Amphiphilic Azo-Anion-Radical Complexes of ChromiumACHTUNTRGNEUNG(III)
FULL PAPER
(N=N), 1285 cmꢀ1 (C O); MS (ESI, CH3CN): m/z (%): 368 (100)
[M+H]+; elemental analysis calcd (%) for C23H33N3O: C 75.16, H 9.05,
N 11.43; found: C 75.14, H 9.08, N 11.46.
B3LYP-optimized geometry were computed using the time-dependent
density functional theory (TD-DFT) formalism[45] in CH2Cl2 using the
conductor-like polarizable continuum model (CPCM).[46]
ꢀ
Preparation of [Cr(La)3] (1a):
A
mixture of Cr(CO)6 (218 mg,
Pressure–area (p–A) isotherm measurements: The computerized LB
trough used was a Teflon-bar-barrier-type trough (model LB2007DC,
Apex Instruments Co., Kolkata, India) enclosed in a plexiglass box to
reduce film contamination. The trough was equipped with a Wilhelmy-
type balance with an accuracy of (ꢁ0.01) mNmꢀ1. The trough width and
length were 200 and 600 mm, respectively. The subphase water (pH=5.5,
1.00 mmol) and ligand La (639 mg, 3.00 mmol) was refluxed in n-octane
(30 mL) for 8 h. The solution was cooled and the solid was collected by
filtration. The crude complex was crystallized by slow evaporation of a
CH2Cl2/n-hexane solution of the compound (93% yield). IR (KBr): n˜ =
1590 (C=N and C=C), 1155 cmꢀ1 (N=N); MS (ESI, CH3CN): m/z (%):
691 (100) [M]+; elemental analysis calcd (%) for C36H33N9CrO3: C 62.51,
H 4.81, N 18.22; found: C 62.53, H 4.79, N 18.20.
resistivity=18.2 MWcmꢀ1
through an ELIX system from Millipore (Billerica, MA). All experiments
were performed at a temperature of 25
(ꢁ0.5)8C unless otherwise men-
) was prepared using a Milli-Q apparatus
Preparation of [Cr(Lb)3] (1b): Compound 1b was synthesized and crys-
tallized by following a similar procedure to that for compound 1a except
that ligand Lb (766 mg, 3.00 mmol) was used in the place of La. Yield=
95% yield; IR (KBr): n˜ =2925, 2850 (alkyl-CH-), 1585 (C=N and C=C),
1155 cmꢀ1 (N=N); MS (ESI, CH3CN): m/z (%): 818 (100) [M]+; elemen-
tal analysis calcd (%) for C45H51N9CrO3: C 66.07, H 6.28, N 15.41; found:
C 66.09, H 6.25, N 15.43.
Preparation of [Cr(Lc)3] (1c): Compound 1c was synthesized and crystal-
lized by following a similar procedure to that for compound 1a except
that ligand Lc (934 mg, 3.00 mmol) was used in the place of ligand La.
Yield=94%; IR (KBr): n˜ =2924, 2850 (alkyl-CH-), 1585 (C=N and C=
C), 1150 cmꢀ1 (N=N); MS (ESI, CH3CN): m/z (%): 985 (100) [M]+; ele-
mental analysis calcd (%) for C57H75N9CrO3: C 69.41, H 7.66, N 12.78;
found: C 69.44, H 7.63, N 12.76.
Preparation of [Cr(Ld)3] (1d): Compound 1d was synthesized and crys-
tallized by following a similar procedures to that for compound 1a
except that ligand Ld (1.1 g, 3.00 mmol) was used in the place of ligand
La. Yield=95%. IR (KBr): n˜ =2925, 2855 (alkyl-CH-), 1605 (C=N and
C=C), 1150 cmꢀ1 (N=N); MS (ESI, CH3CN): m/z (%): 1154 (100) [M]+;
elemental analysis calcd (%) for C69H99N9CrO3: C 71.77, H 8.64, N 10.91;
found: C 71.75, H 8.66, N 10.94.
AHCTUNGTRENNUNG
tioned. At-least three independent runs were performed to check the re-
producibility. To determine the p–A isotherm measurements, the solu-
tions for complex 1d in CHCl3/EtOH (9:1, 10ꢀ4 m) were prepared and
spread at the air/H2O interface on an LB trough. The spreading was
done by a microsyringe in such a manner that the surface pressure
should not rise above 0.5 mNmꢀ1. After spreading, 30 min waiting time
was allowed for solvent evaporation as well as to allow the system to
equilibrate. Subsequently, the monolayer was slowly compressed at a
compression speed of 1 ꢁ2 (molecule.min)ꢀ1
.
Fabrication of Langmuir–Schaefer films: The surface layer was trans-
ferred by the Langmuir–Shaefer (LS) deposition technique, which was
performed by lowering the substrate horizontally until it became in con-
tact with the floating film. During the transfer, we typically used surface
pressures of 10 and 40 mNmꢀ1 and the monolayer was held at a constant
pressure for 30 min to allow for stabilization and then transferred onto
quartz slides, silicon wafers, and Platinum electrodes. Details of the pro-
cedure for cleaning the quartz slides and glass cover-slips have been de-
scribed elsewhere.[47]
Field-emission scanning electron microscopy (FE-SEM) and atomic force
microscopy (AFM) measurements: The surface morphologies of all films
lifted from the pure-water subphase at different surface pressures were
studied on the nanometer scale by high-resolution field-emission scan-
ning electron microscopy (FE-SEM, model No.: JEOL JSM-6700 F) over
the range: 0.5–30 kV with a lateral resolution in the range 2.2–1.2 nm.
The surface morphologies of all the films at different surface pressures
were studied by an atomic force microscope (AFM, VECCO diCP-II;
Model No AP-0100). The tapping mode was used in air to minimize any
kind of force exerted on the sample from the scanning tip. A thin phos-
phorus-doped silicon cantilever (with no coating on the front side and 50-
X-ray structural determination for compound 1a: Single-crystals suitable
for X-ray analysis of compound 1a·CH2Cl2 were obtained by the slow
evaporation of a CH2Cl2/n-hexane solution of the compound. The data
were collected on a Bruker SMART APEX-II diffractometer, equipped
with graphite-monochromated MoKa radiation (l=0.71073 ꢁ), and were
corrected for Lorentz-polarization effects. Crystals of 1a grew as brown
plates, and the sample used for data collection was approximately 0.20ꢂ
0.24ꢂ0.36 mm3. A total of 31903 reflections were collected, of which
6063 were unique (Rint =0.064), thereby satisfying the [I>2s(I)] criterion,
and were used in subsequent analysis. The structure was solved by em-
ploying the SHELXS-97 program package[38] and was refined by the full-
matrix least-squares method based on F2 (SHELXL-97).[39] All hydrogen
atoms were added in calculated positions. CCDC-842681 (1a·CH2Cl2)
contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallograph-
mula=C37H35Cl2CrN9O3; Mr =776.64; space group=P21/n; a=9.806(5),
b=15.808(5), c=23.322(5) ꢁ; a=90.000(5), b=98.115(5), g=90.000(5)8;
V=3579(2) ꢁ3; Z=4; T=293(2) K; 1calcd =1.441 gcmꢀ3; R(F)=4.14%;
wR(F)=11.3%.
(ꢁ10) nm aluminum coating on the back side) of resistance 1–10 Wcm
was used for scanning. The thickness of the cantilever ranged from 3.5–
4.5 mm with a length of 115–135 mm and a width of 30–40 mm. The pro-
cessed images were subsequently analyzed for diameter, height, and sur-
face roughness by Proscan 1.8 image analysis 2.1. The line profiles were
used to calculate surface roughness. The height profile showed the varia-
tion between the highest peak and lowest valley along the line. A scratch
was made in the LS films with a razor blade, being careful not to damage
the quartz itself and the sample was transferred into the AFM instru-
ment. The border of the scratch was then imaged by AFM in a tapping
mode. The scanned data were analyzed by local-depth analysis using the
commercial AFM software by choosing areas within the scratched region
and the intact surface around the trench. To determine the surface
height, the AFM software was used to process the image and perform an
averaged-line analysis over at least 100 lines for each image. The aver-
aged line corresponding to the top of the surface was selected, and from
this height value was subtracted a value corresponding to a point at the
bottom of the surface (step from scratch). Errors in these values were
calculated from standard deviations in the averaged-line-height analyses.
Computational methods: All calculations were performed using density
functional theory as implemented in the Gaussian 03 package.[40] Full ge-
ometry optimization of compound 1a was performed without symmetry
constraints. The hybrid B3LYP exchange-correlation functional[41] was
used in conjunction with the lanL2DZ basis set[42] with effective core po-
tential for the Cr atom and the 6–31G(d) basis set for the C,H, N, and O
atoms. The vibrational frequency calculation was performed to ensure
that the optimized geometry represented the local minima and that there
were only positive Eigen values. To establish the antiferromagnetically
coupled singlet [CrIII(La ꢀ)3] (1a) state (S=0), a symmetry-breaking ap-
ACHTUNGTRENNUNG
C
proach[43] within DFT was appropriate and has been widely used for such
systems.[5,44] Therefore, the calculations of the ground-state singlet states
were performed using either spin-restricted- or spin-unrestricted ap-
proaches (in G03, combined with GUESS=MIX). The stability of this
unrestricted Kohn–Sham solution has been checked by stability analysis
as implemented in G03. Vertical electronic excitations based on the
Acknowledgements
This research was supported by the Department of Science and Technol-
ogy (DST) (Projects SR/S1/IC/0031/2010 and SR/S2/CMP-0051/2006) and
the Council for Scientific and Industrial Research (CSIR) (India, 01/
Chem. Eur. J. 2012, 18, 1761 – 1771
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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