Chemistry of Materials
Article
structures were thoroughly characterized by scanning electron
microscopy (SEM), transmission electron microscopy (TEM),
atomic force microscopy (AFM), optical microscopy, and
confocal Raman imaging techniques. The SCO phenomenon
was also studied by variable temperature bulk magnetic
susceptibility measurements and Raman spectroscopic studies.
field of 0.5 T. Heating and cooling rate of the sample was kept at a 10
K interval in sweep mode.
2.3. Electron Spin Resonance Spectroscopy (EPR) Studies. X-
band EPR spectra were recorded on a Bruker-ER073 spectrometer
equipped with an EMX microX source. For data analysis Xenon
1
.1b.60 software provided by the manufacturer was used. During the
liquid helium measurement the temperature was controlled by a
temperature controller supplied by Oxford instruments (ITC 503S).
2
.4. Method for Patterning. Micro patterning of complex I was
2
. EXPERIMENTAL SECTION
carried out by drop casting 20 μL of a 2 mg/mL solution of complex I
in acetonitrile (Aldrich, ≥ 99% purity) on glass substrate. The
substrate was cleaned by sonication for 2 min in electronic-grade water
Milli-Q-pure quality), 2 min in acetone (Aldrich chromatography
quality), and then with 2-propanol (Aldrich spectroscopic-grade
quality). Before micro patterning the solution of compound I was
filtered through a Whatman filter paper.
2
2
.1. Synthesis. 2,6-Bis(4-(oct-1-ynyl)-1H-pyrazol-1-yl)pyridine
1). A Schlenk flask was charged with 2,6-bis(4-iodo-1H-pyrazol-1-
yl)pyridine 2 (500 mg, 1.07 mmol) together with Pd(PPh ) Cl (37.89
(
3
2
2
(
mg, 0.053 mmol), triphenylphosphene (50 mg, 0.19 mmol) and CuI
(
(
200 mg, 0.262 mmol). Freshly distilled anhydrous triethylamine
Et N, 20 mL) and 1,4-dioxane (10 mL) were added to it. The flask
3
was carefully degassed by freeze-and-thaw cycles several times. 1-
octyne (0.5 mL; d = 0.746 g/mL, 3.24 mmol) was injected into the
flask under argon atmosphere, and the resulting mixture was heated to
12,13
.5. Stamps for Lithography..
Elastomeric poly-
(
dimethylsiloxane) (Sylgard 184 Down Corning) stamps were
prepared by replica molding of a series of structured masters. The
curing process was carried out for 6 h at 60 °C. Once cured, the replica
was carefully peeled off from the master and used as such for nano/
micro patterning techniques. Test gratings TGQ1, TGZ3 and TGG1
were purchased from NT-MDT and used as masters.
8
0 °C for 48 h. It was then cooled to room temperature and left for
stirring for an additional 1 h. The mixture was filtered through filter
paper and washed with tetrahydrofuran (THF), and the filtrate was
evaporated to get a dark brown solid which was column chromato-
graphed on silica (100−200 mesh) using initially (60:40) DCM/
Hexane and finally (80:20) DCM/Hexane to get a white solid of 1.
Yield 350 mg (76%). mp 86−87 °C. H NMR (400 MHz, CDCl ) δ:
2
.6. Atomic Force Microscopy (AFM). AFM imaging was carried
out on NT-MDT Model Solver Pro M microscope using a class 2R
laser of 650 nm wavelength having maximum output of 1 mW. All
calculations and image processing was carried out by a software NOVA
1
3
8
2
0
1
1
2
.6 (s, 2H), 7.92−7.90 (t, 1H), 7.82−7.81 (d, 2H), 7.74 (s, 2H), 2.43−
.39 (t, 4H), 1.66−1.58 (m, 4H), 1.48−1.45 (m, 4H), 1.34 (s, 8H),
1
.0.26.1443 provided by the manufacturer. The images were recorded
13
.93−0.90 (m, 6H) ppm. C NMR (100 MHz, CDCl ) δ: 149.5,
44.6, 141.5, 129.0, 109.6, 106.6, 92.7, 70.6, 31.4, 28.7, 28.6, 22.6, 19.5,
3
in a semicontact mode using a noncontact silicon cantilever (NSG10-
DLC) tip purchased from NT-MDT, Moscow. The dimension of the
tip is as follows: cantilever length = 100 (±5) μm, cantilever width 35
(±5) μm, and cantilever thickness = 1.7−2.3 μm, resonate frequency =
190−325 kHz, force constant = 5.5−22.5 N/m, chip size = 3.6 × 1.6 ×
0.4 mm, reflective side = Au, tip height = 10−20 μm, tip curvature
radius = 1−3 nm, and aspect ratio 3:1−5:1.
2.7. Confocal Raman Micro Spectroscopy Studies. Raman
spectra of the samples were recorded on a WI-Tec confocal Raman
spectrometer equipped with a Peltier-cooled CCD detector. Using a
600 grooves/mm grating BLZ = 500 nm, the accumulation time was
typically 10 s and integration time was typically 2.0000 s. Ten
accumulations was performed for acquiring a single spectrum. For
imaging the integration time was typically 2.000 s, keeping in mind
that the x or y resolution is ∼250 nm four points per line and four line
per image was taken for imaging of a 1 μm × 1 μm area. A He−Ne 633
nm laser was used as an excitation source for the Raman scattering. All
measurements were done at ambient conditions.
−1
4.1 ppm. FTIR (KBr disc; ν in cm ): 3146 (-CC-), 2926, 2848,
361, 1599, 1464, 1026, 953, 800, 656. LC-MS m/z calcd 427.27,
+
found 428.10. ESIMS: m/z calcd 427.27, found 428.2714 [M +H].
Anal. Calcd for C H N : C, 75.84; H, 7.78; N, 16.38%. Found: C,
27
33
5
7
5.92; H, 7.85; N, 16.27%.
,6-Bis(4-octyl-1H-pyrazol-1-yl)pyridine (L). To a degassed sol-
ution of 1 (0.3 g, 00.7 mmol) in EtOAc (60 mL) was added 10% Pd/C
2
(0.073 g, 0.07 mmol), the mixture was stirred under H atmosphere
2
(
at ambient pressure), and monitored by TLC. After 1 h the mixture
was filtered through a Celite plug to remove activated Pd/C. Afterward
the plug was washed with 100 mL of EtOAc, and the collected fraction
was concentrated in vacuum to get compound L as viscous oil. Yield
1
0
7
1
.302 g (>99%) H NMR (400 MHz, CDCl ) δ: 8.33 (s, 2H), 7.90−
3
.86 (t, 1H), 7.77−7.75 (d, 2H), 7.59 (s, 2H), 2.58−2.54 (t, 4H),
.67−1.64 (m, 4H), 1.36−1.29 (m, 20H), 0.89−0.87 (m, 6H)
13
ppm. C NMR (100 MHz, CDCl ) δ: 150.1, 142.5, 141.1, 124.8,
3
1
24.4, 108.5, 31.9, 30.8, 29.7, 29.4, 29.3, 24.3, 22.7, 14.1 ppm. FTIR
2.8. Electron Microscopy Studies. Size and morphology of the
micro structures were examined by using a Philips XL30 ESEM
Scanning Electron Microscope using a beam voltage of 20 kV. TEM
measurement was carried out on Tecnai G2 FEI F12 instrument at an
accelerating voltage of 120 kV. Carbon coated TEM grids (200 Mesh
Type B) were purchased from Ted Pella Inc. U.S.A.
−1
(
KBr disc; ν in cm ): 2958, 2918, 2848, 1604, 1585, 1475, 1390, 970,
8
4
00, 648, 607, 536, 480, 467. LCMS analysis: m/z calcd 435.34, found
36.25 (positive mode). ESIMS: m/z calcd 435.34, found 436.3403
+
[
M + H]. Anal. Calcd for C H N : C, 74.44; H, 9.49; N, 16.08%.
27
41
5
Found: C, 74.28; H, 9.41; N, 16.21%.
II
[
Fe (L) ](BF ) (I). A 100 mL flask was charged with L (80 mg, 0.183
2 4 2
mmol) and 10 mL of DCM was added to it. A solution of Fe(BF4)2
3. RESULT AND DISCUSSION
6
H O (31 mg, 0.091 mmol) in MeOH (10 mL) was added to the
2
Highly soluble ligand L was synthesized from a commercially
available 2,6-dibromopyridine in four steps in good yields
(Scheme 1). Conversion of 2,6-dibromopyridine into 2,6-
above solution. The mixture was heated to reflux for 12 h at nitrogen
atmosphere. After cooling, the solvent was evaporated on a rotary
evaporator in air. The residue was washed with diisopropyl ether (20
mL × 1) and dried in vacuum to get a yellow color powder of I. Yield
14
bispyrazolylpyridine 3 was carried out as reported. Com-
pound 3 was successfully converted to its diiodinated derivative
7
4 mg (73%). The crystals of the complex were obtained by slow
15,16
evaporation from acetonitrile solution. Anal. Calcd for
C H B F FeN : C, 58.92; H, 7.51; N, 12.72%. Found: C, 58.83;
2
as per our previously reported procedure in 74% yield.
5
4
82
2
8
10
Transformation of compound 2 into 1 was achieved via
Sonogashira coupling reaction conditions by using 1-octyne in
Et N/THF solvents using Pd(PPh ) Cl catalyst in 78% yield.
−1
H, 7.61; N, 12.52%. FTIR (KBr disc; ν in cm ): 3118, 2958, 2927,
2
7
856, 1620, 1572, 1491, 1400, 1321, 1103 (broad, B−F), 1014, 991,
3
3 2
2
96, 725, 625. M.p.: ∼80 °C.
The alkyne groups in 1 were reduced using Pd/C under H2
atmosphere to obtain highly soluble 2,6-dioctylated bispyr-
azolylpyridine L in a quantitative 99% yield. The ligands were
characterized by employing NMR, LC-MS, FTIR, and
elemental analysis techniques. The mononuclear iron(II)
2
.2. Bulk Magnetic Studies. The temperature dependent
magnetic susceptibility of complex I in the powder state was measured
on a Quantum Design vibrating sample magnetometer (VSM-SQUID)
setup in the temperature range of 340↔2 K at continuous cooling (↓)
and heating (↑) cycles with an applied direct current (DC) magnetic
B
dx.doi.org/10.1021/cm401058s | Chem. Mater. XXXX, XXX, XXX−XXX