Control of exchange interactions in π dimers of 6-oxophenalenoxyl neutral π radicals: Spin-density distributions and multicentered-two-electron bonding governed by topological symmetry and substitution at the 8-position

Article abstract of DOI:10.1002/chem.201301783

The tri-tert-butylphenalenyl (TBPLY) radical exists as a π dimer in the crystal form with perfect overlapping of the singly occupied molecular orbitals (SOMOs) causing strong antiferromagnetic exchange interactions. 2,5-Di-tert-butyl-6-oxophenalenoxyl (6OPO) is a phenalenyl-based air-stable neutral π radical with extensive spin delocalization and is a counter analogue of phenalenyl in terms of the topological symmetry of the spin density distribution. X-ray crystal structure analyses showed that 8-tert-butyl- and 8-(p-XC₆H₄)-6OPOs (X=I, Br) also form π dimers in the crystalline state. The π-dimeric structure of 8-tert-butyl-6OPO is seemingly similar to that of TBPLY even though its SOMO-SOMO overlap is small compared with that of TBPLY. The 8-(p-XC₆H₄) derivatives form slipped stacking π dimers in which the SOMO-SOMO overlaps are greater than in 8-tert-butyl-6OPO, but still smaller than in TBPLY. The solid-state electronic spectra of the 6OPO derivatives show much weaker intradimer charge-transfer bands, and SQUID measurements for 8-(p-BrC₆H₄)-6OPO show a weak antiferromagnetic exchange interaction in the π dimer. These results demonstrate that the control of the spin distribution patterns of the phenalenyl skeleton switches the mode of exchange interaction within the phenalenyl-based π dimer. The formation of the relevant multicenter-two-electron bonds is discussed. Copyright

Full text of DOI:10.1002/chem.201301783

FULL PAPER
Radicals
S. Nishida, J. Kawai, M. Moriguchi,
T. Ohba, N. Haneda, K. Fukui,
A. Fuyuhiro, D. Shiomi, K. Sato,
T. Takui,* K. Nakasuji,
Y. Morita* ..................... &&&& — &&&&
Radical p dimers: The crystal struc-
tures of 2,5-di-tert-butyl-6-oxophenal-
enoxyl (6OPO) stable neutral p radi-
cals have been determined. In the crys-
tal form, 8-tert-butyl- and 8-(p-XC6H4)-
6OPO derivatives (X=I, Br) form p
dimers (see figure) with weak intra-
dimer antiferromagnetic exchange
interactions due to a small overlap of
the singly occupied molecular orbitals.
These overlapping modes are caused
by both the topological symmetry of
the spin density distribution of the
6OPO p radicals and the steric hin-
drance exerted by substituents in the
molecular frameworks.
Control of Exchange Interactions in p
Dimers of 6-Oxophenalenoxyl Neutral
p Radicals: Spin-Density Distributions
and Multicentered–Two-Electron
Bonding Governed by Topological
Symmetry and Substitution
at the 8-Position
Radical p dimers
2,5-Di-tert-butyl-6-oxophenalenoxyl (6OPO) is a phena-
lenyl-based air-stable neutral p radical with extensive spin-
delocalization, and 6OPO is a counter analogue of phena-
lenyl in terms of the topological symmetry of spin density
distribution. SQUID measurements for 8-(p-BrC6H4)-
6OPO showed that a weak antiferromagnetic exchange
interaction occurs within the p-dimer. These results
demonstrate that control in the spin distribution patterns
of the phenalenyl skeleton switches the mode of exchange
interaction within the phenalenyl-based p dimer. For more
details see the Full Paper by T. Takui, Y. Morita et al. on
page && ff.
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DOI: 10.1002/chem.201301783
Control of Exchange Interactions in p Dimers of 6-Oxophenalenoxyl Neutral
p Radicals: Spin-Density Distributions and Multicentered–Two-Electron
Bonding Governed by Topological Symmetry and Substitution
at the 8-Position
Shinsuke Nishida,[a, b] Junya Kawai,[a] Miki Moriguchi,[a] Tomohiro Ohba,[a]
Naoki Haneda,[a] Kozo Fukui,[a] Akira Fuyuhiro,[a] Daisuke Shiomi,[c] Kazunobu Sato,[c]
Takeji Takui,*[c] Kazuhiro Nakasuji,[a] and Yasushi Morita*[a, b]
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Exchange Interactions in Oxophenalenoxyl Dimer p Radicals
FULL PAPER
Abstract: The tri-tert-butylphenalenyl
(TBPLY) radical exists as a p dimer in
the crystal form with perfect overlap-
ping of the singly occupied molecular
orbitals (SOMOs) causing strong anti-
ferromagnetic exchange interactions.
2,5-Di-tert-butyl-6-oxophenalenoxyl
form p dimers in the crystalline state.
but still smaller than in TBPLY. The
solid-state electronic spectra of the
6OPO derivatives show much weaker
intradimer charge-transfer bands, and
SQUID measurements for 8-(p-
BrC6H4)-6OPO show a weak antiferro-
magnetic exchange interaction in the p
dimer. These results demonstrate that
the control of the spin distribution pat-
terns of the phenalenyl skeleton
switches the mode of exchange interac-
The p-dimeric structure of 8-tert-butyl-
6OPO is seemingly similar to that of
TBPLY even though its SOMO–
SOMO overlap is small compared with
that of TBPLY. The 8-(p-XC6H4) deriv-
atives form slipped stacking p dimers
in which the SOMO–SOMO overlaps
are greater than in 8-tert-butyl-6OPO,
(6OPO) is
a phenalenyl-based air-
stable neutral p radical with extensive
spin delocalization and is a counter an-
alogue of phenalenyl in terms of the
topological symmetry of the spin densi-
ty distribution. X-ray crystal structure
analyses showed that 8-tert-butyl- and
8-(p-XC6H4)-6OPOs (X=I, Br) also
Keywords: absorption
·
density
tion within the phenalenyl-based
p
functional calculations · magnetic
properties · radicals · X-ray diffrac-
tion
dimer. The formation of the relevant
multicenter–two-electron bonds is dis-
cussed.
Introduction
coupling cannot be fully understood, nor controlled. In this
context, exchange interactions based on multicentered
bonds in p dimers are of importance.[4]
The control of intermolecular exchange interactions be-
tween stable organic open-shell molecules[1] is a crucial issue
in the design and development of molecule-based magnetic
materials.[2] Molecular design approaches to the establish-
ment of stronger ferromagnetic exchange interactions within
molecular open-shell entities, such as molecular high spins,
have been well tested from both theoretical and experimen-
tal sides.[2c] Recent trends in open-shell chemistry are to-
wards the weakening of exchange coupling leading to elec-
tromagnetic control of molecular spins for spin qubits
(quantum bits) in quantum computing/quantum information
technology (QC/QIP).[3] On the one hand, magnetic proper-
ties such as intramolecular exchange couplings and magnetic
tensors of organic open-shell systems strongly depend on in-
dividual molecular/electronic structures, and their molecular
design has been well underlain by quantum chemistry. On
the other hand, the control of intermolecular exchange cou-
plings between organic open-shell entities in solids is still a
challenging issue in chemistry and materials science. In par-
ticular, the coupling modes as well as the magnitude of the
Phenalenyl is a neutral hydrocarbon p radical with exten-
sive spin delocalization on the six a-carbon atoms.[5,6] This p
radical easily forms a s-dimer and reacts with oxygen, but
high air-stability can be acquired by introducing steric pro-
tection around the molecular framework through bulky sub-
stituents (tri-tert-butylphenalenyl, TBPLY[7]). In the crystal-
line state, TBPLY forms a p dimer that adopts a staggered
arrangement of the tert-butyl groups so as to avoid steric re-
pulsion.[8,9] We first discovered the existence of a 12-center–
[6,10,11]
ꢀ
2-electron long C C bond
of singly occupied molecular orbitals (SOMOs, Figure 1a),
which gives rise to a strong antiferromagnetic intermolecular
through the perfect overlap
exchange interaction within the
p
dimer (2J/kB =
ꢀ2000 K).[7] This multicenter bond[4] features the dynamic
physical phenomena of phenalenyl-based neutral p radicals;
TBPLY shows thermochromism in solution induced by the
thermal equilibrium between the p dimer and p radical
monomer,[6,10] and zwitterionic bis-phenalenyl–boron com-
plexes exhibit magneto-optical-electronic bistability in the
crystalline state through a change in the electronic interac-
tions within the p-dimeric structures with temperature.[12]
Furthermore, the crystal of tri-tert-butyl-1,3-diazaphenalen-
yl[13] shows a continuous change in color with temperature
due to the equilibrium between a p dimer similar to TBPLY
and a s-dimer.[14]
[a] Dr. S. Nishida, Dr. J. Kawai, M. Moriguchi, T. Ohba, N. Haneda,
Dr. K. Fukui, Prof. A. Fuyuhiro, Prof. K. Nakasuji, Prof. Y. Morita
Department of Chemistry, Graduate School of Science
Osaka University, Toyonaka, Osaka 560-0043 (Japan)
Fax : (+81)6-6850-5395
E-mail: morita@chem.sci.osaka-u.ac.jp
Among the phenalenyl-based p radicals that we have de-
signed and synthesized in the past two decades,[6] 2,5-di-tert-
butyl-6-oxophenalenoxyl (6OPO)[6,15,16] is an air-stable neu-
tral p radical possessing two oxygen atoms on the phenalen-
yl skeleton as both a heteroatomic chemical modification
and an extension of the p conjugation (Figure 1b, R=H).
Notably, 6OPO exhibits extensive spin delocalization similar
to phenalenyl, although this p radical is different to phena-
lenyl (Figure 1b) in terms of the topological symmetry of
spin density distribution.[6,15,17] Furthermore, two-electron re-
[b] Dr. S. Nishida, Prof. Y. Morita
Core Research for Evolutional Science and Technology (CREST)
Japan Science and Technology Agency (JST)
5 Sanban-cho, Chiyoda-ku, Tokyo 102-0075 (Japan)
[c] Prof. D. Shiomi, Prof. K. Sato, Prof. T. Takui
Department of Chemistry, Graduate School of Science
Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)
Fax : (+81)6-6605-2522
E-mail: takui@sci.osaka-cu.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301783.
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the electronic structure of the substituent at the 8-posi-
tion.[25] We emphasize that p-layered packing modes can be
used to develop molecular functional materials in a control-
lable manner.
Results and Discussion
Synthesis and electronic-spin structure of the neutral p radi-
cal 7: The neutral p radical 7 was synthesized from a 1-for-
mylnaphthalene derivative 8[15] in six steps (Scheme 1). The
aldol condensation reaction of 8 with the zinc enolate gener-
ated from ethyl (4-bromophenyl)acetate with lithium diiso-
propylamide (LDA) followed by the addition of ZnCl2
Figure 1. a) Phenalenyl derivatives (left), the spin density distribution of
ꢀ
TBPLY (center), illustration of a 12-center–2-electron long C C bond
with perfect SOMO–SOMO overlap in the p dimer of TBPLY (right).
b) 8-Substituted 6OPOs (left and center) and the spin density distribution
of 1 (right). Red and blue regions denote positive and negative spin den-
sities, respectively. The spin density distributions were calculated by DFT
at the UB3LYP/6-31GACHTUNGTRENNUNG(d,p)//UB3LYP/6-31GHCATUNGTRENN(UGN d,p) level of theory.
duction of this p radical gives the corresponding radical di-
anion species with high stability in a degassed solution, the
ACHTUNGTRENNUNG
spin structure of which is remarkably different to that of the
neutral species.[6,18] These unique spin properties suggest
that 6OPO is an inherently different organic neutral p radi-
cal to phenalenyl and simple aroxyl radicals, thereby provid-
ing new insights into open-shell chemistry. Substitution at
the 8-position with a tert-butyl group (1; Figure 1b)[6,15] or a
p-IC6H4 group (2; Figure 1b)[19] further increases the stabili-
ty of the neutral p radicals. We have recently synthesized
and isolated 8-CN-6OPO (3) with a stability comparable to
1 and 2 despite low steric protection of the 8-position.[20] In
the quest for novel multifunctional molecular spin sys-
tems,[21] electron-donor-substituted 6OPOs 4,[22] 5,[19b] and
6[19b] have been designed and synthesized. Interestingly, the
p radical 4 shows “spin-center transfer” accompanying sol-
vato/thermochromism caused by intramolecular electron
transfer controlled by solvent and temperature.[22] Moreover,
use of the two-stage redox ability of 1 to charge/discharge
afforded high-capacity rechargeable batteries, “molecular
spin batteries”.[23] These studies demonstrated that 6OPO is
a promising building block for next-generation molecular
functional materials.
In this study we have discovered that 1, 2, and 8-(p-
BrC6H4) derivative 7 form p dimers in their crystal forms by
X-ray crystal structure analyses. On the basis of these struc-
tures, electronic absorption spectra, and superconducting
quantum interference device (SQUID) measurements, and
with the help of density functional theory (DFT),[24] we illus-
trate that the magnitude of the antiferromagnetic exchange
coupling is governed by the topological symmetry of the
spin density distribution over the phenalenyl skeleton and
Scheme 1. Synthesis of the neutral p radical 7. Reagents and conditions:
a) LDA, ZnCl2, 4-BrC6H4CH2CO2Et, THF, ꢀ788C, 80%; b) Et3SiH,
CF3CO2H, CH2Cl2, RT, 96%; c) KOH, EtOH/H2O, 1008C, 75%;
d) i. (COCl)2, 658C; ii. AlCl3, CH2Cl2, ꢀ788C, 78%; e) i. LiAlH4, THF,
RT; ii. LiI, hexamethylphosphoric triamide (HMPA), 1708C, 52%;
f) PbO2, benzene, RT, quant.
quantitatively gave hydroxy ester 9. Reductive elimination
of the hydroxy group of 9 and subsequent hydrolysis of the
ethyl ester 10 afforded carboxylic acid derivative 11. The
acid derivative 11 was converted into phenalanone deriva-
tive 12 by Friedel–Crafts cyclization. The carbonyl group of
12 was reduced and subsequently subjected to demethyla-
tion and autoxidation to give 6-hydroxyphenalenone 13. Ox-
idation of 13 with PbO2 yielded 7 as a neutral p radical that
is highly stable to air in the solid state for a long period of
time.
The electronic-spin structure of 7 was studied by EPR
and electron-nuclear multiple magnetic resonance
(1H ENDOR/TRIPLE) spectroscopy at 290 K in toluene
(3.6ꢁ10ꢀ5 m). Figure 2a shows the EPR spectrum of 7 with
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Exchange Interactions in Oxophenalenoxyl Dimer p Radicals
FULL PAPER
Figure 3. a) Observed (black numerals) and calculated hfccs (red numer-
1
als) of 7. The hfccs were determined by H ENDOR/TRIPLE spectrosco-
py. The hfcc of 16-H was not determined experimentally. b) Calculated
spin density distribution of 7. The dihedral angle between the p-BrC6H4
and 6OPO moieties is 358. The red and blue regions denote positive and
negative spin densities, respectively. The calculation was carried out at
the UB3LYP/6-31GACTHNUGTRENNUG(d,p)//UB3LYP/6-31GACHUTNGTREN(NGUN d,p) level of theory.
Figure 2. a) Observed cw-EPR spectrum of
7 (microwave frequency,
9.521982 GHz; field modulation, 12.5 kHz, which was used to eliminate
the effects of a side-band production due to 100 kHz field modulation)
and b) the corresponding simulated spectrum. c) 1H ENDOR and
d) TRIPLE (pump frequency, 17.33 MHz) spectra recorded at 290 K for
7 in toluene (3.6ꢁ10ꢀ5 m). The g value was determined experimentally to
be 2.0045. In (d), the vertical upward and downward arrows denote the
increase and decease in ENDOR intensity at the resonance frequency
during the pumping in TRIPLE spectroscopy. The TRIPLE experiment
directly gives information on the relative signs of the four kinds of pro-
tons (hfcc: a=0.71, 0.34, 2.21, 5.76 MHz; see Figure 3a, in which the
hfccs are given in units of mT with g=2.0045).
well-resolved hyperfine structures with a g value of 2.0045.
1H ENDOR/TRIPLE spectroscopy enabled us to determine
precisely the hyperfine coupling constants (hfccs) of the pro-
tons and their relative signs (Figures 2c,d, and 3a). The signs
of the hfccs give crucial information on the identity of radi-
cals and on their electronic structures. A satisfactory EPR
spectral simulation was achieved on the basis of the hfccs
1
obtained from H ENDOR/TRIPLE spectroscopy. The spin
density distribution of 7 was calculated by DFT at the
UB3LYP/6-31GACHTUNGTRENNUNG(d,p)//UB3LYP/6-31GACHUTNGTREN(NGUN d,p) level of theory.
Figure 3b shows extensive spin delocalization of 7 similar to
that of 2.[19a]
X-ray crystal structure analysis of 1, 2, and 7: Single crystals
of 1, 2, and 7 were obtained by recrystallization from de-
gassed solutions in sealed tubes (hexane at ꢀ208C for 1,
hexane/acetonitrile at 48C for 2, and CHCl3/acetone at
ꢀ208C for 7). Figure 4 shows the molecular structures of 1,
2,[26] and 7[27] determined by X-ray diffraction analysis. Com-
pound 1 is statistically disordered in the crystal, showing a
crystallographic three-fold rotation axis. Thus, the oxygen
Figure 4. ORTEP representations of a) 1, b) 2, and c) 7. For clarity, the
hydrogen atoms of the p radicals and of acetonitrile and acetone mole-
cules contained in the crystals of 2 and 7, respectively, as solvents of crys-
tallization have been omitted. Thermal ellipsoids are drawn at the 50%
probability level.
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T. Takui, Y. Morita et al.
atoms of 1 are located at the a sites of the phenalenyl skele-
cause a smaller SOMO–SOMO overlap within the p dimer
compared with that in TBPLY.
1
2
ton and refined with occupancy factors of = and = for
3
3
oxygen and hydrogen atoms, respectively. The tert-butyl
groups possess two conformations depending on the posi-
The p radicals 2 and 7 form similar p dimers, but in a slip-
ped stacking motif that differs from that of 1 (Figure 5b,c).
In these p dimers, there are overlaps at the 8-, 10-, 11-, and
12-carbon atoms and two oxygen atoms (numbering is
shown in Figure 1b), on which sizable spin densities reside.
The interplanar distances are 3.36–3.43 and 3.38–3.51 ꢂ for
the p dimers of 2 and 7, respectively, which are shorter than
those of 1. The observed slipped stacking structures arise
from both the effect of electronic stabilization by the inter-
molecular overlap interaction and steric repulsion due to
the tert-butyl groups at the 2,5-positions.
The arrangement and interdimer interactions of the p
dimers of 1, 2, and 7 are shown in Figure 6. The oxygen
atoms of the p dimers of 1 are in close contact (Figure 6a
and Figure S5 in the Supporting Information).[30] In contrast,
the p dimers of 2 and 7 form one-dimensional columnar
structures. The p dimers of 2 stack in a head-to-tail manner
along the b axis with an interdimer distance of 3.47–3.56 ꢂ
(Figure 6b and Figure S6). These columns make contact
through the iodine atoms. The p dimers of 7 stack along the
a axis with an interdimer distance of 3.64–3.69 ꢂ (Figure 6c
ꢀ
ꢀ
ꢀ
tions of the oxygen atoms (C6 C10 C11 C12 for O1 and
ꢀ
ꢀ
ꢀ
C6 C7 C8 C9 for O2), which were refined with an occu-
1
pancy factor of = (Figure 4a, Figure S1).
2
Such disorder is not found in the crystals of 2 and 7,
which enables us to discuss precisely their molecular struc-
ture (Figure 4b,c, and Figures S3 and S4 in the Supporting
Information). The bond equalization of 1.38–1.40 ꢂ ob-
ꢀ
served for the C C bonds in the six-membered ring systems
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
of 2 (C7 C8 C9 C10 C13 C12) and 7 (C1 C6 C7 C8
ꢀ
C7* C6*) in the 6OPO skeletons gives experimental evi-
dence for local aromaticity[28] in these ring systems; this is
consistent with our previous studies in terms of quantitative
resonance structures based on the molecular-orbital (MO)-
based valence bond (VB) method[20,29] and nucleus-inde-
pendent chemical shift (NICS) calculations.[17] In addition,
the p-BrC6H4 moiety is co-planar with the 6OPO moiety,
which contrasts with the optimized structure calculated by
the DFT method (Figure 3a). However, theoretical calcula-
tions indicate a negligible difference in spin density distribu-
tion between the X-ray and calculated optimized geometries
(see Figure S2).
The p radical 1 forms a p dimer in an arrangement that
at first sight is similar to that of TBPLY (Figure 5a). A
closer study indicates that the interplanar distance in the p
dimer of 1 (3.49–3.55 ꢂ) is longer than that in TBPLY
(3.201(8)–3.323(6) ꢂ).[7] Importantly, both this long intra-
dimer distance and the topological symmetry of the spin
density distribution of the monomer p radical (Figure 1b)
Figure 6. a) Interdimer interactions between the oxygen atoms of 1. Pack-
ing diagrams of b) 2 (acetonitrile molecules as solvent of crystallization
have been omitted for clarity) and c) 7. Thermal ellipsoids are drawn at
the 50% probability level.
Figure 5. Side views (left) and top views (right) of the p dimers of a) 1,
b) 2, and c) 7. The numbers denote interplanar distances in the p dimers.
Thermal ellipsoids are drawn at the 50% probability level.
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Exchange Interactions in Oxophenalenoxyl Dimer p Radicals
FULL PAPER
and Figure S7) within the column, which is much longer
than the intradimer distance. These columns are discrete
from each other. In the crystals of 2 and 7, acetonitrile and
acetone molecules occupy the spaces between the columns
of the p dimers as solvents of crystallization, respectively.
The results of the X-ray analyses demonstrate that the sub-
stituent at the 8-position of 6OPO plays an important role
in controlling intra- and interdimer interactions.
The disorder in the p dimer of 1 has two possible orienta-
tions, one rotated away from the eclipsed conformation by
608 and the other by 1808 around the three-fold rotation
axis (Figure 7b). The 608 conformer has no SOMO–SOMO
overlap (Figure 7b, left), whereas in the 1808 conformer, the
1,6-carbon atoms with small coefficients of the SOMO can
be superimposed (Figure 7b, right). However, the SOMO–
SOMO overlap is assumed to be small because the interpla-
nar distance (Figure 5a) is longer than the sum of the van
der Waals radii of carbon atoms (3.40 ꢂ). These results indi-
To examine the SOMO–SOMO overlap of these
dimers, we calculated the SOMOs of 1 and 7 by DFT calcu-
lations at the UB3LYP/6-31G(d,p) level of theory. The mo-
p
ꢀ
G
cate that the existence of a multicenter–two-electron C C
bonding interaction is negligible in the p dimer of 1.
lecular geometries used in these calculations were those de-
termined by X-ray crystal structure analysis in the case of 7,
and by DFT calculations in the case of 1 owing to the disor-
der in the crystal of the molecule. Figure 7a shows that the
coefficients of the SOMOs mainly exist on the 1-, 2-, 5-, 6-,
8-, 10-, 11-, and 12-carbon atoms and the two oxygen atoms
in the molecules of 1 and 7 (see also Figure 1b).
In sharp contrast to the p dimer of 1, in the case of the p
dimer of 7, the SOMO–SOMO overlap at the 8-, 10-, 11-,
and 12-carbon atoms and the two oxygen atoms with large
coefficients of the SOMO (Figure 7c). This mode of overlap
ꢀ
implies a multicenter–2-electron long C C bond in the p
dimer, although the bonding interaction is weaker than that
in TBPLY. The difference in the intradimer interaction be-
tween the p dimers of TBPLY and 1 is ascribable to the
topological symmetry of the spin density (also SOMO) dis-
tribution of the monomer p radicals,[31] and the difference
between the p dimers of 1 and 7 (and 2) is caused by the
steric hindrance of the substituents at the 8-position.
Electronic absorption spectra of 1, 2, and 7: To understand
the intermolecular electronic interactions, we recorded the
electronic absorption spectra of 1, 2, and 7 in hexane solu-
tions and as KBr pellets of powders. The p radical 1 shows a
weak absorption band with a maximum at 642 nm in solu-
tion, ascribed to intramolecular transitions. In the solid
state, a weak band centered at 642 nm and an additional
broad band between 800 and 900 nm are observed. The
latter low-energy broad band is presumably due to an inter-
molecular charge-transfer (CT) transition because similar
low-energy bands appear in the electronic absorption spec-
tra of p dimers of organic open-shell molecules,[32] including
phenalenyl-based neutral radicals.[6,7,10,13,14] The intensity of
the CT band is lower than that of TBPLY,[6,7,10] which im-
plies weak electronic interactions within the p dimer in the
solid state. Quantum chemical calculations for these absorp-
tion bands are underway.
The p radical 2 shows a weak broad band with a maxi-
mum at 651 nm due to intramolecular transitions in solution
similar to 1 (Figure 8b). The spectrum of 2 in a KBr pellet
exhibits a broad band between 800 and 1000 nm, which is
ascribable to intermolecular CT transitions. The CT band is
also much weaker than that of TBPLY, which indicates a
weak electronic interaction within the p dimer owing to the
small SOMO–SOMO overlap in comparison to that of
TBPLY.
The p radical 7 shows similar spectra to 2 (Figure 8c),
which is consistent with the similarity in the p-dimeric struc-
tures of 2 and 7. In addition, temperature-dependent elec-
tronic absorption spectra of 7 in CH2Cl2 were recorded that
showed fairly small spectral changes with temperature (see
Figure S8 in the Supporting Information). This result is in
Figure 7. a) SOMOs of 1 (left) and 7 (right) calculated at the UB3LYP/6-
31GACHTUNGTRENNUNG(d,p) level of theory. The molecular geometries used for the calcula-
tions were the optimized structure of 1 and the X-ray crystal structure of
7. Illustrations of possible modes of overlap for the p dimers of b) 1 and
c) 7. d) Schematic diagram of the SOMO–SOMO overlap in the p dimers
of 7. Blue filled circles in (b) and (c) denote the positions at which the
SOMOs overlap.
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Figure 9. Temperature dependence of cP (circles) and cPT (squares) of 7·-
AHCTUNGTRENN(GNU (CH3)2CO) vs. T. The best-fit parameters reproducing the observed cP–T
curves are 2J/kB =ꢀ384 K, a=0.02, the ratio of diamagnetic impurity,
and g=2.005. The observed departure from the theoretical curves above
140 K is noticeable and a possible reason is given in the text.
of the p dimer in a lattice defect. The parameter a denotes
the ratio of impurity (S=1= ) from the defects. The symbols
2
N, g, mB, and kB represent Avogadroꢃs constant, the g factor,
the Bohr magneton, and the Boltzmann constant, respec-
tively.
cp ¼ ð1 ꢀ 2aÞð2g2mB2=kBTÞ=½3þexpðꢀ2J=kBTÞꢁþaNg2mB2=4kB
ð1Þ
Above 140 K the observed cp values deviate upward from
the theoretical curve, which was calculated with 2J/kB =
384 K, a=0.02, and g=2.005.[33,34] We noted that such devia-
tions appeared for different samples. We assume that one of
the causes of this behavior is the partial, gradual vaporiza-
tion of the acetone contained in the crystals of 7 during the
SQUID measurements. The vaporization was found to be
accelerated at higher temperatures. The measurements from
room temperature to 350 K showed an irreversible increase
in cp at around 330 K associated with a loss in weight, giving
support to the above-mentioned assumption: The boiling
point of bulk acetone is 329 K. These results demonstrate a
smaller antiferromagnetic interaction within the p dimers of
Figure 8. Electronic absorption spectra of a) 1, b) 2, and c) 7. Broken and
solid lines denote samples in hexane solutions and KBr pellets, respec-
tively. Concentrations of the p radicals in hexane: 8.0ꢁ10ꢀ5 m 1, 8.0ꢁ
10ꢀ5 m 2, and 8.6ꢁ10ꢀ5 m 7. Insets: Enlargements of the spectra in the
region between 500 and 1000 nm.
sharp contrast to that of TBPLY, which shows a new absorp-
tion band at low temperature due to the formation of a p
dimer in solution.[10]
Magnetic properties of 7: To evaluate the intradimer ex-
change interaction of the 6OPO derivatives, the bulk mag-
netic properties of crystals of 7 were examined by SQUID
measurements in the temperature range of 1.8–298 K at
0.1 T (Figure 9). The data were corrected for the diamagnet-
ic contribution of cd =ꢀ230ꢁ10ꢀ6 emumolꢀ1, calculated by
Pascalꢃs method. The magnetic behavior observed can be
approximately interpreted by using a model comprising a
singlet ground state and a triplet state lying above the
ground state by 384 K (=2J/kB). The theoretical curves were
calculated by using Equation (1) in which the first term rep-
resents the ground-state singlet dimer of 7 with the antifer-
romagnetic interaction J and the second term corresponds to
magnetically independent molecules without the formation
7
(2J/kB =ꢀ384 K, corresponding to the singlet–triplet
energy separation) than that in TBPLY (2J/kB =ꢀ2000 K[7]),
being consistent with the small SOMO–SOMO overlap
within the p dimers of 7. Thus, considering the smaller
SOMO–SOMO overlap in 1, the antiferromagnetic interac-
tion within the p dimers of 1 is expected to be smaller than
that within the p dimers of 7.[35]
The 2J/kB values of the p dimers of 1 and 7 were estimat-
ed by using the DFT method[36] (see Figures S9–S13 in the
Supporting Information). At the UB3LYP/6-31G(d) level of
theory, the calculations predicted a singlet diradical charac-
ter in the p dimers of 1 with a 2J/kB value of ꢀ56.2 to
ꢀ171.2 K. The orbital overlap (T) between magnetic orbitals
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Exchange Interactions in Oxophenalenoxyl Dimer p Radicals
FULL PAPER
was estimated to be 0.00504–0.0891 for 1 by natural orbital
analyses. These results give support to the small SOMO–
SOMO overlap within the p dimer of 1. The negative ex-
change interaction is interpreted in terms of antiferromag-
netic spin polarization effects traveling through the a-
carbon atoms with negative spin densities. The calculations
were also carried out for the p dimers of 7, which show sin-
glet diradical character with 2J/kB values of ꢀ424 K and T
values of 0.1674, in good agreement with the experimental
value.
Experimental Section
1H NMR spectra were recorded at 270 MHz on a JEOL JNM-EX270 FT-
NMR with CDCl3 or [D6]DMSO as solvent and Me4Si or residual solvent
as internal standard. IR spectra were recorded on a Perkin-Elmer 1640
FT-IR by using KBr pellets or in Cl2C=CCl2 solution. X-band liquid-
phase EPR and 1H ENDOR/TRIPLE spectra were recorded on Bruker
EPR ESP300 and ENDOR ESP350 spectrometers by using sample solu-
tions degassed by using the freeze–pump–thaw method prior to the meas-
urements. The static magnetic susceptibility was measured with a Quan-
tum Design MPMS2 SQUID magnetometer with an applied field of
0.1 T in the temperature range of 1.8–298 K. Electronic absorption spec-
tra were recorded on a SHIMADZU UV-3100PC in hexane solutions or
KBr pellets for measurements at room temperature, and in CH2Cl2 for
variable-temperature measurement. EI-MS was performed on a SHI-
MADZU QP-5000 at 70 eV. X-ray crystallographic measurements on
single crystals were made by using a Rigaku RAXIS RAPID Imaging
Plate and graphite-monochromated MoKa radiation (l=0.71075 ꢂ).
These structures were solved by direct methods and refined by full-
matrix least-squares techniques (SHELXS-97).[41] Melting points were
measured with a hot-stage apparatus without correction. Elemental anal-
yses were performed at the Graduate School of Science, Osaka Universi-
ty. TLC was performed on E. Merck precoated (0.25 mm) silica gel 60
F254 plates. The plates were sprayed with a solution of 10% phosphomo-
lybdic acid in 95% EtOH and then heated until the spots became clearly
visible. Silica gel 60 (100–200 mesh) was used for column chromatogra-
phy. Solvents were dried (drying agent in parentheses) and distilled
under argon prior to use: THF (Na benzophenone ketyl), hexamethyl-
phosphoric triamide and CH2Cl2 (CaH2), Cl2C=CCl2 (P4O10). Ethyl (4-
bromophenyl)acetate was prepared by esterification of purchased (4-bro-
mophenyl)acetic acid with EtOH in the presence of a catalytic amount of
conc. H2SO4. 2,5,8-Tri-tert-butyl-6-oxophenalenoxyl (1),[15] 8-(p-iodophen-
Conclusion
In this work we have determined the molecular and p-di-
meric structures of the 6OPO derivatives 1, 2, and 7 by
means of X-ray crystal structure analyses and revealed the
occurrence of relevant weak intradimer exchange interac-
tions. The p dimer of 8-tert-butyl-6OPO (1) in the crystalline
state has an arrangement similar to that of TBPLY, although
the exchange interaction is smaller due to both the topologi-
cal symmetry of the spin density distribution (SOMOs) of
the monomer p radical and the fairly long interplanar dis-
tance within the p dimer. The 8-(p-IC6H4) and 8-(p-BrC6H4)
derivatives 2 and 7, respectively, form slipped stacking p
dimers due to lower steric repulsion around the 8-positions
in comparison with 1. The SOMO–SOMO overlap within
the p dimers are larger than that in 1, however, the ex-
change interactions are still much smaller than those of
TBPLY.
yl)-2,5-di-tert-butyl-6-oxophenalenoxyl (2),[19] 3,6-di-tert-butyl-2,7-dime-
thoxynaphthalene-1-carbaldehyde (8),[15] and active PbO2
were pre-
[42]
pared according to literature methods. All reactions requiring anhydrous
conditions were conducted under argon.
These results demonstrate that the topological symmetry
of spin density (also SOMO) distribution and steric hin-
drance of the substituent at the 8-position play a vital role
in controlling the intermolecular exchange interactions of
spin-delocalized neutral p radicals.[2,37] To develop novel
multifunctional materials comprising stable organic p radi-
cals, it is necessary to build up intermolecular networks with
multidimensional intermolecular interactions in a controlled
manner. In this context, we have noted that exchange inter-
Syntheses
Ethyl 2-(4-bromophenyl)-3-(3,6-di-tert-butyl-2,7-dimethoxynaphthalen-1-
yl)-3-hydroxypropanoate (9): Diisopropylamine (9.0 mL, 64.2 mmol) was
dissolved in THF (150 mL) in a 500 mL round-bottomed flask and cooled
to ꢀ788C under argon. nBuLi (1.6m hexane solution, 39.0 mL,
61.0 mmol) was added to the mixture and stirred for 1 h. Ethyl (4-bromo-
phenyl)acetate (45.9 g, 189 mmol) was added and the mixture stirred for
1 h. Then ZnCl2 (8.60 g, 63.1 mmol) was added to the reaction mixture
and stirred for 1 h. After the addition of the 1-formynaphthalene deriva-
tive 8 (5.00 g, 15.2 mmol) in one portion, the mixture was stirred for 2 h.
It was then poured into a 2m HCl aqueous solution (100 mL) and extract-
ed with ethyl acetate. The organic extracts were dried over Na2SO4, fil-
tered, and concentrated under reduced pressure. The residue was subject-
ed to silica gel column chromatography with a 10:1–2:1 mixture of
hexane and ethyl acetate as eluent to give 9 (6.96 g, 80%) as a yellow
solid. M.p. 83–848C; Rf =0.16 (5:1 hexane/ethyl acetate); 1H NMR
(270 MHz, CDCl3): d=1.17 (s, 9H), 1.45 (s, 9H), 1.25 (m, 3H), 3.77 (s,
ꢀ
actions based on multicentered–two-electron C C long
bonds in p dimers are of importance in assembling neutral p
radicals in the solid state. Detailed theoretical studies of
ꢀ
multicentered–two-electron C C bond formation in the p
dimers are underway. We have recently reported bowl-
shaped stable neutral p radicals,[38] helicene-structured p
radicals,[39] and p-extended radicals[40] as building blocks of
multidimensional networks through p–p interactions. The
results of this study will open up new avenues to control in-
termolecular exchange interactions in multidimensional net-
works in terms of the topological symmetry of spin density
distribution, strongly relevant to the SOMOs of the building
blocks, and importantly contribute to the application of mol-
ecule-based magnetic materials,[2] molecular-spin qubits for
QC/QIP,[3] and molecular spin batteries.[23]
3H), 4.01 (s, 3H), 4.23–4.29 (m, 2H), 4.58 (d, 3J
6.04 (d, 3J(H,H)=10.6 Hz, 1H), 6.58 (d, 3J
(H,H)=8.6 Hz, 1H), 7.07 (d,
3J
(H,H)=8.6 Hz, 2H), 7.43 (s, 1H), 7.55 (s, 1H), 7.99 ppm (s, 1H); IR
ACHTUNGTREN(NUGN H,H)=10.6 Hz, 1H),
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
(KBr): n˜ =3489, 2960, 1718 cmꢀ1
; MS (70 eV): m/z (%): 329 (100)
[MꢀBrC6H4CHCO2C2H5]+; elemental analysis calcd (%) for
C31H39O5Br: C 65.14, H 6.88, N 0.00; found: C 64.85, H 6.94, N 0.00.
Ethyl 2-(4-bromophenyl)-3-(3,6-di-tert-butyl-2,7-dimethoxynaphthalen-1-
yl)propanoate (10): The hydroxy ester 9 (630 mg, 1.10 mmol) was placed
in a 30 mL round-bottomed flask and dissolved in CH2Cl2 (15 mL). Tri-
ACHUTNGRENeNUG thylAHCTUNGTRENNsUGN ilane (0.26 mL, 1.65 mmol) and trifluoroacetic acid (0.37 mL,
4.85 mmol) were added to the mixture, which was stirred at room tem-
perature for 1.5 h. After the addition of a satd. aqueous solution of
NaHCO3 (50 mL) to the reaction mixture, the mixture was extracted
with ethyl acetate. The combined organic extracts were dried over
Na2SO4, filtered, and concentrated under reduced pressure. The residue
Chem. Eur. J. 2013, 00, 0 – 0
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T. Takui, Y. Morita et al.
was subjected to silica gel column chromatography with a 5:1 mixture of
hexane and ethyl acetate as eluent to give the dehydroxylated compound
10 (584 mg, 96%) as an orange oil. M.p. 358C; Rf =0.50 (5:1 hexane/
3.79 (s, 3H), 3.87 (s, 3H), 4.59 (s, 1H), 5.47 (d, 3J
ACTHNGUTERN(UNG H,H)=8.4 Hz, 1H),
7.24 (m, 2H), 7.47 (d, 3J
ACTHNUGRTENUNG(H,H)=8.4 Hz, 2H), 7.58 (s, 1H), 7.67 ppm (s,
1H); MS (70 eV) (mixture of diastereomers), m/z (%): 512 (85) [M]+,
510 (100) [M]+.
1
ethyl acetate); H NMR (270 MHz, CDCl3): d=1.33 (s, 9H), 1.45 (s, 9H),
1.14 (m, 3H), 3.48–3.57 (m, 1H), 3.91–4.01 (m, 1H), 3.72 (s, 3H), 3.93 (s,
The phenalanol (mixture of diastereomers, 380 mg, 0.74 mmol) was
3H), 3.75–3.82 (m, 1H), 4.05–4.10 (m, 2H), 7.01 (d, 3J
ACHTUNGTRENNUNG
placed in
a 20 mL round-bottomed flask and dissolved in HMPA
2H), 7.09 (s, 1H), 7.26 (d, 3J
ACHTUNGTRENNUNG
(10 mL). LiI (1.99 g, 14.9 mmol) was added to the mixture and stirred at
1708C for 6 h. It was then cooled to room temperature and poured into a
2m HCl aqueous solution. The mixture was extracted with ethyl acetate
and the organic layer was dried over Na2SO4, filtered, and concentrated
under reduced pressure. The residue was subjected to deactivated silica
gel column chromatography with a 10:1–1:1 mixture of hexane and ethyl
acetate as eluent to give the hydroxyphenalenone 13 (280 mg, 64%) as a
vivid reddish-orange powder. M.p. 200–2028C; Rf =0.39 (5:1 hexane/
ethyl acetate); 1H NMR (270 MHz, CDCl3): d=1.53 (s, 18H), 7.47 (brs,
4H), 7.65 (brs, 2H), 8.63 ppm (brs, 2H); IR (KBr): n˜ =2930 cmꢀ1; IR
(CCl2CCl2): n˜ =3629, 2958 cmꢀ1; MS (70 eV): m/z (%): 464 (27) [M]+,
(s, 1H); MS (70 eV): m/z (%): 554 (6) [M]+, 552 (4) [M]+, 313 (100)
[MꢀBrC6H4CHCO2C2H5]+; elemental analysis calcd (%) for
C31H39O4Br: C 67.02, H 7.08, N 0.00; found: C 66.75, H 7.01, N, 0.00.
2-(4-Bromophenyl)-3-(3,6-di-tert-butyl-2,7-dimethoxynaphthalen-1-yl)-
propanoic acid (11): The ester 10 (1.18 g, 2.12 mmol) was placed in a
100 mL round-bottomed flask and dissolved in EtOH (40 mL). An aque-
ous solution (20 mL) of KOH (1.13 g, 20.1 mmol) was added to the mix-
ture and heated at reflux under argon for 5 h. The reaction mixture was
cooled to room temperature and then a 2m HCl aqueous solution was
added. The mixture was extracted with ethyl acetate and the organic
layer dried over Na2SO4, filtered, and concentrated under reduced pres-
sure. The residue was subjected to silica gel column chromatography with
a 10:1–1:1 mixture of hexane and ethyl acetate as eluent to give 11
462 (29) [M]+, 407 (90%) [MꢀC
N
(CH3)3]+; ele-
ACHTUNGTRENNUNG
(837 mg, 75%) as
hexane/ethyl acetate); H NMR (270 MHz, CDCl3): d=1.32 (s, 9H), 1.45
a pale-yellow solid. M.p. 91–928C; Rf =0.34 (5:1
8-(4-Bromophenyl)-2,5-di-tert-butyl-6-oxophenalenoxyl (7): The hydroxy-
phenalenone 13 (32 mg, 0.068 mmol) was placed in a 50 mL round-bot-
tomed flask and dissolved in benzene (5 mL, degassed by argon bubbling
for 2 h prior to use). PbO2 (33 mg, 0.14 mmol) was added to the mixture
and stirred for 15 min. It was then filtered through Celite and the filtrate
concentrated in vacuo to give the p radical 7. M.p. 273–2758C (decomp.);
1
(s, 9H), 3.71 (s, 3H), 3.93 (s, 3H), 3.52–3.61 (m, 1H), 3.74–3.84 (m, 1H),
4.04–4.08 (m, 1H), 7.01 (d, 3J(H,H)=8.4 Hz, 2H), 7.28 (d, 3J
ACTHNUTRGENNUG AHCUTNGTREN(NUGN H,H)=
8.4 Hz, 2H), 7.10 (s, 1H), 7.50 (s, 1H), 7.59 ppm (s, 1H); IR (KBr): n˜ =
3700–2400, 2957, 1709 cmꢀ1; MS (70 eV): m/z (%): 528 (6) [M]+, 526 (7)
[M]+, 313 (100) [MꢀBrC6H4CHCO2C2H5]+; elemental analysis calcd (%)
for C29H35O4Br: C 66.03, H 6.69, N 0.00; found: C 65.83, H 6.66, N 0.00.
Rf =0.39 (5:1 hexane/ethyl acetate); IR (KBr): n˜ =2958, 1715, 1594 cmꢀ1
;
UV/Vis (KBr): lmax =704, 424, 255 nm; UV/Vis (hexane): lmax =650, 503,
2-(4-Bromophenyl)-5,8-di-tert-butyl-4,9-dimethoxyphenalanone (12): The
acid 11 (837 mg, 1.59 mmol) was placed in a 100 mL round-bottomed
flask and mixed with oxalyl chloride (5 mL, 57 mmol). After stirring at
658C for 4 h under argon, the reaction mixture was cooled to room tem-
perature. Excess oxalyl chloride was then removed by distillation under
reduced pressure and the residue was dissolved in CH2Cl2 (5 mL) and
concentrated under reduced pressure (twice). After dissolving the residu-
al oil in CH2Cl2 (40 mL) and cooling to ꢀ788C, AlCl3 (757 mg,
5.52 mmol) was added and the mixture and stirred for 3.5 h under argon.
It was then poured into a 2m HCl aqueous solution (50 mL). The organic
layer was separated and dried over Na2SO4, filtered, and concentrated
under reduced pressure. The residue was subjected to silica gel column
chromatography with a 5:1 mixture of hexane and ethyl acetate as eluent
to give the phenalanone 12 (631 mg, 78%) as an orange powder. M.p.
75–768C; Rf =0.51 (5:1 hexane/ethyl acetate); 1H NMR (270 MHz,
CDCl3): d=1.46 (s, 9H), 1.49 (s, 9H), 3.81 (s, 3H), 3.83 (s, 3H), 3.56–3.79
415, 392, 269 nm; elemental analysis calcd (%) for (C27H26O2Br)-
AHCTUNTGRENNG(UN (CH3)2CO): C 69.23, H 6.20, N 0.00; found: C 68.96, H 6.04, N 0.00.
A single crystal, including acetone as a solvent of crystallization, suitable
for X-ray crystal structure analysis was obtained as a black block by the
following method: The p radical 7 (10.5 mg), CHCl3 (0.5 mL), and ace-
tone (2.5 mL) were placed at a glass tube previously filled with argon.
The solution was degassed by a repeated freeze–pump–thaw method
(seven times). After sealing the glass tube, the solution was allowed to
stand at ꢀ208C. The resulting crystals were filtered off in air;
Recrystallization of 2,5,8-tri-tert-butyl-6-oxophenalenoxyl (1): The p radi-
cal 1 (19 mg) and hexane (4 mL) were placed in a glass tube previously
filled with argon. The solution was degassed by a repeated freeze–pump–
thaw method (seven times). After sealing the glass tube, the solution was
allowed to stand at ꢀ208C. The resulting crystals were obtained as a
black block by filtration in air.
ACTHNUTRGNEUNG
(m, 2H), 4.05–4.14 (m, 1H), 7.13 (d, 3J(H,H)=8.6 Hz, 2H), 7.43 (d, 3J-
8-(4-Iodophenyl)-2,5-di-tert-butyl-6-oxophenalenoxyl (2): 8-(4-Iodophen-
yl)-2,5-di-tert-butyl-6-hydroxyphenalenone[19] (28 mg, 0.055 mmol) was
ACHTUNGTRENNUNG(H,H)=8.6 Hz, 2H), 7.63 (s, 1H), 7.90 ppm (s, 1H); IR (KBr): n˜ =2957,
1697 cmꢀ1; MS (70 eV) m/z (%): 510 (74) [M]+, 508 (74) [M]+; elemental
analysis calcd (%) for C29H33O3Br: C 68.36, H 6.53, N 0.00; found: C
67.99, H 6.50, N 0.00.
placed in
a 30 mL round-bottomed flask and dissolved in CH2Cl2
(10 mL). An excess amount of PbO2 (57 mg, 0.24 mmol) was added to
the mixture and stirred for 10 min. The mixture was then filtered through
Celite and the filtrate concentrated in vacuo to give the p radical 2
(24 mg, 86%) as a deep-green powder. M.p. 215–2178C (decomp.); Rf =
0.39 (5:1 hexane/ethyl acetate); IR (KBr): n˜ =2958, 1595 cmꢀ1; UV/Vis
(KBr): lmax =680, 426, 268 nm; UV/Vis (hexane): lmax =651, 415, 392,
270 nm; elemental analysis (powder) calcd (%) for C27H26O2I: C 63.66, H
5.14, N 0.00; found: C 63.75, H 5.15, N 0.00.
8-(4-Bromophenyl)-2,5-di-tert-butyl-6-hydroxyphenalenone (13): The
phenalanone 12 (626 mg, 1.23 mmol) was placed in a 100 mL round-bot-
tomed flask and dissolved in THF (20 mL). LiAlH4 (164 mg, 4.32 mmol)
was added to the mixture and stirred at room temperature for 20 min. It
was then poured into 0.1m phosphate buffer (pH 7) and vigorously stir-
red. The mixture was extracted with ethyl acetate and the organic ex-
tracts dried over Na2SO4, filtered, and concentrated under reduced pres-
sure. The residue was subjected to silica gel column chromatography with
a 40:1–2:1 mixture of hexane and ethyl acetate as eluent to give phenala-
nol derivatives as a mixture of diastereomers (510 mg, 81%).
Single crystals including acetonitrile as a solvent of crystallization suita-
ble for X-ray crystal structure analysis were obtained as green blocks by
the following method: The p radical 2 (3 mg), acetonitrile (1 mL), and
hexane (4 mL) were placed at a glass tube previously filled with argon.
The solution was degassed by a repeated freeze–pump–thaw method
(eight times). After sealing the glass tube, the solution was allowed to
stand at 48C. The resulting crystals were filtered in air.
Characterization data for the more polar diastereomer: yellow powder;
m.p. 93–958C; Rf =0.19 (5:1 hexane/ethyl acetate); 1H NMR (270 MHz,
CDCl3): d=1.48 (s, 9H), 1.49 (s, 9H), 3.08–3.30 (m, 2H), 3.55–3.66 (m,
1H), 3.92 (s, 3H), 4.03 (s, 3H), 4.08–4.14 (m, 1H), 5.42–5.44 (m, 1H),
Crystal data for 1: C25H31O2, Mr =363.50, cubic, a=20.2890 ꢂ, V=
8351(7) ꢂ3, T=200 K, space group Ia3 (#206), Z=16, 25088 reflections
measured, 1602 independent reflections (Rint =0.126), which were used in
all calculations. The final wR(F2) value was 0.2058 (all data).
7.44 (d, 3J
ACHTUNGTRENNUNG ACHTUNGTRENN(UGN H,H)=8.6 Hz, 2H), 7.61 (s,
(H,H)=8.6 Hz, 2H), 7.55 (d, 3J
1H), 7.73 ppm (s, 1H).
Characterization data for the less polar diastereomer: yellow powder; m.p.
100–1028C; Rf =0.44 (5:1 hexane/ethyl acetate); 1H NMR (270 MHz,
CDCl3): d=1.47 (s, 9H), 1.47 (s, 9H), 3.11–3.20 (m, 2H), 3.45 (m, 1H),
Crystal data for 2·
CAHUTTGNNERU(NG CH3CN): (C27H26O2I)ACHTUNGTNERN(UNG CH3CN)0.64, Mr =535.79, mono-
clinic, a=12.5389(9), b=8.3309(5), c=24.5593(12) ꢂ, b=101.6940(10)8,
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Exchange Interactions in Oxophenalenoxyl Dimer p Radicals
FULL PAPER
V=2512.2(3) ꢂ3, T=200 K, space group P21/n (#14), Z=4, 18120 reflec-
tions measured, 5697 independent reflections (Rint =0.043), which were
used in all calculations. The final wR(F2) value was 0.173 (all data).
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Crystal data for 7·ACHTUNGTRENNUNG((CH3)2CO): (C27H26O2Br)ACHUTNGTREN(NUGN C3H6O), Mr =520.48, mono-
clinic, a=12.8650(7), b=17.102(1), c=12.228(1) ꢂ, b=107.661(3)8, V=
2563.5(4) ꢂ3, T=200 K, space group C2m (#12), Z=4, 11359 reflections
measured, 3039 independent reflections (Rint =0.0652), which were used
in all calculations. The final wR(F2) value was 0.142 (all data).
CCDC-238265 (for 1), CCDC-938325 (for 2·
ACHTUNGTERN(NUNG CH3CN)),
and CCDC-238266 (for 7·(CH3)2CO) contain the supple-
AHCTUNGTRENNUNG
mentary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
Acknowledgements
This work was partially supported by grants from the Yazaki Memorial
Foundation for Science and Technology, The Japan Securities Scholarship
Foundation, Kansai Research Foundation for Technology Promotion, a
Grant-in-Aid for Scientific Research on Innovative Areas (No. 20110006
and Quantum Cybernetics), the Elements Science and Technology Proj-
ect of the Ministry of Education, Culture, Sports, Science and Technolo-
gy, Japan, and the Core Research For Evolutional Science and Technolo-
gy (CREST) of the Japan Science and Technology Agency.
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ꢀ
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Exchange Interactions in Oxophenalenoxyl Dimer p Radicals
FULL PAPER
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Received: May 9, 2013
Published online: && &&, 0000
Chem. Eur. J. 2013, 00, 0 – 0
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