Structures and luminescence of mononuclear and dinuclear base-stabilized gold(I) pyrazolate complexes

Article abstract of DOI:10.1016/j.ica.2003.12.006

The mono- and dinuclear base-stabilized gold(I) pyrazolate complexes, (PPh₃)Au(μ-3,5-Ph₂pz)) (1), (TPA)Au(3,5-Ph ₂pz), TPA=1,3,5-triaza-7-phophaadamantane (2), [(PPh ₃)₂Au(μ-3,5-Ph₂pz)]NO₃ (3) and [(dppp)Au(μ-3,5-Ph₂pz)]NO₃, dppp=bis(diphenylphosphino) propane (4), have been synthesized and structurally characterized. The mononuclear gold(I) complexes 1 and 2 show intermolecular Au?Au interactions of 3.1540(6) and 3.092(6) A?, while the dinuclear gold(I) complexes 3 and 4 show an intramolecular Au?Au distances of 3.3519(7) and 3.109(2) A?, respectively, typical of an aurophilic attraction. Complexes 1-4 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.

Full text of DOI:10.1016/j.ica.2003.12.006

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
a
Ahmed A. Mohamed , Tiffany Grant , Richard J. Staples , John P. Fackler Jr.
a
b
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-Ph2pz)) (1), (TPA)Au(3,5-Ph2pz),
TPA ¼ 1,3,5-triaza-7-phophaadamantane (2), [(PPh3)2Au(l-3,5-Ph2pz)]NO3 (3) and [(dppp)Au(l-3,5-Ph2pz)]NO3, dppp ¼ bis-
(diphenylphosphino)propane (4), have been synthesized and structurally characterized. The mononuclear gold(I) complexes 1 and 2
ꢀ
show intermolecular Auꢀ ꢀ ꢀAu interactions of 3.1540(6) and 3.092(6) A, while the dinuclear gold(I) complexes 3 and 4 show an
ꢀ
intramolecular Auꢀ ꢀ ꢀAu distances of 3.3519(7) and 3.109(2) A, respectively, typical of an aurophilic attraction. Complexes 1–4
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
synthesis of tetranuclear gold(I) formamidinate clusters,
[Au(ArNC(H)NAr)]4, by the reaction of Au(THT)Cl
with sodium formamidinates.
Pyrazolates are hard donor ligands and their com-
plexes 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-Ph2Pz)]3, M ¼ Cu(I), Ag(I), Au(I). The hexa-
nuclear gold complex [Au(l-3,5-Ph2Pz]6 also was ob-
tained, although in poor yield [2]. Recently, we reported
[3] the structure and luminescence spectrum of the base-
stabilized tetragold(I) cluster [(dppm)2Au4(l-3,5-
Ph2pz)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 Auꢀ ꢀ ꢀAu distances than those bridged by the
pyrazolate ligands. Recently, we also reported [4] the
The syntheses, structural, and spectroscopic charac-
terizations of (PPh3)Au(l-3,5-Ph2pz) (1), (TPA)Au(l-3,
5-Ph2pz) (2), [(PPh3)2Au(l-3,5-Ph2pz)]NO3 (3), [(dppp)-
Au(l-3,5-Ph2pz)]NO3 (4) are reported here. The mono-
nuclear complexes 1 and 2 exhibit intermolecular
gold–gold interactions, while the dinuclear complexes 3
and 4 exhibit intramolecular interactions. These com-
plexes also exhibit luminescence in the solid state at 77 K.
The structural and spectroscopic properties are discussed.
* Corresponding author. Tel.: +9798450648; fax: +9798452835.
E-mail address: fackler@mail.chem.tamu.edu (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

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A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
PPh3AuCl did not completely dissolve at first. The so-
lution was left to stir overnight. The MeOH was re-
moved under vacuum and CH2Cl2 (20 ml) was added to
precipitate NaCl. The solution was filtered and the sol-
vent 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. 31P{1H}NMR (CDCl3,
H3PO4) 31.6 ppm (s). Anal. Calc. for C33H26N2PAu: 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-triaza-
7-phosphaadamantane)gold(I), (TPA)Au(l-3,5-Ph2pz)
(2)
To a stirred solution of HPh2pz (0.0622 g, 2.82 ꢁ 10ꢂ4
mol) in 20 ml of MeOH was added (1.1 ml, 2.82 ꢁ 10ꢂ4
mol) NaOH (aq). (TPA)AuCl (0.100 g, 2.56 ꢁ 10ꢂ4 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. CH2Cl2 (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 CH2Cl2
solution with diethylether vapor diffusion. 31P{1H}
NMR (CDCl3, H3PO4) )57.8 ppm (s).
Sketch 1.
2. Experimental
2.1. Methods and materials
All syntheses were carried out in a nitrogen atmo-
sphere using standard Schlenk techniques. 3,5-Diph-
enylpyrazole and PPh3 were purchased from Aldrich
and used without further purification. The 31P{1H}
spectra were obtained on a Varian 200 broad band
spectrometer. An 85% solution of H3PO4 was used as an
external reference. Emission and excitation spectra were
recorded on a SLM AMINCO, Model 8100 spectroflu-
orometer 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.
2.4. Synthesis of (l-3,5-diphenylpyrazolato)triphenylphos
phinegold(I), [(PPh3)2Au2(l-3,5-Ph2pz)]NO3 ꢀ CH2Cl2
(3)
To a stirred solution of 3,5-diphenylpyrazole (0.0489
g, 2.22 ꢁ 10ꢂ4 mol) in 20 ml MeOH was added (0.85 ml,
2.22 ꢁ 10ꢂ4 mol) NaOH (aq). PPh3AuNO3 (0.200 g,
4.0 ꢁ 10ꢂ4 mol) was added to this solution. The solution
was left to stir overnight. The MeOH was removed
under vacuum and CH2Cl2 (20 ml) was added to pre-
cipitate 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
CH2Cl2 solution layered with hexane. 31P{1H}NMR
(CDCl3, H3PO4) 31.0 ppm (s).
2.5. Synthesis of (l-3,5-diphenylpyrazolato)diphenylphos
phinepropane gold(I), [(dppp)Au2(3,5-Ph2pz)]NO3 ꢀ
CH2Cl2 (4)
2.2. Synthesis of (l-3,5-diphenylpyrazolato)triphenyl-
phosphinegold(I), (PPh3)Au(l-3,5-Ph2pz) (1)
To a stirred solution of 3,5-diphenylpyrazole (0.0489
g, 2.22 ꢁ 10ꢂ4 mol) in 20 ml MeOH was added (0.85 ml,
2.22 ꢁ 10ꢂ4 mol) NaOH (aq). To this solution
dppp(AuNO3)2 (0.186 g, 2.22 ꢁ 10ꢂ4 mol) was added.
The solution was left to stir overnight. The MeOH was
To a stirred solution of 3,5-diphenylpyrazole (0.0489
g, 2.22 ꢁ 10ꢂ4 mol) in 20 ml MeOH was added (0.85 ml,
2.22 ꢁ 10ꢂ4 mol) NaOH (aq). PPh3AuCl (0.100 g,
2.0 ꢁ 10ꢂ4 mol) was added to this solution. The

A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
1763
removed under vacuum and CH2Cl2 (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 CH2Cl2 solution layered with hexanes.
was performed using the SAINT software, which cor-
rects for Lp and decay [6]. Absorption corrections were
applied using SADABS supplied by George Sheldrick [7].
The structures are solved by direct method using the
SHELXS-97 program and refined by least-squares
method on F2, SHELXL-97, incorporated in SHELXTL-
PC V 5.03 [8,9].
2.6. X-ray diffraction analysis
The structures for 1–4 were solved in the space groups
P21=n, C2=c, P21=c, and P21=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.
The data for 1 were collected at room temperature on
a Nicolet R3m/E diffractometer (SHELXTL 5.1) by em-
ploying monochromated Mo Ka radiation (k ¼ 0:71073
3
ꢀ
A). A colorless block 0.2 ꢁ 0.2 ꢁ 0.2 mm was mounted
on a glass fiber with epoxy cement at room temperature.
The unit cell constants were determined from 25 ma-
chine-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 az-
imuthal (WÞ scans of reflections were made. The struc-
ture was solved using direct methods, SHELXTL 5.1,
with difference Fourier synthesis giving the missing non-
hydrogen atoms.
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-Ph2pz] which is
prepared in situ by the addition of one equiva-
lent NaOH (aq) to 3,5-diphenylpyrazole. The complex
crystallizes in the space group P21=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
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
ꢀ
2.062(6) and 2.054(6) A and the Au–P bond distances
ꢀ
are 2.238(2) and 2.242(2) A. Complex 2 was synthesized
in the same manner to the PPh3 derivative. It crystallizes
in the space group C2=c and the asymmetric unit con-
sists 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
ꢀ
A . The first 50 frames were recollected at the end of
data collection to monitor for decay. Cell parameters
were retrieved using SMART software and refined using
SAINT on all observed reflections [5]. Data reduction
Table 1
Crystal data, data collection, and structure refinement for 1–4
1
2
3 ꢀ CH2Cl2
C52H43Au2Cl2N3O3P2
4 ꢀ CH2Cl2
C43H39Au2Cl2N3O3P2
Empirical formula
Formula weight
Temperature (K)
C33H26AuN2P
678.49
293(2)
C21H23AuN5P
573.38
293(2)
1283.14
110(2)
1171.11
110(2)
0.71073
ꢀ
Wavelength (A)
0.71073
monoclinic
P21=n
12.259(4)
18.532(3), 90.69(2)
24.252(3)
5509(2)
0.71073
monoclinic
C2=c
24.540(4)
11.486(2), 102.52(1)
29.697(4)
8172(2)
0.71073
monoclinic
P21=c
21.287 (6)
24.028 (7)
18.218 (5)
9318 (4)
Crystal system
Space group
monoclinic
P21=c
24.44(2)
ꢀ
a (A)
ꢀ
b (A) (°)
27.19(2), 90.13(2)
12.132(11)
8062(13)
ꢀ
c (A)
Volume (A )
3
ꢀ
Z
8
1.636
5.423
16
1.864
7.296
8
1.889
6.523
8
1.929
14.553
Dcalc (Mg mꢂ3
)
Absorption coefficient (mmꢂ1
Crystal size (mm3)
)
0.2 ꢁ 0.2 ꢁ 0.2
2.01–22.51
8129
0.12 ꢁ 0.1 ꢁ 0.08
1.40–28.32
26 200
0.25 ꢁ 0.15 ꢁ 0.1
1.28–28.30
59 307
0.15 ꢁ 0.1 ꢁ 0.08
0.89–28.29
26 305
h Range (°)
Reflections collected
Data/restraints/parameters
Goodnees-of-fit on F 2
R1, wR2 ½I > 2ðIÞꢃ
7185/0/667
1.244
0.0369, 0.0606
9830/0/505
1.181
0.0451, 0.0785
22 273/0/1154
1.047
0.0496, 0.1422
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. 3. Structure of the cation of 3 at 50% probability. Hydrogen atoms
are omitted for clarity.
Fig. 2. Structure of 2 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.
177.1(2)°. The Au–N bonds are almost identical at
2.049(5) and 2.044(5) A and the Au–P bond lengths are
ꢀ
2.227(2) and 2.213(2) A, typical of Au–P distances. Both
ꢀ
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 CH2Cl2 solu-
tions. One of the angles at P–Au–N is deviated signifi-
cantly 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 Auꢀ ꢀ ꢀAu distance is longer
complexes exhibit Auꢀ ꢀ ꢀAu interactions in the solid state
ꢀ
with distances equal to 3.1540(6) and 3.0962(6) A for 1
and 2, respectively. The slightly longer Auꢀ ꢀ ꢀAu distance
in the 1 is expected, since the PPh3 is the bulkier phos-
phine. The cone angles for PPh3 and TPA are 145° and
102°, respectively.
ꢀ
ꢀ
in 3, 3.3519(7) A, than that in 4, 3.109(2) A, probably
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 fact that the PPh3Au(l-3,5-Ph2pz) complex ex-
hibits 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 pyr-
azolate ring. Complexes of the type, LAuX, where
L ¼ TPA and X ¼ halide, exhibit Auꢀ ꢀ ꢀAu contacts in
ꢀ
the range of 3.09–3.32 A . The short Au–Au distances in
1 and 2 suggest that although two sterically bulky li-
gands are used to coordinate to the gold(I) center,
packing effects are significant in terms of allowing the
two gold(I) centers to interact.
The trapezoidal Au–N–N–Au structure in com-
pound 4 has been compared with the trinuclear species,

A.A. Mohamed et al. / Inorganica Chimica Acta 357 (2004) 1761–1766
1765
Table 5
[Au(l-3,5-Ph2Pz)]3. The former has a N–N–Au ¼ 112–
ꢀ
Selected bond distances (A) and angles (°) for 4
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).
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)
Table 2
ꢀ
Bond angles
Selected bond distances (A) and angles (°) for 1
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)
Bond distances
112.0(10)
64.3(4)
66.5(4)
Au(2)–P(2)
Au(1)–P(1)
Au(1)ꢀ ꢀ ꢀAu(2)
Au(1)–N(1)
Au(2)–N(2)
2.238(2)
2.242(2)
3.1540(6)
2.062(6)
2.054(6)
104.99(14)
116.50(15)
178.5(5)
171.5(5)
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)
82.1(2)
82.2(2)
107.35(6)
107.40(5)
170.6(2)
170.2(2)
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 vi-
brational spectrum of a dinuclear gold(I) dppm complex
[11]. The ligands themselves do not show visible emis-
sion under these experimental conditions and are not
considered responsible for the emission. Because the
vibronic coupling is observed in the TPA derivative,
p–pꢄ 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 ꢁ 10ꢂ7
Table 3
ꢀ
Selected bond distances (A) and angles (°) for 2
Bond distances
Au(2)–P(2)
Au(1)–P(1)
Au(1)ꢀ ꢀ ꢀAu(2)
Au(1)–N(1)
Au(2)–N(2)
2.227(2)
2.213(2)
3.092(6)
2.049(5)
2.044(5)
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)
95.05(4)
87.39(14)
87.2(2)
93.90(5)
174.8(2)
177.1(2)
0.8552
Table 4
ꢀ
Selected bond distances (A) and angles (°) for 3
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)
2.2398(17)
2.2454(16)
3.3519(7)
2.043(5)
2.050(5)
1.388(7)
0.5
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)
119.8(4)
116.9(3)
60.69(15)
61.68(14)
118.82(4)
124.14(5)
174.05(17)
177.60(15)
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
0.3763
0.3
4. Conclusions
The complexes (PPh3)Au(3,5-Ph2pz) and (TPA)Au-
(3,5-Ph2pz) display aurophilic contacts in the solid state
although the sterically bulky 3,5-diphenyl pyrazolate
and triphenylphosphine ligands are utilized. The
Auꢀ ꢀ ꢀAu contacts provide the three-coordination that is
required for the observation of metal-centered lumi-
nescence from gold(I) complexes. However, the emission
has been assigned as a ligand-to-metal charge transfer
process due to the vibronic structure observed. There-
fore, these results supply evidence that the presence of
Auꢀ ꢀ ꢀAu interactions alone is not sufficient for the for-
mation of long lived phosphorescence emission in
complexes of gold(I).
0.2
0.1
0
250
300
400
500
650
Emission (nm)
Fig. 6. Excitation and emission spectra of 2 at 77 K in solid state.
Acknowledgements
Robert A. Welch Foundation of Houston, Texas is
gratefully acknowledged for financial support. Our
thanks are extended to V. Casadonte and D.M. Round-
hill at Texas Tech Univ. for emission measurements.
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Fig. 7. Excitation and emission spectra of 3 at 77 K in solid state.
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Luzuriaga, J.P. Fackler Jr., J. Cluster Sci. (in press).
[5] SMART V 4.043 Software for the CCD Detector System, Bruker
Analytical X-ray Systems, Madison, WI, 1995.
and 2.5 ꢁ 10ꢂ6 s for the PPh3 and the TPA derivatives,
respectively. These radiative lifetimes also suggest that
the transitions are not p–pꢄ, since such transitions are
typically in the order of 10ꢂ8–10ꢂ9 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 cmꢂ1 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.
[6] SAINT V 4.035 Software for the CCD Detector System, Bruker
Analytical X-ray Systems, Madison, WI, 1995.
[7] SADABS. Program for Absorption Corrections Using Siemens
CCD Based on the Method of Robert Blessing R.H. Blessing,
Acta Cryst. A 51 (1995) 33.
[8] G.M. Scheldrick, SHELXS-97, Program for the Solution of Crystal
€
Structure, University of Gottingen, Germany, 1997.
[9] SHELXTL 5.03 (PC-Version), Program Library for Structure
Solution and Molecular Graphics, Bruker Analytical X-ray
Systems, Madison, WI, 1995.
[10] M.K. Cooper, L.E. Mitchell, K. Henrick, M. McPartlin, A. Scott,
Inorg. Chim. Acta 84 (1984) L9.
[11] E.C.-C. Cheng, K.-H. Leung, V.M. Miskowski, V.W.-W. Yam,
D.L. Phillips, Inorg. Chem. 39 (2000) 3690.