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BaNb7O9 a New Oxoniobate with Double Layers of Corner-Sharing Nb6 Octahedra.

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1. As a first approximation restrained MD-simulation in
vacuo is performed. To search a larger conformational space
it is recommended to use different starting structures and to
calculate also at higher temperatures using different force
constants for the restraints. In our experience M D simulation in vacuo without any restrictions yield structures which
disagree with the experimental data. For peptides it is advisable to reduce the vacuum effects by reducing the charge on
amide protons exposed to the solvent (information obtained
from the temperature gradients of the NMR chemical shift
of the amide protons) and by fixing the side chains in the
dominant rotamer population (information obtained from
homo- and heteronuclear coupling constant^).^^]
2. The structure thus obtained is used for restrained M D
simulation including the solvent. The solvent should not be
represented merely by a hypothetical dielectric constant but
should rather be included explicitly in the molecular dynamics.
3. An MD simulation in solution without restraints may
then follow. This calculation proves if the structure is stable
or moves to a structure quite different from the conformation obtained using experimental data.
In all of these calculations one must bear in mind that a
static picture as shown in Figure 1 is only a crude approximation of reality, because it is obtained from an average of
a constantly changing conformation (trajectory). In the case
discussed here the observed vacuum effects are significant
for the entire trajectory. M D simulations for small and polar
molecules should therefore always be performed including
connected by a common apex atom of the two Nb, octahedra. This structure represents the first step to building
chains, sheets, and, ultimately, the three-dimensional NbO
structure in which the octahedra share all apices with their
neighbors. In the meantime, the cluster condensation concept[*’ has been illustrated by many examples, especially
within certain reduced oxide systems, such as structures with
edge-sharing Mo, octahedrat3 51 and with corner-sharing
Nb, octahedra.16- We report here the new compound
BaNb,O, , which holds a special intermediate position in the
path to higher dimensionality in reduced oxoniobates, since
in it the first structural step towards the transition from twoto three-dimensional systems is attained.
Electron microscope investigations on the Ba-Nb-0 systernt9]have shown that a “phasoid”[lo,“ I exists containing
a large variety of different structural assemblies with cornersharing condensed Nb, octahedra, for example chains made
up of four units and double layers. It was therefore of interest to attempt to develop such structural variants in compounds of stoichiometric composition. After extensive
efforts the formation of BaNb,O, was achieved at temperaThe
tures above 1800 K by additional use of BaCI,
size of the crystals formed under these conditions were just
large enough (diameter < 0.01 mm) for a single-crystal
structure determination.[’ 31
The structure of BaNb,O, is made up of double layers of
corner-sharing Nb, octahedra of composition Nb,O, sandwiched between BaO layers (Fig. 1). The structure can be
Received: September 5, 1991 [Z4899 IE]
German version: Angew. Chem. 1992, 104,213
(11 H. Kessler, M. Gehrke, C . Griesinger, Angew. Chem. 1988, 100, 507-554;
Angew. Chem. Inr. Ed. Engl. 1988, 27, 490-536.
[2] W F. van Gunsteren, H. J. C. Berendensen, Angew. Chem. 1990, f02.10201055; Angew. Chem. Int. Ed. Engl. 1990, 29, 992-1023.
[3] G. D. Rose, L. G. Gierasch, J. A. Smith, Adv. Protein Chem. 1985. 37, 1109, and references therein.
[4] W. F. van Gunsteren, H. J. C. Berendsen, Groningen Molecular Simulation
(GROMOS) Library Manual, Biomos B.V., Nijenborgh 16, NL 9747 AG
Groningen. pp. 1-229.
[5] S. Itoh, H. Ohtaki, Z . Natnrforsch. A 1987, 42, 858-862.
[6] W. Feder, H. Creizler, H. D. Rudolf, V. Typke, 2. Narurjiorsrh. A 1969, 24,
[7] D. F. Mierke, H. Kessler, J. Am. Chem. Soc. 1991,113,9466-9470; calculations for molecules in DMSO have already been published: B. G. Rao.
U. C. Singh, ibid. 1990, i12, 3803-3811.
[XI I. L. Karle, J. L. Flippen-Anderson, R. Kishore, P. Balaram, Int. J. Pept.
Protein Res. 1989, 34, 37-41
[Y] H. Kessler, J. W Bats, C. Griesinger, S. Koll, M. Will, K. Wagner, J. Am.
Chem. SOC.1988,110, 1033-1049.
BaNb,O,, a New Oxoniobate with Double
Layers of Corner-Sharing Nb, Octahedra**
By Gunnar Svensson,* Jiirgen Kohler,* and Arndt Simon
We recently reported on the compound K,Al,Nb,,O,,
whose structure consists of two condensed Nb,O,, clusters
[*] Dr. G. Svensson[+], Dr. J. Kohler, Prof. Dr. A. Simon
Max-Planck-Institut fur Festkorperforschung
Heisenbergstrasse 1, D-W-7000 Stuttgart 80 (FRG)
[‘I Permanent address: Department of Inorganic Chemistry
Stockholm University
S-10691 Stockholm (Sweden)
We thank the Alexander-von-Humboldt Foundation for support (fellowship for G. s.)
0 VCH Verlagsgesellschafi mbH, W-6940 Weinheim,1992
Fig. 1. Projection of the crystal structure of BaNb,O, with its double layer of
corner-sharing Nb, octahedra (the further connection of the Nb atoms is indicated).
envisioned as “intergrowths” of BaO and NbO or perovskite
BaNbO, and NbO. The former description is simpler but
does not account for the interconnection of the BaO layers
with the NbO layers. In the latter description one can easily
understand the interrelations between BaNb,O,, BaNb,O,,
and Ba,Nb,O, which along with NbO and BaNbO, all be(n =
long to the homologous series BanNbn+3m03n+3m
number of perovskite layers, rn = number of NbO layers
with complete octahedra).
The Ba atoms in BaNb,O, are surrounded by a cuboctahedron of 12 0 atoms, as in the known Ba,g,Nb0,,t’41 and
the average Ba-0 distance of 292 pm is only slightly longer
than the respective B a - 0 distance of 289 pm in
Bao 95Nb03.The distance from the central Nb (1) atom to
the eight neighboring Nb (2) atoms is 298 pm and thus longer
than both the Nb(2)-Nb(2) and Nb(2)-Nb(3) distances
(297 pm and 290 pm respectively). These are all comparable
to the Nb-Nb distances found in NbO (297 pm). The N b - 0
distances are between 209 and 212 pm as in the other members of the homologous series.
Angew. Chem. Int. Ed. Engl. 31 (1992) No. 2
-1 2
Fig 2 a) Density of stdtes (DOS), b) COOP didgrdm for Nb-Nb interactions,
dnd c) COOP diagram for Nh-O interactions in BaNb.0,
According to the charge balance for the ionic borderline
case, 19 electrons occupy Nb-Nb bonding states (per
Nb,O, double-layer unit). Band-structure calculations (Extended-Huckel approximation,['51 parameters for Nb,",] Sr
parameters["] were used for Ba) lead to the results illustrated in Figure 2. The density of states (DOS) at the Fermi level
EF shows the compound to be metallic (Fig. 2a). As the
COOP (crystal orbital-overlap population) curves show, the
bands with Nb-Nb bonding character are nearly full
(Fig. 2b); this is at the cost of partial occupation of bands
with N b - 0 antibonding character (Fig. 2c). The N b - 0
bonding states lie at - 16 eV. The small band at - 14.8 eV is
of purely (nonbonding) 0 2p-character and typical for perovskitesl'sl as well as evident in the band structure of
Nb0.1191The occupation of all Nb-Nb bonding states and
partial occupation of N b - 0 antibonding states in BaNb,O,
reflects the situation found in isolated Nb,O,, clusters possessing the maximum of 16 valence electrons in Nb-Nb
bonding states.["] Usually one finds that the magic number
of 14 valence electrons[''- 231 will completely fill just the
purely bonding states. Likewise, in Nb0,['91 BaNb,O,, and
K,Al,Nb,,0,,['~241 not all of the Nb-Nb bonding states
are occupied, and strongly N b - 0 antibonding states are
found directly above the Fermi level. Further reduction of
the Nb,O, layer in BaNb,O,, for example through substitution of Ba by La, should not be possible, because this would
necessitate not only the occupation of Nb-Nb bonding but
also strongly N b - 0 antibonding states.
An entire series of structures with isolated Nb,O,, clusters
is now known.[2'-23'25-271The first step in the condensation of Nb, octahedra through shared corners in
K,Al,Nb, ,O,, [ I 1 has been mentioned already. Hypothetical
oligomers of the general composition Nb,,, ,O,,+, for n > 2
(n = number of octahedra) are still unknown; however, the
infinite chain of corner-sharing Nb, octahedra in BaNb,O,
was recently found.['] Quadruple chains of octahedral units
are obviously present in Ba4Nb17026[281
although a refinement of this crystal structure must still be performed. The
Nb, clusters are connected by four shared corners into single
layers in BaNb,O,, Ba,Nb,0,,[6] and Sr,Nb,0,[291. In the
structure of BaNb,O, presented here, the Nb, clusters are
connected by five shared corners into a cluster double-layer.
Certainly further intermediate stages between the two extremes of isolated Nb,O,, clusters on the one side, and the
NbO structure with completely corner-sharing Nb, octahedra on the other, are forseeable.
Received: September 9, 1991 [Z 4908 IE]
German version: Angew,. Chem. 1992, 104, 192
CAS Registry numbers:
BdNh,O, 12291-80-4; NbO,. 12034-59-2; Ba,Nb,O,,,
Sodalite with a PhosphorusNitrogen Framework**
By WoCfgang Schnick* and Jan Liicke
Dedicated to Professor Karl-Heinz Biichel
on the occasion of his 60th birthday
Zeolites have increasingly found application as catalysts,
molecular sieves, adsorbents, or ion exchangers in recent
[*] Dr, W. Schnick, DipLChem. J. Lucke
12291-80-4; Nb, 7440-
[ l ] A. Simon, J. Kohler, R. Tischtau, G. Miller, Angew. Chem. 1989, 101,
1695, Angew. Chem. Int. Ed, Engl. 1989, 28, 1662.
Angew. Cheni. Int Ed. Engl. 31 (1992) No. 2
121 A. Simon, Angeu. Chem. 1981,93,23; Angew. Chem. Int. Ed. Engl. 1981,
20, 1 ; ihid. 1988, 100,163 and 1988, 27, 159.
[ 3 ] C. C. Torardi. R. E. McCarley, J. Am. Chem. Soc. 1979, 101. 3963.
[4] J. D. Corbett, R. E. McCarley in Crystal Chemistry and Properties o/ Muteriuls with Qurrsi-One-Dimensional Structures (Ed.: J. Rouxel), Reidel,
Dordrecht, Netherlands, 1986, p. 179.
151 R. Dronskowski, A. Simon. Angeu. Chem. 1989, 101, 775; Angew. Chem.
I n f . Ed. Engl. 1989, 28, 758.
[6] G. Svensson, J. Kohler, A. Simon, J. Less-Common Met. 1991, 176, 129.
[7] S . A. Davydov, B. N. Goschchitskii, E. A. Karkin, A. V. Mirmelstein, V. 1.
Voronin, V. D. Parkhomenko, V. G. Zubkov, V. A. Perelyayev. I. F
Berger, I. A. Kontzevaya, Int. J. Mod. Phys. B 1990, 4 , 1531.
[8] V. G. Zuhkov, V. A. Perelyayev, I. F. Berger, I. A. Kontzevaya, 0. B.
Makarova, S. A. Turshevskii, V. A. Gubanov. V. I. Voronin, A. V. Mirmelstein, A. E. Karkin, Sverkhprovodimost' : Fiz. Khim. Tekhnol. 1990.
3/Y/. 2121
[9] G. Svensson, Microsr. Microunal. Microsfrurf.1990, I, 343.
[lo] A. Magneli, Chem. S n . 1986, 16, 535.
[ l l ] A. Magneli, Microsc. Microanal. Microstruct. 1990, 1 , 299.
[12] Dried NbO,, Ba,Nb,O,,, and N b in a ratio of 3.75:1:4 together with
10 wt % BaCI, were pressed into a pellet and heated under Ar in a sealed
N b ampule at 1640°C for 1 d. The product contained small black cuboid
crystals (up to 0.01 mm) of BaNb,O, besides larger crystals of BaNh,O,.
The refinement of the lattice constants (tetragonal metrics) from a Guinier
diagram resulted in a = 419.5(1) and c =1242.6(2) pm.
[13] Space group P4/mmm (No. 138), Z =1, (CAD4 diffractometer); Mo,,;
240 Reflections, 207 with F, 2 4.00(&) R = 0.095, R, = 0.066 pca,c=
7 . 0 7 g ~ m - ~Positional
parameters: Ba l a . Nh(1) I d , Nh(2) 41 with
r = 0.3291(2), Nb(3) 2h with I = 0.1681(2), O(1) 2e, O(2) 2g with
z = 0.335(2), O(3) 4i with z = 0.160(1), O(4) 1 c. Due to the extreme
smallness of the crystal the intensity of the weak reflections could not be
measured very accurately, which might explain the relatively htgh R value.
Further details of the crystal structure investigation may be obtained from
the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information, D-W-7514 Eggenstein-Leopoldshafen
(FRG), on quoting the depository number CSD-55880, the names of the
authors, and the journal citation.
[la] 9. Hessen, S. A. Sunshine, T. Siegrist, R. Jimenez, Mafer. Res. Bull. 1991,
26, 85.
1151 Extended-Huckel approximation: R. Hoffmann, J Chem. Phys. 1963,3Y,
1397. H , matrixelements: J. H. Ammeter, H.-9. Biirgi, J. C. Thiheault,
R. Hoffmann, J. Am. Chem. Soc. 1978, 100,3686; tight-binding modification: M.-H. Whangho, R. Hoffmann, ihid. 1978, 100, 6093; special k
points: R. Ramirez, M. C. Bohm, Int. J. Quantum Chem. 1986, 30, 391.
[16] R. H. Summerville, R. Hofmann, J. Am. Chrm. Soc. 1976, 98, 7240.
[17] J. Hinze, H. H. Jaffe, J. Phys. Chem. 1963, 67, 1501.
[18] R. A. Wheeler, J. K. Burdett, M. H. Whangbo, T. Hughbanks. R. Hoffmann, T. A. Allbright, J. Am. Chem. Soc. 1986, 108, 2222.
[I91 J. K. Burdett, T. Hughhanks, J Am. Chem. Soc. 1984, 106, 3101.
[20] F. A. Cotton, T. E. Haas, Inorg. Chem. 1964, 3, 10.
[21] 9. 0. Marinder, Chem. Srr. 1977, l f , 97.
(221 J. Kohler, A. Simon, Z . Anorg. Allg. Chrm. 1987, 553, 106.
1231 J. Kohler, A. Simon, S . J. Hibble, A. K. Cheetham, J. Less-Common M a .
1988, 142, 123.
(241 J. Kohler, G. Svensson, A. Simon, unpublished results.
[25] D. M. Evans, L. Katz, J. Solid Stare Chem. 1973, 6 , 459.
(261 J. Kohler, G. Miller, A. Simon, 2. Anorg. Alig. Chem. 1989, 568, 8.
[27] K. B. Kersting, W. Jeitschko, J. Solid State Chem. 1991, 93. 350.
[28] V. G. Zubkov, V. A. Perelyayev, G. P. Shveikin, unpublished results.
[29] G. Svensson, J. Kohler, A. Simon, A c f a Chem. Scand., in press.
Institut fur Anorganische Chemie der Universitit
Gerhard-Domagk-Strasse 1, D-W-5300 Bonn 1 (FRG)
This work was supported by the Minister fur Wissenschaft und Forschung
des Landes Nordrhein-Westfalen, the Deutsche Forschungsgemeinschaft.
and the Fonds der Chemischen lndustrie.
Erlagsgesellscha~mhH, W-6940 Weinheim. 1992
0570-0833/92/0202-0213 $3.50+.25/0
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sharing, octahedron, nb6, layer, oxoniobate, banb7o9, double, corner, new
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