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BaYbSi4N7ЧUnexpected Structural Possibilities in Nitridosilicates.

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fixed contributors in the last stage of refinement (b',\" = 0.08 A2). During the
refinement the C -C bond distances within the disordered butyl group and
if-hexane molecules were constrained to be 1.54(1) A. For 5086 unique observed rellections [ I > 2u(1)]of a total of 11 208 collected at T = 173 K on a
Rigaku AFC6S diffractometer (6 20 > 140 ) and corrected for absorption. R is 0.073 (wR2 = 0.178). All calculations were carried out on an IBM
PSZ'80 Personal Computer and an ENCORE E91 computer. Crystallographic data (excluding structure factors) for the structure reported in this
paper have heen deposited with the Cambridge Crystallographic Data Centre.
a s supplementoi-y publication no. CCDC-179-62. Copies of the data can be
obtained free of charge on application to the Director. CCDC, 12 Union
Roiid. Camhridge CBZ 1EZ ( U K ) (Fax: Int. code +(1223)336-033: e-mail:
techedw chciiicrys.cam.ac.uk)
[12] B. Cheng. F C'ukiernik, P. H. Fries. JLC. Marchon, W. R. Scheidt. Inorg.
C'Iriw7. 199s. 34. 4627.
[I31 Work in p r o s r e s
1141 a ) R T. Stihrmy. S M . Gorun. Angew. Clrern. 1990. 102, 1195 - 1 197; Angeii..
Clrmr / / i f . E d Engl. 1990. 2Y. 1156 - 1158. b) S. Pal. M . K. Chan, W. H. Armstrong. J. A i m C h n r . Sor.. 1992, 114, 6398; c) K. Wieghdrdt. K. U. Bossek. B.
Nuber. .[. W e i s J. Bonvoisin, M. Corbella, S. E. Vitols. J. J. Girerd, ]hid 1988.
110. 7398: d ) H S. Maslen. N. T. Waters, J Clwni. Soc. Clwni. Coninnin. 1973,
760 761. e ) N. Kitajima, U. P. Singh. H. Amagai. M. Osawa. Y. Moro-oka, J
Ani. Clriwi. S01, 1991, 113. 7757.
1151 a ) A. Niemann. K. U. Bossek. K. Wieghardt, C . Butzlaff, A. X. TrdutWein, 9 .
Nuher. ,411giw.C'/rwir. 1992. 104. 345-347: A n g m Chern. In/. Ed. Engl. 1992.
31. 31 1 31 3. h) M . J. Baldwin, T. L. Stemmler. P. Riggs-Gelasco, M. L. Kirk.
J. E. Penner-Hann. V. L. Pecoraro. J Am. Cl7ern. Soc. 1994.116.11349; c) E. J
Larson. P. 1. Riggs. J. E. Penner-Hahn, V. L. Pecoraro. J Clirm. So(. Cl7ern.
Ciininrini. 1992. 107. d ) K S. Hagen. T. D. Westmoreland, M. J. Scott. W. H
Armstrong. J. Am. Climr. Socc 1989, 111, 1907.
silicon dioxide, in which the molar ratio of tetrahedral centers to
bridging atoms is Si:O = 1 :2. All bridging atoms (Or']) are
bonded to two Si atoms. In nitridosilicates built up from the
SIN, tetrahedra, bridging atoms (NI3]) were found for molar
ratio of Si:N > 1 :2 for the first time. These bridging atoms each
connect three silicon atoms (for instance 2-[(Si~1N~21Nf31)9-]
and ~ [ ( S i ~ 1 N ~ * 1 N i 3 1 ) 4 - ] ) .
Accordingly, nitridosilicates extend the structural possibilities of silicates and lead with a molar ratio Si : N > 1 :2 to higher
condensed network structures, for which there are no analogues
in the oxosilicates. The maximum cross linking is reached in
Si3N,,rS] in which according to :[Siy1Ni3]] all nitrogen atoms
(NC3])are connected to three Si atoms.
In the Si-N networks we have examined to date, no nitrogen
atoms simultaneously connected to four Si tetrahedral centers
(NI4]) were observed. In condensed tetrahedral structures such
a structure motif is only expected to occur when the molar ratio
of tetrahedral centers T to bridging atoms X lies in the range of
1.0>T:X>0.75. In the case of nitridosilicates(rv), this would
require partial cationic Si-N structures, which have not been
observed so far.r61 Herein we report on BaYbSi,N,, the first
compound in which one nitrogen atom connects four silicon
atoms (cf. Scheme 1).
I
I
- N-
BaYbSi,N,-Unexpected
in Nitridosilicates**
-
+
M,[Si,N$
HF-furnace
I650 C
t
3M' 6Si(NH)?
- + M;[Si,,N,,]
ti F-furnace
M' = Ce. PI-
+ N, + 5H,
+
(a)
NZ + 6 H ,
ity of varying the metals and the fact that preparative amounts
of nitridosilicates are accessible as coarse crystalline and singlephase products in short reaction
SiO, and SiN, tetrahedra are characteristic structural elements in 0x0- and nitridosilicates, respectively. These tetrahedra
are connected through corner-sharing to give network structures. I n oxosilicates a maximum cross linkage is reached in
[*] Prof Dr. W. Schnick. Dip1 -Chem H. Huppertz
Lahoratorium lur Anorgitnische Chemie der Universitit
D-95440 Bayi-cuth (Germany)
Fax Int code +(921)55-2788
e-mail. ~ o l f ~ i i i g . \ c h n i c k uni-bdyreuth.de
iif
[**I
This work \+;IS supported by the Fonds der Chemischen lndustrie and
the Deutschi. Forschungsgemeinschaft (Schwerpunktprogramm "Nitridobriicken". project SCHN 377.'7-1 and 2. and the Gottfried Wilhelm Leibniz
program)
Angi'ii.. C ' l i m r .
/if/.
Ed. Eiigl. 1996. 35, No. 17
N"
N"
Recently we developed a novel synthetic approach to ternary
nitridosilicates by reacting alkaline earth or rare earth metals
with silicon diimide in a specially developed high-frequency
( H F ) furnace." -31 These reactions may be interpreted as the
dissolution of an electropositive metal in a nitrido-analogous,
polymeric acid accompanied by the evolution of hydrogen [Eqs.
(a) and (b)]. A specific advantage of this method is the possibil2 M + 5SI(NH)?
M = Ca. Sr. Ba
I
Nl4i
Scheme 1. In nitridosilicates, nitrogen atoms covalently connect two, three, o r four
Si tetrahedral centers.
Dedicuted t(i Professor Huns Ceorg von Schnering
on tho ocwsion of' his 65th birihduy
c
/ N\
Structural Possibilities
Hubert Huppertz and Wolfgang Schnick*
IS00 1650
-N-
The new nitridosilicate BaYbSi,N, was synthesized by reacting stoichiometric
of Ba and Yb metal with silicon
diimide Si(NH), in a H F furnace"] under nitrogen atmosphere
[Eq. (c)]. This process leads to the formation of BaYbSi,N, as
Ba
+ Yb + 4 S i ( N H ) ,
900 1650 C.
__--
185 BaYbSl
HF-furndce
4
7
+, , N 2 + 4 H ,
(4
a single-phase,"' coarse crystalline, colorless solid. Similar to all
the other nitridosilicates we have synthesized so far, BaYbSi,N,
is stable up to 1600 "C and resistant to hot acids and alkalines.
According to the X-ray structure determination on single
crystals,[g1BaYbSi,N, contains a network structure of cornersharing SIN, tetrahedra ~[(Sii41Nb"1N141)s-]).Although a
stoichiometric ratio of Si:N = 4:7 should lead to
2 [ ( S i ~ 1 N ~ z 1 N ~ 3 1 ) sno
- ] , Nf31
atoms were found. Instead,
there is a corresponding number of
bridges, which connect four Si tetrahedral centers.
As expected the bond lengths to
the
atoms in BaYbSi,N,
are significantly longer (Si-N:
188-196 pm) than those to
the NIZ1 atoms (Si-N: 170172 pm) .
Fig. 1 . Four SIN, tetrahedra are
The Si-N network structure
connected through a common niin BaYbSi,N, is built up from
trogen atom t~ give a "(SiNdJ
starlike IN(SiN,),I
building
building block. The entire network
blocks (Fig. 1). By connecting
these groups through common
8.:. VCH ~ i - l ~ r ~ s g e . s e N . ~mbH,
c l i u / ~0-69451 Weinherm,1YY6
structure of BaYhSi,N, is built up
by these starlike-shaped building
blocks.
$ 15.00
M7/1~0X33/96/3517-/9~3
+ .30
1983
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[9] BaYbSi,N,: P6,nic, u = 603.07(2), c = 981.98(4) pm, Z = 2. Siemens P4 dif-
fractometer, Mo,, radiation. graphite monochromator, F(000) = 462.0,
p(MoK,) = 22.07 mm-', w scan. 11456 measured reflections in the range
2' 1 2 0 5 9 5 " . 1144 unique reflections with F:>Oa(F:), empirical absorption
correction ($ scans), R,,, = 0.0728. the crystal structure was solved by direct
methods (SHELXTL-Plus, Vers. 5.03) and anisotropically refined by a leastsquares procedure against F 2 with all data, 32 refined parameters.
R1 = 0.0210. wR2 = 0.0475. G O F = 1.06. The absolute structure was determined. Flack parameter x = 0.151(8). Further details of the crystal structure
investigation may be obtained from the Fachinformationszentrum Karlsruhe.
D-76344 Eggenstein-Leopoldshafen (Germany), on quoting the depository
number CSD-405194.
(lo] W. H. Baur, Crwullugr. Raiz. 1987. 1. 59.
[ l l ] Indeed there are OI3' connections in stishovite according to i[Si'"!'']
but at
the same time the coordination number of the Si atoms in this high-pressure
modification is raised from four to six. Also compare: F. Liebau. Structural
Chemistry o/ Silicum, Springer, Berlin, 1985.
Fig. 2. Crystal structure of BaYbSi,N,. The SIN, tetrahedra are shown as closed
polyhedra, the Ba2' ions as grey and the Yb3+ ions as black spheres.
N atoms a stacking variant of the wurtzite-analogous aluminum
nitride structure type is formed (Fig. 2). Systematic elimination
of tetrahedra from this arrangement along [loo], leads to the
formation of sechser ring channels, in which the Ba2+ and Yb3+
are positioned. The Ba2+ and Yb3+ metal ions show anticuboctahedral and octahedral coordination, respectively, by nitrogen
atoms of the Si,N, network. The Ba-N and Y b - N contact
distances (298-305 pm and 229-231 pm) approximately correspond to the sum of the ionic radii.['']
BaYbSi,N, provides the first example of N14] connections
between four Si tetrahedral centers. This extends the structural
possibilities in nitridosilicates by a surprising dimension. Thoroughly cross-linked Si -N network structures, particularly in
highly condensed nitridosilicates (Si : N > 1 :2), should be possible for which attractive material properties (high mechanical,
thermal, and chemical stability) can be predicted. While the
structural chemistry of oxosilicates is limited to terminal oxygen
atoms and simple bridging Oc2l atoms, the nitridosilicates show
NC31, and N[41conextended structural possibilities with "'I,
nections of Si tetrahedral centers. These variations have not as
yet been found in oxosilicates and may not be possible with
silicon and oxygen." 'I
Received May 2, 1996 [Z90881E]
German version ~ n g e , ,Chrm 1996, 108, 211 5-2116
Keywords: high-temperature synthesis . network Structures
nitridosilicates silicates . structure elucidation
-
.
[I] T. Schlieper, W. Schnick. Z . Anorg. Allg. Chem. 1995, 621. 1037.
(21 T. Schlieper, W Milius. W. Schnick, 2. Anorg. ANg. Chcm. 1995, 62/.
1380.
[3] T Schlieper, W. Schnick, Z . Anorg. AIlg. Cl7rm. 1995. 621, 1535.
[4] Meanwhile some rare earth nitridosilicates Ln,Si,N,, (Ln = La, Ce. Pr. Nd)
and LnSi,N, (Ln = Ce. Pr, Nd) are synthesized by reaction of the silicides
LnSi, and "LnSi," with N,: M. Woike. W. Jeitschko. Inorg. C/7e?n. 1995.
34. 5105. A problem with this procedure is the avoidance of metallic impurities.
[ S ] W. Schnick, Angew. Chem. 1993, 105. 846; A n g w . Chcni. Int. Ed. Engl. 1993,
32, 806.
[6] Well-known examples for NI4' connections In nitrides are BN and AIN.
[?I In a typical charge 1 mmol of the metals were thoroughly mixed with Si(NH),
under inert gas atmosphere in a glove box and transferred in a tungsten crucible
into the H F reactor. Under nitrogen atmosphere the reaction mixture was
slowly heated up to 1650°C. maintained at that temperature for 2 h, and then
cooled down to 1400.C within 15 h. At the end of the reaction the product was
quenched to room temperature.
[8] The composition of BaYbSi,N, was confirmed to be in agreement with the
structure analysis by energy dispersive X-ray microanalysis (Ba,Yb,Si) and
quantitative determination by Pascher (Remagen). The absence of hydrogen
(NH) was checked by IR spectroscopy.
1984
$3
VCH Vei-lag.~ge.~~~llschuJt
mbH, 0.69451 Weinheiin. 1996
LUCY-A Program for Structure Elucidation
from NMR Correlation Experiments**
Christoph Steinbeck*
With the introduction of gradient-supported N M R spectroscopy, the time and effort required to record two-dimensional C,H correlations has now reached such a level that they can
be considered as routine applications. Thus, long-range C,H
correlation (HMBC"]), long appreciated as a very valuable tool
for determining the constitution, is also widely available. The
idea of using this spectroscopic information for computer-supported, automated structure elucidation was close at hand. Although Lindley et a1.['1 demonstrated the use of 2D information
in a computer program for generating structures as early as
1983, it was not until the beginning of the 1990s that useful
attempts in CASE systems (computer assisted structure elucidation) were published.
We now introduce the program LUCY with which one can
determine the constitution of an unknown compound based on
the results of an HMBC experiment by using a standard personal computer. The information required for this task is the empirical formula, the broadband-decoupled 3C, the DEPT-90, the
DEPT-1357 and the C,H cosy spectra (HMQC,[31HSQC'4').
The H,H COSY diagram IS optional, but useful. Here 3 J.....
,,
are used exc'usively.^Eva'uation
Of the DEPT spectrum and the C,H COSY diagram permits the user to exclude
geminal coupling in the H,H COSY spectrum for diastereotopic
protons of CH, groups. Furthermore, statements can be made
as to whether or not a C atom is attached to a heteroatom, as
evidenced by its chemical shift o r its C,H coupling constants.
The authors of programs that use ID NMR, mass, and I R
spectra for structure elucidation have also reported recently on
the use of HMBC data.15,61However, new modules were always
added to existing systems. LUCY, on the other hand, has been
specifically designed to make use of HMBC data.
Our process uses these data to generate larger fragments of
the carbon skeleton already in the first step of the structure
elucidation. The CH, (x = 0-3) fragments and the heteroatoms
obtained from the DEPT experiments are combined in a recur[*] Dr. C Steinbeck
Department of Chemistry, Tufts University
62 Talbot Avenue. Medford. MA 02155 (USA)
Fax: Int. code +(617) 627-3443
e-mail : stein@microvirus.chem. t ufts-edu
I**] M y particular gratitude goes to Prof. Dr. E. Breitmaier for the original idea and
the stimulation to carry out this project.
0570-0833,96i3517-1984 S 15.00+ .25!0
Angew. Chern. In!. Ed. Engl 1996. 35, No. 17
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