478
M. Tu¨mer et al. / Spectrochimica Acta Part A 70 (2008) 477–481
Table 1
ule (BAS PA-1) at a platinum disk electrode and a platinum
microelectrode of 10 m diameter (BAS). Cyclic voltammetric
measurements were made at room temperature in an undi-
vided cell (BAS model C-3 cell stand) with a platinum counter
electrode (BAS). All potentials are reported with respect to
Ag/AgCl. The solutions were deoxygenated by passing dry
nitrogen through the solution for 30 min prior to the experi-
ments, and during the experiments the flow was maintained over
the solution. The ferrocene/ferrocinium (Fc/Fc) redox couple
was used as internal standard: under the experimental conditions
used, E1/2 for the Fc/Fc+ couple was 0.48 and 0.45 V in DMF and
(CH3)2SO, respectively. Prior to use, the Pt working electrode
was polished with an aqueous suspension of 0.05-mm alumina
(Buehler) on a Master-Tex (Buehler) polishing pad, then rinsed
with water and acetone and dried in an oven. Digital simulations
were performed using DigiSim 3.0 for windows (BAS Inc.).
Experimental cyclic voltammograms used for the fitting process
had the background subtracted and were corrected electronically
for ohmic drop.
Crystal data and structure refinement for the title compound
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system, space group
Cell dimensions
C28H40O2
408.60
293(2) K
0.71073 A
¯
Triclinic, P1
˚
˚
˚
◦
a = 6.096(4) A; b = 10.431(8) A;
c = 10.535(5) A; α = 81.410(2) ;
β = 75.950(2)◦; γ = 81.490(2)◦
˚
3
˚
Cell volume
Z
Density (calculated)
Absorption coefficient
F000
Crystal size
θ (◦) range for data collection
Index ranges
Reflections collected/unique
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
R indices [I > 2σ(I)]
Largest diff. peak and hole
638.2(7) A
1
1.1063 mg/m3
0.228 mm−1
224
0.2 mm × 0.2 mm × 0.2 mm
3.47–30.86
−8 ≤ h ≤ 8; −15 ≤ k ≤ 14; −15 ≤ l ≤ 15
16490/3571 [R(int) = 0.2136]
Full-matrix least-squares on F2
3571/0/142
0.932
0.114 and −0.101 e A
−3
˚
2.2. Catalytic oxidation of 2,6-di-tert-butylphenol
In a dichloromethane/methanol solvent mixture (1:1,
50 cm3), the cobalt(II) complexes were dissolved. To it 2,6-di-
tert-butylphenol was added and the solution was stirred for 48 h.
The solution was then filtered and the filtrate was evaporated
to dryness. Five cubic centimetres of methanol was added to
dissolve the excess 2,6-di-tert-butylphenol. For measuring the
progress of the reaction, 50 L from the aliquot was passed
through an Amberlyst cationic ion-exchanger and washed with
10 cm3 (2 × 5) dichloromethane. The changes in the concen-
trations of the oxidation product TTBDQ were monitored by
optical spectroscopy.
solved by SHELXS-97 [15] and refined by SHELXL-97 [16]
software package. All H atoms were located in geometrically
˚
idealized positions, with C H distance of 0.93 A (aromatic
˚
H atoms), and 0.96 A (methyl H atoms). The Uiso(H) values
were set equal to 1.2–1.5 Ueq(C) for aromatic CH and methyl
groups, respectively. The final cycle of the refinement included
142 variable parameters R1 = 0.0777, ωR2 = 0.1485 where
ω = 1/[σ2(F02) + (0.0409P)2] were obtained. The details of the
X-ray data collection, structure solution and refinement details
were given in Table 1. Further experimental details have been
deposited as supplemantary material at the Cambridge Crystal-
lographic Data Centre CCDC 631500. Atomic scattering factors
were taken from International Tables for X-ray crystallography
[17].
Electrochemical data for TTBDQ. Scan rate at 50 mV s−1
:
−0.72, 0.27 (Epc, V), scan rate at 100 mV s−1: −0.15, 0.42 (Epc,
V), scan rate at 500 mV s−1: −0.57, 0.48 (Epc, V). Scan rate at
50 mV s−1: 0.29, 0.20 (Epa, V), scan rate at 100 mV s−1: −0.19,
0.44 (Epa, V), scan rate at 500 mV s−1: −0.38, 0.20 (Epa, V).
3. Results and discussion
2.3. Structure determination
In this study, we used the binuclear cobalt(II) complexes as
a catalyst for the C C coupling reaction of the DTBP [13].
A
needle pale yellow crystal with dimensions
1
0.2 mm × 0.2 mm × 0.2 mm was chosen for the structure
determination. Diffraction experiment was carried out on a
four-circle Rigaku R-AXIS RAPID-S diffractometer equipped
with a two-dimensional area IP detector. The graphite-
The H(13C) NMR spectra of the TTBDQ were recorded
1
using CD3OD as a solvent. In the H NMR spectrum of the
TTBDQ, the sharp singlets in the range 1.49–1.62 ppm can be
attributed to the protons of the t-butyl groups. The aromatic ring
protons are equivalent and seen in the 6.18–6.95 ppm range.
In the 13C NMR spectrum, the signal at 195.89 ppm may be
due to the carbon atom of the C O group on the aromatic
ring. The aromatic ring carbon atoms are seen in the range
114.67–156.43 ppm. The methyl carbon atoms of the t-butyl
groups were seen in the range 31.85–32.10 ppm. In the infrared
spectrum of the TTBDQ, the vibration at 1685 cm−1 can be
attributed to the ν(C O). The aliphatic ν(C H) stretchings of
the t-butyl groups were seen at 1945 cm−1 as a sharp peak.
Benzoquinone, diphenoquinones and their derivatives are
important intermediates for industrial synthesis of a wide vari-
˚
monochromatized Mo K␣ radiation (λ = 0.71073 A) and
oscillation scans technique with ꢀω = 5◦ for one image were
used for data collection. Images for oxidation compound
TTBDQ was taken successfully by varying ω with three sets of
different χ and ϕ values. For each compounds the 108 images
for six different runs covering about 99.7% of the Ewald spheres
were performed. The lattice parameters were determined by
the least-squares methods on the basis of all reflections
with F2 > 2σ(F2). Integration of the intensities, correction
for Lorentz and polarization effects and cell refinement was
performed using Crystal Clear software [14]. The structure was