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instead of toluoyl groups would have self-replicative properReceived: August 26. 1994 [Z 7270 IE]
German version: Angew. C'tirrn. 1995, 107, 616
Keywords: cystine gels . self-assembly . structure elucidation
Y. Osada, S. 9 . Ross-Murphy, Sci. A m . 1993, No. 5, 82.
D. R. Eyre. Science 1980. 207, 13 15.
Y.-L. Yin, R. K. Prud'homme, F. Stanley in Po!w/ectro/yre Geis (Eds.: R. S .
Harland, R. K. Prud'homme), American Chemical Society. Washington. 1992,
Chap 6.
D. A. Gibbs, E. W. Merril. K. A. Smith, E. A Balazs, Biopu/j.rnrrr 1968,6.777.
Y Lin. 8. Kachar. R. G. Weiss, J A m . C/irm. Soc. 1989, lli, 5542.
K. Hanabusa. T. Miki. Y. Taguchi, T. Kogama, H. Shirai. J Chem Sot. Chew
Cornmiin. 1993. 1382.
J.-H. Fuhrhop, S . Svenson, C . Boettcher, E. Rossler, H.-M. Vieth. J A m .
Chrm. Soc. 1990, 112,4307.
G. R. Newkome. G . R. Baker, S. Arai, M. J. Saunders, P. S . Russo, K . J. Theriot, C. N . Moorefield, L. E. Rogers. J. E. Miller, T. R. Lieux, M. E. Murray,
B. Phillips, L. Pascal. J. Ani. Chem. Sor. 1990. 112, 8458.
F. M . Menger, K. S. Venkatasubban, J. Org. Chem. 1978, 43. 3413.
C . G . L. Wolf, E. K . Rideal, Biochern. J. 1922, 16, 548.
B. Panijpan, J C1itwi. Edirc. 1977. 54, 670.
For self-assembled fibers composed of entirely different compounds see .I.-H.
Fuhrhop. W. Helfrich. C k n . Re).. 1993. Y3. 1565; F. Giuljeri, M.-P. Krafft.
J. G. Rieas. Angew. Clieni. 1994. 106. 1583; Angrw. C/iwi. Inr. Ed. Engl. 1994,
33, 1515: F. M. Menger, S. J. Lee. J, An?. Ciirrn. Sor.. 1994. 116. 5987.
Single-crystal structure data for C,,H,,N,O,S, : monoclinic space group P2,
(no.4). ~=11.853(2), h=10.965(3), c=17.641(4). /1=95.45(2), V =
2282.5( 12) A'. Z = 4. Of 3946 measured reflections 3366 were symmetry-independent. of which 2957 (!> 4o(f)) with R = 0.0646. Determination of the
lattice parameters and measurement of the intensities were carried out with a
Siemens P4RA diffractometer ( C u , radiations. p = 2.472,28,,,
= 109.0). Empirical absorption correction and structure determination were carried out with
SHELXS-86 and structure refinement with SHELXTL IRIS. Further details 01
the crystal structure determination are available on request from the Director
of the Cambridge C~-ystallographicData Centre, 12 Union Road, GB-Cambridge, CB2 1EZ (UK), on quoting the full journal citation.
Fig. 1. X-ray crystal structure of
dr(p-toluoyl)-~-cystine (DTC).
Red spheres represent oxygen,
blue nitrogen, and yellow sulfur
atoms. The dotted lines represent
hydrogen bonds between amideN H and carboxyl-CO functionalities. The N . . ' 0 distances (and NU-O angles) from bottom to top
in the structure are 3.156A
3.1 72 A
3.123A (148.0). and 2.8888,
orientation enhanced by hydrogen-bonding and x-n stacking
(or hydrophobic) interactions. This fortuitous blend of structural features accounts for the ability of acylcystines to gelate at
remarkably low concentrations.
Figure 2 shows how two neighboring strands are held together by cooperative hydrogen bonding between carboxyl hydrogens and amide oxygens. The O . . . O distances are all about
2.6 A in length. Single strands assemble into multi-filament
fibers that we postulate can cause the gelation of aqueous solutions." 1'
The beautiful DNA-like structure of DTC in Figure 1 leads
one to wonder whether acylcystines bearing nucleic acid bases
Burkhard Krumm, Ashwani Vij, Robert J. Kirchmeier,*
Jean'ne M. Shreeve," and Heinz Oberhammer"
Fig. 2. X-ray crystal structure of
two DTC strands held together by
cooperative hydrogen bonds between carboxyl-hydrogen atoms
and amide-CO groups (dotted
lines). The O . - . O distances (and
0-H-O angles) moving up the
structure are 2.61481 (172.4 ),
2.653 A
2.609 A
(157.6 ), 2.624 8, (172.4). and
2.614 A (172.3').
/ l ~ ~ ID-64451, fYY5
While no element can compete with carbon in the number of
contiguous atoms in saturated chemical compounds, stable
straight-chain species composed of other elements are known,
especially if fluorine atoms, fluorinated groups, or other electronegative species are present in the molecule, for example
CF,(O),,CF, ( n = 1 -3) and O,F, ( n = 1, 2, 4). Fluorinated N,
compounds do exist and d o exhibit surprising hydrolytic, thermal, and chemical stabilities. In contrast, the hydrogen-substituted analogues such as diazane, triazane, and tetrazane are increasingly unstable with increasing chain length. While tris(perfluor0[*I
Prof. R. L. Kirchmeier, Prof. J. M. Shreeve. Dr. 9. Krumm, Dr. A. Vij
Department of Chemistry. University of ldaho
Moscow, ID 83843 (USA)
Prof. Dr. H. Oberhammer
Institut fur Physikalische und Theoretische Chemie der Universitlt
D-72076 Tubingen (Germany)
Telefax: h i . code + (7071)296910
The work was supported by the U.S. National Science Foundation (CHE9003509) and the Air Force Office of Scientific Research (91-0189).
S 10.00
+ .25:fl
Chum. Int. Ed. Engl. 1995, 34, No. 5
alky1)amines N(R,),l1 - and tetrakis(perfluoroalky1)diazanes
(R,)2NN(R,),[4, 'I are well known, and their gas-phase structures determined, only recently have the synthesis and property
characterization of per- and polyfluoroalkyl-substituted tetrazanes been reported.[', All of the known fluorine-containing
tetrazanes are relatively dense liquids of low volatility which
solidify as glasses, precluding single-crystal X-ray structural
analyses. As a consequence, the smallest, most symmetric perfluoroalkylated compound of this type, hexakis(trifluor0methy1)tetrazane (4), was selected for a structural study in the
gas phase using electron diffraction (GED) .I7]
Our synthesis of 4 differs from the one reported by Emeleus
et al.['I and provides a facile route to these N, compounds
(Scheme 1 ) . The conversion of the N-chloro-N-chlorodifluoro-
(Ck,)2 NN(CI)CF2CI
Scheme 1
methyldiazane 1 to difluoromethylenediazane 2 is achieved by
utilizing only a catalytic amount of chlorotrimethylstannane
with benzonitrile as solvent. Chlorine is removed easily without
the formation of side products. The intermediate trimethylstannyldiazane loses chlorotrimethylstannane at 25 "C and yields 2.
The chlorostannane again reacts with 1 with the evolution of
C12. The process continues until 1 is totally consumed. This is a
convenient method for the preparation of perfluorinated difluoromethylenamines (or -azanes). The double bond can be
chlorofluorinated with CIF to form N-chloro-N-trifluoro
methyldiazane 3. N-Chlorodiazanes are known to lose chlorine
nd dimerize to give tetrazanes."' In this way
hexakis(trifluoromethy1)tetrazane (4) is obtained as a volatile,
colorless liquid with considerable vapor pressure at 25 "C. Furthermore, this compound is air and water stable and does not
decompose even at elevated temperatures. The "F N M R spectrum shows two broad signals for the terminal CF, groups,
which are not equivalent at 25 "C. Another resonance at higher
field for the CF, groups attached to the inner nitrogen atoms is
split into a multiplet due to nonequivalent couplings to the outer
CF, groups. In a variable-temperature N M R study the signals
for the terminal CF, groups were found to coalesce at 58 "C.The
features of the low-temperature N M R spectrum ( - 40 to
- 100 C). which were reported earlier" "I for a solution of 4 in
CFCI,. could not be reproduced. Instead, we observed precipitation of the compound from solution upon cooling.
The radial distribution function ( R D F ) derived by Fourier
transform of the experimental electron diffraction intensities is
shown in Figure 1 . A large number of molecular models with
different torsional angles about the N-N bonds were tested.
The models were evaluated according to two criteria: 1) no
F . . . F contacts shorter than 2.5 A (except within the CF,
groups) and 2) agreement between calculated and experimental
RDF. The RDF range 2.8-3.5 8, contains mainly C . . . F and
F . . F distances between adjacent CF, groups and N . . F distances to CF, groups bonded to the neighboring nitrogen atom
(e.g. from N1 to the CF, group of C2 or from N2 to the CF,
groups of C1 and Cl'). This R D F range can be reproduced only
Fig. 1. Experimental radial distribution function for 4and difference curve between
experimental and calculated functions.
with models having planar or nearly planar coordination at all
nitrogen atoms. The outer part of the R D F can be fitted satisfactorily only with models that have dihedral angles 4 about the
N-N bonds of close to 90" (for q5 = 0" the lone pairs of electrons on adjacent nitrogen atoms are parallel).
The following constraints were applied in the least squares
refinements: 1) local C,, symmetry for the CF, groups, 2) local
C, symmetry for the (CF,),N moieties, in other words the CF,
groups are rotated about the N-C bonds in opposite directions,
and 3) overall C , symmetry. The C, axis is perpendicular to the
N2-N3 bond and bisects the dihedral angle d(NNNN). Only
mean values for the N-N and C - N bond lengths could be
derived. The final results of the electron diffraction analysis are
given in Table 1 ; the nitrogen-carbon skeleton of tetrazane 4 is
Table 1. Structure parameters of [(CF,j2NN(CF,)N(CF),N(CF,),I (4) [a].
(N -C),,
C-F [A]
F-C - F ['I
C1 -N1 -Cl' [ '1
N2-Nl-C1[ ]
Zz(N1) "1 IbJ
1.379 (11)
1.438 (6)
1.329 (3)
108.2 (2)
120.3 (10)
117.6 (5)
355.5 (13)
Nl-N2-N3 [ I
Nl-N2-C2 ['I
N3-N2-C2 [ ]
Z$W "1 [bl
$(Nl-N2 -N3-N4) ["I
$(lp-Nl-N2-lp) ['I [cl
122.6 (15)
120.4 (18)
359.4 (27)
95.2 (11)
90.1 (24)
[a] Error limits are 3u values. Atom numbering is given in Fig. 2. [b] Sum of bond
angles around nitrogen atom. [c] Dihedral angle between lone pairs ofelectrons (Ip)
at N1 and N2.
shown in Figure 2. The coordination geometry at the inner nitrogen atoms N2 and N3 is planar (sum of bond angles Zc((N2)
= 359.4(27)") and that at the outer nitrogens N1 and N4 is
nearly planar (Zx(N1) =
355.5(13)"). The N N N N
chain has a skew conformation with $(NNNN) =
95.2(1 I)'.
The (CF,),N
groups are rotated around
the terminal N-N bonds by
d(lp-N-N-lp) = 90.1(24)",
such that the lone pairs (Ip)
at N1 and N2 (and those
at N3 and N4) are perpendicular to each other.
The structural features of
the two (CF3)2N-N(CF3)Fig. 2. Nitrogen-carbon skeleton of
halves are very similar to
hexakis(trifluoromethy1)tetrazane (4).
those of tetrakis(trifluoromethyl)diazane, which also has planar
coordination a t the nitrogen atoms (Cx(N) = 359.5(26)"), perpendicular nitrogen lone pairs ($(lp-N-N-lp)
= 88.4 (40)"),
and an N - N bond length of 1.402(20) A.141
The unsaturated
tetrazenes R,N-N=N-NR,
have planar nitrogen skeletons
and trans configuration. The N-N single bonds are slightly
longer (1.429(5) A for R = HI1'] and 1.394(5) A for R =
SiMe,l'Z1) than those in the tetrazane 4 (1.379(11) A).
A Model of Semimet Hemerythrin; NMR
Spectroscopic Evidence of Valence Localization
in Bis(pcarboxylato)(p-phenolato)diiron(II,m)
Complexes in Solution**
Wdkako Kanda, William Moneta, Michel Bardet,
Elisabeth Bernard, Noele Debaecker, Jean Laugier,
Azzedine Bousseksou, Sylvie Chardon-Noblat, and
Jean-Marc Latour*
Experimental Procedure
Hemerythrin (Hr), a dioxygen carrier found in sipunculid
2: Diazane I (10 mmol) was condensed into 5 mL benzonitrde containing a catalytic
worms and other marine invertebrates, is considered the protoamount of Me,SnCI. The reaction mixture was stirred at 25 -C for 1 11 before all
type of non-heme proteins with a diiron active site."' Since the
volatile material was held over mercury for 5 h to remove chlorine. Distillation gave
pure 2 as a colorless gas in quantitative yield. after passage through a trap at
early 1980s the structures of four distinct forms of the protein
-90°C. I 9 F N M R (CDCI,): 6 = - 65.2 (d, 5J(F.F) = 4.0 Hz. 6 F ; (CF,),N).
have been solved by X-ray crystallography.I2lIn the deoxy form,
-63.4(d.'J(F,F)=Y3.3Hz,lF;N = C F F ) , -40.2(dofsept.*J(F.F)=93,3Hz.
two Felt ions are bridged by one hydroxy and two carboxy5J(F,F) = 4.0Hz, 1 F ; N = CFF); IR (gas): v[cm-'] =I753 (s. N=C). 1360 (s),
late groups. The coordination spheres of the two iron ions are
1326(s). 1263(s). 1220(s),9X2(m).959(w).734(m);MS(EI):m/;(%):216(Mi.
7 ) , 1 9 7 ( M + - F,6), 128(CF3NN = C F C , l l ) , 109(CF3NNCt,2),69(CF~,100).quite different. One is bound by three histidine residues and is
Elemental analysis for C,F,N, (calcdifound): C 16.68116.00. F 70.35168.2.
thus hexacoordinate; the other is bound by only two histidines,
3: Diazane 2 ( 5 mmol) and CIF (5.5 mmol) were condensed into a stainless steel
thus leaving a coordination site accessible to dioxygen and other
reaction vessel and allowed to react for 12 h a t 25 C. Distillation through a -90' C
substrates. Oxygenation of H r leads to deprotonation of the
trap. in which (CF,),NN(CI)CF, condensed. gave the pure product as a colorless
bridging hydroxo ligands, resulting in a (poxo)diiron(rrr) unit
liquid inquantitative yield. '9FNMR(CDCI,): 6 = - 68.0(sept. 'J(F.F) = 4.7 Hz.
3 F ; N(CI)CF,), -61.4 (4, 'J(F,F) = 4.7 Hz, 6 F : (CF,),N); IR (gas): ~ [ c m - ' ]=
with a terminal hydroperoxo ligand linked to the bridging 0x0
1339(s), 1289 (s). 1265 (s). 1220 (s), 117X (m). 1030 (w). 986 (m). 927 (w), 839 (w).
ligand through a hydrogen bond. The hydroperoxo ligand can
734(m),725(m);MS(CI):miz%:270(Mi. 1).251 ( M ' - F.15).235(Mi - CI,
be replaced by anions (e.g. azide) leading to the corresponding
16). 216 (M' - CIF. 50), 197 ((CF3),NN = CF'. 45). 148 (CF,NNCF2Ht. 3 8 ) ,
met forms, which have been structurally characterized.121Apart
128 (CF,NN=CF'. 3 8 ) . 109 (CF,NNC+. 11). 69 (CF:, 100).
from the [Fe"Fe"] and [Fe"'Fe"'] states, two mixed-valence
4: Diazane 3 ( 5 mmol) was condensed into a 100 mL quartz vessel and photolyzed
for 5 h (1 = 3000 A). Distillation of the contents gave tetrazane 4. which was conforms [Fe"Fe"'] have been detected. These semimet hemerydensed in a trap at -80°C. in 90% yield. I 9 F N M R (CDCI,): 6 = 64.6 (m. 6 F ;
thrins are obtained either by oxidation of the deoxy form
NNCF,), -58.8, -60.3 (br., 12F; (CF,),N): coalescence a t 331 K, AG* =
or by reduction of the met form ((semimet),Hr).
15.2 kcalmol-'; IR (gas): r [ c ~ n - ' ]=1347 (m), 1312 (s), 1300 (s), 1284 (s), 1247
No X-ray structures are available for the semimet forms yet, but
(m). 1201 (w), 11x1 (w),987(m).935(w),735(m).
reported earlier [XI.
EXAFSr3Iand other spectroscopic methods[41have revealed a
Received. September, 13 1994 [Z 7311 IE]
German version' Ange11. Chcrn. 1995. 107. 645
Keywords: electron diffraction analysis . hexakis(trifluoromethy1)tetrazane . nitrogen -fluorine compounds tetrazanes
Fe" (p-OH)Fe"' unit. NMR experiments on (semimet),Hr
derivatives in solution have shown that the valence of the two
ions is localized.[51 Kurtz et a1.l6] and Solomon et al."] have
proposed that the two semimet forms differ in terms of the
location of the valences of the iron atoms in the ligand environment as illustrated in Scheme 1.
[I] H. Bock, I. Gobel, 2.Havlas, S. Liedle. H. Oberhammer. A n g ~ i r .Chrni. 1991.
103, 193; Angex-. Chem. Ini. Ed. Engl. 1991, 30. 187.
121 H . Burger, N. Niepel, G. Pawelke. H. Oberhammer. J. Mol. Slruci. 1979. 54,
[3] M. Gaensslen. U . Gross, H . Oberhammer, S. Rudiger. Angeu. Chein. 1992.
104, 1525; Angew. Chem. Int. Ed. Engl. 1992. 31. 1467.
141 L. S. Bartell. H . K. Higginbotham, Inorg. Chon. 1965, 9. 1346.
[S] R. L. Kirchmeier, J. M. Shreeve, R. D. Verma. Coord. Chwn. Rev. 1992. I / ? ,
169. and references therein.
[6] G. Sarwar, N. R. Patel, Y. Y. Zheng. E. 0. John, R. L. Kirchmeier. J. M.
Shreeve. h r g . Chirn. Acta 1992. 198-200. 527
171 The G E D intensities were recorded with a gas diffractograph KD-G2 at camera distances of 25 and 50 cm and with a n accelerating voltage of about 60 kV.
The temperature of the sample reservoir was -26'C. that of the nozzle 15 C.
The photographic plates were evaluated according to standard methods (H.
Oberhammer. W. Gombler, H. Willner. J. Mol. Strurr. 1981, 70.273). Molecu' ( s = (4n/E.)sinO/2.
lar scattering intensities in the s-ranges 2- 18 and 8-35
1 = electron wavelength. 0 = scattering angle) were used for the structure determination.
[8] R. C. Dohbie, H. J. Emeleus. J. C h m . Soc. A 1966. 933.
[9] G. Sarwar. R. L. Kirchmeier, J. M. Shreeve, Inorg. Cbrm. 1989, 28. 3345
101 M. G. Barlow, K . W. Cheung, J. Fhmrine Cheni. 1977. 10. 191.
111 M. Veith. G. Schlemmer. 2. Anorr. ANg. Chem. 1982. 494. 7.
121 M. Veith. Actn C'rwfa/[ogr. Seci. B 1975, 31. 678.
Q VCH VerlugsgeseIlxhuJt nihH, D-6!245/W&hrim, 1995
( g h asp)
W, asp)
Scheme 1. Proposed structures of the semimet forms of hemerythrin. his =
histidine, glu = L-glutamic acid. asp = L-aspartic acid.
Latour, Dr. W. Moneta. Dr. M. Bardet, E. Bernard, N . Debaecker
CEA/Departement de Recherche Fondamentale sur la Matiere Condensee
Laboratoire SESAMKC. Centre d'Etudes de Grenoble
F-38054 Grenoble Cedex 9 (France)
Telefax: Int. code + 76 88 50 90
Dr. W. Kanda
Department of Chemistry Wakayama University (Japan)
Dr. J. Laugier
Departement de Recherche Fondamentale sur la Matiire Condensee
Laboratoire SP2M:S. Ccntre d'Etudes de Grenoble (France)
Dr. A. Bousseksou
Laboratoire de Chimie de Coordination du CNRS, Toulouse Cedex (France)
Dr. S. Chardon-Noblat
Laboratoire d'Electrochimie Organique et de Photochimie Redox
Universite Joseph Fourier. Grenoble Cedex (France)
This research w i n supported by the Centre National de la Recherche Scientifique (URA 1194). Support from the Japanese Ministry of Education. Science
and Culture (grant to W K.) is gratefully acknowledged.
[*] Dr. J:M.
/O \
[hisg] Fell1
Fell [his2]
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