Synthesis, crystal structures and thermal properties of new ZnBr 2(pyrimidine) coordination compounds

Article abstract of DOI:10.1002/ejic.200700701

Four new bromidozinc(II) coordination compounds with pyrimidine as a ligand were prepared, either in solution or by thermal decomposition reactions, and the thermal reactivity and thermodynamic stability of these compounds were investigated. These results are compared with those for the corresponding ZnI₂(pyrimidine) compounds. The ligand-rich 1:2 compound dibromidobis(pyrimidine-N)zinc(II) (I) crystallizes in the monoclinic space group P2₁/n. In this structure the zinc atoms are coordinated by two bromido ligands and two pyrimidine ligands within distorted tetrahedra. On heating, compound I is transformed into the ligand-deficient 2:3 intermediate bis(dibromido)bis(pyrimidine-N)(μ₂-pyrimidine-N,N′) dizinc(II) (II), which crystallizes in the monoclinic space group C2/c. The crystal structure consists of two ZnBr₂(pyrimidine) subunits, which are connected by an additional pyrimidine ligand through μ-N,N′ coordination. Thermal decomposition of compound II leads to the formation of the ligand-deficient 1:1 compound dibromido(μ₂-pyrimidine-N,N′) zinc(II) (III), which crystallizes in the orthorhombic space group Pmma. In compound III, the zinc atoms are coordinated by four bromine atoms and two pyrimidine ligands within distorted octahedra. The ZnBr₂ units are connected through common edges into chains, which are linked by the pyrimidine ligands into layers. On heating, compound III is transformed into the ligand-deficient 2:1 compound (ZnBr₂)₂-(pyrimidine) (IV), which decomposes to give ZnBr₂. Solvent-mediated conversion experiments in solution show that not all of the compounds can be prepared by treating ZnBr₂ and pyrimidine in the molar ratio given by the formula of the final product. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700701

FULL PAPER
DOI: 10.1002/ejic.200700701
Synthesis, Crystal Structures and Thermal Properties of New
ZnBr (pyrimidine) Coordination Compounds
2
[a]
[a]
[a]
Christian Näther,* Gaurav Bhosekar, and Inke Jeß
Keywords: Coordination compounds / Synthesis / Crystal structure / Thermal reactivity
Four new bromidozinc(II) coordination compounds with pyr-
imidine as a ligand were prepared, either in solution or by
thermal decomposition reactions, and the thermal reactivity
and thermodynamic stability of these compounds were inves-
composition of compound II leads to the formation of the li-
gand-deficient 1:1 compound dibromido(µ -pyrimidine-
N,NЈ)zinc(II) (III), which crystallizes in the orthorhombic
space group Pmma. In compound III, the zinc atoms are coor-
2
tigated. These results are compared with those for the corre- dinated by four bromine atoms and two pyrimidine ligands
sponding ZnI (pyrimidine) compounds. The ligand-rich 1:2 within distorted octahedra. The ZnBr units are connected
compound dibromidobis(pyrimidine-N)zinc(II) (I) crystallizes
in the monoclinic space group P2 /n. In this structure the zinc
2
2
through common edges into chains, which are linked by the
1
pyrimidine ligands into layers. On heating, compound III is
atoms are coordinated by two bromido ligands and two pyr-
imidine ligands within distorted tetrahedra. On heating,
compound I is transformed into the ligand-deficient 2:3 in-
transformed into the ligand-deficient 2:1 compound (ZnBr
(pyrimidine) (IV), which decomposes to give ZnBr . Solvent-
mediated conversion experiments in solution show that not
all of the compounds can be prepared by treating ZnBr and
pyrimidine in the molar ratio given by the formula of the final
product.
2 2
) -
2
termediate bis(dibromido)bis(pyrimidine-N)(µ
N,NЈ)dizinc(II) (II), which crystallizes in the monoclinic space
group C2/c. The crystal structure consists of two ZnBr (pyr-
2
-pyrimidine-
2
2
imidine) subunits, which are connected by an additional pyr-
imidine ligand through µ-N,NЈ coordination. Thermal de-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
in solution can be discovered and prepared as phase-pure
solids.
Investigations on coordination polymers, inorganic–or-
Recently we have reported on new iodidozinc(II) coordi-
ganic hybrid compounds and metal–organic frameworks nation compounds with pyrimidine as a ligand.[ Al-
are attracting increasing interest[ because of the potential together, seven different compounds were obtained, includ-
applications of these systems as electric, magnetic, optical ing three polymorphic modifications (Figure 1). The ligand-
or porous materials.[ Most of these compounds are nor- rich 1:2 compound 1 decomposes in several steps, in which
mally prepared in solution, where different stable and meta- ligand-deficient compounds 2, 3 and 4 [2:3 (2), 1:1 (3) and
stable species exist in equilibrium. In view of this, mixtures 2:1 (4)] are formed as intermediates. Detailed analysis of
of compounds are often obtained during the synthesis, and the crystal structures of these compounds clearly indicates
some specific target compounds cannot be prepared at all. a strong correlation between the crystal structures of the
Recently we have demonstrated that thermal decomposition reactants and the products for the first two thermal reac-
of ligand-rich precursor materials is a suitable alternative tions. Slight changes in the reaction conditions lead to the
method for the convenient synthesis of new coordination formation of a further 1:1 compound of composition
4]
1]
2]
[
3]
compounds. In this method, ligand-rich precursors are [ZnI (pyrimidine)] (acetonitrile)
(5). On heating, com-
2
4
0.25
heated, leading to ligand-deficient coordination compounds pound 5 loses acetonitrile and decomposes to give a new
by stepwise liberation of the ligands. One advantage of this 1:1 polymorphic modification 6. Compound 6 undergoes a
method is that the equilibrium is shifted irreversibly in the polymorphic phase transition to yield the new compound
direction of the ligand-deficient coordination compounds, 7, which is finally transformed into the 1:1 compound 3.
and thus new compounds which are metastable or unstable Solvent-mediated conversion experiments clearly show that
compound 3 represents the thermodynamically most stable
form at room temperature, whereas 5, 6 and 7 are metasta-
[
a] Institut für Anorganische Chemie, Universität zu Kiel,
Olshausenstr. 40 (Otto-Hahn-Platz 6–7), 24098 Kiel
Fax: +49-431-880-1520
ble. Our results clearly show that different stable and meta-
stable species are in equilibrium and that product formation
in such thermal decomposition reactions depends on the
actual structure of the ligand-rich precursor compound.
E-mail: cnaether@ac.uni-kiel.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2007, 5353–5359
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5353

C. Näther, G. Bhosekar, I. Jeß
FULL PAPER
Figure 1. Schematic presentation of the thermal reactions of ZnI
2
(pyrimidine) coordination compounds.[4]
In order to gain more insight into such reactions, we have
investigated the corresponding compounds with ZnBr and
2
pyrimidine. Here we report on the results of these investi-
gations.
Results and Discussion
Crystal Structures
The ligand-rich 1:2 compound I crystallizes in the mono-
clinic space group P2 /n with four formula units in the unit
1
cell and all atoms in general positions. The crystal structure
[4]
of I is isomorphous to ZnI (pyrimidine) . In the crystal
2
2
structure, there are discrete complexes, in which the zinc
atoms are coordinated by two bromine atoms and two ni-
trogen atoms of the pyrimidine ligands within distorted tet-
rahedra (Figure 2: top and Table 1). The pyrimidine ligands
of adjacent complexes are stacked in the direction of the
crystallographic a axis, which indicates π–π interactions
(Figure 2: bottom).
The ligand-deficient 2:3 intermediate II crystallizes in the
monoclinic space group C2/c with eight formula units in
the unit cell. This compound is isomorphous to (ZnI ) -
2
2
[
4]
(
(
pyrimidine)3. In the crystal structure discrete [(ZnBr2)2-
pyrimidine) ] units are found, which are located in special
3
positions (Figure 3: top). Each zinc atom is coordinated by
two bromine atoms and two nitrogen atoms, one on a ter-
minal and one on a bridging pyrimidine ligand (Figure 3:
top and Table 1). The zinc atoms are bridged by a pyrimid-
ine ligand with µ-N,NЈ coordination. The terminal pyrimid-
ine rings are stacked in the direction of the crystallographic
b axis, indicating π–π interactions (Figure 3: bottom).
Figure 2. Crystal structure of compound I with a view of the coor-
The ligand-deficient 1:1 compound III crystallizes in the dination sphere of the zinc cations with labelling and displacement
ellipsoids drawn at the 50% probability level (top) and a view of
orthorhombic space group Pmma with two formula units
in the unit cell. The zinc and the bromine atoms as well as
the crystal structure in the direction of the crystallographic a axis
(
bottom).
the pyrimidine ligands are located on crystallographic mir-
ror planes. This compound is not isomorphous to the corre-
[4]
sponding iodido analogue ZnI (pyrimidine). In this struc-
2
ture the zinc atoms are coordinated by four bromine atoms
and two nitrogen atoms of pyrimidine ligands within graphic a axis (Figure 4: middle). The zinc octahedra are
slightly distorted octahedra (Figure 4: top and Table 1). The additionally connected through common Br edges into cor-
zinc atoms are connected by the pyrimidine ligands into zig- rugated layers, which are located in the ab plane (Figure 4:
zag chains, which elongate in the direction of the crystallo- bottom).
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Eur. J. Inorg. Chem. 2007, 5353–5359

Synthesis and Thermal Properties of New Coordination Compounds
Table 1. Bond lengths [Å] and angles [°] for compounds I, II and
[
a]
III.
Compound I
Zn1–N1
Zn1–Br2
N1–Zn1–Br2
N1–Zn1–Br1
Br2–Zn1–Br1
2.063(3)
2.3489(6) Zn1–Br1
110.55(9) N11–Zn1–Br2
106.94(9) N1–Zn1–N11
124.12(2) N11–Zn1–Br1
Zn1–N11
2.081(3)
2.3500(5)
105.50(9)
102.79(11)
104.78(8)
Compound II
Zn1–N11
Zn1–N1
N11–Zn1–N1
N11–Zn1–Br2
N1–Zn1–Br2
2.070(4)
2.091(4)
101.21(16) N11–Zn1–Br1
110.28(13) N1–Zn1–Br1
110.37(11) Br2–Zn1–Br1
Zn1–Br2
Zn1–Br1
2.3333(8)
2.3523(8)
104.80(12)
105.97(11)
122.10(3)
Compound III
Zn1–N1
Zn1–N1B
Zn1–Br1B
Br1–Zn1E
N1–Zn1–N1B
N1–Zn1–Br1B
N1B–Zn1–Br1B
N1–Zn1–Br1
N1B–Zn1–Br1
Br1B–Zn1–Br1
N1–Zn1–Br1D
N1B–Zn1–Br1D
2.178(3)
2.178(3)
2.6287(3) Zn1–Br1C
2.6287(3) Br1–Zn1–Br1D
180.00(17) N1–Zn1–Br1C
90.07(6)
89.93(6)
89.93(6)
90.07(6)
180.0
Zn1–Br1
Zn1–Br1D
2.6287(3)
2.6287(3)
2.6287(3)
89.056(12)
89.93(6)
N1B–Zn1–Br1C
Br1B–Zn1–Br1C
Br1–Zn1–Br1C
Br1D–Zn1–Br1C
C1–N1–Zn1
C2–N1–Zn1
Br1B–Zn1–Br1D
90.07(6)
89.056(12)
90.944(12)
180.0
122.3(3)
120.8(3)
90.07(6)
89.93(6)
90.944(12)
[
a] Symmetry transformations used to generate equivalent atoms:
A: –x + 3/2, –y, z; B: –x + 1, –y, –z; C: x, y – 1, z; D: –x + 1, –y
1, –z.
+
Figure 4. Crystal structure of compound III with a view of the
coordination sphere of the zinc cations with labelling and displace-
ment ellipsoids drawn at the 50% probability level (top; symmetry
codes: A: –x + 1, –y, –z; B: x, y – 1, z; C: –x + 1, –y + 1, –z) and
a view of the structure in the direction of the crystallographic b
axis (bottom).
Thermoanalytical Investigations
Five mass steps are observed for compound 1 on heating,
of which the first four steps are accompanied by endother-
mic events in the DTA curve (Figure 5). From the MS trend
scan curve it is evident that only pyrimidine ligands (m/z =
80) are liberated in the first four steps and the DTG curve
shows that not all of the steps are well resolved. The experi-
mental mass loss in each of the first four TG steps is in
good agreement with that calculated for the removal of half
of the pyrimidine ligands in each step (∆mtheo –1/2 pyrimid-
ine = –10.4%) (Figure 5). Thus, it can be inferred that in
these steps a ligand-deficient 2:3, 1:1 and 2:1 compound
is formed, which finally decomposes to give ZnBr , which
2
vaporizes on further heating.
In order to determine the nature of the thermal decom-
position products, additional thermogravimetric measure-
ments were performed in which the heating was stopped
after each step. The residues thus obtained were investi-
gated by X-ray powder diffraction (Figure 6) and elemental
analysis; the results are presented in the Experimental Sec-
tion.
Figure 3. Crystal structure of compound II with a view of the coor-
dination sphere of the zinc cations with labelling and displacement
ellipsoids drawn at the 50% probability level (top; symmetry codes:
A = –x, y, –z + 3/2) and a view of the crystal structure in the
direction of the crystallographic b axis (bottom).
Eur. J. Inorg. Chem. 2007, 5353–5359
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5355

C. Näther, G. Bhosekar, I. Jeß
FULL PAPER
with that of the pattern of a solid obtained by stirring a
crystalline suspension of ZnBr and pyrimidine in n-hexane
2
for several days. This result indicates that the ligand-de-
ficient compound IV can also be prepared in solution.
The elemental analysis of the residue formed in the third
TG step corresponds to a new compound of 2:1 stoichiome-
try of composition (ZnBr ) (pyrimidine) (IV). As expected,
2
2
the experimental X-ray powder diffraction pattern of this
compound is completely different from that calculated for
compounds II and III and for ZnBr (Figure 7).
2
Figure 5. DTA, TG, DTG and MS trend scan curves for compound
–1
I [heating rate: 4 °Cmin ; m/z = 80 (pyrimidine)]; given are the
mass changes [%] and the peak temperatures T [°C].
p
Figure 7. Experimental X-ray powder diffraction pattern of the res-
idue obtained after the third TG step during the thermal decompo-
sition of the ligand-rich 1:2 compound I (top) and the experimental
X-ray powder diffraction pattern for compound IV obtained from
solution (bottom).
Investigations on the Stability of the Compounds in
Solution and in the Solid State
The stability of compounds I, II and III as solids was
investigated by time-dependent X-ray powder diffraction.
These investigations show that compounds II and III are
stable over several days, whereas the ligand-rich 1:2 com-
pound I decomposes even at room temperature within a few
days to give compound III.
The stability of these compounds was further investi-
gated in solution by solvent-mediated conversion experi-
ments. In these experiments the metal salt and ligand are
mixed in different stoichiometric ratios by using acetonitrile
Figure 6. Experimental X-ray powder diffraction pattern of the res-
idue obtained after the first (top) and second (bottom) TG step
in the thermal decomposition of the ligand-rich 1:2 compound I,
accompanied by the calculated X-ray powder diffraction patterns as a solvent. These crystalline suspensions were stirred for
for compounds II and III.
a week in order to obtain the thermodynamically most
stable form. Afterwards the products were investigated by
X-ray powder diffraction (Table 2). These experiments
The experimental X-ray powder diffraction patterns of clearly showed that all compounds are stable and can also
the residues formed in the first and second TG steps are in be prepared in solution. However, it is to be noted that not
excellent agreement with those calculated for compounds II all of these compounds can be prepared simply by mixing
and III, clearly indicating that in the first TG step the li- the reactants stoichiometrically as given by the formula.
gand-deficient 2:3 intermediate II is formed, and then it is Thus, the reaction of ZnBr and pyrimidine in 2:3 mol ratio
2
transformed into the ligand-deficient 1:1 compound III on results in the formation of the 1:1 compound III, whereas
further heating (Figure 5 and Figure 6). In addition, the re-
sults of an elemental analysis of the residues agrees with the
expected results for a 2:3 and 1:1 compound (Experimental
Table 2. Result of the crystallization experiments in different sol-
vents as a function of the molar ratio between metal and ligand
Section). These results show that both compounds are ob- (pyrimidine).
tained as phase-pure solids even though the first TG step is
ZnBr
2
/Ligand 1:4
1:3
1:2
2:3
1:1
2:1
not well resolved. It is interesting to note that the powder
pattern of the residue formed in the third step matches well
Compound
I (1:2)
II (2:3)
III (1:1)
IV(2:1)
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Eur. J. Inorg. Chem. 2007, 5353–5359

Synthesis and Thermal Properties of New Coordination Compounds
the reaction in a 1:2 mol ratio leads to the formation of leads directly to the formation of the 2:3 compound (ZnBr ) -
2
2
the 2:3 compound II (Table 2). This indicates that for the (pyrimidine) , regardless of the actual heating rate.
3
preparation of the ligand-rich compounds, an excess of the
In this context, it must be mentioned that for the decom-
ligand must always be used. The ligand-deficient compound position reaction of the discrete units in ZnI (pyrimidine)2
2
IV is difficult to prepare, because in many cases it is con- (1), via the oligomeric units in (ZnI ) (pyrimidine) (2), to
2
2
3
taminated with compound III or ZnBr (Table 2).
the chains in ZnI (pyrimidine) (3), a smooth reaction path-
way can be found (Figure 8: left). In contrast, only for the
2
2
[
4]
reaction of ZnBr (pyrimidine) (I) to give (ZnBr ) (pyrim-
2
2
2 2
Comparison of ZnX (pyrimidine) Coordination Compounds
2
idine) (II) a smooth reaction pathway is found, whereas for
3
(X = Cl, I)
the transformation of the 2:3 intermediate II into the li-
gand-deficient 1:1 compound III, large translational and ro-
tational changes are needed and thus no smooth reaction
pathway can be expected (Figure 8: right).
As mentioned earlier, for the corresponding coordination
compounds with ZnI a variety of compounds and poly-
2
[4]
morphic modifications were found. The different poly-
morphic modifications were detected when the pseudopoly-
morphic 1:1 compound [ZnI (pyrimidine)] (acetonitrile)
0.25
2
4
Conclusions
was decomposed, which was prepared by fast precipitation
under kinetic control from a solution of ZnI and pyrimid-
In this contribution we have presented four new coordi-
2
ine in acetonitrile by adding an antisolvent in which the nation compounds based on ZnBr
compound is insoluble. In view of this observation, several can be prepared by thermal decomposition from the ligand-
attempts were made to prepare the corresponding acetoni- rich compound ZnBr (pyrimidine). These compounds can
and pyrimidine, which
2
2
trile solvate of the bromide compound. However, this al- also be prepared in solution; however, the ligand-rich com-
ways resulted in the formation of the ligand-deficient 1:1 pounds are only accessible if an excess of ligand is used.
compound III. From ZnI and pyrimidine, two metastable The reaction of ZnBr and pyrimidine in a ratio given by
2
2
polymorphic modifications of the 1:1 compound could also the formula of the final compound does not lead to com-
be prepared by performing the crystallization under kinetic pounds I and II. This phenomenon is frequently observed
[
4]
control. Similar attempts to prepare such forms of the in the preparation of such compounds, and therefore new
bromide compound by nucleation-controlled crystalli- compounds can be easily overlooked if the synthesis is per-
[
5]
zation did not result in any polymorphic modifications. It formed only in solution. In contrast, by thermal decompo-
must also be noted that the reaction of ZnCl with pyrimid- sition of the ligand-rich compounds, all ligand-deficient
2
ine leads only to one compound of composition ZnCl (pyr- compounds can be detected in a single measurement. A
2
[
6]
imidine), which shows that the number of possible com- comparison of the thermal properties of these bromido
pounds in the ZnX (pyrimidine) [X = I, Br, Cl] system de- complexes with those of the corresponding iodidozinc(II)
2
creases from iodine to chlorine.
Differences between the ZnI and ZnBr coordination eral differences, which include the influence of the actual
and chloridozinc(II) coordination compounds reveals sev-
2
2
compounds are also found in the thermal reactivity of the heating rate on product formation, the mechanism of such
ligand-rich 1:2 compounds, which are isotypic. On slow reactions and the possibility of the preparation of thermo-
heating ZnI (pyrimidine) (1) is transformed directly into dynamically metastable compounds and different polymor-
2
2
the ligand-deficient 1:1 compound ZnI (pyrimidine) (3), phic modifications.
2
without the formation of the ligand-deficient 2:3 intermedi-
ate 2. Compound 2 can only be obtained by thermal de-
composition if fast heating rates are used, which shows that
Experimental Section
kinetics plays an important role in product formation. In Synthesis of Compound I: ZnBr (112.59 mg, 0.5 mmol) and pyrim-
2
contrast, thermal decomposition of ZnBr (pyrimidine) (I) idine (240.24 mg, 3.0 mmol) were mixed in acetonitrile (0.5 mL).
2
2
2 2
Figure 8. Structural relationships between the crystal structures of the ZnI (pyrimidine) (left) and ZnBr (pyrimidine) coordination poly-
mers.
Eur. J. Inorg. Chem. 2007, 5353–5359
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5357

C. Näther, G. Bhosekar, I. Jeß
FULL PAPER
Afterwards, diethyl ether (1.0 mL) was added to the clear solution
tative yield by thermal decomposition of compound I, II or III.
for precipitation. Yield: 133.6 mg (69.36%) based on ZnBr
Br Zn (385.37): calcd. C 24.93, H 2.09, N 14.54; found C
5.02, H 2.18, N 14.63. IR (KBr): ν˜ = 1591 (s), 1561 (m), 1471 (m),
2
.
4 4 4 2 2
C H Br N Zn (530.46): calcd. C 9.06, H 0.76, N 5.28; found C
9.13, H 0.81, N 5.35. IR (KBr): ν˜ = 3106 (w), 3082 (w), 1684 (w),
C
2
1
8
H
8
2
N
4
1596 (s), 1569 (m), 1465 (s), 1403 (s), 1220 (m), 1180 (s), 1082 (s),
–
1
406 (s), 1369 (w), 1237 (w), 1174 (m), 1082 (m), 1016 (m), 817 1028 (s), 801 (m), 689 (s), 660 (s) cm .
–1
(
w), 705 (m), 688 (m), 643 (m) cm . Single crystals were prepared
by the reaction of ZnBr (56.29 mg, 0.25 mmol) and pyrimidine
120.12 mg, 1.5 mmol) in acetonitrile (0.5 mL). Slow evaporation
Elemental Analysis of the Residues Obtained in the Thermal Decom-
position of Compound I
2
(
(
A) Isolated after the first heating step (compound II)
Zn (690.66): calcd. C 20.87, H 1.75, N 12.17; found
C 20.94, H 1.69, N 12.20. (B) Isolated after the second heating step
compound III) C Br Zn (305.28): calcd. C 15.74, H 1.32, N
.18; found C 15.86, H 1.28, N 9.08. (C) Isolated after the third
heating step (compound IV) C Br Zn (530.46): calcd. C 9.06,
of the solvent from the clear solution yields colourless crystals in
about a week.
C
12
H12Br
4
N
6
2
2
Synthesis of Compound II: ZnBr (112.59 mg, 0.5 mmol) and pyr-
imidine (80.08 mg, 1.0 mmol) were mixed in acetonitrile (0.5 mL).
Afterwards, diethyl ether (1.0 mL) was added to the clear solution
(
4
H
4
N
2
2
9
4
H
4
4
N
2
2
for precipitation. Yield: 161.9 mg (93.77%) based on ZnBr
Zn (690.66): calcd. C 20.87, H 1.75, N 12.17; found
C 21.00, H 1.72, N 12.14. IR (KBr): ν˜ = 3121 (w), 3095 (w), 3064
2
.
H 0.76, N 5.28; found C 8.48, H 1.47, N 4.98.
C
12
H12Br
4
N
6
2
Single Crystal Structure Analysis: All investigations were per-
formed with an Imaging Plate Diffraction System (IPDS-1) from
STOE & CIE. Structure solutions were performed with direct
(
(
m), 1594 (s), 1560 (s), 1472 (s), 1409 (s), 1228 (w), 1173 (m), 1081
–1
s), 1017 (m), 814 (m), 705 (s), 644 (m) cm . Single crystals were
(112.59 mg, 0.5 mmol) and pyr-
[7]
methods by using SHELXS-97, and structure refinements were
prepared by the reaction of ZnBr
2
2
[7]
performed against F with SHELXL-97. For all structures a nu-
imidine (80.08 mg, 1.0 mmol) in a mixture of acetonitrile (2.0 mL)
and water (0.3 mL). Slow evaporation of the solvent yielded colour-
less crystals in about 4 d.
[
8]
merical absorption correction was applied by using X-Red and
X-Shape.[ All non-hydrogen atoms were refined with anisotropic
displacement parameters. All hydrogen atoms were positioned with
idealized geometry and were refined with fixed isotropic displace-
ment parameters [Ueq(H) = 1.2·Ueq(C)] by using a riding model
with dC–H = 0.95 Å. Details of the structural determination are
given in Table 3 and in the Supporting Information.
8]
2
Synthesis of Compound III: ZnBr (112.59 mg, 0.5 mmol) and pyr-
imidine (40.04 mg, 0.5 mmol) were mixed in acetonitrile (0.5 mL).
Afterwards diethyl ether (1.0 mL) was added for precipitation.
4 4 2 2
Yield: 129.3 mg (84.71%). C H Br N Zn (305.28): calcd. C 15.74,
H 1.32, N 9.18; found C 15.87, H 1.29, N 9.09. IR (KBr): ν˜ = 3121
CCDC-651854 (I), -651855 (II) and -651856 (III) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
(
(
(
w), 3075 (w), 1595 (s), 1569 (m), 1465 (s), 1402 (s), 1356 (w), 1220
m), 1180 (m), 1145 (w), 1081 (s), 1028(m), 933 (w), 801 (m), 688
–1
s), 661(s) cm . Single crystals were prepared by the reaction of
(22.51 mg, 0.1 mmol) and pyrimidine (8.08 mg, 0.1 mmol) in
ZnBr
2
water (0.3 mL). Slow evaporation of the solvent yielded colourless
crystals in about one week.
X-ray Powder Diffraction: X-ray powder diffraction experiments
were performed by using a STOE STADI P transmission powder
α
diffractometer with Cu-K -radiation (λ = 154.0598 pm), which is
equipped with a position-sensitive detector (scan range: 5°–45°)
from STOE & CIE.
Synthesis of Compound IV: This compound was difficult to obtain
in solution, because in most cases it was contaminated with com-
pound III. From several reactions with different stoichiometric ra-
tios of ZnBr
2
and pyrimidine, we obtained only one batch which
Differential Thermal Analysis, Thermogravimetry and Mass Spec-
trometry: The heating-rate-dependent DTA-TG measurements
were performed under a nitrogen atmosphere (purity: 5.0) with
was phase-pure. Its X-ray powder diffraction pattern is shown in
Figure 7. However, the pure compound can be prepared in quanti-
Table 3. Crystal data and results of the structural refinement for compounds I, II and III.
Compound
I
II
III
Chemical formula
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C
8
H
8
Br
2
N
4
Zn
C
690.66
monoclinic
C2/c
22.8319(19)
7.7361(5)
11.4845(9)
98.656(10)
2005.4(3)
8
2.288
10.369
2.78 to 28.03
9201
12
H
12Br
4
N
6
Zn
2
4 4 2 2
C H N Br Zn
305.28
385.37
monoclinic
P2 /n
7.6087(6)
12.4580(8)
12.5606(10)
91.854 (10)°
1189.99 (15)
4
2.151
8.751
orthorhombic
Pmma
12.2327(14)
3.7481(3)
7.2659(6)
–
333.14(5)
2
3.043
1
β [°]
Volume [Å ]
3
Z
–3
Calculated density [gcm ]
–1
µ [mm ]
θ range [°]
15.578
2.80 to 28.04
3127
2
2.30 to 28.03
11267
Measured reflections
Unique reflections
2778
2341
0.0360
0.0968
1.026
0.778/–0.918
2394
1809
0.0413
0.1168
1.024
0.908/–0.759
478
441
0.0268
0.0697
1.100
1.106/–1.128
Observed reflections [IϾ2σ(I)]
[
a]
R
1
[IϾ2σ(I)]
[all data]
[
b]
wR
GOF
Residual electron density [eÅ ]
2
–3
2 o c o
a] R = Σ ||F | – |F ||/Σ|F |. [b] wR – F
= {Σ[w(F 2 2)2]/Σ[w(F ) ]}1/2.
2 2
[
1
o
c
o
5358
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5353–5359

Synthesis and Thermal Properties of New Coordination Compounds
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Received: July 4, 2007
Published Online: October 11, 2007
Eur. J. Inorg. Chem. 2007, 5353–5359
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5359