Synthesis, structure, and spectroscopic properties of gold(I)-carbene complexes

Article abstract of DOI:10.1021/om980718b

A series of gold(I)-carbene complexes of the type [Au(R₂-bimy)L] (R = Et, Me; bimy = benzimidazol-2-ylidene; L = Cl, Br, I, bimy, thiophenolate, phenylacetylide) have been prepared. These carbene complexes are luminous in acetonitrile solution and in the solid state with long lifetimes at room temperature. Multiple emissions have been observed for different R and L. The crystal structure of [Au(Me₂-bimy)Cl] shows a relatively short intermolecular Au^I-Au^I contact of 3.1664(10) ? and an intermolecular ring π-π interaction with a ring-ring distance of 3.45 ?. The structure of [Au(Et₂-bimy)Cl], however, shows only intermolecular ring-ring interactions with a distance of 3.53 ?. Crystal structure data suggest that bimy is a high-trans-influence ligand.

Full text of DOI:10.1021/om980718b

1216
Organometallics 1999, 18, 1216-1223
Syn th esis, Str u ctu r e, a n d Sp ectr oscop ic P r op er ties of
Gold (I)-Ca r ben e Com p lexes
Harrison M. J . Wang, Charle Y. L. Chen, and Ivan J . B. Lin*
Department of Chemistry, Fu J en Catholic University, Hsinchuang, Taipei 242, Taiwan
Received August 24, 1998
A series of gold(I)-carbene complexes of the type [Au(R2-bimy)L] (R ) Et, Me; bimy )
benzimidazol-2-ylidene; L ) Cl, Br, I, bimy, thiophenolate, phenylacetylide) have been
prepared. These carbene complexes are luminous in acetonitrile solution and in the solid
state with long lifetimes at room temperature. Multiple emissions have been observed for
different R and L. The crystal structure of [Au(Me2-bimy)Cl] shows a relatively short
intermolecular AuI-AuI contact of 3.1664(10) Å and an intermolecular ring π-π interaction
with a ring-ring distance of 3.45 Å. The structure of [Au(Et2-bimy)Cl], however, shows only
intermolecular ring-ring interactions with a distance of 3.53 Å. Crystal structure data
suggest that bimy is a high-trans-influence ligand.
In tr od u ction
some solution data7 have been reported. Another inter-
esting property of AuI compounds is their luminescent
behavior, especially when AuI-AuI interactions are
present.9-15 AuI-phosphine compounds have been the
most extensively studied in this regard. Recently we
Transition-metal complexes of carbenes derived from
imidazolium salts have received much attention re-
cently. One reason is that this type of carbene is ∼120
kcal/mol more stable than the simple methylidene and
therefore its isolation and preparation are easier.1
Second, imidazol-2-ylidene (imy) can stabilize both high-
and low-oxidation-state metal ions and is therefore a
useful ligand.2 Finally, this type of carbene forms stable
complexes with a wide range of metal ions3 and has been
considered as both an alternative to and extension of
more basic phosphines.4 In this regard, metal-imy
complexes have been found to be good catalysts for a
variaty of transformations, the Heck reaction being one
example.5
reported the luminescence of aggregated annular AuI -
2
diphosphine compounds in the solid and solution states.7b
Herein, this behavior is compared to that of analogous
AuI-imy carbene complexes.
AuI-carbenes have been known for more than a
quarter-century.16 Their emissive behavior17 and chemi-
cal reactions have been less studied than those of AuI-
phosphine complexes. Most published work dealing with
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C. P.; Lin, I. J . B.; Liu, L. S.; Wang, J . C. Inorg. Chem. 1997, 36, 2294.
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A. E.; Bruce, M. R. M. Inorg. Chem. 1993, 32, 2506. (f) Harwell, D. E.;
Mortimer, M. D.; Knobler, C. B.; Anet, F. A. L.; Hawthorne, M. F. J .
Am. Chem. Soc. 1996, 118, 2679.
One of the interesting properties of AuI compounds
is their tendency to form weak AuI-AuI interactions.6
These interactions, which have energies ranging from
29 to 60 kJ /mol, are comparable to those of H-bonds.7
A large amount of crystallographic data8-15 as well as
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10.1021/om980718b CCC: $18.00 © 1999 American Chemical Society
Publication on Web 02/27/1999

Gold(I) Carbene Complexes
Organometallics, Vol. 18, No. 7, 1999 1217
Sch em e 1a
a
R ) Et, Me. Legend: (a) AgBF4 (i) and KX (ii; X ) Br, I); (b) [R2-bimyH]PF6, K2CO3; (c) HCtCPh, K2CO3; (d) HSPh, KOH.
AuI-carbenes concerns oxidative addition reactions.18
Our recently reported19 facile synthesis of Au-bimy
(bimy ) benzimidazol-2-ylidene) compounds suggested
that these may be useful in a general sense. Herein we
report structural variations of AuI-bimy complexes and
photoluminescent behavior in the solid and solution
state. This study may be helpful in designing supramol-
ecules involving AuI-carbene compounds.
(phosphine)X] (X ) Cl, Br, I),20 [Au(phosphine)2]PF6,21
[Au(phosphine)(CtCPh)],22 [Au(phosphine)(SR)],23 and
[Au(phosphine)(py)]+ 24 have been reported. We also
tried to synthesize [Au(R2-bimy)(PPh3)]+ without suc-
cess. Reaction of [Au(R2-bimy)Cl] with AgBF4 followed
by PPh3 produced [Au(PPh3)2]+ and [Au(R2-bimy)2]+
instead of the expected [Au(R2-bimy)(PPh3)]+. All the
AuI-bimy compounds are light and thermally stable.
Conductivity measurements performed in acetonitrile
at ∼10-3 M for the ionic compounds [Me2-bimyH]Br,
[Et2-bimyH]Br, [Au(Me2-bimy)2]PF6, and [Au(Et2-bimy)2-
Resu lts a n d Discu ssion
PF6 gave values of 165, 160, 165, and 162 S cm2 mol-1
,
Syn th esis. Reaction of [R2-bimyH]Br (R ) Et, Me)
in 1:1 CH2Cl2/EtOH with a 0.5 mol equiv of Ag2O,
followed by the addition of 1 mol equiv of Au(SMe2)Cl
produced [Au(R2-bimy)Cl] in high yields (R ) Et, 91%;
R ) Me, 71%). The use of an EtOH mixed solvent is
crucial for a high yield of [Au(R2-bimy)Cl]. Other AuI-
bimy compounds synthesized from [Au(R2-bimy)Cl] are
shown in Scheme 1. [Au(R2-bimy)(CtCPh)] was ob-
tained either by the transfer of CtCPh from [Ag(Ct
CPh)]∞ to [Au(R2-bimy)Cl] or by the direct reaction of
[Au(R2-bimy)Cl] with HCtCPh in the presence of K2-
CO3 in acetone. [Au(R2-bimy)(SPh)] was obtained by the
reaction of [Au(R2-bimy)Cl] with HSPh in CH2Cl2/EtOH
in the presence of NaOH. [Au(R2-bimy)2]PF6 was ob-
tained from [Au(R2-bimy)Cl] by either the transfer of
R2-bimy from [Ag(R2-bimy)2]PF6 or reaction with [R2-
bimyH]PF6 in the presence of K2CO3 in acetone. At-
tempts to prepare the mixed-carbene compound [Au(R2-
bimy)(R′2-bimy)]PF6 produced a mixture of [Au(R2-
bimy)(R′2-bimy)]PF6, [Au(R2-bimy)2]PF6, and [Au(R′2-
bimy)2]PF6. Mixing the last two compounds, however,
did not give the mixed-carbene compound, suggesting
that the homoleptic carbene compounds are not labile.
Note that analogous phosphine compounds such as [Au-
respectively, suggesting that these compounds are 1:1
electrolytes.
Molecu la r St r u ct u r e. The molecular structure of
[Au(Me2-bimy)Cl] is depicted in Figure 1a. Crystal data
and experimental details are given in Table 1, and
selected bond distances and bond angles are given in
the figure caption. The molecule is essentially linear
around the gold atom (C(1)-Au-Cl ) 178.1(3)°). The
Au-C(1) distance is 1.985(11) Å and is comparable to
that reported25 for [Au(carbene)2]+ and [Au(carbene)-
Cl]. The Au-Cl distance (2.338(2) Å) is substantially
longer than the value of 2.257(4) Å found in [AuCl2]-,26
suggesting that the bimy ligand has a higher trans
influence than that of chloride. The averaged C-N
distances of C(1)-N(1) and C(1)-N(2) (1.325 Å) and of
C(2)-N(1) and C(7)-N(2) (1.399 Å) are comparable to
those found in the other carbene complexes.25 Two types
of intermolecular interactions, AuI-AuI and ring π-π
interactions, are observed in the crystal packing of [Au-
(Me2-bimy)Cl] (Figure 1b). Two linear molecules are
crossed at approximately 90° with a short AuI-AuI
contact (3.1664(10) Å) to form a pair. Each molecule in
a pair further interacts with neighboring pairs through
(16) (a) Schmidbaur, H. In Gmelin Handbook of Inorganic Chem-
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Compounds. (b) Grohmann, A.; Schmidbaur, H. In Comprehensive
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1981, 114, 1853. (g) Raubenheimer, H. G.; Lindeque, L.; Cronje, S. J .
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15, 1718. (b) Uson, R.; Laguna, A.; Vicente, J .; Garcia, J .; Bergareche,
B.; Brun, P. Inorg. Chim. Acta 1978, 28, 237. (c) Uson, R.; Lagunna,
A. Coord. Chem. Rev. 1986, 70, 1. (d) Raubenheimer, H. G.; Oliver, P.
J .; Lindeque, L.; Desmet, M.; Hrusak, J .; Kruger, G. J . J . Organomet.
Chem. 1997, 544, 91.
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1994, 472, 371.
(21) King, C.; Wang, J . C.; Khan, M. N. I.; Fackler, J . P., J r. Inorg.
Chem. 1989, 28, 2145.
(22) Cross, R. J .; Davidson, M. F. J . Chem. Soc., Dalton Trans. 1986,
411.
(23) Cookson, P. D.; Tiekink, E. R. T. J . Chem. Soc., Dalton Trans.
1993, 259.
(24) Irwin, M. J .; Vittal, J . J .; Yap, G. P. A.; Puddephatt, R. J . Am.
Chem. Soc. 1996, 118, 13101.
(25) (a) Britten, J . F.; Lock, C. J . L.; Wang, Z. Acta Crystallogr. 1992,
C48, 1600. (b) Lee, K. M.; Lee, C. K.; Lin, I. J . B. Chem. Commun.
1997, 1850. (c) Kruger, G. J .; Olivier, P. J .; Lindeque, L.; Raubenhe-
imer, H. G. Acta Crystallogr. 1995, C51, 1814. (d) Bovio, B.; Burini,
A.; Pietroni, B. R. J . Organomet. Chem. 1993, 452, 287. (e) Bonati, F.;
Burini, A.; Pietroni, B. R. J . Organomet. Chem. 1991, 408, 271.
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2104.
(19) Wang, H. M. J .; Lin, I. J . B. Organometallics 1998, 17, 972.

1218 Organometallics, Vol. 18, No. 7, 1999
Wang et al.
F igu r e 1. (a, top) ORTEP diagram (50% probability
ellipsoids) of [Au(Me2-bimy)Cl] in the crystal state. Selected
bond lengths (Å) and angles (deg): Au-Au, 3.1664(10);
Au-C(1), 1.985(11); Au-Cl, 2.338(2); C(1)-N(1), 1.311(14);
C(1)-N(2), 1.38(2); C(2)-N(1), 1.394(14); C(7)-N(2), 1.401-
(14); C(1)-Au-Cl, 178.1(3); N(1)-C(1)-N(2), 107.6(10);
C(1)-Au-Au(1), 89.1(4). (b, bottom) Polymeric chain of
[Au(Me2-bimy)Cl], showing the AuI-AuI interaction and
ring-ring π-stacking.
Ta ble 1. Cr ysta l Da ta a n d Exp er im en ta l Deta ils
for [Et2-bim yH]Br ‚H2O, [Au (Me2-bim y)Cl], a n d
[Au (Et2-bim y)Cl]
[Et2-bimyH]- [Au(Me2-bimy)-
Br‚H2O Cl]
[Au(Et2-
bimy)Cl]
formula
fw
cryst syst
space group
a, Å
C
11H17N2Br.O C9H10AuClN2
C11H14AuClN2
406.66
triclinic
P1h
7.316(2)
9.698(3)
9.702(3)
619.7(3)
115.32(2)
92.755(8)
92.821(8)
2
273.18
monoclinic
P21/c
8.853(2)
8.788(2)
16.413(2)
1248.4(4)
90
102.15(2)
90
4
1.453
3.271
378.61
monoclinic
C2/c
20.510(2)
8.5624(9)
13.7848(14)
2006.3(4)
90
124.028(7)
90
8
2.507
14.884
1392
b, Å
c, Å
F igu r e 2. (a, top) ORTEP diagram (50% probability
ellipsoids) of [Au(Et2-bimy)Cl] in the crystal state. Selected
bond lengths (Å) and angles (deg): Au-C(1), 2.01(3); Au-
Cl, 2.297(7); C(1)-N(1), 1.33(3); C(1)-N(2), 1.30(4); C(2)-
N(1), 1.38(4); C(7)-N(2), 1.40(3); C(1)-Au-Cl, 179.5(8);
N(1)-C(1)-N(2), 109(2). (b, bottom) Neighboring pairs of
[Au(Et2-bimy)Cl], showing the ring-ring π-stacking.
V, Å3
R, deg
â, deg
γ, deg
Z
D(calcd), Mg/m3
abs coeff, mm-1
F(000)
2.029
12.055
380
560
no. of data collected 2307
1833
1198
no. of unique data
2163
1766
1.106
1190
1.073
goodness of fit on F2 a 1.252
final R indicesb (I >
2σ(I))
the molecular structure of this compound is that the two
ethyl substituents on the bimy moiety point to opposite
sides of the bimy plane. The oppositely oriented ethyl
groups allow a columnar stacking of the bimy planes.
The dihedral angles of C(1)-N(1)-C(9)-C(10) and
C(1)-N(2)-C(11)-C(12) are 91.7 and 93.9°, respec-
tively. The plane formed by the two ethyl carbons and
the adjacent nitrogen atoms are almost perpendicular
to the bimy plane. The crystal packing given in Figure
2b shows that there is only ring π-π interactions (ring-
ring distance 3.53 Å) but no AuI-AuI interaction. Each
molecule interacts through the bimy ring with upper
and lower bimy rings of the neighboring molecules in a
head-to-tail fashion (Figure 2b).
R1
wR2
0.0611
0.1194
0.0404
0.1092
0.0650
0.1687
R indices (all data)
R1
wR2
0.1221
0.1397
0.0490
0.1154
0.0702
0.1770
GOF ) [∑w(Fo - Fc2)2/(n - p)]1/2, where n is the number of
a
2
b
reflections and p is the number of parameters refined. R1 )
∑(||Fo| - |Fc||)/∑|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑wFo
] .
2
4 1/2
ring π-π interactions (ring-ring distance 3.45 Å) in a
head-to-tail fashion. The molecular packing of this
compound can be viewed as a polymeric chain with
alternating AuI-AuI and ring-ring interactions.
The molecular structure of [Au(Et2-bimy)Cl] is de-
picted in Figure 2a. Important bond distances and bond
angles are given in the figure caption. The Au-C(1) and
Au-Cl distances are 2.01(3) and 2.297(7) Å, respec-
tively. The averaged C-N distances of 1.315 Å for C(1)-
N(1) and C(1)-N(2) and of 1.39 Å for C(2)-N(1) and
C(7)-N(2) again are comparable to those of [Au(Me2-
bimy)Cl] and others.25 One of the notable features in
To compare the trans influence of the carbene ligand
with that of other L ligands in L-Au-Cl compounds,
we examined the effect of L ligands on the Au-Cl bond
distance. If we take 2.318 Å, the averaged Au-Cl bond
distance of [Au(Me2-bimy)Cl] and [Au(Et2-bimy)Cl], as
a reference, shorter Au-Cl bond distances are found in
compounds where L is a nitrogen donor atom (2.256(8)

Gold(I) Carbene Complexes
Organometallics, Vol. 18, No. 7, 1999 1219
N(1) and C(7)-N(2) are comparable to those in [Au(Me2-
bimy)Cl] and [Au(Et2-bimy)Cl]. The other bond dis-
tances and angles of the bimy ring are comparable to
those in similar compounds. The two ethyl groups point
to the same side of the bimyH ring. The molecular
packing (Figure 3b) shows that two imidazolium cations
are paired up through bimyH ring-ring interactions
(ring-ring distance 3.41 Å). In a pair, two ethyl groups
in one molecule are pointing to one direction, and the
other two ethyl groups in another molecule are pointing
in the opposite direction. The two bimyH rings in a pair
also stack in a head-to-tail fashion. Note that the
orientation of the ethyl groups influences the packing
fashion of the molecules.
NMR Sp ectr oscop y. The 13C NMR resonances of the
carbene carbon atoms in [Au(R2-bimy)X] complexes with
different R and X occur at δ 179 (Me, Cl), 182 (Me, Br),
187 (Me, I), 177 (Et, Cl), 180 (Et, Br), and 187 (Et, I)
ppm, respectively. These signals are shifted downfield
from the resonance position of the corresponding ben-
zimidazolium 2-carbon (142 ppm). The 13C NMR reso-
nances of the carbene carbon atoms in the bis(carbene)-
gold(I) complexes [Au(Me2-bimy)2]PF6 and [Au(Et2-
bimy)2]PF6 are at 190 ppm. The order of the carbene-
13C chemical shifts of this Au-bimy series decreases in
the order X ) bimy > I > Br > Cl. A similar dependence
of the 31P chemical shifts on halides has been seen for
[Au(phosphine)X] complexes.18 For comparison, the car-
bene-13C chemical shifts of [Au(R2-bimy)(SPh)] and [Au-
(R2-bimy)(CtCPh)] are at 186, 188 ppm and 192, 193
1
ppm, respectively. The H chemical shifts of these AuI-
bimy complexes are not concentration-dependent in the
range 10-2-10-4 M, and no dynamic equilibrium be-
tween the monomeric and dimeric forms of the com-
plexes can be observed in CDCl3 solution. A concentra-
tion dependence of the chemical shift has been observed
for [Au(PPh2Me)I], which is a dimer in the solid state.31
F igu r e 3. (a, top) ORTEP diagram (50% probability
ellipsoids) of [Et2-bimyH]Br‚H2O in the crystal state.
Selected bond lengths (Å) and angles (deg): C(1)-N(1),
1.315(8); C(1)-N(2), 1.317(8); C(2)-N(1), 1.390(7); C(7)-
N(2), 1.386(7); N(1)-C(1)-N(2), 110.8(6). (b, bottom) Neigh-
boring pairs of [Et2-bimyH]Br‚H2O, showing the ring-ring
π-stacking.
Absor p tion Sp ectr oscop y. The electronic absorp-
tion spectra of [Au(R2-bimy)X] (X ) Cl, Br, I) and [Au-
(R2-bimy)2]PF6 in acetonitrile display intense absorption
bands at ca. 270-290 nm (Table 2). These bands are
very similar to those of the carbene precusors [R2-
bimyH]Br in terms of position and band shape (ca. 260-
280 nm; Table 2). Therefore, these bands are assigned
to an intraligand (IL) transition involving the bimy
ligands. For the compounds [Au(R2-bimy)(CtCPh)],
additional peaks due to an intraligand transition of
phenylacetylide appear, and the spectra are similar to
those reported for phenylacetylide complexes.32 [Au(R2-
bimy)(SPh)] also has an additional absorption band
arising from a S f Au charge-transfer transition, which
has also been observed in the analogous phosphine
compounds.33 Although we were able to see the ag-
gregation of AuI-carbene compounds in the solid state,
we have been unable to observe aggregation in solution.
Å, L ) piperidine;27 2.262(3) Å, L ) pyrazole28). Slightly
shorter Au-Cl bond distances are found for [Au(PPh3)-
Cl] (2.279(3) Å)29a and [Au(C(OR)NR)Cl] (2.277(2) Å),29b
but comparable Au-Cl bond distances are found for [Au-
(PEt3)Cl] (2.305(8) and 2.306(8) Å).30 From the length-
ening of the Au-Cl bond distances, the trans influence
can be arranged in the order: bimy g PEt3 > PPh3
≈
C(OR)NR > pyrazole ≈ piperidine. Note that the bimy
carbene has a larger trans influence than that found in
Fischer type carbenes.
To gain a better understanding of the aggregation of
AuI-bimy compounds, the bimy precursor [Et2-bimyH]-
Br‚H2O was structurally characterized. The molecular
structure of this compound is depicted in Figure 3a, and
important bond distances and bond angles are given in
the figure caption. The averaged distances of 1.316 Å
for C(1)-N(1) and C(1)-N(2) and of 1.388 Å for C(2)-
(31) (a) Toronto, D. V.; Weissbart, B.; Tinti, D. S.; Balch, A. L. Inorg.
Chem. 1996, 35, 2484. (b) Attar, S.; Bearden, W. H.; Alcock, N. W.;
Alyea, E. C.; Nelson, J . H. Inorg. Chem. 1996, 35, 2484.
(32) (a) Tzeng, B. C.; Lo, W. C.; Che, C. M.; Peng, S. M. Chem.
Commun. 1996, 181. (b) Yam, V. W. W.; Choi, S. W. K. J . Chem. Soc.,
Dalton Trans. 1996, 4227. (c) Xiao, H.; Cheung, K. K.; Che, C. M. J .
Chem. Soc., Dalton Trans. 1996, 3699.
(33) (a) Assefa, Z.; Staples, J .; Fackler, J . P., J r. Inorg. Chem. 1994,
33, 2790. (b) Narayanaswamy, R.; Young, M. A.; Parkhurst, E.;
Ouellette, M.; Kerr, M. E.; Ho, D. M.; Elder, R. C.; Bruce, A. E.; Bruce,
M. R. M. Inorg. Chem. 1993, 32, 2506.
(27) Guy, J . J .; J ones, P. G.; Meys, M. J .; Sheldrick, G. M. J . Chem.
Soc., Dalton Trans. 1977, 8.
(28) Bonghetti, G.; Banditelli, G.; Bonati, F.; Minghetti, G.; Demar-
tin, F.; Manassero, M. Inorg. Chem. 1987, 26, 1351.
(29) (a) Baenziger, N. C.; Bennett, W. E.; Soboroff, D. M. Acta
Crystallogr. 1976, B32, 962. (b) Zhang, S. W.; Ishii, R.; Takahashi, S.
Organometallics 1997, 16, 20.
(30) Tiekink, E. Acta Crystallogr. 1989, C45, 1233.

1220 Organometallics, Vol. 18, No. 7, 1999
Wang et al.
Ta ble 2. P h otop h ysica l Da ta for [R2-bim yH]Br ‚H2O
a n d Au I-bim y Com p ou n d s
λ
em/nmb
(lifetime/µs)
λ
abs/nm (ꢀ/dm3
mol-1 cm-1
compd
)
λ
ex/nm
[Me2-bimyH]Br
262 (6900)
270 (8360)
277 (7310)
262 (6360)
269 (7180)
277 (6520)
soln 357 (23)
solid 470 (23)
288
288
[Et2-bimyH]Br
soln 357 (21)
solid 470 (23)
288
288
Au(Me2-bimy)Cl
Au(Me2-bimy)Br
Au(Me2-bimy)I
271 (12 100)
280 (20 500)
288 (24 400)
272 (12 400)
280 (20 900)
288 (23 800)
272 (12 400)
280 (21 400)
288 (25 400)
281 (39 400)
290 (47 500)
299 (37 800)
280 (23 400)
288 (21 100)
322 (11 400)
280 (27 800)
289 (41 300)
296 (33 500)
271 (9760)
280 (17 100)
288 (20 400)
272 (10 400)
281 (16 800)
289 (20 500)
274 (12 400)
283 (23 500)
292 (25 600)
284 (32 500)
291 (39 000)
299 (32 900)
281 (24 400)
288 (22 200)
328 (11 200)
282 (26 200)
290 (38 400)
298 (30 800)
soln 334 (41)
solid 420 (30)
620 (23)
soln 334 (23)
solid 438 (27)
620 (28)
soln 335 (23)
solid 440 (44)
620 (25)
soln 421 (53)
solid 421 (32)
280
350
280
350
280
350
Au(Me2-bimy)(CCPh)
Au(Me2-bimy)(SPh)
[Au(Me2-bimy)2]PF6
Au(Et2-bimy)Cl
280
350
soln 350 (28)
solid 425 (22)
475 (29)
soln 325 (22)
solid 441 (24)
280
315
280
350
F igu r e 4. Emission spectra of [Au(R2-bimy)Cl] measured
in the solid state at room temperature: (a, dotted line) R
) Me; (b, solid line) R ) Me; and (c, dashed line) R ) Et.
Excitation at 350 nm.
soln 335 (25)
solid 435 (61)
280
350
Au(Et2-bimy)Br
soln 337 (22)
solid 397 (56)
280
350
Au(Et2-bimy)I
soln 348 (22)
solid 397 (43)
280
350
Au(Et2-bimy)(CCPh)
Au(Et2-bimy)(SPh)
[Au(Et2-bimy)2]PF6
soln 340 (17)
solid 421 (41)
280
350
soln 350 (23)
solid 425 (31)
475 (31)
soln 335 (23)
solid 397 (93)
280
315
280
350
a
b
In acetonitrile soiution. In 1.0 × 10-5 M acetonitrile solution.
Emissions from excimers are not listed.
The ꢀ values of the bands are concentration-independent
in the range 10-3-10-5 M, a result consistent with NMR
studies.
Lu m in escen t P r op er ties. At room temperature, all
the AuI-bimy compounds are luminous in the solid
state and their photophysical data are given in Table
2. Crystalline [Au(Me2-bimy)Cl], which has intermo-
lecular AuI-AuI and ring π-π interactions, displays a
high-energy (HE) emission band at λmax 420 nm (lifetime
44 µs) and an intense low-energy (LE) emission band
at λmax 620 nm (lifetime 23 µs), upon excitation at 360
nm (Figure 4a). If the solid sample is obtained by
dissolving the crystalline sample in CH2Cl2 followed by
rapid precipitation through the addition of hexane, the
intensity of the 620 nm band decreases (Figure 4b) and
varies from batch to batch. The corresponding Br and I
compounds have similar emissive behavior. Crystalline
[Au(Et2-bimy)Cl], which does not show an intermolecu-
lar AuI-AuI interaction, has a band at λmax 397 nm
(lifetime 61 µs) and another band at 435 nm (lifetime
110 µs) upon excitation at 350 nm (Figure 4c). The
corresponding Br and I compounds have similar emis-
sive behavior. [Au(Me2-bimy)(CtCPh)] and the corre-
F igu r e 5. Emission spectra of [Au(R2-bimy)(CtC)Ph]
measured in the solid state at room temperature: (a, solid
line) R ) Me; (b, dashed line) R ) Et. Excitation at 350
nm.
sponding Et2-bimy compound have an intense emission
profile with fine structure from 420 to 650 nm with λmax
at 421 nm (lifetime 41 µs, Figure 5) upon excitation at
350 nm. [Au(Me2-bimy)(SPh)] and [Au(Et2-bimy)(SPh)]
have a relatively intense emission band at 425 nm
(lifetime 22 µs, excitation at 315 nm) and a shoulder at
∼475 nm (lifetime 29 µs). If the spectrum of [Au(Me2-
bimy)(SPh)] is taken at 77 K, the 475 nm band red shifts
to 500 nm (excitation at 390 nm) (Figure 6). Crystalline
[Au(Me2-bimy)2]PF6 has a strong emission at λmax 441
nm (lifetime 24 µs) when excited at 350 nm. If the
excitation wavelength is changed to 290 nm, a weak
emission profile appears at ∼400 nm together with the

Gold(I) Carbene Complexes
Organometallics, Vol. 18, No. 7, 1999 1221
from spin-forbidden intraligand (3IL) transitions involv-
ing bimy rings with different crystal packing. The
additional emission at 620 nm observed for [Au(Me2-
bimy)X], but not for [Au(Et2-bimy)X], is attributed to a
spin-forbidden AuI-AuI metal-centered (3MC) transi-
tion. This assignment is supported by the following
arguments. There is a short intermolecular AuI-AuI
contact in crystalline [Au(Me2-bimy)Cl] but not in [Au-
(Et2-bimy)Cl]. The powder sample of [Au(Me2-bimy)Cl]
obtained from dissolving the crystalline sample followed
by quick precipitation from solution, does not have
enough time to form all the possible AuI-AuI interac-
tions. To further support the latter argument, XRD
spectra of both crystalline and powder samples were
taken. The crystalline sample shows two intense peaks
corresponding to repeating layer distances of 3.83 and
3.43 Å, while the powder sample shows only a weak
peak corresponding to a repeat distance of 3.42 Å,
together with many other weak reflections. This sug-
gests that the powder sample is less organized and has
a smaller number of AuI-AuI contacts. Consequently,
the relative intensity of the 620 nm emission band
decreases. Note that the halides have no influence on
the emission energy of the AuI-AuI 3MC transition.
The emission profile for the solid sample of [Au(R2-
bimy)(CtCPh)] is almost identical with those of [(Au-
(CtCPh))2(µ-dppe)] (dppe ) Ph2P(CH2)2PPh2) and [Au2L-
(CtCPh)2] (L ) 2,6-bis(diphenylphosphino)pyridine).34
Therefore, we presume an identical emission assign-
ment: 3IL transitions involving the CtCPh ligand. A
solid sample of [Au(R2-bimy)(SPh)] has an HE emission
F igu r e 6. Emission spectra of [Au(Me2-bimy)(SPh)]: (a,
solid line) at room temperature upon excitation at 315 nm;
(b, dashed line) at 77 K upon excitation at 315 nm; (c,
dotted line) at 77 K upon excitation at 390 nm.
3
(425 nm) assignable to an IL transition involving the
bimy ligand and an LE emission (475 nm) assignable
to a spin-forbidden S f Au charge transfer (3CT)
transition. These transitions have also been observed
for many [Au(phosphine)(SR)] compounds.35
In acetonitrile at room temperature, all the gold(I)
carbene complexes, except [Au(R2-bimy)(CtCPh)], ex-
3
hibit only IL emissions at HE. The emission data are
given in Table 2. These emissions are concentration and
temperature dependent. Take [Au(Me2-bimy)2]PF6, as
an example. At the concentration of 5.0 × 10-6 M, two
emission bands at 345 and 397 nm with long lifetimes
(Figure 8a) are observed. If the concentration is raised
to 5.0 × 10-5 M, the relative intensity of the band at
397 nm increases but the relative intensity of the band
at 345 nm decreases (Figure 8b). When the temperature
decreases from 25 to 10 °C, the relative intensity of the
397 nm band also increases (Figure 8c). Other com-
pounds, including the carbene precusors [R2-bimyH]X,
behave similarly. The emission of [Au(R2-bimy)(Ct
CPh)] in acetonitrile is dominated by the IL CtCPh
transition, and only very weak HE emission bands
appear at λmax 330 nm. Since [R2-bimyH]X species have
similar emission behavior at HE, these HE bands are
assigned to IL transitions involving the bimy ligands.
F igu r e 7. Emission spectra of [Au(R2-bimy)2]PF6 upon
excitation at 290 nm: (a, solid line) R ) Me; (b, dotted line)
R ) Et.
strong band at 441 nm. Crystalline [Au(Et2-bimy)2]PF6,
on the other hand, has a strong emission at λmax 394
nm (lifetime 93 µs), and the ∼440 nm (lifetime 109 µs)
band appears as a shoulder (Figure 7). For comparison,
the emission spectrum of the crystalline [Et2-bimyH]-
Br was taken. Relatively weak emissions appear at
400-500 nm, with a major band at 470 nm and a
shoulder at ∼400 nm.
(34) (a) Shieh, S. T.; Hong, X.; Peng,. M.; Che, C. M. J . Chem. Soc.,
Dalton Trans. 1994, 3067. (b) Li, D.; Che, C. M.; Lo, W. C.; Peng, S.
M. J . Chem. Soc., Dalton Trans. 1993, 2929. (c) Irwin, M. J .; Vittal, J .
J .; Puddephatt, R. J . Organometallics 1997, 3541. (d) Irwin, M. J .;
Vittal, J . J .; Puddephatt, R. J . Organometallics 1996, 51 and references
therein.
(35) (a) Shi, J . C.; Huang, X. Y.; Wu, D. X.; Liu, Q. T. Inorg. Chem.
1996, 35, 2742. (b) J ones, W. B.; Yuan, J .; Narayanaswamy, R.; Young,
M. A.; Elder, R. C.; Bruce, A. E.; Bruce, M. R. M. Inorg. Chem. 1995,
34, 1996. (c) Forward, J . M.; Bohmann, D.; Fackler, J . P., J r.; Staples,
R. J . Inorg. Chem. 1995, 34, 6330 and references therein.
Examining the emission spectra of the AuI-bimy
compounds, we noticed that all the compounds except
[Au(R2-bimy)(CtCPh)] exhibit HE emission bands at
∼420 ( 20 nm with long lifetimes. Since [Et2-bimyH]-
Br is emissive at 400-500 nm, we suggest that the HE
emissions observed for the AuI-bimy compounds arise

1222 Organometallics, Vol. 18, No. 7, 1999
Wang et al.
Exp er im en ta l Section
The compounds [R2-bimyH]X (R ) Et, Me; X ) Br) were
prepared by known methods.36 The 1H and 13C{1H} NMR
spectra were recorded on a Bruker AC-F300 spectrometer at
300 and 75 MHz, respectively. Chemical shifts, δ, are reported
relative to the internal standard TMS for both 1H and 13C
NMR. Conductivities were measured with a Suntex SC-17A
conductivity meter at room temperature with continuous
stirring. The cell, fitted with platinum electrodes, was cali-
brated by use of an aqueous 10-2 N KCl solution. The
background conductivity for CH3CN was 0.28 µ Ω-1 cm-1
.
Absorption spectra were obtained by a Shimadzu UV-2101 PC
spectrophotometer. Emission, excitation, and lifetime spectra
were obtained with an Aminco Bowman AD2 luminescent
spectrofluorometer. Microanalyses were performed by the
Taiwan Instrumentation Center.
[Au (Me2-bim y)Cl]. Ag2O (77 mg, 0.33 mmol) was added
to a dichloromethane (30 mL) and ethanol (30 mL) mixed
solution of 1,3-dimethylbenzimidazolium bromide (150 mg,
0.66 mmol). The suspension became clear after it was stirred
for 2 h at room temperature. Au(SMe2)Cl (195 mg, 0.66 mmol)
was then added, and the resultant solution was stirred for an
additional 2 h. After the white precipitate was filtered, the
solvent was removed to give white residue. Recrystallization
from CH2Cl2/hexane gave colorless [Au(Me2-bimy)Cl] in 71%
F igu r e 8. Emission spectra of [Au(Me2-bimy)2]PF6 upon
excitation at 270 nm: (a, dashed line) 5.0 × 10-6 M, 300
K;, (b, solid line) 5.0 × 10-5 M, 300 K; (c, dotted line) 5 ×
10-5 M, 280 K.
1
yield (178 mg). Mp: 279 °C. H NMR (CDCl3): δ 7.47 (s, 4H,
CH), 4.04 (s, 6H, CH3). Anal. Calcd for C9H10N2AuCl: C, 28.55;
H, 2.66; N, 7.40. Found: C, 27.78; H, 2.62; N, 7.24.
[Au (Me2-bim y)Br ]. AgBF4 (76 mg, 0.39 mmol) in 20 mL
of EtOH was added to a CH2Cl2 (20 mL) solution of [Au(Me2-
bimy)Cl] (147 mg, 0.39 mmol), and the resultant solution was
stirred for 5 min. A white precipitate was filtered out, and the
filtrate was added to an EtOH (20 mL) solution of KBr (47
mg, 0.39 mmol). The solution was stirred for 30 min, and the
solvent was removed under vacuum. The residue was recrys-
tallized from CH2Cl2/hexane to give colorless [Au(Me2-bimy)-
Br] (yield 115 mg, 70%). Mp: 284 °C. 1H NMR (CDCl3): δ 7.48
(s, 4H, CH), 4.05 (s, 6H, CH3). Anal. Calcd for C9H10N2AuBr:
C, 25.55; H, 2.38; N, 6.62. Found: C, 25.50; H, 2.27; N, 6.55.
[Au (Me2-bim y)I]. This compound was prepared by the
method decribed for [Au(Me2-bimy)Br]. Yield: 55%. Mp: 272
°C. 1H NMR (CDCl3): δ 7.48 (s, 4H, CH), 4.05 (s, 6H, CH3).
Anal. Calcd for C9H10N2AuI: C, 23.00; H, 2.14; N, 5.96.
Found: C, 23.03; H, 2.02; N, 5.93.
[Au (Me2-bim y)(CtCP h )]. Meth od a . K2CO3 (58 mg, 0.42
mmol) was added to an acetone solution (50 mL) of phenyl-
acetylene (43 mg, 0.42 mmol) and [Au(Me2-bimy)Cl] (159 mg,
0.42 mmol). The resultant solution was stirred for 1 day and
then dried under vacuum. To remove the salts, the white
residue was washed with 20 mL of CH2Cl2 and filtered. The
clear filtrate was dried to give pale yellow [Au(Me2-bimy)(Ct
CPh)] (yield 151 mg, 81%). Recrystallization from CH2Cl2/
hexane yielded a pale yellow crystalline product.
The transition at ∼350 nm is an IL transition that
arises from monomeric Au-bimy compounds, while the
transition at ∼400 nm arises from dimeric (Au-bimy)2
compounds. Studies using electronic absorption and
NMR spectroscopy suggest that, in the concentration
range 10-2-10-6 M, no molecular association takes
place for the Au-bimy complexes in their ground state.
The dimers observed in emission spectroscopy are likely
excimer in nature.
Con clu sion
This work demonstrates that [AuI(R2-bimy)Cl] com-
plexes are readily accessible and are useful starting
materials for the synthesis of AuI-bimy-containing
compounds. Thus, compounds with the general formula
[AuI(R2-bimy)L] (L ) chloride, bromide, iodide, thiophe-
nolate, phenylacetylide, R2-bimy) have been obtained in
high yields. The starting material [Au(R2-bimy)Cl] and
its bromo and iodo analogues have interesting proper-
ties. When the substituent R is methyl, crystalline
samples show AuI-AuI and ring π-π intermolecular
interactions and exhibit multiple emissions originating
from bimy 3IL transitions and AuI-AuI 3MC transitions.
When R is ethyl, only emissions originating from the
3IL transitions of bimy are observed. Other AuI-bimy
complexes are also highly emissive. Multiple emissions
can be observed with the proper choice of L ligand.
Because many functionalized imy carbene derivatives
can be designed and prepared, the electronic and steric
effects of the imy type carbenes can be more finely tuned
than those of phosphines. The imy ligands are poten-
tially more useful than phosphine ligands in the design
of supramolecules. While both [Au(R2-bimy)X] and [AuI-
(phosphine)X] are stable complexes, the trans influence
of the bimy ligands is slightly larger or comparable to
that of phosphine ligands and is greater than that of
nitrogen donor ligands and halides.
Meth od b. [Ag(CtCPh)]∞ (65 mg, 0.31 mmol) was added
to a CH2Cl2/EtOH solution (25 mL/25 mL) of [Au(Me2-bimy)-
Cl] (118 mg, 0.31 mmol). The resultant solution was stirred
for 1 h and then filtered and dried. Recrystallization from CH2-
Cl2/hexane produced a pale yellow crystalline product (yield
1
107 mg, 78%). Mp: 241 °C dec. H NMR (DMSO-d6): δ 7.74
and 7.47 (dd, 3J ) 6 Hz, 4J ) 3 Hz, 4H, CH), 7.19-7.27 (m,
5H, Ph), 4.01 (s, 6H, CH3). Anal. Calcd for C17H15N2Au: C,
45.96; H, 3.40; N, 6.31. Found: C, 45.85; H, 3.38; N, 6.25.
[Au (Me2-bim y)(SP h )]. To a mixture of dichloromethane
(40 mL) and ethanol (20 mL) were added with stirring 1,3-
dimethylbenzimidazolium bromide (94 mg, 0.41 mmol) and
(36) (a) Abdul-Sada, A. K.; Greenway, A. M.; Hitchcock, P. B.;
Mohammed, T. J .; Seddon, K. R.; Zora, J . A. J . Chem. Soc., Chem.
Commun. 1986, 1753. (b) Harlow, K. J .; Hill, A. F.; Welton, T. Synthesis
1996, 697. Molar conductivity (1.0 × 10-3 M acetonitrile): [Me2-bimyH]-
Br, 165 S cm2 mol-1; [Et2-bimyH]Br, 160 S cm2 mol-1
.

Gold(I) Carbene Complexes
Organometallics, Vol. 18, No. 7, 1999 1223
Ag2O (48 mg, 0.21 mmol). After 1 h, Au(SMe2)Cl (120 mg, 0.41
mmol) was added and allowed to react for another 1 h. After
the precipitate was removed, the clear solution was mixed with
another solution made of thiophenol (46 mg, 0.41 mmol) and
NaOH (0.10 N, 0.42 mmol) in a mixture of CH2Cl2 (40 mL)
and EtOH (20 mL). The resultant solution was allowed to react
for additional 3 h and then dried under reduced pressure.
Extracting the residue with CH2Cl2, followed by the addition
of hexane, produced pale yellow crystals. Yield: 65%. Mp: 142
°C dec. H NMR (CDCl3): δ 7.66 (d, 2H, J ) 8 Hz, SPh), 7.47
(s, 4H, CH), 7.11 (d, 2H, 3J ) 7 Hz, SPh), 6.98 (s, H, SPh),
4.07 (s, 6H, CH3). Anal. Calcd for C15H15N2AuS: C, 39.83; H,
3.34; N, 6.19. Found: C, 39.25; H, 3.33; N, 6.13.
cm2 mol-1. Anal. Calcd for C22H28N4AuPF6: C, 38.26; H, 4.02;
N 8.22. Found: C, 38.27; H, 4.09; N, 8.11.
X-r a y Str u ctu r e Deter m in a tion s. A colorless cuboid
crystal of [Et2-bimyH]Br‚H2O was grown from a mixture of
dichloromethane and hexane at room temperature. A crystal
with dimensionsf 0.6 × 0.4 × 0.4 mm was used for X-ray
structural analysis. The diffraction experiments were carried
out on a Siemens P4 diffractometer with the XSCANS software
package37 using graphite-monochromatized Mo KR radiation
(λ ) 0.710 73 Å). A total of 2307 reflections were collected in
the θ range of 2.4-25.0° (0 e h e 10, 0 e k e 10, -19 e l e
19) in the ω scan mode. The data were corrected for Lorentz-
polarization factors. An empirical absorption correction based
on a series of ψ scans was applied to the data. The structure
was solved by direct methods and was refined by full-matrix
least squares on F2 in SHELXTL-PC version 5.03. All the non-
hydrogen atoms were refined anistropically. The experimental
details and crystal data are given in Table 1.
A colorless crystal of [Au(Me2-bimy)Cl] was grown from a
mixture of dichloromethane and hexane at room temperature.
A crystal with dimensions 0.3 × 0.2 × 0.1 mm was used for
X-ray structural analysis. A total of 1833 reflections were
collected in the θ range 2.4-25.0° (-16 e h e 24, -10 e k e
10, -16 e l e 16) in the ω scan mode. The maximum and
minimum transmission factors are 0.8935 and 0.2148. An
empirical absorption correction based on a series of ψ scans
was applied to the data. The structure was solved by direct
methods and refined by full-matrix least-squares on F2 in
SHELXTL-PC version 5.03. All the non-hydrogen atoms were
refined anisotropically. The hydrogen atoms were calculated
in ideal positions with rC-H ) 0.95 Å. The experimental details
and crystal data are given in Table 1.
1
3
[Au (Me2-bim y)2]P F 6. K2CO3 (57 mg, 0.41 mmol) was added
to an acetone (50 mL) solution containing the PF6 salt of 1,3-
dimethylbenzimidazolium (120 mg, 0.41 mmol) and [Au(Me2-
bimy)Cl] (156 mg, 0.41 mmol) and was stirred for 1 day. The
resultant solution was dried, and the white residue was
extracted with 30 mL of CH3OH/H2O (1:1 by volume). After
the filtrate was dried, white [Au(Me2-bimy)2]PF6 (213 mg, 82%)
was obtained. Recrystallization from CH3CN yielded a colorless
1
crystalline product. Mp: 351 °C dec. H NMR (DMSO-d6): δ
3
4
7.85 and 7.54 (dd, J ) 6 Hz, J ) 3 Hz, 4H, CH), 4.17 (s, 6H,
CH3). Molar conductivity (1.0 × 10-3 M acetonitrile): 165 S
cm2 mol-1. Anal. Calcd for C18H20N4AuPF6: C, 34.08; H, 3.18;
N, 8.83. Found: C, 33.99; H, 3.18; N, 8.84.
Ethyl-substituted compounds were synthesized by the meth-
ods described for the corresponding methyl compounds. Char-
acterizations of these compounds are given below.
[Au (Et2-bim y)Cl]. Yield: 91%. Mp: 204 °C. 1H NMR
(CDCl3): δ 7.41-7.50 (m, 4H, CH), 4.54 (q, 3J ) 7 Hz, 4H,
3
CH2), 1.54 (t, J ) 7 Hz, 6H, CH3). Anal. Calcd for C11H14N2-
AuCl: C, 32.49; H, 3.47; N, 6.89. Found: C, 32.48; H, 3.46; N,
6.90.
A colorless crystal of [Au(Et2-bimy)Cl] was grown from a
mixture of dichloromethane and hexane at room temperature.
A crystal with dimensions 0.3 × 0.1 × 0.1 mm was used for
X-ray structural analysis. A total of 1198 reflections were
collected in the θ range of 2.3-25.0° (-8 e h e 8, -9 e k e
10, 0 e l e 11) in the ω scan mode. The structure was solved
by direct methods and was refined by full-matrix least squares
on F2 in SHELXTL-PC version 5.03. In the final difference
Fourier synthesis, the electron density ranged from 1.823 to
-2.224 e Å-3, the largest four peaks of which were associated
with Au atoms at distances of 1.011 and 1.422 Å. The
experimental details and crystal data are given in Table 1.
[[Au (Et2-bim y)Br ]. Yield: 88%. Mp: 223 °C. 1H NMR
(CDCl3): δ 7.42-7.51 (m, 4H, CH), 4.55 (q, 3J ) 7 Hz, 4H,
3
CH2), 1.54 (t, J ) 7 Hz, 6H, CH3). Anal. Calcd for C11H14N2-
AuBr: C, 29.29; H, 3.13; N, 6.21. Found: C, 29.24; H, 3.12; N,
6.13.
[Au (E t 2-b im y)I]. Yield: 82%. Mp: 197 °C. 1H NMR
(CDCl3): δ 7.43-7.52 (m, 4H, CH), 4.55 (q, 3J ) 7 Hz, 4H,
3
CH2), 1.55 (t, J ) 7 Hz, 6H, CH3). Anal. Calcd for C11H14N2-
AuI: C, 26.52; H, 2.83; N, 5.60. Found: C, 26.59; H, 2.83; N,
5.56.
[Au (Et2-bim y)(CtCP h )]. Yield: 86%. Mp: 172 °C dec. 1H
3
4
NMR (DMSO-d6): δ 7.83 and 7.46 (dd, J ) 6 Hz, J ) 3 Hz,
Ack n ow led gm en t. This work was supported by the
National Science Council of Taiwan, Republic of China
(Grant No. NSC88-2113-M-030-008).
4H, CH), 7.19-7.28 (m, 5H, Ph), 4.53 (q, 3J ) 7 Hz, 4H, CH2),
1.45 (t, J ) 7 Hz, 6H, CH3). Anal. Calcd for C19H19N2Au: C,
3
48.31; H, 4.05; N, 5.93. Found: C, 48.31; H, 4.05; N, 5.83.
[Au (E t2-bim y)(SP h )]. Yield: 65%. Mp: 95 °C. 1H NMR
(CDCl3): δ 7.66 (d, 2H, 3J ) 7 Hz, SPh), 7.44-7.51 (m, 4H,
Su p p or tin g In for m a tion Ava ila ble: Tables giving posi-
tional and isotropic thermal parameters, anisotropic thermal
parameters, and bond lengths and angles for the structural
analysis. This material is available free of charge via the
Internet at http://pubs.acs.org.
3
C6H4), 7.10 (d, 2H, J ) 8 Hz, SPh), 6.97 (s, H, SPh), 4.56 (q,
4H, 3J ) 7 Hz, CH2), 1.56 (t, 6H, 3J ) 7 Hz, CH3). Anal. Calcd
for C17H19N2SAu: C, 42.15; H, 3.99; N, 5.83. Found: C, 42.05;
H, 4.01; N, 5.79.
[Au (Et2-bim y)2]P F 6. Yield: 89%. Mp: 281 °C. 1H NMR
(DMSO-d6): δ 7.94 and 7.54 (dd, 3J ) 6 Hz, 4J ) 3 Hz, 8H,
CH), 4.66 (q, 3J ) 7 Hz, 8H, CH2), 1.55 (t, 3J ) 7 Hz, 12H,
CH3). Molar conductivity (1.0 × 10-3 M acetonitrile): 162 S
OM980718B
(37) XSCANS; Siemens Analytical X-ray Instruments, Inc., Madison,
WI, 1990.