вход по аккаунту


Bromides of Rare Earth Metal Boride CarbidesЧA System of Building Blocks.

код для вставкиСкачать
Though no detailed miscibility studies have been carried out.
preliminary contact preparations suggest that the smectic A
phases of compounds 1 and 3 and those of the compounds 3 and
8 are completely miscible.
Intermolecular hydrogen bonding is also found in carboxylic
acids that are known to form dimers. In Figure 6 the carboxylic
acid 10 is compared with its acid chloride 9 and the methyl
carboxyliite 4. Again the carboxylic acid (the compound that
111 H. Ringsdorf, B. Schlarb. J. Venzmer. 4ngm C'lwni. 1988. 100. 117.- 162;
Angrit.. C / i m . Int. Ed. Engl. 1988, 27. 113 15X.
[2] D. Joachimi, C. Tschierske. H. Miiller. J. H . Wendorff. L Schiieider. R. Kleppinger. 4wgei1,. Chrm. 1993, 1/15, 1205 1207: Anjirii. ~ ' / i ~ w z/ n. / . Ed. Engl.
1993.32, 1165 1367.
[3] F. Hentrich. C . Tschierske. S. Diele, C. Sauet-. J. Marcr ( ' / i w ~1994.
4. 15471558.
141 Compound 3 was obtained by phasc-transfcr-cat;ilyLe~l ethcrilication o f 2'bromoinethyl-4.4-d1dccyloxyterphen~I 151 with 4-liqdroxytiicthq1-2,I-dimethyl-1.3-dioxolane ( 5 0 % NaOH, cat. Bu,NHSO,. 100 C. 2 h) followed by
acid-ca talyred hydrolysis (pyridiniuin tolueiie-4-sull~~n~1tc
(Py TosOH.
MeOH)) of the isopropylidene protective group (yield 3 0 " 0 ) . For the aynlhcsis
of 2 n-propatiol was used.
(51 J. Aiidersch. S. Diele. P. Gdring, L A . Schrbter, c'. Tschienke. 1. C/irn?.Sw.
Chiwii. Ciininiun. 1995, 107-108.
[6] W. Weissflog, D. Demus. Crj.\l. RCL Teckriol. 1984, I Y . i S 64.
ynthesised by Pd-catalyzed cross-coupiing of nieihyl2.5-dibromobcnioate with two equiv. 4-decyloxyphenyl boi-onic acid [S] (yield
93"/0). Saponification gave the carboxylic acid 10. which wab transformed into
the acid chloride 9 by treatment with oxalyl chloride ( R A d a m . L. H. Ulich,
J. Am. Chrm Soc. 1920, 42,599). Compounds 6 8 wcrc obtained by aminolqsis of crude compound 9 with excess 2-aniinoethanol. ?.3-dihydroxypropylamine. and I,-glucamine. respectively (yields 76-91 % )
[8] Rcviews: B. Pfannemiiller, Sturch 1988. 40. 476-480. G A. Jeffrey. . k c .
Cheni. Rev. 1986, I Y . 168: G. A. Jeffrey, L . M Wingert. L i q C,:l,\i 1992. 12.
179- 202.
[Y] W Weissflog, D . Demus. S. Diele, P. Nitschke, W. Wedlei-. Liq CS.1 \I. 1989.5,
11 1 123: A. C. Griffin, S. F Thames. M S. Ronner. M r r / C n .sf. Liq. Crr.vr.
1977. 34. I35 139.
I101 M. C. Carey. D. M. Small. Arch. Inrern. Mcd. 1972, 110, 506, 7319-7320:
T. M . Stein, S. H. Gellman, J. .4n7 Cliern. S i x 1992. 11.1. 3943 3950: D G .
Barrett. S. H. Gcllman, ?hid 1993, 115, 9343-9344.
68 73
4 X
(40j 5 8
Fig. 6. ('oinp;ii-imi of the phase-transition temperatures T' 'C of 2,5-bia(4-decyloxyphenyl)btii7uic acid (LO) and the corresponding acid chloride 9 and methyl
bcn7o:ite 4 (determined by po1;irization microscopy).
can form hydrogen bonding) displays the higher mesophase
stability. The recently described laterally connected Siamese
twin m e s o g e n ~ [ ~and
l also the covalent. laterally connected
trimesogens151may be looked upon as examples for covalent,
laterally fixed molecules. These compounds also display higher
mesophase stabilities compared with structurally related
calaniitic single mesogens.
If one coinpares the compounds 1-10 it is obvious that lateral fixing of calamitic molecules by hydrogen bonding also increases the structural order, which stabilizes the layered smectic
A phase with respect to the nematic phase (N) of the nonamphiphilic compounds. These new compounds also differ in this
respect from laterally alkyl substituted calamitic compounds
which usually favor the nematic phase."]
In summary, we have shown that there is an ambivalent influence of hydrophilic lateral substituents. Their steric requirements tend to separate the rigid cores from each other. which
decreases the molecular order and should thus give rise to a
significant mesophase destabilization. However, attractive
forces between these substituents-such as hydrogen bonding-strongly fix the individual molecules to each other. If these attractive forces exceed the repulsive forces, the longitudinal order
of the molecules is increased, and smectic liquid-crystalline
phases are stabilized. In this way, lateral fixing of calamitic
mesogens by hydrogen bonding is a new approach to smectic
materials with broad mesomorphic ranges.
Furthermore. these new amphiphilic diol derivatives resemble
an amphiphilic architecture which closely resembles that of the
naturally occurring cholic acid salts and some peptides;["] both
consist of rigid stuctures with surfaces of different polarity.
Thc biomimetic potential of these facial amphiphiles makes it
exciting to study their ability to form other self-organizing
supramolecular systems, such as lyotrophic mesophases, micelles. and thin films. These investigations are under way.
Bromides of Rare Earth Metal Boride Carbides
-A System of Building Blocks**
Hansjiirgen Mattausch and Arndt Simon*
Onlya few metal-rich rare earth metal halides MX,, with n I 2
are known namely MZX3[1-31and LaLL4IOther compounds
described as binary phases and accessible in low yields, however,
finally turned out to be "stabilized" by interstitial atoms.r51Due
to the electropositive nature of the rare earth metals these
interstitial atoms have anionic character.
Addition of H, C, N, 0 in experiments to reduce rare earth
trihalides led to numerous new ternary coinpounds, whose
structures could be systematized in terms of a condensation of
characteristic building units[,]: M,O tetrahedra, M6N, double
tetrahedra, M,H tetrahedra, and M,H, octahedra as well as
M,C and M,C, octahedra were repeatedly found. These units
can be combined as was demonstrated recently with compounds
containing the interstitial atoms C/H.[" C/O.['. and C!"'",
simultaneously. Here we report new phases with B/C which
particularly well illustrate this building block principle.
Gd,Br,C,B, La,Br,C,B, and Ce,Br,C,B, are the first members of a presumably large class of compounds. They can be
[*] Prof. Dr. A. Simon. Dr. H. Mattauach
Max-Planck-Inatitut fur Festkorperforschung
Heisenbergstrdsse I, D-70569 Stuttgart (German>)
Telefax: Int code + (713)689-1642
The help of C. Hochrathner, R. Eger. R Pdttgen, and N Weishaupt in d r a w
ing, preparation, X-ray diffraction and electrical measuruiiient?. respectively. I S
gratefully acknowledged.
obtained as black needles or bars by heating stoichiometric
amounts of MBr,, M, C, and B for several days.['21
Figure 1 shows the building blocks that occur in the structures of Gd,Br,C,B. La,Br,C,B, and Ce,Br,C,B,.['31 In these
building blocks discrete C atoms are always octahedrnlly coordinated by M atoms, and B-C units are formed with a trigonal
prism around the B atoms connected to a tetragonal pyramid
around C. The structure of Gd,Br,C,B contains molecular BC units with (1, -c = 156 pm and discrete C atoms (Fig. 1 a, 1 b).
Fig. 2. Projection of the structure of Gd,Br,C,B along [OIO]. Units (1 a ) and (1 b)
(see Fig. I ) are condensed into layers with Br atoms (large circlcs) arranged between
the layers. To illustratc the environment of the B-C unit the prisins and the tetragonal pyramids are drawn separately on the lower left-hand side. The unit cell is
Fig. 1. Monomeric units in the structures of Gd,Br,C,B, La,Br,C,B, and
Ce,Br,C,B,. B: small filled circles, C . small open circles. M : large circles.
a) Octahedral coordination of discrete C atonis by M atoms; b) B C unit with the
B atom residing in a trigonal prism and the C atom in a tetragonal pyramid,
c ) Condensation of two B-C (cf. Fig 1 b) units to form a C-B-B-C group. d ) C-B-C
unit with the B atom residing in a trigonal prism around and both C atoms in
tetragonal pyramids
In the structure of Ce,Br,C,B, single C atoms occur together
with C-B-B-C groups (Fig. 1 a, 1 c) which form by condensation
of two units of the building blocks shown in Figure 1 b through
the prism faces. The distances in the B,C, group are
d c - B =153pm and d,-B = 1 6 4 p m ; the C-B-B angle is 139".
The structure of La,Br,C,B contains exclusively BC, units
characterized by a d, - c distance of 149 pm and C-B-C angle
of 148".
The units shown in Figure 1 are condensed in layers according to Figures 2-4.[15] The space between the layers is filled by
Br atoms which belong to a single layer in Ce,Br,C,B, and
but some of them interconnect layers in
Gd,Br,C,B. In the chosen projection of the structure of
Gd,Br,C,B the layers are composed of alternating double
chains of the building blocks shown in Figures 1 a and 1 b. The
octahedra and prisms are condensed through edges and square
faces, respectively. The expansion of these faces leads to long
distances between neighboring B-C units (d, - B = 208 pm). In
the chosen projection for Ce,Br,C,B, and La,Br,C2B the
prisms condensed through their triangular faces are clearly visible. The resulting chains of prisms alternate with chains of octahedra in the case of Ce,Br,C,B, and are directly coupled in
La,Br,C,B. The interatomic distances between adjacent B-C
groups exceed 380 pm.
The described discrete B-C, C-B-B-C, and C-B-C units are
characteristic fragments of the structures of boride carbides of
transition metals, lanthanoids, and actinoids. For example,
the B,C, units characteristic for Ce,Br,C,B, are linked to
give chains in the structures of UBC[161 and ThBC"']
by the formation of B-B bonds, and the structure of
Th,B,C, ( = Th,C(BC),)"81 contains C-B-B-C units and discrete C atoms. The incorporation of halogen atoms, leads to a
breakdown of such three-dimensional networks into layers. The
Fig. 3 . Projection of the structure of Ce,Br,C,B, along [OIO]. Alternating strings of
units ( 1 a) and (1 c) (see Fig. I ) are condensed into layers which are linked through
Br atoms. The unit cell is outlined.
Fig. 4. Projection of the structure of La,Br,C,B along [OIO]. Slightly corrugated
layers, parallel to (001) are composed of unit (1 d ) (see Fig. 1 ) and separated by Br
atoms. The unit cell is outlined.
fragmentation gives access to a local description of the complex
bonding situation in carbide borides.
The structural units found in Gd,Br,C,B can be discussed
within the Zintl-Klemm concept as (Gd3+),(Br-),(C4-)(CB5 -).
The B-C distance of 155 pm is in agreement with that calculated for the '.methyl borane"-derived BC5- anion.""] However,
it is clear from the low electrical resistivity (van der Pauw
of this compound, p = 8 mQcm in the range between 50 and 300 K , that the treatment of chemical bonding in
terms of localized electrons is only applicable in certain cases. In
fact. the distanced, - D = 208 pm corresponds to a Pauling bond
order of0.22.[l9]The existence of weak bonds between B atoms
of adjacent B-C units is verified by COOP (COOP = crystal
orbital overlap population) analysis on the basis of extended
Hiickel calculations.r2 Although the "intermolecular" distances between B,C, units in Ce,Br,C,B, are sufficiently large
to exclude bonding interactions, the question remains, whether
B,C; ' anions can be formulated or whether electrons are partially delocalized in bands exhibiting metal-metal bonding
character. For La,Br,C,B the anionic species B C i - , which is
isoelectronic with SO,, can be derived according to the ZintlKlemm concept (La3+),(Br-),(BC;-). The BC, unit, however,
is less bent than SO, (KO-S-0 =119", KC-B-C =148"). In
Sc,BC, the BC, unit is even linear. Evidently, in agreement with
the metallic conductivity[221and the results of band structure
calculations~23'one electron per formula unit is delocalized in
bands with M -M bonding character in accordance with the
formulation (Sc3+),(BCi-)e-. La,Br,C,B also shows metallic
conductivity so that a partial delocalization of electrons in
bands with La character is also expected in this metallic phase.
I n the structures of rare earth metal carbide halides zero-,
one- and two-dimensional fragments of the three-dimensional
carbide structures are realized. We aim to develop a similar
structural chemistry with carbide borides.
Received: April 4. 1995 [Z 7864 IE]
Get-man version. Angel\ . C i i ~ ~1995,
i . 107. 1164 1766
Keywords: boron compounds. bromides. carbides. lanthanoids
. solid-state structures
0.4997(2); ~ ( 2 ) 0.?760(2).
1.4. 0.2527(2): B ( Ij . o.?iix(2). 3.4. o.x757(3).
R , = 0.027, I( R, = 0.04X (all 2719 independent rellccttons). Gd,Br,C,B:
P2t.'ni. u=Y54.7(4). h = 3 6 9 . 3 ( 1 ) . i ' = l 2 3 4 , 5 ( 3 ) p m . / / = 1 0 6 . 6 8 ( l ) . C;d(l):
0.6266(1), 1.4. 0.4596(1): Gd(2): 0.4565(1). 1 4 . 0.805X(I): ( 3 4 3 ) . 0.2813(1).
1:4. 0.2664(1); Gd(4): 0.7594(1), 1:4. 00207(1), f i r ( [ ) : 09686(1). 1 9 .
0.8678(1): Br(2): 0.1358(1). 1.4, 0.4443(1): Br(3): 0.7136(1). 3'4. 0 7238(1):
C(1). 0.5491(9). 1.4, 0.6330(2); C ( 2 ) : 0.3704(10). I 4. 0.104Y(6): B(1):
0.4647(12). 3:4. 0.0217(8). R , = 0.053. WR, = 0.113 (all 2775 independent reflections). Ce,Br,C,B,: P-7.1ii:LI = X60.2CZ). h = 382.911). i = 1022.0(2) pm,
/i= 112.53(3) . Ce(l): 0.2867(1). 0, 0.4836(1).Ce(2): 0 M 3 ? ( I ) . .:1: 0.1633(1):
Ce(3): 0.3721[1). 1'2. 02223(1): Br(1). 0. 1'1. 1 2 . Br(1). 0.6505(1). 0.
O.l868(I):C(I)- 1 . 2 . 1 ' 2 . l,2:C(2):0.1673(3),0.0.126411):B(1):00928(4),0.
0.0650(3). R , = 0.027, ivR2 = 0.049 (all 2410 independent reflections). Thc
correct assignment of B and C shows up clearl) in the R value\ and the displacement parameters. Further details of the crystal structtire inwstlgations may
he obtained from the Fachiiiformations7eiitruni Karlst-uhe. D-76344 Eggenstein-Leopoldshafen (Germany. on quoting thc depovtor) numbers CSD401744 (Ce,Br,C,B,).
CSD-401745 (Gd,Br,C,B). and CSD-401746
(La Br, C , B)
[I41 G. M. Sheldrick. SHELXTL-PLC'S, Giirringwr, 1992 iind SI1EL.Y-93.
Giittingcn. 1993
11 51 C. K. Johnson. ORTEP-ORNL-3794. Oak Ridge Nat. L;ih.. Oak Ridge. 1971.
1161 P. Rogl. B. Rupp. I . Felner. I' Fischer, J Si~liilSrule(hm?r. 1993. 110. 377.
I171 P. Reel. J. N u d M u l i , r . 1978. 73. 298.
[IX] P. Rogl. J. nlud Muto.. 1979. 7Y. 154.
[I91 L. Pauling, Die, ,Varur ilw clri~nii.~c/i~w
Bindung. Verlag Chernie. Wetnheirn. 1973.
[20] L. J. van der Pauw, P/iiIips Rm Rep. 1958. 13, 1 .
121] J. Kiihler. PC- C+r.srofi P ~ J WE~. ~ / e n d ~ , d - H i i ~ k e / - P r ~ ~ , ~unpublished,
r u r n ~ i i ~ ~ i1993.
[22] J. Bauer, M. Potel. P.Gougeon. J. Padiou, H. Nod. Pro<.Y / h In1 Conf. 0 1 1 .%/id
of ~ U J l . \ l ~ l O fE/enienr.\,
ROj U / SiJc;<,Ij' Of C/tCWl~.\Irj, DdlOJi DIb'isioti, Oxford. 1988.
[23] J F. Halet. .I-Y. Saillard. J. Bauer. J, LL~<\-CUnlnl<JJl
M r , i 1990. 1.58. 239
A New Application of Capillary Zone Electrophoresis: Determination of Energy Barriers of
Configurationally Labile Chiral Compounds**
Gerald Weseloh, Christian Wolf, and
Wilfried A. Konig*
Various techniques may be applied in the investigation of
configurationally labile compounds. The racemates may be resolved into their enantiomers, and the energy barrier of enantiomerization investigated by chiroptical methods. Alternatives
avoiding enantiomeric enrichment or separation are dynamic
N M R spectroscopy, HPLC, or GC.[*'Kinetic parameters must,
however, be determined by computer simulation of the experimental data.
We describe a new procedure for the determination of energy
barriers of enantiomerization reactions based on capillary zone
electrophoresis (CZE) .I2] With this method enantiomerization
reactions may be investigated in the temperature range 25 ' C95'C by using small amounts of racemic samples, which are
typical for CZE. Subsequent computer simulation is unnecessary.
1, which is present as
its diamnionium dication in the buffer of pH 3.0, is excellently
resolved into its enantiomers
by the chiral additive heptakis(2,3,6- tri - O-methyl)-P-cyHzN
0 NHz 1
clodextrin in the electrophoretic buffer. Figure 1 shows sche-
D A . Lokkcn. J. 0 Corbett. Ittorg. C/icm. 1973. 12. 556.
A . Simon, N. Ilolzer. H . Mattausch, Z. A ~ i ~ r A&.
g . Chmi. 1979. 456. 207.
H . Mnttaujch. .I. B. Hendricks. R. Eger, J. D. Corbett, A. Simon. Itiorg. CAiw
1980. I Y . 1128
.I. I 1 Martiti. J. 1). Corbett. Angeii ( % P J ~ . 1995, 107. 234, A n p t w Chern. Inr.
Ei/ Enxi. 1995. 34. 2.73.
A . Simon. 4 i i g r i i . Clicwi. 1981. Y3. 23; Ang'i'. Clretn I n l . E d Eny/. 1981. -70.
A . Simon. H. Mattausch. G . J. Miller, W, Bauhofer. R. K. Krenier. H i i ~ i i l h o ~ X
on rlw P / J ~ . . s\ I[ ci r i [ / ~ ' / i [ , J i i i . \ l i - io, / R a r r Eurr/r, Voi. I5 (Eds.: K.A. Gschneidner.
Jr. 1.. Eyrtng). Elsevier. Amsterdam. 1991. p. 191.
M. Ruck. A Simon. %. Anorg. , 4 / / ~ .Cltrnr. 1992. 617. 7.
G. M q e r . H . Mattfeld, K. Kraemer. 2. A~iorg.A/%. Chon. 1993. 6 1 Y . 13x4.
t l Miittausch. H. Borrmann. A Simon. 2. Nutur/or.\ch. B 1993. 48. 1x28.
H Mattau\ch. 14. Borrmann. R. Eger. R. K. Kremer. A. Simon. Z . Anorg.
,q//,q. <'/t<,Jll 1994. 62(!. 18x9.
l i . M a t t a u w h . 11. Horrinann. R. Eger. R. K. Kremer. A. Simon. Z. A'N~uI./ I J J Y / J . H. IYYS. SO. 931
Thc htarting materials ( - 2 g) were heated in Ta-containers welded under 1 atm
A r d n d p r w x t r d against oxidation by quartz glass ampoules (10 days at
1370 K Tor La,Br,CZB. 12days at 1320K for Gd,Br,C,B and 10days at
1470 K for Ce,>Br,C,B2)and quenched to room temperature. For the preparatioii :ind put i k i t i o n of the starting materiills compare ref. [lo].
Mc;iwrcmcnt of the single-crystal intensities on a four-circle diffrdctometer
(CAI14, E n i - d N o n i u \ ) . Ag,, radiation. Empirical absorption correction ($scan). Full inatrrx least-squares refinement on F 2 [14]. La,Br2C,B: P ~ J I I U :
if =153?.3(1).h = 397.3(1),~=1156.7(l)pm.La(l):0.3315(1),1.'4.0.7003(1):
L a ( ? ) : 0 1360(1 I , 1:4. 0.8775(1): La(3): 0.3411(1). 1'4, 0.0527(1); Br(1):
0.0270(1). 1 4.0.1151(1). Br(2): 0.0089(1).1:4,0.634X(I);C(l): 0.2682(2), 1'4.
Prof. Dr W. A. Kiinig. DipLChem. G. Weseloh, Dip1 -Chem. C Wolf
Institut fur Organische Chemie der Universitit
Martin-Luther-King-Platz 6. D-20146 Hamburg (Germ'iny)
Telefax: Int. code + (40)4123-2893
e-mail: doenneckro
C W. t h i n k s the Fonds der Chcmischen lndustrie for ii \cholarship.
Без категории
Размер файла
475 Кб
boride, block, metali, building, system, rare, carbidesчa, bromide, earth
Пожаловаться на содержимое документа