Synthesis and structural characterization of several dirhenium(III) compounds

Article abstract of DOI:10.1016/j.ica.2006.06.044

Reaction between Re₂(OAc)₄Cl₂ and N,N′-dicyclohexylbenzamidine (HDCyBA) under molten conditions yielded Re₂(DCyBA)₂Cl₄ (1); reaction of [Bu₄N]₂[Re₂Cl₈] with N,N′-di(3-methoxyphenyl)formamidine (HDmAniF) resulted in Re₂(DmAniF)₂Cl₄ (2); reaction of cis-Re₂(OAc)₂Cl₄ with HDmAniF under reflux conditions resulted in cis-Re₂(OAc)₂(DmAniF)₂Cl₂ (3). Reaction between Re₂(OAc)₄Cl₂ and α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid (H₂esp) under reflux conditions led to Re₂(esp)₂Cl₂ (4). Crystallographic studies of compounds 1-4 revealed Re-Re bond lengths of 2.1679(6), 2.1804(5), 2.2468(7), and 2.2304(6) A?, respectively, which are consistent with the presence of Re-Re quadruple bond. Also reported are electrochemical properties of compounds 1-4.

Full text of DOI:10.1016/j.ica.2006.06.044

Inorganica Chimica Acta 359 (2006) 4191–4196
www.elsevier.com/locate/ica
Synthesis and structural characterization of several
dirhenium(III) compounds
a
b
b,
*
Michael Q. Dequeant , Phillip E. Fanwick , Tong Ren
a
Department of Chemistry, University of Miami, Coral Gables, FL 33146, USA
Department of Chemistry, Purdue University, 5186 Brown Laboratory, 560 Oval Drive, West Lafayette, IN 47907, USA
b
Received 12 May 2006; accepted 28 June 2006
Available online 5 July 2006
Abstract
Reaction between Re2(OAc)4Cl2 and N,N0-dicyclohexylbenzamidine (HDCyBA) under molten conditions yielded Re2(DCyBA)2Cl4
(1); reaction of [Bu4N]2[Re2Cl8] with N,N0-di(3-methoxyphenyl)formamidine (HDmAniF) resulted in Re2(DmAniF)2Cl4 (2); reaction
of cis-Re2(OAc)2Cl4 with HDmAniF under reflux conditions resulted in cis-Re2(OAc)2(DmAniF)2Cl2 (3). Reaction between
Re2(OAc)4Cl2 and a,a,a0,a0-tetramethyl-1,3-benzenedipropionic acid (H2esp) under reflux conditions led to Re2(esp)2Cl2 (4). Crystallo-
˚
graphic studies of compounds 1–4 revealed Re–Re bond lengths of 2.1679(6), 2.1804(5), 2.2468(7), and 2.2304(6) A, respectively, which
are consistent with the presence of Re–Re quadruple bond. Also reported are electrochemical properties of compounds 1–4.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Dirhenium(III); N,N0-Bidentate ligand; Supramolecule building block; Crystal structures
1. Introduction
2. Results and discussion
Research of metallosupramolecules represents a new
frontier of inorganic chemistry [1,2]. Advantages of using
bimetallic building blocks have been demonstrated with
the elegant work on Mo2- and Rh2-based supramolecules
[3,4]. In comparison, dirhenium compounds have received
limited attention as to their utility in supramolecular
assemblies [5–11]. Previously, one-dimensional coordina-
tion polymers of interesting photophysical properties were
assembled via metathesis reactions between a dirhenium
synthon containing labile axial ligands, i.e. Re2(DMBA)4-
(NO3)2 (DMBA is N,N0-dimethylbenzamidinate) [12], and
various dianions [13]. In order to broaden the scope
beyond 1-D assembly, building blocks containing labile
equatorial ligand(s) are being sought. Described here are
several dirhenium(III) compounds containing equatorial
halide or acetate ligands, which may undergo substitution
reaction under mild conditions.
2.1. Preparation
Several bidentate bridging ligands were utilized in sup-
porting the Re2 core, and they are shown in Scheme 1. In
an attempt to prepare Re2(DCyBA)4Cl2 (DCyBA = N,N0-
dicyclohexylbenzamidinate), an analog of the previously
reported Re2(DMBA)4Cl2 [12], Re2(OAc)4Cl2 was reacted
with 10 equiv. of HDCyBA (N,N0-dicyclohexylbenzami-
dine) under molten conditions. Instead of Re2(DCyBA)4-
Cl2, compound Re2(DCyBA)2Cl4 (1) was isolated as the
predominant product in a yield of 48%. Clearly, two of
four equatorial Cl ligands were scavenged from another
equivalent of Re2(OAc)4Cl2, which limits the theoretical
yield of 1 at a maximum of 50%. Using the conditions
developed for the synthesis of Re2(DPhF)2Cl4 by Walton
[14], compound Re2(DmAniF)2Cl4 (2) was prepared in a
satisfactory yield (79%) through the reaction between
[Bu4N]2[Re2Cl8] and HDmAniF (di(3-methoxyphenyl)-
formamidine). Reaction between cis-Re2(OAc)2Cl4(H2O)2
and 2 equiv. of HDmAniF in the presence of Et3N resulted
*
Corresponding author. Tel.: +1 765 494 5466; fax: +1 765 494 0239.
E-mail address: tren@purdue.edu (T. Ren).
0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.06.044

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M.Q. Dequeant et al. / Inorganica Chimica Acta 359 (2006) 4191–4196
OCH3
OCH3
Cy
Cy
N
N
N
N
H
H
HDCyBA
HDmAniF
CO2H
HO2C
H2esp
Scheme 1. Ligands utilized in this work.
in compound cis-Re2(OAc)2(DmAniF)2Cl2 (3) in good
yield. Aided by an acetic acid scrubbing setup previously
described [15], refluxing Re2(OAc)4Cl2 with H2esp in tolu-
ene led to compound Re2(esp)2Cl2 (4).
Fig. 2. ORTEP plot of Re2(DmAniF)2Cl4 (2) at 30% probability level.
Hydrogen atoms were omitted for clarity.
2.2. Molecular structures
Molecular structures of compounds 1–4 were elucidated
with single crystal diffraction studies, and they are shown in
Figs. 1–4, respectively. Compound 1 crystallized in the I2/a
space group and the asymmetric unit contains one half of
the molecule with an inversion center that bisects the Re–
Re bond. Compound 2 crystallized in the P21/c space
group and the asymmetric unit also contains one half of
the molecule with an inversion center that bisects the Re–
Re bond. For compound 3, the compound crystallized in
the P21 space group and the asymmetric unit contains
one molecule of 3 and an ethyl acetate solvent molecule.
Compound 4 crystallized in the Pbca space group and
the asymmetric unit contains one half of the molecule with
an inversion center that bisects the Re–Re bond.
Fig. 3. ORTEP plot of Re2(OAc)2(DmAniF)2Cl2 (3) at 30% probability
level. Hydrogen atoms were omitted for clarity.
As shown in Figs. 1 and 2, coordination spheres of the
Re2 core in both 1 and 2 consist of two bidentate bridging
ligands in trans deposition, and four chloro ligands occupy-
Fig. 4. ORTEP plot of Re2(esp)2Cl2 (4) at 30% probability level.
Hydrogen atoms were omitted for clarity.
ing the remaining equatorial sites. Similar ligand arrange-
ments were previously reported for Re2[(PhN)2CPh]2Cl4
[16], Re2(DMBA)2Cl4 [17], and Re2[(PhN)2CH]2Cl4 [18].
Fig. 1. ORTEP plot of Re2(DCyBA)2Cl4 (1) at 30% probability level.
Hydrogen atoms were omitted for clarity.
˚
˚
The Re–Re bond in 1 (2.1679(6) A) and 2 (2.1804(5) A)

M.Q. Dequeant et al. / Inorganica Chimica Acta 359 (2006) 4191–4196
4193
˚
Table 2
Selected bond lengths (A) and bond angles (°) for compound 3
are comparable to those of Re2(DMBA)2Cl4 (2.178(1) A),
˚
˚
Re2[(PhN)2CPh]2Cl4 (2.177(2) A), and Re2[(PhN)2CH]2Cl4
˚
Re1–Re2
Re1–N1
Re1–N3
Re1–O1
Re1–O3
Re1–Cl1
Re2–N2
Re2–N4
Re2–O2
Re2–O4
Re2–Cl2
2.2468(7)
2.046(12)
2.044(12)
2.069(9)
2.062(9)
2.503(4)
2.036(11)
2.063(12)
2.081(10)
2.088(10)
2.502(4)
Re2–Re1–N1
Re2–Re1–N3
Re2–Re1–O1
Re2–Re1–O3
Re2–Re1–Cl1
Re1–Re2–N2
Re1–Re2–N4
Re1–Re2–O2
Re1–Re2–O4
Re1–Re2–Cl2
90.7(3)
90.7(3)
89.7(3)
91.5(3)
171.54(10)
90.9(3)
90.8(3)
90.1(3)
88.2(3)
169.15(11)
(2.177(1) A), and consistent with a Re–Re quadruple bond
[19]. The relative short Re–Re bond distances of com-
pounds 1 and 2 are attributed to the absence of axial chloro
ligands that may donate electron density into the r(Re–Re)
orbital and destabilize the Re–Re quadruple bond (see
Table 1).
It is clear from Fig. 3 that the cis-arrangement of two
acetate ligands in the precursor compound Re2(OAc)2Cl4-
(H2O)2 is retained in compound 3. As a paddlewheel spe-
cies of mixed carboxylate and diarylformamidinate (DArF)
bridging ligands, compound 3 has a Re–Re bond length of
˚
Table 3
2.2468(7) A, which is slightly longer than those of Re2-
˚
Selected bond lengths (A) and bond angles (°) for compound 4
˚
(O2CR)4Cl2 type compounds (2.224–2.240 A) [20], and
shorter than those of Re2(DArF)4Cl2 compounds (2.232–
2.284 A) [21,22]. It is interesting to note that the Re–N
bond length in 3 (ca. 2.05 A) is significantly shortened from
those in Re2(DArF)4Cl2 (ca. 2.10 A) [21,22], while the
Re–O bond length in 3 (ca. 2.07 A) is elongated from that
of Re2(O2CCMe3)4Cl2 (2.025 A) [23]. The bond length
variations compared with the homoleptic species reflect
the enhancement/weakening of bond strengths in the mixed
ligand species, and are consistent with the fact that
N-donor ligands have much stronger trans-influence than
O-donor ligands. Structural evidences of trans-influence
can also be found in Re2(P–P)2(O2CR)2Cl2 type com-
pounds (P–P is bidentate diphosphine) [20] (see Table 2).
Structural study of compound 4, shown in Fig. 4, con-
firms the ‘‘strapping’’ coordination mode of ‘esp’ ligand
that was first reported for Rh2(esp)2(acetone)2 [24]. The
Re1–Re10
Re1–O1
Re1–O2
Re1–O3
Re1–O4
Re1–Cl
2.2304(6)
2.024(5)
2.031(6)
2.043(6)
2.010(6)
2.477(3)
˚
˚
˚
˚
˚
Re10–Re1–O1
Re10–Re1–O2
Re10–Re1–O3
Re10–Re1–O4
91.59(16)
88.98(17)
89.00(16)
91.35(17)
Re10–Re1–Cl
171.91(7)
anodic region (0–1.5 V), DPVs in the cathodic region are
shown in Fig. 5. Compound 1 undergoes a quasireversible
reduction at ꢀ1.08 V (A) and an irreversible reduction at
ꢀ2.19 V (B). The irreversibility of couple B is possibly
due to the decomposition of compound 1 via the loss of
equatorial chloro ligand(s). Voltammograms for analogous
compounds Re2((PhN)2CPh)2Cl4, Re2((PhN)2CCH3)2Cl4,
and Re2((PhN)2CH)2Cl4 were not recorded, and hence no
˚
Re–Re bond length in 4 is 2.2304(6) A, which is within
the range reported for Re2(O2CR)4Cl2 type compounds
(2.224–2.240 A) (see Table 3).
˚
2.3. Electrochemical properties
B
A
1
Redox behaviors of compounds 1–4 were probed with
both cyclic and differential pulse voltammetric methods
(CV and DPV) in the potential range from ꢀ2.5 to 1.5 V.
Since none of the compounds exhibit redox activity in the
A
2
Table 1
˚
Selected bond lengths (A) and bond angles (°) for compounds 1 and 2
B
A
Compound 1
Compound 2
Re1–Re10
Re1–N1
Re1–N2
Re1–Cl1
Re1–Cl2
2.1679(6)
2.036(6)
2.047(7)
2.3313(18)
2.3323(19)
2.1804(5)
2.057(4)
2.065(5)
2.3226(18)
2.3208(17)
3
4
A
N1–Re1–N2
N1–Re1–Cl1
N1–Re1–Cl2
Re10–Re1–N1
Re10–Re1–N2
Re10–Re1–Cl1
Re10–Re1–Cl2
175.8(2)
176.72(18)
87.92(15)
90.92(15)
91.26(13)
91.95(13)
106.26(5)
106.74(4)
91.33(17)
87.99(17)
92.34(16)
91.56(16)
101.54(5)
106.77(5)
0
-0.5
-1
-1.5
-2
-2.5
E/V, vs Ag/AgCl
Fig. 5. Differential pulse voltammograms of compounds 1–4 recorded in
THF at a scan rate of 0.0084/s.

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M.Q. Dequeant et al. / Inorganica Chimica Acta 359 (2006) 4191–4196
comparison can be made. Compound 2 displays only a
quasireversible reduction at ꢀ0.69 V (A). The cathodic
shift of couple A in compound 1 from that of 2 is about
ꢀ0.40 V, and reflects the extraordinary donor ability of
N,N0-di(cyclohexyl)benzamidinate compared with diaryl-
formamidinates. Compound 3 exhibits a reversible reduc-
tion at ꢀ0.87 V (A) and an irreversible reduction at
ꢀ1.78 V (B). For compound 4, there is a single reversible
reduction at ꢀ0.35 V, similar to that reported for other
dirhenium carboxylate compounds with axial chloride
ligands [25].
remove excess ligand and by-products. The solid residue
collected was dissolved in CH2Cl2 and filtered. The filtrate
was concentrated to ca. 2 mL and layered with 30 mL of
hexanes. Re2(DCyBA)4Cl2 was collected as dark red needle
crystals (0.076 g, 48%). MS-FAB (m/e, based on 186Re):
1
1045 [(Re2(DCyBA)2Cl3)+]. H NMR: 7.52 (m), 3.79 (m),
2.01 (d), 1.52 (m), 1.38 (m), 0.93 (t), 0.79 (m). Anal. Calc.
for C38H54N4Cl4Re2: C, 42.10, H, 5.04, N, 5.18. Found:
C, 42.26, H, 5.23, N, 4.91%. Electrochemical data (CV),
E1/2(A), ꢀ1.08 V (DEp, 0.058 V; ibackward/iforward, 0.57);
Epa(B), ꢀ2.15 V. Vis–NIR, kmax/nm (e/Mꢀ1 cmꢀ1): 418
(11620) and 558 (2250).
3. Conclusion
4.3. Synthesis of Re2(DmAniF)2Cl4 (2)
Several new dirhenium(III) species have been prepared
and structurally characterized. Compounds 1 and 2 contain
four equatorial chloro ligands that may serve as the entries
for Re2-alkynyl species. Structural studies also revealed the
weakening of equatorial Re–O(OAc) bonds by the trans-
influence of DArF ligands in 3, and interesting supramole-
cules may be obtained by displacing these labile acetates
with a strong donor ditopic linker. These aspects are being
examined in our laboratory.
[Bu4N]2[Re2Cl8] (0.200 g, 0.175 mmol) and N,N0-di-
(3-methoxyphenyl)formamidine (0.134 g, 0.523 mmol) were
heated under argon atmosphere at 150 °C for 36 h. The
resultant solid was extracted with 25 mL of dichlorometh-
ane. The solid residue was dissolved in THF and re-crystal-
lized from hexanes/THF to provide the desired product.
The dichloromethane filtrate was rotovapped, and the resul-
tant solid was washed with hot ethanol and re-crystallized
from Et2O/THF to afford an additional crop of the prod-
uct. Yield: 0.14 g (79%). Anal. Calc. for C31H32N4Cl6Re2:
C, 33.55, H, 2.91, N, 5.05. Found: C, 33.57, H, 2.88, N,
5.18%. Electrochemical data (CV), E1/2(A), ꢀ0.69 V (DEp,
0.069 V; ibackward/iforward, 0.59). Vis–NIR, kmax/nm (e/
4. Experimental
4.1. General conditions, reagents, and instruments
Isobutyronitrile was purchased from Strem Chemicals;
m-methoxyaniline, butylithium, and tetrafluoroboric acid
were purchased from Aldrich; and all other reagents were
purchased from ACROS. All solvents were purchased from
VWR. Re2(OAc)4Cl2 [26], N,N0-di(cyclohexyl)benzamidine
(HDCyBA) [27], Re2(OAc)2Cl4(H2O)2 [28,29], N,N0-di(3-
methoxyphenyl)formamidine [30], and a,a,a0,a0-tetra-
methyl-1,3-benzenedipropionic acid (H2esp) [24] were
M
ꢀ1 cmꢀ1): 430 (11500) and 584 (3640).
4.4. Synthesis of Re2(OAc)2(DmAniF)2Cl2 (3)
Re2(OAc)2Cl4(H2O)2 (0.100 g, 0.150 mmol), N,N0-di-
(3-methoxyphenyl)formamidine (0.076 g, 0.300 mmol), and
0.75 mL of NEt3 were mixed in 30 mL of THF and refluxed
under argon for 24 h. After the removal of insoluble mate-
rials via filtration, solvents were removed on a rotovap. The
resultant residue was dissolved in dichloromethane and fil-
tered, and the solvent was removed subsequently from the
filtrate. The same procedure was repeated with methanol
and ethyl acetate, and the ethyl acetate solution was
reduced to 5 mL, layered with hexanes to afford powdery
product. Yield: 0.12 g (75%). Orange block crystals were
obtained through the slow evaporation of an ethyl acetate
solution. MS-FAB (m/e, based on 186Re): 1037 [(Re2(DmA-
niF)2(OAc)2Cl)+]. 1H NMR: 8.65 (s), 7.19 (t), 6.86 (d), 6.80
(d), 6.75 (s), 3.66 (s), 3.24 (s). Anal. Calc. for C34H46N4O4-
Cl2Re2: C, 35.14, H, 3.99, N, 4.82. Found: C, 34.92, H, 3.65,
N, 5.13%. Electrochemical data (CV), E1/2(A), ꢀ0.87 V
(DEp, 0.107 V; ibackward/iforward, 0.64); Epa(B), ꢀ1.78 V.
Vis–NIR, kmax/nm (e/Mꢀ1 cmꢀ1): 414 (5650).
1
prepared as previously described. H NMR spectra were
recorded on a Bruker AVANCE300 NMR spectrometer,
with chemical shifts (d) referenced to the residual solvent
CDCl3. Electronic absorption spectra in CH2Cl2 were
obtained on either a Perkin–Elmer Lambda-900 UV–Vis–
NIR spectrophotometer or a Hewlett–Packard diode array
spectrometer (HP 8453). Cyclic and differential pulse vol-
tammograms were recorded in 0.2 M n-Bu4NPF6 solution
(THF, N2-degassed) on a CHI620A voltammetric analyzer
with a glassy carbon working electrode (diameter = 2 mm),
a Pt-wire auxiliary electrode and a Ag/AgCl reference elec-
trode. The concentration of dirhenium species is always
1.0 mM. Elemental analysis was performed by Atlantic
Microlab.
4.2. Synthesis of Re2(DCyBA)2Cl4 (1)
4.5. Synthesis of Re2(esp)2Cl2 (4)
Re2(OAc)4Cl2 (0.100 g, 0.147 mmol) and N,N0-dic-
yclohexylbenzamidine (0.418 g, 1.47 mmol) were heated at
210 °C for 48 h under argon. Upon cooling, the reaction
mixture was washed with 20 mL of CH3OH in order to
Re2(OAc)4Cl2 (0.100 g, 0.147 mmol) and a,a,a0,a0-tetra-
methyl-1,3-benzenedipropionic acid (0.082 g, 0.294 mmol)
were placed in a 50 mL Schlenck flask fitted with soxhlet

M.Q. Dequeant et al. / Inorganica Chimica Acta 359 (2006) 4191–4196
4195
Table 4
Crystal data and structure refinement of compounds 1–4
Compound
1
2
3 Æ EtOAc
4
Chemical formula
Formula weight
Space group
C38H54Cl4N4Re2
1081.05
I2/a
16.4360(13)
13.0541(9)
19.0354(13)
98.332(2)
4041.1(5)
4
C30H30Cl4N4O4Re2
1024.78
P21/c
11.3030(7)
15.6769(10)
9.7168(6)
112.2370(10)
1593.72(17)
2
C38H44Cl2N4O10Re2
1160.07
P21
11.0678(5)
15.8044(8)
12.0515(6)
90.4660(10)
2107.98(18)
2
C32H40Cl1.66O9.36Re2.34
1068.90
Pbca
˚
a (A)
16.9838(5)
12.0023(3)
17.3998(5)
90
3546.86(17)
4
˚
b (A)
˚
c (A)
b (°)
3
˚
V (A )
Z
T (°C)
27
0.71073
1.777
6.282
0.039
27
0.71073
2.135
7.967
0.030
27
0.71073
1.828
5.923
0.044
ꢀ123
˚
k (Mo Ka) (A)
0.71073
2.002
qcalc (g/cm3)
l (mmꢀ1
R
wR2
)
8.257
0.053
0.106
0.064
0.063
0.095
extraction apparatus and put under argon. To this was
added 30 mL of distilled toluene and the thimble of the
soxhlet apparatus was filled with K2CO3. The solution
was refluxed in a sand bath for 5 days with frequent
changes of K2CO3 pad. On cooling to ambient tempera-
ture, crude product was collected via filtration. The crude
product was redissolved in dichloromethane, and slow
evaporation of dichloromethane solution afforded pure 4
as red plate crystals. Yield: 0.10 g (70%). MS-FAB (m/e,
Compound 4. X-ray intensity data were collected at
150(1) K on a Nonius Kappa CCD-based X-ray diffractom-
eter. The frames were integrated with the DENZO-SMN [33]
and Lorentz and polarization corrections were applied to
the data. Absorption corrections were applied using SCALE-
PACK [33] and a secondary extinction correction was applied
[34]. The structure of compound 4 was solved and refined
using the structure solution program PATTY in DIRDIF-99
[35] in the space group of Pbca. The non-hydrogen atoms
were located in succeeding difference Fourier syntheses.
During the course of structural analysis, the axial chloro
ligand (Cl1) was found to be disordered with a ReO4 anion,
a phenomenon observed and rationalized previously [36–
38]. The disordered Cl/ReO4 was refined to convergence
with the occupancy constraint at the occupancy ratio of
85/15 for Cl/ReO4. All non-hydrogen atoms are anisotropic
and the hydrogen atoms were put in calculated positions
and riding mode. The structure was refined to convergence
by least squares method on F2 using SHELXL-97 [35]. Crystal-
lographic data are also given in Table 4.
1
based on 186Re): 961 [(Re2(esp)2Cl)+]. H NMR: 7.08 (d),
6.79 (s), 3.19 (s), 1.57 (s). Anal. Calc. for C32H42O9ClRe2:
C, 39.27, H, 4.33. Found: C, 39.27, H, 4.42%. Electrochem-
ical data (CV), E1/2(A), ꢀ0.35 V (DEp, 0.089 V; ibackward
/
iforward, 0.88) Vis–NIR, kmax/nm (e/Mꢀ1 cmꢀ1): 399 (310)
and 498 (352).
4.6. Structure determination
Compounds 1–3. Single crystals were obtained as previ-
ously stated. X-ray intensity data were measured at
300 K on a Bruker SMART1000 CCD-based X-ray diffrac-
5. Supplementary materials
˚
tometer system using Mo Ka (k = 0.71073 A). Crystals
used for data collection were cemented to a quartz fiber
with epoxy glue. Data were measured using omega scans
of 0.3° per frame for 10 s for 1 and 2, and 40 s for 3, so that
a hemisphere (1271 frames) was collected. The frames were
Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 604647, 604648, 604649 and 604913
for compounds 1–4, respectively. Copies of this informa-
tion may be obtained free of charge from the director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK.
Ó
integrated with the Bruker SAINT software package [31]
using a narrow-frame integration algorithm, which also
corrects for the Lorentz and polarization effects. Absorp-
tion corrections were applied using SADABS.
Acknowledgements
Structures were solved and refined using the Bruker
Ó
SHELXTL (Version 5.1) software package [32] in space
We thank the generous support from the National Sci-
ence Foundation (CHE 0242623 to T.R.) and Purdue
University.
groups of I2/a (1), P21/c (2), and P21 (3). Positions of all
non-hydrogen atoms were revealed by direct method. All
non-hydrogen atoms are anisotropic and the hydrogen
atoms were put in calculated positions and riding mode.
Each structure was refined to convergence by least squares
method on F2, SHELXL-93, incorporated in SHELXTL.PC V
5.03. Crystallographic data are given in Table 4.
References
[1] S. Leininger, B. Olenyuk, P.J. Stang, Chem. Rev. 100 (2000) 853.
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