Synthesis, crystal structures, and properties of the copper(I) halide coordination polymers ∞2[CuX(μ-2-chloropyrazine-N,N′)] (X = Cl, Br), ∞1[CuI(2-chloropyrazine-N)], and [Cu2I2(2-chloropyrazine)]

Article abstract of DOI:10.1002/1521-3749(200202)628:2<394::AID-ZAAC394>3.0.CO;2-R

The new copper coordination polymers _∞²[CuX(μ-2-chloropyrazine-N,N′)] (X = Cl (I), Br (II), _∞¹[CuI(2-chloropyrazine-N)] (III) and [Cu₂I₂(2-chloropyrazine)] (IV) has been prepared by the reaction of the copper(I) halides with 2-chloropyrazine at room-temperature or under hydrothermal conditions. The crystal structures of the 1:1 compounds I and II consist of zig-zag CuX single chains running parallel to the crystallographic a-axis which are linked by the 2-chloropyrazine spacer molecules to sheets parallel to (010). For the iodine compound III a one-dimensional structure is Found which consists of CuX double chains running parallel to the crystallographic a-axis. The thermic properties of all compounds were investigated in different gas atmospheres using simultaneously differential thermal analysis and thermogravimetry (DTA-TG) as well as temperature resolved X-ray powder diffraction. On heating, tire 1:1 compounds I and II decompose directly to the corresponding copper(I) Halides, whereas the thermal decomposition of III occcur via IV as an intermediate.

Full text of DOI:10.1002/1521-3749(200202)628:2<394::AID-ZAAC394>3.0.CO;2-R

Synthesis, Crystal Structures, and Properties of the Copper(I) Halide
2
Coordination Polymers [CuX(µ-2-chloropyrazine-N,N’)] (X ؍ Cl, Br),
ϱ
1ϱ[CuI(2-chloropyrazine-N)], and [Cu2I2(2-chloropyrazine)]
Christian Näther*, Mario Wriedt, and Inke Jeß
Kiel, Institut für Anorganische Chemie der Christian-Albrechts-Universität
Received July 19th, 2001.
Abstract. The new copper coordination polymers 2ϱ[CuX(µ-2-chlor-
opyrazine-N,N’)] (X ϭ Cl (I), Br (II), 1ϱ[CuI(2-chloropyrazine-N)]
(III) and [Cu2I2(2-chloropyrazine)] (IV) has been prepared by the
reaction of the copper(I) halides with 2-chloropyrazine at room-
temperature or under hydrothermal conditions. The crystal struc-
tures of the 1:1 compounds I and II consist of „zig-zag“ CuX single
chains running parallel to the crystallographic a-axis which are
linked by the 2-chloropyrazine spacer molecules to sheets parallel
to (010). For the iodine compound III a one-dimensional structure
is found which consists of CuX double chains running parallel to
the crystallographic a-axis. The thermic properties of all com-
pounds were investigated in different gas atmospheres using simul-
taneously differential thermal analysis and thermogravimetry
(DTA-TG) as well as temperature resolved X-ray powder diffrac-
tion. On heating, the 1:1 compounds I and II decompose directly
to the corresponding copper(I) Halides, whereas the thermal de-
composition of III occcur via IV as an intermediate.
Keywords: Copper; 2-Chloropyrazine; Coordination polymers;
Crystal structure; Thermochemistry
Synthese, Kristallstruktur und Eigenschaften der Kupfer(I)-halogenid-
2
Koordinationspolymere [CuX(µ-2-Chlorpyrazin-N,N’)] (X ؍ Cl, Br),
ϱ
1ϱ[CuI(2-Chlorpyrazin-N)] und [Cu2I2(2-Chlorpyrazin)]
Inhaltsübersicht. Die neuen Kupfer-Koordinationspolymere
2ϱ[CuX(µ-2-Chlorpyrazin-N,N’)] (X ϭ Cl (I), Br (II), 1ϱ[CuI(2-
Chlorpyrazin-N)] (III) und [Cu2I2-(2-Chlorpyrazin)] (IV) wurden
durch Reaktion der Kupfer(I)-halogenide mit 2-Chlorpyrazin bei
Raumtemperatur oder unter hydrothermalen Bedingungen darge-
stellt. Die Kristallstrukturen der 1:1-Verbindungen I und II beste-
hen aus „zick-zack-förmigen“ CuX-Einfachketten, welche parallel
zur kristallographischen a-Achse verlaufen und durch die 2-Chlor-
pyrazinmoleküle zu Schichten parallel zu (010) verknüpft sind. Für
die Iodverbindung III wird eine eindimensionale Struktur gefun-
den, welche aus CuX-Doppelketten besteht die parallel zur kristal-
lographischen a-Achse verlaufen. Die thermischen Eigenschaften
der Verbindungen wurden in unterschiedlichen Gasatmosphären
mit simultaner Differenzthermoanalyse und Thermogravimetrie
(DTA-TG) sowie mit temperaturaufgelöster Röntgen-Pulverbeu-
gung untersucht. Beim Aufheizen zersetzen sich die 1:1-Verbindun-
gen I and II direkt zu den entsprechenden Kupfer(I)-halogeniden,
während bei der thermischen Zersetzung von III die Verbindung
IV als eine Zwischenphase auftritt.
Introduction
which are connected by the organic spacer molecules to
one-, two- or three-dimensional inorganic-organic coordi-
nation polymers [1Ϫ16].
Inorganic organic coordination polymers based on cop-
per(I) halides or pseudohalides and multidendate amino li-
gands show a great structural diversity. They are built up
of inorganic CuX substructures (X ϭ Cl, Br, I, SCN, CN)
which are linked by the organic spacer molecules to multidi-
mensional structures. Dependent on the copper(I) halide
and the nature of the organic ligand used in the synthesis
interesting inorganic substructures like CuX dimers, “zig-
zag” single or staircase-like double chains are observed,
During our investigations on the synthesis, the structures
and properties of such compounds we have found that
some amine rich CuX coordination polymers can be quan-
titatively transformed to the phase pure amine poor CuX
coordination polymers via controlled thermal decompo-
sition. Therefore this method might be an alternative tool
for the preparation of new compounds which cannot be
synthesised or which are always obtained as phase mixtures
out of different compounds if classical chemical solvent
chemistry is used.
2
This is the case for the 1:1 coordination polymer
ϱ
* Dr. Christian Näther
[CuX(µ-pyrazine-N,N’)] (X ϭ Cl, Br) which transforms
completely to the 2:1 compound 2ϱ[Cu2Cl2(µ-pyrazine-
N,N’)] on heating [16, 17]. Whereas the former compound
can be synthesised very pure and in large amounts by the
Institut für Anorganische Chemie, Universität Kiel
Olshausenstr. 40, D-24098 Kiel
Telefax: ϩ49 431 880 1520
E-mail: cnaether@ac.uni-kiel.de
394
WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0044Ϫ2313/02/628/394Ϫ400 $ 17.50ϩ.50/0 Z. Anorg. Allg. Chem. 2002, 628, 394Ϫ400

Synthesis and Crystal Structure of Rb2CuNbSe4, Cs2CuNbSe4
reaction of CuCl with pyrazine, the latter compound is al-
ways obtained as the minor phase in a phase mixture with
the 1:1 coordination polymer [16]. Concerning the thermal
reactivity similar observations were made for the CuX com-
pounds with 4,4’-bipyridine [16, 18] and 2-methylpyrazine
[19]. Whereas the crystal structures of the 1:1 CuX com-
pounds (X ϭ Cl, Br) with pyrazine [11,16] and 2-methyl-
pyrazine [3] are very similar, the 1:1 coordination polymers
with 4,4’-bipyridine [12Ϫ14] exhibit a completely different
crystal structure. These results suggest that the thermal re-
activity is independent from the structure of the starting
material. To investigate if this is a general phenomenon we
have started systematic investigations on the synthesis, the
structures and the thermal behaviour of such coordination
polymers. Strating from our results on the pyrazine and the
2-methylpyrazine compounds we want to investigate sys-
tematically compounds in which the organic part is only
slightly modified, and if possible, the crystal structure is
unaltered. From systematic studies of organic crystal struc-
tures containing methyl or chloro substituents it is well
known that the replacement of a chloro group by a methyl
group leaves the crystal structure mostly unaltered and very
often solid solutions between the chloro and the methyl
compound are formed [20Ϫ24]. The rationale which under-
lies this so called ‘chloro-methyl’ rule is that the volumes of
these two substituents are almost the same [20]. Therefore
we have decided to study the CuX compounds with 2-chlor-
opyrazine. Here we report on the synthesis, the crystal
structures and the thermal properties of these compounds.
Fig. 1 Crystal structure of 2ϱ[CuX(µ-2-chloropyrazine-N,N’)]
(X ϭ Cl (I), Br (II)) with view along the crystallographic b-axis
(top) and a-axis (bottom).
Results and discussion
Table 1 Selected crystal data for CuX compounds (X ϭ Cl, Br)
with 2-chloropyrazine and 2-methylpyrazine.
Crystal structures
The 1:1 compounds 2ϱ[CuCl(µ-2-chloropyrazine-N,N’)] (I)
and 2ϱ[CuBr(µ-2-chloropyrazine-N,N’)] (II) crystallise in the
monoclinic space group P21/c with Zϭ4 formula units in
the unit cell. The asymmetric unit contains one copper cat-
ion, one halide anion and one 2-chloropyrazine ligand all
of them located in general positions. Each copper cation is
in a distorted tetrahedral environment of two halide anions
and two nitrogen atoms of the 2-chloropyrazine ligands.
For compound I the Cu-Cl bond lengths amount to 2.3780
CuCl(2-chloro- CuCl(2-methyl- CuBr(2-chloro- CuBr(2-methyl-
pyrazine)
pyrazine)
pyrazine)
pyrazine)
space
group
P21/c
P21/c
P21/c
P21/c
˚
a/A
3.7752 (4)
3.862 (1)
12.887 (3)
12.585 (3)
95.59 (2)
623.2 (2)
[3]
3.9068 (3)
4.023 (1)
12.940 (4)
12.801 (4)
96.83 (2)
661.6 (3)
[3]
˚
b/A
12.859 (1)
12.709 (2)
90.72 (2)
614.1 (1)
13.159 (2)
12.765 (2)
90.53 (1)
656.3 (1)
This work
˚
c/A
˚
β/A
˚
V/A3
Literature This work
˚
(4) and 2.3799 (4) A and the Cu-N bond lengths to 2.017
˚
(2) and 2.026 (2) A with the longer one to the nitrogen atom
which is in the neighbourhood of the chloro substituent.
The X-Cu-X angles (X ϭ Cl, N) vary between 102.71 (4)
and 132.20 (5)°. In compound II the Cu-Br bond lengths
sheets parallel to (010) (Fig. 1). As expected, the structure
of compound I and II is very similar to those of 2ϱ[CuX(µ-
2-methylpyrazine-N,N’)] (X ϭ Cl, Br) [3], which is obvious
from their similar cell parameters (Tab. 1). Therefore, the
οchloro-methyl’ rule mentioned in the introduction works
even for these compounds.
In contrast to compounds I and II, the iodine compound
1ϱ[CuI(2-chloropyrazine-N)] (III) adopts a completely dif-
ferent crystal structure. This compound crystallises in the
orthorhombic, chiral space group P212121 with Zϭ4 for-
mula units in the unit cell. As in compound I and II, the
asymmetric unit contains one copper cation, one halide
˚
amount to 2.4874 (7) and 2.4878 (4) A, the Cu-N bond
˚
lengths to 2.024 (2) and 2.027 (3) A and the X-Cu-X angles
(X ϭ Br, N) vary between 103.4 (1) and 133.3 (3)°. As in
compound I the longer Cu-N distance is found to the nitro-
gen atom which is vicinal to the halide substituent. The
copper cations in both compounds are connected via com-
mon corners forming infinite zig-zag CuX chains parallel
to the a-axis (Fig. 1). These chains are linked through µ-
N,N’ coordinated 2-chloropyrazine spacer molecules into
Z. Anorg. Allg. Chem. 2002, 628, 394Ϫ400
395

C. Näther, M. Wriedt, I. Jeß
Table 2 Crystal data and results of the structure refinement for 2ϱ[CuCl(µ-2-chloropyrazine-N,N’)] (I), 2ϱ[CuBr(µ-2-chloropyrazine-N,N’)]
(II) and 1ϱ[CuI(2-chloropyrazine-N)] (III).
Compound
I
II
III
Formula
C4H3N2CuCl
213.53
red
monoclinic
P21/c
3.7752 (4)
12.859 (1)
12.709 (2)
90.72 (2)
614.1 (1)
293
C4H3N2ClCuBr
257.98
red
monoclinic
P21/c
3.9068 (3)
13.159 (2)
12.765 (2)
90.53 (1)
656.3 (1)
293
C4H3N2CuI
304.98
yellow
orthorombic
P212121
4.1128 (6)
10.482 (2)
17.9852 (4)
90.00
775.4 (2)
293
4
2.613
560
MW/g·(molϪ1
Crystal colour
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
β/°
V/A
3
˚
Temperature/K
Z
4
4
Dcalc. g·(cmϪ3
F(000)
2.302
416
2.611
488
2θ-range
3Ϫ60°
3Ϫ60°
3Ϫ60°
Ϫ5/1, Ϫ13/9, Ϫ23/2
none
7.5
Ϫ
2800
0.037
h/k/l ranges
Absorption corr.
µ(MoKα)/mmϪ1
Max./min. transm.
Measured refl.
Rint.
0/5, Ϫ18/18, Ϫ17/17
face-indexed
4.3
0.4161/0.6469
4112
0/5, Ϫ18/14, Ϫ17/17
face-indexed
9.72
0.1468/0.3783
4144
0.0262
0.023
Independent refl.
Refl. with I>2σ(I)
Refined parameters
R1 [I>2σ(I)]
wR2 [all data]
GoF
1802
1626
83
0.0204
0.0546
1.068
0.53/Ϫ0.62
1928
1520
83
0.0334
0.1120
1.058
1.28/Ϫ0.96
1848
1586
83
0.0256
0.0619
1.025
Ϫ3
˚
Min./max. res./e·A
0.55/Ϫ0.67
anion and one 2-chloropyrazine ligand, all of them located
in general positions. The copper cations are 4-fold coordi-
nated by three halide anions and one nitrogen atoms of the
2-chloropyrazine ligands within distorted tetrahedrons.
These tetrahedrons are connected via common edges
formed by the iodine anions leading to infinite CuI double
chains in the direction of the crystallographic a-axis (Fig.
2). The Cu-I bond lengths amount to 2.625 (1) and 2.638
˚
˚
(1) A and the Cu-N bond length to 2.069 (4) A. The X-Cu-
X angles (X ϭ Br, N) vary between 102.23 (2) and 116.11
(3)°. Due to the connection of the tetrahedra via common
˚
edges a short Cu-Cu distance of 2.792 (1) A is found. In
contrast to the chlorine and bromine compounds I and II
in this compound only one nitrogen atom of the 2-chlorop-
yrazine ligand is involved in copper coordination leading to
infinite CuX-2-chloropyrazine chains instead of sheets (Fig.
1 and 2).
Thermoanalytical investigations
On heating compound I in a simultaneously differential
thermoanalysis and thermogravimetry (DTA-TG) experi-
ment under an air atmosphere an endothermic signal is ob-
served in the DTA curve at about 180°C which is ac-
companied with a strong loss in mass observed in the TG
curve (Fig. 3). The experimental loss in mass of about
47.3% corresponds roughly to that calculated for the re-
moval of all organic ligands (∆mtheo. ϭ Ϫ53.6%). On
Fig. 2 Crystal structure of 1ϱ[CuI(2-chloropyrazine-N)] (III) with
view along the b-axis (top) and the c-axis (below).
396
Z. Anorg. Allg. Chem. 2002, 628, 394Ϫ400

Synthesis and Crystal Structure of Rb2CuNbSe4, Cs2CuNbSe4
further heating the mass of the sample raises continually
and at about 392°C an increase of about 5% is detected in
an exothermic reaction. At about 430°C the sample mass
decrease by about 6.7% and at 461°C a mass loss of 9.8%
is detected. If the reaction is stopped after the first TG step
and the residue is investigated by X-ray powder diffraction
it can be shown that CuCl [25Ϫ29] has formed which is
contaminated with some small amounts of CuO [30]. For
the thermal reactions each intermediate product was ident-
ified by X-ray powder diffraction. The investigations show
that in the second step the CuCl is oxidised to Cu2Cl2O
[31], which loses the oxygen on further heating forming
again CuCl, and that the last step corresponds to the oxi-
dation of CuCl to CuO. For compound II in the first TG
step a loss in mass of 42.3% is detected which is ac-
companied with an endothermic peak in the TG curve at
about 171°C. The experimental loss in mass of about 42.3%
corresponds roughly to that calculated for the removal of
all organic ligands (∆mtheo. ϭ Ϫ44.6%). The product after
this thermal reaction was identified as CuBr [32] by X-ray
powder diffraction. On further heating the CuBr is oxidised
to CuO. If a sample of compound III is heated in a DTA-
TG experiment an endothermic signal is observed at about
138°C which is accompanied with two TG steps of about
16.1 and 16.2%. The theoretical value for the removal of
half of the organic ligands amounts to 18.8%. Therefore,
from the TG curve one can assume that in contrast to com-
pound I and II the decomposition of the compound III
occurs in two different steps with the corresponding 2:1
compound Cu2I2(2-chloropyrazine) formed as an inter-
mediate phase in the first step. The residue isolated after
the second TG step was identified as CuI [32], which is oxi-
dised at about 340°C to CuO.
Fig. 3 DTA-TG-curves for 2ϱ[CuCl(µ-2-chloropyrazine-N,N’)] (I),
2ϱ[CuBr(µ-2-chloropyrazine-N,N’)] (II) and 1ϱ[CuI(2-chloropyraz-
ine-N)] (III) (simultaneously measurement; powdered single crys-
tals; heating rate: 1°C/min.; dynamic air atmosphere (flow rate: 100
ml/min.); Al2O3-crucible; mass changes are given in % and peak
temperature in parentheses).
The measurements under an air atmosphere show that
the CuCl phase formed as an intermediate product is con-
taminated with oxide and that the observed mass changes
do not exactly correspond to the theoretical values, which
might be due to a partial oxidation of the starting products.
In addition the thermal decomposition of compound III
obviously contains two different steps which cannot be re-
solved successfully. Therefore additional measurements un-
der an dynamic argon atmosphere were performed (Fig. 4).
Under these reaction conditions the experimental mass
changes correspond much better to the theoretical values
and the isolated copper(I) halides are extremely phase pure.
For compound I the Cu2Cl2O phase cannot occur. Con-
cerning the thermal decomposition of compound III, even
at extremely slow heating rates of 0.2°C/min. the two dis-
tinct TG steps cannot be sufficient resolved. To prove that
the 2:1 compound has formed during the thermal reaction
of compound III a sample was heated until the first thermal
reaction had finished and the residue was investigated by
X-ray powder diffraction. The experimental powder pattern
shows clearly that a new crystalline phase has formed which
is contaminated with the starting material III and with cop-
per(I)iodide (Fig. 5). The remaining reflections correspond
to those measured for [Cu2I2(2-chloropyrazine)] IV pre-
pared at room-temperature (see experimental part), which
proves that this compound was formed during this thermal
reaction. Dependent on the temperature to which the
sample is heated, one can isolate mixtures of compounds
III and IV or CuI and IV but unfortunately there is no
chance to isolate phase pure [Cu2I2(2-chloropyrazine)].
However, this compound can be prepared directly from CuI
and 2-chloropyrazine (see experimental part).
To obtain further insight into the thermal decomposition
reactions of all compounds mentioned, experiments with
temperature resolved X-ray diffraction were performed in
glass capillaries (Fig. 6). Under these “static” reaction con-
ditions the reaction could take place in part under a “self-
produced” atmosphere because the compound which is
emitted during a thermal reaction is now only slowly trans-
ported out of the capillary. Therefore it might be that suc-
cessive thermal reactions can be much better resolved. In
addition, one can ascertain whether if the decomposition
reaction is much more complicated due to the occurrence
of additional phases.
If compounds I and II are heated starting at about 220°C
(I) or 200°C (II) a phase transition occurs which is obvious
Z. Anorg. Allg. Chem. 2002, 628, 394Ϫ400
397

C. Näther, M. Wriedt, I. Jeß
Fig. 4 DTA-TG-curves for 2ϱ[CuCl(µ-2-chloropyrazine-N,N’)] (I),
2ϱ[CuBr-µ-2-chloropyrazine-N,N’)] (II) and 1ϱ[CuI(2-chloropyraz-
ine-N)] (III) (simultaneously measurement; powdered single crys-
tals; heating rate: 1°C/min.; dynamic argon atmosphere (flow rate:
100 ml/min.); Al2O3-crucible; mass changes are given in % and
peak temperature in parentheses).
Fig. 5 (A): Powder pattern measured for the residue obtained
after the first transition in a DTA-TG experiment of 1ϱ[CuI(2-chlor-
opyrazine-N)] (III) (CuI corresponds to the reflections of the cop-
per(I) iodide which is included in the sample); (B): Powder pattern
measured for phase pure [Cu2I2(2-chloropyrazine)] (IV); (C): Pow-
der pattern calculated for 1ϱ[CuI(2-chloropyrazine-N)] (III) from
single crystal data (CuKα-radiation).
from the dramatic change of the diffraction pattern. The
phases formed during the transformation can be easily
identified as CuCl and CuBr. If the CuCl formed as an
intermediate phase is heated above 320°C, a second phase
occurs which can be identified as the copper oxychloride
Cu2Cl2O [31]. From the experiments performed there are
no hints for the occurrence of additional phases. In contrast
to compounds I and II, on heating the iodine compound
III at temperatures above 150°C a phase transition occurs
leading to the 2:1 phase [Cu2I2(2-chloropyrazine)] (IV). The
diffraction pattern obtained after the transformation is in
nice agreement with that obtained from synthesised samples
of this compound. If the sample is heated again compound
IV transforms completely to CuI. However, the experimen-
tal results show that the preparation of phase pure [Cu2I2(2-
chloropyrazine)] by controlled thermal decomposition is
difficult to achieve because after formation it decompose
very rapidly to CuI.
we know that in solution both, the 1:1 and the 2:1 com-
pounds can exist simultaneously. Dependent on the exper-
imental conditions some of the 1:1 compounds transform
after formation to the 2:1 compounds within minutes or
hours and also the opposite transformation has been ob-
served. In these cases one can suggest that at first one com-
pound is formed by kinetic control, which transforms in a
second step to the thermodynamically more stable phase.
Because the solid compounds I and II transform directly to
the copper halides on heating, we have tried to prepare the
corresponding 2:1 phases in solution. However, indepen-
dent of the experimental conditions the red coloured 1:1
compounds are always obtained. There is absolutely no evi-
dence for a kinetic controlled formation of the 2:1 com-
pounds at the beginning of the reaction. This is in agree-
ment with our recent results which show that the 2:1 com-
pounds, for example with pyrazine, become more stable on
Synthetic aspects
From our recent work on the synthesis of the CuX com-
pounds with pyrazine, 2-methylpyrazine and 4,4’-bipyridine
398
Z. Anorg. Allg. Chem. 2002, 628, 394Ϫ400

Synthesis and Crystal Structure of Rb2CuNbSe4, Cs2CuNbSe4
Experimental Section
Synthesis of 2ϱ[CuCl(µ-2-chloropyrazine-N,N’)] (I): 518.7 mg (5.24
mmol) copper(I) chloride (freshly prepared according to ref. 33)
and 600 mg (5.24 mmol) 2-chloropyrazine were stirred in 9 ml
acetonitrile at room-temperature. After 3 days the red microcrystal-
line precipitate was filtered off and washed with ethanol and di-
ethylether. Yield: 88.1 %. Elementary analysis (%) calculated: C:
22.50, N: 13.12, H: 1.42; found: C: 22.86, N: 13.14, H: 1.55; X-ray
powder diffraction: phase pure.
Single crystals of this compound were prepared by the reaction of
400 mg (3.5 mmol) 2-chloropyrazine with 172.9 mg (1.75 mmol)
freshly prepared CuCl in 2 ml acetonitrile in a glass container
which was heated in a teflon lined steal autoclaves at 120°C. After
3 days the reaction mixture was cooled down with 1°C/min and
the product was filtered off and washed with ethanol and diethyl-
ether. The product is phase pure and consists of red crystals embed-
ded in a microcrystalline powder.
Synthesis of 2ϱ[CuBr(µ-2-chloropyrazine-N,N’)] (II): 250.5 mg (1.75
mmol) copper(I) bromide (freshly prepared according to ref. [33])
and 200 mg (1.75 mmol) 2-chloropyrazine were stirred in 3 ml
acetonitrile at room-temperature. After 2 days the dark red microc-
rystalline precipitate was filtered off and washed with ethanol and
diethylether. Yield: 94.1%. Elementary analysis (%) calculated: C:
18.62, N: 10.86, H: 1.17; found: C: 18.62, N: 10.80, H: 1.29; X-ray
powder diffraction: phase pure.
Fig. 6 Results of the temperature resolved X-ray powder diffrac-
tion experiment on 2ϱ[CuCl(µ-2-chloropyrazine-N,N’)] (I), 2ϱ[CuBr-
(µ-2-chloropyrazine-N,N’)] (II) and 1ϱ[CuI(2-chloropyrazine-N)]
(III) measured in transmission geometry (CuKα-radiation, pow-
dered samples; static air atmosphere; heating rate 5°C/min.; pow-
der patterns were measured every 5°C; glass-capillaries).
Single crystals of this compound were prepared by the reaction of
400 mg (3.5 mmol) 2-chloropyrazine with 250.5 mg (1.75 mmol)
freshly prepared CuBr in 2 ml acetonitrile in a glass container
which was heated in a teflon lined steal autoclaves at 120°C. After
3 days the reaction mixture was cooled down with 1°C/min and
the product was filtered off and washed with ethanol and diethyl-
ether. The product is phase pure and consists of red crystals embed-
ded in a microcrystalline powder.
going from CuCl to CuI. Therefore our experimental results
in this work suggest that the stability of the possible 2:1
compounds with CuX (XϭCl, Br) and 2-chloropyrazine are
decreased compared to the pyrazine or methylpyrazine
compounds to such an extend, that these phases cannot
be obtained.
Synthesis of 2ϱ[CuI(2-chloropyrazine-N)] (III): 332.6 mg (1.75
mmol) copper(I) iodide (freshly prepared according to ref. 33) and
400 mg (3.5 mmol) 2-chloropyrazine were stirred in 5 ml water at
room-temperature. After 2 days the yellow microcrystalline precipi-
tate was filtered off and was washed with ethanol and diethylether.
Yield: 93.6% (based on CuI). Elementary analysis (%) calculated:
C: 15.75, N: 9.03, H: 0.99; found: C: 15.67, N: 9.12, H: 1.10; X-
ray powder diffraction: phase pure.
Conclusions
Single crystals of this compound were prepared by the reaction of
400 mg (3.5 mmol) 2Ϫchloropyrazine with 332.6 mg (1.75 mmol)
freshly prepared CuI in 3 ml water at room temperature in a glass
container. After 2 days the phase pure compound can be filtered
off. It consists of yellow crystals embedded in a microcrystalline
powder.
In the present contribution we have shown that in contrast
to the 1:1 CuX coordination compounds with pyrazine, 2-
methylpyrazine and 4,4’-bipyridine the thermal decompo-
sition of the 2-chloropyrazine compounds leads only for
X ϭ I to the corresponding 2:1 compounds. This is surpris-
ing because the crystal structure of compound I and II is
very similar to that of [CuX(2-methylpyrazine)] (X ϭ Cl,
Br), which decomposes quantitatively to the corresponding
2:1 coordination polymers. For compound III, which ad-
opts a completely different crystal structure compared to
the CuI 2-methylpyrazine compound, the transformation
into the 2:1 compound can be observed. This shows again
that the ability of the amine rich CuX coordination poly-
mers to transform into the amine poor phases does not de-
pend on the crystal structure. The reason for this behaviour
is not clear and therefore, this will be the subject of
further investigations.
Synthesis of [Cu2I2(2-chloropyrazine)] (IV): 332.6 mg (1.75 mmol)
freshly prepared copper(I) iodide and 100 mg (0.87 mmol) 2-chlor-
opyrazine were stirred in 3 ml acetonitrile at room-temperature.
After 2 days the orange microcrystalline precipitate was filtered off
and washed with ethanol and diethylether. Yield: 87.7%. Elemen-
tary analysis (%) calculated: C: 9.70, N: 5.65, H: 0.61; found: C:
9.74, N: 5.66, H: 0.78; X-ray powder diffraction: phase pure.
Structure determination: All data were measured using a 4-circle
diffractometer from STOE & CIE. For compound I and II a face-
indexed absorption correction on the basis of Psi-scan reflections
using X-SHAPE [34] and XEMP [35] was applied. The structure
solution was performed using SHELXS-97 [36] and structure re-
Z. Anorg. Allg. Chem. 2002, 628, 394Ϫ400
399

C. Näther, M. Wriedt, I. Jeß
finement was done against F2 using SHELXL-97 [37]. All non-
hydrogen atoms were refined using anisotropic displacement par-
ameters. The hydrogen atoms were positioned with idealised ge-
ometry and refined with isotropic displacement parameters using
the riding model. For compound III the absolute structure was
determined and is in agreement with the selected setting (Flack x-
parameter: Ϫ0.02 (5)). In addition, inversion of the structure leads
to significant worse reliability factors (R1 for all reflections with I
> 2σ(I) ϭ 0.0283; wR2 for all data ϭ 0.0706).
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Crystallographic data have been deposited with the Cambridge
Crystallographic Data Centre (CCDC 169138 (I), (CCDC 169137
(II), (CCDC 169139 (III). Copies may be obtained free of charge
on application to the Director, CCDC, 12 Union Road, Cambridge
CB2 1E2, UK (fax: int.Code ϩ(44)01223/3 36-033, e-mail: deposit-
@chemcrys.cam.ac.uk).
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X-ray powder diffraction: Powder diffraction experiments were per-
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formed using
a
STOE STADI
P
transmission powder dif-
˚
fractometer with CuKα-radiation (λ ϭ 1.540598 A) and a Siemens
D-5000 diffractometer in reflection geometry with CuKα-radiation
(λ ϭ 1.540598 A). For temperature and time resolved X-ray powder
˚
diffraction the diffractometer is equipped with a graphite oven and
a position sensitive detector (scan range: 5° Յ 2θ Յ 50°) from
STOE & CIE. All experiments were performed in glass capillaries
under a static air atmosphere.
Differential thermal analysis and thermogravimetry: DTA-TG meas-
urements were performed simultaneously using a STA-429 balance
from Netzsch. All investigations were performed using heating
rates of 1 and 3 K/min. in Al2O3 crucibles under a dynamic argon
or air atmosphere (flow-rate: 100 ml/min).
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45, 163.
Elementary analysis: C, H, N analysis was performed using a CHN-
O-RAPID combustion analyser from Heraeus.
Acknowledgements. We gratefully acknowledge the financial sup-
port by the State of Schleswig-Holstein. We are very thankful to
Professor Dr. Wolfgang Bensch for financial support and the facility
to use his experimental equipment.
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