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Bond Interaction in Sulfur Rings Crystal and Molecular Structure of cyclo-Heptasulfur Oxide S7O.

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Bond Interaction in Sulfur Rings: Crystal and Molecular
Structure of cycfo-Heptasulfur Oxide, S,O['l
By R a y Strudel, Richard Reinhardt, and Torsten Sandow[*]
S 7 0 arises on oxidation of S7 with CF3C03Hand forms
orange-yellow crystals which are stable only at low temperatures[']. In contrast to other sulfur rings (&, S7, &, SsO,
SS,Slo,SI2),S 7 0fails to show any Raman lines in the stretching region of SS single bonds (410--500cm-'), i. e. all the
bonds must be considerably longer or shorter than the SS
single bond length (206~rn[~"l).
In order to establish the reason
for this unusual bonding we have carried out an X-ray structure
analysis on a single crystal at - 1 10°C.
de Jong-Bouman and precession diagrams revealed the
monoclinic space group P2'/n with Z = 4 , a = 1296.3(7),
b = 872.3(9), c = 660.1(5)pm, p= 88.73(9)", dcalc.= 2 . 1 4 0 g ~ m - ~
( - 110°C). Using an automatic single-crystal diffractometer
4110 independent reflections up to 0=30" were measured
with MoKmradiation and corrected in the usual way; 85
reflections were classified as unobserved ( I 5 2 0).
The proposed
structure (direct methods) could be refined with anisotropic
temperature factors to R = 0.068. An absorption correction
(p= 19.25 cm- ') has yet to be performed.
The asymmetric unit contains one molecule whose internuclear distances and bond and torsional angles are given in
Figure 1 and Table 1. Exceptionally small intramolecular
contacts are observed between atoms S4."S5 (332.8pm) and
S7...01 (295.2pm). The smallest intermolecular SO and SS
distances are S5.-.01 (288.6pm) and S5".S7 (325.3pm).
Fig. 1 . Conformation, numbering, and internuclear distances [pm] of S 7 0 ;
standard deviations in parentheses.
Valence angles
S2-SI-S3
s 1-s2-s4
Sl-S3--S5
S2-S4-S6
s3--S5-s7
S4--S6-S7
SS-S7-S6
s 1-s3-0
S5-S3-0I
r] in S,O: standard deviations in
- 208
-
0
20L -
200 196
101.76(7)
9n.n0(6)
106.57(7)
99.~8)
106.70(8)
f05.45(8]
I 06.74(8)
101.45(8)
s3-s1-s2-s4
s2-s 1-s3-s5
Sl-S2-S4-S6
Sl-S3-S5-S7
S2-S4-S6-S7
S3-S5-S7-S6
S4--S6-S?-S5
S2-Sl-S3-01
s7-s5-s3-01
196
200
2OL
208 212 216
Id,+d31 [pml--,
220
224
internuclear distances d l and d 3 of the two adjacent bonds.
The rings having bonds of equal length (S6, s8, SI2) lie near
the discontinuity of the curve. On extrapolation of d z to
the van der Waals distance of 3 4 0 ~ m [ ~ "i.e.
] , for the case
of homolytic cleavage of a bond in the S, ring, it is seen
that the internuclear distances dl and d3 of the terminal bonds
of the resulting diradical 4,- must be about 196pm, i.e.
correspond to multiple bonds. The resulting increase in bond
energy facilitates homolysis and also explains why nonionic
compounds with cumulated SS bonds are thermally very
sensitive and often decompose at as low a temperature as
50-150°C.
Received: July 5, 1977 [ Z 802b IE]
German version: Angew. Chem. 89, 757 ( I 977)
- 79.4
79.3
112.0
- 112.3
- 82.1
87.6
- 6.2
~-25.6
-3.1
CAS Registry number:
s70,60828-66-2
-
"1
121
131
141
1'1 Prof. Dr. R. Steudel, Dip].-Chem. T. Sandow
lnstitut fur Anorganische und Analytische Chemie der Technischen Universitlt
Strasse des 17. Juni 135, D-1000 Berlin 12 (Germany)
Dip].-Chem. R. Reinhardt
Institut fur Kristallographie der Freien Universitdt
Takustrasse 6, D-1000 Berlin 33 (Germany)
716
212
Torsional angles
1 00.21(6)
1
-tE,
Fig. 2. Dependence of the internuclear distance d 2 of the SS bond upon
the arithmetic mean ofthe internuclear distances d , and d 3 of the neighboring
bonds in the compounds S,. S 7 0 , S,, S 8 0 , S I 2 , S z 0 , and S.02- (n=4-6).
For large values of 0.5 ( d , + d 3 ) . the distance <I2 approaches to 189 pm, the
bond length in S 2 .
s5
Table 1. Valence and torsional angles
parentheses.
The conformation of the S 7 0 molecule corresponds to
expectations based on comparison with S7['] and S71+[41.
The average SS distance of 211.7pm is larger than in S7
(206.8 pm), which is attributable to bond weakening by the
The torsional
exocyclic oxygen atom as first observed in S80[51.
angles S+S&S7-S5
(-4") and S7-SS-S3--01
(-37,
which are energetically unfavorable for SS bondsr3"1, lead
to the extremely large internuclear distances of the S3-S5
and S C S 7 bonds. The bonds adjacent to the long ones
are shortened by the influence of bond interaction[3], the
shortest bond plainly lying next to the longest one, as also
found in S80[51,S71+[41,S7[11,and S20[61.
It is shown in Figure 2 that a relation exists between the
internuclear distance between two divalent sulfur atoms d2
in neutral sulfur rings[71 and the arithmetic mean of the
[51
[61
171
Sulfur Compounds, Part 50.---Part 49: R . Steudel, R. Reinhardt, F .
Schuster, Angew. Chem. 89, 756 (1977); Angew. Chem. Int. Ed. Engl.
16, 715 (1977).
R. Sreudel, 7: Sandow, Angew. Chem. 88, 854 (1976); Angew. Chem.
Int. Ed. Engl. 15, 772 (1976).
a) R . Steudel, Angew. Chem. 87, 683 (1975); Angew. Chem. Int. Ed.
Engl. 14, 655 (1975); b) Spectrochim. Acta 31 A , 1065 (1975).
J . Passmore, P. Tujlor, 7: Whidden. P . White, J. Chem. Soc. Chem.
Commun. 1976,689.
P . Luger, H . Bradaczek, R. Steudel, M . Rebsrh, Chem. Ber. 109, 3441
(1 976).
M . Schmidt, E. Wilhelm, 7: Debaerdemaeker, E . Hellner, A . Kurogiu,
2. Anorg. Allg. Chem. 405, 153 (1974).
The values for the S:' and S71i ions are shifted towards the origin
owing to the additional bond energy [3a]; however. an analogous
relation apparently also applies t o S71+.
c_
Angew. Chem. I n t . Ed. Engl. 16 ( 1 9 7 7 ) N o . 10
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crystals, bond, structure, oxide, molecular, interactiv, sulfur, ring, cycle, s7o, heptasulfur
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