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Compounds of Phosphorus with Silicon and Aluminum.

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Compounds of Phosphorus with Silicon and Aluminum
Dedicated to Prof: W. Klemm on the occasion of his 70th birthday
The formation and properties of silicon-phosphorus and aluminum-phosphorus compounds
are described. Silylphosphines are decomposed solvolytically by H 2 0 , CzHsOH, NH3,
hydrogen halides, C Z H ~ Iand
, boron halides at the Si-P bond; decomposition may be
preceded by formation of an addition compound. Extensive side reactions during the reaction
of halogenosilanes with LiPEt2
(jormation of EtzP-PEt2, HPEt2, Si-rich residues) are
due to an excess of LiPEt2 in the reaction mixture. The reaction of LiPEt2 with AICl3,
AIHC12, and AIH2Cl leads to definite aluminum-phosphorus compounds if only one PEt2
group is present per A1 atom, e.g. in ( C I Z A I - P E ~ and
~ ) ~( H Z A I - P E ~ ~or) ~if, salts such
as Li[AI(PEt2)4] and Li[AlH2(PEt2)2] can be formed with an excess of LiPEt2.
A. Silylphosphines
The first hydrides containing an Si-P bond were
prepared in 1953 by two groups of workers. While Aylett, Emelkus, and Maddock [21 found the compounds
SiH3PI2, (SiH3)2PI, and (SiH&P by the action of SiH3I
on white phosphorus, G . Fritz 131 obtained SiH3PH2 by
the reaction of SiH4 with PH3.
SiH4 decomposes at about 400 "C via intermediate products into hydrogen and silicon, whereas appreciable
thermal decomposition of PH3 takes place only above
550°C. Equation (1) shows the first step in the decomposition of SiH4 [41.
about 600 "C into Si and Sip [61, remains behind. Si3PH2
is also formed by an electric discharge in mixtures of
gaseous SiH4 and PH3, as shown by mass-spectrometric
investigation of the products 171. An electric discharge in
mixtures of SiH3PH2 and SiH4 or of Si2H6 and PH3
gives (SiH3)zPH 181, Si2H5PH2, and other products.
1. Reactions of Silylphosphine, SiH3PH2
SiH3PH2 ignites spontaneously in air [91. In alkaline
solution, the compound is hydrolysed quantitatively in
accordance with Equation (4).
-+ P H Z + H ~
+ SiH3PH2
SiH3PH2 (b.p. 12.7 "C) can be distilled off from less
volatile silicon-phosphorus compounds such as
SiH2(PH& 151. A blue-black substance of composition
Si2P and amorphous to X-rays, which decomposes at
[ I ] The following abbreviations are used in this paper: Et =
C2H5; M e = CH3; M = alkali metal.
[ 2 ] B. J . Aylett, H . J . Emelgus, and A. G. Maddock, Research
(London) 6 , 30 (1953); J . inorg. nuclear Chem. I , 187 (1955).
[3] C . Fritz, Z. Naturforsch. 8 h , 776 (1953).
[4] K . Stocklond, Trans. Faraday SOC.44, 545 (1948); H . J .
L311ek;idsand C. Ried, J. chem. SOC.(London) 1939, 1021; G.
Fritz, Z . Naturforsch. 7 6 , 507 (1952).
[ 5 ] G. Fritz, Z . anorg. allg. Chem. 280, 332 (1955).
Aiigcw. Cliciii. iiiteriiot. Edit.
+ 3 H2 + PH3
The following free-radical reactions must be assumed in
connection with Equation (1) for the pyrochemical
formation of SiH3PH2 (450 "C, gas phase, reduced
+ 4 H20
Vol. 5 (1966)
1 No. I
In an acidic medium the hydrolysis is substantially more
complicated. With dilute hydrochloric acid, evolution
of Hz, PH3, and SiH4 (traces) sets in even below O"C,
solid silicon oxyhydrides[*l being formed. All of the
phosphorus of the SiH3PH2 is evolved as PH3. Treatment of these decomposition products with alkali
liberates the same amount of hydrogen as the alkaline
hydrolysis of the SiH3PH2, namely three moles per mole
of Si3PH2. Consequently, in acid hydrolysis cleavage of
the Si3PH2 molecule begins at the Si-P bond:
H3SiOH i~PH3
[6] G . fritz and H . 0. Berkenhoff; Z . anorg. allg. Chem. 300, 205
[7] J. E. Drake and W. L. Jolly, Chem. and Ind. 1962, 1470.
[8] S . D . Gokhale and W. L . Jolly, Inorg. Chem. 3 , 1141 (1964);
4 , 596 (1965).
[9] G. Fritz and H. 0. Beykenhoff, Z . anorg. allg. Chem. 289, 250
[*I Silicon oxyhydrides are high-molecular weight silicon compounds of uncertain composition, containing SiH, SiO, and SiOH
followed with rising temperature by the decomposition
of the silanol according to:
n H6OH
HZ t silicon oxyhydrides
+ traces of SiH4
On solvolysis with CzHsOH, it is possible by working at
two temperatures to cause the evolution of PH3 and the
formation of Hz from the SiH groups to take place successively 191. Cleavage of the Si-P bond with CzHsOH
(anhydrous, saturated with gaseous HCl), in which 1
mole of PH3 is formed according to Equation (7), begins
at temperatures as low as about -80 "C.
H3SiOEt + PH3
If the alcoholic solution is now allowed to warm up
slowly to room temperature, evolution of HZ sets in,
at first slowly and then more vigorously, according to
Equation (8).
n H3SiOEt + H2
+ traces of SiH4 SiH-containing esters of polysilicic acid
When the reactions (5) and (7) are carried out in the
presence of dissolved HCI, H3SiC1 could be formed
first, which would then react with HzO or CzH5OH to
give H3SiOH or H3SiOCzH5, respectively.
In liquid ammonia the Si-P bond of the SiH3PH2 is
split primarily in accordance with Equation (9).
The SiH3NHz produced gives rise to subsequent reactions leading to high-molecular SiH-containing siliconnitrogen compounds and Hz. SiH3PHz reacts with HBr
at temperatures as low as about -80 "C:
low temperature, but the formation of this compound indicates a series of parallel and/or subsequent reactions. In
order to reduce the likelihood of side reactions, compounds
were used which have no or only a few SiH groups, and in
which the other valences of the silicon and phosphorus atoms
are substantially blocked by unreactive groups (alkyl groups).
The simplest reaction is that of Me3SiC1 with LiPEt2, which
gives Me3Si-PEt2 [ I * ] and EtzP-PEtz simultaneously.
Some silylphosphines have been prepared by the reaction of
LiPEt2 with methylchlorosilanes and SiC14. These preparations are always accompanied by side reactions. Thus large
amounts of diethylphosphine were produced in reactions
which were intended to give SiH-containing substituted silylphosphines, and in reactions with SiH-free chlorosilanes Sic14 and Me3SiC1 - tetraethyldiphosphine and silicon-rich
residues were formed. The yields of the desired products were
correspondingly low [ l o , 131. The initial assumption that silylphosphines are transformed into these by-products at higher
temperatures can be dismissed, since MeHSi-PEt2 undergoes
no change on heating to 80 "C (with the exclusion of air and
moisture) [ 1 4 J .
In the reaction of chlorosilanes with LiPEt2, it was observed that the side reactions leading to HPEt2 and
EtZP-PEtz occur to a smaller extent or not at all when
an excess of the halogenosilane is maintained in the
mixture during the whole reaction. Side reactions are
always favored when the chlorosilane is added in drops
to the LiPEtz solution. In this case, moreover, a red
color of the solution is generally observed, which is
absent in the presence of an excess of the chlorosilane
(addition of LiPEt2 solution in drops to the chlorosilane) [141. Under these conditions, it was possible to
obtain MezHSi-PEtz (b.p. 58.5 'C/25 mm Hg) in accordance with Equation (12).
Me2HSiCI + LiPEt2
+ LiCl
This compound reacts further with an ethereal solution
of LiPEtz [Equation (13)], as NMR investigations and
the isolation of the product have shown.
MezHSi-PEtz+ LiPEt2 + Me2Si(PEtz)z + LiH
2. Syntheses of Organo-Substituted Silylphosphines
The pyrochemical reaction of -SiH4 with PH3 yields
SiH3PHz and some other compounds of this type which
have not been investigated; however, the preparation of
relatively large amounts in this way is very laborious.
We therefore attempted to make polar Si and P compounds react with one another [Eq. (II)] in order to
facilitate formation of the Si-P bond by the formation
of the salt MX.
= S i x + M P = + ESi-P=i- M X
= CI, Br, I ; M = alkali metal)
The reaction of LiPH2 with H3SiBr, H3Si1, or SiH2I2 (in
diethyl ether) has so far not led to the desired silylphosphines.
Instead, sublimable products of as yet unknown composition
are formed. Similar results were obtained [lo] in the reaction
of H3SiI with the ether-soluble LiPEt2. Amberger and
B o e t e r s [ l l ] obtained (SiH3)3P from KPH2 and HJSiBr at a
G. Frifz, G . Poppenburg, and M . G . Rocholl, Naturwissenschaften 49, 255 ( 1 962).
[ I 1 1 E. Amberger and H . Boeters, Angew. Chem. 74, 32 (1962)
Angew. Chem. internat. Edit. I , 52 (1962).
( I 2)
MeZSi(PEt2)z (b.p. 83 "C/3 mm Hg) is also formed from
MezSiClZ and LiPEtz.
With an excess of H3SiBr, LiPEt2 reacts primarily as
follows :
H,SiBr+ LiPEt2 + H3Si-PEt2 i~
In spite of the excess of H3SiBr the compounds
H2Si(PEtz)zVand HSi(PEt2)3 arise as by-products
[Equations (1 5) and (16)] as shown by proton resonance
+ LiPEt2
+ LiPEt2
+ LiH
HSi(PEt2)3+ LiH
+ H2Si(PEt&
Subsequently the LiH gives LiBr and SiH4 with the
excess of H3SiBr.
HSiC13 reacts with LiPEtz with the formation of SiHcontaining silylphosphines only if the trichlorosilane is
[I21 G. Fritz and G . Poppenburg, Angew. Chem. 72, 208 (1960).
[13] G . Fritz and G. Poppenburg, Angew. Chem. 7S, 297 (1963);
Angew. Chem. internat. Edit. 2, 262 (1963).
[I41 G. Fritz and G. Becker, unpublished work.
[I51 G. Fritz, G. Becker, and D. Kummer, unpublished work.
A n g e w . Chem. interticit. Edit.
f VoI. 5
i No. I
permanently in excess [141. However, even from such
mixtures it is impossible to isolate pure HSi(PEt2)3,
since chlorine-containing silylphosphines are formed
simultaneously. Thus CIHSi(PEt2)2 is formed in addition
to HSi(PEt2)3, but rearranges in accordance with
Equation (17), as seen from NMR investigations "51.
The reaction of HSiC13 with LiPEt2 (molar ratio 1 :3) at
room temperature, or more rapidly on slow heating to
lOO"C, leads to a red-brown solution from which diethylphosphine and a red-brown solid of unknown
constitution can be isolated.
The compounds obtained are summarized in Table 1.
The investigations described give the following picture:
In addition, a secondary reaction of LiPR2 with the Si-P
bond must be considered. Final proof of the reactions represented by Equations (18)-(21) has not yet been obtained.
The reaction of alkali-metal phosphides with silicon
halides gives compounds which contain several SiR3
groups on the same phosphorus atom. Thus the reaction of Me3SiF and KPHz at low temperatures leads
to (Me3Si)2PH and (Me3Si)3P [161. The same products
are formed, together with Me3SiPH2, in the reaction
of a mixture of LiPH2, Li2PH, and Li3P with
Me3SiCl[17.181. A mixture of LizPH and Li3P reacts
with Et2SiClz with the formation of cyclic compounds
for which Parshall and Lindsey 1171 propose formulae
( I ) and (2).
T a b l e I . Silylphosphines fornie.1 by t h e reaction of L i P E t r or L i P M e J
with silicon halides. M e
C H 3 , Et -~ CzHr
Silicon halide
B.p. ( C / m m H g )
120/-- I
160/ I
60-61/ > 1
cu. 110/13
cu. 110113
Alkyl-substituted and SiH-containing silylphosphines
such as MezHSi-PEt2 and H3Si-PEt2 are stable when
atmospheric moisture is excluded, and do not decompose on heating into HPEt2 and compounds of higher
molecular weight with Si-Si bonds.
Tetraethyldiphosphine and diethylphosphine are formed
in relatively large amounts in the reaction of halogenosilanes with LiPEt2 only if an excess of LiPEt2 is present
in the reaction mixture. If, on the other hand, an excess
of halogenosilane is maintained, this side reaction is
SiH-containing silylphosphines, such as Me2HSi-PEtz,
react further with LiPEtz, the SiH group being converted into an Si-PEt2 group. Even fully alkylated silylphosphines react slowly with LiPEt2.
The side reactions probably can be explained by a first reaction step involving a metal-halogen or metal-hydrogen exchange between silylphosphines containing SiCl or SiH
groups [Equations (18) and (19)l; the starting materials and
products then react further according to Equations (20) and
(21) (in the reaction of (RzP)3SiCI).
Me3Si-P(C6H5)2 has been obtained by cleavage of
tetraphenyldiphosphine with sodium and the subsequent reaction of the (C6H&PNa formed with
Compounds of the type of Et3Si-PO(OEt)2 and
(Et0)3Si-PO(OEt)2 have been obtained, with other
products, from the reaction of Et3SiBr and (Et0)3SiCl,
respectively, with P(OEt)3 or [(EtO)zPO]Na [20-221.
3. Reactions of Organo-Substituted Silylphosphines
In distinction to SiH3PH2, organo-substituted silylphosphines have only one reactive position in the
molecule: the Si-P bond. Thus Me3Si-PEt2 is hydrolysed quantitatively [231 in accordance with Equation
+ H2O
Me3SiOH -t HPEt2
With an excess of EtI or EtBr (or with HI), Me3Si-PEt2
is split according to Equation (23).
+ 2 EtX
+ Me3SiX
+ [Et4P]X
I, Br
In the reaction of equivalent amounts at -78'C, the
stable addition product Me3Si-PEtz.EtI (m.p. 122 "C)
is formed, and with the equivalent amount of HI the
colorless, crystalline Me3Si-PEtz.HI, which is stable
[I61 A . B. Bruker, L. D. Balashova, and L. 2. Suborovskii, Dokl.
Akad. Nauk SSSR, Otdel khim. Nauk 135, 843 (1960); Chern.
Abstr. 55, 13301 (1961).
[I71 G . W . Pnrslinll and R . I/. Lindsqv, J. Amer. chern. SOC.81,
6273 (1959).
[I81 A . J. Lefler and E. G . Teach, J. Amer. chern. SOC.82, 2710
[I91 W. Kuclrert and K. Buchwald, Angew. Chem. 69, 307 (1957).
1201 B. A. Arbuzov and A . N . Puduvik, Dokl. Akad. Nauk SSSR
59, 1435 (1948); Chern. Abstr. 47, 4281 (1953).
[21] F. FehPr, G. Kuhlborscli, A. Blumcke, H . Keller, and K .
Lippert, Chern. Ber. 90, 134 (1957); N . W. Newlands, Proc. chern.
SOC. (London) 1960, 123.
1221 W. H. Keeher and H . W . Post, J. org. Chemistry 21, 509
[23] G . Fritz and G . Poppenburg, Z . anorg. allg. Chern. 331, 147
only at -78 'Cl241. The adduct with ethyl iodide reacts
further with an excess of ethyl iodide, giving the products of Equation (23).
Investigations of Noth and Schragle [251 have also shown
the existence of addition compounds of Me3Si-PEt2
with (BH3)2, BF3, BCl3, and BBr3. These addition compounds - Me3Si-PEtz.BH3 (m.p. 12 "C), Me3Si-PEt2BF3 (decomposition at room temperature), Me3Si-PEtz.
BC13 (stable for short periods at room temperature),
and Me3si-PEt2.BB1-3 (m.p. w 5 "C) - decompose as
3 Me3Si-PEtz.BHj
3 Me3SiH
MejSiLPEtz-BF3 + Me3SiF
2 MejSi-PE12.BX3
+ (E~ZP-BH~)~
+ Et2P-BF2
+ Me3SiX
+ (EtzP-BX&
LiAI(PH2)4, formed from LiAIH4 and PH3 o n prolonged
heating, has also been reported [281.
These investigations show that the formation of definite
aluminum-phosphorus compounds by thermal decomposition of the adducts is very complicated, and
unsatisfactory from the preparative point of view.
Consequently, attempts have been made to convert polar
compounds of the two elements (aluminum halides and
alkali-metal phosphides) into substances containing the
AI-P bond, since the fcrniation of LiCl favors this
route. LiPEt2 and AlCl3 (molar ratio 1 :1) react quantitatively in ether according to
+ AIC13
+ CIzAI-PEt2
(X = C1, Br).
Cleavage in accordance with Equation (24) sets in only
above 80 "C, while with the chlorine and bromine compounds it begins already at room temperature. Silylphosphines containing Sic1 and SiH groups, such as
C13Si-PEt2 or H3Si-PEt2, are more sensitive to oxidation and hydrolysis than the completely alkylated compounds. The influence of the substituents on the Si-P
bond cannot yet be reviewed.
After the bulk of the LiCl has precipitated, a clear
ethereal solution is obtained, which separates into two
layers when most of the ether is distilled off. White
crystals of composition C12AI-PEt2 separate from the
lower layer on cooling, and these do not redissolve in an
excess of hot ether [291. As is evident from the change in
solubility, the substance is no longer monomeric. According to cryoscopic molecular weight determinations
in POCl3, (C12Al-PEt2)3 (3) is present.
A1 '.
c 12
B. Aluminum-Phosphorus Compounds
Whereas substitution predominates in reactions between compounds of elements of groups IV and V of
the periodic systems, with compounds of elements of
groups I11 and V the formation of adducts is preferred
because of their electronic structure. Interesting compounds can sometimes be formed from the adducts by
elimination of atoms or groups. The best known example is borazole, which is formed from the adduct
H3B.NH3 by the elimination of H2.
The thermal treatment of addition compounds derived from
aluminum and phosphorus compounds, however, leads only
in a few cases to definite compounds, and is much less productive preparatively than the corresponding treatment of
adducts of the compounds of boron and nitrogen. Davidson
and Brown[261 obtained (MezAI-PMe&
from Me3AI :
PHMe2[*1 by elimination of CH4 at 215°C. Burg and
Miidrirzerr271 obtained aluminum-phosphorus compounds
by heating mixtures of aluminum-hydrogen compounds and
HPMe2. In the reaction of CIPMe2 with LiAIH4 in liquid
HPMe2, they obtained a solid of compositionjMe2PAIHz:
PHMe2,"which could not be separated from the lithium
chloride formed at the same time. In the treatment of HPMez
with LiAIH4 (three weeks, 50 "C), these authors observed the
formation of LiAlHo.9s(PMe2)2.93 with evolution of H2.
Similarly, withfHPMe2 they obtained substances of the composition (Me2P)zAlCI and MezPAIClZ from H2AIC1 and
HAIC12, respectively (two weeks, 60 "C). A substance
[24] G. Fritz and G . Poppenburg, Naturwissenschaften 49, 449
[25] H . Noth and W. Schragle, Chem. Ber. 98, 352 (1965).
[26] N. Davidson and H . C . Brown, J. Amer. chem. SOC.6 4 , 3 16
( 1942).
[*I The colon denotes the lone electron pair of the phosphorus,
to which the aluminum compound adds.
[27] A . B. Burg and K . Modritzer, J. inorg. nuclear Chem. 13, 3 I8
The trimerization is understandable because it leads to a
six-membered ring in which the electron pair of the
phosphorus atoms occupy the octet vacancies of the
aluminum atoms. The solution of (3) in POC13 is stable
for only a short time, as can be seen both from the yellow
coloration and from the change in the freezing point depression with time. The decomposition takes the course
+ 3 POCIj
3 Et2P-AIC12:OPCI3
The breakdown of the cyclic compound (3) is to be
expected when a reactant with a lone electron pair displaces the phosphorus from its coordination position
with respect to the aluminum. POCl3 evidently is such a
reagent. The reaction of 1 mole of AICl3 with 3 voles
of LiPEt2 in ether is also quantitative. Highlyviscous
products are formed, which contain aluminum and
phosphorus in the expected ratio of 1 : 3 but which
can hardly be regarded as compounds of definite molecular weight [30,31J. These products contain [AI(PEt2)3],
units with n > 3, and probably also the ether adduct
(Et2P)3AI: OEt2.
[Al(PEt2)3], is also obtained by the reaction of crystalline (Cl2Al-PEt2)3 (3) with 6 moles of LiPEt2, a
reaction in which one had hoped to obtain [Al(PEt2)3]3.
It must be assumed that the appearance of oligomers
[28] A . E. Finkelt, C. Helling, V . Imhoh L . Nielsen, and E. J m o h sen, Inorg. Chem. 2, 504 (1963).
[29] G. Frifr and G . Trencrek, Z . anorg. allg. Chem. 313, 236
( I 96 I).
[30] K . Issleib and H . J . Deyling, 2. Naturforsch. 17h, 198 (1962).
[31] G. Fritz and G . Trenczek, Z . anorg. allg. Chcm. 331, 206
Angew. Cliem.
1 Vol. 5
No. I
with n > 3 is based on the same principle as the formation of [CI2A1-PEt2]3 ( 3 ) . However, when several PR2
groups are attached to the aluminum, these can form
cross-links, as shown in Scheme 1.
Hz I
A1-P: fi1-P:Al-
The reactions of AlCI3 and H2AICI with LiPEt2 are
summarized in Schemes 2 and 3.
weight compounds [-311. Li[AIH3PEt2] can be obtained
directly from freshly-prepared AIH3 [Equation (34)].
: Al--P
Scheme I .
: Al-
Etz l
n LiPEt,
The reaction of HAIC12 with 2 moles of LiPEt2 also
gives a highly viscous product of indefinite molecular
Aluminum-phosphorus compounds of definite molecular weight are formed when cross-linking is suppressed
by limiting the number of coordinating groups on the
A1 atom to one[31]. Thus the reaction
3 H2AICI f 3 LiPEt2 ->
(H2AI - PEt2)j t 3 LiCl
leads to the compound (H2Al-PEt&, which melts at
1-2 "C and spontaneously ignites in air but which can
be distilled without decomposition [321.
Aluminum-phosphorus compounds prepared in this
way have a pronounced tendency to form salt-like compounds with an excess of LiPEt2 [331. Thus the viscous
[AI(PEt2)3], obtained from 1 mole of AlCl3 and 3 moles
of LiPEt2 reacts with further LiPEt2:
Scheme 2. Reactions of AlCli with LiPEt,.
Scheme 3. Reactions of AIH2CI with LiPEt,.
to give a compound of m.p. 224--226"C. This conipound is also formed directly from AlC13 and the
stoichiometric amount of LiPEt2 [Equation (3 l)].
The colorless, crystalline Li[AIH2(PEt2)2], which
ignites spontaneously in air, is formed by the following
+ 2 LiPEtz
+ Li[AIHz(PEt2)zJ t LiCl
(HzAI--PEt2)3 t 3 LiPEtz + 3 Li[AIH2(PEt2)2]
Evidently the formation of salt-like compounds is
favored over that of the trimeric and higher-molecular[32] G. Fritz and G. Trewzck, Angew. Chem. 75, 723 (1963); AnChern. internat. Edit. 2, 452 (1963).
[ 3 3 ] G. Fritz and G. Trenczck, Angcw. Chem. 74, 942 (1962); Angcw. Chern. ~nternat.Edit. /, 663 (1962).
Clrcnr. itrlcrtiat. Edit. Vol. 5 (1966)
No. I
According to investigations by Issleib et al. [341, tetraalkyldiphosphines are cleaved by LiAlH4, Li [AIH(PR2)3]
being formed via intermediate stages.
The compounds formed in accordance with Equations
(30), (32), and (34) are very sensitive to hydrolysis and
oxidation. Hydrolysis yields LiOH, AI(OH)3, HPEt2
and - except in the first example - H2.
The author thanks the Fonds der Cheniie and the Deutsche
Forschirngsgemeinschaft for jinancial support of' these
investigations, which were carried out in part at the Anorganisch-chemisches Institrrt der Universitat Munster
and in part at the Institiit fur Anorganische irnd Analytische Chemie der Universitat Giesseii.
Received: O c t o b x IIth. 1965 [A 498/271 IE]
German version: Angew. Chem. 78, 8 ) (1966)
Translated by Express Translation Service, London
[34] K. Issleib, A. Tzsclincli, and R . Scliirrrrzer, Z. anorg. allg.
Chem. 338, 141 (1965).
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compounds, silicon, aluminum, phosphorus
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