Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals of the New Coordination Polymer Poly[(CuBr)2(μ2- pyrimidine-N,N')]

Article abstract of DOI:10.1515/znb-2003-1112

Reaction of copper(I) bromide with pyrimidine in acetonitrile leads to the formation of crystals of the new coordination polymer poly[(CuBr) ₂(μ₂-pyrimidine-N,N')]. Indexing of the reflections yields a monoclinic primitive cell with a = 3.9119(2), b = 13.525(1), c = 15.346(1) A?, ?= 97.29(1)° and V = 805.4(1) A?³. Inspection of the reciprocal space shows weak reflections which might be indicative of a superstructure leading to a doubling of the crystallographic c-axis. The structure can be solved in space group P2₁/m but the refinement leads to very poor reliability factors (wR2 for all refl.: 62.57%, R₁ for all Fo > 4σ(Fo) = 27.84%). A twin refinement assuming merohedral twinning drastically reduces the R-values (wR2 for all refl.: 7.27%, R₁ for all Fo > 4σ(Fo) = 2.64%) and a structure model is obtained which consists of two crystallographically independent copper and bromine atoms and two pyrimidine ligands in the asymmetric unit. However, carefull inspection of this structure shows that the two crystallographically independent layers formed by the connection of the building blocks are very similar and that they are related by a translation by half of the crystallographic c-axis. As a result of that, the crystal is just a partial merohedral twin and the reflections which led to the assumption that the c-axis is twice as long are generated by the second twin domain. The structure was refined with the correct twin law (wR2 for all refl.: 6.70%, R₁ for all Fo > 4σ(Fo) = 2.57%). By this procedure a reasonable structure model is obtained which consists of one crystallographically independent copper and bromine atom and one pyrimidine ligand. In the crystal structure CuBr double chains are formed which are connected into layers via μ-N,N' coordination by the N-donor ligands. On heating, the compound loses all of the ligands and transforms into CuBr within only one single step in an exothermic reaction.

Full text of DOI:10.1515/znb-2003-1112

Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals
of the New Coordination Polymer Poly[(CuBr) (µ -pyrimidine-N,N’)]
2
2
a
a
b
Christian N a¨ ther , Inke Jeß , and Michael Bolte
a
Institut f u¨ r Anorganische Chemie der Christian-Albrechts-Universit a¨ t zu Kiel,
Olshausenstraße 40, D-24098 Kiel, Germany
Institut f u¨ r Organische Chemie, Johann-Wolfgang-Goethe-Universit a¨ t Frankfurt,
Marie-Curie-Straße 11, D-60439 Frankfurt am Main, Germany
b
Reprint requests to Dr. Christian N a¨ ther. E-mail: cnaether@ac.uni-kiel.de
Z. Naturforsch. 58b, 1105 – 1111 (2003); received August 11, 2003
Dedicated to Professor Hans Bock on the occasion of his 75th birthday
Reaction of copper(I) bromide with pyrimidine in acetonitrile leads to the formation of crystals of
the new coordination polymer poly[(CuBr) (µ -pyrimidine-N,N’)]. Indexing of the reflections yields
2
2
˚
◦
a monoclinic primitive cell with a = 3.9119(2), b = 13.525(1), c = 15.346(1) A, β = 97.29(1) and
V = 805.4(1) A . Inspection of the reciprocal space shows weak reflections which might be indicative
of a superstructure leading to a doubling of the crystallographic c-axis. The structure can be solved in
˚
3
space group P2 /m but the refinement leads to very poor reliability factors (wR2 for all refl.: 62.57%,
1
R for all Fo > 4σ(Fo) = 27.84%). A twin refinement assuming merohedral twinning drastically
1
reduces the R-values (wR2 for all refl.: 7.27%, R for all Fo > 4σ(Fo) = 2.64%) and a structure
1
model is obtained which consists of two crystallographically independent copper and bromine atoms
and two pyrimidine ligands in the asymmetric unit. However, carefull inspection of this structure
shows that the two crystallographically independent layers formed by the connection of the building
blocks are very similar and that they are related by a translation by half of the crystallographic c-axis.
As a result of that, the crystal is just a partial merohedral twin and the reflections which led to the
assumption that the c-axis is twice as long are generated by the second twin domain. The structure
was refined with the correct twin law (wR2 for all refl.: 6.70%, R for all Fo > 4σ(Fo) = 2.57%). By
1
this procedure a reasonable structure model is obtained which consists of one crystallographically in-
dependent copper and bromine atom and one pyrimidine ligand. In the crystal structure CuBr double
chains are formed which are connected into layers via µ-N,N’ coordination by the N-donor ligands.
On heating, the compound loses all of the ligands and transforms into CuBr within only one single
step in an exothermic reaction.
Key words: Coordination Polymers, Crystal Structures, Partial Merohedral Twinning
Introduction
halide atom and the ratio between the organic and in-
organic part. For one definite copper(I) halide or pseu-
Recently, we have become interested in the syn- dohalide and one specific nitrogen donor ligand fre-
thesis, crystal structures and properties of coordina- quently several compounds are found, which contain
tion polymers based on copper(I) halides or pseudo a different CuX : ligand ratio like, e. g. 1:2, 1:1, 3:2,
halides and aromatic nitrogen donor ligands. Several 2:1 or 4:1. We have found that most of the ligand-
of such compounds with interesting structural features rich copper(I) halide or pseudo halide compounds can
are known [1 – 31], some also with inorganic building be transformed into ligand poorer compounds by ther-
units other than amine ligands [33, 34]. These com- mal decomposition, which therefore, is an alternative
pounds consist of typical CuX substructures like 4- or route for the preparation of new CuX (X = Cl, Br, I)
6
-membered rings, “zig-zag” or helical single chains coordination polymers which cannot be prepared in
or “ladder-like” double chains which are connected solution or which are always obtained as phase mix-
by the N donor ligands into 1-, 2- or 3-dimensional tures [21, 32]. In some cases several amine poorer in-
coordination polymers. The dimensionality of these termediates can be isolated. In order to investigate
compounds depends predominantly on the coordina- the influence of the organic ligands on the structure
tion behaviour of the organic ligands, the nature of the of these coordination polymers we have prepared and
0
932–0776 / 03 / 1100–1105 $ 06.00 ꢀc 2003 Verlag der Zeitschrift f u¨ r Naturforschung, T u¨ bingen · http://znaturforsch.com
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106
C. N a¨ ther et al. · Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals
structurally characterised several of these compounds. Table 1. Intensity statistics for different groups of reflec-
In most cases we have used small 6-membered nitro- tions for the data set measured for the large unit cell of
gen heterocycles like e.g. pyrazine. To investigate the poly[(CuBr) (µ -pyrimidine-N,N’).
2
2
influence of the position of the nitrogen donor atoms on
the structure we were also interested in the pyridazine
or pyrimidine coordination compounds. With pyrim-
idine only the 1:1 compound CuBr(pyrimidine) [4]
I/σ max
360.5
uuu 257.4
uug 238.0
ugu 192.0
ugg 262.9
I/σ min
−3.5
−1.7
−2.2
−2.5
−2.3
−3.3
−2.6
−3.5
−2.2
−3.3
−2.6
−3.5
−2.0
−2.5
−1.4
−0.1
2.2
I/σ mean
26.6
23.6
32.7
25.8
39.5
0.1
50.5
0.0
41.5
0.1
n
n > 3σ
4929
750
807
745
811
0
all
8523
1050
1033
1051
1051
1097
1091
1082
1068
334
322
320
317
103
67
and the 2:1 compound (CuCN) (pyrimidine) [13, 19]
2
are known. Some other compounds were only charac-
terised by elemental analysis [20]. The crystal struc-
ture of CuBr(pyrimidine) consists of alternating CuBr
single chains and (CuBr)2 dimers which are con-
nected into layers by the pyrimidine ligands [4]. The
structures of the amine poorer compound with cop-
per(I) bromide are unknown. Here we report on the
synthesis and the crystal structure determination of
twinned crystals of the new 2:1 coordination polymer
poly[(CuBr) (µ -pyrimidine-N,N’)].
guu
gug 360.5
ggu 3.7
ggg 353.7
0uu 2.8
0ug 360.5
2.9
906
4
906
0
253
2
255
77
0
90
58
42
61
63
41
8
67.2
0.0
0gu
3.7
gg 230.2
u0u 169.3
g0u 1.2
u0g 239.3
g0g 353.7
uu0 180.4
ug0 131.1
gu0 134.5
gg0 287.5
0
56.4
41.5
−0.1
63.4
53.6
29.3
36.2
45.5
33.0
23.7
44.4
0.3
105
63
66
70
64
2
2
−0.4
−0.9
2.9
Results and Discussion
−2.2
55
Crystal structure investigations
u00
g00
53.8
49.1
1.8
7.0
8
2
39.8
−0.9
0.3
2
0
12
1
15
Search for reflections and indexing of these re-
0
0
0
u0
16
14
23
20
flections yield a monoclinic primitive cell with a =
g0 230.2
94.1
0.0
35.7
˚
3
9
.9119(2), b = 13.525(1), c = 15.346(1) A, β =
0u
3.7
80.6
−1.9
˚
3
7.288(7) and V = 805.4(1) A which can be trans-
00g
1.1
formed into an orthorhombic C-centred cell with a =
˚
˚ 3
3
.912, b = 30.444, c = 13.525 A, and V = 1610.8 A . Table 2. Selected results of some structure refinements for
However, analysis of the intensities of symmetry
equivalent reflections clearly shows that the true sym-
poly[(CuBr) (µ -pyrimidine-N,N’)].
2
2
Refinement
without
twinning
with
merohedral
twinning
3.9119(2)
13.525(1)
15.346(1)
97.288(7)
805.4(1)
8523
with partial
merohedral
twinning
3.9119(2)
13.525(1)
7.6733(5)
97.288(7)
402.70(4)
4243
987
900
0.0313
50
metry should be monoclinic (R (monoclinic) = 3.7%,
int
R (orthorhombic) = 15.6%). The ratio (I/σ(I) =
int
˚
a / A
3.9119(2)
13.525(1)
15.346(1)
97.288(7)
805.4(1)
8523
2
6.6) was high but inspection of the reciprocal space
˚
b / A
using RECIPE [36] shows some weak reflections in-
dicative of a super structure leading to a doubling of
the crystallographic c-axis (Table 1). All reflections V [A ]
with h even and l odd are weak. Determination of the
space group was straightforward, because the system-
˚
c / A
β / A˚ 3
˚
3
Refl. collected
Independent refl.
1982
1982
1312
Refl. Fo < 4σ(Fo)
[%]
1312
0.0373
98
atic absence conditions show a 2 screw axis parallel
1
R
0.0373
99
0.0264
0.0727
0.991
int
2
to b and the |E −1| value points to the centrosymmet- Parameters
R1(Fo < 4σ(Fo)
0.2784
0.6257
1.259
0.0257
0.0670
1.057
ric space group P2 /m. However, the structure could
1
wR2 (all refl.)
only be solved with great difficulty by direct methods
using SHELXS-97 [37]. Anisotropic refinement with
SHELXL-97 [38] by full-matrix least-squares leads to
GOOF
˚ −3
δF [eA
]
15.03 / −10.79 0.53 / −0.71 0.55 / −0.79
poor reliability factors and large residual electron den- (Fig. 1). From this diagram it can be seen that the orig-
∗
∗
sities in the difference map (Table 2). Since the data inal b /c plane acts as a mirror plane and transforms
looked reasonable, it was suspected that the crystal was the reciprocal cell into its twin counterpart. The twin
merohedrally twinned.
law for this operation is (−1 0 1 / 0 1 0 / 0 0 1). In
In order to derive a twin law, a picture of the recip- order to refine the structure, this twin law for the recip-
rocal space has been drawn showing the a /c plane rocal cell parameters has to be inverted and transposed
∗
∗
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C. N a¨ ther et al. · Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals
1107
∗
∗
Fig. 1. Reciprocal space plot with view onto the a /c plane
showing the relationship between both twin domains in the
∗
∗
∗
large unit cell. Full lines: a , c prime component, dotted
ꢀ
ꢀ
ꢀ
∗
∗
∗
lines: a , c twin component (c and c are identical), dot-
dashed lines: a orth, b orth orthorhombic C-centred setting.
∗
∗
Fig. 3. View of the HK1 (top: left), HK2 (top: right), 1KL
(middle: left), 2KL (middle: right), H1L (bottom: left) and
H2L (bottom: right) layers calculated with SPACE [36] the
data set measured on a crystal of [(CuBr) (µ -pyrimidine-
2
2
N,N’)].
terestingly no structural differences can be found for
Fig. 2. Crystal structure of poly[(CuBr) (µ -pyrimidine- both layer units and analysis of the positional parame-
2
2
ters reveals that for any atom, there was a second atom
on x, y, z + 0.5. This means that the c-axis is too long
by a factor of 2.
When the c-axis is halved the space group remains
the same, but unfortunately, the twin law is no longer
N,N’)] with labelling and displacement ellipsoids drawn at
the 50% probability level (The plot originates from a twin
refinement in the large unit cell assuming merohedral twin-
ning.).
to obtain the twin law for the reflection indices. The re- valid, because now only some of the reflections of
sult of this matrix operation is (−1 0 0 / 0 1 0 / 1 0 1). the two domains overlap, while others are not affected
Applying this twin law all reliability factors drop down by the twinning. This means that the crystal is not a
dramatically leading to a reasonable structure model merohedral twin, but a non-merohedral twin. From Ta-
(Table 2).
ble 1 it is obvious that all reflections with h = 2n and
For this unit cell the asymmetric unit consists of two l = 2n + 1 are not observed, which is a quarter of all
crystallographically independent CuBr(pyrimidine) measured reflections. This is also obvious from diffrac-
units with the copper and bromine atom in general po- tion images calculated with SPACE [36] from the data
sitions and the pyrimidine ligands located on a crystal- set measured (Fig. 3). From these images it is obvi-
lographic mirror plane (Fig. 2). The crystal structure ous that some zones have twice as much reflections
consist of CuBr double chains which are connected than others, which is an indication for a twinning of
into layers by the pyrimidine ligands. In this model two the crystal. Therefore, a second diagram of the recip-
crystallographically independent layers are found. In- rocal space was drawn which shows the relationship
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108
C. N a¨ ther et al. · Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals
˚
◦
Cu(1) - N(1)
Cu(1) - Br(1)
Cu(1) - Cu(1B)
2.033(3)
2.530(1)
2.820(2)
Cu(1) - Br(1A)
Cu(1) - Br(1B)
Cu(1) - Cu(1A)
2.460(1)
2.545(1)
2.838(2)
106.85(9)
Table 3. Selected bond lengths (A) and angles ( )
for poly[(CuBr) (µ -pyrimidine-N,N’)].
2
2
N(1) - Cu(1) - Br(1A) 119.47(10)
N(1) - Cu(1) - Br(1)
Br(1A) - Cu(1) - Br(1)
Br(1A) - Cu(1) - Br(1B)
N(1) - Cu(1) - Cu(1B)
Br(1) - Cu(1) - Cu(1B)
111.20(2)
102.79(2)
133.58(9)
54.44(2)
N(1) - Cu(1) - Br(1B) 104.31(9)
Br(1) - Cu(1) - Br(1B) 112.00(3)
Br(1A) - Cu(1) - Cu(1B)
56.77(2)
Br(1B) - Cu(1) - Cu(1B) 121.95(3)
Br(1A) - Cu(1) - Cu(1A) 121.39(3)
N(1) - Cu(1) - Cu(1A) 118.70(10)
Br(1) - Cu(1) - Cu(1A)
Cu(1B) - Cu(1) - Cu(1A)
Cu(1B) - Br(1) - Cu(1A)
56.25(2)
87.48(3)
102.79(2)
Br(1B) - Cu(1) - Cu(1A)
Cu(1B) - Br(1) - Cu(1)
Cu(1) - Br(1) - Cu(1A)
55.75(2)
68.80(2)
68.00(3)
∗
∗
Fig. 4. Reciprocal space plot with view onto the a /c plane
showing the relationship between the original cell (dotdashed
lines) the correct cell (full lines) and the twin component
(
dotted lines). The correct cell and its twin counterpart are
∗
∗
related via a mirror plane in the b /c plane.
Fig. 5. Crystal structure of poly[(CuBr) (µ -pyrimidine-
2
2
N,N’)] with labelling and displacement ellipsoids drawn at
the 50% probability level (top) and with view in the direc-
tion of the crystallographic c-axis (bottom) (The plot origi-
nates from a twin refinement in the correct unit cell using the
HKLF 5 option).
between the original cell (which is actually too big)
and the correct cell (Fig. 4). This shows that the crystal
is in fact twinned by a mirror plane located in the b /c
∗
∗
plane. However, the correct twin law describing the re-
lationship of the two reciprocal cells is (−1 0 0.5 / 0 1
0
/ 0 0 1). Inverting and transposing this matrix leads
twinned) is, that the cell can be transformed to a cell
of higher symmetry with an only slightly worse R(int)
value. In the present case the monoclinic cell can
be transformed into an orthorhombic C-centred one
to (−1 0 0 / 0 1 0 / 0.5 0 1), which is the matrix for
the transformation of the reflection indices of the two
domains. As can be seen from Fig. 4, reflections with
h = 2n overlap, whereas reflections with h = 2n+1 do
not overlap. Therefore, refinement with SHELXL must
be performed using the HKLF 5 option and a modified
data set (see exp. part). This procedure leads to a rea-
sonable structure model and very good reliability fac-
tors (Table 2 and 4).
(Fig. 1).
Crystal structure
The asymmetric unit of poly[(CuBr) (µ -pyrimi-
2
2
dine-N,N’)] contains one crystallographically indepen-
A further interesting feature of the data (which can dent copper and bromine atom in general positions
be a warning sign that a structure may possibly be as well as one pyrazine ligand which is located on
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C. N a¨ ther et al. · Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals
1109
layers by the pyrazine ligands (Fig. 6: top). For sterical
reasons this connection is no longer possible if the ni-
trogen donor atoms are located in the 1- and 2-position
like in pyridazine [29]. In this compound a novel and
interesting CuBr substructure occurs. The actual mo-
tif of CuBr double chains remains the same but these
double chains are expanded by two CuBr single chains
(Fig. 6: bottom). These CuBr tetra-chains are con-
nected to layers by two pyridazine ligands (Fig. 6: bot-
tom). This comparison clearly shows the influence of
the position of the nitrogen donor atoms onto the topol-
ogy and the structure of such coordination polymers.
Thermal properties
The thermal properties of the title compound were
investigated in order to find out if amine poorer inter-
mediates are formed during the thermal decomposition
as it is observed in many other CuX coordination poly-
mers. If poly[(CuBr) (µ -pyrimidine-N,N’)] is heated
2
2
in a thermobalance an endothermic event occurs at a
◦
peak temperature of about 247 C which is accompa-
nied with a strong mass loss in the TG curve (Fig. 7).
The experimental mass loss of 21.9% is in perfect
agreement with that calculated for the removal of all
ligands (∆mtheo. = 21.9%). The DTG curve shows only
one single step and from mass spectroscopic investi-
gations it is obvious that only pyrimidine (m/z = 80)
is emitted (Fig. 7). From these investigations there is
no hint for the occurrence of amine poorer intermedi-
ate phases. It must be pointed out that the decomposi-
tion of poly[(CuBr) (µ -pyrimidine-N,N’)] into CuBr
Fig. 6. Crystal structures of poly[(CuBr) (µ -pyrazine-
2
2
N,N’)] with view along the c-axis (top) and of poly[(CuBr)2-
µ2-pyridazine-N,N’)] with view along the b-axis (bottom).
(
a crystallographic mirror plane. Each copper atom
is coordinated by three symmetry related bromine
atoms and one nitrogen atom of the pyrimidine lig-
and within a strongly distorted tetrahedron (Fig. 5).
˚
The Cu-N bond length of 2.033(3) A and the Cu-
2
2
˚
Br bond lengths between 2.460(1) and 2.545(1) A
proceeds via a strong exothermic reaction. This is in
contrast to the decomposition reactions of all copper(I)
are in the range observed in other CuBr(amine) com-
pounds with similar structures (Table 3). There are
two additional short contacts to neighbouring cop-
˚
per atoms of 2.820 and 2.838 A (Table 3). The cop-
per atoms in the double chains are connected by
the bromine atoms into double chains along the di-
rection of the crystallographic a-axis. These double
chains are connected by the pyrimidine ligands via µ-
N,N’ coordination into layers parallel to the a/b plane
(Fig. 5: bottom).
In this context it is interesting to compare the struc-
tures of the 2:1 compounds with the different diazine
ligands pyrimidine, pyrazine and pyridazine (Fig. 6).
The 2:1 CuBr compound with pyrazine in which the ni-
trogen donor atoms are located in the 1- and 4-position
exhibit a similar structure like the title compound [6]. Fig. 7. DTA, TG, DTG and MS trend scan curve for
CuBr double chains occur, which are connected into poly[(CuBr) (µ -pyrimidine-N,N’)].
2
2
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C. N a¨ ther et al. · Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals
halide coordination polymers investigated previously. Table 4. Selected crystal data and details of the structure de-
However, to be sure that the decomposition reaction termination for poly[(CuBr)2(µ2-pyrimidine-N,N’)].
is not more complex, experiments using temperature
resolved X-ray powder diffraction were performed. In
agreement with the DTA-TG-MS investigations there
is no hint for additional intermediate phases.
Formula
MG [g/mol]
4 4 2 2 2
C H N Cu Br
366.99
yellow needle
Crystal colour/shape
Crystal size / mm
0.1×0.04×0.04
3.9119(2)
13.525(1)
7.6733(5)
97.288(7)
402.70(4)
room-temperature
monoclinic
P21/m
˚
a / A
˚
b / A
Experimental Section
c / A˚
◦
β /
Synthesis of poly[(CuBr) (µ -pyrimidine-N,N’)]:
˚ 3
2
2
V / A
1
.0 mmol of CuBr and 0.5 mmol of pyrimidine and 2 ml ace-
Temperature
Crystal system
Space group
Z
tonitrile were filled into a glass ampoule which was sealed
◦
and heated for 1 week at 120 C. The reaction mixture
2
was cooled to r.t. and the residue filtered off and washed
with ethanol and diethylether. Yield: 83%. Elemental anal-
ysis (%): calcd. C 13.09, H 1.10, N 7.63; found C 13.02,
H 1.04, N 7.60.
Scan range
3◦ ≤ 2θ ≤ 56◦
−
3
dcalc. / g·cm
3.027
−1
µ / mm
15.12
Index range
−5 ≤ h ≤ 5
Single crystal structure analysis: The data were mea-
sured using an Imaging Plate Diffraction System IPDS-
−17 ≤ k ≤ 17
−
10 ≤ l ≤ 10
Refl. collected
Independent refl.
Refl. Fo < 4σ(Fo)
Rint [%]
4243
1
. The structure solution was performed with direct meth-
987
900
0.0313
50
ods using SHELXS-97 [37]. Structure refinement was per-
2
formed against F using SHELXL-97 [38]. All non-hydrogen
atoms were refined with anisotropic displacement parame-
Parameters
ters. The C-H hydrogen atoms were positioned with ide-
˚
R1(Fo < 4σ(Fo))
wR2 (all refl.)
GOOF
0.0257
0.0660
1.057
0.55 / −0.79
alised geometry (d
= 0.93 A) and were refined with fixed
C−H
isotropic displacement parameters (Ueq(H) = 1.2 · Ueq(C))
using the riding model. In order to refine the structure
as a non-merohedral twin using the HKLF 5 option in
˚
−3
]
δF [eA
4
SHELXL-97, the reflection file was modified using the pro- Table 5. Atomic coordinates [·10 ] and isotropic displace-
gram HKLF 5 [39]. For every overlapped reflection the re- ment parameters [ A˚ ·10 ] for poly[(CuBr) (µ -pyrimidine-
2
3
2
2
flection of the second twin domain calculated by the twin
law has to be inserted before the prime reflection. Because
this reflection is generated by a second domain its batch num-
N,N’)].
x
2785(2)
1872(1)
3879(8)
3074(17)
5603(11)
6529(19)
y
327(1)
731(1)
1622(2)
2500
z
Ueq
43(1)
33(1)
30(1)
31(1)
35(1)
39(1)
Cu(1)
1211(1)
-2034(1)
2507(4)
1774(6)
4141(5)
5007(7)
ber has to be set to −2. The negative sign informs the pro- Br(1)
gram that contributions from other twin components follow. N(1)
C(1)
C(2)
C(3)
The intensity and the standard deviation of the second re-
flection are set to the same value as for the prime reflection.
The refinement is finally performed adding a BASF instruc-
1628(3)
2500
2
2
∗2
tion in order to refine the ratio of the two twin components The temperature factor exponent has the form: −2π (h · a U11 +
∗
∗
and the data are read in by the HKLF 5 instruction BASF = ... +2hka b U ).
1
2
0
.376(2). By this procedure equivalent reflections were not
◦
◦
merged. The internal R-values given in this manuscript were mission powder diffractometer equipped with a 4 and 44
calculated from the original data. Details of the structure de- PSD (position sensitive detector) using CuKα radiation (λ =
˚
termination, atomic coordinates and isotropic displacement 1.540598 A). For the temperature dependent X-ray powder
parameters are given in Table 4 and 5.
measurements the instrument is equipped with a graphite
furnace.
Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC 221254.
Copies of the data can be obtained, free of charge, on appli-
cation to CCDC, 12 Union Road, Cambridge CB2 1 EZ, UK.
Differential thermal analysis, thermogravimetry and mass
spectrometry: DTA-TG-MS measurements were performed
using the STA-409CD with Skimmer coupling from Netzsch,
which is equipped with a quadrupole mass spectrometer
QMA 400 (max. 512 amu) from Balzers. The MS measure-
(fax: +44-(0)1223-336033 or email: deposit@ccdc.ca.ac.uk).
X-ray powder diffraction: X-Ray powder diffraction ex- ments were performed in analog and trend scan mode, in
periments were performed using a STOE STADI P trans- Al O crucibles under helium atmosphere (purity: 4.6) using
2
3
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C. N a¨ ther et al. · Synthesis, Thermal Properties and Crystal Structure of Twinned Crystals
1111
◦
heating rates of 4 C/min. All measurements were performed Acknowledgements
with a flow rate of 75 ml/min. and were corrected for buoy-
ancy and current effects. The instrument was calibrated using
standard reference materials.
CHN analysis: CHN-O-RAPID combustion analyser
from Heraeus.
This work was supported by the State of Schleswig-
Holstein. We are very thankful to Professor Dr. Wolfgang
Bensch for financial support and for access to equipment.
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