2,2′-Bipyridines carrying a diazo moiety and their complexes with bis(hexafluoroacetylacetonato)copper: Synthesis, structures, electronic and magnetic properties of their photoproducts in frozen solutions

Article abstract of DOI:10.1039/b007375j

4-(α-Diazobenzyl)-2,2′-bipyridine 2, diazodi{4-(2,2′-bipyridyl)}methane 3, and 1,3-benzenediyl{4-(4′-methyl-2.2°prime;-bipyridyl)diazomethane} 4 were prepared as new types of spin sources/magnetic couplers. The molecular structures of bipyridine ligands,

Full text of DOI:10.1039/b007375j

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2,2'-Bipyridines carrying a diazo moiety and their complexes with
bis(hexa¯uoroacetylacetonato)copper: synthesis, structures,
electronic and magnetic properties of their photoproducts in frozen
solutions{
Hiroshi Morikawa,a Fumika Imamura,a Yasuo Tsurukami,a Tetsuji Itoh,a Harumi Kumada,a
Satoru Karasawa,a Noboru Koga*a and Hiizu Iwamurab
aGraduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-
ku, Fukuoka 812-8582, Japan. E-mail: koga@phar.kyushu-u.ac.jp
bThe University of the Air, 2-11 Wakaba, Mihama-ku, Chiba 261-8586, Japan
Received 12th September 2000, Accepted 13th November 2000
First published as an Advance Article on the web 10th January 2001
4-(a-Diazobenzyl)-2,2'-bipyridine 2, diazodi{4-(2,2'-bipyridyl)}methane 3, and 1,3-benzenediyl{4-(4'-methyl-2,2'-
bipyridyl)diazomethane} 4 were prepared as new types of spin sources/magnetic couplers. The molecular
structures of bipyridine ligands, 2, 3, 4, and [Cu(hfac)2?2] were revealed by X-ray analyses. Photolysis of 2, 3, 4,
and their complexes with Cu(hfac)2 in MTHF frozen solutions at cryogenic temperature was followed by UV±
Vis and EPR spectroscopy. UV±Vis and EPR spectra after photolysis showed strong two absorptions; at 508
and 471 nm for 2, and 511 and 476 nm for 3, and characteristic sets of EPR signals due to the triplet states; |D/
hc|~0.418, and 0.436 cm21 and |E/hc|~0.021 and 0.022 cm21 for 2 and 3, respectively. Diazo compound 4 after
photolysis also showed absorptions at 506 and 471 nm and EPR signals characteristic of a quintet. Their
complexes with Cu(hfac)2 showed a red shift of 3±14 nm in the visible spectra and gave EPR spectra
characteristic of the high-spin complexes under similar conditions. Magnetic susceptibility measurements on a
SQUID magnetometer were carried out using a sample similar to the one employed in the UV±Vis and EPR
studies. The ®eld dependence of magnetization in frozen solution suggested that the ground-state spin
multiplicities of the photoproducts of 2, 3, and 4 were triplet, triplet, and quintet, respectively. Similarly, those
of their complexes with Cu(hfac)2 were quartet, quintet, and septet, respectively.
ligands so that they could lead to complexes having extended
Introduction
structures by coordinating with metal ions. 4-(a-Diazobenzyl)-
2,2'-bipyridine 2 was also prepared as a reference compound. In
the ®rst step, the complexes of Cu(hfac)2 coordinated with 2, 3,
and 4 were photolysed and their electronic and magnetic
properties were investigated. The electronic and magnetic data
are important in understanding magnetic couplings between
generated carbene(s) and copper(II) ion(s) through 2,2'-
bipyridine rings. In the previous work, we employed crystalline
samples for photolysis and often encountered problems
associated with the optical transparency of the samples. To
overcome these dif®culties, it was deemed necessary to develop
studies in frozen solution systems for the SQUID measure-
ments and con®rm the ground-state spin multiplicity.7 In
frozen solution, two new factors have to be taken into account.
One is dissociation of the metal complexes; generally high
association constants of 2,2'-bipyridine ligands will be favor-
able in this respect. Secondly, a small amount of paramagnetic
species and a large amount of diamagnetic solvent molecules
are present in the sample and they compete with each other
magnetically. In particular, it is dif®cult to estimate the
diamagnetic contribution accurately in a sample for para-
magnetic species with a small S value. A problem for magnetic
experiments in frozen solution lies in how accurately the
diamagnetic contribution of the solvent in a sample is
estimated. In our diazo-carbene system, however, this problem
can be resolved by using the difference between the magnetiza-
tion values (M) before and after irradiation without touching
the sample in between. An additional advantage of frozen
solution conditions is that we may neglect intermolecular
antiferromagnetic interactions which are often observed at low
Heterospin systems consisting of 2p spins of diarylcarbenes and
3d spins of transition metal ions have been employed in our
laboratories for the construction of photoresponsive super-
high-spin complexes.1 Photolysis of 1 : 1 polymeric complexes
of bis(hexa¯uoroacetylacetonato)-manganese(II) and -cop-
per(II), {Mn(hfac)2 and Cu(hfac)2}, coordinated with di-
azodi(4-pyridyl)methane 1 indeed produced ferri- and ferro-
magnetic chains with average spins of approximately S~300
(at 1.9 K) and 30 (3.0 K), respectively.2,3 Since the obtained
metal complexes with 1 were basically one-dimensional,
spontaneous magnetization was not obtained at ®nite tem-
perature. These studies revealed the usefulness of the hetero-
spin complexes and, at the same time, the necessity of a two- or
three-dimensional (2D and 3D) structure for the realization of
molecule-based magnets.4 One approach to the construction of
2D or 3D structures in our heterospin systems lies in the use of
a metal ion with only one type of ligand, such as hfac. The
bidentate ligand 2,2'-bipyridine is a candidate5 for such a base
ligand; 2,2'-bipyridine is well known to produce bis and tris
complexes coordinated with various central metal ions.6 For
this purpose, diazodi{4-(2,2'-bipyridyl)}methane 3 and 1,3-
benzenediyl{4-(4'-methyl-2,2'-bipyridyl)diazomethane} 4 were
designed and prepared as new photoresponsive spin precursor/
magnetic couplers. Compounds 3 and 4 are bis-bidentate
{Electronic supplementary information (ESI) available: EPR spectra
after irradiation of 2, 3, 4; M/Msat vs. H/T plots after irradiation of 3 in
frozen solutions of MTHF. See http://www.rsc.org/suppdata/jm/b0/
b007375j/
DOI: 10.1039/b007375j
J. Mater. Chem., 2001, 11, 493±502
This journal is # The Royal Society of Chemistry 2001
493

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temperatures (v10 K) in a crystalline sample. In this paper, we
report SQUID measurements under frozen 2-methyltetrahy-
drofuran (MTHF) solutions (similar to those for UV±Vis and
EPR studies) and the determination of the ground state spin
multiplicity for [(Cu(hfac)2)2?3] and [(Cu(hfac)2)2?4]. According
to previous studies8 of the copper complexes with 4-tert-
butylaminoxyl-2,2'-bipyridine 5, high-spin copper complexes
with S~4/2 and 6/2 are expected to be produced after
photolysis of [(Cu(hfac)2)2?3] and [(Cu(hfac)2)2?4], respectively.
Results and discussion
Preparation of diazo-bipyridines and their copper complexes
4-Bromo-2,2'-bipyridine9 and 4-methyl-4'-formyl-2,2'-bipyri-
dine were used as starting materials for 3 and 4, respectively.
The bromide 3'Br was lithiated, reacted with 2-bromo-4-
formylpyridine, followed by oxidation with MnO2. The
obtained bipyridyl pyridyl ketone 3'k was reacted with 2-
trimethylstannylpyridine in the presence of Pd(PPh3)4 to give
bis(4-(2,2'-bipyridyl)) ketone 3k. The diketone 4k was prepared
by the reaction of 4-methyl-4'-formyl-2,2'-bipyridine with the
dilithiated salt of 1,3-dibromobenzene, followed by oxidation
with MnO2. The diazo groups that are precursors to the
carbenes were synthesized from the corresponding carbonyl
groups via hydrazones using a standard procedure.2 The
preparations of diazo-bipyridines 3 and 4 are summarized in
Scheme 1. A reference diazo compound 2 was prepared in a
manner similar to the procedure for 1 using 4-benzoyl-2,2'-
bipyridine in place of di(4-pyridyl) ketone.1
CH2Cl2/ether (2 : 1 : 1), and CH2Cl2/n-hexane (10 : 1), bipyr-
idine ligands 2, 3, and 4 were obtained as red needles, orange
plates, and red plates, respectively.
After recrystallization from n-hexane/ether (1 : 1), MeOH/
Scheme 1 i) 2-Bromo-4-formylpyridine, n-BuLi/ether, 278 ³C; ii) MnO2/CHCl3, re¯ux; iii) 2-trimethylstannylpyridine, Pd(PPh3)4/toluene, re¯ux; iv)
NH2NH2, NH2NH2?HCl/DMSO; v) MnO2/CH2Cl2; vi) 1,3-dibromobenzene, n-BuLi/THF, 278 ³C; vii) hn.
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Fig. 1 ORTEP drawings of molecular structures for (a) 2, (b) 3, (c) 4, and (d) [Cu(hfac)2?2 ] with thermal ellipsoid plot at the 30% probability level.
The copper complexes [(Cu(hfac)2)2?2], [(Cu(hfac)2)2?3], and
[(Cu(hfac)2)2?4] were prepared by mixing the solutions of 2, 3, and
4 with that of Cu(hfac)2 in MTHF in the appropriate ratios. After
recrystallization, the complex of [Cu(hfac)2?2] was obtained as
single crystals and the 2 : 1 complexes, [(Cu(hfac)2)2?3], and
[(Cu(hfac)2)2?4], were obtained as powders.
2049 cm21 for 2, 3, and 4 shifted to 2061, 2074, and 2064 cm21
,
respectively, after the complexation with Cu(hfac)2.
Molecular structures of 2, 3, 4, and [Cu(hfac)2?2]
The molecular and crystal structures of the diazo-bipyridines 2,
3, and 4, and the copper complex [Cu(hfac)2?2] were revealed
Characteristic IR absorptions due to the diazo moieties at
Table 1 Selected bond lengths, angles and dihedral angles for 2, 3, 4, and [Cu(hfac)2?2]
Ê
Bond length/A
Bond angle/³
C8±C11±C12
C8±C11±C8*
Dihedral angle/³
2
3
4
127.76
127.29
N1C2C4±N2C7C9
N2C7C9±C13C15C17
N1C2C4±N2C7C9
14.87
59.36
2.95
50.28
8.74
9.69
51.85
38.74
8.59
N2C7C9±N2*C7*C9*
N1C2C4±N2C7C9
N5C20C22±N6C25C27
N2C7C9±C14C16C18
N6C25C27±C14C16C18
N1C2C4±N2C7C9
C8±C12±C13
C15±C30±C26
128.24
129.92
[Cu(hfac)2?2]
Cu±N1
Cu±N2
Cu±O1
Cu±O2
Cu±O3
Cu±O4
1.999(4)
1.983(4)
2.232(4)
1.960(4)
1.994(4)
2.385(4)
N1±Cu±O2
N2±Cu±O3
O1±Cu±O4
173.1(2)
174.7(2)
163.2(1)
N2C7C9±C13C15C17
36.46
C8±C11±C12
128.03
J. Mater. Chem., 2001, 11, 493±502
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by X-ray analyses. The molecular structures of 2, 3, 4, and
[Cu(hfac)2?2] are shown in Fig. 1.
Selected bond lengths, angles, and dihedral angles for 2, 3, 4,
and [Cu(hfac)2?2] are given in Table 1.
The molecular structures of the bipyridine ligands 2 and 4
have no symmetry axis and 3 has a C2 symmetry axis through
the C(11)±N(3)±N(4) bond. As shown in Fig. 1, the 2,2'-
bipyridine units in 2, 3, and 4 have trans conformations10 and
the dihedral angles between the pyridine planes of the
bipyridine moiety are 14.87, 2.95, and 8.74(9.69³), respectively.
The bond angles of C(8)±C(11)±C(12) in 2, C(8)±C(11)±C(8*)
in 3 and C(8)±C(12)±C(13) (C(15)±C(30)±C(26)) in 4 are
127.76, 127.29, and 128.24(129.92)³, respectively. The dihedral
angles between the pyridine ring of bipyridine and phenyl rings
for 2 and 4, and that between the pyridine rings for 3 through
the diazo moiety, are 59.36, 51.85 and 38.74, and 50.28³,
respectively.
The crystal of [Cu(hfac)2?2] contained four molecules of
acetone per unit cell as solvent of recrystallization. The
molecular structure of the complex [Cu(hfac)2?2] has no
symmetry axis and the coordination geometry is a distorted
octahedron. As listed in Table 1, the elongation axis for
[Cu(hfac)2?2] is through O(1)±Cu±O(4). Therefore, the mag-
netic orbital (dx22y2) of the copper ion is judged to be directed
to the nitrogens (N1 and N2) of the bipyridine in the complex.
The dihedral angle between the two pyridine rings in the 2,2'-
bipyridine moiety is 8.59³ and the one between the planes of the
bipyridine and the phenyl ring is 36.46³. The crystal packing
showed the head-to-tail dimer structures consisting of a pair of
Fig. 2 Change of UV±Vis spectra after irradiation (lw380 nm) of
[Cu(hfac)2?2] for 0, 10, 20, and 80 s in MTHF frozen solution
(1.061023 M) at 10 K. The ®nal spectrum of 2 (Ð?Ð) is shown in the
inset.
parameters (zfs) obtained from EPR spectra are summarized
in Table 2 together with the data for compound 1 and its
Cu(hfac)2 complex.
(A) UV±Vis spectra of 2, 3, 4 and their complexes with
Cu(hfac)2. UV±Vis spectra for diazo-bipyridine 2 in MTHF
solution (1 mM) at room temperature showed two absorptions
at 283 and 500 nm. The latter is characteristic of the n±p*
transition due to the diazo group. When the irradiation
(lw380 nm) started at 10 K, this absorption decreased and two
new absorptions appeared at 508 and 471 nm. Similarly, diazo-
bipyridines 3 and 4 had absorptions at 477 and 493 nm due to
the n±p* transition and exhibited absorptions at 511 and 476,
and 506 and 471 nm, respectively, after irradiation under
similar conditions. Although the value of lmax showed a red
shift of ca. 40 nm, the spectra after irradiation of 2, 3, and 4
closely resembled that for diphenylcarbene (465 nm) reported
previously.11
The complexation of Cu(hfac)2 with 2 in MTHF was
con®rmed by titration by means of UV±Vis absorption
(360 nm) at room temperature. The binding constant (log K)
for 2 was thus estimated to be 5.8 M21 which is smaller that for
2,2'-bipyridine with Cu(II)(NO3)2 (log K~7.92 M21 at 30 ³C in
H2O±EtOH) reported previously.12 The 2 : 1 complexes of
Cu(hfac)2 with 3 and 4 showed strong absorptions at 291 and
293 nm together with a new shoulder at 355 and 353 nm,
respectively.
The change of the UV±Vis spectrum of [Cu(hfac)2?2] in
frozen MTHF after irradiation at 10 K is shown in Fig. 2 in
addition to the spectrum after complete photolysis of 2 under
similar conditions (inset in Fig. 2). The absorption at 378 nm
due to [Cu(hfac)2?2] decreased with the irradiation time and
was replaced with new ones at 522 and 488 nm with isosbestic
points at 360 and 420 nm (Fig. 2).
The 2 : 1 complexes of Cu(hfac)2 with 3 and 4 in MTHF
frozen solutions were also measured under similar conditions.
They gave UV±Vis spectra similar to that from [Cu(hfac)2?2];
514 and 477 nm from [(Cu(hfac)2)2?3], and 513 and 477 nm
from [(Cu(hfac)2)2?4]. As listed in Table 2, characteristic
absorptions due to the carbene species in the visible region
showed a red shift of 3±14 nm after complexation with
Cu(hfac)2.
Ê
D and L isomers (the nearest contacts are 3.19 A for O(1)±
Ê
C(17) within the dimers and 3.25 A for O(4)±C(2) between the
dimers). This dimer structure was similar to that for the
corresponding [Cu(hfac)2?5] reported previously.8
UV±Vis, EPR spectra and SQUID measurements in frozen
solutions
Solutions of the bipyridine ligands 2, 3, 4, and mixed solutions
of bipyridines and Cu(hfac)2 in MTHF were used for the
sample. They were placed in the cryostats of low-temperature
EPR and UV±Vis spectrometers and in the SQUID magnet-
ometer/susceptometer sample room. The sample was irradiated
with light of lw380 nm through a colored glass ®lter from a
high-pressure Hg lamp for EPR and UV±Vis experiments and
the light from an argon laser (l~514 nm) and or a He±Cd laser
(l~442 nm) for SQUID measurements. Selected spectroscopic
data (nCLN /cm21 and
lmax/nm) and zero-®eld splitting
2
Table 2 Selected spectroscopic data for the pyridines and their copper
complexes
IRa
CLN /cm21
UV±Vis
max/nm
EPR
n
l
|D/hc|/cm21 |E/hc|/cm21
2
1
1c
2060b
2072
2049
2061
2049
484, 304b
453, 421
0.434b
0.418
0.436
0.020b
0.021
0.022
[Cu(hfac)2?1]
[Cu(hfac)2?1c]
2
2c
[Cu(hfac)2?2]
[Cu(hfac)2?2c]
3
3c
[(Cu(hfac)2)2?3] 2074
[(Cu(hfac)2)2?3c]
4
4c
[(Cu(hfac)2)2?4] 2064
[(Cu(hfac)2)2?4c]
500, 283c
508, 471
360, 295c
522, 488, 378
477, 285c
511, 476
355, 291c
514, 477
493, 285c
506, 471
353, 293c
513, 477
2049
In these 2,2'-bipyridine derivatives and their complexes with
Cu(hfac)2, the absorptions at ca. 500 nm due to the generated
carbene widely overlapped with those of the diazo moieties; the
absorption of the carbenes was over ten times larger than that
for the diazo moieties (e~y100 for 2). These strong
c
aIn KBr pellets. bRef. 14. At room temperature.
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absorptions due to the generated carbenes might prevent the
effective photolysis of starting diazo moieties.
All new absorptions observed after irradiation of 2, 3, 4, and
their complexes of Cu(hfac)2 disappeared at temperatures
higher than 60 K.
(B) EPR spectra of 2, 3, 4 and their complexes with
Cu(hfac)2. The EPR spectra after irradiation of 2, 3, and 4
and their copper complexes in frozen MTHF solutions were
measured at cryogenic temperatures.
When the irradiation for 2, 3, and 4 started at 10 K, new
signals appeared. Those for 2 and 3 constituted typical sets of
signals due to triplet carbenes13,14 with zero-®eld splitting
parameters (zfs) |D/hc|~0.418 and 0.436 cm21 and |E/
hc|~0.021 and 0.022 cm21, respectively. Interestingly, these
zfs values are good agreement with those for the correspond-
ing pyridyl carbenes; |D/hc|~0.418 and 0.434 cm21 and |E/
hc|~0.021 and 0.020 cm21 for phenyl pyridyl carbene13 and
dipyridyl carbene,14 respectively, under similar conditions.
This agreement suggested that the degrees of delocalization
of the 2pp spin of the carbene center in 2,2'-bipyridines are
similar to those for pyridines and the magnitude of the
magnetic coupling similar to [Cu(hfac)2?1]2, J/kB~67 K, is
expected to depend on the copper(II). Bisdiazo compound 4
also showed a typical quintet spectrum (|D/hc|~ca. 0.06±
0.13 cm21 15
having characteristic signals at around 280 and
)
400 mT, which resemble that after photolysis of 1,3-
benzenediylbis(a-diazobenzyl).
On the other hand, the EPR spectrum after irradiation of the
solution of 2 and Cu(hfac)2 in a ratio of 1 : 1 under similar
conditions showed a drastic change. When irradiated, a set of
new signals appeared in the ®eld range 0±600 mT at the expense
of signals at 269, 285, 301, and 322 mT due to copper(II) in
[Cu(hfac)2?2]. They were more complicated than those expected
for an unoriented sample of a quartet molecule.16
Mixed solutions of Cu(hfac)2 with 3 and 4 in MTHF were
also measured under similar conditions. When the solutions
of Cu(hfac)2 with 3 in 1 : 1 and 2 : 1 ratios were irradiated,
EPR spectra similar to that for [Cu(hfac)2?2] with a strong
signal at 254 mT and two broad ones at 100 and 450 mT were
obtained, respectively. In the spectrum after irradiation of
the 1 : 2 complex of Cu(hfac)2 with 4, a strong signal at 83
and a broad one at 293 mT appeared at the expense of the
signals at g~2 due to isolated Cu(II) ion in Cu(hfac)2 units.
EPR spectra after photolysis of the complexes of Cu(hfac)2
with 2, 3, and 4 in frozen MTHF are shown in Fig. 3.
In the observed spectra for all copper complexes, a
signi®cant number of signals due to metal-free carbene were
not observed, indicating that the 2,2'-bipyridine moiety binds
with Cu(hfac)2 quantitatively under these cryogenic conditions.
As the temperature was increased from 10 K, the intensity of
all new signals linearly decreased according to the Curie law
and all signals disappeared at temperatures higher than
60 K. The observed temperature dependence of the signal
intensity suggests that the signals were due to the species in the
ground state.
Fig. 3 X-Band (n0~9.45 GHz) EPR spectra after irradiation
(lw380 nm) of the solution (1.061023 M) of the complexes of
Cu(hfac)2 with (a) 2, (b) 3, and (c) 4 in MTHF at 8 K. 6 indicates
the signals due to copper(II) ions of unphotolyzed Cu(hfac)2 units.
5 K in a constant ®eld of 20 kOe with irradiation time for 2 is
shown in Fig. 4a. As irradiation was continued, M values
gradually increased and reached a plateau after 150 min. The
®eld dependences of the magnetization at 2, 3, and 5 K before
and after irradiation (Ma and Mb, respectively) for 2 are given
in Fig. 4b. The observed M vs. H pro®le was affected by a large
diamagnetic contribution due to the solvent. The magnetiza-
tion (M) due to the paramagnetic species generated by
photolysis was obtained as the difference between Ma and
Mb: M~FMa2Mb. The difference of the magnetization before
and after irradiation is expressed as follows:
M~FMa{Mb~FNgmBSB(x)
(1)
where x~gSmBH/(kBT), F stands for a photolysis factor and
the other symbols have their usual meaning. Eqn. (1) ®tted
experimental data (M vs. H/T) to give S~1.00¡0.01 and
F~0.89¡0.01 for 2, S~0.99¡0.01 and F~0.88¡0.01 for 3,
and S~1.93¡0.01 and F~0.63¡0.01 for 4. Field dependences
of M for 2 and 4 are demonstrated via the M/Ms vs. H/T plots
in Fig. 4c together with theoretical curves with S~1/2, 2/2, 3/2,
4/2, and 5/2 in which the Ms values obtained from the best-
®tted curves were used. As shown in Fig. 4c, the experimental
data for 2c and 4c exactly traced the theoretical curves with
S~2/2 and 4/2, respectively, indicating that they are triplet and
quintet ground states, respectively. Similarly, the experimental
data for 3c indicated a triplet ground state.
(C) SQUID Measurements of 2, 3, 4 and their complexes with
Cu(hfac)2. Magnetization data (Mb and Ma) before and after
irradiation of 2, 3, 4, and their copper complexes in frozen
MTHF solutions, were obtained at 2.0, 3.0, and 5.0 K in the
®eld range 0±50 kOe. Taking the UV±Vis spectral character-
istics into account, we employed an argon ion laser
(l~514 nm) and a He±Cd laser (l~442 nm) for the irradiation
of the diazo compounds and the copper complexes, respec-
tively, in the SQUID experiments.
(C)-1 2,2'-Bipyridine ligand, 2, 3, and 4. The solutions
(1.0 mM) of 2, 3, and 4 in MTHF were used as the samples for
SQUID measurements. The development of magnetization at
From the difference of the absorptions due to diazo moieties in
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Fig. 5 M vs. H/T plots for the complexes of Cu(hfac)2 with (a) 2, (b) 3
and (c) 4 at 2.0 (#), 3.0 (%), and 5.0 K (©) in frozen MTHF solutions.
Theoretical data are shown as solid lines.
Fig. 4 (a) M vs. irradiation time plot for 2 in a constant ®eld of
20 kOe at 5 K. (b) Field dependences of magnetization for 2 at 2.0
(#), 3.0 (%), and 5.0 K (©) before (open) and after (®lled)
irradiation (l~514 nm) of 2 in MTHF frozen solution. (c) M/Ms vs.
H/T plot for 2 (open) and 4 (®lled). The inset in Fig. 4c shows the
low ®eld region 0±4 kOe K21. Curves show theoretical data for
The M vs. H/T plots for the complexes of Cu(hfac)2 with 2, 3,
and 4 are shown in Fig. 5.
¼
S~2/2 (Ð?Ð), 3/2 (Ð), 4/2 ( ), and 5/2 (± ± ±).
The points where the experimental data deviate from the
theoretical curves observed in Fig. 5 are caused by the raw data
crossing the zero point of M (from the paramagnetic to the
diamagnetic region). The raw data beyond the sensitivity range
of the SQUID magnetometer, which were seen as discontin-
uous data points, were omitted.
UV±Vis spectra before and after SQUID measurements, the
degrees of photolysis of 2, 3, and 4 were estimated to be 100, 100,
and 75%, respectively. These values are close to the photolysis
factor (F~0.89, 0.88, and 0.63 for 2c, 3c, and 4c, respectively)
obtained by ®tting eqn. (1) to the experimental data.
The magnetization of the copper complexes before and after
irradiation (Mb and Ma, respectively) is expressed as follows:
Mb~MCuzMdia
(2)
(3)
(C)-2 Complexes of Cu(hfac)2 with 2, 3, and 4. Mixed
solutions (1.1, 3.5, and 0.5 mM, respectively) of Cu(hfac)2 with
2, 3, and 4 in MTHF in ratios of 1 : 1, 2 : 1, and 2 : 1,
respectively, were used as the samples. The magnetic measure-
ments were performed under conditions similar to those for the
corresponding free ligand.
Ma~FMcompz(1{F)MCuzMdia
where Mcomp and MCu are the magnetizations due to the
carbene-Cu complexes and the diazo-copper complexes,
respectively, and F is a photolysis factor. The magnetization
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(M) due to the species generated by photolysis was obtained as
the difference between Ma and Mb: M~Ma2Mb~F
(Mcomp2MCu). The experimental data were analyzed by
best-®tting the Brillouin function B(x) as given by eqn. (4):
Experimental
General methods
Infrared spectra were measured on a JASCO FT/IR 420 IR
spectrometer. 1H NMR spectra were measured on a JEOL 270
Fourier transform spectrometer using CDCl3 as solvent and
referenced to TMS. FAB mass spectra (FAB MS) were
recorded on a JEOL JMS-SX102 spectrometer. Melting
points were obtained with a MEL-TEMP heating block and
are uncorrected. Elemental analyses were performed at the
Analytical Center of the Faculty of Science in Kyushu
University. Irradiations for UV±Vis and EPR spectroscopic
experiments consisted of light of lw380 nm shone through a
colored glass ®lter (Toshiba L-40) from a high-pressure Hg
lamp (USHIO; Model UI-501C).
M~Ma{Mb~F(Mcomp{MCu)~
FNgmBfSB(x){B(x')=2g
(4)
where x~gSmBH/(kBT), x'~g'mBH/(2kBT), and the other
symbols have their usual meaning. The g' values for the
complexes of Cu(hfac)2 with 2, 3, and 4 were 2.16, 2.17, and
2.15, respectively, which were obtained from EPR spectra
before irradiation under similar conditions. Eqn. (4) ®tted
experimental data (M vs. H/T) for the 1 : 1 mixture of Cu(hfac)2
and 2 after irradiation for 90 min to give S~1.53¡0.01 and
F~0.87¡0.01. Similarly, magnetic ®eld dependences of M for
1 : 2 mixtures of Cu(hfac)2 with 3 and 4 in solutions of MTHF
were investigated under similar conditions.
UV±Vis spectra
M~Ma{Mb~F(Mcomp{2MCu)~FNgmBfSB(x){B(x')g (4')
UV±Vis spectra were recorded on a JASCO V570 spectrometer
and a NACC Cryo-system LTS-22X was attached for the low-
temperature measurements. The degassed sample solution was
placed in a quartz cell of path-length 1 mm.
Eqn. (4') ®tted experimental data (M vs. H/T) to give
S~2.14¡0.03 and 2.86¡0.04 and F~0.44¡0.01 and
0.86¡0.02 for 2 : 1 mixtures of Cu(hfac)2 with 3 and 4,
respectively. The ®tting curves for the complexes of Cu(hfac)2
with 2, 3, and 4 are shown in Fig. 5.
X-Ray crystal and molecular structural analyses
From the difference of the absorption (ca. 360 nm) due to
diazo moieties in the UV±Vis spectra before and after the
SQUID measurements, the degrees of photolysis of the
complexes of Cu(hfac)2 with 2, 3, and 4 were estimated to be
100, 51, and 100%, respectively. These values are close to the
photolysis factors (F~0.87, 0.44 and 0.86) obtained by ®tting
eqn. (4) and (4') to the experimental data.17 The obtained S
values of 1.53, 2.14, and 2.86 for the complexes of Cu(hfac)2
with 2, 3, and 4 are close to the theoretical ones of 1.5, 2.0, and
3.0, respectively. Therefore, this result of the ®eld dependence
of M for the complexes of Cu(hfac)2 with 2, 3, and 4 suggests
that the generated carbene centers interacted with copper(II)
ions ferromagnetically to form high-spin complexes with the
quartet, quintet and septet ground states, respectively.
Diffraction data were collected using MoKa radiation on a
Rigaku RAXIS-IV imaging plate area detector system at room
temperature for 2 and 4, and 2100 ³C for 3 and [Cu(hfac)2?2].
The structures for 2, 3, 4, and [Cu(hfac)2?2] were solved in space
groups P21/n (no. 14), Pbcn (no. 60), Pca21 (no. 29), and P21/c
(no. 14), respectively, by direct methods18 and re®nement
converged using full-matrix least squares methods from the
teXsan19 crystallographic software package (ver. 1.9). All non-
hydrogen atoms were re®ned anisotropically; hydrogen atoms
Ê
were included at standard positions (C±H 0.96 A, C±C±H 120³)
and re®ned isotropically using a rigid model.
Crystallographic data and experimental parameters for
diazo-bipyridines and their copper complexes are summarized
in Table 3. CCDC reference number 1145/265. See http://
www.rsc.org/suppdata/jm/b0/b007375j/ for crystallographic
®les in .cif format.
Conclusions
The observed UV±Vis and EPR spectra after irradiation of
copper(II) complexes in frozen solutions were obviously
different from those for metal-free diazo compounds, indicat-
ing that the complexes of Cu(hfac)2 coordinated with diazo-
bipyridines were formed in quantitative yields under these
frozen solution conditions. In particular, the lack of EPR
signals due to free carbenes strongly supported complexation.
It became possible to determine the ground-state spin multi-
plicity of carbene±metal complexes by SQUID measurements
before and after irradiation of the diazo±metal precursors
under frozen solution conditions. Thus the ®eld dependence of
magnetization in solid MTHF solution obviously indicates that
the generated carbene interacts ferromagnetically with the
copper(II) through the 2,2'-bipyridine ring to produce a high-
spin species: quartet, quintet, and septet for [Cu(hfac)2?2],
[(Cu(hfac)2)2?3], and [(Cu(hfac)2)2?4], respectively, in the
ground state. The sign for exchange coupling between copper
and carbene is consistent with the one for [Cu(hfac)2?1];
ferromagnetic coupling with J/kB~z67 K. Although the
simulation of the EPR spectra for the copper complexes was
unsuccessful at this point, the observed EPR and UV±Vis
spectra were concluded to be due to the corresponding high-
spin species in the ground state. The preparation and
investigation of the magnetic properties of 1 : 1 and 2 : 3
complexes of Cu(NO3)2 coordinated with 3 and 4 which are
expected to produce super higher-spin species, are in progress.
Magnetic measurements
(A) EPR spectra. EPR spectra were recorded on a Bruker
ESP300 X-band (9.4 GHz) spectrometer equipped with a
Hewlett Packard 5350B microwave frequency counter. An
Air Products LTD-3-110 liquid helium transfer system was
attached for the low-temperature measurements. Sample
solutions were placed in 5 mm o.d. quartz tubes, degassed by
three freeze-and-thaw cycles, and sealed.
(B) SQUID measurements. Magnetic susceptibility data
were obtained on a Quantum Design MPMS-5S (0-50 kOe)
SQUID magnetometer/susceptometer. Irradiation with light
from an argon ion laser (514 nm, 200 mW, Omnichrome 543-
200M) and a He±Cd laser (442 nm, 100 mW, Omnichrome
100B-110V) through a ¯exible optical ®ber (Newport F-MBD;
3 m length, 1.0 mm core size, 1.4 mm diameter) which passes
through the inside of the SQUID sample holder was performed
inside the SQUID sample room of SQUID at 7 K. One end of
the optical ®ber was located 40 mm above the sample cell
(capsule) and the other was attached to a coupler (Body;
Newport M-F-916T and lens; M-10X) for the lasers. The
bottom part of the capsule (6 mm610 mm) without a cap was
used as a sample cell. 100 ml of the sample solution (1.1, 3.5 and
0.5 mM for the Cu complexes with 2, 3, and 4, respectively) in
MTHF was placed in the cell which was held by a straw.
J. Mater. Chem., 2001, 11, 493±502
499

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Table 3 Crystal data and structure re®nements for 2, 3, 4, and [Cu(hfac)2?2]
2
3
4
[Cu(hfac)2?2]
Empirical formula
Formula weight
C17H12N4
272.31
C21H14N6
350.38
C30H22N8
494.56
C27H14N4O4F12Cu?C3H6O
808.04
Crystal colour, habit
Crystal dimensions/mm
Crystal system
Red, needles
0.760.560.2
Monoclinic
Orange, plates
0.160.160.02
Orthorhombic
Red, plates
0.160.160.1
Orthorhombic
Green, needles
0.360.160.1
Monoclinic
Lattice parameters:
Ê
a/A
Ê
11.518(2)
6.492(1)
18.766(2)
97.041(5)
1392.7(3)
P21/n (no. 14)
4
1.299
2517
190
0.047; 0.065
6.5760(3)
12.5789(7)
20.624(1)
12.5836(2)
7.4541(1)
26.0718(5)
15.659(1)
8.8664(8)
24.206(2)
99.801(4)
3311.7(5)
P21/c (no. 14)
4
1.621
3987
525
0.063; 0.059
b/A
Ê
c/A
b/³
V/A
Ê 3
1706.0(4)
Pbcn (no. 60)
4
1.364
1204
2445.52(7)
Pca21 (no. 29)
4
1.343
2480
Space group
Z
Dcalc/g cm23
No. observations
No. variables
Residuals: R, Rw
125
0.074; 0.053
344
0.046; 0.049
Preparation of the 2,2'-bipyridine ligands and the metal
complexes
278 ³C and then left overnight after removal of the cooling
bath. After the usual work-up, the crude mixture was
chromatographed (silica gel; eluent, CHCl3) to give carbinol
3'oh as a brown solid in 27% yield (0.9 g, 2.6 mmol). Mp 49±
Unless otherwise stated, preparative reactions were carried out
under a high-purity dry nitrogen atmosphere. Diethyl ether was
distilled from sodium benzophenone ketyl. Bis(hexa¯uoro-
acetylacetonato)copper(II), 4-bromo-2,2'-bipyridine,9 and 4-
formyl-4'-methyl-2,2'-bipyridine20 were prepared and puri®ed
by the literature procedures.
51 ³C; IR (KBr) 3336 cm21 1H NMR (CDCl3, 270 MHz) d
;
8.49 (dd, J~5.9 and 1.1 Hz, 2H), 8.25 (d, J~7.4 Hz, 1H), 8.16
(d, J~5.1 Hz, 2H), 7.89±7.70 (m, 2H), 7.27±7.22 (m, 1H), 7.19±
7.13 (m, 2H), 5.69 (s, 1H); mass spectrum (FAB, m-nitrobenzyl
alcohol matrix) m/z 342 (Mzz1).
4-(a-Hydroxybenzyl)-2,2'-bipyridine 2oh. To a solution of
2.06 g (8.76 mmol) of 4-bromo-2,2'-bipyridine in 120 ml of
anhydrous ether were added 14.0 ml (22.4 mmol) of a 1.6 M
solution of n-butyllithium in n-hexane at 278 ³C. After stirring
for 1 h, 4 ml (39.3 mmol) of benzaldehyde were added
dropwise. The reaction mixture was stirred for 1 h at
278 ³C. After the usual work-up, crude carbinol 2oh was
chromatographed on silica gel with n-hexane±ethyl acetate
(1 : 2) to give 2oh (350 mg, 1.33 mmol) as a white solid in 15.1%
yield. Mp 115±116 ³C; IR (KBr) 3229 cm21; 1H NMR (CDCl3,
270 MHz) d 8.55±8.53 (m, 2H), 8.45 (s, 1H), 8.31 (d, J~8.0 Hz,
1H), 7.77 (td, J~7.8 and 1.7 Hz, 1H), 7.39±7.36 (m, 2H), 7.33±
7.22 (m, 5H), 5.85 (s, 1H), 4.04 (s, 1H); mass spectrum (FAB,
m-nitrobenzyl alcohol matrix) m/z 263 (Mzz1); Anal. Calcd.
for C17H14N2O: C, 77.84; H, 5.38; N, 10.64. Found: C, 77.77;
H, 5.38; N, 10.59%.
4-(2,2'-Bipyridyl) 4-(2-bromopyridyl) ketone 3'k. To a solu-
tion of 0.88 g of this crude carbinol 3'oh in 30 ml of anhydrous
CHCl3 were added 2.0 g of freshly prepared MnO2. The
suspension was stirred and re¯uxed for 2 h and ®ltered. After
®ltration, the solvent was evaporated and the crude mixture
was chromatographed (Silica gel; eluent, CHCl3) to give ketone
3'k as a white solid in 71% yield (0.62 g, 1.8 mmol). Mp 142±
1
143 ³C; IR (KBr) 1645 cm21; H NMR (CDCl3, 270 MHz) d
8.92 (dd, J~4.9 and 1.1 Hz, 1H), 8.69±8.67 (m, 2H), 8.62 (d,
J~5.0 Hz, 1H), 8.49 (m, 1H), 7.90±7.87 (m, 1H), 7.84 (s, 1H),
7.64±7.60 (m, 1H), 7.59 (d, J~1.5 Hz, 1H), 7.39±7.34 (m, 1H);
mass spectrum (FAB, m-nitrobenzyl alcohol matrix) m/z 340
(Mzz1); Anal. Calcd. for C16H11N2O2: C, 56.49; H, 2.96; N,
12.35. Found: C, 56.40; H, 2.97; N, 12.17%.
Di(4-(2,2'-bipyridyl)oxomethane 3k. A solution of 0.62 g
(1.8 mmol) of ketone 3'k, 0.58 g (2.4 mmol) of 2-trimethyl-
stannylpyridine,22 and 0.03 g of Pd(PPh3)4 in 20 ml of
anhydrous toluene was re¯uxed for 6 h. After the usual
work-up, the crude mixture was chromatographed (Al2O3:
activity I; eluents, CH2Cl2 : n-hexane~2 : 1) to give ketone 3k
as white solids in 48% yield (0.30 g, 0.86 mmol). Mp 140±
4-Benzoyl-2,2'-bipyridine 2k. To a solution of 0.30 g of the
crude carbinol 2oh in 20 ml of anhydrous CHCl3 were added
1.5 g of freshly prepared MnO2. The suspension was stirred and
re¯uxed for 1 h and ®ltered. After ®ltration, the solvent was
evaporated and the crude mixture was chromatographed (silica
gel; eluent, n-hexane : AcOEt~1 : 1) to give ketone 2k as a
white solid in 83% yield (0.25 g, 0.96 mmol). Mp 95±96 ³C; IR
1
142 ³C; IR (KBr) 1671 cm21, H NMR (CDCl3, 270 MHz) d
(KBr) 1666 cm21 1H NMR (CDCl3, 270 MHz) d 8.85 (dd,
;
8.92 (dd, J~4.9 and 0.9 Hz, 2H), 8.73 (dd, J~1.6 and 0.9 Hz,
2H), 8.65 (ddd, J~4.8, 1.8, and 1.0 Hz, 2H), 8.47 (d,
J~7.5 Hz, 2H), 7.84 (td, J~7.5 and 1.8 Hz, 2H), 7.67 (dd,
J~4.9 and 1.6 Hz, 2H), 7.35 (ddd, J~7.5, 4.8, and 1.0 Hz, 2H);
mass spectrum (FAB, m-nitrobenzyl alcohol matrix) m/z 339
(Mzz1); Anal. Calcd. for C21H14N4O: C, 74.54; H, 4.17; N,
16.56. Found: C, 74.59; H, 4.20; N, 16.59%.
J~4.9 and 0.9 Hz, 1H), 8.67±8.64 (m, 2H), 8.44 (ddd, J~8.0,
0.9, and 0.9 Hz, 1H), 7.89±7.80 (m, 3H), 7.64 (tt, J~7.3 and
1.8 Hz, 1H), 7.60 (dd, J~4.9 and 1.6 Hz, 1H), 7.54±7.48 (m,
2H), 7.32 (ddd, J~7.5, 4.8, and 0.9 Hz, 1H); mass spectrum
(FAB, m-nitrobenzyl alcohol matrix) m/z 261 (Mzz1); Anal.
Calcd. for C17H12N2O: C, 78.44; H, 4.65; N, 10.76. Found: C,
78.49; H, 4.68; N, 10.72%.
1,3-Phenylenebis(4-(4'-methyl-2,2'-bipyridyl)oxomethane)
4k. To a solution of 1.78 g (7.5 mmol) of 1,3-dibromobenzene
in 40 ml of anhydrous ether were added 24.6 ml (37.1 mmol) of
4-(2,2'-Bipyridyl) 4-(2-bromopyridyl) carbinol 3'oh. To a
solution of 2.3 g (9.8 mmol) of 4-bromo-2,2'-bipyridine in
150 ml of anhydrous ether were added 13.5 ml (21.5 mmol) of a
1.53 M solution of n-butyllithium in n-hexane at 278 ³C. After
stirring for 40 min, a solution of 2.2 g (11.8 mmol) of 2-bromo-
4-formylpyridine21 in 70 ml of anhydrous ether was added
dropwise. The reaction mixture was stirred for 30 min at
a
1.51 M solution of tert-butyllithium in n-pentane at
278 ³C. After stirring for 30 min, 3.0 g (15 mmol) of 4-
formyl-4'-methyl-2,2'-bipyridine20 in 30 ml of anhydrous
THF were added dropwise. The reaction mixture was stirred
for 1 h at 278 ³C and then the temperature was raised by the
500
J. Mater. Chem., 2001, 11, 493±502

View Article Online
removal of the cooling bath. After the usual work-up, 4.61 g of
crude carbinol 4oh was obtained as a brown oil. The obtained
mixture was used for the oxidation without separation and
puri®cation of the carbinol.
ratio of 1 : 1 and the mixtures were left in a refrigerator. Single
crystals of complexes [Cu(hfac)2?2] were obtained as green
needles in 17.4% yield. Mp 106±107 ³C (decomp.); Anal. Calcd.
for C27H14N4O4F12Cu?0.3C3H6O: C 43.67; H, 2.08; N, 7.30.
Found: C, 43.77; H, 2.08; N, 7.33%.
To a solution of 4.61 g of this crude carbinol 4oh in 100 ml of
anhydrous CHCl3 were added 14.9 g of freshly prepared
MnO2. The suspension was stirred and re¯uxed for 3 h and
®ltered. After ®ltration, the solvent was evaporated and the
crude mixture was chromatographed (Al2O3, activity IV;
eluent, CHCl3 : n-hexane~1 : 1) to give ketone 4k as a white
solid in 28.5% yield (1.01 g, 2.14 mmol). Mp 170±171 ³C; IR
[(Cu(hfac)2)2?3]. The complex was prepared in a manner
similar to the procedure for [Cu(hfac)2?2] using 3 in a molar
ratio of 2 : 1. [(Cu(hfac)2)2?3] was obtained as a greenish
powder. Mp 122±124 ³C (decomp.); Anal. Calcd. for
C41H18N6O8F24Cu2: C 37.76; H, 1.39; N, 6.44. Found: C,
38.04; H, 1.41; N, 6.31%.
(KBr) 1670 cm21 1H NMR (CDCl3, 270 MHz) d 8.74 (dd,
;
J~4.9 and 0.7 Hz, 2H), 8.69 (m, 2H), 8.53 (d, J~4.9 Hz, 2H),
8.27 (m, 3H), 8.18 (dd, J~7.7 and 1.7 Hz, 2H), 7.73 (t,
J~7.7 Hz, 1H), 7.64 (dd, J~4.9 and 1.7 Hz, 2H), 7.17 (d,
J~4.9 Hz, 2H), 2.46 (s, 6H); mass spectrum (FAB, m-
nitrobenzyl alcohol matrix) m/z 471 (Mzz1); Anal. Calcd.
for C30H22N4O2: C, 76.58; H, 4.71; N, 11.91. Found: C, 76.57;
H, 4.72; N, 11.97%.
[(Cu(hfac)2)2?4]. The complex was prepared in a manner
similar to the procedure for [Cu(hfac)2?2] using 4 in a molar
ratio of 2 : 1. [(Cu(hfac)2)2?4] was obtained as a greenish
powder. Mp 120±122 ³C (decomp.), Anal. Calcd. for
C50H26N8O8F24Cu2: C 41.23; H, 1.81; N, 7.73. Found: C,
41.35; H, 1.86; N, 7.61%.
General procedure for the preparation of diazo compounds
Acknowledgements
A solution of 0.40 g (1.52 mmol) of ketone 2k and 1 ml of
anhydrous hydrazine in 2 ml of dimethyl sulfoxide in the
presence of hydrazine monohydrochloride (1 g) was heated at
60±80 ³C. The cooled reaction mixture was treated with ice-
water and the white precipitate was collected and dried under
vacuum to give 0.35 g (1.27 mmol) of the corresponding
hydrazone in 83% yield. To a solution of 0.35 g (1.27 mmol)
of the hydrazone in 10 ml of CH2Cl2 was added 1 g of freshly
prepared active MnO2. The mixture was stirred vigorously for
1 h with careful exclusion of light and ®ltered. The ®ltrate was
concentrated under vacuum to give reddish solids which were
recrystallized from suitable solvents.
This work was supported by a Grant-in-Aid for COE
Research ``Design and Control of Advanced Molecular
Assembly Systems'' (#08CE2005) from the Ministry of
Education, Science, Sports and Culture, Japan.
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N. Koga and H. Iwamura, Magnetic Properties of Organic
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S. Karasawa, Y. Sano, T. Akita, N. Koga, T. Itoh, H. Iwamura,
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2
in MTHF, lmax (log e): 283 (4.46) and 500 (2.06) nm; 1H NMR
(270 MHz, CDCl3) d 8.65 (d, J~4.8 Hz, 1H), 8.54 (d,
J~5.5 Hz, 1H), 8.38 (d, J~7.9 Hz, 1H), 8.24 (d, J~2.0 Hz,
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K. Inoue, T. Hayamizu, H. Iwamura, D. Hashizume and
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Mp 165±166 ³C (decomp.); IR (KBr disc) nCLN 2049 cm21
;
2
UV±Vis in MTHF, lmax (log e): 285 (4.56) and 477 (2.11) nm;
1H NMR (270 MHz, CDCl3) d 8.76±8.60 (m, 4H), 8.49±8.39
(m, 4H), 7.89 (dt, J~7.6 and 1.6 Hz, 2H), 7.39±7.32 (m, 4H);
FAB mass (in NBA matrix), (Mzz1) 351; Anal. Calcd. for
C21H14N6: C, 71.99; H, 4.03; N, 23.99. Found: C, 71.86; H,
4.02; N, 23.85%.
7
8
9
1,3-Benzenediyl{4-(4'-methyl-2,2'-bipyridyl)diazomethane}
4. Recrystallization from CH2Cl2±n-hexane (10 : 1) gave diazo
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Reinhold Co., New York, 1983.
4 as red plates. Mp 105 ³C (decomp.); IR (KBr disc) nCLN
2
2049 cm21; UV±Vis in MTHF, lmax (log e): 285 (4.91) and 493
(2.38) nm; H NMR (270 MHz, CDCl3) d 8.52 (d, J~5.1 Hz,
1
2H), 8.45 (dd, J~5.3 and 0.7 Hz, 2H), 8.29 (dd, J~2.0 and
0.7 Hz, 2H), 8.23±8.22 (m, 2H), 7.54 (t, J~7.8 Hz, 1H), 7.47 (t,
1.8 Hz, 1H), 7.32 (dd, J~7.8 and 1.8 Hz, 2H), 7.16 (dd, J~5.5
and 2.0 Hz, 2H), 7.16±7.13 (m, 2H), 2.44 (s, 6H); FAB mass (in
NBA matrix), (Mzz1) 495; Anal. Calcd. For C30H22N8: C,
72.86; H, 4.48; N, 22.66. Found: C, 72.72; H, 4.45; N, 22.35%.
17 Whereas the F and S values are correlated, the former are more
sensitive to the height of the ®tted curve and the latter values are
sensitive to the curvature. The F values obtained by the ®tting tend
[Cu(hfac)2?2]. A solution of 2 in acetone±H2O (5 : 1) was
mixed with solutions of Cu(hfac)2 in acetone±H2O in a molar
J. Mater. Chem., 2001, 11, 493±502
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to be smaller by 10±20% than the degree of photolysis estimated
from the UV±Vis absorptions before and after SQUID measure-
ments. The discrepancy between the UV±Vis results and F values
might be due to the stability of the generated carbene especially
under frozen solution conditions. This is an important problem in
this work and is being investigated in detail.
A. Guagliardi, G. Polidori and R. Spagna, J. Appl. Cryst., 1999,
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20 L. D. Ciana, I. Hamachi and T. J. Meyer, J. Org. Chem., 1989, 54,
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18 SIR92: A. Altomare, M. C. Burla, M. Camalli, M. Cascarano,
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1994, 27, 435 for 2, 3, and [Cu(hfac)2?2]; SIR97: A. Altomare,
M. C. Burla, M. Camalli, M. Cascarano, C. Giacovazzo,
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502
J. Mater. Chem., 2001, 11, 493±502