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Molecular and Crystal Structure of -SeBr.

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Molecular and Crystal Structure of p-SeBr'"]
f
By Detlef Katryniok and Riidiger Kniepl'l
Contributions to the structural chemistry of compounds
belonging to the class A2Bz(A = S, Se; B = F, C1, Br) have so
far come mainly from spectroscopic studies''! Most of these
electron-rich chalcogen halides are readily accessible and
have been known for several decades. We now report the
first crystal structure analysis of a representative of this class,
i. e. P-SeBr; both the structure of the individual molecule and
the three-dimensional structure of the crystalline state are
considered. A resemblance to a tellurium subiodide''] is
clearly seen.
DTA and powder photographs show the Se-Br system to
contain the thermodynamically stable phases a-SeBr and aSeBr4l3I;both compounds are dimorphous, each with another
P-phase which is metastable with regard to the phase diagram. A single crystal of P-SeBr was grown from the melt
(SeBr) in a glass capillary (i.d. 0.2 mm) on a diffractometer
assembly as described by Simon et al.141in a temperature gradient of 25"C+-13"C; its structure was analyzed at
- 80 OClSl.
The crystals of P-SeBr contain BrSeSeBr molecules, whose
geometry and bonding are shown in Figure 1. The Se-Se distance of 2.241 A in the molecule is significantly smaller than
in the elemental structure (Sehex,2.373; Semclr
2.318 A'61),
and
comparable with the corresponding distance determined by
IR spectroscopy in FSeSeF (2.25 All1); the Se-Br bond
lengths in P-SeBr correspond to the terminal bond lengths in
the cubane-type molecules (SeBr4)4of a-SeBr, (average values 2.368(1) and 2.36(3)
2 366111
Fig. 1. Se2Br2molecular geometry in P-SeBr (bond lengths [A], bond angles (dihedral angles) ["I; standard deviations in brackets).
The P-SeBr structure also exhibits some intermolecular
Se.. . Br contacts which are significFntly closer than the sum
of the van der Waals radii of 3.95 A''] (cf. Fig. 2). The shortexists between the
est interaction of this kind (3.373(1)
Se(2) and Br(1) atoms of two adjacent BrSeSeBr molecules
(generated via symmetry centers of the structure). Along the
short crystallographic c-axis, translationally equivalent adjacent molecules exhibit Se(1). . . Br(2) contacts of 3.514(1) A.
Each Se(1) atom also has a relatively short distance of
3.773(1) A to Br(1) atoms of molecules that are adjacent
along the b-axis.
A certain degree of similarity between the X-ray powder
diagrams of P-SeBr and macromolecular P-TeI has already
A)
been rep~rted'~'.If the
-structural unit['] extending
along the direction of the shortest repeat distance
(b =4.182(2) A)-a Te chain with alternatingly bridging and
terminal I atoms-is regarded as being made up of n covalently bonded ITeTeI units, then a similar sequence of
['I
I")
Priv.-Doz. Dr. R. Kniep, Dr D. Katryniok
Institut fur Anorganische Chemie und Strukturchemie der Universitat
Universitatsstrasse I , D-4000 Diisseldorf (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft.
Angew. Chem. Int. Ed. Engl. 19 (1980) No. 8
b
Fig. 2. Intermolecular Se.. . Br distances <3.95
dii [7]); standard deviations in brackets.
A (sum of the van der Waals ra-
BrSeSeBr moleculesfx1is found for P-SeBr along the shortest
repeat distance ( c = 4.974(2)
see also Fig. 2).
A;
Received: April 10, 1980 [ Z 538 IE]
German version: Angew. Chem. 92, 646 (1980)
CAS Registry number:
p-SeBr, 7789-52-8
[ l ] Review: K. Seppelt, Angew. Chem. 91, 199 (1979); Angew. Chem. In[. Ed.
Engl. 18, 186 (1979); selenium fluorides. A. H a m , H. Willner, Z . Anorg. Allg.
Chem. 454, 17 (1979); chlorides and bromides: e.g. P. J. Henda, P. J. D.
Park, J. Chem. SOC A 1968.908.
121 R. Kniep, D.Mootr, A . Rabenau, Z . Anorg. Allg. Chem. 422, 17 (1976).
[31 P. Born, R. Kniep, D. Moo% Z . Anorg. Allg. Chem. 45!, 12 (1979).
141 A. Simon, H . J. Deiseroth, E. Westerbeck, B. Hiilenkotter, Z . Anorg. Allg.
Chem. 423, 203 (1976).
IS] 1503 symmetry-independent reflections (MoK'., P2, four-circle drffractometer, w scan), 1168 being significant (F0>3u+). Structure analysis with E-XTL
program system: monoclinic. P2,/c, a=7.345(2), b= 14.282(5), r=4.974(2)
8=97.11(3)o, Z = 4 Se2Br2,p,,,,=4.01 gem-': R=4.8%. Identification of
the phase as P-SeBr from the X-ray powder diagram calculated from the
structural model. Crystal growth and structure analysis of a-SeBr (m. p. 5 "C;
growth conditions according to 131) are under study.
[6] P. Cherin, P. Unger, Acta Crystallogr. 21, A 46 (1966).
171 L. Paulmg: The Nature of the Chemical Bond, 3rd Ed. Cornell University
Press, Ithaca, N. Y.1960.
[8] Further structural resemblances between @-SeBrand a-TeI will be discussed
in greater detail in connection with the crystal structure of a-SeBr 151.
A,
Photolysis of Water Catalyzed by Transition Metal
Dithiolenes
By Rainer Henning, Wilhelm Schlamann, and Horst Kischl"
The photochemical cleavage of water permits the conversion of solar energy into the environmentally unobjectional
energy source hydrogen"]. One of the principal prerequisites
for this conversion is the availability of a suitable photocatalyst (A,,
~400-800 nm). Since many transition metal complexes absorb in this wavelength region, their photochemical
behavior-especially their photoredox reactions-lie at the
center of current interest. All the systems so far described as
~~
['I
Priv.-Doz. Dr. H. Kisch, Dr. R. Henning, W. Schlamann
Institut fur Strahlenchemie im Max-Planck-Institut fur Kohlenforschung
Stiftstrasse 34-36, D4330 Miilheim/Ruhr (Germany)
0 Veriag Chemie, GmbH, 6940 Weinheim, 1980
0570-0833/80/0808-0645
$02.50/0
645
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