I. Haiduc Babes-Bolyai University Chi, Romania
A Systematization of h0rgtlniC Cyclic Compounds
In recent years, more and more information has accumulated to show that carbon is not the only element which forms cyclic compounds. A selfconsistent chapt,er of inorganic chemistry can be written on ring compounds involving atoms other than carbona chapter which may prove as important and interesting as those which now systematize coordination compounds. It is the purpose of t,his paper t o suggest an organization of the available information and thus to focus atteution on this type of regularity among inorganic compounds. I n many cases, identical repeating units occur bot,h in low molecular weight cyclic species and in long chain, high molecular weight aggregates. A few examples will illust,rate this fact ( 1 ) : Cyclic low molecular weight compounds. Corresponding linear high polymers.
(4)
(6)
Tetratomic compounds have heen reported for both silicon and germanium: RzSi-SiR2
RsGe-GeRl
I
I 1. RS-b&
I
R2Ge--GeR, (7)
(6)
Ilomooyclic phosphorus compounds contaiuing four, five, and six atoms are now known:
(RBS),, (RiSiO),, (PNClJ,, (MePO&,Ss (RBS),, (RsO),, (PNCld,, (MePo&, S,
Recent reviews (2, 3) on inorganic polymers have been concerned mainly with the high molecular weight species, the cyclic lower homologs being discussed only incidentally. A gross classification int,o mono- and poly-cyclic systems can be made on the basis of the complexity of the cyclic structures. Monocyclic compounds, depending on the uature and arrangement of the atoms in the rings, can be further sub-divided into three classes: Homocyclic compounds arc those in which the ring systems are composed of like atoms. Systems consisting of four, five. and six atoms are known. "Pseudo heleroc~,clie" conzpoz~nrlsarc characterized by ring systems of alternate A and R atamr. In many cases homalogs eontaining the skeleton ( A R h and ( A R h are known, while with the metaphosphst~ea,phasphonitriles, and related compounds, extensive homologous series have bern rrcognised. This class is sufficiently defined and extensive to be discusued separatrly. "True heleroeydic" cornpoands are analogous to the organic heterocyclics, in which one or marc different atoms are inscrted into s homocyclic system.
I n the case of polycyclic systems, sub-classification is suggest,ed on the basis of the number of common atoms between adjacent rings or whether the cyclic skeletons are linked by bridging groups. Monocyclic Systems
Homocyclic Compounds. At t,he present time, this class includes compounds formed by silicon, germanium, nitrogen, phosphorus, arsenic, sulfur, and selenium. Silicon may form both saturated and ~nsaturat~ed six-membered ring compounds such as:
while nitrogen and arsenic form the following molecules. R As
r
7
I h e well-known six- and eight-membered ring systems of elementary sulfur and selenium are also examples in this rategory. S S-S-S Se Be-Se-Sr / \
d BI I
\g
S
A A L A
He
Sr I
\ /
Se
SQ
Se I
Se-Se-Se
I
Se
I
Be
. Pseudo-Helerocy-lie Compoz~nds. A wide variety of rompounds are known which contain six- and eightmembered cyclic systems of alternat,ing A and B atoms. The best known substances occur when A is boron, silicon, germanium, phosphorus, or sulfur, and B is nitrogen, oxygen, or sulfur.
Six-membered cyclic horon compounds based on repeating units of B-X, B-0, and R S are kuown:
In the rase of silicon, it. is found that cyrlosiloxanes, silaeanes, and sikhianes occur hot,h as six-, eight,., and higher-membered homologs. This is especially t,me in S i 4 syst,em, where many higher homologs have heen obtained (16) : R, Si
01 0 '
H
I
i n
HJi
\0/
Rz Si
Rs Si
d \H
S/ \S
I sin,
i
\K/
u
I R2ki sin, V S
1>,!
Systems based on alternate sulfur and nitrogen at,oms have heen examined thoroughly in recent years and this couple forms probably the widest variety of eompounds (28, 29). Some of t,hese are showu helom. S=N-S
S
\in,
n,q/
I
S
I1
F-?=T-S-F
h'
I
N
II
S
S-NH-S
O=S-NH-S=O
HA
AH
HJ
I
NH
\ / S
With germanium, cyclic oxides and probably an imide have been prepared: I12
Arsenic containing monocyclic rompounds have not heen recognized as such, but it seems likely that t,he compounds with empirical formulas R-AsO, R-Ass, and It-AsNH are cyclic compounds and belong in this rat,egory.
R*
OP
The r or "ice-like" modifirat,ion of sulfur trioxide is a cyrlic trimer; recently mass spectrographic methods (50) have demonstrated the existence of cyrlic trimers, tetramers, aud pentamers in the vapor of molyhdenum (VI) and tungsten (VI) oxides:
Cyrlic phosphorus rompounds have been kno~vnfor many years. I'hosphorus-oxygen rings are formed in t,he polyhomologous metaphosphates and phosphorusnitrogen rings in t,he rhlorophospho~~itriles and their derivati\-es. This lat,ter series of compounds has recently been extended to include compounds containink up to seventeen 1'-N units. Some phosphorus qvlir compounds are listed helom. Table I lists the most important monoryrlir rompounds t,hat have been reported. Gaps in this s,vstematir presentat,ion suggest compounds which may he synthesized or identified by further research. D u e Heterocuclic Compounds. This class has not. been as extensively studied as the previous one. Some sulfur compounds have been identified (28) : SS-S
I I S NII I I s-S--s
S
S
/ \ H NH I I S 8 \ /
/ NN N I I S
S
/
N
I
.
S
N
0?S
I
SO.
S
In both the siloxanes and the metaphosphates (81). the ring oxygens may be partially replaced hy imide groups: Volume 38, Number 3, Morch 196 1
/
135
Table 1
B
C
Si
... CS ... etc.
P
Ce
Sb
As
S
. . . . . . . . . . . . 88 . . . . . . . . . . . . . . . . . ($3)
......
N
etc.
B3N1 CSNl SisN3 . . . . . . Si,N,
. . . . . . . .
etc.
~ & PaN3 k ~ .....
. . . I',N4 As4N4 ete. . . . B2S1 Si& ... B S S ~ dsSn Sirs* ... p,Sa A& . . . CS, SilSI . . . . A+,
S
.. . . .. . . ..
SJNa S,N4
. . . .
. . .. . . ..
(13)
Compounds such as phosphorus (111), phosphorus (V), arsenic (III), and antimony (111) oxides, together with Pro&, consist of discrete molecules in certain solid modifications or in the vapor state and are&dso included in this class (55).
Polycyclic Systems
Bridged Cyclic Compounds. In these compounds, cyclic systems are linked together hut there are no common atoms shared between t,he rings. Examples of this type are: S--5
I
N
I
S
N-SZ-N
SI S - S
I
I sSS
/
S H:N-C
I
N
C
N
I
N
H
-
/ \
II
N
C-NHI
I
(32)
Spiro-Compounds Compounds in this classification are characterized by the sharing of one atom by adjacent cyclic systems as in the strnrture of silicon sulfide shown below.
Similarly, the sulfides 1'& and PISi (55) and the hetero- and iso-polyacids have structures which are based on fused ring systems. Polycondensation of ring systems in one dimension can lead to structures of the "infinite double chain" type such as is found in the naturally occurring amphiboles and in a solid modification of antimony (111) oxide: n
n
n
This process can be repeated in a second dimension giving layer structures characteristic of boron nitride and many natural silicate minerals:
Condensed CyAic Compounds. This class covers ring compounds which are linked together by at least two common atoms, and contains not only compounds with a discrete number of fused ring systems, but also many highly polymeric substances. Examples of the former case are: 136
/
loumal o f Chemical Education
Compounds such as silica and boron phosphate have structures that can be derived from basic monocyclic units by three-dimensional polycondensation. We should mention that this is by no means an exhaustive listing of all the known cyclic inorganic compounds. At the present time, rapid advances are being made in the elucidation of the chemistry of the known ring compounds and new methods of preparation are being sought. Undoubtedly within a few years, a greater variety of these compounds will be recognized. A clmsificat,ion of t,his type proves most useful in systematizing compounds consisting of a limited number of ring systems. Since comparisons can now be made, based on reactivity, structure, and other properties, the compounds are recognized as being similar. On the other hand, many inorganic highly polymeric substances seem to arise by polycondensation of simple cyclic units and so ran be included in the general scheme, hut the general properties of these substances make similar comparisons very difficult. Acknowledgment
The author wishes to.thank Dr. D. B. Sowerhy of the University of Illinois for help received during the preparation of this article. Literature Cited (1) HAIDUC,I., Rev. Chim. (Bucarest), 7, 721 (1956). H. J., Prm. C h m . Soe., 1959, 202. (2) EMELEUR, 11. B., A N D AUDRIETH, L. F., J. CHEM.EDUC., (3) SOWERBY, 37, 2, 86, 134 (1960). C. A., J. Am. Chem. Soe., 71, 963 (1949). (4) BURCKHARI), (5) URRY.G._ Angew. C h m . , 70, 379 (1958). (6) KIPPING,F. A,, J . Chem. Soe., 119, 830 (1921). (7) KRAWS,C. A,, A N D BROWN,C. L., J . Am. Chem. Soc., 52, 4031 (1930). (8) MAHLER,W., A N D BURG,A. B., J . Am. Chem. Soe., 80, 6161 (1958). B., A N D WORMS,K. H., Z. anorg. allgem. Chem., (9) BLAZER, 300, 225 (1959).
H., A N D BEHRINGER, L.. Chem. Re?.. (10) UGI. I.. PERLINGER, 91, 2324 (1958). K., HUGHES,E. W., A N D WASER,J., reported at (11) HEDBERO, the 115th Meetinn. -, ACS., San Frsnciuco. March. 1949. (12) BURNS,J. H., A N D WASER,J., J. Am. Chem SO& 79, 859 (lQ57). \----,-
(13) SMOLIN, E. M., A N D RAPOPORT, L., "S-Triazinrs and Dwiwtives," Interscience Publishers. Inc., New York, 1959. (14) LAPPERT,M. F., C A a . Rev., 56, 959 (1956). (15) WIBERG,E., A N D STURM, W., Anfew. C h m . , 67,483 (1955). (16) Rocaow, E. G., "Introduct,ion to the Chemistry of thc Silicones," 2nd ed., John Wile? and Sons, Inc., New York, 1951. K., J . Am. Chern. Soc., 75,4131) (17) YOKOI, M., AND YAMASAKT, 11- 9.5'7) -- ,. (18) YOKOI,M., N o ~ u n a T., , AND YAMASAKI, K., J . Am. C h m . Soc., 77, 4184 (1955). (19) FLOOD,E. A., J . Am. Chem. Soe., 5 4 , 1663 (1932). (20)MORGAN, G. T., AND DREW,H. 1). K., J . Ckem. Soc.. 127, 1760 (1925). (21) VAN WAZER.J. R., "Phoephorus and Its Compounds," Vol. 1, Interscience Publishers, Inr., New York, 1958. L. F., STEINMAN, R., A N D TOY,A. D. F., Chrm. (22) AUDRIETH, Rew., 32, 109 (1943). N. L., A N D SEARLE,H. T., in "Advances in In(23) PADDOCK, organic Chemistry and Radiochemistry," Vol. 1, Academic Press, Ino., New York, 1959. L., A N D WIRTH,H., Nattwwis~.,43, 16 (1956). (24) ANSCHWI~, (25) . BLICKE.F. F.. A N D SMITH.F. D.. J . Am. Chem. Soe... 51.. 3479 '(1929): (26) KRETOV, A. E.; AND BERLIN,A. YA.,J . Gen. Chem. (USSR), 1. 411 --- fIQRl\~ ~- --,. (27) IPATIEW,W., RAZUWAIEW, H., A N D STROMSKI, V., R ~ T . , 628,598 (1929). M.,Qtm11. Rev., l o , 437 (1956); "Ergehnisse (28) GOEHR~NG, und Probleme dcr Chemie der Schwefelstiekstoffverbingungen," Aoademie-Verlag, Berlin, 1957. L. F.. J. CHEM.EDUC..34. 545 (1957). (291 AUDRIETH, \
.
-.
'
Chem. ~hj,s.,'26,842 (1'957); 27, 85 (1957). QUIMRY, 0. T., NARATH, A,, A N D LOHMANN, F. H., J . Chem. Soc., 82, 1099 (1960). BECKEGOEMRING, M., JENNE, H., A N D REKA~.IC, Chem. Rer., 92, 855 (1959). SCOTT,H. W., J . Am. C h m . Soc., 68, 356 (1946). SCHWARTZ, R., Angem. Chem., 67, 117 (1955). WELLS,A. F., "Str~cturalInorganic Chemistry," 2nd Oxford University Press, London, 1950.
Volume 38, Number 3, March 196 1
/
137
