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Crystal Structure of Strontium Disilicide.

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197 “ C , the vermilion-red bismuth(II1) salt, m. p. I32 ’C, t h e
bright yellow indium(ll1) salt, m . p . 146OC, a n d t h e pale
yellow thallium(1) salt, m. p. I29 “C.
Crystal Structure of Strontium Disilicide
By Dipl.-Chem. K. Janzon, Dr. H. Schafer, and
Prof. Dr. Armin Weiss
Potentiometric determination 161 of t h e apparent dissociation
aqueous isopropanol a t 2 0 ° C gave t h e
constants in 80
following sequence for the strengths of t h e various phosphinic
acids:
(C2H5)2P(S)OH [PK 4.981
.-rC
(C2H5)2P(S)SeH [pK 2.291
= (CzH&P(Se)SeH [pK 2.181
(CzH-j)zP(S)SH [PK 2.601
Received: January 19th, 1965
[ Z 899/725 IE]
German version: Angew. Chem. 77, 259 (1965)
111 By analogy to the preparation of (CjH,)2P(S)CI, cf. W . Kuchen, H . Buclzwald, K . Strolenberg, and J . Metten, Liebigs Ann.
Chem. 652, 28 (1962).
[ 2 ] See H . Ulmer, L . C . D . Groenwghe, and L. Maier, J. inorg.
nucl. Chem. 20, 82 (1961).
131 A. Markowska and J. Mirhalski, Roczniki Chem. 34, 1675
(1960); Chem. Abstr. 56, 7346 (1962).
141 Reaction in analogy with the preparation of (C>H&P(S)SNa
by T. A . Mastryukova, A. E. Shipov, and M . J. Kabachnik, Zhur.
obshch. Khim. 31, 507 (1961); Chem. Abstr. 55, 22101 (1961).
151 The molecular weight could not yet be determined because
solutions of this substance decompose rapidly.
[6] H . Hertel, Diploma Thesis, Technische Hochschule Aachen,
1965.
Synthesis and Properties of 5-Chloromethylcytosine
By Priv.-Doz. Dr. Dr. R. Brossmer a n d E. R o h m
Max-Planck-Institut fur Medizinische Forschung,
lnstitut f u r Chemie, Heidelberg (Germany)
U p t o the present, reactive chloromethyl derivatives of naturally occurring pyrimidine bases were known only in the uracil
series.
When 5-hydroxymethylcytosine or its hydrochloride is heated
with thionyl chloride in tetrahydrothiophene I,l-dioxide [I],
t h e hydrochloride of 5-chloromethylcytosine ( I ) is obtained
in 9 5 X yield a s slightly grey crystals, m . p . above 3OO0C.
Ano:ganisch-Chemisches lnstitut
der Universitit Heidelberg (Germany)
In calcium disilicide CaSiz, the silicon a t o m s are linked
together in a two-dimensionally infinite, corrugated net of
hexagons [I]. I n contrast, in barium disilicide BaSi2 [2],
sodium silicide NaSi 131, a n d potassium silicide KSi 141,
isolated Si? tetrahedra occur.
In strontium disilicide SrSiz, the silicon a t o m s form a threedimensional framework. T h e shortest Si ~ S distances
i
are
2.41 8, a n d thus comparable with those in elemental silicon
(2.34 A). T h e Si-Si-Si angles a r e 113O 2‘ each, i.e. very
close t o the angles in a regular tetrahedron. A s the electronegativity of the G r o u p 11 elements decreases, the shortest
Si--Si distance falls off from 2.48 A in CaSiz via 2.41 8, in
SrSiz t o 2.34-2.37 8, in BaSi2. Despite t h e differences in the
structural framework of the silicon in these three compounds,
each silicon atomislinkeddirectlytothreeneighboringsilicons.
Each strontium a t o m in SrSiz is surrounded by six silicon
neighbors at distances of 3.21 A and two further silicons a t
3.43 A.
Crystallographic d a t a for SrSiz:
Cubic pentagonal-icositetrahedral, space g r o u p 06-P4332,
a = 6.540 .. 0.002 A ; d, = 3.40
0.05 g/cm3; d x = 3.42
g/cm3.
T h e unit cell contains f o u r Sr atoms, which occupy the 4a
positions, and eight silicon a t o m s in the 8 c positions of the
space group with x = 0.428. T h e minimum for thediscrepancy
index R is very unsharp a s a function of xsi.
*
xsi
I
R
10.143
0.420
1
0.422
IO.128
I
0.424
10.114
I
0.426
I
0.428
I 0 . 1 0 ~ ]0.108
I
0.430
10.114
I
0.434
10.165
Hence the parameter x cannot be given with very great
accuracy. When x = 0.428, R for the series (hkO) becomes
0.108, for the series ( h k l ) 0.092, a n d for t h e series (hk2)
0.114. I n v.ork with the CUka radiation, “Umweganregung”
is observed.
Received: January 21st. 1965
[ Z 900/742 IE]
German version: Angew. Chem. 77, 258 (1965)
.-
For reasons of analogy a n d o n the basis of the infrared spectra, we assume that the basic nitrogen a t o m of the ring is protonated. On acccuni of its high reactivity, t h e free base of ( I )
is rather difficult t o isolate. Proof of structure ( I ) is supplied by the e!emental analysis, by its chemical reactions, and
by its infrared spectrum [the 7 strongest bands in order of decreasing intensity occur a t 1665, 1725, 2855 (part of a group
of bands a t 3280--2740), 1215, 1235, 1600, a n d 760cm-1; the
band a t 1025 cm-1 typical of t h e alcohol is n o t observed].
Under mild conditions t h e allyllic chlorine a t o m can he displaced with compounds containing a nucleophilic group.
Ethers, thioethers, amines, or esters a r e formed in mostly good
yields [2]. Ethers, for example, a r e produced by heating ( I ) i n
a n alcohol or phenol or by treating ( I ) with alkali metal alkoxidesorphenoxides. Manyamines reactwith ( I ) even a t room
temperature in acetone. In this manner, many substances can
be linked vin t h e methylene bridge t o t h e cytosine nucleus,
wich can act a s a low molecular-weight mobile carrier.
Received: January 20th, 1965; supplemented: February lst, 1965
German version: Angew. Chem. 77, 260 (1965)
[ Z 911/735 IE]
[ I ] This solvent (Sulfonal from Shell) has proved to be extremely
valuable for other reactions a s well. Its properties (strongly polar,
chemically inert, heat-stable, miscible with water and organic
solvents) make it appear suitable for use in various fields of
nucleic acid chemistry.
[ 2 ] Reported at the Fall Meeting of the Deutsche Gesellschaft
fur Physiologische Chemie in Koln (Germany), October 22nd
t o 24th. 1964.
Angew.
Chem. internut. Edit. 1 Vol. 4 (1965)
/
No. 3
[I] I. Bohm and 0.Hassel, Z . anorg. allg. Chem. 160, 152 (1927).
[2] H . Schafer, K. Janzon, and A. Weiss, Angew. Chem. 75, 451
(1963); Angew. Chem. internat. Edit. 2, 393 (1963).
[3] J. Witte and H . G. Schnering, Z . anorg. allg. Chem. 327, 260
(1964).
[4] E. Busmann, Naturwissenschaften 47, 82 (1960); 2. anorg.
allg. Chem. 313, 90 (1961).
Preparation of Tetrachlorotellurophene and
Tetrachloroselenophene
By Dr. W. Mack
Consortium fur elektrochemische Industrie G m b H . ,
Miinchen (Germany)
T h e ring system of tellurophene was so far known only from
the synthesis of its tetraphenyl derivative [ I ] . We have now
prepared tetrachlorotellurophene (2) by the reaction of hexachloro-l,3-butadiene ( I ) with tellurium.
c1-c--c-c1
It
I,
CI-c. ,c-CI
Te
‘2j
CI-c-c-CI
I1
I1
CI-c, ,c-CI
I$e
Ci ‘cl
,‘?.
I
c1-c-c-Cl
I1
I1
cl-c.s;c-cI
(5,
Finely pulverized tellurium (0.3 mole) is shaken for 40 h a t
250 “Cwith 0. I mole o f / l / . T h e tellurium tetrachloride formed
245
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