable photoluminescence in the solid state nor in the
solution even at low temperatures. This contrasts with the data
for the luminescence of an Ir(III) complex in which a
pentafluorophenyl moiety is attached at different positions on
INTRODUCTION
■
The chemistry of group 11 nitrogen ligand complexes and gold
in particular has witnessed a major expansion in synthesis and
applications.1 There are wide applications for these materials in
medicine,2 light emitting diodes fabrication,3 catalysis,4
chemical vapor deposition,5 and liquid crystals.6 This class of
compounds is unique in the heterogeneous catalysis of CO
oxidation by gold since metal−nitrogen precursors provide an
attractive route for the preparation of chloride-free gold
catalysts. A Au/TiO2 catalyst, synthesized from a tetranuclear
gold amidinate complex, showed the best performance for
room temperature CO oxidation by nanogold.7 Metal
amidinates have been found to be suitable precursors for the
Atomic Layer Deposition of transition metals and metal
oxides.8 Even with the growing number of experimental and
theoretical studies, the detailed structures of the excited states
in complexes with amidinate nitrogen ligands remains poorly
understood and warrants further photophysical study.1c
Previously, several tetranuclear gold(I) amidinate complexes,
[Au(ArN)2C(H)]4: Ar = −C6F5; 3-CF3−Ph; 3,5-Cl2−Ph; 4-
OMe−Ph; 4-Me−Ph; 1-naphthyl], have been synthesized in
Received: May 19, 2011
Published: January 30, 2012
© 2012 American Chemical Society
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Inorganic Chemistry
Article
a phenylpyridine ligand.1d,eFurthermore, the pentafluorophenyl
amidinate derivative [Au(C6F5N)2C(H)]4 did not show any
oxidation below 1.8 V, in contrast to the other tetranuclear
complexes with substituents such as Ar = 4-OMeC6H4, 4-
MeC6H4, and 3,5-Cl2C6H3, which showed three reversible
waves.9 We report here our study of the syntheses and
spectroscopy of phenylamidinate gold(I) complexes of
fluorinated amidinates with 1−5 fluorine atoms on the phenyl
rings.
atom model system. The quantum mechanical part was the
tetranuclear metallic core and the amidinate ligand skeleton and was
fully optimized at the DFT-B3LYP level. The molecular mechanics
parts are the fluorinated rings on the N atoms, and they were treated
with a Universal Force Field. The model systems were constrained to
C2 symmetry. The obtained optimized structures are very close to the
experimental, although the gold···gold interaction distances are slightly
larger than experimental ones (3.16−3.21 Å, theoretical, vs 2.93−2.97
Å, experimental). This trend is due to the fact that DFT methods are
not able to reproduce completely the aurophilicity of the Au(I)···Au(I)
interactions since all the correlation effects are not included at this
level of calculation. Nevertheless, we have used this level of theory
combined with the ONIOM methodology because these very large
tetranuclear model systems can be optimized at an accessible
computational cost.
2.3.2. DFT-B3LYP Single Point Calculations. Once the model
systems were optimized using the ONIOM methodology, a single
point energy calculation was performed for all model systems in order
to analyze the electronic structures (HOMO and LUMO orbitals).
2.3.3. Basis Sets. The 19-valence electron (VE) quasirelativistic
(QR) pseudopotential (PP) of Andrae14 was employed for gold
together with two f-type polarization functions (exponents, 0.2 and
1.19). The diffuse f-type function is required for describing the
aurophilic attraction and the compact one for describing the covalent
bonds.15 The N, C, and F atoms were treated by Stuttgart
pseudopotentials,16 including only the valence electrons for each
atom. For these atoms, double-ζ basis sets of ref 16 were used,
augmented by d-type polarization functions.17 For the H atom, a
double-ζ plus a p-type polarization function were used.18
2.4. Crystallographic Studies. Cell parameters and refinement
results from the check cif for the gold amidinate complex 4 are in an
endnote19 with the important distances listed in Table 2. X-ray data
were collected using a Siemens (Bruker) SMART CCD (charge
coupled device) based diffractometer equipped with a LT-2 low
temperature apparatus operating at 110 K. A suitable crystal was
chosen and mounted on a glass fiber using cryogenic grease. Data were
measured using omega scans of 0.3° per frame for 60 s. The first 50
frames were recollected at the end of data collection as a monitor for
decay. Unfortunately, the structure of 5 was not deemed suitable for
publication although the .cif is included with this Article in the
Supporting Information. No decay was detected for either structure.
Cell parameters were retrieved using SMART software and refined
using SAINT on all observed reflections. Data reductions were
performed using SAINT software. The structures were solved by direct
methods using SHELXS-97 and refined by least-squares on F2, with
SHELXL-97 incorporated in SHELXTL-PC V 5.03. The structures
were determined in the space groups reported in Table 1 by analysis of
systematic absences. Hydrogen atom positions were calculated by
geometrical methods and refined as a riding model.20
2. EXPERIMENTAL SECTION
2.1. Materials and Methods. All chemicals and reagents of
reagent grade were commercially available and used without further
purification. X-ray crystallographic data were collected as reported
previously.9
2.2. Preparation of the Complexes. All the amidine ligands were
synthesized according to modified literature procedure.9 In these
preparations, the aniline derivative, triethylorthoformate (orthoester)
and a catalytic amount of acetic acid (1 mL), were mixed and the
reaction mixture was heated to 140−160 °C in a reflux vessel for 1−2
h. The reaction mixture was distilled at the same temperature to
remove the ethanol. The product was cooled to room temperature to
form an off-white solid. The solid was recrystallized from THF/
hexanes to give a white solid in 70−80% yield. The tetranuclear
gold(I) amidinate complexes, [Au(ArN)2C(H)]4, Ar = 1, 4-FC6H4; 2,
3,5-F2C6H3; 3, 2,4,6-F3C6H2; 4, 2,3,5,6-F4C6H], were synthesized
using the synthetic procedure described below for 4. The yields were
close to 70% for each complex. Details for the synthesis of each of the
ligands are in the Supporting Information.
2.2.1. Synthesis of [Au4(ArNC(H)NAr)4], Ar = 2,3,5,6-C6HF4, 4.
N,N′-di(2,3,5,6-tetrafluoro)phenylformamidine (226 mg, 0.67 mmol)
was stirred with 37 mg (0.67 mmol) of KOH in 20 mL of 50/50%
THF/ethanol mixture for 24 h. Au(THT)Cl (213 mg, 0.67 mmol) was
added, and stirring continued for an additional 4−5 h. The solution
was filtered, and the volume was decreased under reduced pressure
and hexanes was added to form an off-white precipitate. The product
was filtered and recrystallized from THF/hexanes to give the
tetranuclear gold(I) complex in 70% yield.
Anal. Calcd. for C52H36F8N8Au4, 1: C, 36.44; H, 2.10. Found: C,
1
36.15; H, 1.89. 19F NMR (CDCl3, ppm): −123 (bm, F4). H NMR
(CDCl3, ppm): 8.2 (s, 4H, CH amidinate), 6.8 (16H), 7.0 (16H).
Yield 70%. UV−vis (CH2Cl2) λmax (nm), ε (L/M−1cm−1): 255-
(26,490), 295(16,584), 325(12,012), 354(8,492), and 397(4,528).
Anal. Calcd. for C52H28F16N8Au4, 2: C, 33.64; H, 1.61. Found: C,
1
33.90; H, 1.75. 19F NMR (CDCl3, ppm): −112 (bm, F3,5). H NMR
(CDCl3, ppm): 8.3 (s, 4H, CH amidinate), 6.5 (16H), 6.7 (8H). Yield
67.4%. UV−vis (CH2Cl2) λmax (nm), ε (L/M−1cm−1): 255(18,646),
290(11,652), 318(10,732), and 353(4,974).
3. RESULTS AND DISCUSSION
Anal. Calcd. for C52H20F24N8Au4, 3: C, 31.20; H, 1.00. Found: C,
31.40; H, 0.80. 19F NMR (CDCl3, ppm): −121 (bt, F4); −129 (bd,
F2,6). 1H NMR (CDCl3, ppm): 7.9 (s, 4H, CH amidinate),
6.98(16H). Yield 75%. UV−vis (CH2Cl2) λmax (nm), ε (L/
M−1cm−1): 253(73,456), 275(46,236), 297(31,352), and 355(3,644).
Anal. Calcd. for C52H12F32N8Au4, 4: C, 29.10; H, 0.55. Found: C,
29.47; H, 0.50. 19F NMR (CDCl3, ppm): −143 (m, F3,5); −152 (b,
3.1. Structures. Tetranuclear gold(I) fluorinated amidinate
complexes, [Au(ArN)2C(H)]4, (Ar = 1, 4-FC6H4; 2, 3,5-
F2C6H3; 3, 2,4,6-F3C6H2; 4, 2,3,5,6-F4C6H) are synthesized in
70−80% yield by the reaction between Au(THT)Cl and the
potassium salt of the ligands in THF/ethanol, and the product
was recrystallized from hexanes. Two tetranuclear structures
[Au(ArN)2C(H)]4, Ar = 2,3,5,6-F4C6H, 4, and C6F5, 5, were
characterized by X-ray crystallography, Figure 1 (see Support-
ing Information).
In both structures, each gold atom is coordinated to two
amidinate ligands in a nearly linear coordination. The average
Au···Au bond lengths in complexes 4 and 5 are ∼2.9 Å. The
packing diagram of 4 and 5 shows weak Au···F (∼3.1 Å,
intramolecular) and Au···F (∼3.55 Å, intermolecular) inter-
actions.
1
F2,6). H NMR (CDCl3, ppm): 8.0 (s, 4H, CH amidinate); 6.9(8H).
Yield 70%. UV−vis (CH2Cl2) λmax (nm), ε (L/M−1cm−1): 258
(79,225), 272 (68,865), 293 (47,175), and 375 (2,090).
Anal. Calcd. for C52H4F40N8Au4, 5: C, 27.27; N, 4.89. Found: C,
27.75; N, 4.64. 19F NMR (CDCl3, ppm): −166 (bt, F4); −162 (t,
1
F3,5); −153 (bd, F2,6). H NMR (CDCl3, ppm): 8.3 (s, 4H, CH
amidinate). Yield 77%. UV−vis (CH2Cl2) λmax (nm), ε (L/M−1cm−1):
260(102,800), 285(76,900), 300(46,700).
2.3. Computational Details. All calculations were performed
using the Gaussian03 suite of programs.10
2.3.1. Hybrid DFT-B3LYP/UFF (QM/MM) ONIOM Calculations.11
Hybrid quantum mechanical (DFT-B3LYP)12/molecular mechan-
ical (Universal Force Field, UFF)13 calculations were carried out for all
3.2. Spectroscopic Results. The absorption data for
complexes 1−4 are summarized in Table 1. The absorption
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Table 1. Spectroscopic and Photophysical Properties of
Complexes 1−4
medium/
(deg)
λem (λexc
)
−1
complex
λabs [nm] (ε [mol−1dm3cm ])
[nm]/τ (ns)
1
CH2Cl2
(298)
255 (26490), 295 (16584),
325 (12012), 354 (8492),
397 (4528)
solid
(298)
470 (375)
/102, 737
solid (77)
462, 491,
532 (375)
2
3
4
CH2Cl2
(298)
255 (18646), 290 (11652),
318 (10732), 353 (4974)
solid
(298)
478 (375)
/169, 914
solid (77)
505 (375)
CH2Cl2
(298)
253 (73456), 275 (46236),
297 (31352), 355 (3644)
Figure 2. Absorption spectrum of 1 solution in 5 × 10−5 M CH2Cl2
(black), excitation (red), and emission spectra (red) in the solid state
at 77 K. Emission spectra for 2 (green), 3 (blue), and 4 (magenta) in
solid state at 77 K.
solid
(298)
508 (375)
/142, 857
solid (77)
490 (375)
CH2Cl2
(298)
258 (79225), 272 (68865),
293 (47175), 375 (2090)
character, indicating a substantial difference in the excited state.
The energies of the bands in the excitation spectra in the four
complexes resemble the absorption spectra. This fact, together
with the small separation between excitation and emission
maxima and the lifetimes in the nanosecond range (1, 102.7
and 737.4; 2, 169.4 and 914.5; 3, 141.9 and 856.6; 4, 59.1 and
433.8 ns) suggest that the transitions that are responsible for
the emissions probably are heavy atom influenced fluorescence
arising from the strong spin−orbit coupling of the four gold
atoms. Also, the small shifts in the emissions from room
temperature to liquid nitrogen temperatures imply that little
structural change occurs from the ground state to the excited
state consistent with ligand centered or LMCT (especially with
3 and 4) transitions having little reorganizational behavior.
The weak absorption band at 397 nm for 1 was of some
concern. Its origin is uncertain and may be associated with a
Au···Au interaction as suggested by a referee. However, using
an excitation frequency at 397 nm or elsewhere in the 300−420
nm range produced no change in the emission spectrum.
3.3. DFT Calculations. We have carried out a full
optimization of model systems [Au(ArN)2C(H)]4, Ar = 4-
C6H4F, 1, 3,5-C6H3F2, 2, 2,4,6-C6H2F3, 3, 2,3,5,6-C6HF4, 4, and
2,3,4,5,6-C6F5, 5, using the ONIOM (QM/MM) DFT-B3LYP/
solid
450 (375)
/59, 234
(298)
solid (77)
447 (375)
spectra in 5 × 10−5 M CH2Cl2 at 298 K show in all cases
intense peaks between 225 and 400 nm (Figure 2). The free
ligands show the corresponding absorptions at 240−400 nm,
and the potassium salts of these ligands show no observable
luminescence. The resemblance of the absorption spectra for
the amidinate complexes with those of the free amidine ligands
suggests that the absorptions arise from ligand centered π→π*
transitions.
The four gold amidinate complexes, 1−4, display a weak
luminescence at room temperature and at 77 K in the solid
state or in EtOH/MeOH/CH2Cl2 (8:2:1) glass media at 77 K,
Table 1. Complexes [Au(ArN)2C(H)]4 (Ar = C6H4F 1,
C6H3F2 2, C6H2F3 3, and C6HF4 4) emit in the blue-green
region at 470 1, 478 2, 508 3, and 450 nm 4 by excitation at ca.
375 nm at room temperature. The emissions observed at 77 K
in the solid state are structured for complexes 1 and 2, showing
a vibrational spacing of ca. 1200 and 1500 cm−1, Figure 2,
corresponding to the vibrational modes of the amidinate
ligand.21 Complexes 3 and 4 do not display this vibronic
Figure 1. Thermal ellipsoid drawings of the tetranuclear gold(I) tetrafluorophenyl-, 4 (left), and pentafluorophenylamidinate, 5 (right), complexes at
50% probability.
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Table 2. Selected Theoretical (QM Part) and Experimental Structural Parameters for Model Systems 1−5 and Complexes 4 and
a
5
Au···Au
Au−N
N−C(H)
1.323
N−Cring
N−Au−N
N−C−N
theor model 1
theor model 2
theor model 3
theor model 4
complex 4
3.163−3.165
3.158−3.167
3.215−3.216
3.209−3.213
2.933−2.934
3.213
2.045−2.048
2.043−2.048
2.042−2.048
2.042−2.048
2.038−2.050
2.043−2.048
1.967−2.087
1.417−1.418
1.417−1.418
1.418−1.419
1.418−1.419
1.419−1.433
1.418−1.419
1.397−1.485
176.71−176.73
176.78−177.08
173.55−173.81
173.87−164.38
174.47−174.50
173.95−174.23
167.96−171.68
124.73−124.75
124.64−124.70
124.89−124.93
124.92−124.93
124.92−125.01
124.96
1.322
1.322
1.322
1.304−1.330
1.322
theor model 5
complex 5
2.954−2.971
1.311−1.339
124.60−126.13
a
Distances are given in Å and angles in deg.
UFF level of theory. In order to save computational costs, we
have calculated the perhalophenyl substituents using the
Molecular Mechanics/UFF level, optimizing the rest of the
molecule, i.e., the four gold atoms and the amidinate skeleton,
at the DFT-B3LYP level of theory. The optimized structures
are close to the experimental ones (see Table 2 for
comparison) which makes these models valid for electronic
structure analysis. The optimized Au−Au distances, although
slightly larger, fall in the range of aurophilic interaction. It is
important to note that the higher correlated method MP2
would lead to closer values, but the very large size of the model
systems, between 1288 and 1640 basis functions for models 1
and 5, respectively, would make these calculations very time-
consuming.
content is higher. A qualitative trend can be concluded by
analyzing the composition of the frontier orbitals; the less
fluorinated complexes 1 and 2 display a large π-ligand character
both in the bonding HOMO and in the antibonding LUMO
orbitals, leading to metal-perturbed intraligand transitions (IL),
which relate to the vibrational structure observed in the
emission spectra. When three 3 or four 4 fluorine atoms are
placed on each phenyl ring, a Au dz2σ* character emerges in the
HOMO, while the π* character for the LUMO orbital is
unchanged. This change, and the lack of vibronic character in
the emissions of 3 and 4, indicates a different vibronic coupling
caused by the increased gold character in the corresponding
wave functions.
In view of the electronic structures obtained from the DFT
calculations and the experimental measurements for the five
model gold fluoroamidinate systems, the photophysical proper-
ties appear theoretically predictable. The less fluorinated
amidinate complexes 1 and 2 display structured emissions
due to metal perturbed intraligand transitions with a low
influence from the gold(I) centers, while the higher metal
contribution to the frontier orbitals of the more fluorinated
complexes 3 and 4 lead to highly metal-perturbed unstructured
emissions, Figure 2. The fact that the pentafluorophenyl
amidinate complex 5 is not luminescent appears to be related to
a nonradiative de-excitation process caused by a ππ*−πσ*
crossover in the pentafluorophenyl amidinate ligands.22
Fluorescence was not observed for the pentafluorophenyl
amidinate complex, 5. This contrasts with data obtained when a
fluorinated phenyl ring is attached to various positions on a
coordinated phenylpyridine ligand bonded to Ir(III).1d,e
However, for the Ir(III) complex, both red and blue shifts
were observed depending on the position of the attachment of
the pentafluorophenyl ring. For 5, DFT results show that the
frontier orbital composition becomes mainly metal composed
(ligand-perturbed). This change might have been expected to
The DFT calculations of the five models optimized at the
ONIOM (QM/MM) DFT-B3LYP/UFF level of theory and
based on the X-ray crystallographic data support the assignment
of the emissive states. Thus, by looking at Figure 3, which
Figure 3. Frontier orbitals (HOMO and LUMO) for model systems
[Au(ArN)2C(H)]4, (Ar = 4-FC6H4, 1; 2,3,5,6-F4C6H, 4; and C6F5, 5).
The HOMO−LUMO gaps are in cm−1 H atoms removed.
3
lead to a metal centered (MC) excited state of the type Au
dz2σ* → Au 6s/6pσ and a long-lived phosphorescent emission;
but this is not observed. The lack of a normal phosphorescent
emission for this tetranuclear Au(I) complex is likely due to the
ππ*−πσ* crossover in the pentafluorophenyl group attached to
the coordinated amidinate, Figure 4. Zgierski, Lim, and co-
workers studied the photophysics of fluorinated benzenes
where this crossover was first observed.22 The first excited
states (S1) of pentafluorobenzene and hexafluorobenzene (S1
state of πσ* character) are different from that of the less
fluorinated benzenes (S1 state of ππ* character), and exhibit
very small fluorescence yields and short fluorescence life-
times.22 Our results suggest that there is a strong coupling
between the π states of the phenyl group and the amidinate π
system. The electron withdrawing effect of the pentafluorinated
represents the orbital composition of the HOMO and LUMO
orbitals for complexes 1, 4, and 5, important differences in
metal and ligand compositions can be noticed. A qualitative
progressive decrease in the contribution of the amidinate
ligands to the corresponding HOMO orbital is observed. When
the fluorine content increases, there is a slight decrease in the
ligand contributions and an exchange of the character of the
orbitals of the gold centers in the LUMO (Supporting
Information). The character of the orbitals of gold in the
HOMO remains antibonding for the five models, while the
LUMO is clearly antibonding for models 1 and 2 and bonding
for model 5. Additionally, the contribution of the gold centers
to the LUMO orbitals in the models with more fluorine
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Figure 4. Schematic energy level diagram for the tetranuclear gold
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tetranuclear Au(I) complexes.
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Goodman, D. W. J. Am. Chem. Soc. 2005, 127, 1604. (b) Yan, Z.;
Chinta, S.; Mohamed, A. A.; Fackler, J. P. Jr.; Goodman, D. W. Catal.
Lett. 2006, 111, 15.
4. CONCLUSIONS
On the basis of the DFT calculations and the luminescence
measurements for the gold fluoroamidinate complexes, the less
fluorinated amidinate complexes display structured emissions
due to metal-perturbed intraligand transitions with a low
influence from the gold(I) centers, while the higher metal
contribution to the frontier orbitals of the more fluorinated
complexes lead to highly metal-perturbed unstructured LMCT
emissions. The pentafluorinated amidinate complex, 5, is not
luminescent. This is consistent with a nonradiative de-excitation
process caused by a ππ*−πσ* crossover in the perfluorophenyl
amidinate ligands. Zgierski et al.22 attributed this crossover to
distortion of the benzene ring in the fluorinated benzenes. One
suspects that there are other metal/ligand systems having a
ligand excited state ππ*−πσ* crossover, which also show a
similar LMCT emission quenching, although this apparently is
not the case with the Ir(III) complexes having a pentafluor-
ophenyl moiety attached to a phenylpyridine ligand.1d,e
(8) Lim, B. S.; Rahtu, A.; Gordon, R. G. Nat. Mater. 2003, 2, 749.
́
(9) (a) Abdou, H. E.; Mohamed, A. A.; Lopez-de-Luzuriaga, J. M.;
Fackler, J. P. Jr. J. Cluster Sci. 2004, 15, 397. (b) Abdou, H. E.;
Mohamed, A. A.; Fackler, J. P. Jr. J. Cluster Sci. 2007, 18, 630.
́
(c) Abdou, H. A.; Mohamed, A.; Lopez-de-Luzuriaga, J. M.; Fackler, J.
P. Jr. J. Chin. Chem. Soc. 2007, 54, 1107−1113. The structure of 5 was
not deemed to be of sufficient X-ray quality to be published, but the
.cif file has been submitted with this Article.
(10) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
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Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J.
J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
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W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision
C.02; Gaussian, Inc.: Wallingford, CT, 2003.
ASSOCIATED CONTENT
■
S
* Supporting Information
Syntheses of ligands and tetranuclear gold(I) amidinate
complexes, computational details, CIF files of complexes 4
and 5, ORTEPs of complexes 4 and 5, frontier orbitals
(HOMO and LUMO) for model systems 1−5, and
luminescence measurements. This material is available free of
charge via the Internet at http://pubs.acs.org.
(11) Vreven, T.; Morokuma, K. J. Comput. Chem. 2000, 21, 1419.
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Chem. Phys. 1993, 98, 5648. (c) Lee, C.; Yang, W.; Parr, R. G. Phys.
Rev. Lett. 1998, B 37, 785.
AUTHOR INFORMATION
■
(13) Rappe,
́
A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, K. S. III;
Corresponding Author
Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024.
*E-mail: fackler@chem.tamu.edu.
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Theor. Chim. Acta 1990, 77, 123.
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ACKNOWLEDGMENTS
■
3, 1451.
The Robert A. Welch Foundation of Houston, Texas, is
acknowledged for financial support to J.P.F. through grant No.
A-0960. J.M.L-de-L. and M.M. thank the CTQ2010-20500-
C02-02 for financial support.
(16) Bergner, A.; Dolg, M.; Kuchle, W.; Stoll, H.; Preuss, H. Mol.
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Phys. 1993, 80, 1431.
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Elsevier: Amsterdam, 1984; p 16.
2014
dx.doi.org/10.1021/ic2010634 | Inorg. Chem. 2012, 51, 2010−2015

Inorganic Chemistry
Article
(18) Huzinaga, S. J. Chem. Phys. 1965, 42, 1293.
(19) Crystallographic parameters for 4: C52H12F32N8Au4; space
group, I41/a; a = 21.85(3), b = 21.85(3), c = 11.41(3); α = β = γ =
90.00, V = 5445(17), Z = 4, fw = 2144.58; R (reflections) =
0.0361(2577) ; wR2 (reflections) = 0.1187(3672). Crystal data for 5
recognizing that the data obtained is not publishable quality:
C52H4F40N8Au4; space group, C2/c; a = 30.64(3), b = 11.801(10), c
= 21.78(2); α = γ = 90.00, β = 133.891(15), V = 5675.39; Z = 4; R
(reflections) = 0.1281(1917) ; wR2 (reflections) = 0.2132(4853).
(20) X-ray programs used are in ref 9a.
(21) Piraino, P.; Bruno, G.; Tresoldi, G.; Faraone, G.; Bomieri, G. J.
Chem. Soc., Dalton Trans. 1983, 2391−2395.
(22) (a) Zgierski, M. Z.; Fujiwara, T.; Lim, E. C. Acc. Chem. Res.
2010, 43, 506. (b) Zgierski, M. Z.; Fujiwara, T.; Lim, E. C. J. Chem.
Phys. 2005, 122, 144312.
2015
dx.doi.org/10.1021/ic2010634 | Inorg. Chem. 2012, 51, 2010−2015