Isomerism and blue electroluminescence of a novel organoboron compound: B2III(O)(7-azain)2Ph2

Full text of DOI:10.1002/(SICI)1521-3773(19990401)38:7<985::AID-ANIE985>3.0.CO;2-C

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36, 1967; b) T. J. R. Weakley, J. Chem. Soc. Chem. Commun. 1984,
1406.
Keywords: clusters
O ligands
´ cobalt ´ magnetic properties ´
[9] a) K. S. Murray, Adv. Inorg. Chem. 1995, 43, 261; b) E. K. Brechin,
S. G. Harris, S. Parsons, R. E. P. Winpenny, Chem. Commun. 1996,
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Physica B 1979, 97, 365.
[1] a) L. Thomas, F. Lionti, R. Ballou, D. Gatteschi, R. Sessoli, B. Barbara,
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S. P. Perlepes, A. Terzis, Angew. Chem. 1997, 109, 1165; Angew. Chem.
Int. Ed. Engl. 1997, 36, 1083; b) V. Tangoulis, C. P. Raptopoulou, A.
Terzis, S. Paschalidou, S. P. Perlepes, E. G. Bakalbassis, Inorg. Chem.
1997, 36, 3996; c) V. Tangoulis, C. P. Raptopoulou, S. Paschalidou,
A. E. Tsohos, E. G. Bakalbassis, A. Terzis, S. P. Perlepes, Inorg. Chem.
1997, 36, 5270.
Isomerism and Blue Electroluminescence
of a Novel Organoboron Compound:
BI2II(O)(7-azain)2Ph2**
Qingguo Wu, Mohammad Esteghamatian,
Nan-Xing Hu, Zoran Popovic, Gary Enright,
Steven R. Breeze, and Suning Wang*
Organic electroluminescent (EL) devices based on organic
or organometallic materials have attracted much attention
because of their high luminance, low driving voltage, and easy
fabrication.[1±4] To achieve a full color display, the three basic
color components red, green, and blue are required. Red and
green emitters for organic EL devices have become readily
available. Useful and efficient organic or organometallic blue
emitters are however still very rare. Previously reported blue
emitters of organometallic or coordination compounds in
organic EL devices employed either derivatives of 8-hydroxy-
quinoline or azomethine as the emitting ligands.[3, 4] The
common feature of those previously reported blue emitting
ligands is that they are all chelating ligands and bind to the
central atom through both nitrogen and oxygen donor atoms.
We have been interested in the application of organometallic
and coordination compounds in EL devices because the
properties of this class of compounds such as volatility and
stability can be modified readily by manipulating the coordi-
nation environment around the central atom.[5] We have
discovered recently that 7-azaindole and di-2-pyridylamine
ligands yield a strong blue luminescence when bound to an
aluminum or boron center.[6] The 7-azaindole or di-2-pyridyl
amine ligands contain nitrogen donor atoms only and can bind
to the central atom by either a bridging mode or a chelating
mode. They are therefore very different from the previously
[4] E. Kefalloniti, A. E. Tsohos, C. P. Raptopoulou, A. Terzis, J. C.
Huffman, S. P. Perlepes, G. Christou, unpublished results.
[5] Crystal data for 1: C60H87.2Co9N8O40.6, crystal dimensions 0.10 Â 0.10 Â
0.30 mm, monoclinic, space group C2/c, a ˆ 14.37(1), b ˆ 39.28(3), c ˆ
3
16.62(1) Š, b ˆ 115.69(3)8, Vˆ 8451(1) Š3, Z ˆ 4, 1calcd ˆ 1.651 gcm
,
2qmax ˆ 508, MoKa radiation (l ˆ 0.71073 Š), q ± 2q scan, Tˆ 298 K,
7637 measured reflections, 7369 independent reflections (Rint
ˆ
0.0384) all included in the refinement. Lorentzian, polarization, and
Y-scan absorption corrections were made, m ˆ 1.814 mm 1, [D/s]max
ˆ
0.075, 560 parameters refined, R1 ˆ 0.0642 (for 5734 reflections with
I > 2s(I)), wR2 ˆ 0.1712 (on jF 2 j ). Max./min. residual peaks in the
3
final difference map 0.840/ 0.901 eŠ
. Crystal data for 2:
C52H50Co4N8O17, crystal dimensions 0.15 Â 0.30 Â 0.50 mm, monoclin-
ic, space group I2/a, a ˆ 27.49(1), b ˆ 19.020(7), c ˆ 20.744(7) Š, b ˆ
91.31(1)8, Vˆ 10841.9(6) Š3, Z ˆ 8, 1calcd ˆ 1.586 g cm 3, 2qmax ˆ 508,
MoKa radiation (l ˆ 0.71073 Š), q ± 2q scan, Tˆ 298 K, 9833 meas-
ured reflections, 9550 independent reflections (Rint ˆ 0.0221) all
included in the refinement. Lorentzian, polarization, and Y-scan
absorption corrections were applied, m ˆ 1.282 mm 1, [D/s]max ˆ 0.025,
923 parameters refined, R1 ˆ 0.0404 (for 6908 reflections with I >
2s(I)), wR2 ˆ 0.1056 (on jF 2 j ). Max./min. residual peaks in the final
difference map 0.993/ 0.349 eŠ 3. Crystals of 1 and 2 were mounted
in capillaries filled with drops of mother liquor and in air, respectively.
The structures were solved by direct methods with SHELXS-86 and
refined by full-matrix least-squares techniques on F 2 by using
SHELXL-93. For both structures, all non-hydrogen atoms were
refined anisotropically. All hydrogen atoms of the ligands in 1 were
introduced at calculated positions as riding on bonded atoms; no
hydrogen atoms of H2O molecules were included in the refinement.
All hydrogen atoms in 2 were located by difference maps and their
positions refined isotropically. Crystallographic data (excluding struc-
ture factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publications no. CCDC-102038 and CCDC-102039.
Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk).
[*] Prof. Dr. S. Wang, Q. Wu
Department of Chemistry
Queenꢁs University
Kingston, Ontario, K7L 3N6 (Canada)
Fax : (‡ 1)613-533-6669
E-mail: wangs@chem.queensu.ca
M. Esteghamatian, N.-X. Hu, Z. Popovic
Xerox Research Center of Canada, Mississauga
Ontario (Canada)
G. Enight, S. R. Breeze
Steacie Institute for Molecular Science, National Research Council,
Ottawa (Canada)
[6] a) J. G. Bergman, F. A. Cotton, Inorg. Chem. 1966, 5, 1208; b) W. O.
Koch, J. T. Kaiser, H.-J. Krüger, Chem. Commun. 1997, 2237.
[7] E. K. Brechin, A. Graham, S. G. Harris, S. Parsons, R. E. P. Winpenny,
J. Chem. Soc. Dalton Trans. 1997, 3405, and references therein.
[8] a) E. K. Brechin, S. G. Harris, S. Parsons, R. E. P. Winpenny,
Angew. Chem. 1997, 109, 2055; Angew. Chem. Int. Ed. Engl. 1997,
[**] This work was supported by the Natural Sciences and Engineering
Research Council of Canada and Xerox Research Foundation.
7-azain ˆ 7-azaindole anion.
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reported blue emitting ligands. Furthermore, the commonly
used central ions in previously known organometallic or
coordination blue emitters[3, 4] are AlIII, ZnII, and BeII. Blue
emitters using boron as the central atom are previously
unknown, although a few blue photoluminescent boron-
containing polymers and small molecules and electron-trans-
porting organoboron compounds have been reported recent-
ly.[7] The main advantage of boron over aluminum is that
boron ± ligand bonds are in general much more covalent than
the corresponding aluminum ± ligand bonds.[8] As a conse-
quence, boron compounds, in general, are much more stable
than the corresponding aluminum compounds,[8] making them
an attractive and potentially useful class of compounds for
electroluminescence. Recently, we reported the synthesis and
structure of B2III(O)(7-azain)2(C2H5)2.[6a] Although this com-
pound has a bright blue photoluminescence, it is however not
stable enough for EL applications. To improve the stability of
the boron compound so that electroluminescence can be
achieved, we investigated the syntheses of new 7-azaindole
boron compounds, B2III(O)(7-azain)2R2, where R is an aryl
group. We have successfully synthesized the new boron
compound, BI2II(O)(7-azain)2Ph2 (1) which is not only stable
and emits blue electroluminescence, but also displays an
unusual structural isomerism. We report herein the synthesis,
structures, and blue electroluminescence of 1.
Compound 1 can be obtained by several synthetic routes, of
which the best (50% yield) is to react PhBCl2 with 7-azaindole
and H2O in a 2:2:1 ratio in the presence of a base such as
triethylamine. Compound 1 was found to exist in two isomeric
forms, one with an approximate twofold rotation symmetry
(A) and the other with an approximate mirror plane
symmetry (B) (Figure 1), as established by NMR spectro-
scopy, elemental analysis, and single-crystal X-ray diffrac-
tion.[9] These two isomers can be separated by repeated
crystallization from CH2Cl2/hexane (A is less soluble than B).
Both isomers have an oxo ligand bridging two boron atoms. A
similar oxo bridge has been observed in the compound
BI4II(2,2'-biimidazole)2(O)(C2H5)6 reported by Niedenzu
et al.[10a] The B O, B N, and B C bond lengths in A and B
are similar and typical.[10, 11] The structure of A is similar to
that of BI2II(O)(7-azain)2(C2H5)2 where the environment around
both boron centers is identical. In 1H and 13C NMR spectra of
A, only one set of resonances due to the phenyl group are
observed, while one resonance is present in 11B NMR
spectrum of A, indicating that the structure of A in solution
is the same as that in the solid state. The structure of B is very
unusualÐone of the boron centers is bound by two nitrogen
atoms of the six-membered rings, while the other boron center
is bound by two negatively charged nitrogen atoms of the five-
membered rings. Thus, the two boron centers and the two
phenyl groups in B are chemically inequivalent. Indeed, two
distinct boron chemical shifts are present in the 11B NMR
spectrum of B. There are also two sets of distinct chemical
shifts for the protons and carbon atoms at 2,6 positions of the
Figure 1. Molecular structures of A (top) and B (bottom) in the crystal
(50% thermal ellipsoids). Hydrogen atoms are omitted for clarity.
Important bond lengths [Š] and angles [o]: A: B(1) ± O(1) 1.429(6),
B(2) ± O(1) 1.414(6), B(1) ± N(1) 1.619(6), B(1) ± N(4) 1.582(7), B(2) ±
N(2) 1.591(7), B(2) ± N(3) 1.628(7), B(1) ± C(20) 1.584(7), B(2) ± C(30)
1.625(7); B(1)-O(1)-B(2) 120.4(4). B (There are two similar and independ-
ent molecules of B in the asymmetric unit. The structure for one of them is
shown here.): B(1) ± O(1) 1.399(12), B(2) ± O(1) 1.422(12), B(1) ± N(1)
1.611(11), B(1) ± N(3) 1.648(12), B(2) ± N(2) 1.578(12), B(2) ± N(4)
1.613(12), B(1) ± C(20) 1.591(14), B(2) ± C(30) 1.589(14); B(1)-O(1)-B(2)
120.4(7).
has not been observed previously in either boron or aluminum
7-azaindole complexes.
Isomers A and B are stable in the solid state upon exposure
to air, which can be attributed to the oxo bridge and the
covalent B N and B C bonds. The thermal stability of these
two isomers is however very different. Compound A has a
melting point of 2748C and can be sublimed readily. In
contrast, compound B decomposes at temperature greater
than 1508C in the solid state, as established by differential
scanning calorimetry (DSC) and thermogravimetric analysis
(TGA). Compound A and[12] B3IIIO3Ph3(7-azainH) were found
among the decomposition products. The details of the thermal
decomposition mechanism of B are not yet fully understood.
The other exciting property of compounds A and B is that
they produce an intense photoluminescence (PL) when
irradiated by UV light in solution and the solid state. The
PL spectra of both isomers are very similar with an emission
1
two phenyl rings in H NMR and 13C NMR spectra of B,
respectively, again indicating that B retains its structure in
solution. There is no interconversion between A and B in
solution as established by NMR studies. The unusual geo-
metric structural isomerism exhibited by BI2II(O)(7-azain)2Ph2
986
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added to the mixture slowly and the solution was heated at 608C for 5 h.
After the solution was allowed to cool to room temperature, THF (40 mL)
was added to the solution and then the mixture was filtered. The filtrate was
collected and evaporated to dryness in vacuum. Recrystallization of the
resulting white powder from CH2Cl2/hexane yielded colorless crystalline 1
in 50% yield (isomer A dominant). Pure isomer A can be obtained by
repeated recrystallization from CH2Cl2/hexane. Pure isomer B can be
obtained from the concentrated mother liquor after the removal of A.
Single crystals suitable for X-ray diffraction analyses were obtained from
THF/hexane for A and CH2Cl2/hexane for B. A: 1H NMR (CDCl3, 258C):
d ˆ 8.13 (d, 3J ˆ 6.0 Hz, 2H, 7-azain ), 8.05 (d, 3J ˆ 7.8 Hz, 2H, 7-azain), 7.78
(d, 3J ˆ 6.8 Hz, 4H at 2,6 positions of Ph), 7.69 (d, 3J ˆ 3.3 Hz, 2H, 7-azain),
7.44 ± 7.35 (m, 6H at 3,4,5 positions of Ph), 7.03 (dd, 3J ˆ 6.0 Hz, 3J' ˆ 7.8 Hz,
2H, 7-azain ), 6.51 (d, 3J ˆ 3.3 Hz, 2H, 7-azain); 13C NMR (CDCl3, 258C):
d ˆ 134.28 (7-azain), 134.19 (3,5-Ph (the prefix indicates the positions of the
carbon atoms)), 133.54 (7-azain), 132.33 (4-Ph), 127.71 (2,6-Ph), 127.31 (7-
azain), 113.64 (7-azain), 100.88 (7-azain); 11B NMR (CDCl3, relative to
BCl3, 258C): d ˆ 42.75; m.p. 2748C. B: 1H NMR (CDCl3, 258C): d ˆ 8.17
(d, 3J ˆ 6.0 Hz, 2H, 7-azain), 8.08 (d, 3J ˆ 7.8 Hz, 2H, 7-azain), 7.83 (d, 3J ˆ
6.9 Hz, 2H at 2,6 positions of Ph), 7.67 (d, 3J ˆ 3.3 Hz, 2H, 7-azain), 7.60 (d,
3J ˆ 6.0 Hz, 2H at 2,6 positions of Ph'), 7.40 ± 7.33 (m, 6H at 3,4,5 positions of
Ph and Ph'), 7.05 (dd, 3J ˆ 6.0, 3J' ˆ 7.8 Hz, 2H, 7-azain), 6.49 (d, 3J ˆ 3.3 Hz,
2H, 7-azain); 13C NMR (CDCl3, 258C): d ˆ 134.33 (7-azain), 133.82 (3,5-
Ph, Ph' ), 133.53 (7-azain), 132.66 (4-Ph, Ph'), 127.77 (2,6-Ph), 127.58 (2,6-
Ph' ), 126.96 (7-azain), 113.08 (7-azain), 100.10 (7-azain); 11B NMR
maximum at l ˆ 450 nm, attributable to a p* !p transition of
the 7-azaindole anion. The role of the boron atoms in 1 is
believed to stabilize the 7-azaindole anion, as the aluminum
ion does in related 7-azaindole compounds reported pre-
viously.[6b,c] The high air and thermal stability of compound A
along with its intense blue photoluminescence makes it an
ideal candidate as a blue emitter in EL devices.
To investigate the electroluminescent properties of com-
pound A, an EL device using A as the light-emitting layer and
indium-tin-oxide (ITO) as the substrate was constructed by
using vacuum deposition methods. Tris(8-hydroxyquinoli-
no)aluminum (Alq3) and N,N'-di-1-naphthyl-N,N'-diphenyl-
benzidine (NPB) doped with 1% of 9,10-diphenylanthracence
were used as the electron-transporting and hole-transporting
layer, respectively. A magnesium silver alloy (Mg0.9Ag0.1) was
used as the cathode. When a positive bias was applied to the
ITO electrode, the EL device produced a bright blue emission
with a peak at 450 nm. The EL spectrum shown in Figure 2 is
(CDCl3, relative to BCl3, 258C): d ˆ 40.70,
45.15; m.p. ꢀ 1508C,
decompose. Elemental analysis calcd. for the mixture of A (60%) and B
(40%), C26H20N4OB2 ´ 0.4CH2Cl2 (%): C 66.60, H 4.40, N 11.77; found: C
60.71, H 4.57, N 11.82.
EL device: The device was fabricated on an indium-tin-oxide (ITO)
substrate which was cleaned by an ultraviolet ozone cleaner immediately
before use. Organic layers and a metal cathode composed of magnesium
silver alloy (Mg0.9Ag0.1) were deposited on the substrate by conventional
vapor vacuum deposition. Prior to the deposition, all the organic materials
were purified by a train sublimation method.[13] The device structure used
in this experiment is as follows: ITO /hole transport layer/light-emitting
layer/electron-transport layer/MgAg, in which NPB-doped with 1% of
9,10-diphenylanthracence was employed as the hole-transport layer and
Alq3 as the electron transport layer. To obtain the photoluminescence
spectrum of A, a thin film (100 nm) deposited on a quartz substrate was
measured with a fluorescence spectrophotometer. The current-voltage
characteristics were measured by using a Keithley 238 current/voltage unit.
The light intensity was measured by a Minolta Chroma Meter CS100. The
EL spectrum was obtained by an in-house setup made up of a series of
electronic components including a monochromator (Instruments SA Inc), a
photomultiplier tube, and a photon counter.
Received: August 24, 1998 [Z12322IE]
German version: Angew. Chem. 1999, 111, 1039 ± 1041
Figure 2. a) The PL (solid line) and EL (dashed line) spectra of A. I ˆ
intensity. b) The current density (J), voltage (E), and luminance (L)
characteristics of the EL device.
Keywords: boron ´ electroluminescence ´ isomerism
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Yonemoto, S. Kawami, K. Imai, Appl. Phys. Lett. 1994, 65, 80; b) Y.
Hamada, T. Sano, M. Fujita, T. Fujii, Y. Nishio, K. Shibata, Jpn. J.
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very similar to the PL spectrum of A, indicating that the light
emission originates from compound A. As shown in Figure 2,
the device has a turn-on voltage of approximately 7 V and
2
provides a luminance of 1024 cdm at 14 V. These prelimi-
nary results indicate that compound A is very promising for
EL applications. Further investigation on the chemistry and
EL device optimization of new organboron compounds is also
in progress.
[2] a) T. Tsutsui, MRS Bull. 1997, 22, 39; b) H. J. Brouwer, V. V.
Krasnikov, A. Hilberer, G. Hadziioannou, Adv. Mater. 1996, 8, 935;
c) A. Edwards, S. Blumstengel, I. Sokolik, R. Dorsinville, H. Yun, K.
Kwei, Y. Okamoto, Appl. Phys. Lett. 1997, 70, 298; d) Y. Ohmori, M.
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Appl. Phys. 1993, 32, L511.
Experimental Section
1: 7-Azaindole (0.474 g, 4 mmol) was added to phenylboron dichloride
(0.635 g, 4 mmol) in THF (20 mL) at 238C under N2. After the mixture was
stirred for 10 min, water (0.036 g, 2 mmol) was added, and the mixture was
stirred for another 10 min. Finally, triethylamine (0.8096 g, 8 mmol) was
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[4] a) C. P. Moore, S. A. VanSlyke, H. J. Gysling (Eastman Kodak Co.,
Rochester, NY), US-A, No. 5484922, 1996; b) T. Sano, M. Fujita, T.
Fujii, Y. Nishio, Y. Hamada, K. Shibata, K. Kuroki (Sanyo Electric
Co., Osaka, Japan), US-A, No. 5432014, 1995; c) Y. Hironaka, H.
Nakamura, T. Kusumoto (Idemitsu Kosan Co., Tokyo, Japan), US-A,
No. 5466392, 1995; d) S. A. VanSlyke, P. S. Bryan, F. V. Lovecchio
(Eastman Kodak Co., Rochester, NY), US-A, No. 5150006, 1992; e) P.
Bryan, F. V. Lovecchio, S. A. VanSlyke (Eastman Kodak Co., Ro-
chester, NY), US-A, No. 5141671, 1992.
The Melting Point Alternation in the
Short-Chain n-Alkanes: Single-Crystal X-Ray
Analyses of Propane at 30 K and
of n-Butane to n-Nonane at 90 K**
Roland Boese,* Hans-Christoph Weiss, and
Dieter Bläser
[5] a) Inorganic Materials (Ed.: D. W. Bruce, D. OꢁHare), Wiley, New
York, 1992; b) The Chemistry of Metal CVD (Ed.: T. T. Kodas, M. J.
Hampden-Smith), VCH, Weinheim, 1994.
Dedicated to Professor Reiner Sustmann
on the occasion of his 60th birthday
[6] a) A. Hassan, S. Wang, Chem. Commun. 1998, 211; b) W. Liu, A.
Hassan, S. Wang, Organometallics 1997, 16, 4257; c) J. Ashenhurst, L.
Brancaleon, A. Hassan, W. Liu, H. Schmider, S. Wang, Q. Wu,
Organometallics 1998, 17, 3186.
[7] a) N. Matsumi, K. Naka, Y. Chujo, J. Am. Chem. Soc. 1998, 120, 5112;
b) Z. Yuan, N. J. Taylor, R. Ramachandran, T. B. Marder, Appl.
Organomet. Chem. 1996, 10, 305; b) T. Noda, Y. Shirota, Y. Chujo, J.
Am. Chem. Soc. 1998, 120, 9714.
It was probably A. Baeyer who first stated in 1877 that the
melting points of the fatty acids do not show a monotonic
increase with increasing chain length as do their boiling
points. Instead the melting points of the members with even
numbers of C atoms are relatively higher than those of the
members with odd numbers.[1] The longer the chain length, the
smaller are the relative differences. This is true for the n-
alkanes as well as for most[2] of the a-substituted and a,w-
disubstituted n-alkane derivatives; a fact that is mentioned in
almost all standard text books of organic chemistry. Mostly,
ªpacking effectsº are given as an explanation for such an
alternation in melting points. This is justified insofar as
physical properties, such as sublimation enthalpy and solu-
bility, that are related to the solid state display a similar
alternation whereas the properties of the liquid phase have a
monotonic dependency on increasing chain length.[3]
For the n-alkanes with n ˆ 6 ± 24 (n ˆ number of C atoms)
the even numbered members crystallize at low temperatures
in a triclinic space group, while for n ˆ 26 monoclinic packing
is observed. It is possible to define an orthorhombic sub-cell
for the latter,[3a] which is also found as the real cell for
polyethylene[4] and mixed paraffins.[5] When n ˆ 7 the odd-
numbered n-alkanes also crystallize in a triclinic, ordered
modification with an orthorhombic sub-cell. Glassy crystalline
ªrotator phasesº with hexagonal symmetry are found below
the melting points for the odd-numbered n-alkanes with n ꢁ 9,
and the difference between the phase transition and melting
point increases with an increase in the chain length. From n ˆ
22 hexagonal modifications are also observed for the even-
numbered n-alkanes.
[8] a) F. A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed.,
Wiley, New York, 1988; b) N. N. Greenwood, A. Earnshaw, Chemistry
of The Elements, Pergamon Press, Oxford, 1984; c) E. L. Muettertues,
The Chemistry of Boron and Its Compounds, Wiley, New York, 1967.
[9] Crystal data for A: C26H20N4OB2 ´ 0.5THF, monoclinic, space group
P21/n, a ˆ 11.184(6), b ˆ 13.891(8), c ˆ 16.281(8) Š, b ˆ 108.72(3)o,
Vˆ 2395(2) Š3, Z ˆ 4, GOF on F2 ˆ 1.048, R1 (I > 2s(I)) ˆ 0.0693,
wR2 ˆ 0.1540. Crystal data for B: C26H20N4OB ´ CH2Cl2, triclinic, space
Å
group P1, a ˆ 12.5473(13), b ˆ 13.4960(13), c ˆ 16.7659(17) Š, a ˆ
90.345(10), b ˆ 102.211(10), g ˆ 116.055(10)o, Vˆ 2476.5(4) Š3, Z ˆ
4, GOF on F ˆ 3.67, R1 (I > 2.5s(I)) ˆ 0.093, wR2 ˆ 0.076. For A, data
were collected on a Siemens P4 X-ray diffractometer operated at
50 kV and 40 mA at ambient temperature. Data for B were collected
on a Siemens SMART CCD diffractometer operated at 50 kV and
35 mA at 1008C. The structural solution and refinement of A were
performed on a PC using Siemens SHELXTL software package while
the structural solution and refinement of B were performed on a
workstation using NRCVAX software package. Crystallographic data
(excluding structure factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Center as supplementary publication no. CCDC-113985 and CCDC-
113986. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:
(‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[10] a) K. Niedenzu, H. Deng, D. Knoeppel, J. Krause, S. G. Shore, Inorg.
Chem. 1992, 31, 3162; b) L. Y. Hsu, J. F. Mariategui, K. Niedenzu, S. G.
Shore, Inorg. Chem. 1987, 26, 143; c) W. Kiegel, G. Lubkowitz, S. J.
Rettig, J. Trotter, Can. J. Chem. 1991, 69, 234; 1217; 1227.
[11] a) G. Heller, Top. Curr. Chem. 1986, 131, 39; b) A. Dal Negro, L.
Ungaretti, A. Perotti, J. Chem. Soc. Dalton Trans. 1972, 1639; c) H.
Binder, W. Matheis, H.-J. Deiseroth, F. S. Han., Z. Naturforsch. B
1984, 39, 1717; d) W. Clegg, N. Noltemeyer, G. M. Shelderick, W.
Maringgele, A. Meller, Z. Naturforsch. B 1980, 35, 1499.
Although the phenomenon of the even/odd alternation has
been known for a very long time, there does not exist a
plausible explanation pattern, not even for the short chain
(n < 10) n-alkanes with a triclinic crystal system. Kitaigo-
rodski[6a] analyzed the arrangements of sections through the
long axes of the aliphatic chains, and distinguished between
triclinic, monoclinic, and hexagonal subcells. At longer chain
lengths these represent the real cells. Further considerations
referred to parallel arrangements of cylinderlike units, in
[12] Q. Wu, S. Wang, unpublished results.
[13] H. J. Wagner, R. O. Loutfy, C. K. Hsiao, J. Mater. Sci. 1982, 17, 2781.
[*] Prof. Dr. R. Boese, Dipl.-Chem. H.-C. Weiss, D. Bläser
Institut für Anorganische Chemie der Universität-GH
Universitätsstrasse 5 ± 7, D-45117 Essen (Germany)
Fax: (‡49)201-1832535
E-mail: boese@structchem.uni-essen.de
[**] This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie. The authors wish to express
their gratitude to Mr. Bonk from the in-house glass blowing work-
shop, his engagement and abilities enabled us to perform the
experiments especially with the liquid helium in order to crystallize
propane.
988
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Angew. Chem. Int. Ed. 1999, 38, No. 7