Synthesis and crystal structure of the [Re2(CH 3COO)2Cl4((CH3) 2NCOCH3)2] complex

Article abstract of DOI:10.1023/B:RUCO.0000047465.70746.fd

Compound [Re₂(CH₃COO)₂Cl ₄((CH₃)₂NCOCH₃)₂] is synthesized. The influence of parameters of the hydrothermal synthesis under elevated pressure on the yield of a target product and its molecular structure and physicochemical properties is studied. In the neutral complex with cis-arrangement of the bridging acetate and terminal chloride ligands with respect to the multiply bonded Re₂⁶⁺ complex-forming center, the Re-Re bond length is 2.2418(3) A. Dimethylacetamide molecules are in the axial positions, the Re-O bond lengths being 2.304(3) and 2.321(4) A. The influence of the donor ability of the axial substituents in analogous structures of the rhenium(III) binuclear clusters on the Re-Re and Re-L_ax bond lengths is analyzed.

Full text of DOI:10.1023/B:RUCO.0000047465.70746.fd

Russian Journal of Coordination Chemistry, Vol. 30, No. 11, 2004, pp. 786–791. Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 11, 2004, pp. 835–840.
Original Russian Text Copyright © 2004 by Mel’nik, Filinchuk, Shtemenko.
Synthesis and Crystal Structure
of the [Re2(CH3COO)2Cl4((CH3)2NCOCH3)2] Complex
S. G. Mel’nik*, Ya. E. Filinchuk**, and A. V. Shtemenko*
* Dnepropetrovsk State University of Chemical Technology, pr. Gagarina 8, Dnepropetrovsk, 320640 Ukraine
** Laboratory of Crystallography, University of Geneva, Switzerland
Received November 11, 2003
Abstract—Compound [Re2(CH3COO)2Cl4((CH3)2NCOCH3)2] is synthesized. The influence of parameters of
the hydrothermal synthesis under elevated pressure on the yield of a target product and its molecular structure
and physicochemical properties is studied. In the neutral complex with cis-arrangement of the bridging acetate
and terminal chloride ligands with respect to the multiply bonded Re62+ complex-forming center, the Re–Re
bond length is 2.2418(3) Å. Dimethylacetamide molecules are in the axial positions, the Re–O bond lengths
being 2.304(3) and 2.321(4) Å. The influence of the donor ability of the axial substituents in analogous struc-
tures of the rhenium(III) binuclear clusters on the Re–Re and Re–Lax bond lengths is analyzed.
INTRODUCTION
EXPERIMENTAL
Synthesis
Complexes of rhenium(III) with the metal–metal
quadruple bond containing the Re62+ binuclear frag-
ment are of interest both from a theoretical viewpoint
and in practical application for the low-temperature
production of rhenium in CVD processes [1, 2].
Complex II was synthesized by the reduction of
potassium perrhenate in a mixture of glacial acetic acid
and concentrated hydrochloric acid under an elevated
hydrogen pressure.A weighed sample of KReO4 (0.245 g,
0.85 mmol) was dissolved in a ëç3ëééç–çël (2 :
1 vol/vol) mixture. A quartz container with the reaction
mixture was placed in a steel autoclave in which a
hydrogen pressure of ~3 MPa was created. The auto-
clave was heated to 300°ë and stored at this tempera-
ture for 4 h; the pressure in the autoclave increased to
59 MPa. The resulting brown-green reaction solution
was filtered, and DMAA (1–2 ml) was immediately
added, bringing about the equilibrium shift [4] toward
A search for compounds suitable for production of
metallic rhenium by the low-temperature method
resulted in dirhenium cis-tetrahalodi-µ-carboxylates.
The detailed study of their thermal destruction showed
that these are the most suitable compounds for the pro-
duction of metallic rhenium and its coatings. The ther-
mal decomposition of binuclear dirhenium cis-tetra-
chlorodi-µ-acetates is accompanied by cis–trans
isomerization to form stable volatile trans-
[RÂ2(ëç3ëéé)2Cl4] cluster (I), which undergoes
phase transitions (solid–gas–solid) without decomposi-
tion, can be easily transferred by an inert gas, and
decomposes to metal in almost 100% yield [3].
ε, l mol–1 cm–1
1400
1200
Previously [2, 3], it has been shown that, among
dirhenium(III) chloroacetates with a general formula
[RÂ2(ëç3ëéé)2Cl4L2], where L is the axial ligand (for
instance, N,N-dimethylacetamide (DMAA, II), H2O
(III), triphenylphosphineoxide (TPPO, IV), N,N-di-
methylformamide (DMF, V), or pyridine (Py)), only the
derivatives with H2O and DMAA can eliminate axial
ligands without decomposition of the binuclear com-
plex under thermal destruction conditions. Therefore, it
is important to study the atomic structure of complex
II, to compare it with the available structural data for
other compounds of this class, and to establish the
influence of the axial substituent nature on the struc-
tures of the substances under study.
1000
II
800
600
400
200
0
I
10
12
14
16
18
20
ν × 10–3, cm–1
Fig. 1. Electronic absorption spectra of acetonitrile solu-
tions of I and II.
1070-3284/04/3011-0786 © 2004 åÄIä “Nauka /Interperiodica”

SYNTHESIS AND CRYSTAL STRUCTURE
787
Table 1. Crystallographic data and details of data collection
for complex II
the formation of complex II, which precipitated as
well-faceted dark green crystals (0.299 g, 0.37 mmol).
The high yield of the target product was achieved by
optimization of the autoclave synthesis parameters
according to [4, 5], upon changing the composition of
the starting mixture of acids and by varying the heating
temperature and time.
The product isolated is stable in air and well soluble
in polar organic solvents, water, and inorganic acids. In
an aqueous solution, complex II is slowly hydrolyzed
with cleavage of the metal–metal bond and formation
of the hydrated rhenium dioxide. When boiling in ace-
tic acid, the substance under study is transformed into
dirhenium(III) dichlorotetra-µ-acetate, while heating in
hydrochloric acid produces dirhenium(III) octachloride
[Re2Cl8]2–. To isolate the latter in ~100% yield, the reac-
tion mixture should contain a bulky organic cation.
Parameter
Value
Formula
C6H12Cl2NO3Re
403.265
M
Crystal system, space
group
Monoclinic, C2/c
Unit cell parameters
at 200/293 K:
a, Å
29.422(1)/29.623(7)
10.9580(6)/11.015(3)
14.2470(5)/14.378(3)
97.560(5)/97.59(3)
4553.4(4)/4650(2)
16, 2.353
Heating of complex II in an inert atmosphere or in
vacuum results in the formation of volatile product I,
which was identified using the data of electronic spec-
troscopy [2]. The electronic absorption spectra of solu-
tions of complexes I and II are presented in Fig. 1. The
spectral patterns of both substances are characterized
b, Å
c, Å
β, deg
by an absorption band attributed to the δ
δ* elec-
tron transition [6] at 15 873 cm–1 for II and a doublet at
12 500 and 16 129 cm–1 for I.
V, Å3
Z, ρ(calcd), g/cm3
F(000)
X-ray Diffraction Analysis
The low-temperature (200 K) measurement from a
needle-like crystal (0.38 × 0.095 × 0.043 mm in size)
was carried out on a Stoe IPDS diffractometer (åÓKα
radiation) equipped with an image plate detector. The
lattice parameters at 293 K were determined from pre-
liminary measurements. The crystallographic data,
details of recording [7], and structure refinements [8]
are presented in Table 1.
In the ϕ 0°–180° range, 300 oscillation patterns with
3-min exposure were obtained. The distance from the
crystal to the detector was 60 mm. The data were cor-
rected for the Lorentz and polarization effects, and a
numerical correction for absorption was applied (12
faces, µ = 11.1 mm–1, ímin/max = 0.3214/0.7072). The
unit cell parameters were refined by the least-squares
3008
2θmax, deg
Range of indices
55.94
–38 ≤ h ≤ 38, –14 ≤ k ≤ 14,
–17 ≤ l ≤ 17
Number of reflections
collected/independent
(I > 2σ)(I))
19573/5146
Number
of refined parameters
243
method using angular parameters of 8000 reflections in R-factors (I > 2σ(I))
R1 = 0.0241, wR2 = 0.0482
R1 = 0.0394, wR2 = 0.0499
the angle interval 4.8° < 2θ < 56.0°. No changes in the
average intensity of reflections were observed during
R-factors (all data)
recording.
Systematic extinctions correspond to space groups
0.840,
GOOF against F2, weigh-
ing scheme
C2/c and Cc. The structure was solved by the direct
w = [σ2(Fo2 ) + (0.024Fo2 )2]–1
methods (SHELXS97 [8]) in space group C2/c, and
light atoms were found from the subsequent Fourier
syntheses. Hydrogen atoms of the methyl groups were
localized from the difference Fourier syntheses, and
their positions were refined in the rider model with the
isotropic temperature factors (equal to 1.5U) of the car-
bon atom bound to the H atom under study. The full-
matrix least-squares refinement against F2 was per-
(∆/σ)max
0.038
∆ρ(max), ∆ρ(min), e Å–3
2.38 (0.8 Å
from the Re(2) atom),
–1.19
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 11 2004

788
MEL’NIK et al.
Table 2. Coordinates and thermal parameters of atoms in structure II
Atom
x
y
z
Uequiv(Uiso), Å2
Re(1)
Re(2)
Cl(1)
Cl(2)
Cl(3)
Cl(4)
O(1)
O(2)
O(3)
O(4)
O(5)
0.143378(6)
0.117817(7)
0.21062(4)
0.17344(5)
0.10508(4)
0.06597(5)
0.1804(1)
0.1551(1)
0.0892(1)
0.0647(1)
0.1662(1)
0.0890(2)
0.1961(1)
0.0558(2)
0.1788(2)
0.2054(2)
0.1954
0.2003
0.2381
0.0612(2)
0.0239(2)
0.009
0.001
0.037
0.1510(2)
0.133
0.131
0.53847(2)
0.73136(2)
0.5531(1)
0.8376(1)
0.4512(2)
0.7382(1)
0.5727(3)
0.7628(3)
0.4883(3)
0.6793(3)
0.3428(3)
0.9181(4)
0.1698(4)
1.0918(5)
0.6778(5)
0.7009(6)
0.778
0.634
0.706
0.5680(5)
0.5305(6)
0.603
0.481
0.483
0.2960(5)
0.372
0.229
0.08949(1)
0.07925(2)
0.1923(1)
0.1768(1)
0.2054(1)
0.1891(1)
–0.0204(3)
–0.0301(3)
–0.0101(3)
–0.0210(3)
0.0593(3)
0.0221(4)
0.0130(3)
–0.0205(6)
–0.0595(4)
–0.1394(5)
–0.170
–0.185
–0.115
–0.0466(4)
–0.1232(4)
–0.153
–0.096
–0.171
–0.1061(4)
–0.108
–0.129
0.02631(5)
0.03438(6)
0.0366(3)
0.0474(4)
0.0392(3)
0.0475(4)
0.0353(8)
0.046(1)
0.0344(8)
0.0417(9)
0.0406(9)
0.082(2)
0.035(1)
0.077(2)
0.039(1)
0.054(2)
0.08
0.08
0.08
0.038(1)
0.0491(2)
0.07
0.07
0.07
0.045(1)
0.07
0.07
O(6)
N(1)
N(2)
C(1)
C(2)
H(2A)
H(2B)
H(2C)
C(3)
C(4)
H(4A)
H(4B)
H(4C)
C(5)
H(5A)
H(5B)
H(5C)
C(6)
0.175
0.304
–0.146
0.07
0.1715(2)
0.2176(2)
0.221
0.248
0.198
0.2013(2)
0.182
0.192
0.233
0.0891(3)
0.061
0.108
0.106
0.0767(3)
0.0401(3)
0.008
0.042
0.059
0.0427(3)
0.058
0.053
0.2706(4)
0.1480(5)
0.226
0.111
0.093
0.0748(6)
0.093
–0.004
0.071
1.0822(8)
1.106
1.154
1.023
1.0221(6)
1.2145(6)
1.214
1.258
1.256
1.0321(8)
0.952
1.085
–0.0068(4)
0.1107(5)
0.145
0.110
0.142
–0.0558(5)
–0.115
–0.031
–0.067
0.1374(6)
0.162
0.133
0.180
0.0341(7)
–0.0130(8)
–0.001
–0.072
0.039
–0.1212(6)
–0.123
–0.170
0.031(1)
0.049(2)
0.07
0.07
0.07
0.057(2)
0.09
0.09
0.09
0.078(2)
0.12
0.12
0.12
0.081(3)
0.089(3)
0.13
0.13
0.13
0.086(3)
0.13
0.13
C(7)
H(7A)
H(7B)
H(7C)
C(8)
H(8A)
H(8B)
H(8C)
C(9)
H(9A)
H(9B)
H(9C)
C(10)
C(11)
H(11A)
H(11B)
H(11C)
C(12)
H(12A)
H(12B)
H(12C)
0.009
1.022
–0.134
0.13
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 11 2004

SYNTHESIS AND CRYSTAL STRUCTURE
Table 3. Bond lengths and bond angles in structure II
789
formed in the anisotropic approximation for all non-
hydrogen atoms using the SHELXL97 program [8].
The structural data were tested with the PLATON 2002
program [9], revealing the absence of higher crystal
symmetry or additional symmetry elements. No cavi-
ties that could be occupied by solvent molecules were
found.
The coordinates of atoms and their temperature fac-
tors for structure II are presented in Table 2. The inter-
atomic distances and bond angles are presented in
Table 3.
Bond
d, Å
Angle
ω, deg
Re(1)–Re(2) 2.2418(3)
Re(1)–Cl(1) 2.307(1)
Re(1)–Cl(3) 2.324(1)
O(1)Re(1)O(3)
O(1)Re(1)O(5)
O(3)Re(1)O(5)
O(1)Re(1)Cl(1)
O(3)Re(1)Cl(1)
O(5)Re(1)Cl(1)
O(1)Re(1)Cl(3)
O(3)Re(1)Cl(3)
O(5)Re(1)Cl(3)
Cl(1)Re(1)Cl(3)
87.9(1)
80.3(1)
80.9(1)
88.6(1)
167.2(1)
86.40(9)
166.2(1)
88.6(1)
86.0(1)
91.89(5)
Re(1)–O(1)
Re(1)–O(3)
Re(1)–O(5)
O(5)–C(6)
2.055(4)
2.065(3)
2.304(3)
1.256(6)
RESULTS AND DISCUSSION
Complex II is characterized by cis-arrangement of
the bridging acetate and terminal chloride ligands with
Re62+
respect to the quadruple-bonded
complex-form-
ing center (Fig. 2). The framework of the complex pos-
sesses a mirror pseudoplane, whereas two independent
DMAA molecules are linked by the inversion pseudo-
center localized between the rhenium atoms.
The Re–Re bond length is 2.2418(3) Å. The axial
positions of the rhenium polyhedra are occupied by the
oxygen atoms of the DMAA molecules (Re–Oax
2.304(3) and 2.321(4) Å). The complex molecule is
characterized by the completely screened conformation
of equatorial ligands (Fig. 3); the Cl–Re–Re–Cl torsion
angles involving cis-Cl atoms are 0.33(6)° and
0.78(5)°. The oxygen atoms of the axial DMAA mole-
cules are shifted from the axis of the Re–Re bond, and
the ReReOax angles are 165.6(1)° and 163.3(1)°. Both
organic molecules are shifted from the axis of the Re–
Re bond toward the carboxylate bridges to form a hin-
dered conformation: the Oeq–Re–Re–Oax torsion angles
lie within 42.6(4)°–44.8(4)°, and the O(5)–Re(1)–
Re(2)–O(6) angle is equal to 0.8(7)°. The ReOaxC
angles in the amide group are nonlinear (142.7(3)° and
151.6(6)°). The angles between the planes of non-
hydrogen atoms of the carboxylate groups and DMAA
molecules vary within 28.8(3)°–55.8(2)°. The angle
between the conjugation planes of the organic mole-
cules is 9.1(3)°. The absence of a rigidly linear axial
ligand indicates a substantial role of weak interactions
in the complex structure. The characteristics of the
most important intra- and intermolecular hydrogen
contacts in structure II are presented in Table 4.
As has already been mentioned in [3], a necessary
condition for the cis–trans isomerization and formation
of a volatile rhenium compound by the thermal decom-
position of cis-[RÂ2(ëç3ëéé)2Cl4L2] is the prelimi-
nary removal of the axial substituent, i.e., the cleavage
of the Re–L bond. The published data [11–13] for the
cis-[RÂ2(ëç3ëéé)2Cl4L2] complexes (II, III–V)
(Table 5) indicate the following tendency: the Re–Oax
bond length decreases and the Re–Re bond length
increases with an enhancement of the donor ability of
the axial ligand. For example, the Re–Oax bond length
in hydrate III is maximum and equals 2.50 Å, whereas
Re(2)Re(1)O(5) 165.6(1)
Re(1)O(5)C(6)
O(2)Re(2)O(4)
O(2)Re(2)O(6)
O(4)Re(2)O(6)
O(2)Re(2)Cl(2)
O(4)Re(2)Cl(2)
O(6)Re(2)Cl(2)
O(2)Re(2)Cl(4)
O(4)Re(2)Cl(4)
O(6)Re(2)Cl(4)
Cl(2)Re(2)Cl(4)
142.7(3)
87.3(2)
78.0(2)
78.0(2)
88.0(1)
165.8(1)
87.9(1)
166.0(1)
88.3(1)
88.1(2)
93.11(5)
Re(2)–Cl(2) 2.317(1)
Re(2)–Cl(4) 2.325(2)
Re(2)–O(2)
Re(2)–O(4)
Re(2)–O(6)
2.048(4)
2.055(3)
2.321(4)
O(6)–C(10) 1.215(8)
Re(1)Re(2)O(6) 163.3(1)
Re(2)O(6)C(10) 151.6(6)
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 11 2004

790
MEL’NIK et al.
O(2)
N(2)
O(1)
O(4)
C(6)
O(3)
N(1)
C(10)
O(6)
Re(2)
Re(1)
O(5)
Cl(2)
Cl(1)
Cl(4)
Cl(3)
Fig. 2. Molecular structure of II (30% probability ellipsoids are shown).
it decreases to 2.36 Å in the derivatives with TPPO (IV) for the dirhenium cis-tetrachlorodi-µ-acetate complex
and DMF (V). This explains the most favorable (among with both ç2é (III) and DMAA (II) molecules. During
the cis-[RÂ2(ëç3ëéé)2Cl4L2] complexes) thermal heating in an inert atmosphere, these axial substituents
destruction with elimination of water molecules at are completely removed below the sublimation temper-
160–180°ë in complex III.
However, the highest yield in the syntheses of the
volatile rhenium compounds (80–90%) was observed
ature and do not react on heating with the main part of
the [RÂ2(ëç3ëéé)2Cl4] complex. Other substituents
(TPPO in IV, DMF in V) are not completely removed
and partially interact on heating with the starting com-
pound, which decreases sharply the yield (to 40–50%)
of the volatile product.
Table 4. Characteristics of hydrogen bonds in structure II
It is of interest that the similar lability of the axial
ligand in complexes II and III does not correlate with
different donor abilities of the axial substituents and,
correspondingly, with the Re–Oax distances. At much
higher (as compared to that of water molecules) nucleo-
philicity of DMAA molecules, the latter cannot form
stable hydrogen bonds, which, probably, explains the
unusually easy thermal destruction of complex II.
Distance, Å
D–H···A,
D–H···A
angle, deg
D–H H···A D···A
C(11)–H(11A)···O(4)i 0.96
2.51 3.389
2.75 3.691
2.41 3.205
2.29 2.663
152
165
140
102
106
C(2)–H(2B)···Cl(1)ii
C(5)–H(5A)···O(3)
C(7)–H(7A)···O(5)
C(12)–H(12A)···O(6)
0.96
0.96
0.96
0.96
2.18 2.618
i
ii
Note: Symmetry operators: –x, –y, 1 – z; x, 1 – y, –1/2 + z.
Table 5. Main bond lengths (Å) for some dirhenium(III) chloroacetates and donor numbers (DNSbCl ) according to Gutman
5
[10] for axial substituents
Compound
Re–Re
Re–Oax
DNSbCl
References
[11]
5
[Re2(CH3COO)2Cl4(H2O)2] (III)
2.224(2)
2.50(2)
2.51(2)
2.36(2)
2.36(2)
2.35(2)
2.304(3)
2.321(4)
18.0
[Re2(CH3COO)2Cl4(TPPO)2] (IV)
[Re2(CH3COO)2Cl4(DMF)2] (V)
2.236(2)
2.239(2)
23
[12]
[13]
26.6
[Re2(CH3COO)2Cl4(DMAA)2] (II)
2.2418(3)
27.8
This work
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 11 2004

SYNTHESIS AND CRYSTAL STRUCTURE
791
2. Shtemenko, A.V., Bovykin, B.A., Shram, V.P., et al., Zh.
Neorg. Khim., 1985, vol. 30, no. 12, p. 3085.
3. Shtemenko, A.V., Matrosov, A.S., and Tikhonov, V.I.,
Vopr. Khim. Khim. Tekhnol., 2000, no. 2, p. 24.
C(3)
4. Golovaneva, I.F., Bovykin, B.A., Shtemenko, A.V.,
C(1)
N(1)
et al., Zh. Neorg. Khim., 1987, vol. 32, no. 2, p. 387.
5. Shtemenko, A.V., Kotel’nikova, A.S., Bovykin, B.A.,
and Golovaneva, I.F., Zh. Neorg. Khim., 1986, vol. 31,
no. 2, p. 399.
O
N(2)
Re
6. Shtemenko, A.V., Golichenko, A.A., and Kozhura, O.V.,
Vopr. Khim. Khim. Tekhnol., 2000, no. 2, p. 21.
7. Stoe & Cie, X-RED (Version 1.19) and IPDS Software
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8. Sheldrick, G.M., SHELXS97 and SHELXL97. Programs
for the Solution and Refinement of Crystal Structures,
Gottingen (Germany): Univ. of Gottingen, 1997.
C(1)
9. Spek, A.L., PLATON99. Multipurpose Crystallographic
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10. Gutman, V., Coordination Chemistry in Non-Aqueous
Solutions, Vienna: Springer, 1968.
Fig. 3. Projection of binuclear complex II along the Re–Re
bond (hydrogen atoms are not shown).
11. Koz’min, P.A., Surazhskaya, M.D., and Kuznetsov, V.G.,
Zh. Strukt. Khim., 1970, vol. 11, no. 2, p. 313.
12. Kotel’nikova, A.S., Misailova, T.V., Koz’min, P.A.,
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 11 2004