A. Paulovicova, U. El-Ayaan, K. Shibayama, T. Morita, Y. Fukuda
FULL PAPER
assigned to ν(CϭN) are shifted to lower wavenumbers in a common equal-in-length bidentate coordination of o,oЈ-
the complex formation indicating, the coordination of both iPr2C6H3-BIAN was observed. In complex 2, the pro-
diimine nitrogen atoms of o,oЈ-iPr2C6H3-BIAN ligand to nounced shielding effect introduced by the o,oЈ-diisopropyl-
the copper(II) ion. Strong bands observed in the 1695 and phenyl groups, resulting from the more perpendicular ar-
1705 cmϪ1 regions for complex 1 and 2, respectively, indic- rangement, was identified by the relatively longer (CuϪN)
ate the coordination of an acetic acid molecule.
bond, and by the respective changes inside the o,oЈ-
iPr2C6H3-BIAN ligand. UV/Vis absorption spectra of both
complexes indicate a strong π-back-bonding and a smaller
HOMOϪLUMO energy gap.
Table 2. IR spectra (cmϪ1) of o,oЈ-iPr2C6H3-BIAN ligand and com-
plexes 1 and 2
Ϫ
Compound
ν(CϭN)
ν(ClO4
)
ν(AcOH)
Experimental Section
o,oЈ-iPr2C6H3-BIAN 1671, 1652, 1642
Ϫ
Ϫ
Ϫ
1695
1705
Complex 1
Complex 2
1661, 1635
1668, 1640
Materials and Instrumentation: All chemicals were purchased from
the Wako Pure Chemical Industries Ltd., and used without fur-
ther purification.
1110, 622
IR spectra of complex 2 show two peaks, 1570 and 1519
cmϪ1, that can be assigned to ν(CϭO) and ν(CϭC) of the
acac ligands, respectively, consistent with those observed for
[Cu(acac)2].[25] The strong band observed at 1110 cmϪ1
(antisymmetric stretch) and the sharp band at 622 cmϪ1
(antisymmetric bend), suggest uncoordinated perchlorate
anions[26] in agreement with the X-ray structure of 2.
Solid-state room-temperature electronic spectra of 1 and
2 exhibit a broad d-d band at 700 and 625 nm, respectively,
typical for square-pyramidal copper(II) complexes.[27Ϫ29]
Another band appeared in the visible spectral region, 558
and 545 nm, of complexes 1 and 2, respectively, assigned to
the MLCT transitions from copper(II) to the π* orbitals of
o,oЈ-iPr2C6H3-BIAN. This shift to much longer wavelength
than those of other diimine ligands can be explained on
the basis that the o,oЈ-iPr2C6H3-BIAN ligand provides π*
orbitals at rather low energies[17,30,31] that results in the in-
creased overlap with the metal d orbitals. Consequently, this
results in a stronger π-bonding interaction accompanied by
a red-shift of the MLCT transition. Electrochemical stud-
ies[32] on the π-acceptor properties of the bis(arylimino)
acenaphthene reveal a much larger positive potential than
those of other diimine ligands confirming the larger π-ac-
ceptor strength of bis(arylimino)acenaphthene.
Elemental analyses (C, H, N) were performed on a PE 2400 Series
II CHNS/O Analyzer. Ϫ Electronic spectra were recorded on a UV-
3100PC Shimadzu spectrophotometer using 10 mm quartz cells at
room temperature. Powder reflectance spectra were obtained using
the same instrument equipped with an integrating sphere and using
BaSO4 as a reference. Ϫ Infrared spectra were recorded on a
PerkinϪElmer FT-IR Spectrometer Spectrum 2000 in a KBr pellet
and as a Nujol mull in the 4000Ϫ370 cmϪ1 spectral range. Ϫ Mag-
netic susceptibilities were measured at room temperature on a Shi-
madzu MB-100 Torsion Magnetometer. Diamagnetic corrections
were considered by using Pascal’s constants.[33] Ϫ Thermogravi-
metric measurements were performed on a DTG-50 Shimadzu in-
1
strument. Ϫ H and 13C NMR spectra were run on a JEOL JNM
LA 300 WB spectrometer at 300.40 and 75.45 MHz, respectively,
using a 5 mm probe head. CD2Cl2 and CDCl3 were used as a solv-
ent. Chemical shifts are given in ppm relative to the internal TMS
1
standard. The typical pulse width was 6.25 µs for H and 4.25 µs
for 13C measurements. Assignment of the 13C signals based on
ref.[15] was confirmed by off-resonance decoupled and DEPT-135
measurements.
Synthesis of [N-(2,6-Diisopropylphenyl)imino]acenaphthene: This li-
gand was prepared using a method different to that published by
Asselt, Elsevier et al.[15] Acenaphthenequinone (1.35 g, 7.4 mmol)
in 65 mL of acetonitrile was heated under reflux (80 °C) for 30 min.
Then 12 mL of acetic acid was added and heating was continued
until the acenaphthenequinone had completely dissolved. To this
hot solution, 3 mL (16 mmol) of 2,6-diisopropylaniline was added
directly and the solution was heated under reflux for a further
1.5 h. It was then cooled to room temperature and the solid filtered
off to give a yellow product that was washed with hexane and air-
dried. Yield 3.15 g (85%). Ϫ C36H40N2 (500.7): calcd. C 86.35, H
8.05, N 5.60; found. C 85.85, H 8.03, N 5.34%. Ϫ 1H NMR
(CDCl3, 300.40 MHz, 24 °C): δ ϭ (0.97 d, 15-H), 1.23 (d, 16-H),
3.03 (sept, 14-H), 6.63 (d, 3-H), 7.26 (s, 12-H, 11-H, 10-H), 7.36
(pst, 4-H), 7.88 (d, 5-H). Ϫ 13C NMR (CD2Cl2, 300.40 MHz, 25.4
°C): δ ϭ 23.1 (C-16), 23.2 (C-15), 29.1 (C-14), 123.5 (C-11), 123.9
(C-10, C-12), 124.6 (C-3), 128.3 (C-4), 129.2 (C-5), 130.0 (C-2),
131.6 (C-6), 135.5 (C-9, C-13), 141.2 (C-7), 148.0 (C-8), 161.1 (C-1).
Absorption spectra of both complexes show various
bands below 420 nm that can be assigned to intraligand
transitions of the free diimine ligand, which absorbs in the
same spectral region. Electronic spectra were also recorded
in solution using a variety of solvents (DCE, THF, toluene,
and chloroform). All solution spectra of both complexes 1
and 2 are very similar to the corresponding solid-state spec-
tra.
Conclusion
From the X-ray structure analysis of both copper(II)
complexes 1 and 2 we can conclude that the two diisopro-
pylphenyl moieties on the imine nitrogens of the o,oЈ-
iPr2C6H3-BIAN ligand are flexible and show no conjuga-
tion with the naphthalene-diimine backbone. We have
shown the difference in the coordination behaviour of this
Synthesis of [Cu(AcOH)(o,oЈ-iPr2C6H3-BIAN)Cl2] (1): Bis[N-(2,6-
diisopropylphenyl)imino]acenaphthene,
o,oЈ-iPr2C6H3-BIAN,
(0.35 g, 0.7 mmol) was dissolved in a small amount of chloroform
(99%). A mixture of chloroform/acetic acid (15 mL, the 2:1 ratio)
was then added, and the solution was heated for 10 min at 60 °C.
Subsequently, a methanolic solution (7 mL) of CuCl2·2H2O (0.12 g,
ligand when bound to the copper(II) ion. In complex 1, 0.7 mmol) was added dropwise to the o,oЈ-iPr2C6H3-BIAN solu-
2644 Eur. J. Inorg. Chem. 2001, 2641Ϫ2646
Paulovicova, Adriana
