B. Ay et al. / Journal of Solid State Chemistry 244 (2016) 61–68
63
Table 3
appear to play a large role in the overall three-dimensional net-
work. The ladder structures are connected by H–bonding through
the piperazine solvent cations. Piperazine fills the channels be-
tween the samarium ladders (Fig. 5).
Hydrogen bonds for 1 [Å and °].
D–H…A
d (D–H)
d (H…A)
d (D…A)
o(DHA)
O(9)–H(9X)…O(3)#2
N(3)–H(3X)…O(2)
N(3)–H(3Y)…O(8)#5
C(5)–H(5 A)…O(7)#3
0.84(3)
0.93(2)
0.87(2)
0.95
1.80(3)
1.72(2)
1.99(2)
2.53
2.6347(16)
2.6384(18)
2.7804(17)
3.4467(19)
172(2)
171(2)
149(2)
163.5
3.2. IR spectra
The infrared spectrum of the free H
bands attributed to (O-H), (CQO),
3063, 1688, 1573 and 1080 cm , respectively (Fig. S1). The IR
spectrum of the free H pip shows stretching bands attributed to
N-H), (C-H) and (C-N) at 3271, 2936 and 1324 cm , respec-
2
pydc shows stretching
υ
υ
υ
(CQN) and (C-H) at
υ
Symmetry transformations used to generate equivalent atoms:
ꢁ
1
#
1 xþ1,y,z #2 ꢁxþ1, ꢁy, ꢁzþ1 #3 xꢁ1,y,z #4 ꢁxþ2,ꢁy, ꢁzþ2 #5 ꢁxþ2,ꢁ
yþ1, ꢁzþ2.
2
υ
ꢁ
1
(
υ
υ
stirrer, a reflux condenser, and a temperature controller in an oil
bath. Thymol (1.5 g, 10 mmol) and 10 mL acetonitrile were added
successively into the flask. Then, the appropriate amount of oxi-
tively (Fig. S2). In the IR spectra of 1 (Fig. S3), O-H stretching vi-
bration of coordinated water molecules was observed at
ꢁ1
ꢁ1
3
247 cm [19]. The band, having medium intensity at 3426 cm
,
dant 30 wt% of the aqueous H
2 2
O (3.5 mL, 34.90 mmol) and
can be assigned to the (N-H) stretching vibrations of H pip which
υ
2
8
0 wt% aqueous of the tert-Butyl hydroperoxide (3.0 mL, 24 mmol)
is outside the coordination sphere in the structure [20]. CQO
were added in the reaction mixture. After heating this mixture to
be 25 °C and 60 °C, the metal complex (0.05, 0.10 and 0.15 g) was
joined to start the reaction and stirred constantly for 3, 6, 9, 12 and
ꢁ1
stretching frequency appeared at 1688 cm
gand, after coordination, this peak shifted to 1622 cm
in the spectra of li-
ꢁ1
in the
spectra of 1. This shift indicates that the oxygen atoms in the
2
4 h. 20 mL aliquots were collected at given time intervals and
were analyzed by HPLC for determining the thymoquinone
Scheme 1).
carbonyl groups were coordinated to samarium ions. The new
ꢁ1
bands between 764–433 cm , can be assigned to the
υ
(Sm-O)
(
and
υ
(Sm-N) stretching vibrations [21,22]. These new bands also
indicate that O and N atoms of H
ions.
2
pydc coordinate the samarium
3
. Results and discussion
3.3. PXRD patterns and thermal analysis
2 n 2 4 2 2 n
3.1. Description of crystal structure of (H pip) [Sm (pydc) (H O) ]
The powder X-ray diffraction data of the 1 was obtained and
The asymmetric unit consists of the Sm(III) ion, two pyridine-
,6-dicarboxylate anionic ligands coordinated through the pyr-
idine nitrogen and one of each of the carboxylate oxygen atoms,
and a coordinated water. The asymmetric unit also contains a half
compared with the corresponding simulated single-crystal dif-
fraction data. PXRD pattern (Fig. 6) indicates that the MOF syn-
thesized under hydrothermal condition is highly crystalline and is
in good agreement with the simulated pattern. However, the dif-
ferences in intensity may be due to the preferred orientation of the
microcrystalline powder sample. Thermal analysis was performed
2
2
piperazine dication located on an inversion center. One H pip is
present for every two samarium. Each nitrogen in piperazine has
two hydrogen to establish charge balance (Fig. 1). The Sm complex
is situated near an inversion center (on 0.5, 0, 0.5) resulting in
dimers through the coordination of Sm1 and O5 (and their sym-
metry equivalents; 1ꢁx, ꢁy, 1ꢁz). To the best of our knowledge,
and after an extensive search of the 2016 version of the Cambridge
Structural Database (version 1.18) [17,18], we present here the first
pure Samarium coordinated pyridine-2,6-dicarboxylate ladder
structure (Figs. 2 and 3). Literature searches reveal reports of many
Sm(III) extended structures including 1-D chains, 2-D sheets, and
in the temperatures range of 50–800 °C under N
atm with a heating rate of 10 °C min . The TGA curve of 1 is
2
atmosphere at
ꢁ
1
1
shown in Fig. S4, which indicates that it decomposes in main two
steps. The slight slop could be moisture in initiate. The first stage
between 290 and 340 °C were attributed to the loss of H
mol coordinated water molecules per formula unit with weight
loss percentage of 13.71% (Calcd.:11.25%). The third weight loss of
5.49%, which occurred between 398 and 548 °C, corresponds to
the decomposition of remaining H pydc ligands (Calcd. 46.20%).
The fact that H pydc ligands are lost at a higher temperature
2
pip and
2
4
2
3
-D networks. Published ladder structures of samarium are
2
formed by H–bonding between two adjacent chains. A 1-D chain
of dimers was also reported, but it does not fit the ladder de-
scription. Rungs of the ladder are formed by the dimers through
the two Sm(III) centers and atoms O5 and O5a (1ꢁx, ꢁy, 1ꢁz)
suggests that they are coordinated with the samarium atoms. The
remaining weight of 29.70% corresponds to the final product
Sm O . The observed weight was in good agreement with the
2 3
calculated value (28.80%). Thermal results fundamentally agree
with the single crystal structure of the 1, and the observed thermal
behavior reflects the structural features.
(
Fig. 4). The ladder structure is formed by simple translation along
the a-axis, of the dimers through coordination of the Sm(III) cen-
ters with the O4 atoms. The counter piperazine dications pack in
columns, also along the a-axis, filling channels between the lad-
ders. The cations are strongly H–bonded to the Sm ladders. The
coordinated water shows some H–bonding interaction with one of
the coordinated carboxylate oxygens, O3, though it does not
3.4. Luminescence property
The luminescence properties of the ligand and its polymeric
complex containing Sm(III) were performed in solid state at room
temperature, and in the same conditions to understand the nature
of the luminescence of 1. As shown in Fig. 7, the free ligand ex-
hibited broad emission band (
20 nm in the solid state. The observed emission band may be
related to the * transition of aromatic/pyridine rings [23,24]. 1
λmax: 370 nm) when excited at
3
π-π
showed one maximum and sharp emission band at 534 nm upon
excitation with a wavelength of 440 nm, which is mainly caused
by the ligands and Sm(III) ions. The wavelength of maximum
emission peaks of 1 is largely red shifted as 164 nm compared
Scheme 1. Oxidation of the thymol to thymoquinone using Sm(III) catalyst.
2
with that of H pydc. The red-shift emissions are likely related to
Ay, Burak
