Inorganica Chimica Acta 357 (2004) 1761–1766
www.elsevier.com/locate/ica
Structures and luminescence of mononuclear and dinuclear
base-stabilized gold(I) pyrazolate complexes
Ahmed A. Mohamed a, Tiffany Grant a, Richard J. Staples b, John P. Fackler Jr.
a
a,*
Laboratory for Molecular Structure and Bonding, Department of Chemistry, Texas A&M University, College Station, TX 77843-3255, USA
b
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
Received 12 September 2003; accepted 6 December 2003
This paper recognizes a great scientist and a true gentleman, Helmut Werner
Abstract
The mono- and dinuclear base-stabilized gold(I) pyrazolate complexes, (PPh3 )Au(l-3,5-Ph2 pz)) (1), (TPA)Au(3,5-Ph2 pz),
TPA ¼ 1,3,5-triaza-7-phophaadamantane (2), [(PPh3 )2 Au(l-3,5-Ph2 pz)]NO3 (3) and [(dppp)Au(l-3,5-Ph2 pz)]NO3 , dppp ¼ bis(diphenylphosphino)propane (4), have been synthesized and structurally characterized. The mononuclear gold(I) complexes 1 and 2
while the dinuclear gold(I) complexes 3 and 4 show an
show intermolecular Au Au interactions of 3.1540(6) and 3.092(6) A,
respectively, typical of an aurophilic attraction. Complexes 1–4
intramolecular Au Au distances of 3.3519(7) and 3.109(2) A,
exhibit luminescence at 77 K when excited with ca. 333 nm UV light with an emission maximum at ca. 454 nm. The emission has
been assigned to ligand-to-metal charge transfer, LMCT, based upon the vibronic structure that is observed.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Gold(I) pyrazolate; Aurophilicity; Luminescence
1. Introduction
Pyrazolates are hard donor ligands and their complexes of group 11 elements are generally trinuclear.
Previous work in our laboratory [1] has led to the
structural characterization of the homogeneous series
[M(l-3,5-Ph2 Pz)]3 , M ¼ Cu(I), Ag(I), Au(I). The hexanuclear gold complex [Au(l-3,5-Ph2 Pz]6 also was obtained, although in poor yield [2]. Recently, we reported
[3] the structure and luminescence spectrum of the basestabilized tetragold(I) cluster [(dppm)2 Au4 (l-3,5Ph2 pz)2 ](NO3 )2 (Sketch 1). This structure shows that the
four gold atoms are located at the corner of a distorted
square with the pyrazolates and the dppm ligands
bridged above and below the near plane of the four
gold(I) atoms. The gold(I) atoms bridged by dppm show
shorter Au Au distances than those bridged by the
pyrazolate ligands. Recently, we also reported [4] the
*
Corresponding author. Tel.: +9798450648; fax: +9798452835.
E-mail address: [email protected] (J.P. Fackler Jr.).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.12.006
synthesis of tetranuclear gold(I) formamidinate clusters,
[Au(ArNC(H)NAr)]4 , by the reaction of Au(THT)Cl
with sodium formamidinates.
The syntheses, structural, and spectroscopic characterizations of (PPh3 )Au(l-3,5-Ph2 pz) (1), (TPA)Au(l-3,
5-Ph2 pz) (2), [(PPh3 )2 Au(l-3,5-Ph2 pz)]NO3 (3), [(dppp)Au(l-3,5-Ph2 pz)]NO3 (4) are reported here. The mononuclear complexes 1 and 2 exhibit intermolecular
gold–gold interactions, while the dinuclear complexes 3
and 4 exhibit intramolecular interactions. These complexes also exhibit luminescence in the solid state at 77 K.
The structural and spectroscopic properties are discussed.
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A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
PPh3 AuCl did not completely dissolve at first. The solution was left to stir overnight. The MeOH was removed under vacuum and CH2 Cl2 (20 ml) was added to
precipitate NaCl. The solution was filtered and the solvent was removed under vacuum to isolate a white oily
solid. This was recrystallized from benzene and ether.
Yield: 66%. Single crystals were grown from a THF
solution layered with hexane. 31 P{1 H}NMR (CDCl3 ,
H3 PO4 ) 31.6 ppm (s). Anal. Calc. for C33 H26 N2 PAu: C,
58.41; N, 4.13; H, 3.86. Found: C, 58.08; N, 4.13; H,
3.86%.
2.3. Synthesis of (3.5-diphenylpyrazolato)(1,3,5-triaza7-phosphaadamantane)gold(I), (TPA)Au(l-3,5-Ph2 pz)
(2)
Sketch 1.
2. Experimental
2.1. Methods and materials
All syntheses were carried out in a nitrogen atmosphere using standard Schlenk techniques. 3,5-Diphenylpyrazole and PPh3 were purchased from Aldrich
and used without further purification. The 31 P{1 H}
spectra were obtained on a Varian 200 broad band
spectrometer. An 85% solution of H3 PO4 was used as an
external reference. Emission and excitation spectra were
recorded on a SLM AMINCO, Model 8100 spectrofluorometer using a Xenon lamp. Spectra were corrected
for instrumental response. The radiation was filtered
through a 0.10 M KNO2 solution to reduce the amount
of scattered light. Solid-state room-temperature and
low-temperature measurements were made with a
cryogenic sample holder of local design. Powder samples
were attached to the holder with colloidon. The lifetime
measurements were obtained at Texas Tech University
at 77 K using a Laser Photonics Model LN300C sealed
nitrogen/dye laser and an SLM 8000 monochromator.
The output was sent to a LeCroy 9130M 300 MHZ
oscilloscope couple to a Gateway 2000 486 DX/33
computer for data analysis.
2.2. Synthesis of (l-3,5-diphenylpyrazolato)triphenylphosphinegold(I), (PPh3 )Au(l-3,5-Ph2 pz) (1)
To a stirred solution of 3,5-diphenylpyrazole (0.0489
g, 2.22 104 mol) in 20 ml MeOH was added (0.85 ml,
2.22 104 mol) NaOH (aq). PPh3 AuCl (0.100 g,
2.0 104 mol) was added to this solution. The
To a stirred solution of HPh2 pz (0.0622 g, 2.82 104
mol) in 20 ml of MeOH was added (1.1 ml, 2.82 104
mol) NaOH (aq). (TPA)AuCl (0.100 g, 2.56 104 mol)
was added. After stirring for 1 h the (TPA)AuCl had
dissolved and the solution was clear and colorless. It was
allowed to stir overnight and the MeOH was removed
under vacuum. CH2 Cl2 (20 ml) was added to precipitate
NaCl. The solution was filtered and the solvent was
removed under vacuum to isolate an oily, white solid.
This solid was recrystallized from THF and diethylether.
Yield: 77%. Single crystals were grown from a CH2 Cl2
solution with diethylether vapor diffusion. 31 P{1 H}
NMR (CDCl3 , H3 PO4 ) )57.8 ppm (s).
2.4. Synthesis of (l-3,5-diphenylpyrazolato)triphenylphos
phinegold(I), [(PPh3 )2 Au2 (l-3,5-Ph2 pz)]NO3 CH2 Cl2
(3)
To a stirred solution of 3,5-diphenylpyrazole (0.0489
g, 2.22 104 mol) in 20 ml MeOH was added (0.85 ml,
2.22 104 mol) NaOH (aq). PPh3 AuNO3 (0.200 g,
4.0 104 mol) was added to this solution. The solution
was left to stir overnight. The MeOH was removed
under vacuum and CH2 Cl2 (20 ml) was added to precipitate NaCl. The solution was filtered and the solvent
was removed under vacuum to isolate a white solid. This
was recrystallized from dichloromethane and ether.
Yield: 150 mg, 65%. Single crystals were grown from a
CH2 Cl2 solution layered with hexane. 31 P{1 H}NMR
(CDCl3 , H3 PO4 ) 31.0 ppm (s).
2.5. Synthesis of (l-3,5-diphenylpyrazolato)diphenylphos
phinepropane gold(I), [(dppp)Au2 (3,5-Ph2 pz)]NO3 CH2 Cl2 (4)
To a stirred solution of 3,5-diphenylpyrazole (0.0489
g, 2.22 104 mol) in 20 ml MeOH was added (0.85 ml,
2.22 104 mol) NaOH (aq). To this solution
dppp(AuNO3 )2 (0.186 g, 2.22 104 mol) was added.
The solution was left to stir overnight. The MeOH was
A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
removed under vacuum and CH2 Cl2 (20 ml) was added
to precipitate NaCl. The solution was filtered and the
solvent was removed under vacuum to isolate a white
solid. This was recrystallized from dichloromethane and
hexanes. Yield: 160 mg, 76%. Single crystals were grown
from a CH2 Cl2 solution layered with hexanes.
1763
was performed using the SAINT software, which corrects for Lp and decay [6]. Absorption corrections were
applied using S A D A B S supplied by George Sheldrick [7].
The structures are solved by direct method using the
S H E L X S -97 program and refined by least-squares
method on F2 , S H E L X L -97, incorporated in S H E L X T L P C V 5.03 [8,9].
The structures for 1–4 were solved in the space groups
P 21 =n, C2=c, P 21 =c, and P 21 =c, respectively, by analysis
of systematic absences. All non-hydrogen atoms are
refined anisotropically. Hydrogens atom positions were
calculated by geometrical methods and refined as a
riding model. No decomposition was detected. The
crystallographic details are given in Table 1.
2.6. X-ray diffraction analysis
The data for 1 were collected at room temperature on
a Nicolet R3m/E diffractometer (S H E L X T L 5.1) by employing monochromated Mo Ka radiation (k ¼ 0:71073
A colorless block 0.2 0.2 0.2 mm3 was mounted
A).
on a glass fiber with epoxy cement at room temperature.
The unit cell constants were determined from 25 machine-centered reflections. Intensities of all reflections
with 2h values 4–45° were measured by x-scanning
technique. Lorentz and polarization corrections were
applied. Empirical absorption corrections based on azimuthal (WÞ scans of reflections were made. The structure was solved using direct methods, S H E L X T L 5.1,
with difference Fourier synthesis giving the missing nonhydrogen atoms.
Data for 2, 3, and 4 were collected using a Siemens
(Bruker) SMART CCD (charge coupled device) based
diffractometer equipped with an LT-2 low-temperature
apparatus operating at 213 K. A suitable crystal was
chosen and mounted on a glass fiber using grease. Data
were measured using omega scans of 0.3° per frame for
60 s, such that a hemisphere was collected. A total of
1271 frames were collected with a final resolution of 0.75
. The first 50 frames were recollected at the end of
A
data collection to monitor for decay. Cell parameters
were retrieved using SMART software and refined using
SAINT on all observed reflections [5]. Data reduction
3. Results and discussion
3.1. Syntheses and structures
Complex 1 was synthesized by addition of (PPh3 )AuCl to an MeOH solution of Na[3,5-Ph2 pz] which is
prepared in situ by the addition of one equivalent NaOH (aq) to 3,5-diphenylpyrazole. The complex
crystallizes in the space group P 21 =n and the asymmetric
unit consists of two gold molecules that have a crossed
structure, Fig. 1. The N–Au–P angles are nearly linear at
170.6 (2) and 170.2(2)°. The Au–N bond distances are
and the Au–P bond distances
2.062(6) and 2.054(6) A
Complex 2 was synthesized
are 2.238(2) and 2.242(2) A.
in the same manner to the PPh3 derivative. It crystallizes
in the space group C2=c and the asymmetric unit consists of two gold molecules with a crossed molecular
structure, Fig. 2. The gold(I) centers are nearly linearly
coordinated with N–Au–P angles equal to 174.8(2) and
Table 1
Crystal data, data collection, and structure refinement for 1–4
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
a (A)
(°)
b (A)
c (A)
3 )
Volume (A
Z
Dcalc (Mg m3 )
Absorption coefficient (mm1 )
Crystal size (mm3 )
h Range (°)
Reflections collected
Data/restraints/parameters
Goodnees-of-fit on F 2
R1 , wR2 ½I > 2ðIÞ
1
2
3 CH2 Cl2
4 CH2 Cl2
C33 H26 AuN2 P
678.49
293(2)
0.71073
monoclinic
P 21 =n
12.259(4)
18.532(3), 90.69(2)
24.252(3)
5509(2)
8
1.636
5.423
0.2 0.2 0.2
2.01–22.51
8129
7185/0/667
1.244
0.0369, 0.0606
C21 H23 AuN5 P
573.38
293(2)
0.71073
monoclinic
C2=c
24.540(4)
11.486(2), 102.52(1)
29.697(4)
8172(2)
16
1.864
7.296
0.12 0.1 0.08
1.40–28.32
26 200
9830/0/505
1.181
0.0451, 0.0785
C52 H43 Au2 Cl2 N3 O3 P2
1283.14
110(2)
0.71073
monoclinic
P 21 =c
21.287 (6)
24.028 (7)
18.218 (5)
9318 (4)
8
1.889
6.523
0.25 0.15 0.1
1.28–28.30
59 307
22 273/0/1154
1.047
0.0496, 0.1422
C43 H39 Au2 Cl2 N3 O3 P2
1171.11
110(2)
0.71073
monoclinic
P 21 =c
24.44(2)
27.19(2), 90.13(2)
12.132(11)
8062(13)
8
1.929
14.553
0.15 0.1 0.08
0.89–28.29
26 305
16 941/0/991
0.749
0.0627, 0.1811
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A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
Fig. 1. Structure of 1 at 50% probability. Hydrogen atoms are omitted
for clarity.
Fig. 2. Structure of 2 at 50% probability. Hydrogen atoms are omitted
for clarity.
177.1(2)°. The Au–N bonds are almost identical at
and the Au–P bond lengths are
2.049(5) and 2.044(5) A
typical of Au–P distances. Both
2.227(2) and 2.213(2) A,
complexes exhibit Au Au interactions in the solid state
for 1
with distances equal to 3.1540(6) and 3.0962(6) A
and 2, respectively. The slightly longer Au Au distance
in the 1 is expected, since the PPh3 is the bulkier phosphine. The cone angles for PPh3 and TPA are 145° and
102°, respectively.
The fact that the PPh3 Au(l-3,5-Ph2 pz) complex exhibits aurophilic contacts in the solid state is somewhat
surprising due to the bulkiness of the PPh3 ligand and
the phenyl substituents at the 3,5 positions of the pyrazolate ring. Complexes of the type, LAuX, where
L ¼ TPA and X ¼ halide, exhibit Au Au contacts in
. The short Au–Au distances in
the range of 3.09–3.32 A
1 and 2 suggest that although two sterically bulky ligands are used to coordinate to the gold(I) center,
packing effects are significant in terms of allowing the
two gold(I) centers to interact.
Fig. 3. Structure of the cation of 3 at 50% probability. Hydrogen atoms
are omitted for clarity.
Fig. 4. Structure of the cation of 4 at 50% probability. Hydrogen atoms
are omitted for clarity.
Complexes 3 and 4 were synthesized by the reaction
of the phosphine gold(I) nitrate species with the sodium
salt of 3,5-diphenylpyrazolate in THF or CH2 Cl2 solutions. One of the angles at P–Au–N is deviated significantly from linearity, 171–174°; however, the other
angle is close to linearity (Figs. 3 and 4). The P–Au–N
angle is distorted from linearity presumably due to
aurophilic interactions. The Au Au distance is longer
than that in 4, 3.109(2) A,
probably
in 3, 3.3519(7) A,
caused by the bulkiness of PPh3 versus the bridging
dppp ligand which brings the gold atoms into close
proximity. The structures 3 and 4 each contains one
dichloromethane solvent molecule with nitrate counter
anions well removed from the gold(I) centers. The two
P–Au–Cl arms of the dppp(AuCl)2 molecule point away
from each other and the two gold atoms do not possess
aurophilic interaction [10].
The trapezoidal Au–N–N–Au structure in compound 4 has been compared with the trinuclear species,
A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
[Au(l-3,5-Ph2 Pz)]3 . The former has a N–N–Au ¼ 112–
117°, while the latter has an angle of 120.20°. The
smaller angle at N in 4, compared to the trinuclear
structure, probably is caused by the dppp ligand, which
brings the gold atoms into close proximity (see Tables
2–5).
Table 2
and angles (°) for 1
Selected bond distances (A)
Bond distances
Au(2)–P(2)
Au(1)–P(1)
Au(1) Au(2)
Au(1)–N(1)
Au(2)–N(2)
Bond angles
N(1)–Au(1) Au(2)
N(2)–Au(2) Au(1)
P(2)–Au(2) Au(1)
P(1)–Au(1) Au(2)
N(1)–Au(1)–P(1)
N(2)–Au(2)–P(2)
2.238(2)
2.242(2)
3.1540(6)
2.062(6)
2.054(6)
82.1(2)
82.2(2)
107.35(6)
107.40(5)
170.6(2)
170.2(2)
Table 3
and angles (°) for 2
Selected bond distances (A)
Bond distances
Au(2)–P(2)
Au(1)–P(1)
Au(1) Au(2)
Au(1)–N(1)
Au(2)–N(2)
Bond angles
P(2)–Au(2) Au(1)
N(1)–Au(1) Au(2)
N(2)–Au(2) Au(1)
P(1)–Au(1) Au(2)
N(1)–Au(1)–P(1)
N(2)–Au(2)–P(2)
2.227(2)
2.213(2)
3.092(6)
2.049(5)
2.044(5)
95.05(4)
87.39(14)
87.2(2)
93.90(5)
174.8(2)
177.1(2)
1765
Table 5
and angles (°) for 4
Selected bond distances (A)
Bond distances
Au(2)–P(2)
Au(1)–P(1)
Au(1) Au(2)
Au(1)–N(1)
Au(2)–N(2)
N(1)–N(2)
2.242(5)
2.246(6)
3.109(2)
2.035(16)
2.038(17)
1.41(2)
Bond angles
Au(1)–N(1)–N(2)
Au(2)–N(2)–N(1)
N(1)–Au(1) Au(2)
N(2)–Au(2) Au(1)
P(2)–Au(2) Au(1)
P(1)–Au(1) Au(2)
N(1)–Au(1)–P(1)
N(2)–Au(2)–P(2)
117.2(11)
112.0(10)
64.3(4)
66.5(4)
104.99(14)
116.50(15)
178.5(5)
171.5(5)
3.2. Photoluminescence studies
Complexes 1–4 are visibly luminescent in the solid
state at temperatures below )20 °C. Excitation at ca.
300 nm produces an emission maxima located at ca. 454
nm. A phosphorescent emission originating from a
metal centered (MC) state is common in polynuclear
gold(I) phosphine derivatives. The Stokes shift between
the excitation and emission bands suggests a distortion
in the excited state which is consistent with strengthened
Au(I) Au(I) bonding as has been observed in the vibrational spectrum of a dinuclear gold(I) dppm complex
[11]. The ligands themselves do not show visible emission under these experimental conditions and are not
considered responsible for the emission. Because the
vibronic coupling is observed in the TPA derivative,
p–p transitions of the phenyl rings in the PPh3 complex
can be ruled out as the source of the emission in 1. The
lifetimes of the emissions were found to be 2.5 107
0.8552
Bond distances
Au(2)–P(2)
Au(1)–P(1)
Au(1) Au(2)
Au(1)–N(1)
Au(2)–N(2)
N(1)–N(2)
Bond angles
Au(1)–N(1)–N(2)
Au(2)–N(2)–N(1)
N(1)–Au(1) Au(2)
N(2)–Au(2) Au(1)
P(2)–Au(2) Au(1)
P(1)–Au(1) Au(2)
N(1)–Au(1)–P(1)
N(2)–Au(2)–P(2)
2.2398(17)
2.2454(16)
3.3519(7)
2.043(5)
2.050(5)
1.388(7)
119.8(4)
116.9(3)
60.69(15)
61.68(14)
118.82(4)
124.14(5)
174.05(17)
177.60(15)
Fluorescence
Table 4
and angles (°) for 3
Selected bond distances (A)
0.5
0
250
300
400
500
600
Emission (nm)
Fig. 5. Excitation and emission spectra of 1 at 77 K in solid state.
1766
A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
4. Conclusions
0.3763
Fluorescence
0.3
0.2
0.1
0
250
300
400
500
650
The complexes (PPh3 )Au(3,5-Ph2 pz) and (TPA)Au(3,5-Ph2 pz) display aurophilic contacts in the solid state
although the sterically bulky 3,5-diphenyl pyrazolate
and triphenylphosphine ligands are utilized. The
Au Au contacts provide the three-coordination that is
required for the observation of metal-centered luminescence from gold(I) complexes. However, the emission
has been assigned as a ligand-to-metal charge transfer
process due to the vibronic structure observed. Therefore, these results supply evidence that the presence of
Au Au interactions alone is not sufficient for the formation of long lived phosphorescence emission in
complexes of gold(I).
Emission (nm)
Fig. 6. Excitation and emission spectra of 2 at 77 K in solid state.
Acknowledgements
Intensity (a.u.)
Robert A. Welch Foundation of Houston, Texas is
gratefully acknowledged for financial support. Our
thanks are extended to V. Casadonte and D.M. Roundhill at Texas Tech Univ. for emission measurements.
References
250
300
350
400
450
500
550
600
Wavelength (nm)
Fig. 7. Excitation and emission spectra of 3 at 77 K in solid state.
and 2.5 106 s for the PPh3 and the TPA derivatives,
respectively. These radiative lifetimes also suggest that
the transitions are not p–p , since such transitions are
typically in the order of 108 –109 s (see Figs. 5–7).
Based on the vibronic coupling observed in the
emission spectra of both complexes, the emissions are
assigned to a ligand-to-metal charge transfer process
(LMCT). The spacings of the bands are indicative of the
vibrational levels in the ground electronic state. The
average energy difference between the emission maxima
is approximately 1454 cm1 and therefore corresponds
to a C@N or N@N vibration of the pyrazolate ligand.
The lifetimes exhibited by these complexes suggest that
the emissions may occur from a triplet excited state.
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