Synthesis, emission, and molecular orbital studies of luminescent hafnium thiolate complexes. Crystal structures of (η5-C5Me5)2Hf(SR)2 (R = nBu, C6H5, C6H4OMe-p)

Article abstract of DOI:10.1021/om980602f

A series of luminescent hafnium thiolate complexes (η⁵C₅Me₅)₂Hf(SR)₂ (R = ⁿBu, C₆H₅, C₆H₄OMe-p, C₆H₄^tBu-p) have been synthesized by the reaction of (η⁵-C₅Me₅)₂HfCl₂ with LiSR and shown to exhibit rich luminescence behavior. The crystal structures of (η⁵-C₅Me₅)₂Hf-(S ⁿBu)₂, (η⁵-C₅Me₅)₂Hf(SC ₆H₅)₂, and (η⁵-C₅Me₅)₂Hf(SC ₆H₄OMe-p)₂ have been determined. Fenske-Hall molecular orbital calculations on the hafnium thiolate complexes reveal a thiolate-based HOMO and a LUMO that is mainly composed of hafnium d character.

Full text of DOI:10.1021/om980602f

5448
Organometallics 1998, 17, 5448-5453
Articles
Syn th esis, Em ission , a n d Molecu la r Or bita l Stu d ies of
Lu m in escen t Ha fn iu m Th iola te Com p lexes. Cr ysta l
n
Str u ctu r es of (η5-C5Me5)2Hf(SR)2 (R ) Bu , C6H5,
C6H4OMe-p)
Vivian Wing-Wah Yam,* Gui-Zhong Qi, and Kung-Kai Cheung
Department of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong, P.R. China
Received J uly 14, 1998
n
A series of luminescent hafnium thiolate complexes (η5-C5Me5)2Hf(SR)2 (R ) Bu, C6H5,
t
C6H4OMe-p, C6H4 Bu-p) have been synthesized by the reaction of (η5-C5Me5)2HfCl2 with LiSR
and shown to exhibit rich luminescence behavior. The crystal structures of (η5-C5Me5)2Hf-
(SnBu)2, (η5-C5Me5)2Hf(SC6H5)2, and (η5-C5Me5)2Hf(SC6H4OMe-p)2 have been determined.
Fenske-Hall molecular orbital calculations on the hafnium thiolate complexes reveal a
thiolate-based HOMO and a LUMO that is mainly composed of hafnium d character.
In tr od u ction
excited states. To extend our research efforts in lumi-
nescent metal chalcogenolates, herein, we report the
synthesis and luminescence studies of a series of
hafnium thiolates, (η5-C5Me5)2Hf(SR)2 (R ) nBu, C6H5,
In contrast to the metal-to-ligand charge-transfer
(MLCT) excited states, which have been the dominant
subjects of study in inorganic photochemistry over the
past two decades,1 complexes that show ligand-to-metal
charge-transfer (LMCT) emissive states are very scarce.2
We have explored the class of d0 zirconium chalcogeno-
lates,3 as part of our efforts in the study of metal
chalcogenides and chalcogenolates,4 because the chal-
cogenolates, being good σ-donor type ligands, together
with the good electron-accepting ability of d0 metal
centers, may give rise to low-lying emissive LMCT
t
C6H4OMe-p, C6H4 Bu-p). The X-ray crystal structures
of (η5-C5Me5)2Hf(SnBu)2, (η5-C5Me5)2Hf(SC6H5)2, and (η5-
C5Me5)2Hf(SC6H4OMe-p)2 have been determined. The
electronic structures and the nature of the excited states
of these luminescent complexes have been probed by
Fenske-Hall molecular orbital calculations.
Exp er im en ta l Section
Ma ter ia ls a n d Rea gen ts. Bis(pentamethylcyclopentadi-
enyl)hafnium dichloride was purchased from Strem Chemicals
Inc. 1-Butanethiol, thiophenol, 4-methoxythiophenol, and
4-tert-butylthiophenol were obtained from Lancaster Synthesis
Ltd. n-Butyllithium was purchased from Aldrich Chemical Co.
Analytical grade toluene, dimethoxyethane, and hexane were
dried over sodium and distilled over sodium benzophenone
ketyl using standard procedures before use.
Syn th esis of Ha fn iu m Th iola te Com p lexes. All reac-
tions and manipulations were carried out under strictly
anaerobic and anhydrous conditions using standard Schlenk
technique.
(1) (a) Kalyanasundaram, K. Photochemistry of Polypyridine and
Porphyrin Complexes; Academic Press: San Diego, 1992. (b) Roundhill,
D. M. Photochemistry and Photophysics of Metal Complexes; Plenum
Press: New York, 1994.
(2) See for example: (a) Heinselman, K. S.; Hopkins, M. D. J . Am.
Chem. Soc. 1995, 117, 12340. (b) Lee, Y. F.; Kirchhoff, J . R. J . Am.
Chem. Soc. 1994, 116, 3599. (c) Pfennig, B. W.; Thompson, M. E.;
Bocarsly, A. B. J . Am. Chem. Soc. 1989, 111, 8947. (d) Pfennig, B. W.;
Thompson, M. E.; Bocarsly, A. B. Organometallics 1993, 12, 649. (e)
Vlcek, A., J r. Chemtracts: Inorg. Chem. 1993, 5, 141. (f) Thorn, D. L.;
Harlow, R. L. Inorg. Chem. 1992, 31, 3917. (g) Paulson, S.; Sullivan,
B. P.; Caspar, J . V. J . Am. Chem. Soc. 1992, 114, 6905. (h) Bandy, J .
A.; Cloke, F. G. N.; Cooper, G.; Day, J . P.; Girling, R. B.; Graham, R.
G.; Green, J . C.; Grinter, R.; Perutz, R. N. J . Am. Chem. Soc. 1988,
110, 5039.
(3) Yam, V. W. W.; Qi, G. Z.; Cheung K. K. J . Chem. Soc., Dalton
Trans. 1998, 1819.
(η5-C5Me5)2Hf(Sn Bu )2 (1). To a solution of (η5-C5Me5)2HfCl2
(0.14 g, 0.27 mmol) in DME (15 mL) at 0 °C was added LiS-
nBu (0.60 mmol) in DME (20 mL), prepared in situ at 0 °C
from HSnBu (0.054 g, 0.60 mmol) and nBuLi (0.60 mmol in
n-hexane). The reaction mixture was slowly warmed to 50 °C
and stirred at that temperature for 48 h. After removal of
the solvent under reduced pressure, the solid residue was
extracted with toluene. The toluene extract was subsequently
concentrated and addition of hexane followed by cooling gave
1 as pale yellow crystals. Yield: 0.11 g (65%). 1H NMR (300
MHz, C6D6, 298 K, relative to Me4Si): δ 0.95 (t, 6H, CH3), 1.53
(m, 4H, CH3CH2), 1.73 (m, 4H, CH3CH2CH2), 2.06 (s, 30H, C5-
Me5), 2.99 (t, 4H, CH2S). UV-vis in toluene (298 K), λmax/nm
(4) See for example: (a) Yam, V. W. W.; Lee, W. K.; Lai, T. F. J .
Chem. Soc., Chem. Commun. 1993, 1571. (b) Yam, V. W. W.; Lo, K. K.
W.; Cheung, K. K. Inorg. Chem. 1996, 35, 3549. (c) Yam, V. W. W.; Lo,
K. K. W.; Wang, C. R.; Cheung, K. K. Inorg. Chem. 1996, 35, 5116. (d)
Yam, V. W. W.; Yeung, P. K. Y.; Cheung, K. K. J . Chem. Soc., Dalton
Trans. 1994, 2587. (e) Yam, V. W. W.; Yeung, P. K. Y.; Cheung, K. K.
J . Chem. Soc., Chem. Commun. 1995, 267. (f) Yam, V. W. W.; Yeung,
P. K. Y.; Cheung, K. K. Angew. Chem., Int. Ed. Engl. 1996, 35, 739.
(g) Yam, V. W. W.; Chan, C. L.; Cheung, K. K. J . Chem. Soc., Dalton
Trans. 1996, 4019. (h) Yam, V. W. W.; Wong, K. M. C.; Cheung, K. K.
Organometallics 1997, 16, 1729. (i) Yam, V. W. W. J . Photochem.
Photobiol. A 1997, 106, 75. (j) Yam, V. W. W.; Lo, K. K. W.; Wang, C.
R.; Cheung, K. K. J . Phys. Chem. A 1997, 101, 4666. (k) Yam, V. W.
W.; Lo, K. K. W. Comments Inorg. Chem. 1997, 19, 209.
10.1021/om980602f CCC: $15.00 © 1998 American Chemical Society
Publication on Web 11/13/1998

Luminescent Hafnium Thiolate Complexes
Organometallics, Vol. 17, No. 25, 1998 5449
(ꢀmax/dm3 mol-1 cm-1): 318 (4300), 368 (2300). Positive ion
EI-MS: m/z ) 628 {M}+, 571 {M - C4H9}+, 538{M - SC4H9}+,
481 {M - SC4H9 - C4H9}+. Anal. Found: C, 53.41; H, 7.67.
Calcd for C28H48S2Hf: C, 53.56; H, 7.65.
structure was solved by direct methods (SIR92)5a and ex-
panded by the Fourier method; refinement was by full-matrix
least squares using the software package TeXsan5b on a Silicon
Graphics Indy computer. A crystallographic asymmetric unit
consists of half of one molecule with the Hf atom at special
position. All 16 non-H atoms of the asymmetric unit were
refined anisotropically, and the 24 H atoms at calculated
positions with thermal parameters equal to 1.3 times that of
the attached C atoms were not refined. Convergence for 141
variable parameters by least-squares refinement on F with w
) 4Fo2/σ2(Fo2), where σ2(Fo2) ) [σ2(I) + (0.020 Fo2)2] for 2167
reflections with I > 3σ(I) was reached at R ) 0.019 and wR )
0.025 with a goodness-of-fit of 1.58. (∆/σ)max ) 0.01. The final
difference Fourier map was featureless, with maximum posi-
tive and negative peaks of 0.51 and 0.55 e Å-3, respectively.
(η5-C5Me5)2Hf(SC6H5)2 (2). The procedure was similar to
that of 1 except HSC6H5 (0.066 g, 0.60 mmol) was used in place
of HSnBu to give 2 as yellow crystals. Yield: 0.12 g (67%). 1H
NMR (300 MHz, C6D6, 298 K, relative to Me4Si): δ 1.93 (s,
30H, C5Me5), 6.89 (t, J ) 8 Hz, 2H, aryl protons para to S),
6.97 (t, J ) 8 Hz, 4H, aryl protons meta to S), 7.86 (d, J ) 8
Hz, 4H, aryl protons ortho to S). UV-vis in toluene (298 K),
λ
max/nm (ꢀmax/dm3 mol-1 cm-1): 332 (11000), 392 (7600).
Positive ion EI-MS: m/z ) 668 {M}+, 559 {M - SC6H5}+, 533
{M - Cp*}+. Anal. Found: C, 57.56; H, 5.92. Calcd for
C
32H40S2Hf: C, 57.58; H, 5.99.
Cr ysta l Da ta for 2: C32H40S2Hf, Mr ) 667.28, monoclinic,
space group C2/c (No. 15), a ) 14.414(5) Å, b ) 11.466(3) Å, c
) 18.190(3) Å, â ) 103.18(2)°, V ) 2927(1) Å3, Z ) 4, Dc )
1.732 g cm-3, µ(Mo KR) ) 37.18 cm-1, F(000) ) 1344, T ) 301
K. A yellow crystal of dimensions 0.25 × 0.20 × 0.35 mm
mounted on a glass fiber was used for data collection at 28 °C
on an Enraf-Nonius CAD4 diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å) using ω-2θ
scans with ω-scan angle (0.66 + 0.35 tan θ)° at a scan speed
of 1.18-5.49 deg min-1. Intensity data (in the range of 2θmax
) 50°; h, 0 to 17; k, 0 to 13; l, -21 to 21 and 3 standard
reflections measured after every 300 reflections showed no
decay) were corrected for Lorentz and polarization effects and
empirical absorption corrections based on the ψ-scan of four
strong reflections (minimum and maximum transmission
factors 0.833 and 1.000). A total of 2831 reflections were
measured, of which 2732 were unique and Rint ) 0.011; 2484
reflections with I > 3σ(I) were considered observed and used
in the structural analysis. The space group was determined
on the basis of systematic absences and a statistical analysis
of intensity distribution, and the successful refinement of the
structure was solved by direct methods (SIR92)5a and ex-
panded by the Fourier method; refinement was by full-matrix
least squares using the software package TeXsan5b on a Silicon
Graphics Indy computer. A crystallographic asymmetric unit
consists of half of one molecule with the Hf atom at special
position. All 18 non-H atoms of the asymmetric unit were
refined anisotropically, and the 20 H atoms at calculated
positions with thermal parameters equal to 1.3 times that of
the attached C atoms were not refined. Convergence for 159
variable parameters by least-squares refinement on F with w
) 4Fo2/σ2(Fo2), where σ2(Fo2) ) [σ2(I) + (0.028Fo2)2] for 2484
reflections with I > 3σ(I) was reached at R ) 0.024 and wR )
0.038 with a goodness-of-fit of 2.17. (∆/σ)max ) 0.02. The final
difference Fourier map was featureless, with maximum posi-
tive and negative peaks of 0.61 and 1.18 e Å-3, respectively.
(η5-C5Me5)2Hf(SC6H4OMe-p)2 (3). The procedure was
similar to that of 1 except HSC6H4OMe-p (0.084 g, 0.60 mmol)
was used in place of HSnBu to give 3 as pale yellow green
crystals. Yield: 0.13 g (66%). 1H NMR (300 MHz, C6D6, 298
K, relative to Me4Si): δ 1.97 (s, 30H, C5Me5), 3.25 (s, 6H, OMe),
6.63 (d, J ) 8 Hz, 4H, aryl protons meta to S), 7.77 (d, J ) 8
Hz, 4H, aryl protons ortho to S). UV-vis in toluene (298 K),
λ
max/nm (ꢀmax/dm3 mol-1 cm-1): 330 (8800), 396 (5600). Positive
ion EI-MS: m/z ) 728 {M}+, 589 {M - SC6H4OMe-p}+. Anal.
Found: C, 56.28; H, 6.07. Calcd for C34H44O2S2Hf: C, 56.16;
H, 6.06.
(η5-C5Me5)2Hf(SC6H4tBu -p)2 (4). The procedure was simi-
t
lar to that of 1 except HSC6H4 Bu-p (0.10 g, 0.60 mmol) was
used in place of HSnBu to give 4 as pale yellow crystals.
Yield: 0.15 g (71%). 1H NMR (300 MHz, C6D6, 298 K, relative
t
to Me4Si): δ 1.14 (s, 18H, Bu), 1.99 (s, 30H, C5Me5), 7.03 (d,
J ) 8 Hz, 4H, aryl protons meta to S), 7.84 (d, J ) 8 Hz, 4H,
aryl protons ortho to S). UV-vis in toluene (298 K), λmax/nm
(ꢀmax/dm3 mol-1 cm-1): 332 (9700), 394 (6200). Positive ion
EI-MS: m/z ) 780 {M}+, 615 {M - SC6H4 Bu-p}+. Anal.
t
Found: C, 61.77; H, 7.29. Calcd for C40H56S2Hf: C, 61.66; H,
7.19.
P h ysica l Mea su r em en ts a n d In str u m en ta tion . UV-
visible spectra were obtained on a Hewlett-Packard 8452A
diode array spectrophotometer and steady-state excitation and
emission spectra on a Spex Fluorolog 111 spectrofluorometer
equipped with a Hamamatsu R-928 photomultiplier tube
detector. Low-temperature (77 K) spectra were recorded by
using an optical Dewar sample holder. 1H NMR spectra were
recorded on a Bruker DPX300 Fourier transform NMR spec-
trometer. Chemical shifts were reported relative to tetra-
methylsilane. Positive ion EI mass spectra were recorded on
a Finnigan MAT95 mass spectrometer.
Cr ysta l Str u ctu r e Deter m in a tion . Cr ysta l Da ta for 1:
28H48S2Hf, Mr ) 627.30, monoclinic, space group C2/c (No.
C
15), a ) 14.843(3) Å, b ) 13.233(2) Å, c ) 16.332(5) Å, â )
116.07(2)°, V ) 2881(1) Å3, Z ) 4, Dc ) 1.446 g cm-3, µ(Mo
KR) ) 37.72 cm-1, F(000) ) 1280, T ) 301 K. A pale yellow
crystal of dimensions 0.15 × 0.15 × 0.30 mm mounted on a
glass fiber was used for data collection at 28 °C on an Enraf-
Nonius CAD4 diffractometer with graphite-monochromated
Mo KR radiation (λ ) 0.710 73 Å) using ω-2θ scans with
ω-scan angle (0.80 + 0.35 tan θ)° at a scan speed of 1.50-8.24
deg min-1. Intensity data (in the range of 2θmax ) 48°; h, 0 to
17; k, 0 to 15; l, -18 to 18 and 3 standard reflections measured
after every 300 reflections showed decay of 4.75%) were
corrected for decay and for Lorentz and polarization effects
and empirical absorption corrections based on the ψ-scan of
four strong reflections (minimum and maximum transmission
factors 0.836 and 1.000). A total of 2479 reflections were
measured, of which 2416 were unique and Rint ) 0.010; 2167
reflections with I > 3σ(I) were considered observed and used
in the structural analysis. The space group was determined
on the basis of systematic absences and a statistical analysis
of intensity distribution, and the successful refinement of the
Cr ysta l Da ta for 3: C32H44O2S2Hf, Mr ) 727.33, monoclinic,
space group C2/c (No. 15), a ) 18.034(3) Å, b ) 11.105(2) Å, c
) 16.835(3) Å, â ) 109.69(2)°, V ) 3174(1) Å3, Z ) 4, Dc )
1.522 g cm-3, µ(Mo KR) ) 34.40 cm-1, F(000) ) 1472, T ) 301
K. A yellow green crystal of dimensions 0.25 × 0.15 × 0.30
mm on a glass fiber was used for data collection at 28 °C on
an MAR diffractometer with a 300 mm image plate detector
using graphite-monochromated Mo KR radiation (λ ) 0.710 73
Å). Data collection was made with 3° oscillation (60 images)
at 120 mm distance and 280 s exposure. The images were
interpreted and intensities integrated using the program
DENZO.5c A total of 3073 unique reflections were obtained
(5) (a) SIR 92: Altomare, A.; Cascarano, M.; Giacovazzo, C.; Gua-
gliardi, A.; Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr.
1994, 27, 435. (b) TeXsan: Crystal Structure Analysis Package;
Molecular Structure Corporation: The Woodlands, TX, 1985 & 1992.
(c) DENZO: In The HKL ManualsA description of programs DENZO,
XDISPLAYF, and SCALEPACK; written by Gewirth, D. with the
cooperation of the program authors Otwinowski, Z., and Minor, W.;
Yale University: New Haven, CT, 1995.

5450 Organometallics, Vol. 17, No. 25, 1998
Yam et al.
from a total of 13 424 measured reflections (Rint ) 0.033); 2863
reflections with I > 3σ(I) were considered observed and used
in the structural analysis. These reflections were in the range
h, 0 to 21; k, 0 to 13; l, -20 to 20 with 2θmax ) 51.0°. The
space group was determined on the basis of systematic
absences and a statistical analysis of intensity distribution,
and the successful refinement of the structure was solved by
direct methods (SIR92)5a and expanded by the Fourier method;
refinement was by full-matrix least squares using the software
package TeXsan5b on a Silicon Graphics Indy computer. One
crystallographic asymmetric unit consists of half of one
molecule with the Hf atom at special position. In the least-
squares refinement, all 20 non-H atoms were refined aniso-
tropically, and the 22 H atoms at calculated positions with
thermal parameters equal to 1.3 times that of the attached C
atoms were not refined. Convergence for 177 variable param-
eters by least-squares refinement on F with w ) 4Fo2/σ2(Fo2),
where σ2(Fo2) ) [σ2(I) + (0.032Fo2)2] for 2863 reflections with
I > 3σ(I) was reached at R ) 0.025 and wR ) 0.044 with a
goodness-of-fit of 1.92. (∆/σ)max ) 0.01. The final difference
Fourier map was featureless, with maximum positive and
negative peaks of 0.78 and 1.51 e Å-3, respectively.
F igu r e 1. Perspective drawing of 1 with atomic number-
ing scheme. Thermal ellipsoids are shown at the 50%
probability level. Starred atoms have coordinates at -x, y,
0.5-z.
Com p u ta tion a l Deta ils. Nonparametrized Fenske-Hall
MO calculations6 were carried out on the complex (η5-C5Me5)2-
Hf(SnBu)2. This method is based on a self-consistent-field
method, which is an approximation of the Hartree-Fock-
Roothaan procedure. The molecular geometry and the atomic
basis sets used completely determine the resulting eigenvalues
and eigenvectors. The calculation was based upon crystal-
lographic data of (η5-C5Me5)2Hf(SnBu)2. The relative positions
of the two S atoms and the two centroids of Cp* were adjusted
to an idealized microsymmetry of Cs (C1 for overall symmetry,
two Cp* rings being staggered). The idealized atomic coordi-
nates were taken such that the x direction of the master
coordinate system originating on the Hf atom bisects the
S-Hf-S bond angle, the y direction is normal to the HfS2
plane, and the z direction is normal to the plane that bisects
the S-Hf-S angle. The basis sets used were those provided
with the Fenske-Hall program package version 5.1. All
calculations were carried out on a VAX 780 computer at The
University of Hong Kong.
F igu r e 2. Perspective drawing of 2 with atomic number-
ing scheme. Thermal ellipsoids are shown at the 50%
probability level. Starred atoms have coordinates at -x, y,
0.5-z.
Resu lts a n d Discu ssion
Reaction of (η5-C5Me5)2HfCl2 with 2.2 equiv of LiSR
in DME gave (η5-C5Me5)2Hf(SR)2 [R ) nBu (1), C6H5 (2),
t
C6H4OMe-p (3), C6H4 Bu-p (4)] in reasonable yield.
However, unlike the zirconium analogues,3 reaction of
(η5-C5Me5)2HfCl2 with NaSR instead of LiSR did not
give the desired (η5-C5Me5)2Hf(SR)2 complexes. Instead
only the monosubstituted (η5-C5Me5)2Hf(SR)Cl was
obtained. All the newly synthesized complexes gave
satisfactory elemental analyses and were characterized
by 1H NMR spectroscopy and EI mass spectrometry. The
structures of 1-3 have been determined by X-ray
crystallography and represent the first report on the
X-ray structure of this class of (η5-Cp′)2Hf(SR)2 (Cp′ )
C5Me5 or C5H5) compounds.
The perspective drawings of complexes 1-3 are
depicted in Figures 1-3. The crystal and structure
determination data for these complexes are collected in
Table 1. Selected bond distances and angles are sum-
marized in Tables 2, 3, and 4, respectively. For all three
complexes, the coordination geometries about the Hf
atom, defined by the pentamethylcyclopentadienyl ring
centroids and the S atoms, are distorted tetrahedral. A
projection onto the Hf-S(1)-S(1*) plane shows that the
pentamethylcyclopentadienyl rings have a staggered
F igu r e 3. Perspective drawing of 3 with atomic number-
ing scheme. Thermal ellipsoids are shown at the 50%
probability level. Starred atoms have coordinates at -x, y,
0.5-z.
conformation. The Hf-S distances in 1-3 of 2.4761-
(9), 2.502(1), and 2.5044(8) Å are comparable to the
values observed in (η5-C5H5)2HfS5 of 2.512 Å,7 while as
(7) Shaver, A.; McCall, J . M.; Day, V. W.; Vollmer, S. Can. J . Chem.
1987, 65, 1676.
(6) Hall, M. B.; Fenske, R. F. Inorg. Chem. 1972, 11, 768.

Luminescent Hafnium Thiolate Complexes
Organometallics, Vol. 17, No. 25, 1998 5451
Ta ble 1. Cr ysta l a n d Str u ctu r e Deter m in a tion Da ta for Com p lexes 1-3
Cp*2Hf(SnBu)2
Cp*2Hf(SC6H5)2
Cp*2Hf(SC6H4OMe-p)2
(3)
(1)
(2)
mol formula
Mr
T, K
C
627.3
301
28H48S2Hf
C32H40S2Hf
667.28
301
C34H44O2S2Hf
727.33
301
a, Å
b, Å
c, Å
14.843(3)
13.233(2)
16.332(5)
116.07(2)
2881(1)
14.414(5)
11.466(3)
18.190(3)
103.18(2)
2927(1)
18.034(3)
11.105(2)
16.835(3)
109.69(2)
3174(1)
â, deg
V, Å3
cryst color
cryst syst
space group
Z
pale yellow
monoclinic
C2/c (No. 15)
4
yellow
yellow green
monoclinic
C2/c (No. 15)
4
monoclinic
C2/c (No. 15)
4
F(000)
1280
1.446
1344
1.732
1472
1.522
Dc, g cm-3
cryst dimens, mm
λ, Å (graphite-monochromated, Mo KR)
µ(Mo KR), cm-1
0.15 × 0.15 × 0.30
0.25 × 0.20 × 0.35
0.710 73
37.18
2θmax ) 50° (h, 0 to 17;
k, 0 to 13; l, -21 to 21)
ω-2θ; 1.18-5.49
0.66 + 0.35 tan θ
2831
0.25 × 0.15 × 0.30
0.710 73
0.710 73
37.72
34.40
collection range
2θmax ) 48° (h, 0 to 17;
k, 0 to 15; l, -18 to 18)
ω-2θ; 1.50-8.24
0.80 + 0.35 tan θ
2479
2θmax ) 51° (h, 0 to 21;
k, 0 to 13; l, -20 to 20)
oscillation
scan mode and scan speed, deg min-1
scan width, deg
no. of data collected
no of unique data
13 424
3073
2416
2732
no. of data used in refinement, m
no. of parameters refined, p
Ra
2167
141
0.019
0.025
2484
159
0.024
0.038
2863
177
0.025
0.044
1.92
wRa
goodness-of-fit, S
1.58
2.17
maximum shift, (∆/σ)max
residual maximum in final
difference map, e Å-3
0.01
+0.51, -0.55
0.02
+0.61, -1.18
0.01
+0.78, -1.51
w ) 4Fo2/σ2(Fo)2, where σ2(Fo)2 ) [σ2(I) + (0.020Fo2)2] with I > 3σ(I) for 1; w ) 4Fo2/σ2(Fo)2, where σ2(Fo)2 ) [σ2(I) + (0.028Fo2)2] with
a
I > 3σ(I) for 2; w ) 4Fo2/σ2(Fo)2, where σ2(Fo)2 ) [σ2(I) + (0.032Fo2)2] with I > 3σ(I) for 3.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 1
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 2
Hf(1)-S(1)
Hf(1)-C(2)
Hf(1)-C(4)
Hf-Cp*centroid
C(1)-C(2)
C(3)-C(4)
C(1)-C(5)
C(2)-C(7)
C(4)-C(9)
C(11)-C(12)
C(13)-C(14)
2.4761(9)
2.529(3)
2.596(4)
2.269
1.410(5)
1.410(5)
1.402(5)
1.506(5)
1.500(5)
1.477(6)
1.447(8)
Hf(1)-C(1)
Hf(1)-C(3)
Hf(1)-C(5)
S(1)-C(11)
C(2)-C(3)
C(4)-C(5)
C(1)-C(6)
C(3)-C(8)
C(5)-C(10)
C(12)-C(13)
2.546(3)
2.577(3)
2.555(4)
1.828(4)
1.415(5)
1.430(5)
1.507(5)
1.502(5)
1.503(5)
1.536(7)
Hf(1)-S(1)
Hf(1)-C(2)
Hf(1)-C(4)
Hf-Cp*centroid
C(1)-C(2)
2.502(1)
2.504(4)
2.595(4)
2.261
1.425(7)
1.406(7)
1.416(6)
1.498(7)
1.506(6)
1.390(8)
1.412(10)
1.429(9)
Hf(1)-C(1)
Hf(1)-C(3)
Hf(1)-C(5)
S(1)-C(11)
C(2)-C(3)
C(4)-C(5)
C(1)-C(6)
C(3)-C(8)
C(5)-C(10)
C(12)-C(13)
C(14)-C(15)
2.545(4)
2.566(5)
2.560(4)
1.778(4)
1.436(6)
1.442(6)
1.507(6)
1.510(7)
1.480(5)
1.367(7)
1.340(1)
C(3)-C(4)
C(1)-C(5)
C(2)-C(7)
C(4)-C(9)
C(11)-C(12)
C(13)-C(14)
C(15)-C(16)
S(1)-Hf(1)-S(1*)
S(1)-C(11)-C(12)
C(12)-C(13)-C(14) 113.2(5)
95.90(6) Hf(1)-S(1)-C(11)
112.5(3) C(11)-C(12)-C(13)
Cp*centroid-Hf-Cp*centroid 135.1
111.6(2)
111.8(4)
S(1)-Hf(1)-S(1*)
S(1)-C(11)-C(12)
Cp*centroid-Hf-Cp*centroid 135.54
100.52(5) Hf(1)-S(1)-C(11) 119.0(1)
123.4(3) S(1)-C(11)-C(16) 116.6(4)
a result of lanthanide contraction effect, they are
slightly shorter than the Zr-S distances observed in the
related zirconocene thiolate complexes (η5-C5Me5)2Zr-
tion as reflected by their S(1*)-Hf-S(1)-C(11) torsion
angles of 48.17°, 48.79°, and 52.07°, respectively. This
is in accord with theoretical calculations on this class
of compounds and is favored by d0 metal centers in order
to maximize the pπ-dπ overlap between sulfur and the
metal center.9 The larger deviation from 90° of the
S-Hf-S-C torsion angle in 1-3 is in line with the
steric requirement of the pentamethylcyclopentadienyl
units, which direct the alkyl/phenyl substituents further
away from the more sterically demanding pentameth-
ylcyclopentadienyl groups.
n
(SR)2 [R ) Bu (2.4987(8) Å);3 R ) C6H5 (2.522(1) Å)8].
The S(1)-Hf(1)-S(1*) angles of 95.90(6)°, 100.52(5)°,
and 100.62(4)° in 1-3 are comparable to the corre-
sponding S(1)-Zr(1)-S(1*) angles in (η5-C5Me5)2Zr(SR)2
n
[R ) Bu (96.14°);3 R ) C6H5 (101°)8] and are consis-
tentwith the difference in the steric demand of the -Sn-
Bu and -SPh moieties. The Hf-Cp*centroid distances in
1-3 of 2.269, 2.261, and 2.265 Å are slightly shorter
than the Zr-Cp*centroid distances of 2.27 Å in (η5-C5Me5)2-
Zr(SnBu)2.3 The Cp*centroid-M-Cp*centroid angles (M )
Zr,3 Hf) are also similar and are consistent with the
steric demand of the ligands. Similar to the zirconium
analogues,3,8 complexes 1-3 exhibit an endo conforma-
The luminescent behavior of complexes 1-4 has been
studied. Their photophysical data together with those
of the precursor complex (η5-C5Me5)2HfCl2 and the
(9) (a) Lauher, J . W.; Hoffmann, R. J . Am. Chem. Soc. 1976, 98,
1729. (b) Calhorda, M. J .; Carrondo, M. A. A. F. d. C. T.; Dias, A. R.;
Frazao, C. F.; Hursthouse, M. B.; Simoes, J . A. M.; Teixeira, C. Inorg.
Chem. 1988, 27, 2513.
(8) Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg. Chem. 1995, 34,
5900.

5452 Organometallics, Vol. 17, No. 25, 1998
Yam et al.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 3
Hf(1)-S(1)
Hf(1)-C(2)
Hf(1)-C(4)
Hf-Cp*centroid
C(1)-C(2)
2.5044(8)
2.508(4)
2.598(4)
2.265
1.418(6)
1.427(6)
1.421(6)
1.496(6)
1.492(5)
1.388(5)
1.387(6)
1.392(6)
1.419(5)
Hf(1)-C(1)
Hf(1)-C(3)
Hf(1)-C(5)
S(1)-C(11)
C(2)-C(3)
C(4)-C(5)
C(1)-C(6)
C(3)-C(8)
C(5)-C(10)
C(12)-C(13)
C(14)-C(15)
O(1)-C(14)
2.549(4)
2.576(4)
2.548(3)
1.787(3)
1.421(6)
1.423(6)
1.501(5)
1.495(6)
1.510(4)
1.396(6)
1.376(5)
1.376(5)
C(3)-C(4)
C(1)-C(5)
C(2)-C(7)
C(4)-C(9)
C(11)-C(12)
C(13)-C(14)
C(15)-C(16)
O(1)-C(17)
S(1)-Hf(1)-S(1*)
S(1)-C(11)-C(12)
100.62(4) Hf(1)-S(1)-C(11) 117.4(1)
118.3(3) S(1)-C(11)-C(16) 122.7(4)
F igu r e 5. Electronic absorption spectrum of 2 in toluene
at room temperature.
Cp*centroid-Hf-Cp*centroid 134.5
Ta ble 5. P h otop h ysica l Da ta for Ha fn iu m
Th iola te Com p lexes
Ta ble 6. Id ea lized Bon d Len gth s (Å) a n d An gles
(d eg) of 1 Used for Non p a r a m etr ized F en sk e-Ha ll
MO Ca lcu la tion s
medium
emission
lifetime
compound
(T/K)
(λem/nm)
(τo/µs)
Hf-Cp*centroid
Hf-S
2.269
2.48
1.83
135.1
95.90
111.6
48.17
44.82
1
2
PE/Tol (v/v 10:1)
glass (77)
solid (77)
Tol (298)
PE/Tol (v/v 10:1)
glass (77)
542
S-C
Cp*centroid-Hf-Cp*centroid
S-Hf-S
Hf-S-C11
C11-S-Hf-S*
C12-C11-S*-Hf
538
540
526
<0.1
solid (77)
522
513
545
solid (298)
PE/Tol (v/v 10:1)
glass (77)
1.5 ( 0.1
9.0 ( 0.5
of their emission spectra shows that the emission energy
follows the order Hf > Zr and C5H5 > C5Me5. With
reference to previous spectroscopic work on the related
titanocene derivatives10 and the observed emission
trends, the emissions observed in (η5-C5Me5)2MCl2 are
tentatively assigned as derived from the respective C5-
Me5 f M ligand-to-metal charge-transfer (LMCT) states.
Complexes 1-4 exhibit intense emission at ca. 520-
540 nm upon visible light excitation in the solid state
at 77 K. The much lower emission energies in 1-4
relative to (η5-C5Me5)2HfCl2 may suggest an emission
of different origin. An assignment of the emission origin
in complexes 1-4 as derived from the C5Me5 f Hf
LMCT transition is not favored since the thiolate
ligands, being a better σ-donor than the electronegative
chloro group, would be expected to render the Hf center
less electron deficient and, hence, a poorer electron
acceptor. This would cause the C5Me5 f Hf LMCT
transition to shift to higher energies instead. The
observation of an opposite trend would disfavor such an
assignment. A comparison of the emission energies of
the complexes in the solid state at 77 K shows that 1 <
4 < 3 < 2, which is in line with the σ-donating effect of
3
4
solid (77)
527
520
528
solid (298)
PE/Tol (v/v 10:1)
glass (77)
solid (77)
solid (298)
solid (77)
solid (77)
solid (77)
solid (77)
532
513
455
427
494
452
<0.1
(η5-C5Me5)2HfCl2
(η5-C5H5)2HfCl2
a
(η5-C5Me5)2ZrCl2
a
(η5-C5H5)2ZrCl2
a
From ref 3.
the thiolate ligands SnBu > SC6H4 Bu-p > SC6H4OMe-p
t
> SC6H5. A similar trend has also been found in the
related zirconium chalcogenolate complexes.3 The ob-
servation of such an emission trend is suggestive of
either a thiolate to hafnium (SR f Hf) LMCT origin or
a thiolate to pentamethylcyclopentadienyl (SR f C5Me5)
LLCT origin. Although one cannot exclude the possibil-
ity of a LLCT state, we prefer its assignment as an
origin with predominant LMCT character since the
emission energies are found to be sensitive to the nature
of the metal center. A comparison of the emission
F igu r e 4. Excitation spectrum (‚‚‚) and emission spectrum
(s) of 2 in petroleum ether/toluene (v/v 10:1) glass at 77
K.
related complexes (η5-C5H5)2HfCl2, (η5-C5Me5)2ZrCl2,
and (η5-C5H5)2ZrCl2 are collected in Table 5. The
excitation and emission spectra of 2 in petroleum ether/
Et2O glass at 77 K are shown in Figure 4. The
excitation spectrum closely resembles that of the elec-
tronic absorption spectrum (Figure 5). The complexes
(η5-C5Me5)2HfCl2, (η5-C5H5)2HfCl2, (η5-C5Me5)2ZrCl2, and
(η5-C5H5)2ZrCl2 emit at 455, 427, 494, and 452 nm,
respectively, in the solid state at 77 K. A comparison
(10) See for example: (a) Kenney, J . W., III; Boone, D. R.; Striplin,
D. R.; Chen, Y. H.; Hamar, K. B. Organometallics 1993, 12, 3671. (b)
Bruce, M. R. M.; Sclafani, A.; Tyler, D. R. Inorg. Chem. 1986, 25, 2546.
(c) Bruce, M. R. M.; Kenter, A.; Tyler, D. R. J . Am. Chem. Soc. 1984,
106, 639.

Luminescent Hafnium Thiolate Complexes
Organometallics, Vol. 17, No. 25, 1998 5453
HOMO is approximately 77% SnBu and 22% C5Me5 in
character, while that of the LUMO is approximately
73% Hf and 10% C5Me5. The large percent composition
of thiolate character in the HOMO has also been found
Ta ble 7. En er gies a n d P er cen t Com p osition s for
th e F r on tier Or bita ls of (η5-C5Me5)2Hf(Sn Bu )2
% composition
molecular
orbital
energy
(eV)
SR
Hf
C5Me5
3
in the analogous (η5-C5Me5)2Zr(SnBu)2 and in the
HOMO(88)
LUMO(89)
-9.48
-2.65
77.4
16.4
0.8
73.2
21.8
10.4
related (η5-C5H5)2Ti(SH)2.11 Based on the results of the
calculations, an assignment of the origin of emission as
derived from a predominant thiolate-to-hafnium (RS f
Hf) LMCT state mixed with some C5Me5 f Hf LMCT
character is favored. A similar assignment has been
made for the related zirconium complexes.3
spectra of (η5-C5Me5)2M(SR)2 shows that, for the same
thiolate ligand, the emission for the hafnium complexes
occurs at a higher energy than that of the zirconium
counterparts. For example, the 77 K solid-state emis-
sion of (η5-C5Me5)2Hf(SnBu)2 occurs at 538 nm, while
that of (η5-C5Me5)2Zr(SnBu)2 occurs at 610 nm.3
The electronic structures of this class of compounds
have been probed by Fenske-Hall molecular orbital
calculation on complex 1. Table 6 summarizes the
idealized bond lengths and angles used for the MO
calculations. Table 7 shows the percent composition for
the frontier molecular orbitals of complex 1. The
calculation results show that the composition of the
Ack n ow led gm en t. V.W.W.Y. acknowledges finan-
cial support from the Research Grants Council and The
University of Hong Kong.
Su p p or tin g In for m a tion Ava ila ble: Tables giving frac-
tional coordinates and thermal parameters, general displace-
ment parameter expressions (U), and all bond distances and
bond angles for 1-3 (28 pages). Ordering information is given
on any current masthead page.
(11) Petersen, J . L.; Lichtenberger, D. L.; Fenske, R. F.; Dahl, L. F.
J . Am. Chem. Soc. 1975, 97, 6433.
OM980602F