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Light Absorption as well as Crystal and Molecular Structure of N N-Dimethylindigo An Example of the Use of Synchrotron Radiation.

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121.5 1J(1'9Sn,'I7Sn) = 4666Hz). MS (CI, isobutane): mlz 1115 ( M @ + 1,
23%). UVIVIS: L,,, [nm] ( E ) = 391 (756).
Subsequently, 0.40 g (19%) of colorless 4 was obtained from a small amount of
ti-pentane: m.p. 234-236°C. 'HNMR: 5 = 1.14 (d, 24H), 1.22 (d, 'J(H,H) =
7 Hz, 48H), 2.69 (sept, 3J(H,H) = 7 Hz, 4H), 3.92 (m, broad, 8H), 7.06 (s,
4J("9Sn,'H) = 28.3 Hz, 8H). ''CNMR: 6 = 24.02, 25.17, 34.55, 37.05,
122.57, 142.56, 150.96, 155.06. 'I9SnNMR: 6 = - 46.9 (zJ(119Sn,1'7Sn)
174 Hz).
6: Addition o f 5 (0.14 g, 1.90 mmol) in 7 mL of toluene to l(2.00 g, 1.27 mmol)
in 50 mL of toluene at 90°C resulted in a spontaneous color change from red
to yellow. Toluene was replaced by n-pentane and the sparingly soluble products were removed by filtration. Crystallization from about 5 mL of n-pentane
gave 1.2 g (58%) of 6 as bright yellow crystals, m.p. 169-172°C. 'HNMR
(300 MHz, C,D,): b = 1.22 (m, 72H), 2.72 (sept, 4H), 3.77 (very broad, 4H),
3.90 (very broad, 4H), 7.06 (s, 4J(119Sn,'H) = 24.4 Hz, 8 H). I3CNMR
(75.44 MHz,C,D,):6 = 24.08,24.57,25.18,25.64,34.55, 37.04, 39.13(broad),
122.35, 150.62, 155.08 (broad), 155.30 (broad). "9SnNMR (93.23 MHz,
= 5745 Hz). UVjVlS: E.,
C,D,, versus Me&): 6 = -309 (1J('19Sn,1'7Sn)
[nm] ( E ) = 340 (12320).
Further treatment of 6 with 5 under the same conditions gave exclusively 4 and
no 3 (HPLC, NMR analysis).
7: Compound 1 (2.00 g, 1.27 mmol) and selenium (0.20 g, 2.53 mmol) were
heated in 50 m L of toluene for about 1 h at 90°C until the deep red color of 2
had vanished. Toluene was replaced by n-pentane and unreacted selenium was
filtered off. Fractional crystallization from n-pentane resulted initially in a
mixture of 7 and 8, followed by precipitation of 0.50 g (23%) of 7 as light
yellow crystals, m.p. 158-162°C. 'HNMR (300 MHz, C,D,): 6 = 1.17 (m,
72H). 2.72 (sept, 4H), 3.69 (very broad, 8H), 7.06 (s, 4J("9Sn,'Hf = 21.9 Hz,
= 24.09,24.58,25.19,25.77,34.53,39.83
(broad), 122.33, 150.56, 155.34. '19SnNMR (93.23 MHz, C6D,, versus
Me&): 6 = - 393, (IJ('19Sn,''7Sn) = 4873Hz). 77SeNMR (47.67 MHz,
C,D,, versus Me,Se) 6 = - 378 ('J('19~''7Sn,77Se)= 4321413 Hz). UVIVIS:
, , %,
[nm] (&)0345(6790).
8: Compound 1 (2.00g, 1.27 mmol) and selenium (0.31 g, 3.90 mmol) were
refluxed in 40 mL of toluene for 15 h. The workup was analogous to that of 7.
Crystallization from n-pentane gave 2.1 g (91%) of colorless 8, m.p. 243245°C. 'HNMR: 6 = 1.15 (d, 'J(H,H) = 6Hz, 24H), 1.22 (d, 'J(H,H): =
6 Hz,48H), 2.71 (sept, 4H), 3.97(m, 8H), 7.04(s, 4J(1'9Sn,'H) = 28 Hz, 8H).
' T N M R : 6 = 24.06, 25.20, 34.56, 37.01, 122.56, 140.16, 150.87, 154.89.
= 318 Hz). 77SeNMR: 6 = 84
'I9SnNMR: 6 = - 253 (2J(119Sn,117Sn)
(1J(1'9'''7Sn,77Se)= 868/831 Hz).
All new compounds gave correct C,H,S(Se) elemental analyses
Received: March 25, 1991 [Z 4533 IE]
German version: Angew. Chem. f03 (1991) 978
CAS Registry numbers:
1, 98526-67-1 ; 3, 134391-62-1; 3.0.5 pentane, 134391-63-2;4, 126857-71-4;5,
1072-43-1; 6. 126851-72-5;I, 134391-64-3;8, 134391-65-4.
[11 R. West, D. J. De Young, K. J. Haller, J. Am. Chem. Soc. 107 (1985) 4942.
(21 R. P.-K. Tan, G. R. Gillette, D. R. Powell, R. West, Urganometallics f0
(1991) 546.
131 T. Tsumuraya, S . Sato, W. Ando, Organometallics 7 (1988) 2015.
[4] S . Batcheller, S. Masamune, Tetrahedron Lefr.29 (1988) 3383.
[5] T. Tsumuraya, Y. Kabe, W. Ando, J Chem. Sac. Chem. Cornniun. 1990,
[6] S. Masamune, L. R. Sita, J. Am. Chem. Soc. f07 (1985) 6390.
[7] A. Schafer, M. Weidenbruch, W. Saak, S. Pohl, H. Marsmann, Angew.
Chem. 103 (1991) 873; Angew. Chem. fnr. Ed. Engl. 30 (1991) 834.
181 P. Brown, M. E Mahon, K. C. Molloy, J. Chem. Soc. Chem. Commun.
1989, 1621.
[9] 3 ' 0.5 pentane: monoclinic, space group C2lc,a = 1542.0(1), b =
2715.8(2), c = 1675.4(1)pm; fl = 104.93(2)", V = 6779 x 10, pm3, Z =
4,ecalrd= 1.163 gcm-'. 5563 uniquereflections,4596observed(I > 20(1))
305 parameters, R = 0.046, R, = 0.045. Programs: G. M. Sheldrick,
SHELX-76, Program for Crystal Structure Determination, University of
Cambridge, Cambridge 1976; G. M. Sheldrick, SHELX-86, Gottingen
1986; Drawing: C. K. Johnson, ORTEP 11, Report ORNL-5138; Oak
Ridge National Laboratory, Oak Ridge, TN, 1976. Further information
on the crystal structure determination is available on request from the
Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlichtechnische Information mbH, W-7514 Eggenstein-Leopoldshafen 2
(FRG), by quoting the depository number CSD-55363, the names of the
authors, and the journal citation.
[lo] H. B. Yokelson, A. J. Millevolte, G. R. Gillette, R. West,J. Am. Chem. Soc.
fO9 (1987) 6865.
[Ill K. C . Nicolaou, C.-K. Kwang, M. E. Duggan, P. J. Carroll, J. Am. Chem.
Soc. 109 (1987) 3801.
0 VCH Verlagsgesellschaft mbH, W-6940 Weinheim, 199i
Light Absorption as well as Crystal and Molecular
Structure of N,N-Dimethylindigo : An Example
of the Use of Synchrotron Radiation**
By Gerhard Miehe,* Peter Siisse,* Vladimir Kupcik, t
Ernst Egert, Martin Nieger, Gerold Kunz, R a y Gerke,
Burkhard Knieriem, Matthias Niemeyer,
and Wolfsang Liittke*
Dedicated to Professor Horst Prinzbach on the occasion
of his 60th birthday
N,N'-Dialkylindigos (1) absorb at considerably longer
wavelengths than the parent compound 2 [ 1 - 4 1(Table 1);
their solutions in organic solvents appear green to the eye,
whereas those of indigo appear blue. This phenomenon was
first recognized by K . 1 Braakman,r3]who ascribed it to the
inductive effect of the N-alkyl groups. His finding that the
color band shifts to longer wavelengths as the steric bulk of
the N-alkyl groups increases indicated, however, that the
bathochromism is due less to their inductive effects than to
their steric interaction with the carbonyl groups.[',
Bathochromism due to steric hindrance was first observed in
1942 by K . J. Brunings and A . H . Corvin['l for cyanine dyes
and was interpreted theoretically in 1956 by E. Heilbronner
and R . Gerdil.['olAccording to their studies, such an effect is
expected when the degree of double bonding in the central
bond undergoing twisting is greater in the electronic ground
state than in the excited state. In this case, the loss of resonance energy due to sterically induced torsion around the
central bond and the resulting decrease in overlap of the n
orbitals is greater in the ground state than in the excited
state, assuming the torsion angles are the same; the energy of
the ground state is thereby increased more than that of the
excited state and the excitation energy is correspondingly
decreased. An important argument favoring this model in
the case of the N,N'-dialkylindigos 1 has been provided by
M . Klessinger on the basis of HMO and PPP calculations:[6v71Indeed, the n bond order of the central bond of
indigo (2) is substantially higher in the ground state (HMO,
0.628; PPP, 0.688) than in the first excited state (HMO,
0.453; PPP 0.494).
I R = alkyl
4 R=CH,
3 R=CH,
However, experimental proof has been lacking so far; it
should provide information on whether, for example, NJ"'
[*I Dr. G. Miehe
lnstitut fur Kristallographie und Mineralogie der Universitat
Senckenberganlage 30, W-6000 Frankfurt am Main 1 (FRG)
Prof. Dr. P. S h e , Prof. Dr. V. Kupcikt
Mineralogisches Institut der Universitat
Goldschmidtstrasse 1, W-3400 Gottingen (FRG)
Prof. Dr. E. Egert, M. Nieger
Institut fur Organische Chemie der Universitat
Niederurseler Hang, W-6000 Frankfurt am Main 50 (FRG)
Prof. Dr. W. Luttke, Dipl.-Chem. G. Kunz, R. Gerke, Dr. B. Knieriem,
Dr. M. Niemeyer
Institut fur Organische Chemie der Universitat
Tammannstrasse 2, W-3400 Gottingen (FRG)
['*I Theoretical and SpectroscopicInvestigationsof Indigo Dyes, Part. 23. This
work was supported by the Bundesministerium fur Forschung und Technologie (Project: Structure Analysis with Synchrotron Radiation 05320
IAB 8). Part 22: H. Meier. W. Luttke, Liebigs Ann. Chem. 1981, 1303.
0S70-0833/91j0808-0964 $3.SO+.2S/O
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 8
Table 1 . Wavelengths E. [nm] of the longest-wavelength absorption band of indigo
dyes. The values measured in n-hexane were taken from [3], the others were measured.
In solution
n-Hexane p-Xylene CH,CI, CHCI,
indigo 2
NN-dimethylindigo 3
with those of the N-CH, groups. It is clearly revealed that the
N-CH, groups do not rotate freely, but merely undergo a
torsional vibration with a relatively large amplitude (Fig. 1).
To our knowledge, this work represents the first physically
meaningful determination of the hydrogen vibrational ellipsoids from X-ray diffraction data.
Although the two molecules in the asymmetric unit of the
unit cell of 3 are crystallographically independent, their
molecular shapes are practically identical. They have trans
configuration; their C,-symmetric shape is best described as
that of a “bent” propeller (Fig. 2). The six carbon atoms of
dimethylindigo (3)--like indigo (2)[’ - 51-is planar or
twisted. An X-ray structure analysis of 3 was therefore carried out;‘‘6. ‘’I in addition, its structure was calculated using
the n-SCF force-field program P1MM.L’ 8 .
the crystal structure of N-methylisatin (4) was determined.f20’2’1
In 4, which may be regarded as a “half-molecule” of N,N’-dimethylindigo (3), the inductive effect of the
methyl groups is retained, but their steric effects are eliminated.
The first structure determination of 3, carried out with
Mo,, radiation, yielded correct results,[’’] but was inadequate owing to the low scattering ability of the small crystals,
which were free of a multidomain texture. We therefore used
synchrotron radiation (five-circle diffractometer in the HASYLABc2’I)to determine the structure once again. A total of
2055 unique reflections (97 YOof which were significant) were
measured for a crystal with the dimensions 0.05 x 0.08 x
0.18 mm3 at a wavelength of 1 = 1.2127 A. The available
intensity of the primary beam was about 40 times greater
than that of a conventional X-ray tube. These data were
easily refined and led to an R value of 0.032 ( R , = 0.027).
The standard deviations of the distances of the “heavy”
atoms were 0.003 8, on average, those of the C-H distances
0.015 A (C-ring-H). The statistical variance of the individual
values is on the order of magnitude of the experimental standard deviations. A reasonable determination of the anisotropic temperature factors of the hydrogen atoms was accomplished in addition to the refinement of their site
parameters. Their physical relevance is immediately evident
when the H atoms bonded to the aromatic ring are compared
Fig. 1. The molecular shapes and thermal vibrations of 3 (top, molecule I:
bottom. molecule 11). The large amplitudes of the torsional vibrations of the
N-methyl groups are clearly evident.
30 (1991) No. 8
each benzene ring and all six atoms directly bonded to each
ring are exactly coplanar within the standard deviations;
only the C atoms of the central bond (C2 and C2’) deviate
slightly from this plane (<0.1 A). The two planar halves of
the molecule are twisted by p = 26” with respect to each
other; moreover, they are tilted in the same direction by an
average of 51 = 9.5” with respect to the central C-C bond.
The two C atoms of the central bond thereby adopt a slightly
pyramidal bonding geometry and undergo a hybridization
change from sp2 toward sp3. This is revealed in the fact that
the length of the C=C bond of 3 (1.376A) considerably
and the standard
exceeds the value for indigo (2; 1.342
value for a C=C bond (1.337 A) (cf. Table 2). The two NTable 2. Comparison of the average interatomic distances
Angeu.. Cheni. Int. Ed. Engi.
Fig. 2. Molecular shape of 3: a) schematic; b) viewed along the C=C bond.
[A] in 3 and 4 [a].
N.N’-Dimethylindigo 3
[18, 191
N-Methylisdtin 4
[IS, 191
C-C (ring)
C = C (central)
C-N (ring)
C-N (methyl)
C-H (ring)
C-H (methyl)
1.219 [b]
1.206 [b]
[a] The bond lengths [A] of 3 were obtained by averaging over the four crystallographically independent “half-molecules”. [b] This value corresponds to the
C2-02 bond length of 4.
Q VCH Veriagsgeseiischafi mbH, W-6940 Weinheim, 1991
0570-0833l9llO808-0965S 3.50f.2510
CH, groups are bent away from the planes of the five-membered rings; the N-CH, bending angles are 14 and 19.5".
Analogously, but in an opposite direction to the bending of
the CH, groups, the two carbonyl oxygen atoms lie at an
angle of 6 = 4.5" on average with respect to the planes. Noticeably, the interatomic distances in 3 (Fig. 3 and Table 2)
Fig. 4. Schematic representation of the crystal structure o f 3. The molecules I
are stacked along the edges of the unit cell, the molecules I1 in between.
Fig. 3. Bond lengths [A] and angles ["I of 3 (top) and 4 (bottom). The values for
3 correspond to a structure averaged from four half-molecules.
are systematically shorter than those calculated using the
force-field PIMM[lS7 and than the standard distances
found in tables,[231because none of the distances have been
corrected for vibrations.
N-Methylisatin (4; Table 2),[211like isatin (5),[241is completely planar. The C-C bonds in the benzene ring of 4 are
practically just as long as those in 3. There are differences in
the five-membered rings, however, especially for C2 -C3 and
C2-N, as well as for N-CH, and the C=O bond. These
differences are explained by the planar structure of 4 and
probably also by the differing polarity of the C 2 - 0 bond of
4 compared to the C=C bond of 3.
The high accuracy of the structure determination made
possible by synchrotron radiation allows a detailed analysis
of the effect of stacking of the molecules in the lattice on the
molecular structure of 3. The molecular shape is not significantly influenced by the intermolecular interactions in the
lattice. This is also indicated by the observation that the IR
spectra of the solid and of solutions of 3 in nonpolar solvents
are very similar and that, on going from the solid to nonpolar solution, only a small frequency shift of 420 cm- is
found for the longest-wavelength band in the visible spectrum. Thus, the twisted shape of the free molecule 3, due to
steric hindrance, is responsible for the complicated lattice
structure (Fig. 4). The structure strives to achieve the greatest possible planarity of the packed layers, like that realized
in the lattices of most planar indigo dyes. Although not
possible for the entire N,N'-dimethylindigo molecule owing
to its sterically induced nonplanarity, planar stacking is realized for its mutually twisted halves. As shown in Figure 4,
Verlagsgesellschafr mbH, W-6940 Weinheim, 1991
each molecule of 3 is involved in two stacking systems which
are tilted toward each other. In contrast to biphenyl, for
example, which is strongly twisted in the gas
but is
planar in the
the lattice energy is not sufficient in
3 to achieve a planar shape in the face of strong intramolecular steric hindrance. It may be assumed with certainty that
3 possesses the same twisted shape in solution as in the crystal.
The crystal structure of 3 is characterized by a large unit
cell ( V = 2806 A,; indigo (2), V = 580.5 A3[l5])and by different stacking of the two crystallographically independent
molecules I and 11. They each form separate layers; in the
case of molecules I-arranged along the edges of the unit
cells-this feature is expressed in a somewhat stronger twisting and a smaller aplanarity of the N-CH, groups as well as
in a stronger vibrational motion compared to 11.
Thus, NJ"'dimethy1indigo (3) is deformed in a very complex way; therefore, the bathochromism of 3 and of its alkyl
to indigo (2) is in fact a conseh o m o l o g u e ~in~comparison
quence of the steric interaction of the C=O groups with the
N-CH, groups, in the sense proposed by E. Heilbronner and
R. Gerdil.["] This conclusion is confirmed by PPP CI calculations,[2]which we undertook in order to determine separately the effect of torsion around the central C=C bond and
of pyramidalization at the N and CO groups on the excitation energy AE (So-S,) and on the oscillator strength of the
longest-wavelength band of 1. As shown by the data in
Table 3, each of these moiecular deformations causes roughly the same bathochromism and the effects are additive.
Table 3. Effect ofmolecular deformation on thelight absorption of 1 according
to PPP calculations.
Molecular shape
Excitation energy
AE (So-Si)
[cm - '1
central torsion 26"
N and CO pyramidalization
central torsion 26" and
According to the theory of deformation of C=C
bonds,[28- their torsion is necessarily associated with a
pyramidalization of the two C atoms, which leads to a local
increase in the electron density and to a decrease in the C=C
7t bond order. The C=C pyramidalization found in the structure analysis of 3 (a = 9.5') and the analogous deformation
of the N-CH, groups ( y = 14 and 19.5') explain the higher
reactivity of N,N'-dimethylindigo (3) relative to planar indigo (2):
0570-0833/91j0808-0966$ 3 . 5 0 + .2S/O
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 8
(1) On irradiation with visible light, >but not indigo
(2)-is transformed into its cis f0rm;[5334-361
the latter, in
turn, transforms back into the trans isomer in the dark. In
comparison to planar photoisomerizable indigoids, such as
t h i ~ i n d i g o , [351~ ~both
processes are appreciably facilitated
in 3 by the sterically caused torsion of the molecule. Since, in
the photoisomerization of 3, in contrast to that of other
indigo dyes, no short-lived triplet intermediate has been observed, the trans-cis rearrangement presumably occurs via a
singlet mechanism in the case of 3.r37%
(2) The high electron density at the central C atoms of 3
makes it readily oxidizable in solution.t391Apparently, this
oxidation occurs via a [2+ 21 cycloaddition of singlet oxygen
to form a dioxetane, since we have found that N-methylisatin
(4) is ultimately formed by cleavage of the C=C bond of 3.
(3) Because of the pyramidalization of the N atoms, N,Ndimethylindigo (3) is more basic than planar indigo (2). This
explains why 3, unlike 2, reacts with mineral acids to form
soluble salts.t5.331
(4) The twisted structure of 3, together with its inability to
form hydrogen bridges, explains why 3 possesses a much
lower melting point (182°C) and a lower density
(1.31 g ~ m - thanindigo
(2: 392°C and 1.518 g ~ m - ~Fur).
thermore, it is responsible for the fact that 3, in contrast to
the planar indigo dyes, is soluble even in nonpolar solvents
and that 3, in contrast to planar thioindigo, has no affinity
for cotton fibers.
[22] V. Kupcik, M. Wendschuh-Josties, A. Wolf, R. Wulf, Nucl. Instrum. Methods Phys. Res. Sect. A 246 (1986) 624.
[23] Taken from: International Tables for X-ray Crystallography, Kynoch
Press, Birmingham 1969.
[24] G. H. Goldschmidt, F. J. Llewellyn, Acta Crystallogr. 3 (1950) 291.
[25] A. Almenningen, 0. Bastiansen, L. Fernholt, B. N. Cyvin, S . J. Cyvin, S .
Samdal, J. Mol. Struct. 128 (1985) 59.
[26] G. P. Charbonneau, Y. Delugeard, Acta Crysrallogr. B 33 (1977) 1586.
[27] The CI calculations take into account the 45 lowest-energy singly excited
configurations. The deviations of the molecule from planarity have been
accounted for by the angle dependence of the B integrals of the respective
bonds according to the equation B(8) = ~ ( O ) C O S ~ .
[28] 0. Ermer: Aspekte von Krafrfeldrechnungen, W.-Baur-Verlag, Munchen
1981, p. 62ff.
[29] W. L. Mock, Tefrahedron Lett. 1972,475.
[30] L. Radom, J. A. Pople, W. L. Mock, Tetrahedron Lett. 1972, 479.
[31] K. N. Houk in W. H. Watson (Ed.): Stereochemistry and Reactivity of
Systems Containing n-Electrons, Verlag Chemie International, Deerfield
Beach, FL, USA 1983, p. 1 ff.
[32] N. G. Rondan, M. N. Paddon-Row, P. Caramella, K. N. Houk, J. Am.
Chem. Soc. 103 (1981) 2436.
[33] R. C. Haddon, Ace. Chem. Res. 21 (1988) 243.
(341 R. Pummerer, G. Marondel, Justus Liebigs Ann. Chem. 602 (1957) 228;
Chem. Ber. 93 (1960) 2384.
[35] G. M. Wyman, A. Zenhausern, Ber. Bunsenges. 72 Phys. Chem. (1968) 326.
[36] C. R. Giuliano, L. D. Hess, J. D. Margerum, J. Am. Chem. SOC.90 (1968)
[37] D. Schulte-Frohlinde, H. Hermann, G. M. Wyman, Z. Phys. Chem. N . E
101 (1976) 115.
[38] H. Corner, J. Pouliquen, J. Kossanyi, Can. L Chem. 65 (1987) 708.
Am. Chem. SOC.91 (1969) 3851.
1391 G. A. Russell, G. Kaupp, .
Received: March 7, 1991 [Z 4477 IE]
German version: Angew. Chem. 103 (1991) 1008
[l] L. Ettinger, P. Friedlander, Ber. Dtsch. Chem. Ges. 45 (1912) 2074.
[2] E. B. Knott, J. SOC.Dyers Colour. 67 (1951) 302.
131 K. J. Braakmann, Dissertation, Universitat Amsterdam 1943.
[4] The UV bands of 3 are also shifted to longer wavelengths to varying
extents in comparison of those of 2.
[5] J. Weinstein, G. M. Wyman, J. Am. Chem. Sor. 78 (1956) 4007.
[6] M. Klessinger, Diplomarbeit, Universitat Freiburg 1959.
[7] W. Luttke, M. Klessinger, Chem. Ber. 97 (1964) 2352.
181 This interpretation is also supported by the largely identical group electronegativities of alkyl groups with different volumes: J. Mullay, L Am.
Chem. Soc. 107 (1985) 7271.
[9] K. J. Brunings, A. H. Corvin, L Am. Chem. Soc. 64 (1942) 593.
[lo] E. Heilbronner, R. Gerdil, Helv. Chim. Acta 39 (1956) 1966.
[I 11 A. Reis, W. Schneider, Z. Kristallogr., Kristallgeom., Kristallphys.,
Kristallchem. 68 (1928) 543.
[I21 H. von Eller, Bull. Soc. Chim. Fr. 106 (1955) 1444.
[I31 E. A. Gribowa, Kristallografiva 1 (1956) 53.
[I41 G. Miehe, V. Kupcik, P. Susse, Z. Kristallogr. 149 (1979) 149.
[15] P. Susse, M. Steins, V. Kupcik, Z. Kristallogr. 184 (1988) 269.
[16] Synthesis of 3: P. Friedlander, L. Ettinger, Ber. Dtsch. Chem. Ges. 45
(1912) 2074.
[I71 Crystal structure determination of 3: space group P2Jc (needlelike crystals along c), a = 13.99, b = 27.54, c =7.35 A, p = 97.75"; V = 2806A3,
e = 1.31 g ~ m - ~The
asymmetric unit contains two molecules
C,,H,,NzOz (Z = 8). Additional information on the probable molecular
shape and a stacking vector revealed by the Patterson function afforded
normalized structure factors, which were used successfullywith MULTAN
77 (Mo,,: 2624 unique reflections, 1774 of which were observed
R , = 0.064). See also [21].
[18] H. J. Lindner, Tetrahedron 30 (1974) 1127.
[19] H. Beck, Staatsexamensarbeit, Universitat Gottingen 1985.
[20] Synthesis of 4: G. Heller, Ber. Dtsch. Chem. Ges. 40 (1907) 1291.
[21] Structure determination of 4 : space group P2,/c, a = 8.327(1), b =
10.802(2), c = 17.609(3) A, p = 103.26(1)", V = 1542 A3, Z = 8; crystal
dimensions: 0.2 x 0.3 x 0.7 mm3; 4868 measured dimensions 28,,, =
50" (Mo,), 1690 symmetry-independent reflections with IF1 > 3 4 F )
used in the structure solution (direct methods) and refinement (223
parameters); C, N and 0 atoms were refined anisotropically, H atoms were
located by difference electron density determination and refined with the
riding model R = 0.081 ( R , = 0.068, w - ' = o f f / * + 0.0004 x P ) [17].
Further details on the crystal structure determination are available on
request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur
wissenschaftlich-technischeInformation mbH, W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-52827, the
names of the authors, and the journal citation.
Angew. Chem. Int. Ed. Engl. 30 (1991) N o . 8
d-Electron Density in Formal do Systems from
Multiplet Splitting in the Photoelectron Spectrum
of Permanganates**
By Michael Schmalz, Robert Schollhorn,
and Robert Schlogl*
An important aspect of current ideas on the bonding in
high-temperature superconductors of the oxocuprate type is
electron transfer from the 2p band of the oxygen ions to the
copper d band. The resulting holes in the anion band lead to
a mixed-valence state. This can be formulated according to
the ionic model as shown in Equation (a).['. 21
In order to assess how real the differences in charge density are in Equation (a), it is necessary to quantify the difference between formal oxidation state and real charge density.
The magnitude of this difference allows an assessment of the
relevance of the ionic model, which is used throughout structural chemistry, to a discussion of bonding.
A proven method for the spectroscopic analysis of charge
density distribution is photoelectron spectroscopy (PES). It
has been applied, for example, to transition-metal chalcogenides of the type CuCr,X,, which were shown to have
["I Prof. Dr. R. Schlogl
Institut fur Anorganische Chemie der Universitat
Niederurseler Hang, W-6000 Frankfurt am Main 50 (FRG)
Dipl.-Chem. M. Schmalz, Prof. Dr. R. Schollhorn
Institut fur Anorganische und Analytische Chemie
der Technischen Universitiit
Strasse des 17. Juni 135, W-1000 Berlin 12 (FRG)
[**I This work was supported by the Fonds der Chemischen Industrie and by
the Bundesministerium fur Forschung und Technologie. We thank the
Fritz-Haber-Institut, Berlin, fur allowing us to use their Leybold EAll
photoelectron spectrometer.
Verlagsgesellschafi mbH. W-6940 Weinheim, 1991
0570-0833j91jO808-0967 d 3.50+-.25/0
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crystals, radiation, structure, example, molecular, dimethylindigo, synchrotron, light, use, absorption, well
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