Synthesis and structure of rhenium(IV) chloride complexes with acetonitrile

Article abstract of DOI:10.1134/S0036023607020088

Cis and trans isomers of the tetrachlorodiacetonitrile rhenium(IV) complex were synthesized and isolated. The structure of cis-ReCl₄(N≡C- CH₃)₂ was studied by X-ray crystallography. It was shown that the coordination polyhedron of the central Re(IV) atom is formed by the four chlorine atoms and the nitrogen atoms of two coordinated acetonitrile molecules. The vibrational (IR and Raman) spectra of the cis isomer of the complex in solid state were interpreted by factor-group analysis. A comparison of the IR spectra of two isomers confirmed that they are cis and trans isomers. Nauka/Interperiodica 2007.

Full text of DOI:10.1134/S0036023607020088

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 2, pp. 186–190. © Pleiades Publishing, Inc., 2007.
Original Russian Text © S.V. Volkov, B.M. Mykhalichko, V.I. Pekhn’o, O.G. Yanko, N.G. Aleksandrova, L.B. Khar’kova, K.I. Arsenin, 2007, published in Zhurnal Neorgan-
icheskoi Khimii, 2007, Vol. 52, No. 2, pp. 226–231.
COORDINATION COMPOUNDS
Synthesis and Structure of Rhenium(IV) Chloride Complexes
with Acetonitrile
S. V. Volkova, B. M. Mykhalichkob, V. I. Pekhn’oa, O. G. Yankoa, N. G. Aleksandrovaa,
L. B. Khar’kovaa, and K. I. Arsenina
a Vernadsky Institute of General and Inorganic Chemistry, Ukrainian National Academy of Sciences, Kiev, Ukraine
b Ivan Franko National University of L’vov, L’vov, Ukraine
Received April 18, 2006
Abstract—Cis and trans isomers of the tetrachlorodiacetonitrile rhenium(IV) complex were synthesized and
isolated. The structure of cis-ReCl4(N≡C–CH3)2 was studied by X-ray crystallography. It was shown that the
coordination polyhedron of the central Re(IV) atom is formed by the four chlorine atoms and the nitrogen atoms
of two coordinated acetonitrile molecules. The vibrational (IR and Raman) spectra of the cis isomer of the com-
plex in solid state were interpreted by factor-group analysis. A comparison of the IR spectra of two isomers con-
firmed that they are cis and trans isomers.
DOI: 10.1134/S0036023607020088
The study of halide complexes of transition metals inert atmosphere was necessary. A short-term shaking
with acetonitrile, [M(Hal)n(CH3CN)2] (M is metal, Hal of the vessel without heating resulted in dissolving of
rhenium pentachloride in acetonitrile with the forma-
tion of a green solution. Upon heating (T ~ 90°C) of the
bottom part of the vessel containing the reaction mix-
ture, the solution color changed from green to brown.
The upper part of the vessel acted as a reflux condenser.
After a short-term heating of the reaction mixture, a
brown precipitate was formed. From time to time, the
hot solution was poured from the heated bottom part of
the vessel into the upper cold part. As a result, large
green crystals and an insignificant amount of a fine-
crystalline brown precipitate were formed from the
cooled solution. Heating and crystallization were con-
ducted until green crystals stopped forming. When the
synthesis was over, the reaction vessel was unsealed,
the products were separated from the mother solution
and dried in vacuum. Thus, the synthesis in an
L-shaped reaction vessel resulted in the formation of
two final products: a brown powder (yield 0.85 g, 50%)
in the heated bottom part of the vessel and green crys-
tals (yield 0.6 g, 35%) with an insignificant impurity of
a fine-crystalline brown precipitate in the upper part.
Both products were hygroscopic.
To purify the green product from the brown impu-
rity, it was placed in an L-shaped reaction vessel with a
small amount of acetonitrile. The vessel was sealed off
and heated at ~90°ë. The complex dissolved with the
formation of a brown solution, and a brown precipitate
appeared at the bottom of the heated part. This fact
points to the transformation of the green phase into the
brown one. Upon cooling the solution, green crystals
were formed again.
is halogen, n = 2–4), shows a possibility of the soft syn-
thesis of metal halide complexes with acetonitrile for
use as precursors for more complex metal coordination
compounds through the substitution of other ligands for
neutral monodentate donor acetonitrile molecules.
Magnetochemical and spectroscopic data for the
product of the interaction of ReCl5 with acetonitrile
[1−5] show the formation of cis and trans isomers of
ReCl4(CH3CN)2 as a result of the synthesis. Subsequent
recrystallization from CH3CN–CH2Cl2 separates these
isomers. The crystals of the cis complex are green,
while the crystals of the trans complex are brown. The
assignment of the green and brown products to cis and
trans isomers, respectively, was done in [2] on the basis
of a comparative analysis of their vibrational spectra
and the spectral data for the isomers of adducts PtCl2 :
2CH3CN and SnCl4 : 2CH3CN. To date, no X-ray dif-
fraction data for chloride Re(IV) complexes with aceto-
nitrile have been obtained.
This work reports the X-ray diffraction study of the
structure of cis-ReCl4(CH3CN)2 and the interpretation
of vibrational spectra of cis and trans isomers of the
complex in a solid state.
EXPERIMENTAL
To synthesize the complex, 1.5 g of ReCl5 (obtained
by the chlorination of previously reduced powder rhe-
nium) and 15 mL of purified and dehydrated CH3CN
were placed into an L-shaped glass reaction vessel. The
vessel was sealed off, which made it possible not to use
The quantitative chemical analysis was performed
inert atmosphere in contrast to [2, 4], where the use of as follows. Rhenium proportion in both products was
186

SYNTHESIS AND STRUCTURE OF RHENIUM(IV) CHLORIDE COMPLEXES
187
Table 1. Crystallographic parameters and experimental de-
tails for the structure of cis-[ReCl4(N≡CCH3)2] · 1.5H2O
determined gravimetrically by heating their samples in
hydrogen flow at 20–1000°ë. The liberating gases were
absorbed by NaOH solution. Chlorine proportion in
these products was determined argentometrically using
the Mohr method and the above NaOH solution. The
proportion of the organic component was found by dif-
ference.
Parameter
[ReCl4(N≡CCH3)2] · 1.5H2O
FW
443
Space group
Pnma
For ReCl4(CH3CN)2 anal. calcd., %: Re, 45.41; Cl,
34.58; CH3CN, 20.01.
Unit cell parameters
a, Å
b, Å
c, Å
V, Å3
Z
10.387(2)
13.504(3)
9.809(3)
1375.9(9)
4
Found (for green crystals and brown precipitate,
respectively),%: Re, 45.70 and 45.30; Cl, 34.20 and
34.50; CH3CN, 20.10 and 20.20.
These data allow one to assume that the obtained
products are isomers of the ReCl4(CH3CN)2 complex.
The free-radical mechanism of rhenium(V) reduction
to rhenium(IV) with the formation of HCl, N≡C–CH2–
CH2–C≡N, and CH2Cl–C≡N is suggested in [2].
Only the green crystals were suitable for an X-ray
diffraction study. Since the studied compound is hygro-
scopic, the X-ray diffraction experiment was carried
out on a single crystal covered with cyanoacrylate glue,
which created a thin film indifferent to X-rays on the
surface of the crystal. However, the X-ray diffraction
experiment did not permit sample preparation in an
inert atmosphere and as a consequence did not prevent
the contact of the sample with atmospheric moisture.
The complex was crystallized in clear yellow-green
rhombic prisms.
ρ
ρ
found, g/cm3
calcd, g/cm3
2.0(1)
2.058(1)
100.79
0.3 × 0.2 × 0.7
716
µ(MoKα), cm–1
Crystal dimensions, mm
F(000)
Number of reflections
617
Number of independent re-
flections with |F ≥ 4σ(F)|*
238
2θmax, deg
49
[σ(F0)2 + 0.0097F20 ]–1
Weighting scheme
The crystal density was measured by the flotation
method in a mixture of chloroform and bromoform.
The crystal was studied photometrically, then the X-ray
diffraction study was carried out on a DARTCH diffracto-
meter (åÓäα radiation, graphite monochromator, θ/2θ
scan mode).
R
0.054
0.056
Rw
* Correction for the Lorentz and polarization effects was applied.
The structure was solved by the direct method with
subsequent use of difference Fourier syntheses. After
the location of all non-hydrogen atoms and the least-
squares refinement of the structure in the isotropic
approximation, correction for absorption was applied
using the DIFABS program package. The positions of
the hydrogen atoms of the methyl group of the acetoni-
trile molecule were not determined due to a significant
rotation of this group about the C–C line. The positions
of the hydrogen atoms of the crystal water molecules
were not determined either, because the oxygen atoms
of these molecules do not completely occupy the corre-
The IR spectra of the green and brown crystals of
the synthesized complex (KBr pellets prepared in a dry
box) were recorded on a Specord M-80 spectrophotom-
eter. The Raman spectrum of the green crystalline pow-
der of the complex sealed in a glass capillary was
recorded on a DFS-24 spectrometer with a laser excita-
tion source (He–Ne, 6328 Å).
RESULTS AND DISCUSSION
According to the X-ray diffraction data (Tables 1, 2),
sponding positions. The final structure refinement was the crystals of the green isomer are orthorhombic
carried out anisotropically for all atoms except for the (space group êÔÚ‡, Z = 4); this isomer is the mononu-
oxygen atoms of the ç2é molecules. The CSD pro- clear complex [ReCl4(CH3CN)2] · 1.5H2O, where the
gram package was used for calculations [6].
central rhenium atom coordinates six ligand molecules.
The coordination polyhedron of the rhenium(IV) atom
is a distorted octahedron formed by the four chlorine
ions and the two nitrogen atoms of two coordinated
acetonitrile molecules cis to each other (Fig. 1).
The crystallographic parameters of the compound
and selected experimental details are listed in Table 1.
The atomic coordinates and thermal parameters in the
structure are listed in Table 2; geometric parameters, in
Table 3. The configuration of the coordination core and
The emergence of a cis-isomer proceeds according
the structure of the complex are displayed in Fig. 1 and to the Peyrone rule [7], because the trans effect of chlo-
2, respectively.
rine atoms is for more significant than that of the neu-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 2 2007

188
VOLKOV et al.
Table 2. Atomic coordinates and thermal parameters in the Table 3. Bond lengths (d) and bond angles (ω) in the struc-
structure of cis-[ReCl4(N≡CCH3)2] · 1.5H2O ture of cis-[ReCl4(N≡CCH3)2] · 1.5H2O
Atom
Re
x
y
z
B, Å2
Angle
ω, deg
Bond
d, Å
0.9405(1)
0.250
0.4816(1)
0.3085(9)
2.58(3)*
4.6(3)*
4.4(2)*
4.5(2)*
3.3(5)*
4.1(7)*
7.2(11)*
3.6(13)
5.3(27)
3.2(14)
3.1(24)
Re–Cl(1)
Re–Cl(2)
Re–Cl(3)
2.325(10) Cl(1)ReCl(2) 172.2(3)
Cl(1)
Cl(2)
Cl(3)
N
0.0934(10) 0.250
0.7684(10) 0.250
2.303(10) Cl(3)ReCl(3')
93.5(3)
88.3(5)
89.9(7)
92.5(3)
92.9(3)
86.2(5)
88.3(5)
175.0(2)
176.0(3)
0.6296(8)
0.0435(7)
0.846(2)
0.790(2)
0.722(3)
0.1271(5)
0.5976(5)
2.279(7)
Cl(3)ReN
NReN'
0.1408(14) 0.369(2)
C(1)
C(2)
0.088(2)
0.011(3)
0.082(5)
0.250
0.305(2)
0.221(3)
0.507(6)
0.533(12)
0.524(7)
0.500
Re–N
2.090(2)
Cl(1)ReCl(3)
Cl(2)ReCl(3)
Cl(1)ReN
Cl(2)ReN
ReNC(1)
O(1)** 0.479(6)
O(2)** 0.410(11)
O(3)** 0.436(8)
O(4)** 0.500
N≡C(1)
1.120(3)
1.500(4)
0.146(6)
0
C(1)–C(2)
* B = 1/3
B a*a*(aiaj) .
ij i j
∑∑
eq
i
j
** Occupancy factors G: O(1) = 0.27(4), O(2) = 0.32(6),O(3) =
NC(1)C(2)
= 0.20(3), O(4) = 0.14(5).
tral acetonitrile molecule, which is confirmed by the
is confirmed by a decrease of its length (N≡C, 1.12(3) Å)
geometric parameters of the coordination polyhedron compared to a free acetonitrile molecule (N≡C, 1.158 Å)
of Re(IV). The chlorine atoms in the trans position to [8]. In this case, the π-acceptor abilities of the nitrile
each other are at greater distances from the rhenium group are almost not manifested, because the electron
atom (Re–Cl(1) and Re–Cl(2) are 2.325(10) and density on the dε orbitals of the metal atom in the high-
2.303(10)Å, respectively) than the chlorine atoms in
the trans position to the nitrogen atoms of the coordi-
nated N≡Cëç3 molecules (Re–Cl(3) and Re–Cl(3') are
2.279(7) Å). The nitrogen atoms are closer to the rhe-
nium atom than the chlorine atoms (Re–N and Re–N'
are 2.09(2) Å) (Table 3). The N≡C bond in a coordi-
nated N≡Cëç3 molecule is somewhat stronger, which
spin rhenium(IV) complex is lower.
The packing of the structural units in the crystal
lattice is shown in Fig. 2. The canals between cis-
[ReCl4(CH3CN)2] units along axis [010] in the cells
are randomly populated by the éw (O(1), O(2),
O(3), and O(4)) atoms of crystal-water molecules.
The water molecules are linked into chains
···ç2éw···çéwç···éwç2··· running along axis [010]
through strong hydrogen bonds (the éw···éw distances
within a chain are 2.40(8)–2.81(12) Å). These chains
are kept in the canals of the complex owing to less
strong hydrogen bonds çéwç···Cl (the éw···Cl dis-
tances are 3.62(12) Å).
The presence of crystal water is not established by
quantitative chemical analysis of the green crystals just
after the synthesis (for [ReCl4(CH3CN)2] · 1.5H2O
anal. calcd. (%): Re, 42.61; Cl, 32.45; CH3CN, 18.76;
H2O, 6.18), which is in accordance with the absence of
characteristic absorption bands of the stretching vibra-
tions of crystal water molecules in the range 1600–
1700 and 3400–3600 cm–1 in the IR spectrum of a her-
metically isolated sample of the green isomer. The crys-
tal-water molecules in the structure of the complex
probably appeared during of the preparation of single
crystals for the X-ray diffraction experiment.
Cl(1)
C(2)
C(1)
N
Re
Cl(3)
Cl(2)
It is of interest to compare the [ReCl4(CH3CN)2] ·
1.5H2O complex with its structural cogener K2[ReCl6]
Fig. 1. Configuration of the coordination core of cis-
[ReCl (NꢀCCH ) ].
4
3 2
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SYNTHESIS AND STRUCTURE OF RHENIUM(IV) CHLORIDE COMPLEXES
189
z
y
0
Cl
C
N
Re
Ow
x
Fig. 2. Structure of complex cis-[ReCl (NꢀCCH ) ] · 1.5H O.
4
3 2
2
(space group Fm3m, Z = 4, a = 9.88 Å). K2[ReCl6] crys- Γ = 10Ä' + 5Ä" (Ä1, B1
Ä'; Ä2, Ç2
Ä") and every
tallizes in the K2[PtCl6] structure type [9], where the local vibration is transformed into the following vibra-
octahedral anions [ReCl6]2– form a face-centered cubic
tions of the crystal:
packing with ä+ counterions in its cavities. In the struc-
ture of the studied complex, the cis-[ReCl4(CH3CN)2]
subunits are neutral, and only neutral particles pene-
trate the cavities of the packing. They are molecules of
the solvent CH3CN in the case of its excess (as in the
synthesis of [OsCl4(CH3CN)2] · 0.5CH3CN [10], which
is isostructural to the studied complex), they are or
crystal-water molecules in the process of hydrolysis of
the complex in the atmosphere. Thus, the structure of
cis-[ReCl4(CH3CN)2] · 1.5H2O may be considered as
Ä'
Ag(Raman) + B2g(Raman) + B1u(IR) + B3u(IR),
Ä''
B1g(Raman) + B3g(Raman) + Au(not active) +
B2u(IR);
i.e., in the statistical field of the crystal, the number
of the components of internal vibrations of the coordi-
nation core does not change, whereas in the correlation
field, all the components are quadruple. The vibrations
of the rhenium coordination core in the cis isomer, in
derived from K2[ReCl6], where ä+ cations are replaced accordance with correlations C2v
ës
D2h, are
by ç2é molecules and two cis-Cl– ions by acetonitrile.
distributed in the crystal according to the types of factor-
group symmetry in a way that theoretically 12 Raman and
11 IR bands can appear in the region of the stretching
vibrations of the coordination core in the vibrational
spectra; and in the region of the bending vibrations,
18 Raman and 14 IR bands corresponding to the above
vibrational modes can appear. The experimentally
observed number of these bands or lines may differ
from the calculated one, among other reasons, because
of their overlapping at close values of component fre-
quencies, especially upon their splitting in the correla-
tion field of the crystal.
The cis configuration of the MX4Y2 particles is
characterized by symmetry C2v due to the trigonal dis-
tortion of the MX6 octahedron. The vibrations of these
particles may be classified in accordance with symme-
try types as following:
Γ = 6Ä1(Raman, IR) + 4B1(Raman, IR) + 3Ç2(Raman,
IR) + 2Ä2(Raman).
According to the results of the factor-group analysis
[11] for the coordination core cis-[ReCl4N2] in the crys-
tal of the studied complex (the point group of the free
According to the literature data [1–5], the brown (or
structural unit is C2v, positional (local) symmetry ës, mustard) crystals correspond to the trans isomer of
[ReCl4(CH3CN)2]. The trans-configuration of MX4Y2
particles, i.e., the tetragonally distorted octahedron
åï6, is characterized by symmetry D4h. The vibrations
the factor-group of the crystal D2h), the classification of
the internal vibrations according to local group symme-
try gives:
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 2 2007

190
VOLKOV et al.
Table 4. Stretching vibrations of the coordination core [ReCl4N2] in the rhenium(IV) complex
trans-[ReCl4N2]
cis-[ReCl4N2]
vibration
vibration frequencies
free structural unit frequencies
free structural unit
local
ν, cm–1
ν, cm–1
local
symmetry
Cs
factor group of crystal
D2h
local
mode
symmetry
IR
mode
symmetry
IR
Raman
D4h [14]
C2ν [14]
νs(Re–Cl) A1g(ν1)
380
430
ν(Re–Cl)
ν(Re–N)
ν(Re–Cl)
ν(Re–N)
A1
A1
B1
B2
A'
A'
A'
A''
Ag + B2g + B1u + B3u
Ag + B2g + B1u + B3u
Ag + B2g + B1u + B3u
380
430
367, 360
~425
νs(Re–N)
ν(Re–Cl)
A1g(ν5)
B1g(ν2)
300, 290
441
300, 290 315, 290
νas(Re–N) A2u(ν4)
B1g + B3g + B2u + Au
(not active)
440
near ~435
νas(Re–Cl) Eu(ν3)
335
ν(Re–Cl)
ν(Re–Cl)
A1
B1
A'
Ä'
Ag + B2g + B1u + B3u
Ag + B2g + B1u + B3u
347, 337 340, 335
of such particles are classified by symmetry type as fol-
lows:
ACKNOWLEDGMENTS
This study was supported by the Scientific Engi-
neering Center of Ukraine (project Gr-32(j)) and
INTAS (project 00-00689).
Γ = 2A1g(Raman) + B1g(Raman) + B2g(Raman)
+ Eg(Raman) + 2A2u(IR) + B2u(IR) + 3Eu(IR).
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