Mixed gold(I)-gold(III) complexes with bridging selenido ligands. Theoretical studies of the gold(I)-gold(III) interactions

Article abstract of DOI:10.1021/om010474m

The gold(I) compounds [Se(AuPPh₃)₂] and [Se{Au₂(μ-dppf)}] (dppf = 1,1′-bis(diphenylphosphino)ferrocene) react with 1 and 2 equiv of [Au(C₆F₅)₃OEt₂] to give the mixed gold(I)-gold(III) derivatives [Se(AuPPh₃)₂{Au(C₆ F₅)₃}_n] and [Se{Au₂(μ-dppf)}{Au(C₆ F₅)₃}_n] (n = 1, 2). The reaction of [Se(AuPPh₃)₂] with [Au(C₆F₅)₂Cl]₂ affords the complex [{Se(AuPPh₃)}₂{μ-Au-(C₆ F₅)₂}₂]. The crystal structures of [Se{Au₂(μ-dppf)}{Au(C₆F₅)₃}] and [{Se(AuPPh₃)}₂{μ-Au-(C₆ F₅)₂}₂] have been characterized by X-ray diffraction studies. They show dissimilar Au(I)??Au(III) distances, indicating the presence of weak interactions. Quasi-relativistic pseudopotential calculations on [Se(AuPH₃)₂(AuR₃)], [Se(AuPH₃) (AuR₃)₂]^- (R = -H, -CH₃), and [{Se(AuPH₃)}₂ {Au(CH₃)₂}₂] models have been performed at Hartree-Fock and second-order M?ller-Plesset perturbation theory levels. There is a good agreement between experimental and theoretical geometries at the MP2 level.

Full text of DOI:10.1021/om010474m

4812
Organometallics 2001, 20, 4812-4818
Mixed Gold (I)-Gold (III) Com p lexes w ith Br id gin g
Selen id o Liga n d s. Th eor etica l Stu d ies of th e
Gold (I)-Gold (III) In ter a ction s
Silvia Canales,† Olga Crespo,† M. Concepcio´n Gimeno,† Peter G. J ones,‡
Antonio Laguna,*,† and Fernando Mendizabal§
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain, Institut fu¨r Anorganische und
Analytische Chemie der Technischen Universita¨t, Postfach 3329, D-38023 Braunschweig,
Germany, and Facultad de Ciencias, Universidad de Chile, Casilla 653,
Santiago de Chile, Chile
Received J une 4, 2001
The gold(I) compounds [Se(AuPPh3)2] and [Se{Au2(µ-dppf)}] (dppf ) 1,1′-bis(diphenylphos-
phino)ferrocene) react with 1 and 2 equiv of [Au(C6F5)3OEt2] to give the mixed gold(I)-gold-
(III) derivatives [Se(AuPPh3)2{Au(C6F5)3}n] and [Se{Au2(µ-dppf)}{Au(C6F5)3}n] (n ) 1, 2). The
reaction of [Se(AuPPh3)2] with [Au(C6F5)2Cl]2 affords the complex [{Se(AuPPh3)}2{µ-Au-
(C6F5)2}2]. The crystal structures of [Se{Au2(µ-dppf)}{Au(C6F5)3}] and [{Se(AuPPh3)}2{µ-Au-
(C6F5)2}2] have been characterized by X-ray diffraction studies. They show dissimilar Au(I)‚
‚‚Au(III) distances, indicating the presence of weak interactions. Quasi-relativistic
pseudopotential calculations on [Se(AuPH3)2(AuR3)], [Se(AuPH3)(AuR3)2]- (R ) -H, -CH3),
and [{Se(AuPH3)}2{Au(CH3)2}2] models have been performed at Hartree-Fock and second-
order Møller-Plesset perturbation theory levels. There is a good agreement between
experimental and theoretical geometries at the MP2 level.
In tr od u ction
energies, 5-15 kcal/mol, similar to or even higher than
for conventional hydrogen bonding.2 This type of inter-
action has been the subject of a number of theoretical
treatments. The dispersion forces, essential in the
stabilization of the systems that show these interac-
tions, are not found at the HF (Hartree-Fock) level.
Therefore, it is necessary to use at least MP2 (second-
order Møller-Plesset perturbation theory)3 level meth-
ods for the complete description of the dispersion forces,
which are included among the correlation effects.4
We are currently working on chalcogenide-centered
gold complexes, and we have previously reported the
synthesis of several sulfur-centered complexes of gold-
(I) and gold(III);5 also, we have described the prepara-
tion of selenium-centered gold(I) species,6 together with
the theoretical studies of the found structures. In both
cases we have described the first example of a quadruply
A strongly attractive and energetically favorable
interaction has been observed between gold(I) atoms
with d10 configurations in numerous polynuclear gold
compounds. The attraction between closed-shell systems
of the type d10-d10 and d10-d8 among heavy metals has
been classified as a metallophilic or van der Waals type.1
Experimental evidence for the aurophilic Au(I)‚‚‚Au(I)
attraction is available from crystallography, NMR and
Raman spectroscopy, and optical spectroscopic measure-
ments of the interaction strength.2 It is manifested in
molecular conformations with metal-metal distances
generally of ca. 3.0 Å and surprisingly high bond
† Universidad de Zaragoza-CSIC.
‡ Institut fu¨r Anorganische und Analytische Chemie der Technis-
chen Universita¨t.
§ Universidad de Chile.
(1) (a) Schmidbaur, H.Chem. Soc. Rev. 1995, 391. (b) Laguna, A. In
Gold, Progress in Chemistry, Biochemistry and Technology; Schmid-
dbaur, H., Ed.; Wiley: New York, 1999. (c) Schmidbaur, H. Pure Appl.
Chem. 1993, 65, 691. (d) Gimeno, M. C.; Laguna, A. Gold Bull. 1999,
32, 90. (e) Crespo, O.; Gimeno, M. C.; Laguna, A. Metal Clusters in
Chemistry; Braunstein, P., Oro, L. A., Raithby, P. R., Eds.; Wiley-
VCH: Weinheim, Germany, 1999. (f) Crespo, O.; Laguna, A.; Ferna´n-
dez, E.; Lo´pez-de-Luzuriaga, J .; J ones, P.; Teichert, M.; Monge, M.;
Pyykko¨, P.; Runeberg, N.; Schu¨tz, M.; Werner, H. Inorg. Chem. 2000,
39, 4786.
(2) (a) J ones, P. G. Gold Bull. 1981, 14, 102. (b) Schmidbaur, H.
Gold Bull. 1990, 23, 11. (c) Gade, L. H. Angew. Chem., Int. Ed. Engl.
1997, 36, 1171. (d) Mansour, M. A.; Connick, W. B.; Lachicotte, R. J .;
Gysling, H. J .; Eisenberg, R. J . J . Am. Chem. Soc. 1998, 120, 1329. (e)
Dziwok, K.; Lachmann, J .; Wilkinson, D. L.; Mu¨ller, G.; Schmidbaur,
H. Chem. Ber. 1990, 123, 423. (f) Schmidbaur, H.; Graf, W.; Mu¨ller,
G. Angew. Chem., Int. Ed. Engl. 1988, 27, 417. (g) 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.
(h) Harwell, M. E.; Mortimer, M. D.; Knobler, C. B.; Anet, F. A. L.;
Hawthorne, M. F. J . Am. Chem. Soc. 1996, 118, 2679.
(3) Møller, C.; Plesset, M. S. J . Chem. Phys. 1934, 46, 618.
(4) (a) Pyykko¨, P. Chem. Rev. 1997, 97, 597. (b) Pyykko¨, P.; Zhao,
Y.-F. Angew. Chem. 1991, 103, 622. (c) Pyykko¨, P.; Li, L.; Runeberg,
N. Chem. Phys. Lett. 1994, 218, 133. (d) Pyykko¨, P.; Mendizabal, F.
Inorg. Chem. 1998, 37, 3018. (e) Runenberg, N.; Schu¨tz, M.; Werner,
H.-J . J . Chem. Phys. 1999, 110, 7210.
(5) (a) Canales, F.; Gimeno, M. C.; J ones, P. G.; Laguna, A. Angew.
Chem., Int. Ed. Engl. 1994, 33, 769. (b) Canales, F.; Gimeno, M. C.;
Laguna, A.; Villacampa, M. D. Inorg. Chim. Acta 1996, 244, 95. (c)
Canales, F.; Gimeno, M. C.; J ones, P. G.; Laguna, A. J . Am. Chem.
Soc. 1996, 118, 4839. (d) Canales, F.; Gimeno, M. C.; Laguna, A.; J ones,
P. G. Organometallics 1996, 15, 3412. (e) Calhorda, M. J .; Canales,
F.; Gimeno, M. C.; J ime´nez, J .; J ones, P. G.; Laguna, A.; Veiros, L. F.
Organometallics 1997, 16, 3837. (f) Canales, F.; Canales, S.; Crespo,
O.; Gimeno, M. C.; J ones, P. G.; Laguna, A. Organometallics 1998,
17, 1617.
(6) (a) Canales, S.; Crespo, O.; Gimeno, M. C.; J ones, P. G.; Laguna,
A. J . Chem. Soc., Chem. Commun. 1999, 679. (b) Canales, S.; Crespo,
O.; Gimeno, M. C.; J ones, P. G.; Laguna, A.; Mendizabal, F. Organo-
metallics 2000, 19, 4985.
10.1021/om010474m CCC: $20.00 © 2001 American Chemical Society
Publication on Web 10/05/2001

Au(I)-Au(III) Complexes with Selenido Ligands
Organometallics, Vol. 20, No. 23, 2001 4813
Sch em e 1a
a
Legend: (i) MeOH, Na2CO3; (ii) [Au(C6F5)3OEt2]; (iii) 2 [Au(C6F5)3OEt2]; (iv) [Au(C6F5)2Cl]2.
bridging sulfido or selenido ligand. Here we report the
synthesis of mixed-valence selenium-centered deriva-
tives whose crystal structures have revealed the pres-
ence of gold(I)-gold(I) and gold(I)-gold(III) interactions.
Our aim is to determine the length and estimate the
strength of these contacts, which are present between
gold(I) and gold(III) in the complexes described here,
and to compare them with corresponding parameters
of gold(I)-gold(I) interactions. For this we will use
quasi-relativistic pseudopotential calculations at the
Hartree-Fock and second-order Møller-Plesset per-
turbation theory levels.
four multiplets for the ortho and meta fluorine in the
ratio 2:2:1:1 and two triplets for the para fluorine in a
ratio 2:1.
In the positive liquid secondary-ion mass spectra
(LSIMS+) the molecular peaks do not appear but the
fragments arising at the loss of pentafluorophenyl units
are present at m/z 1529 (11%) [Se(AuPPh3)2Au(C6F5)2]+
and 1195 (14%) [Se(AuPPh3)2Au]+.
The structure of these compounds has not been
established without ambiguity, but we propose (see
Scheme 1) for complex 1 a structure similar to that
reported below with 1,1′-bis(diphenylphosphino)fer-
rocene (dppf) as the ligand, consisting of a trigonal
pyramid with basal gold atoms and selenium at the
apex. The structure of complex 2 may be similar to that
found in the related sulfur species, [S(AuPPh3)2{Au-
(C6F5)3}2], previously described by us, which involves a
tetrahedral geometry with no short gold-gold inter-
actions.5c
The treatment of [Se(AuPPh3)2] with the gold(III)
compound [Au(C6F5)2Cl]2 in the molar ratio 2:1 leads
to the mixed species [{Se(AuPPh3)}2{µ-Au(C6F5)2}2] (3),
with [AuClPPh3] as byproduct. The mixture could not
be separated, and thus in the spectroscopic data both
compounds were observed and the analytical data are
not reliable.
Resu lts a n d Discu ssion
The reaction of the gold(I) complex [Se(AuPPh3)2] with
1 and 2 equiv of [Au(C6F5)3OEt2] gives the mixed gold-
(I)-gold(III) derivatives [Se(AuPPh3)2{Au(C6F5)3}] (1)
and [Se(AuPPh3)2{Au(C6F5)3}2] (2), respectively. The
products are air-stable colorless solids that behave as
nonconductors in acetone solutions. The IR spectra show
absorptions at around 1505 (s), 996 (s), 805 (s), and 795
(s) cm-1 arising from the presence of pentafluorophenyl
groups bonded to a gold(III) center.
The 31P{1H} NMR spectra show a sharp singlet
resonance at 35.4 (1) and 35.6 ppm (2), indicating the
equivalence of both phosphorus groups. The low-tem-
perature NMR spectra show a different behavior be-
cause the spectrum of compound 1 splits into two
resonances, whereas the single resonance of complex 2
remains unchanged. This is probably attributable to the
presence of a weak gold(I)-gold(III) interaction in
compound 1, which renders the phosphorus atoms
inequivalent. In complex 2 this type of interaction is
absent, probably because the tetrahedral geometry
around the selenium atom does not allow short gold-
(I)-gold(III) interactions.
In the 31P{1H} NMR spectrum the resonance for
[AuClPPh3] is easily identifiable and one more reso-
nance appears for compound 3 as a consequence of the
equivalence of the phosphorus atoms. The low-temper-
ature NMR spectrum also shows only one signal for the
two phosphorus atoms. The 19F NMR spectrum presents
three signals for the equivalent pentafluorophenyl units.
At -55 °C these three signals split into five due to the
lack of rotation of the pentafluorophenyl rings.
In the LSIMS+ spectrum the molecular peak appears
at m/z 2138 (1%); fragmentation peaks are produced for
+
The 19F NMR spectra show a typical pattern for a tris-
(pentafluorophenyl) derivative, consisting of six signals
in a 2:1 ratio for the trans and cis pentafluorophenyl
groups. Each group presents two multiplets for the ortho
and meta fluorine and a triplet for the para fluorine.
At low temperature the rotation of the pentafluorophe-
nyl rings is restricted, and then the spectrum of 1 shows
the loss of AuPPh3 at m/z 1681 (7%).
The crystal structure of complex 3 has been estab-
lished by an X-ray diffraction study, and the molecule
is shown in Figure 1. A selection of bond lengths and
angles is collected in Table 1. The molecule displays
crystallographic inversion symmetry. It consists of two
“SeAu(PPh3)” units bridged by two “Au(C6F5)2” frag-

4814 Organometallics, Vol. 20, No. 23, 2001
Canales et al.
Au(I) interactions). As expected, the narrowest Au-Se-
Au angle, Au(1)-Se-Au(2) ) 88.20(3)°, corresponds to
the shorter Au-Au distance, the other angle Au(1)-
Se-Au(2)#1 is 95.82(3)° with an Au(1)-Au(2)#1 dis-
tance of 3.6385(6) Å. The gold center lies in the plane
formed by the Se, Se#1, C(41), and C(51) atoms and
exhibits square-planar geometry; the narrowest angle
is that in the four-membered ring. The AuIII-Se dis-
tances, Au(2)-Se ) 2.4802(8) Å, are similar to that
found in [AuCl3(SePh2)] (2.445(1) Å).8 The Au-C dis-
tances are somewhat dissimilar (Au-C(41) ) 2.046(8)
Å, Au-C(51) ) 2.070(7) Å), with the shortest trans to
the selenide ligand of the same asymmetrical unit.
The linear geometry exhibited by the Au(1) center is
slightly distorted (P-Au(1)-Se ) 175.14(5)°). The AuI-
Se distance (Au(1)-Se ) 2.4225(9) Å) is similar to the
shortest distance found in [(Au2dppf){Se(Au2dppf)}2]-
(OTf)2 (2.4240(10)-2.4704(10) Å). The value of 2.273-
(2) Å found for the Au(1)-P distance is of the same order
as the highest value found in [(Au2dppf){Se(Au2dppf)}2]-
(OTf)2 (2.259(3)-2.280(2) Å). Both distances compare
well with those found in [Se(AuPPh3)3]PF6.7
F igu r e 1. Structure of complex 3 in the crystal form with
the atom-numbering scheme. Displacement parameter
ellipsoids represent 50% probability surfaces. The H atoms
are omitted for clarity.
The reaction of [Se{Au2(µ-dppf)}] with 1 and 2 equiv
of [Au(C6F5)3OEt2] affords the mixed-valence compounds
[Se{Au2(µ-dppf)}{Au(C6F5)3}] (4) and [Se{Au2(µ-dppf)}-
{Au(C6F5)3}2] (5), respectively (Scheme 2). Complexes
4 and 5 are air- and moisture-stable orange solids that
are nonconductors in acetone solutions. Their IR spectra
show the absorptions arising from the pentafluorophe-
nyl groups bonded to a gold(III) center. The 31P{1H}
NMR spectra present one singlet for the equivalent
phosphorus atoms. The 1H NMR spectra show, apart
from the multiplets due to the phenylic protons, two
broad multiplets for the R- and â-protons of the cyclo-
pentadienyl rings. The low-temperature NMR spectrum
is different for complex 4 or 5; for compound 4 in the
1H NMR spectrum the cyclopentadienyl protons are
inequivalent and then seven resonances appear in the
ratio 1:1:2:1:1:1:1 for the eight protons, whereas the 31P-
{1H} NMR spectrum shows two signals for the two
different phosphorus atoms. Again the different gold-
(I)-gold(III) distances may be responsible for the in-
equivalence of the two phosphorus atoms. For compound
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 3a
Au(1)-P
Au(1)-Se
Au(2)-C(41)
2.273(2)
2.4225(9)
2.046(8)
Au(2)-C(51)
Au(2)-Se
2.070(7)
2.4802(8)
P-Au(1)-Se
175.14(5) Au(2)-Se-Au(2)#1
94.23(3)
110.5(2)
111.3(2)
116.3(2)
C(41)-Au(2)-C(51) 89.7(2)
C(31)-P-Au(1)
C(41)-Au(2)-Se
C(51)-Au(2)-Se
C(41)-Au(2)-Se#1
177.92(18) C(21)-P-Au(1)
92.37(17) C(11)-P-Au(1)
92.14(18) C(42)-C(41)-Au(2) 122.2(5)
C(51)-Au(2)-Se#1 177.94(18) C(46)-C(41)-Au(2) 121.9(5)
Se-Au(2)-Se#1
Au(1)-Se-Au(2)
Au(1)-Se-Au(2)#1
85.77(3) C(52)-C(51)-Au(2) 123.4(5)
88.20(3) C(56)-C(51)-Au(2) 119.6(5)
95.82(3)
a
Symmetry transformations used to generate equivalent at-
oms: (#1) -x, -y, -z + 1.
ments. Because of the symmetry the Se, Au(2), Se#1 and
Au(2)#1 atoms exhibit a perfect rhomboidal arrange-
ment, with internal angles of 85.77(3)° at gold and
94.23(3)° at selenium. Association of two “SeAu3” cores
has been described in [Se(AuPPh3)3]+ 7 and [(Au2dppf)-
{Se(Au2dppf)}2](OTf)2.6b In the first case the association
is only supported by gold‚‚‚gold interactions, whereas
in the second, there are further interactions with an
“Au2dppf” unit connecting two “Se(Au2dppf)” fragments.
1
5 the H NMR spectrum at low temperature shows four
resonances for the cyclopentadienyl protons, whereas
the 31P{1H} NMR spectrum shows the same pattern as
at room temperature.
In the LSIMS+ spectrum of 4 the molecular peak does
not appear but the fragment arising at the loss of one
pentafluorophenyl unit appears at m/z 1558 (41%). For
compound 5 the molecular peak is also not present, but
the fragment at m/z 2254 (7%), arising at the loss of
two pentafluorophenyl units, is observed.
The structure of complex 4 has been determined by
X-ray diffraction studies, and the molecule is shown in
Figure 2. Selected bond lengths and angles are collected
in Table 2. The selenido ligand is bonded to two gold(I)
atoms of an “Au2(µ-dppf)” unit, with a gold-gold contact
of 2.9457(9) Å, and to a gold(III) center. The structure
of the heavy-atom core is therefore trigonal pyramidal
with the selenium at the apex, lying 1.408 Å out of the
plane formed by the three gold atoms. The structure is
similar to those obtained for the trinuclear gold(I)
6b
The compound [Au{Se(Au2dppf)}2]NO3 also contains
triply bridging selenide ligands, but the geometry is
more complicated; two “Au{Se(Au2dppf)}2” units are
bonded through gold‚‚‚gold interactions over and above
those responsible for the association of “SeAu3” cores.
Compound 3 exhibits two triply bridging selenide
ligands. The structure is not supported by gold‚‚‚gold
interactions; the geometry is more comparable to that
in [{S(Au2dppf)}2{Au(C6F5)2}]OTf,5 in which two “S(Au2-
dppf)” units are bridged by an “Au(C6F5)2” fragment. The
shorter gold(I)-gold(III) distance, Au(1)-Au(2) ) 3.4120-
(6) Å, lies between those found in [{S(Au2dppf)}2{Au-
(C6F5)2}]OTf (3.2195(8), 3.366(1), 3.799(1) Å; the short-
est of these distances are comparable to those of Au(I)-
(7) Lensch, C.; J ones, P. G.; Sheldrick; G. M. Z. Naturforsch., B 1982,
37B, 944.
(8) J ones, P. G.; Tho¨ne, C. Z. Naturforsch., B 1990, 46B, 50.

Au(I)-Au(III) Complexes with Selenido Ligands
Organometallics, Vol. 20, No. 23, 2001 4815
Sch em e 2a
a
Legend: (i) MeOH, Na2CO3; (ii) [Au(C6F5)3OEt2]; (iii) 2 [Au(C6F5)3OEt2].
similar Au(I)-Au(III) distances, 3.5330(8) and 3.8993-
(8) Å, one much shorter than the other. These distances
are of the same order as those obtained for the similar
complex with a bridging sulfido ligand, 3.404(1) and
3.759(1) Å.5d These data indicate the existence of an Au-
(I)‚‚‚Au(III) interaction that, although weak, is able to
reduce the symmetry in the molecule and thus render
the gold(I) atoms inequivalent, as also detected in the
31P{1H} NMR spectrum. The Au-Se-Au angles are also
dissimilar. Of necessity, narrower Au-Se-Au angles
are correlated with shorter gold-gold contacts, and thus
the narrower angle corresponds to that between the two
gold(I) atoms, Au(1)-Se-Au(2) ) 73.81(3)°, whereas the
angles subtended by the gold(I) and the gold(III) atoms
are 91.01(4) and 103.63(4)°. The Au-Se distances to the
gold(I) atoms are 2.4486(12) and 2.4569(11) Å, slightly
longer than those in the starting material, 2.4218(11)
and 2.4055(11) Å.6b The AuIII-Se bond distance of
2.5038(13) Å is longer than that found in complex 3 and
also in [AuCl3(SePh2)] (2.445(1) Å).8 The geometry for
the gold atoms is in accordance with their oxidation
state, with a slight deviation of the gold(I) atoms from
linearity (angles 174.16(7) and 175.51(8)°).
F igu r e 2. Structure of complex 4. Displacement param-
eter ellipsoids represent 50% probability surfaces. The H
atoms are omitted for clarity.
Th eor et ica l Ca lcu la t ion s. The compounds de-
scribed in the Experimental Section show AuI-AuI,
AuI-AuIII, and AuIII-AuIII contacts. It is observed that
as the oxidation state of the gold center increases the
metal-metal distance increases, and thus the order is
AuIII-AuIII > AuIII-AuI > AuI-AuI. We have carried
out ab initio calculations at the MP2 and HF levels with
quasi-relativistic pseudopotentials with the objective of
understanding the origin of metal-metal interactions.
In complex 4, [Se{Au2(µ-dppf)}{Au(C6F5)3}], the two
Au(I) centers are separated by 2.95 Å and are bridged
by a ferrocenyl phosphine. This distance is classical in
gold(I) complexes. The two AuI-AuIII distances, on the
other hand, are 3.53 and 3.89 Å, whose average is 3.72
Å. These data indicate the existence of a weak but
important AuI-AuIII interaction. Similar short distances
involving gold(III) are observed in the compound 3, [{Se-
(AuPPh3)}2{µ-Au(C6F5)2}2]; that between Au(I) and Au-
(III) is 3.41 Å and that between Au(III) and Au(III) is
3.63 Å, clearly longer than those observed for AuI-AuI
systems.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 4
Au(1)-P(1)
Au(1)-Se
Au(1)-Au(2)
Au(2)-P(2)
Au(2)-Se
2.266(3)
Au(3)-C(61)
Au(3)-C(71)
Au(3)-C(51)
Au(3)-Se
2.060(12)
2.079(11)
2.079(11)
2.5038(13)
2.4569(11)
2.9457(9)
2.269(3)
2.4486(12)
P(1)-Au(1)-Se
174.16(7) Au(1)-Se-Au(3)
121.34(7) C(1)-P(1)-Au(1)
52.97(3) C(11)-P(1)-Au(1)
175.51(8) C(21)-P(1)-Au(1)
122.77(7) C(6)-P(2)-Au(2)
53.23(3) C(31)-P(2)-Au(2)
103.63(4)
111.0(3)
115.8(3)
113.9(3)
109.7(3)
112.3(3)
115.4(3)
P(1)-Au(1)-Au(2)
Se-Au(1)-Au(2)
P(2)-Au(2)-Se
P(2)-Au(2)-Au(1)
Se-Au(2)-Au(1)
C(61)-Au(3)-C(71)
C(61)-Au(3)-C(51)
88.8(4)
90.2(4)
C(41)-P(2)-Au(2)
C(56)-C(51)-Au(3) 121.7(7)
C(52)-C(51)-Au(3) 124.3(7)
C(66)-C(61)-Au(3) 123.4(7)
C(62)-C(61)-Au(3) 121.7(8)
C(76)-C(71)-Au(3) 121.0(7)
C(71)-Au(3)-C(51) 177.5(3)
C(61)-Au(3)-Se
C(71)-Au(3)-Se
C(51)-Au(3)-Se
Au(2)-Se-Au(1)
Au(2)-Se-Au(3)
177.7(2)
92.4(3)
88.4(3)
73.81(3) C(72)-C(71)-Au(3) 122.7(7)
91.01(4)
derivatives with a central selenium atom6b,7 that present
short gold-gold contacts. In this molecule the shortest
distance corresponds to gold(I)-gold(I), 2.9457(9) Å,
which is of the same order as that found in the starting
material, [Se{Au2(µ-dppf)}],6b and there are two dis-
In addition to the models [Se(AuPH3)2(AuR3)] (R )
-H (a), -CH3 (b)) and [(Se(AuPH3))2(Au(CH3)2)2] (e),
which represent the experimental complexes, we have

4816 Organometallics, Vol. 20, No. 23, 2001
Ta ble 3. Ma in P a r a m eter s of th e Selen iu m -Cen ter ed System s (Dista n ces in Å)
Canales et al.
system
method
exptl
Se-AuI
Se-AuIII
AuI-AuI
AuI-AuIII
AuIII-AuIII
[Se(Au2dppf){Au(C6F5)3}]
2.453
2.504
2.946
3.72
(3.53/3.89)
3.412
3.729
3.545
3.717
3.602
3.562
3.346
3.862
3.615
3.895
3.477
[{Se(AuPPh3)}2{Au(C6F5)2}2]
[Se(AuPH3)2(AuH3)] (Cs) (a)
exptl
HF
MP2
HF
MP2
HF
MP2
HF
2.423
2.483
2.452
2.481
2.453
2.471
2.423
2.473
2.432
2.458
2.431
2.480
2.661
2.664
2.584
2.551
2.636
2.552
2.582
2.547
2.623
2.551
3.634
3.648
2.937
3.640
2.930
[Se(AuPH3)2{Au(CH3)3}] (Cs) (b)
[Se(AuPH3)(AuH3)2]- (Cs) (c)
4.266
3.494
4.310
3.970
3.899
3.702
[Se(AuPH3){Au(CH3)3}2]- (Cs) (d)
[{Se(AuPH3)}2{Au(CH3)2}2](Cs) (e)
MP2
HF
MP2
Ta ble 4. Ma in P a r a m eter s of th e Selen iu m -Cen ter ed System s (Dista n ces in Å a n d An gles in d eg)
system
method
Au-H
Au-C
Au-P
AuI-Se-AuI
AuI-Se-AuIII
AuIII-Se-AuIII
[Se(Au2dppf){Au(C6F5)3}]
[{Se(AuPPh3)}2{Au(C6F5)2}2]
[Se(AuPH3)2(AuH3)] (Cs) (a)
exptl
exptl
HF
MP2
HF
MP2
HF
MP2
HF
2.062
2.070
2.255
2.273
2.410
2.307
2.412
2.313
2.393
2.279
2.384
2.285
2.407
2.407
73.8
91.0
88.2
92.8
80.0
94.4
92.1
88.39
84.52
99.6
93.1
100.1
87.9
94.2
1.617
1.627
94.55
73.58
94.20
73.61
[Se(AuPH3)2{Au(CH3)3}] (Cs) (b)
[Se(AuPH3)(AuH3)2]- (Cs) (c)
2.083
2.068
1.623
1.633
108.1
86.4
113.3
102.4
96.04
93.1
[Se(AuPH3){Au(CH3)3}2]- (Cs) (d)
[{Se(AuPH3)}2{Au(CH3)2}2](Cs) (e)
2.082
2.066
2.079
2.071
MP2
HF
MP2
an estimation of the contribution of the electronic
correlation to the intramolecular contacts for these
clusters. Since it has been suggested that aurophilic
attraction is primarily a correlation effect, when we
compare the results at HF level, we can recognize the
real effect of the electronic correlation.4
[Se(Au P H3)2(Au R3)]. This model was partially op-
timized with Cs symmetry, although the real cluster
does not exhibit this symmetry, as one AuI-AuIII
distance is shorter than the other. The distance Au-
(III)-R (R ) -H and -CH3) is also allowed to change,
but not the square-planar Au(III) environment. The
final geometry around the selenium atom is pyramidal,
with shorter Se-Au(I) than Se-Au(III) bonds. The MP2
results show a better agreement with the experimental
results, whereas the HF calculations lead to relatively
long distances. The distance Au(I)-Au(I) in both models
(2.94 and 2.92 Å) is close to that of the original complex
at MP2 level (see Table 3). On the other hand, the
distance AuI-AuIII in the model with R ) -CH3 (3.60
Å (MP2)) is closer to the experimental average (3.64 Å).
However, this distance in the system with R ) -H is
below the experimental value. This implies that the use
of the -H ligands bonded to gold(III) produces an exag-
geration of the attraction among both metallic centers.
F igu r e 3. Geometries of the models.
It is also possible to recognize this effect in some
angles. For example, the Au(I)-Se-Au(I) angle in both
models at MP2 level is close to the experimental value
73°. Whereas the Au(I)-Se-Au(III) angle with R )
-CH3 shows the value of 92° at MP2 level, close to the
89° experimental value. However, the angle with R )
-H is 80°, which again indicates an exaggerated
interaction between Au(I) and Au(III) (see Table 3).
[Se(Au P H 3)(Au R3)2]-. We have proposed to study
this model, which has no experimental prototype, to
estimate the AuIII-AuIII contact. The clusters (R ) -H,
-CH3) were optimized following the same lines as
described above. In both models the AuI-AuIII distances
included one hypothetical cluster: [Se(AuPH3)(AuR3)2]-
(R ) -H (c), -CH3 (d)). This will complete the range of
the AuI-AuIII and AuIII-AuIII interactions in the sys-
tems under study.
The optimized geometries are shown in Tables 3 and
4, together with relevent experimental structural data.
The models are illustrated in Figure 3. It can be seen
that the structural parameters change substantially
when they are compared at HF and MP2 levels. The
gold-gold distances and Au-Se-Au angles are signifi-
cantly shortened for the latter method and comparable
in magnitude to the experimental values. This allows

Au(I)-Au(III) Complexes with Selenido Ligands
Organometallics, Vol. 20, No. 23, 2001 4817
Ta ble 5. NBO Ch a r ges for th e Mod els
system
method
Au(I)
Au(III)
Se
P
H(bond to Au)
C
[Se(AuPH3)2(AuH3)] (a)
HF
MP2
HF
MP2
HF
MP2
HF
MP2
HF
MP2
0.39
0.23
0.39
0.28
0.40
0.23
0.40
0.29
0.37
0.22
0.69
0.49
0.96
0.87
0.71
0.50
0.88
0.78
0.89
0.67
-0.94
-0.63
-0.91
-0.66
-0.94
-0.68
-0.86
-0.55
-0.97
-0.63
0.19
0.17
0.20
0.18
0.21
0.18
0.21
0.19
0.20
0.17
-0.15
-0.11
[Se(AuPH3)2{Au(CH3)3}] (b)
[Se(AuPH3)(AuH3)2]- (c)
-0.82
-0.84
-0.21
-0.18
[Se(AuPH3){Au(CH3)3}2]- (d)
[{Se(AuPH3}2{Au(CH3)2}2] (e)
-0.82
-0.85
-0.83
-0.85
are much shorter than the AuIII-AuIII, at HF and MP2
levels (see Table 3). However, the [Se(AuPH3)(AuH3)2]-
system shows an overestimated attraction Au-Au at
Syn th esis of [Se(Au P P h 3)2{Au (C6F 5)3}] (1). To a solution
of [Se(AuPPh3)2] (0.100 g, 0.1 mmol) in 20 mL of dichlo-
romethane was added [Au(C6F5)3(OEt2)] (0.0772 g, 0.1 mmol)
and the mixture stirred for 15 min. Concentration of the
solution to ca. 5 mL and addition of hexane (10 mL) gave
MP2 level, 3.34 and 3.49 Å for AuI-AuIII and AuIII
-
AuIII, respectively. In the [Se(AuPH3)(Au(CH3)3)2]- model,
on the other hand, the AuI-AuIII distance is 3.62 Å, and
AuIII-AuIII is 3.97 Å at the MP2 level. The AuI-AuIII
distances in the [Se(AuPH3)2(Au(CH3)3)] model are
comparable to the observed values.
[Se2(Au P H3)2(Au (CH3)2)2]. This model describes the
experimental complex [Se2(AuPPh3)2(Au(C6F5)2)2]. We
have optimized the structure assuming Cs symmetry.
The results are shown in Tables 3 and 4. Compared with
experimental values, the HF Au-Au distances and the
Au-Se-Au angles are too large. The results change at
the MP2 level; the calculated Au-Au distances are close
to the experimental values. A similar trend is observed
for the Au-Se-Au angles. Due to the effect of the
electronic correlation at the MP2 level, the distances and
angles are shorter than at the HF level.
The MP2 calculations are able to reproduce the
structural trends found in the experimental complexes.
Before proceeding, we wish to compare the charges
obtained on the natural bond orbital (NBO)9 population
at the HF and MP2 levels, which are shown in Table 5.
The data show in all the models a reduction of the
formal oxidation state by the gold and selenium atoms
when the calculation methods go from HF to MP2,
although the charge distribution on the gold(I) atoms
at HF and MP2 levels in the different models does not
change substantially. However, the charge on the gold-
(III) atoms at the MP2 level is less when the ligand
bonded at gold (III) is -H rather than the group -CH3.
The -H ligand produces an increase in the charge
density on the gold(III), and thus this ligand is not a
good model.
complex 1 as a white solid. Yield: 56%. ΛM ) 15 Ω-1 cm2 mol-1
.
Anal. Found: C, 38.01; H, 1.45. Calcd for C54H30Au3F15P2Se:
C, 38.23; H, 1.76. 31P{1H} NMR (δ): room temperature, 35.4
(s); -55 °C, 33.85 (s), 34.65 (s). 19F NMR (δ): -119.1 (m, 4F,
o-F), -121.6 (m, 2F, o-F), -160.40 (t, 1F, p-F, 3J (FF) ) 19 Hz),
-160.47 (t, 2F, p-F, 2J (FF) ) 20 Hz), -163.1 (m, 2F, m-F);
-55 °C, -118.6 (m, 2F, o-F), -119.6 (m, 2F, o-F), -122.6 (m,
3
1F, o-F), -122.7 (m, 1F, o-F), -158.4 (t, 1F, p-F, J (FF) = 21
3
Hz), -159.4 (t, 2F, p-F, J (FF) = 21 Hz), -161.8 (m, 3F, m-F),
-162.2 (m, 1F, m-F), -162.8 (m, 2F, m-F).
Syn th esis of [Se(Au P P h 3)2{Au (C6F 5)3}2] (2). To a solution
of [Se(AuPPh3)2] (0.100 g, 0.1 mmol) in 20 mL of dichlo-
romethane was added [Au(C6F5)3(OEt2)] (0.1544 g, 0.2 mmol)
and the mixture stirred for 15 min. Concentration of the
solution to ca. 5 mL and addition of hexane (10 mL) gave
complex 2 as a white solid. Yield: 60%. ΛM ) 18 Ω-1 cm2 mol-1
.
Anal. Found: C, 35.87; H, 1.31. Calcd for C72H30Au4F30P2Se:
C, 36.12; H, 1.25. 31P{1H} NMR (δ): 35.6 (s). 19F NMR (δ):
-120.2 (m, 8F, o-F), -122.3 (m, 4F, o-F), -156.6 (t, 4F, p-F,
3
3J (FF) ) 20 Hz), -157.1 (t, 2F, p-F, J (FF) ) 20 Hz), -161.1
(m, 8F, m-F), -161.5 (m, 4F, m-F).
Syn th esis of [{Se(Au P P h 3)}2{µ-Au (C6F 5)2}2] (3). To a
solution of [Se(AuPPh3)2] (0.200 g, 0.2 mmol) in 20 mL of
dichloromethane was added [Au(C6F5)2Cl]2 (0.1133 g, 0.1
mmol) and the mixture stirred for 15 min. Concentration of
the solution to ca. 5 mL and addition of diethyl ether (10 mL)
gave complex 3 as a white solid. Yield: 55%. ΛM ) 9 Ω-1 cm2
mol-1 31P{1H} NMR (δ): 37.8 (s, 2P, AuPPh3), 33.8 (s, 1P,
.
[AuCl(PPh3)]). 19F NMR (δ): room temperature, -120.9 (m, 8F,
o-F), -158.3 (t, 4F, p-F, 3J (FF) ) 20 Hz), -161.8 (m, 8F, m-F);
-55 °C, -120.8 (m, 4F, o-F), -121.0 (m, 4F, o-F), -157.4 (t,
4F, p-F, 3J (FF) ) 21 Hz), -160.8 (m, 4F, m-F), -161.3 (m, 4F,
m-F).
Syn th esis of [Se{Au 2(µ-d p p f)}{Au (C6F 5)3}] (4). To a
solution of [Se{Au2(µ-dppf)}] (0.102 g, 0.1 mmol) in 20 mL of
dichloromethane was added [Au(C6F5)3(OEt2)] (0.0772 g, 0.1
mmol) and the mixture stirred for 15 min. Concentration of
the solution to ca. 5 mL and addition of hexane (10 mL) gave
complex 2 as an orange solid. Yield: 66%. ΛM 1.4 Ω-1 cm2
Exp er im en ta l Section
In str u m en ta tion . Infrared spectra were recorded in the
range 4000-200 cm-1 on a Perkin-Elmer 883 spectrophotom-
eter using Nujol mulls between polyethylene sheets. Conduc-
tivities were measured in ca. 5 × 10-4 mol dm-3 solutions with
a Philips 9509 conductimeter. C, H, and S analyses were
carried out with a Perkin-Elmer 2400 microanalyzer. Mass
spectra were recorded on a VG Autospec, with the LSIMS
technique, using nitrobenzyl alcohol as matrix. NMR spectra
were recorded on a Varian Unity 300 spectrometer or Bruker
ARX 300 spectrometer in CDCl3 (otherwise stated). Chemical
shifts are cited relative to SiMe4 (1H, external) and 85% H3-
PO4 (31P, external).
mol-1. Anal. Found: C, 36.40; H, 1.75. Calcd for C52H28Au3F15
-
FeP2Se: C, 36.17; H, 1.62. 1H NMR (δ): room temperature,
4.5 (m, br, 4H, C5H4), 3.9 (m, br, 4H, C5H4); -55 °C, 5.01 (m,
1H, C5H4), 4.92 (m, 1H, C5H4), 4.47 (m, 2H, C5H4), 4.23 (m,
1H, C5H4), 4.02 (m, 1H, C5H4), 3.35 (m, 1H, C5H4), 4.29 (m,
1H, C5H4). Room temperature 31P{1H} NMR (δ): 28.8 (s); -55
°C, 28.9 (s), 27.1 (s). 19F NMR (δ): room temperature, -118.7
3
(m, 4F, o-F), -122.5 (m, 2F, o-F), -158.7 (t, 2F, p-F, J (FF) )
21.3 Hz), -159.7 (t, 1F, p-F, 3J (FF) ) 19.2 Hz), -162.7 (m, 2F,
Ma ter ia ls. The starting materials [Se(AuPPh3)2],10 [Se{Au2-
12
(µ-dppf)}],5 [Au(C6F5)3(OEt2)],11 and [Au(C6F5)2Cl]2
were
(10) J ones, P. G.; Tho¨ne, C. Chem. Ber. 1991, 124, 2725.
(11) Uso´n, A.; Laguna, A.; Laguna, M.; J ime´nez, J .; Durana, E.
Inorg. Chim. Acta 1990, 168, 89.
prepared by published procedures.
(12) Uso´n, A.; Laguna, A.; Laguna, M.; Abad, A. J . Organomet.
Chem. 1983, 249, 437.
(9) Raghavachari, K.; Trucks, G. W. J . Phys. Chem. 1989, 91, 2457.

4818 Organometallics, Vol. 20, No. 23, 2001
Canales et al.
Ta ble 6. Ba sis Sets a n d P seu d op oten tia ls (P P s)
Used in th e P r esen t Wor k
Ta ble 7. Deta ils of Da ta Collection a n d Str u ctu r e
Refin em en t for Com p lexes 3 a n d 4
atom
PP
VE
basis
remarks
3
4
chem formula
C
61H32Au4Cl2-
C60H48Au3Cl2F15
FeOP2Se
-
H
C
P
Se
Au
(4s1p)/[2s1p]
Rp ) 0.80
Rd ) 0.80
Rd ) 0.34
Rd ) 0.25
Rf ) 0.20
F
20P2Se2
Bergner
Bergner
Bergner
Andrae
4
5
6
(4s4p1d)/[2s2p1d]
(4s4p1d)/[2s2p1d]
(4s4p1d)/[2s2p1d]
(8s6p5d1f)/[6s5p3d1f]
cryst habit
cryst size/mm
cryst syst
space group
a/Å
b/Å
c/Å
colorless plate
0.40 × 0.25 × 0.10
triclinic
P1h
9.4464(12)
12.4953(14)
14.279(2)
102.892(10)
92.724(10)
99.303(10)
1515.2(4)
1
orange tablet
0.70 × 0.30 × 0.10
triclinic
P1h
19
12.344(2)
17.362(2)
17.889(3)
97.78(10)
108.15(10)
109.65(10)
3305.2(9)
2
m-F), -162.9 (m, 4F, m-F); -55 °C, -117.1 (m, 2F, o-F), -119.9
3
(m, 2F, o-F), -122.7 (m, 2F, o-F), -157.7 (t, 2F, p-F, J (FF) )
20.0 Hz), -158.7 (t, 1F, p-F, 3J (FF) ) 20.9 Hz), -161.6 (m,
2F, m-F), -161.7 (m, 2F, m-F), -162.3 (m, 2F, m-F).
R/deg
â/deg
γ/deg
Syn th esis of [Se{Au 2(µ-d p p f)}{Au (C6F 5)3}2] (5). To a
solution of [Se{Au2(µ-dppf)}] (0.102 g, 0.1 mmol) in 20 mL of
dichloromethane was added [Au(C6F5)3(OEt2)] (0.1544 g, 0.2
mmol) and the mixture stirred for 15 min. Concentration of
the solution to ca. 5 mL and addition of hexane (10 mL) gave
complex 5 as an orange solid. Yield: 60%. ΛM 8.3 Ω-1 cm2
U/Å3
Z
Dc/g cm-3
M
2.286
2223.49
1026
1.38
1928.53
1824
F(000)
T/°C
-100
-100
2θmax/deg
µ(Μo KR)/mm-1
transmissn
no. of rflns measd
no. of unique rflns
Rint
50
50
mol-1. Anal. Found: C, 34.96; H, 1.27. Calcd for C70H28Au4F30
-
10.41
7.61
FeP2Se: C, 34.67; H, 1.15. 1H NMR (δ): room temperature,
4.35 (m, 4H, C5H4), 3.50 (m, 4H, C5H4); -55 ° C, 4.56 (m, 2H,
C5H4), 4.40 (m, 2H, C5H4), 4.16 (m, 2H, C5H4), 3.31 (m, 2H,
C5H4). 31P{1H} NMR (δ): room temperature, 29.5 (s); -55 °C,
0.409, 0.990
6025
0.5165, 0.0758
12 286
11 290
0.051
5652
0.0262
R(F > 4σ(F))a
Rw(F2, all rflns)b
no. of rflns used
no. of params
no. of restraints
Sc
0.0318
0.0477
0.1332
11 290
744
28.7 (s, 2P, J (PSe) ) 484 Hz). 19F NMR (δ): room tempera-
2
0.0613
5652
409
365
0.878
1.196
ture, -121.7 (m, 4F, o-F), -122.3 (m, 8F, o-F), -156.3 (t, 4F,
p-F, 3J (FF) ) 20 Hz), -157.1 (t, 2F, p-F, 3J (FF) ) 20 Hz),
-161.4 (m, 12F, m-F); -55 °C, -119.5 (m, 4F, o-F), -122.4
698
1.038
3
(m, 4F, o-F), -122.5 (m, 4F, o-F), -155.9 (t, 4F, p-F, J (FF) )
max ∆F/e Å-3
1.61
20 Hz), -156.5 (t, 2F, p-F, 3J (FF) ) 20 Hz), -160.5 (m, 4F,
m-F), -160.8 (m, 4F, m-F), -161.6 (m, 4F, m-F).
a
b
2
R(F) ) ∑||Fo| - |Fc|/∑|Fo|. Rw(F2) ) [∑{w(Fo - Fc2)2}/
∑{w(Fo2)2}]0.5; w-1 ) s2(Fo2) + (aP)2 + bP, where P ) [Fo2+2Fc2]/3
Cr ysta l Str u ctu r e Deter m in a tion s. The crystals were
mounted in inert oil on glass fibers and transferred to the cold
gas stream of the Siemens P4 diffractometer. Data were
collected using monochromated Mo KR radiation (λ ) 0.71073
Å) in ω-scan mode (3) or θ-2θ (4). Absorption corrections were
applied on the basis of Ψ-scans. The structures were solved
by the heavy-atom method and refined on F2 using the
program SHELXL-97.13 All non-hydrogen atoms were refined
anisotropically except for solvent. Hydrogen atoms were
included using a riding model. Further crystal data are given
in Table 6. Special details of refinement: The dichloromethane
solvent in 3 is disordered over an inversion center. In 4 the
dichloromethane is disordered over two positions, and further
solvent regions were tentatively identified as a pentane and
an ethanol molecule. These assignments, and the associated
occupation factors and derived parameters, should obviously
be interpreted with caution.
Ga u ssia n 98 Ca lcu la tion s. The Gaussian 98 package14
was used. The basis sets and pseudopotentials (PP) used in
the production runs are given in Table 7. The 19-valence-
electron (VE) quasi-relativistic (QR) pseudopotential (PP) of
Andrae15 was employed for gold. We have employed one f-type
polarization function for Au. The f orbital is necessary for the
weak intermolecular interactions, as was demonstrated previ-
ously for various metals.4 The atoms C, P, and Se were also
2
and a and b are constants adjusted by the program. c S ) [∑{w(Fo
- Fc2)2}/(n - p)]0.5, where n is the number of data and p the
number of parameters.
treated by Stuttgart pseudopotentials,16 including only the
valence electron for each atom. For these atoms, double-ú basis
sets were used, augmented by d-type polarization functions.
For the H atom, a double-ú plus one p-type polarization
function was used (see Table 6).17
We have optimized the structures for the models [Se-
(AuPH3)2(AuR3)] (R ) -H, -CH3; Cs), [Se(AuPH3)(AuR3)2]- (R
) -H, -CH3; Cs), and [Se2(AuPH3)2(Au(CH3)2)2] (Cs) at the
Hartree-Fock (HF) and second-order Møller-Plesset pertur-
bation theory (MP2) levels (see Figure 3). In the experimental
structures, the triphenylphosphine, -P(C6H5)3, is replaced by
-PH3, the ferrocene-bridged ligands by -H, and -C6F5 by -H
and -CH3. The original ligands would involve a large compu-
tational effort. If the rotation of the terminal -PH3 and -CH3
ligands would have broken the symmetry, their dihedral angle
was fixed.
Ack n ow led gm en t. We thank the Direccio´n General
de Investigacio´n Cient´ıfica y Te´cnica (No. PB97-1010-
C02-01), the Caja de Ahorros de la Inmaculada (CB16/
99), and the Fonds der Chemischen Industrie for
financial support. This work was partially supported by
Project CSIC-Universidad de Chile, and Fondecyt No.
1990038.
(13) Sheldrick, G. M. SHELXL-97, a Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
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