One-dimensional pyrazine bridged M(II)-saccharinato coordination polymers: Synthesis, characterization, crystal structures and thermal studies

Article abstract of DOI:10.1016/j.poly.2007.02.018

Three new coordination polymers with a general formula [M(sac)₂(μ-pyz)(H₂O)₂]_n [M = Mn(II) (1), Fe(II) (2), Co(II) (3), pyz = pyrazine, and sac = saccharinate] have been synthesized and characterized by elemental analyses, IR, UV-VIS, magnetic measurements, thermal analysis techniques and single crystal X-ray diffraction. All three complexes are isomorphous, crystallizing in the triclinic space group P over(1, ?) (No. 2). Each metal(II) ion in 1-3 is octahedrally coordinated by two sac, two pyz and two aqua ligands. The sac ligands are N-coordinated, while the pyz ligands bridge the metal centers leading to an one-dimensional linear chain structure. Intra-chain M-M separations in complexes 1, 2 and 3 are 7.381(2), 7.259(3) and 7.188(3) A?, respectively. The individual chains are linked into two-dimensional layers by O-H?O hydrogen bonds involving the hydrogens of aqua ligands and carbonyl and sulfonyl O atoms of sac ligands. The hydrogen bonded layers are further assembled into three-dimensional supramolecular networks by weak aromatic π?π stacking interactions between the phenyl rings of sac ligands or CH?π interactions involving pyz. These complexes exhibit similar decomposition characteristics. In the first stages, endothermic removal of the aqua and pyz ligand takes place leading to an intermediate probably in the form of [M(sac)₂], which undergoes highly exothermic decomposition at higher temperatures to give corresponding metal oxides.

Full text of DOI:10.1016/j.poly.2007.02.018

Polyhedron 26 (2007) 3199–3204
www.elsevier.com/locate/poly
One-dimensional pyrazine bridged M(II)-saccharinato
coordination polymers: Synthesis, characterization, crystal
structures and thermal studies
a,
a
b
Veysel T. Yilmaz *, Evrim Senel , Canan Kazak
a
Department of Chemistry, Faculty of Arts and Sciences, Ondokuz Mayis University, 55139 Kurupelit, Samsun, Turkey
Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis University, 55139 Kurupelit, Samsun, Turkey
b
Received 8 January 2007; accepted 21 February 2007
Available online 24 February 2007
Abstract
Three new coordination polymers with a general formula [M(sac)2(l-pyz)(H2O)2]n [M = Mn(II) (1), Fe(II) (2), Co(II) (3), pyz = pyr-
azine, and sac = saccharinate] have been synthesized and characterized by elemental analyses, IR, UV–VIS, magnetic measurements,
thermal analysis techniques and single crystal X-ray diffraction. All three complexes are isomorphous, crystallizing in the triclinic space
ꢀ
group P1 (No. 2). Each metal(II) ion in 1–3 is octahedrally coordinated by two sac, two pyz and two aqua ligands. The sac ligands are N-
coordinated, while the pyz ligands bridge the metal centers leading to an one-dimensional linear chain structure. Intra-chain M–M sep-
˚
arations in complexes 1, 2 and 3 are 7.381(2), 7.259(3) and 7.188(3) A, respectively. The individual chains are linked into two-dimensional
layers by O–HÁ Á ÁO hydrogen bonds involving the hydrogens of aqua ligands and carbonyl and sulfonyl O atoms of sac ligands. The
hydrogen bonded layers are further assembled into three-dimensional supramolecular networks by weak aromatic pÁ Á Áp stacking inter-
actions between the phenyl rings of sac ligands or CHÁ Á Áp interactions involving pyz. These complexes exhibit similar decomposition
characteristics. In the first stages, endothermic removal of the aqua and pyz ligand takes place leading to an intermediate probably
in the form of [M(sac)2], which undergoes highly exothermic decomposition at higher temperatures to give corresponding metal oxides.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Saccharin; Pyrazine; 1D chain; Hydrogen bond; Pi–pi interaction
1. Introduction
has been investigated and successfully employed in the for-
mation of a wide range of supramolecular networks [9,10].
We have long been interested in the preparation and
characterization of metal complexes of saccharin. Saccha-
rin (C7H5NO3S and also named o-benzosulfimide) is
currently the most widely used non-caloric artificial sweet-
ener and commercially available as water soluble alkali
salts. The coordination chemistry of saccharin seems to
be very interesting. Although no metal complex of the
molecular saccharin is known, the corresponding deproto-
nated saccharinate anion (sac) behaves as a versatile poly-
functional ligand. It coordinates to different metal ions
rather easily, owing to the presence of the negatively
charged imino nitrogen atom and the carbonyl and sulfo-
nyl oxygen atoms and exhibits different coordination
The design of new coordination polymers has attracted
much attention due to their potential applications in the
areas of catalysis, conductivity, magnetism and optical
behaviors [1–8]. So far, well-defined supramolecular arrays
have been realized based on the concept of self-assembly,
generated by non-covalent interactions such as coordina-
tion bonding, hydrogen bonding, aromatic pÁ Á Áp stacking,
etc. Among various assembling strategies, self-assembly of
metal-containing building blocks via coordination bonds
*
Corresponding author. Tel.: +90 362 312 1919; fax: +90 362 457 6081.
E-mail address: vtyilmaz@omu.edu.tr (V.T. Yilmaz).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.02.018

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V.T. Yilmaz et al. / Polyhedron 26 (2007) 3199–3204
modes such as monodentate (through the N- or the car-
bonyl O-atom), bidentate (N, O), tridentate (N, O, O) or
bridging forming [11]. In spite of coordination abilities,
the donor sites also act as good hydrogen bond acceptors
to generate supramolecular networks.
3474sb, 3140–3011w, 1630vs, 1591vs, 1463vs, 1423vs,
1345s, 1286vs, 1266vs, 1168vs, 1128vs, 1060vs, 961vs,
823vs, 789vs, 734vs, 685vs, 656s, 606vs, 538vs, 459m.
[Fe(sac)2(l-pyz)(H2O)2]n 2: Yield 85%. Anal. Calc. for
C18H16N4O8S2Fe: C, 40.31; H, 3.01; N, 10.46. Found C,
Recently, we reported several mixed-ligand coordina-
tion polymers of sac containing Hg(II) [12], Pb(II)
[13–15], Ag(I) [16–21] and Cu(II) [22]. Although most of
the structures are formed through coordination bonds, in
some of them, the building blocks are linked by way of
M–M interactions. Now, we have extended our work using
pyrazine (pyz) as a secondary ligand, since pyz is a good
candidate for designing polymeric metal complexes as well
as molecular building blocks because of its good bridging
ability and rod like rigidity [23]. In this paper, we report
three new coordination polymers with a general formula
[M(sac)2(l-pyz)(H2O)2]n [M = Mn(II) (1), Fe(II) (2), Co(II)
(3)] constructed from assembly of pyz with the correspond-
ing metal(II)-sac complexes. Supramolecular interactions
such as hydrogen bonds and aromatic p–p stackings
responsible for the extended networks based on the pyraz-
ine bridged one-dimensional coordination polymers are
discussed.
40.55; H, 3.10; N, 10.67%. (Solid KBr pellet): m (cmÀ1
)
3490sb, 3127–3011w-m, 1630vs, 1594vs, 1461s, 1419s,
1340s, 1275vs, 1265vs, 1172vs, 1162vs, 1121vs, 1059vs,
966vs, 822vs, 791s, 750vs, 688s, 657s, 606s, 534vs, 472m.
[Co(sac)2(l-pyz)(H2O)2]n 3: Yield 80%. Anal. Calc. for
C18H16N4O8S2Co: C, 40.08; H, 2.99; N, 10.39. Found C,
40.22; H, 3.14; N, 10.58%. IR (Solid KBr pellet): m
(cmÀ1
) 3494sb, 3130–3019w, 1626vs, 1594vs, 1469s,
1427s, 1353s, 1280vs, 1259vs, 1165vs, 1123vs, 1070vs,
966vs, 861m, 830s, 788s, 756vs, 683s, 610s, 536vs, 473m.
2.3. X-ray crystallography
Intensity data for the title complexes were collected
using a Stoe-IPDS-2 diffractometer equipped with a graph-
˚
ite monochromated (Mo Ka radiation, k = 0.71073 A) at
293 K. The structure was solved by direct methods using
SHELXS–97 [26] and refined by a full-matrix least-squares
procedure using the program SHELXL-97 [26]. All non-
hydrogen atoms were easily found from the difference Fou-
rier map and refined anisotropically. All carbon hydrogen
atoms were included using a riding model, while the water
H atoms were refined freely. Details of crystal data, data
collection, structure solution and refinement are given in
Table 1.
2. Experimental
2.1. Materials and measurements
All reagents were purchased from commercial sources
and used as supplied. The starting complexes [M(sac)2-
(H2O)4] Æ 2H2O, where M is Mn(II), Fe(II), and Co(II),
were prepared according to the literature methods [24,25].
The elemental analyses (C, H and N) were performed on
a Vario EL Elemental Analyser. IR spectra were recorded
on a MATTSON 1000 FT/IR spectrophotometer as KBr
pellets in the frequency range 4000–400 cmÀ1. Room tem-
perature magnetic susceptibility measurements were car-
ried out using a Sherwood Scientific MXI model Evans
magnetic balance. Thermal analysis curves (TG and
DTA) were obtained from a Rigaku TG8110 thermal ana-
lyzer in a static air atmosphere using a sample size of 5–
10 mg.
Table 1
Crystallographic data for complexes 1–3
Complex
1
2
3
Molecular
formula
Formula
weight
C
18H16N4O8S2Mn C18H16N4O8S2Fe C18H16N4O8S2Co
535.41
536.32
539.40
Crystal
triclinic
triclinic
triclinic
system
ꢀ
ꢀ
ꢀ
Space group
P1
P1
P1
˚
a (A)
7.381(5)
7.708(5)
10.638(5)
105.316(5)
96.509(5)
109.055(5)
538.4(6)
1
7.259(1)
7.670(1)
10.649(2)
106.381(1)
95.999(2)
108.455(2)
527.1(1)
1
7.188(1)
7.657(1)
10.636(2)
106.468(12)
95.816(13)
108.515(12)
520.4(2)
1
2.2. Synthesis of the metal complexes
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
All three complexes were prepared using the same syn-
thesis procedure. The pyz ligand (0.16 g, 2.0 mmol) was
added drop-wise to a solution of [M(sac)2(H2O)4] Æ 2H2O
[M = Mn(II), Fe(II), and Co(II)] (1 mmol) in a aqueous
solution of MeOH (30 cm3, H2O: MeOH = 6:1) and the
reaction mixture was stirred for 15 min at room tempera-
ture. The resulting solution was allowed to stand at room
temperature and X-ray quality crystals were formed after
a few days.
3
˚
V (A )
Z
Dcalc
1.651
1.690
1.721
(g cmÀ3
)
l (mmÀ1
)
0.862
7916
0.969
5299
1.082
6443
Reflections
collected
Data/
2335/163
2065/157
2402/163
[Mn(sac)2(l-pyz)(H2O)2]n 1: Yield 65%. Anal. Calc. for
C18H16N4O8S2Mn: C, 40.38; H, 3.01; N, 10.46. Found C,
parameters
R1 [I > 2r]
wR2
0.0330
0.0841
0.0535
0.1512
0.0341
0.0787
40.19; H, 3.08; N, 10.63%. (Solid KBr pellet): m (cmÀ1
)

V.T. Yilmaz et al. / Polyhedron 26 (2007) 3199–3204
3201
3. Results and discussion
3.1. Synthesis and characterization
The use of [M(sac)2(H2O)4] Æ 2H2O as synthetic precur-
sors became a common practice in the synthesis of
mixed-ligand metal complexes of sac, since the aqua
ligands in these octahedral metal complexes are labile
and readily exchanged by neutral ligands. The new com-
plexes were simply prepared by the direct reaction of the
pyz ligand with the respective tetraaquabis(sacchari-
nato)M(II) dihydrate complexes in solution. The addition
of pyz resulted in the substitution of the two aqua ligands,
and the formation of the air-stable polymeric complexes of
[M(sac)2(l-pyz)(H2O)2]n [M = Mn(II) (1), Fe(II) (2), Co(II)
(3)]. All the complexes were obtained in good yields (over
65%) and the analytical data are consistent with the pro-
posed formulation of the complexes, and also confirmed
by X-ray crystallography as reported in this paper. All
the complexes are soluble in water, methanol and ethanol.
The IR spectra of all the complexes resemble each other
indicating a similar structural relationship. The strong and
broad absorption bands centered at around 3490 cmÀ1 are
attributed to the m(OH) vibrations of aqua ligands. The rel-
atively weak bands in the range 3140–3011 cmÀ1 are due to
the m(CH) vibrations. The bands for the carbonyl group of
sac appear characteristically at ca. 1630 cmÀ1 as very
strong bands for all complexes, while the stretching vibra-
tions of masym.(SO2) and msym.(SO2) occur at ca. 1280 and
1165 cmÀ1, respectively. Additional strong peaks at ca.
1350 and 965 cmÀ1 may be assigned to the symmetric
and asymmetric stretching of the CNS moiety of the sac
ligands. The strong bands centered around 1420, 1125
and 1060 cmÀ1 are assignable to pyz [27,28]. Furthermore,
the bands at around 470 cmÀ1 is particularly assigned to
the bridging mode of pyz compared to the band of
417 cmÀ1 in the spectrum of free pyz [29].
Fig. 1. The building block unit and coordination environment of MnII in
1 with the atom labelling scheme. Symmetry code (i) = Àx, Ày, Àz.
Table 2
˚
Selected bond lengths (A) and angles (°) for complexes 1–3
1
2
3
M1–N1
M1–N2
M1–OW1
M1–M1i
2.276(2)
2.300(2)
2.160(2)
7.381(2)
2.218(3)
2.266(2)
2.101(3)
7.259(3)
2.197(2)
2.199(2)
2.062(2)
7.188(3)
N1–M1–N2
92.04(6)
94.75(8)
92.33(6)
87.96(6)
85.25(8)
87.67(6)
92.27(11)
85.65(11)
87.42(10)
87.73(11)
94.35(12)
92.58(10)
91.85(7)
93.69(8)
92.15(6)
88.15(7)
86.31(8)
87.85(6)
N1–M1–OW1
N2–M1–OW1
N1–M1–N2i
N1–M1–OW1i
N2 –M1– OW1i
Symmetry operations: (i) Àx, Ày, Àz for 1 and 3; 1 À x, 1 À y, 1 À z for 2.
The room temperature magnetic moments indicate that
the metal complexes exhibit high-spin configuration. The
effective magnetic moments are consistent with the calcu-
lated values of the spin-only magnetic moments of the octa-
hedral coordination geometry around the metal ions.
The repeating units have symmetry center passing through
the center of the pyz plane. The sac ligand behaves as a
monodentate donor through the imino N atom. The cis
bond angles within the octahedral geometry range from
85.25(8) to 94.75(8)°, indicating a significant distortion of
the geometry compared to a regular octahedron. The M–
3.2. Description of the crystal structures
˚
The title complexes 1–3 are isomorphous and crystallize
Nsac bond distances ranging from 2.197(2) to 2.276(2) A
ꢀ
in the triclinic space group P1. Since they have identical
are similar to the corresponding values of reported metal-
sac complexes [24,30]. The M–Npyz bond distances are in
structures in terms of coordination geometry around met-
als and intra- or intermolecular interactions, only the views
of complex 1 are presented in this paper. The fundamental
building unit of 1 is shown in Fig. 1, together the atom
labeling scheme. The selected bond lengths and angles are
listed in Table 2. The crystallographic analysis of the three
complexes showed that their structures consists of the
[M(sac)2(l-pyz)(H2O)2] building block units, in which each
MII ion is octahedrally coordinated by two sac, two pyz
and two aqua ligands constituting a MN4O2 chromophore.
˚
the range 2.199(2)–2.300(2) A, and compare well with those
of the related pyz complexes [31–34].
The pyz ligand acts as a bidentate bridging ligand
between the metal centers leading to one-dimensional lin-
ear chains running along the crystallographic axis a.
Intra-chain M–M separations in complexes 1, 2 and 3 are
˚
7.381(2), 7.259(3) and 7.188(3) A, respectively. These linear
chains are linked by strong hydrogen bonds into a two-
dimensional supramolecular array parallel to the crystallo-

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V.T. Yilmaz et al. / Polyhedron 26 (2007) 3199–3204
Fig. 2. The assembly of polymeric chains of 1 into a 2D layer by OW–HÁ Á ÁO hydrogen bonds. CH hydrogen atoms are omitted for clarity.
Table 3
The hydrogen bonding geometry in complexes 1–3 are
given in Table 3. One of the water hydrogens involves in
intramolecular hydrogen bonding with the carbonyl O
atoms in complexes 1–2, but with the sulfonyl O atom in
complex 3, while the other hydrogen atom of the aqua
ligands form hydrogen bonds between the individual
chains. In complex 3, the water hydrogen atoms participate
in bifurcated hydrogen bonds.
Hydrogen bond data for complexes 1–3
˚
˚
˚
D–HÁ Á ÁA
1
D–H (A) HÁ Á ÁA (A) DÁ Á ÁA (A) D–HÁ Á ÁA (°)
O1W–H1WÁ Á ÁO3i
0.91(2)
1.91(2)
1.73(3)
2.771(3)
2.610(3)
156(3)
167(4)
O1W–H2WÁ Á ÁO1ii 0.90(3)
2
O1W–H1WÁ Á ÁO1
0.80(2)
1.82(2)
2.13(3)
2.591(5)
2.772(4)
160(4)
137(3)
O1W–H2WÁ Á ÁO3iii 0.81(2)
The packing of the sheets in the lattice produces an
interesting alternating sheet motif. As shown in Fig. 3,
the ring systems of sac and pyz are essentially planar and
the phenyl rings of the sac ligands within a hydrogen
bonded assembly form almost parallel array with the other
sac rings in the neighboring hydrogen bonded sheets, and
consequently, this result in weak aromatic face-to-face
p(sac)–p(sac) stackings or CH–p(pyz) interactions. In com-
plex 1, the sac ligands form weak p–p interactions with
3
O1W–H1WÁ Á ÁO2
0.75(3)
2.66(3)
2.12(3)
1.76(4)
3.139(3)
2.775(2)
2.580(3)
124(3)
147(3)
165(4)
O1W–H2WÁ Á ÁO2iv 0.75(3)
O1W–H2WÁ Á ÁO3ii 0.84(4)
Symmetry operations: (i) Àx, 1 À y, Àz; (ii) Àx, Ày, Àz; (iii) x, y À 1, z;
(iv) Àx, À1 À y, Àz.
graphic ac-plane as shown in Fig. 2. The nearest M–M dis-
tances between the adjacent chains are 7.708(3), 7.669(3)
and 7.657(4) A for complexes 1, 2 and 3, respectively.
their inversion-symmetry generated partners [Cg Á Á Á Ci
g
˚
˚
3.783(3) A; Cg = centroid of atoms C2–C7; (i): Àx, 1 À y,
Fig. 3. Packing of 2D layers into 3D network in 2 viewed down the b axis, showing aromatic pÁ Á Áp stacking interactions between sac ligands. CH hydrogen
atoms are omitted for clarity.

V.T. Yilmaz et al. / Polyhedron 26 (2007) 3199–3204
3203
1 À z)]. In complexes 2 and 3, there are two p(sac)–p(sac)
175 and 329 °C, accompanied by a mass loss of 21.91%
(calc. 21.51%), corresponds to the simultaneous endother-
mic removal of both aqua and pyz ligands. In the last
two stages, in the temperature range 383–591 °C, the
decomposition of the intermediate [Co(sac)2] to Co2O3
occurs.
i
˚
interactions [Cg Á Á Á Cg 3.750(3) A; (i): 1 À x, Ày, Àz and
ii
i
˚
Cg Á Á Á Cg 3.995(3) A; (ii): Àx, Ày, Àz in 2, and Cg Á Á Á Cg
ii
˚
˚
3.705(4) A; (i): Àx, 1 À y, 1 À z and Cg Á Á Á Cg 3.950(3) A;
(ii): 1 À x, 1 À y, 1 À z in 3] and moreover, some of the
phenyl hydrogen atoms of sac are also involved in two sim-
ilar
C–HÁ Á Áp(pyz)
interactions
[C4–H4 Á Á Á Cgi and ii
˚
2.965(5) A; (i): 1 À x, 1 À y, 1 À z and (ii): À1 + x,
À1 + y, À1 + z in 2, and (i): 1 + x, 1 + y, 1 + z and (ii):
Àx, 1 À y, 1 À z in 3]. Thus, the molecular packing in com-
plexes 1–3 is reinforced by the hydrogen bonds, aromatic
p–p stacking interactions or C–HÁ Á Áp interactions to gener-
ate the final three-dimensional supramolecular network
(Fig. 3).
Complex 1
80
In conclusion, the crystallographic study indicates that
the structures of coordination polymers are controlled by
the pyz ligand, but are not greatly influenced by the metal
ions, while the supramolecular interactions in assemblies
are mainly controlled by the sac and aqua ligands.
60
40
20
3.3. Thermal analysis
Thermal behavior of the complexes was studied by DTA
and TG in the temperature range 20–700 °C in the atmo-
sphere of air. Thermal analysis curves of complexes 1–3
are illustrated in Fig. 4. All three complexes begin to
decompose without melting and exhibit similar decomposi-
tion characteristics. In the first stage, endothermic removal
of the aqua and pyz ligand takes place leading to an inter-
mediate probably in the form of [M(sac)2] and then, highly
exothermic DTA peaks at higher temperatures characterize
the decomposition of the sac moiety in these intermediates
[35]. The experimental mass losses are consistent with the
calculated data.
0
100
Complex 2
80
60
40
20
Complex 1 exhibits five distinct decomposition stages.
Both DTA and TG curves show that the removal processes
concerning the aqua and pyz ligands are not well separated
and therefore, the simultaneous elimination of one pyz and
two aqua ligands occurs in the first three stages in the tem-
perature range 146–280 °C with three endothermic peaks at
184, 217 and 270 °C. The experimental mass loss of 21.02%
for the three stages agrees well with the calculated value of
21.11% (6.15% from two H2O molecules and 14.96% from
pyz). The intermediate, [Mn(sac)2], formed at the end of
the third step is stable up to 368 °C and then, undergoes
highly exothermic decomposition in the range 368–579 °C
to give MnO.
0
100
Complex 3
80
60
40
Complex 2 is thermally stable up to 174 °C and then
begins to decompose. The elimination of two aqua and a
pyz molecules takes place in the temperature range 174–
262 °C with two endothermic DTA peaks at 202 and
239 °C, with a 21.84% mass loss (calc. 21.65%). The decom-
position of the sac residue occurs between 270 and 474 °C
with two extremely exothermic DTA peaks at 405 and
530 °C to give an end product FeO.
20
0
0
100
200
300
Temperature / oC
Fig. 4. Thermal analysis (TG and DTA) curves of complexes 1–3.
400
500
600
700
Complex 3 undergoes complete decomposition in five
stages, similar to complex 1. The first three stages between

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V.T. Yilmaz et al. / Polyhedron 26 (2007) 3199–3204
[14] V.T. Yilmaz, S. Hamamci, O. Andac, K. Guven, Z. Anorg. Allg.
4. Supplementary material
Chem. 629 (2003) 172.
[15] V.T. Yilmaz, S. Caglar, W.T.A. Harrison, Z. Anorg. Allg. Chem. 630
(2004) 948.
[16] V.T. Yilmaz, S. Hamamci, C. Thone, Z. Anorg. Allg. Chem. 630
(2004) 1641.
[17] S. Hamamci, V.T. Yilmaz, W.T.A. Harrison, J. Mol. Struct. 734
(2004) 191.
[18] S. Hamamci, V.T. Yilmaz, W.T.A. Harrison, C. Thone, Solid State
Sci. 7 (2005) 423.
CCDC 628875, 628876, and 628877 contain the supple-
mentary crystallographic data for 1–3. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk.
[19] V.T. Yilmaz, S. Hamamci, C. Kazak, Z. Anorg. Allg. Chem. 631
(2005) 1961.
[20] S. Hamamci, V.T. Yilmaz, W.T.A. Harrison, Struct. Chem. 16 (2005)
379.
Acknowledgement
[21] S. Hamamci, V.T. Yilmaz, C. Kazak, Struct. Chem. 17 (2006) 57.
[22] V.T. Yilmaz, V. Kars, C. Kazak, Z. Anorg. Allg. Chem. 632 (2006)
505.
We thank Dr. O. Z. Yesilel for his assistance in obtain-
ing DTA and TG curves.
[23] B.Q. Ma, S. Gao, J. Yi, G.X. Xu, Polyhedron 20 (2001) 1255.
[24] B. Kamenar, G. Jovanovski, Cryst. Struct. Commun. 11 (1982) 257.
[25] Z. Haider, K.M.A. Malik, K.J. Ahmed, Inorg. Synth. 23 (1985) 47.
[26] G.M. Sheldrick, SHELX-97. Programs for Crystal Structure Analysis,
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