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NaNb3O3FЦa Niobium-Niobium Triple Bond with УSide-OnФ Coordination by Nb Atoms.

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Comparative bond length-bond strength calculations1"'
for N b 0 2 and NaNb,05F show that the Nb(2) atoms are
present in the t 4 oxidation state. Thus, a formal charge of
- 12 i s obtained for the [Nb,XxJ unit with Nb(l) in the oxidation state f 2 . In analogy to molecular species, e.g.,
Mo2(OR)(,,["I a &t4
triple bond comes into question for
the Nb-Nb dumbbell.
However, Figure 2, right, indicates that each Nb2 pair in
the structure of NaNb,O,F is "side-on" coordinated by
four Nb" ions. The Nb4+ ions are displaced by about
15 pm from the centers of gravity of the (distorted) coordination octahedra in the direction of an edge X(S)-X(3) toward the Nb2 dumbbell [d(Nb(l)-Nb(2))=309 pm, distance to the center of gravity of the dumbbell 281 pm)].
The d ' ion Nb4+ apparently tends to engage in metal-metal bonding as observed in the structures of the tetrahalides
NbX, ( X = C l , Br,
For N a N b 3 0 5 Fthese bonds can
be regarded as two-electron three-center bonds between
Nb4' (dxz-,2) and n orbitals of the Nb, dumbbell; other
configurations are also conceivable. The diamagnetism
found for N a N b 3 0 5 F is in agreement with the assumption
of a spin pairing of all ten valence electrons in the resulting [ 1.1.1. I]propelIane-Nb, cluster, but is not a proof for
this idea of bonding, since NaNb02F1i31also does not
show the magnetism for a d ' configuration.
It is remarkable that the arrangement M2M4X8(Fig. 2,
right) is also found in the structure of Gd2Cl3,IZ3Ialthough
as part of an infinite chain. The electronic band structure
calculated for the chain can also be interpreted in terms of
the presence of 02n4-bonded Gd, pairs, which form GdGd bonds in the direction of the chain via their TI systern~.l'~'
[I51 C . C . Addison, M. G . Barker, R. M. Lintonbon, R. J. Pulham, Spec. Publ.
Chem. Soc. 22 (1967) 460.
[I61 Space group I m m m (No. 71), a=649.7(1), h=1030.5(1), c=711.8 pm,
2 = 4 , Syntex R3 diffractometer: MoK,; 338 reflections, of which 322
had IFJ >3oIFgJ,R(aniso) =0.0193, R(w) =0.0197: p'.,ie..,
= 5.58 g/cm'.
On account of the similarity of the lattice constants it may be concluded
that the phase Ca,17SNb,06 (orthorhombic, a=711.2, b = 1028.9.
c=656.1 pm), characterized by electron diffraction, is isotypic with
N a N b 3 0 s F (S. J. Hibble, A. K. Cheetham: IIlrd European Conference 017
Solid State Chemistry. Book of Abstracts. Vol. I . Regensburg 1986, p.
136). Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Energie, Physik, Marhematik
GmbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG), o n quoting the depository number CSD-5 1994, the names of the authors, and the journal
1171 R. Hoppe, Angew. Chem. 82 (1970) 7; Angew. Chem. Int. Ed. Engl. Y
(1970) 25.
[IS] 1. D. Brown in M. O'Keeffe, A. Navrotsky (Eds.): Struc/ure and Bonding
in Crystals. Vol I / . Academic Press, New York 1981.
1191 A. Broll, H. G. Schnering, H. Schafer, J . Les-Common M e t . 22 (1970)
1201 A. I. Gusev, N. I. Kirillova, Ya. T. Struchkov, Zh. Strukt. Khim. I 1
(1970) 62.
[21] F. A. Cotton, R. A. Walton: Multiple Bonds Between MetalAtoms, Wiley.
New York 1982.
[22] L. F. Dahl, D. L. Wampler, Acta Crystalluyr. I5 (1962) 946; R. E.
McCarley, B. A. Torp, Inorg. Chem. 2 (1963) 540.
[23] J. E. Mee, J. D. Corbett, Inorg. Chem. 4 (1965) 85.
[24] P. W. Bullett, Inorg. Chem. 19 (1980) 1780.
Conformational Prerequisites for the in vitro
Inhibition of Cholate Uptake in Hepatocytes by
Cyciic Analogues of Antamanide and
Somatostatin* *
By Horst Kessler, * Mechtild Klein, Arndt Muller,
Klaus Wagner, Jan Willem Bats, Kornelia Ziegler. and
Max Frimmer
Experimental Procedure
Dried NaF (p.A Merck) was ground into a mass with Nb powder (LAB,
Merck) and NbZOs (Merck, Patinale) and placed in a corundum crucible.
This was fused under argon in a quartz ampoule and annealed for 3 d at
800°C. In addition to NbO, NbOz, and oxide fluorides (e.g., NaNb02F),
black. metallic appearing, parallelepiped-shaped single crystals of
N a N b l O i F were formed. By repeated grinding, compression, and annealing
of a tablet containing NaF, Nb, and N b 2 0 5(molar ratio 1.2 ; I : I ; each I d at
750"C), NaNb,O,F in ca. 80% yield was obtained. Such a product, washed
with hydrochloric acid, contained 5.6% F. This value exceeds the calculated
one for NaNbiOsF (4.7%) by only 0.9% and can be explained by the higher F
content for the side products, e.g., NaNbOIF ( I 1.4% F).
Received: June 21, 1986;
revised: August 21, 1986 [Z 1833 IE]
German version: Angew. Chem. 98 (1986) 101I
It is well known1']that liver cells are protected by antamanide 1I2lagainst poisons such as ethanol, dimethyl sulfoxide (DMSO), cysteamine, or p h a l l ~ i d i n , ' ~a ] toxin isolated from the mushroom Amanifa phalloides. In recent
years a similar cytoprotective effect has also been found
for somatostatin 2,14) a naturally occurring peptide horm~ne.[~
in vitro investigations of 1 and 2 as
II] a ) H. Schafer, H. G. Schnering, Angew. Chem.
76 (1964) 833; b ) A. Simon, ibid. 93 (1981) 2 3 ; Angew. Chem. I n t . Ed. Engl. 20 (1981) I .
R. E. McCarley, K.-H. Lii, P. A. Edwards, L. F. Brough, J. Solid State
Chem. 57 (1985) 17.
a) A. Simon, H. Mattausch. E.-M. Peters, Z . Kristallugr. 174 (1986) 188;
b) H. Mattausch, A. Simon, E.-M. Peters, Inorg. Chem. 25 (1986) 3428;
c) A. Simon, M. Mertin, H. Mattausch, R. Gruehn, Angew. Chem. 98
( 1986) 83 I ; Angew Chem. I n / . Ed. Engl. 25 (1986) 845.
B. 0. Marinder, Chem. Scr. I 1 (1977) 97.
K . Waltersson, Acta Crystallogr. Sect. 8 3 2 (1976) 1485.
N. L. Morrow, L. Katz, Acta Crystallogr. Sect. B24 (1968) 1466.
K.-A. Wilhelm, E. Lagervall, 0 . Muller, Acta Chem. Scand. 24 (1970)
181 R b. McCarley, private communication, 1985.
19) P. C . Donohue, L. Katz, R. Ward, Inorg. Chem. 4 (1965) 306.
[lo] a ) G. Meyer, R. Hoppe, J . Less-Common Met. 46 (1976) 55: b) 2. Anorg.
Ally. Chein. 424 (1976) 128.
[ I I ] J K. Burdett, T. Hughbanks, Inorg. Chem. 24 (1985) 1741.
1121 H. Schafer, H. G. Schnering, K.-J. Niehaus, H. G . Nieder-Vahrenholz. J .
LewCommon Me! 9 (1965) 95.
(131 W. Rudorff, D. Krug, 2. Anorg. Allg. Chem. 329 (1964J 21 I .
[I41 0. Ruff, E. Schiller, Z . Anorg. Chem. 72 (191 I ) 329; P Ehrlich, F. Pflogcr. G. Pietzka, 2. Anorg. Allg. Chem 282 (1955) 19.
Anyew. Chem.
Ed. Engl. 25 (1986) No. 11
antarnanrde 1
somatostatin 2
well as of their derivatives have shown that the cause of
this biological effect is the inhibition of a transport system.[,] This system is responsible for the transport of cholate from blood into the bile and also for the detoxification
of the blood via the bile.@l Searching for a common structural feature for the activity of antamanide and somatostatin, we found that cyclic peptides containing the modified
[*] Prof. Dr. H. Kessler, M. Klein, Dr. A. Muller, K. Wagner, J. W. Bats
lnstitut fur Organische Chemie der Universitat
Niederurseler Hang, D-6000 Frankfurt am Main 50 (FRG)
Dr. K. Ziegler, Prof. Dr. M. Frimmer
lnstitut fur Pharmakologie und Toxikologie
Mehrzweckinstitut der Universitat
Frankfurter Strasse, D-6300 Giessen (FRG)
This work was supported by the Fonds der Chemischen lndustrie and
the Deutsche Forschungsgemeinschaft.
0 VCH Verlagsgesellschafr mhH. 0-6940 Weinheim. 1986
0570-0833/86/111l-0997 $ 02.50/0
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bond, onф, coordination, atom, niobium, triple, nanb3o3fцa, уside
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