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Chains Ladders and Two-Dimensional Sheets with Halogen Halogen and Halogen Hydrogen Interactions.

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R. L. Letringer. T. Wu. J. Am. Chem. Sor. 1995, 117, 7323-7328.
M . K . Herrlein. J. S Nelson. R L. Letsinger. J. Am. Chem. SOC.1995, 117,
10151 -10152.
For comparison, no reaction was observed when Y-O-tosyl-dT,OP(O)(OH)S~
was allowed 10 stand for 16 h in water
I. Hirao. Y Nishimura. Y Tagawa, K. Watanabe, K. Miura, Nucleic Acids Res.
1992, 20, 3891 -3896.
a ) R. L. Letsinger. T. Wu, J Am. Chem. Soc. 1994, 116, 811-812; b) F. D.
Lewis, T Wu. E. L. Burch, D. M Bassani. J.3. Yang, S. Schneider, W. lager,
R. L. Letsinger, ihrd. 1995, 117, 8785-8792.
This result is consistent with the cyclic structure 2 and inconsistent with a cyclic
dimer, in which two stilbene units would be aligned in the base-stacked conformation and therefore exhibit excirner fluorescence.
tion. Other closely related compounds did not exhibit the pattern and adopted a minimal energy conformation in the crystal
structure. Recognition of the pattern and its apparent role in
stabilizing an otherwise unfavorable molecular conformation
prompted us to characterize the nature and extent of this interaction. The results indicate that this pattern is not uncommon
and can be used for designing supramolecular arrays.
Characterization of the pattern is based on a survey of the
Cambridge Structural Database (CSD, April 1996).[51which
was carried out by searching for and analyzing structures containing the five-membered intermolecular ring pattern I and C1
or Br substituents on the aromatic
group. The search was subsequently
expanded to find other structures in
which the two intermolecular haloX-AA
gen. . . halogen and H . . . halogen infi-E"
teractions are still present, but aro3
matic substitution was no longer a
restriction (see structure 11). X . . . X
11, x = cl, B~
and X I . . H distances were defined
AA = C,N, P, B
by van der Waals radii (Br = 1.85,
C1 = 1.75, H = 1.2 A) with a tolerance of0.2 A. Table 1 contains
data for which the C-H bond length was normalized to
This search led to 41 1 hits, indicating the widespread
1.089 A.161
nature of this intermolecular pattern. Of these hits, 157 do not
contain a metal atom.
Chains, Ladders, and Two-Dimensional Sheets
with Halogen Halogen and
Halogen Hydrogen Interactions
Oshrit Navon, Joel Bernstein,* and
Vladimir Khodorkovsky
Intermolecular interactions have been traditionally classified
by the nature of their energetic relationship: hydrogen-bonding,
van der Waals interactions, charge-transfer forces, and others."]
Many of these, in turn, are based on models best defined by a
particular atom . . atom potential. With the advent of
supramolecular chemistry, there has been an increasing focus on
recognizing the structural patterns of interactions as driving
forces to a particular aggregation state.['] As any crystal structure represents a balance of forces, these structural patterns may
be comuosed of one kind of intermolecular interaction. if a
single interaction dominates the formation of patterns (for example hydrogen bonds), or may arise from a combination
of different types of interactions.['. 31 The term recently proposed for describing structural patterns is supramolecular synth~n.[~]
The recognition of structural patterns and their use in understanding intermolecular interactions and subsequently designing desired structures has been particularly relevant for hydrogen bonds.['] This is a natural consequence of their being among
the strongest and most highly directional of the intermolecular
forces. Considerably less attention has been paid to the structural patterns exhibited by other interactions. In the course of
investigating the relationship between molecular conformation
and crystal forces,[41we recently
noted a recurring pattern of intermolecular interactions I, which inI, X, Y = C1, Br
clude both halogen . . halogen
and C-H . . . halogen contacts.
A number of crystallographically isostructural compounds
with similar substitution all contained this pattern, which was
accompanied by a nonminimal energy molecular conforma[*I
Prof. J. Bernstein, 0. Navon, V. Khodorkovsky
Department of Chemistry
Ben-Gurion University of the Negev
Beer Sheva, 84105 (Israel)
Fax: Int. code +(7)647-2943
e-mail: yoelm bgumail-bgu
We thank the U. S.-Israel Binational Source Foundation (BSF, Jerusalem) and
the Gemany- Israel Binational Science Foundation (GIF) for support of this
C%vm In, Ed.
E n d 1997, 36, N o . 6
Table 1. Results of the CSD search for structures of form I1
B r . . - Br
CI . . CI
Br . . . CI
X . . .X
X . - .H
0 ["I
2 90-3.90
A A = metal,
AA = C, N, P, B
2 70-4.00
Examination of the metal-free compounds found in the
search showed that this intermolecular ring motif virtually always results in one of three recurring infinite crystal packing
patterns (Table 2): 1) a single-stranded chain with one fiveTable 2. Frequency of pattern types for the 157 compounds with AA
Pattern type
c1.. CI
No. of cmpds with X-X
Br . . B r
C, N, P, B.
CI . . . Br
membered ring per molecule (111, Scheme 1 a), 2) a ''ladder''
with two patterns per molecule (IV, Scheme Ib), and 3) a twodimensional pattern with more than two rings per molecule (V;
Scheme lc).
For most hits AA is a carbon atom, as was expected from the
frequency of structure types studied and compiled in the CSD.
Of the 157 hits for nonmetallic AA, 152 were with C, three with
N (one hit included also P), and two with B.
Despite the preponderance of structural evidence for the intermolecular interaction I, the question still remains whether
0 VCH Verla~sgrsellyrhaftmbH, D-69451 Weinheim, I997
such an interaction is energetically stabilizing. We therefore investigated the energetics of this pattern with a number of molecular orbital computational techniques at various levels of sophistication. The test structure was a pair of benzene rings with
one halogen atom arranged as in I, and the reference energy was
computed for the two molecules at infinite separation. Calculations were performed on the four possible pairing combinations
for X, Y = C1, Br in I (Table 3). Furthermore, ab initio calculaTable 3. Computed AM1 stabilization energy upon formation of 1.
X-Y in I
C1' ' ' C1
Br ' ' Br
C1. . . Br
E, [kcal mol-
tionsL7]were carried out for N-(p-chlorobenzylideneaniline/mchloroaniline) , one of the isostructural structures also containing this pattern, in the different basis sets presented above
(Table 4).
Table 4. Stabilization energies (E,) for N-(p-chlorobenzy1idene)-m-chloroaniline
determined by a b initio calculations.
Scheme 1. Examples of the three types of crystal networks resulting from the pattern I. Each indicates schematically the chemical structural formula for the pattern
at the molecular level, an idealized representation of the network, and its manifestation in the crystal structure. Halogen atoms are represented as solid spheres. a) The
chain network for VAKFES CSD reference code. b) The ladder network for
BCFPLB. c) The two-dimensional network for BRNPHL.
Q VCH VeilagrgerellschaftmbH 0-69451 Weinhelm, 1997
Basis set
E, [kcal m o l '~
Basis set
E, [kcalmol-'1
These results clearly indicate a stabilizing interaction for this
pattern irrespective of X or the basis set. The energetics thus
support the qualitative observation, based on the recurring
structural pattern, that the intermolecular atomic arrangement
I is indeed a motif for molecular recognition and the generation
of crystal structures.
Received: July 26, 1996 [Z9388IE]
German version: Anpew. Chem. 1997, 109, 640-642
0570-0X33/97/3606-0602$ 1 7 50+ 5010
A n g e ~ Chem Int Ed Engl 1997, 36, No 6
Keywords: halogens
- solid-state structures
. hydrogen bonds
[l] J. D. Dunitz, X-Ra? Ana1ysi.s and the Structure of Organic Molecules, Cornell
University Press. Ithaca, London, 1979, part 2; J. M. Lehn, Angew. Ckem. 1990,
102, 1347; Angeu. Ckem. Int. Ed. Engl. 1990, 29, 1304; A. I . Kitaigorodsky,
Molecular CrJsrals and Molecules, Academic Press, New York, London, 1973,
chap. 2.
[2] M. C. Etter. A r t . Ckem. Res. 1990,23,120; J Pkys. Ckem. 1991,95,4601; J. A.
Zerkowski, G M. Whitesides, J Am. Ckem. SOC.1994, 116,4298; S. Subramanian, M. Zaworotko, Can. J Ckem. 1995, 73,414; I. Bernstein, R. E. Davis, L.
Shimoni. N. L. Chang, Angew. Ckem. 1995, 107, 1689; Angew. Ckem. Int. Ed.
Engl 1995. 34, 1555.
[3] G. R. Desiraju, Angeu'. Ckem. 1995, 107, 2541; Angew. Chem. Int. Ed. Engi.
1995, 34. 2311.
[4] 0 Navon. J. Bernstein, Strucr. Ckem., submitted, and references therein.
[5] F. H. Allen, S . Bellard, M. D. Brice, B. A. Cartwright, A. Doubleday, H. Higgs,
T. Hummlink, B G. Hummlink-Peters, 0.Kennard, W. D . S. Motherwell, J. R.
Rodgers. D. G. Watson, Acta Crystallogr. Sect. B 1979,35,2331, F. H. Allen, 0
Kennard, R. Taylor, Arc. Ckem. Res. 1983, 16, 146.
[6] F. H. Allen. 0. Kennard, D. G. Watson, L. Brammer, A. G. Orpen, R. Taylor,
J Ckrnr SOC.Perkin Trans. 2 1987, 1
[7] GAMESS: M. W. Schmidt, K. K . Baldridge, J. A. Boatz, S. T. Elbert, M. S.
Gordon. J. H. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. Su, T. L.
Windus. M. Dupuis, J. A. Montgomery, J Comput. Ckem. 1993, 14, 1347.
The First Crystalline Solids in the
Ternary Si-C-N System**
Ralf Riedel,* Axel Greiner, Gerhard Miehe,
Wolfgang Dressler, Hartmut Fuess, Joachim Bill,
and Fritz Aldinger
Dedicated to Professor Ekkehard Fluck
on the occasion of his 66th birthday
Advanced non-oxide ceramics and ceramic composites with
compositions in the ternary Si-C-N system (Figure 1) are of high
technical relevance. Carbon, in the form of graphite and diamond, is industrially used as electrode and abrasive material.
The binary compounds silicon carbide (Sic) and silicon nitride
(Si,N,) have received much attention in the past two decades
with respect to their application as cutting tools or structural
materials in engine components.['] The existence of the carbonitride C,N, with a P-Si,N, structure has been postulated since
1989 and is still controversial.[21
Recently polycrystalline Si,N,/SiC composites with superplastic behaviorL3]and enhanced mechanical propertiesr4] or
ultra-high oxidation resistance[s] relative to monolithic Si,N,
Prof. Dr. R Riedel, Dip[.-Chem. A. Greiner, Dr. W. Dressler
Fachgebiet Disperse Feststoffe, Fachbereich Materialwissenschaft
Technische Hochschule Darmstadt
Petersenstrasse 23, D-64287 Darmstadt (Germany)
Fax: Int. code +(6151)166-346
e-mail dg9bur
Dr. G. Miehe. Prof. Dr. H. Fuess
Fachgebiet Strukturforschung, Fachbereich Materialwissenschaft
Technische Hochschule Darmstadt
Dr. J. Bill, Prof Dr. F Aldinger
Max-Planck-lnstitut fur Metallforschung, Institut fur Werkstoffwissenschaft,
Pulvermetallurgisches Ldboratorium, Stuttgart (Germany)
[**I We gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft. the National Energy Development Organization (Japan), and the
Fonds der Chemischen Industrie. We thank Dr. N. Egger (Hoechst AG, Frankfurt. Germany) and Dr. G. Simon(Varian GmbH, Darmstadt. Germany) for
"Si and "C MAS-NMR measurements.
Angeu Cfwm Int Ed Engl 1997, 36, No 6
0 VCH Verlagsgesellsckafi
and Sic counterparts
have been reported.
Composite ceramic materials comprising polycrystalline Si,N, and
S i c are presently produced by 1)sintering of
Si,N,/SiC powder mixtures, 2) chemical vapor deposition with
as the reaction gas,[,]
or 3) thermally induced Figure 1. Isothermal section of the ternary Siconversion of poly- C-N phase diagram valid below 1440°C and
organosilazanes under 0.1 MPa N, pressure [30]. Solid lines: Si,N,/C
and Si,N,/SiC tie lines, dashed line: hypothetiAr, N,, or NHJN,
atmospheres at 1000- cal Si,N,/C,N, tie line.
1100 oC.[6.7l
Procedures 2 and 3 provide intermediate amorphous solids in the
ternary Si-C-N system of general composition Si,,+,C, -,N,,
with 0 5 x I
1 and 0 5 y 2 1. Subsequent in situ crystallization of
the amorphous phase results in the formation of a,P-Si3N4and
a,b-SiC polymorphs with nanosized Sic particulates.[4s61
Kawamura has found a 8-SiC with interstitial nitrogen atoms
that prevent 3C- Sic transformation to hexagonal a-SiC.['"I
However, crystalline ternary solids with a covalently bonded
Si-C-N network structure have not yet been reported.[8b1These
are of basic fundamental and technical interest for further development of single source Si,N,/SiC precursors with well-defined
structural features and adjusted compositions.
In the course of our work on the synthesis of alternative
Si,N,/SiC precursor materials, we recently developed a novel
class of organosilicon polymers, denoted as polyorganosilylcarbodiimides, that are synthesized by the reaction of dichloroorganosilanes with cyanamide or bis(trimethylsily1)carboThe polyorganosilylcarbodidiimide [l, Eq. (a) and (b)].['.
imides can be thermally decomposed at 1100°C under Ar to
form amorphous Si-C-N solids in 30-64 wt% yield.
MeRSiC12 + H2N-CN + 2n Py
+ 2n Py HCI
Py = pyridine; R = H, Me, CH =CH2
n Me2SiC12 + n M e 3 S t N = C = N - - S i M e L
+ 2n Me3SiC1
The reaction of SiCI, with 1 at temperatures between 25 and
100 "C directly provides silicon dicarbodiimide SiC2N, (2)
with a polymeric inorganic network structure [Eq. (c)] . This
reaction is catalyzed by pyridine and provides 2 in quantitative
yields as a colorless, X-ray-amorphous powder with residual
trimethylsilyl end groups, as analyzed by FT-IR and 29SiMASNMR spectroscopy. Subsequent calcination in vacuum at
n SiCl,
+ 2n M e 3 S t - N ~ C z N - s i M e 3
mbH, 0-69451 Wernkerm, 1997
+ 4n Me3SiC1
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hydrogen, two, dimensions, interactions, chains, halogen, sheet, ladder
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