Syntheses, structures and DFT study of [W(CO)5(Ph2SbX)] X = Cl, Br, I

Article abstract of DOI:10.1016/j.jorganchem.2007.03.007

The complexes [W(CO)₅(Ph₂SbX)], X = Cl (1), Br (2) and I (3) were prepared by reaction of [W(CO)₅(tetrahydrofuran)] with Ph₂SbX. The structures of 1-3 were studied by X-ray diffraction. In the crystals there are weak contacts between the oxygen atoms of the CO ligands and antimony atoms of neighbouring molecules. DFT calculations were carried out for 1 using gradient corrected functional B3LYP. The bonding between Ph₂SbCl and the W(CO)₅ fragment in 1 was analysed using charge decomposition analysis.

Full text of DOI:10.1016/j.jorganchem.2007.03.007

Journal of Organometallic Chemistry 692 (2007) 2593–2598
www.elsevier.com/locate/jorganchem
Syntheses, structures and DFT study of [W(CO)5(Ph2SbX)]
X = Cl, Br, I
a,
b
a
a
H.J. Breunig *, T. Borrmann , E. Lork , C.I. Raßt
Institut fu¨r Anorganische und Physikalische Chemie, Fachbereich 2 der Universita¨t Bremen, Postfach 330 440, D-28334 Bremen, Germany
a
b
Institut fu¨r Organische Chemie, Fachbereich 2 der Universita¨t Bremen, Postfach 330 440, D-28334 Bremen, Germany
Received 16 January 2007; received in revised form 26 February 2007; accepted 2 March 2007
Available online 12 March 2007
Abstract
The complexes [W(CO)5(Ph2SbX)], X = Cl (1), Br (2) and I (3) were prepared by reaction of [W(CO)5(tetrahydrofuran)] with Ph2SbX.
The structures of 1–3 were studied by X-ray diffraction. In the crystals there are weak contacts between the oxygen atoms of the CO
ligands and antimony atoms of neighbouring molecules. DFT calculations were carried out for 1 using gradient corrected functional
B3LYP. The bonding between Ph2SbCl and the W(CO)5 fragment in 1 was analysed using charge decomposition analysis.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Antimony; Tungsten; X-ray structure; DFT
1. Introduction
2. Results and discussion
Pentacarbonyl metal complexes with diorganoanti-
mony halide ligands of the type [M(CO)5(R2SbX)] possess
a functional group at antimony and hence they can be
useful as antimony reagents with protection by the metal
carbonyl fragment. The inspection of their crystal struc-
tures and theoretical calculations allow to study the effect
of coordination on the geometry of the R2SbX unit.
Several complexes of this type have been synthesised
[1–5]; none of them was studied by X-ray diffraction.
We chose the series [W(CO)5(Ph2SbX)], X = Cl (1), Br
(2) and I (3) for an inspection of the crystal structures
and selected 1 for a study at the DFT level. The synthesis
and characterisation of 1 [1] and the crystal structures of
the free ligands Ph2SbX (X = Cl [6], Br [7], I [8]) were
reported before.
[W(CO)5(Ph2SbCl)] (1) was prepared by the exchange
reaction between [W(CO)5(THF)] (THF @ tetrahydrofu-
ran) and diphenylantimony chloride as described by
Wieber and Graf [1]. An analogous procedure led to
[W(CO)5(Ph2SbX)] [X = Br (2), I (3)]. Yellow green (1) or
yellow (2, 3) single crystals were obtained by cooling solu-
tions in petroleum ether. The crystals are air stable and well
soluble in organic solvents. Also thermally 1–3 are rela-
tively stable. They melt without decomposition above
80 ꢁC but become slowly brown after further heating of
the liquids. The structures of 1–3 were determined by single
crystal X-ray diffraction. The molecules are composed of
pyramidal Ph2SbX units coordinated through the anti-
mony atoms to tetragonal pyramidal W(CO)5 fragments.
The phenyl groups adopt a propeller like arrangement.
As a representative example the structure of 3 is depicted
in Fig. 1. Relevant bond lengths and bond angles of 1–3
and of the non-coordinated diphenylantimony halides are
listed in Table 2.
*
The Sb–W bonds in 1: 2.7184(10), 2: 2.7243(8), 3:
2.7256(7) A are slightly shorter than the corresponding
Corresponding author. Tel.: +49 421 218 2266; fax: +49 421 218 4042.
E-mail address: breunig@chemie.uni-bremen.de (H.J. Breunig).
˚
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.03.007

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H.J. Breunig et al. / Journal of Organometallic Chemistry 692 (2007) 2593–2598
between oxygen atoms of carbonyl groups and antimony
atoms of the neighbouring molecules. These distances are
close to the sum of van der Waals radii of antimony and
P
˚
oxygen [ rvdW(Sb, O) 3.52 A] [12]. Although it appears
that the intermolecular Sbꢀ ꢀ ꢀO contacts are very weak it
is remarkable that the oxygen atoms of the neighbouring
molecules occupy positions trans to the Sb–Cl bonds
(Cl–Sbꢀ ꢀ ꢀO 172.39(14)ꢁ). This pattern is typical for
Lewis-acid–base interactions between diorgano antimony
halides and donor molecules [13]. In an analogous manner
also the dimeric association of 1 in the crystal may result
from a very weak intermolecular Lewis-acid–base interac-
tion, which leads to the bridging coordination of the CO
molecule between tungsten and antimony. The interaction
M–COꢀ ꢀ ꢀM0 in 1 leads to an elongation of the C–O bond.
In fact the bond length of the CO group involved in the
Fig. 1. ORTEP style representation at 50% probability and the numbering
scheme of [W(CO)5(Ph2SbI)] (3).
˚
intermolecular interaction with 1.154 A is the longest
encountered in 1–3. Examples of complexes with a CO
group coordinated to a second metal centre are well known
[14,15]. Bridging CO groups between a transition metal and
a p block elements were reported in the structures of [{g-
˚
bonds in [W(CO)5(Ph3Sb)] 2.745(1) A [9], [{W(CO)5}n-
˚
{(Ph2Sb)2CH2}], n = 1; 2.743(1), n = 2; 2.756(2) A [10], or
[{W(CO)5}2(Ph2Sb2)] 2.749(1) A [11]. The values for the
W–C bond lengths in 1–3 range from 1.989(8) to
2.056(6) A. The W–C bonds trans to the Ph2SbX ligands
˚
C5H5W(CO)3(AlMe2)}2]
1.793(18) A) [16] and [Co(Ph3P)2(CO)3BEt3] (C–O
(C–O
1.18(3),
COꢀ ꢀ ꢀAl
˚
˚
˚
1.157(4), COꢀ ꢀ ꢀB 1.601(5) A) [17]. In crystals of 1 there
˚
˚
˚
are in average 3% (0.048 A in 1, 0.047 A in 2 and 0.044 A
in 3) shorter than those in cis positions. The C–O bond
lengths lie between 1.114(8) and 1.154(11) A close to the
values encountered in related complexes [9–11]. The Sb–C
and the Sb–halogen bonds are a little shorter in the com-
plexes than in the free ligands. A remarkable result of the
coordination is the widening of the C–Sb–C and C–Sb–X
bond angles. The sum of the bond angles, i. e. C–Sb–C
and C–Sb–X at antimony is between 8ꢁ and 11ꢁ larger in
the complexes 1–3 than in the free ligands.
are also weak intermolecular contacts between the oxygen
atom of the bridging CO group and the ortho hydrogen
atoms of the closest phenyl ring. The contact distance
˚
˚
(Hꢀ ꢀ ꢀO 2.641 A) is close to the sum of van der Waals radii
P
˚
of the respective elements [ vdW(H, O) ca. 2.72 A].
˚
Weak intermolecular Sbꢀ ꢀ ꢀO contacts [3.368(5) A] exist
also in crystals of 2. The Br–Sbꢀ ꢀ ꢀO angle of 156.58(9)ꢁ
indicates a considerable deviation from an ideal trans
arrangement. Through the Sbꢀ ꢀ ꢀO interactions the mole-
cules of 2 are arranged to infinite chains. Between the
Interesting differences emerge also when the packing of
1–3 in the crystal is inspected. Crystals of 1 contain pairs
of molecules (Fig. 2), with contact distances of 3.451(8) A
˚
chains there are weak contacts (Hꢀ ꢀ ꢀO 2.64 A) connecting
the oxygen atoms of carbonyl groups and para-hydrogen
atoms of phenyl groups. A section of two chains in the
crystals of 2 is shown in Fig. 3.
˚
Also the molecules of 3 are arranged in infinite chains
through weak intermolecular interactions between anti-
mony and oxygen atoms of carbonyl groups. The shortest
˚
Sbꢀ ꢀ ꢀO distance is 3.548(6) A, right at the van der Waals
limit. The angle I–Sbꢀ ꢀ ꢀO is 155.65(11)ꢁ. Besides the weak
interactions listed above the molecular units are connected
through a net of interactions between the hydrogen atoms
of the phenyl groups and the oxygen atoms of the carbonyl
groups.
For a better understanding of the coordinative bond-
ing in 1 theoretical studies using DFT, NBO and CDA
methods were carried out. The DFT and NBO calcula-
tions were performed for the free ligand, Ph2SbCl and
for the complex 1. In particular, we wanted to explain
the experimentally observed increase in the sum of bond
angles at antimony in the Ph2SbCl unit as a result of the
complexation. The calculated geometrical parameters are
in good agreement with the experimental data. The bond
lengths and bond angles are listed in Table 1. The former
Fig. 2. Dimeric association of [W(CO)5(Ph2SbCl)] (1).

H.J. Breunig et al. / Journal of Organometallic Chemistry 692 (2007) 2593–2598
2595
Fig. 3. Supramolecular assembly of [W(CO)5(Ph2SbBr)] (2) in the crystal.
are slightly longer than the experimental values [18].
HOMO-3 represents the sigma bonding between anti-
mony and the tungsten pentacarbonyl unit. The largest
contribution to HOMO and HOMO-1 comes from the
orbitals dxz, respectively, dxy of tungsten. Nevertheless
both orbitals feature also some electron density delocali-
sation from tungsten toward antimony representing the
p back bonding where antibonding Sb–Cl and Sb–C orbi-
tals are involved.
The natural bonding orbital (NBO) [19,20] analysis
reveals that the contributions of the atomic orbitals of
antimony to the lone pair in Ph2SbCl are 74.22% s and
25.78% p. The corresponding values for the contribution
of antimony orbitals to the W–Sb bond in 1 are 16.91%
s and 83.05% p. These data show that the configuration
at antimony changes from close to p3 with the lone pair
having mainly s character towards a close to sp3 hybrid-
isation. This change leads to the experimentally observed
widening of the bond angles at antimony and to a
strengthening of the dative bond between antimony and
tungsten.
A quantitative description of the bonding in 1 in terms
of donation, back donation and repulsion can be drawn
using the charge decomposition analysis scheme (CDA)
[21,22]. The method is based on the model of Dewar–
Chatt–Duncanson of the synergistic metal–ligand bonding
[22,23]. Good descriptions of the technical details regarding
CDA application and examples of the usage on metal car-
bonyls can be found in the literature [22,24,25].
The CDA of 1 confirms the donor–acceptor nature of
the interaction between the Ph2SbCl and W(CO)5 moieties,
through the low value of the residual term D(ꢁ0.018).
Although CDA does not provide any information about

2596
H.J. Breunig et al. / Journal of Organometallic Chemistry 692 (2007) 2593–2598
by iterative simulation using the MestReC software pack-
age and compared with the experimental spectra. The cal-
culated values of the chemical shifts and of the coupling
constants obtained are listed in Table 2 (see Fig. 4).
The complexation leads to a shielding of the ortho pro-
tons with an increment of 0.1 ppm and a deshielding of the
meta and para protons of the phenyl groups with 0.4 ppm
in all complexes compared to the analogous values from
the free ligands. The coupling constants of the complexes
1–3 and the free ligands are very similar.
Fig. 4. Simulated (down) and experimental in C6D6 (up) spectra of 2. The
additional signal (d, 7.15 ppm) in the experimental spectrum is the residual
peak of C6D5H.
3. Conclusion
The high stability and the easy syntheses of the com-
plexes 1–3 open perspectives for various applications. With
the antimony halogen bond the complexes possess func-
tional groups for further synthetic reactions of the coordi-
nated ligands avoiding scrambling reactions which occur
frequently in the chemistry of free diphenylantimony(III)
halides. The comparison of the geometrical parameters of
the diphenylantimony halide moieties in crystals of the free
ligands and in the complexes 1–3 together with DFT calcu-
lations reveal that major effects of the complexation are the
widening of the bond angles at antimony allowing a
strengthening of the bond to the tungsten centres and an
increase of intermolecular contacts.
the contributions to the bond energy between the ligand
and the metal centre it is a measurement for the changes
of the electronic structure [24]. Both donation and back
donation terms have positive values, 0.379 and 0.211,
respectively.
In an attempt to understand also the nature of the inter-
molecular interaction between antimony and oxygen from
1 we have optimized the molecular geometry of the dimer
(12). The DFT calculation was made at the same level of
theory and using the same basis sets as for the monomer.
The geometrical parameters are listed in the column 5 of
Table 1. The Sbꢀ ꢀ ꢀO distances are overestimated at the
B3LYP level of theory, the calculated values for the dimer
4. Experimental and computational
˚
being 3.765 and 3.764 A [18]. These theoretical values are
˚
0.314, respectively, 0.313 A larger than the experimental
All experiments were performed in an argon atmosphere
using modified Schlenck techniques in carefully dried sol-
vents. Ph2SbCl [6] and Ph2SbI [8] were prepared as
described. 1H and 13C NMR spectra were recorded in
C6D6 solutions at room temperature using a Bruker Avance
DPX-200 spectrometer operating at 200.1 MHz, and
50.3 MHz, respectively. The chemical shifts are reported
in d units (ppm) relative to the residual peak of solvent
C6D5H (1H 7.15 ppm) and C6D6 (13C 128.02 ppm). Infra-
red spectra were recorded as Nujol mulls on a Perkin–
Elmer Spectrum 1000 instrument. Mass spectra were
recorded on a Finnigan MAT 95 spectrometer for 3 and
on a Finnigan MAT 8200 spectrometer for 1, 2. The C, H
elemental analysis for 2 and 3 were made by Mikroanalytis-
ches Labor Beller–Matthies, Go¨ttingen, Germany.
ones. Another source of error is the neglect of packing
forces in the crystal. The calculated Bond Dissociation
Energy (BDE) of one Sbꢀ ꢀ ꢀO interaction in (12) is
18.719 kJ molꢁ1. This value suggests a very weak interac-
tion compared to a Sb–O single bond where the BDE is
434.3 kJ molꢁ1 [26]. The Mulliken charges in the optimized
structure of the dimer are 0.774 for antimony, and ꢁ0.273
for the oxygen atom of the neighbouring molecule. This
result suggests an electrostatic contribution to the weak
Sbꢀ ꢀ ꢀO Lewis acid base interaction.
1
The complexes 1–3 were characterised also by H- and
1
13C NMR spectroscopy. The H NMR spectra show two
multiplet signals. The NMR parameters were determined
Density functional theory calculations were performed
using Gaussian 98 Revision A.7 software package [27].
Geometry optimizations were made using the gradient cor-
rected functional B3LYP [28]. The basis sets used were: 6-
31 G(d,p) for hydrogen, carbon and oxygen atoms [29],
LANL2DZ for chlorine and tungsten [30,31], and
LANL2DZ with two polarization functions for antimony
[31,32]. The energy minima were confirmed by frequency
calculations.
For charge decomposition analysis the program CDA
2.1 was used [21]. The relative orbital contributions were
taken from the NBO analysis performed by Gaussian,
using the partitioning scheme of Weinhold [19,20].
Table 2
1H Chemical shifts (d, ppm) and coupling constants (J, Hz) of Ph2SbX,
X = Cl, Br, I [8] and 1–3
Ph2SbCl
1
Ph2SbBr
2
Ph2SbI
3
d 2, 6
d 3, 5
d 4
7.662
7.458
7.416
7.61
1.24
0.56
1.37
7.50
1.57
7.510
6.980
6.930
7.64
1.30
0.54
1.37
7.50
1.44
7.686
7.436
7.396
7.51
1.28
0.64
1.47
7.48
1.44
7.540
6.970
6.925
7.64
1.30
0.54
1.37
7.50
1.44
7.728
7.394
7.360
7.64
1.30
0.54
1.37
7.50
1.44
7.560
6.938
6.889
7.64
1.30
0.54
1.37
7.50
1.44
3J2,3
4J2,4
5J2,5
4J2,6
3J3,4
4J3,5
,
,
,
3J5,6
4J4,6
5J3,6
,
3J4,5

H.J. Breunig et al. / Journal of Organometallic Chemistry 692 (2007) 2593–2598
2597
4.1. Synthesis of Ph2SbBr
(3.60) [Mꢁ5CO]+, 614 (0.86) [Mꢁ4CO]+, 670 (4.86)
[Mꢁ2CO]+, 728 (8.47) [M]+. IR (nujol, 25 ꢁC, cmꢁ1):
1953 (E), 2077 (A1). Anal. Calc. for C17H10O5ISbW
(726.75): C, 28.10; H, 1.39. Found: C, 28.22; H, 1.61%.
To a solution of 3.11 g (10 mmol) Ph2SbCl in ethanol
was added 3.09 g (30 mmol) NaBr. The reaction mixture
is stirred for 16 h at room temperature. The solvent was
removed under vacuum and the solid product was
extracted with benzene. After the removal of the benzene
a green yellow oil which crystallizes at 7 ꢁC remained.
Yield: 2.74 g (76.95%). 1H NMR: d 6.95–7.09 ppm (m,
6H, –C6H5-m + p), 7.44–7.50 ppm (m, 4H, –C6H5-o) [8].
4.3. X-ray structure determination
Crystals suitable for X-ray diffraction of 1, 2 and 3 were
obtained from petroleum ether solutions at 7 ꢁC. Cell
refinement gave constants corresponding to the triclinic
crystal system for all three structures. Data were collected
4.2. Syntheses of [W(CO)5(Ph2SbX)], X = Cl (1), Br (2),
I (3)
at 173(2) K on a Siemens P4 diffractometer using
0.71073 A Mo Ka radiation and corrected for absorption
˚
To solutions of [W(CO)5(THF)] in 120 ml THF, pre-
pared from 1.76 g (5 mmol) W(CO)6, photolyzed for
2.5 h, 5 mmol of the respective diphenylantimony halide
(1.56 g Ph2SbCl, 1.78 g Ph2SbBr, 2.01 g Ph2SbI) were
added. The reaction mixtures were stirred for 16 h at room
temperature and the solvent was removed at reduced pres-
sure. Recrystallization of the remaining solid from petro-
leum ether at 7 ꢁC afforded crystals of 1–3.
Table 3
X-ray diffraction data and structure refinement for 1–3
Compound
1
2
3
Empirical
formula
Formula weight 635.30
Crystal size
(mm3)
C
17H10O5ClSbW C17H10O5BrSbW C17H10O5ISbW
679.76
0.6 · 0.5 · 0.4
726.75
0.7 · 0.6 · 0.2
0.7 · 0.5 · 0.2
ꢀ
ꢀ
ꢀ
1: yield 1.89 g (59.4%, lit.: 60% [1]), m.p.: 83–85 ꢁC, lit.
65 ꢁC [1]. 1H NMR: d 6.87–7.01 ppm (m, 6H, –C6H5-
m + p), 7.50–7.55 ppm (m, 4H, –C6H5-o). 13C-{1H}
NMR: d 129.96 ppm (s, –C6H5-p), 131.66 ppm (s, –C6H5-
m), 133.20 ppm (s, –C6H5-o), 139.08 ppm (s, –C6H5-i),
194.96 ppm (s, –CO-trans), 197.13 ppm (s, –CO-cis). MS
(EI, 70 eV): 28 (46.83) [CO]+, 77 (27.52) [Ph]+, 154 (100)
[Ph2]+, 198 (9.50) [SbPh]+, 235 (4.83) [PhSbCl]+, 275
(24.24) [Ph2Sb]+, 310 (4.58) [Ph2SbCl]+, 418 (26.64)
[W(PhSbCl)]+, 459 (5.94) [W(Ph2Sb)]+, 494 (12.12)
[Mꢁ5CO]+, 524 (3.60) [Mꢁ4CO]+, 580 (10.63) [Mꢁ2CO]+,
636 (9.97) [M]+. IR (nujol, 25ꢁC, cmꢁ1): 1954 (E), 2078
(A1).
Space group
P1
P1
P1
˚
a (A)
8.981(3)
9.264(3)
12.215(3)
107.60(2)
104.25(1)
91.03(1)
934.2(5)
2
7.026(3)
9.784(3)
13.783(4)
83.58(2)
88.84(2)
87.83(3)
940.7(6)
2
7.228(2)
9.757(5)
13.876(3)
82.47(2)
87.65(1)
86.94(2)
968.2(6)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
Volume (A)
Z
Absorption
coefficient
(mmꢁ1
˚
7.763
9.691
8.947
)
F(000)
588
624
2.70–27.49
660
2.73–27.50
h range for data 2.35–27.50
collections (ꢁ)
Index ranges (h,
k, l)
Reflections
collected
2: yield: 1.31 g (38.6%), m.p.: 82–83 ꢁC.1H NMR: d
6.88–7.03 ppm (m, 6H, –C6H5-m + p), 7.51–7.57 ppm
11, 11, 15
ꢁ8/+9, 12,
9, 12, 18
9013
17
8608
5444
(m, 4H, –C6H5-o).13C–{1H} NMR:
d
129.91 ppm
Independent
reflections/
Rint
4239/0.0244
4309/0.0305
4439/0.0237
(s, –C6H5-p), 131.54 ppm (s, –C6H5-m), 133.58 ppm (s, –
C6H5-o), 136.77 ppm (s, –C6H5-i), 195.35 ppm (s, –CO-
trans), 197.27 ppm (s, –CO-cis). MS (EI, 70 eV): 28
(13.37) [CO]+, 77 (21.19) [Ph]+, 154 (100) [Ph2]+, 198
(9.54) [PhSb]+, 275 (54.33) [Ph2Sb]+, 341 (10.65)
[WPh2]+, 462 (50.33) [W(SbPh2)]+, 540 (23.72) [Mꢁ5CO]+,
568 (10.39) [Mꢁ4CO]+, 624 (26.72) [Mꢁ2CO]+, 680
(22.21) [M]+. IR (nujol, 25 ꢁC, cmꢁ1): 1955 (E), 2077
(A1). Anal. Calc. for C17H10O5BrSbW (679.76): C, 30.04;
H, 1.48. Found: C, 30.08; H, 1.51%.
Data with I > 2 4064
r(I)
Goodness-of-fit 1.105
(on F2)a
Data/
parameters/
restraints
Final R indices
[I > 2 r(I)]
(R1, wR2)b
R indices
4112
4319
1.169
1.179
4239/227/0
4309/227/0
4439/227/0
0.0527, 0.1513
0.0539, 0.1531
3.731, ꢁ4.343
0.0330, 0.0898
0.0345, 0.0907
2.967, ꢁ1.413
0.0348, 0.0991
0.0356, 0.0996
2.723, ꢁ2.1
1
3: yield: 3.23 g (89.0%), m.p.: 107–108 ꢁC. H NMR: d
6.84–6.99 ppm (m, 6H, –C6H5-m + p), 7.52–7.58 ppm
(m, 4H, –C6H5-o). 13C–{1H} NMR: d 129.80 ppm (s, –C6
H5-para), 131.32 ppm (s, –C6H5-m), 132.48 ppm
(s, –C6H5-o), 134.26 ppm (s, –C6H5-i), 196.14 ppm (s,
–CO-trans), 197.62 ppm (s, –CO-cis). MS (EI, 70 eV): 77
(19.30) [Ph]+, 154 (100) [Ph2]+, 198 (23.24) [SbPh]+, 248
(12.91) [SbI]+, 275 (42.85) [Ph2Sb]+, 402 (10.42) [Ph2SbI]+,
459 (12.69) [W(Ph2Sb)]+, 510 (7.13) [W(PhSbI)]+, 586
(all data)
(R1, wR2)
Largest
difference
peak and hole
ꢁ3
˚
(e A
)
P
2
1=2
a
GoF ¼ S ¼ f ½wðF 2o ꢁ F 2c Þ ꢂ=ðn ꢁ pÞg
.
P
P
P
P
2
2
1=2
b
R1 = iFoj ꢁ jFci/ jFoj; wR2 ¼ f ½wðF 2o ꢁ F c2Þ ꢂ= ½wðF o2Þ ꢂg
.

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effects using DIFABS [33]. The structures were solved by
Patterson method [34]. Structure solutions and refinements
(full-matrix least-squares on F2, anisotropic displacement
parameters and H atoms in calculated positions) were car-
ried out using WINGX software package [35]. All the non-
hydrogen atoms were treated anisotropically. Hydrogen
atoms were included in idealized positions with isotropic
thermal parameters set at 1.2 times that of the carbon atom
to which they were attached. Crystallographic data are
summarized in Table 3. The diagrams of the X-ray struc-
tures were created with the Diamond software package.
Acknowledgements
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´
We thank Dr. Gabor Balasz (Universita¨t Regensburg)
´
and Marius Retegan (Universite Joseph Fourier Grenoble)
for valuable discussions of the theoretical data. We thank
the Deutsche Forschungsgemeinschaft for financial
support.
Appendix A. Supplementary material
[27] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A.
Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery, Jr.,
R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D.
Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q.
Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghava-
chari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.
Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham,
C.Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe,
P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C.
Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian,
Inc., Pittsburgh, PA, 1998.
CCDC 631375, 631376, 631377, contain the supplemen-
tary crystallographic data for 1, 2 and 3. These data can be
obtained free of charge via www.ccdc.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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