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Caro's Acid Molecular Structure and Association in the Solid State at 130░C.

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Caro's Acid: Molecular Structure
and Association in the Solid State at
- 130 OC
By Walter Frank* and Birgit Bertsch-Frank*
Caro's acid (trioxoperoxosulfuric acid H,SO,),['I one of
the best known named compounds in inorganic chemistry, is
representative of the class of inorganic peroxoacids. Its high
oxidation potential and its instability-which can also result
in spontaneous, explosive degradati~n[~~--complicates
preparation and study of the pure acid. Since the crystallization of the extremely hygroscopic and low-melting compound (m.p. = 47 "C) is also difficult to control, the possibility of obtaining a single crystal for structural analysis was
considered doubtful.[31
Pure H2S0, (I) was first prepared by D'Ans and
Friedrich, not without danger, by reacting H,O, with
HS0,C1.r41If H,O, is treated with SO,, a reaction which
formally yields the desired compound directly, substantial
amounts of side products and degradation products are
formed.[51 Much simpler is the preparation of defined
H,SO,/H,SO, mixtures, which when cooled under moisture-free conditions are storable indefinitely, and from
which we could crystallize the peroxoacid 1 at low temperature without danger. Methods that have proved useful in the
study of thermolabile crystals were employed for the further
treatment of the crystalline material.[61
From the vibration spectraL7.81 a molecular structure with
an intramolecular 0 - H .. ' 0 hyrogen bond, in which the hydrogen atom of the peroxo group is close to an 0x0 oxygen
atom, was postulated for crystalline 1. The actual molecular
structure in the solid at - 130 3 "C, however, shows that
no intramolecular hydrogen bond is present (Fig. l).C9]The
bonds is intermediate between that of double and single
The shape of the molecule (point group symmetry 1) is
determined by the conformation of the H 1 - 0 1 -S-0 40 5-H 2 chain and the torsion angles H 1-0 1 4 - 0 4 (- 68 "),
0 1-S-0 4-0 5 (- 59.4 "), and S - 0 4-0 5-H 2. The value for
the latter of - 104" lies between that for the potential minimum for rotation in gaseous H,O, (120")['s1 and that in
solid H,02 enforced by the molecular association (90.2 "). It
also gives an impression of the structure modifying forces of
the solid state association for 1.
The molecules in the crystal of 1 are linked in layers parallel to the a,b plane by a system of unsymmetric, almost linear
0-H.. .O hydrogen bonds. If the 0 . .' 0 distance (265.6 and
272.1 pm) is used as criterium, the hydrogen bonds are
strong.['61 There are only slight differences between these
distances and those between the oxygen atoms involved in
hydrogen bonding in H,SO, and H,O, [263(2) and
276.1(5) pm, respectively], which explains the relationship
between the two halves of the molecule 1 with the parent
compounds, the different acidity of the OH and OOH functions, and indirectly the monobasic character of the acid.
Further details of the linkage of the associated molecules and
layered structure may be seen in Figure 2. Viewed in an
10 1 01
Fig. 2. Hydrogen-bond system and layer structure. Section of a layer of O-H0 linked H,SO, molecules. (Distances [pm]: 0 1 " . . . 0 5 265.6(4), H 1 " . . ' 0 5
173(5), 0 5 . . . 0 2 272.1(4), H2...02'178(5); angles["]: 0 5 . . . H l " - O l " 173(10),
02'".H2-05 172(10);symmetrycoding:': 1-x, -y. 1-2,": -0.5 + x,O.5-y, 1-2).
Fig. 1. The molecular structure of Caro's acid in the solid state at - 130 "C.
The ellipsoids of the thermal movement correspond to a residence probability
of 50 YO;
the radius of the hydrogen atoms was chosen arbitrarily. Bond lengths
[pm] and angles["]: 0 4 - 0 5 146.4(3)(in H,O, 145.8(4)[10]), S-03 152.4(2), S-02
141.8(2), S - 0 3 143.2(2) (in H,SO, S-OH 153(2), S - 0 142(2) [ll]),S-04 160.2 (in
S,Oi- anion 164.4(5) [12]), 0 1 - H I 94(4), 05-H2 9514); 01-S-02 106.8(1),
01-S-03 112.9(1), 01-S-04 104.0(1), 02-S-03 121.4(2), 02-5-04 109.3(1), 03S-04 lOl.O(l), S-04-05 108.7(2), HI-01-S 112(2), H2-05-04 98(3).
0-0 bond length does not differ notably from that of solid
hydrogen peroxide,["] and the S-0 distances also lie within
the expected range." 31 From them, using simple empirical
relationship^,['^] we estimated a bond order of about 1 for
the bond from S to the peroxo group, about 413 for the bond
to the OH group, and about 5/3 each for the bonds to the 0x0
oxygen atoms. Thus, in contrast to H,SO, (2 x 7/4 and 2 x
5/4),["] in H,SO, the character of only three of the S-0
Prof. Dr. W. Frank
Fachbereich Chemie der Universitit
Erwin-SchrBdinger-Strasse,D-W-6750 Kaiserslautern (FRG)
Dr. B. Bertsch-Frank
Degussa AG, Forschung Anorganische Chemie
Rodenbacher Chaussee 4, D-W-6450 Hanau 1 (FRG)
Verlug~gesellschafrmbH. W-6940 Weinheim, 1992
abstract way['71a layer may be seen as a (8.42)network with
the S and 0 5 atoms as knots or as a (4.4) network of
(H,SO,) enantiomeric pairs. Only van der Waals forces hold
the layers together.
Experimental Procedure
Oleum (65%, 33.1 mL; i.e., 42.9g (0.535 mol) SO,) was added to an 87.3%
hydrogen peroxide solution (14.3 mL; 17.2 g (O.SO5 mol) H,O,) over a period
of 1 h at 0- 10 "C. Half an hour thereafter the iodometric and cerimetric analysis of the viscose liquid revealed 62.9% H,SO, and 0.5% unreacted H,O,.
After many attempts, crystals suitable for a single-crystal X-ray analysis were
obtained by slow cooling to - 20 "C over 24 h. They were selected and transferred to a glass capillary at low temperature and freed of adhered mother
liquor in a stream of argon. All apparatus for the preparation and the structural
analysis was of glass and was treated with concentrated H,SO,, rinsed with
distilled water, and dried in a dust-free environment.
Received: September 25, 1991 [Z4931 IE]
German version: Angew. Chem. 1992, 104,469
CAS Registry numbers:
H,SO,, 7722-86-3; H,O,, 7722-84-1; oleum, 8014-95-7
[l] H. Caro, Z . Angew. Chem. 1898, 845.
[2] J. 0. Edwards, Chem. Eng. News 1955. 33. 3336
0S70-0833/92/0404-0436 $3.50 .25/0
Angen. Chem. Int. Ed. Engl. 31 (1992) No. 4
[3] J. Flanagan, W. P. Griffith, A. C. Skapski, J. Chem. Soc. Chem. Commun.
1984, 1574.
[4] J. D'Ans, W. Friedrich, 2. Anorg. Chem. 1912, 73, 325.
[5] H. Ahrle, J. Prakt. Chem. 1909, 79, 129.
[6] M. Veith, W Frank, Chem. Rev. 1988, 88, 81.
(71 A. Simon, Z . Anorg. Chem. 1939, 242, 369.
[8] J. L. Arnau, P. A. Giguire, Can. J. Chem. 1970, 98, 3903.
[9] Crystal structure analysis of 1: H,SO,, M , =114.08, a = 628.5(3), b =
1420.0(4), c =773.4(3) pm, 2 = 8, V, = 0.6902 nm', space group Pbca,
crystal size 0.69 x 0.66 x 0.21 mm', four-circle diffractometer, Mo,. radiation, 912 measured reflections, 713 independent reflections with J > 0,
numerical absorption correction, 64 refined parameters, R = 0.047, R, =
0.041. Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur
wissenschaftlich-technische Information rnbH, D-W-7514 EggensteinLeopoldshafen 2 (FRG) on quoting the depository number CSD-55888,
the names of the authors, and the journal citation.
[lo] 3. Savariault, M. S. Lehmann, J. Am. Chem. Soc. 1980, 1U2, 1298.
[Ill C. Pascdrd-Billy, Acta Crystallogr. 1965, 18, 827.
[12] B. K. Sivertsen, H. Sorum, Z . Kristallogr. Mineral. 1969, 130, 449.
[13] Compare with the distances given in the legend of Figure 1. Closer inspection shows that the bond S-02 is shorter than S-03, although the former
participates in an intermolecular hydrogen bond. This finding should be
seen, for example, in connection with the variance of the distances between
sulfur atoms and terminal oxygen atoms in trimeric sulfur trioxide.
[I41 I. D. Brown, D. Altermatt, Acta Crystallogr. Sect. I3 1985, 41, 244.
[15] R. C. Redington, N. B. Olsen, P. C. Cross, J. Chem. Phys. 1962,36,1311.
(161 J. Emsley, D. J. Jones, 3. Lucas, Rev.Inorg. Chem. 1981, 3, 105.
[17] A. F. Wells, Structurai Inorganic Chemistry, 5. Ed., Clarendon, Oxford,
1984, p. 81.
compound 5, which is formally a stannaketenimine and thus
comparable to the silaketenimine tBu,Si=C=NR (R = Ph,
Mesityl, 2,4,6-tBu3C,H,)['] postulated by Weidenbruch et
al. as an intermediate.
R R p = C Q N
c _ _
2 tBuOH
- 2 RH
R = 2,4,6-(CF,)3CsHz
R'= 2,4,6-(CH,),CsH2
A solution of equimolar amounts of 3 and 4 cooled to
- 78 "C provided pale yellow crystals of 5.[*]Crystals suit-
Investigations of the Structure and Reactivity
of a Stannaketenimine**
By Hansjorg Grutzmacher,* Stefanie Freitag,
Regine Herbst-Irmer,* and George S. Sheldrick
able for X-ray structural analysis were obtained by sublimation at 40 oC/O.Ol Torr. The structure of stannaketenimine 5
shows atoms Cll(C20), Snl, C1, and N1 to have a very bent
orientation (Fig. 1). In an idealized ketenimine these atoms
Dedicated to Professor Hans-Friedrich Grftzmacher
on the occasion of his 60th birthday
Investigations of the existence or nonexistence of systems
with multiple bonds to elements of the higher periods have
long entertained experimental and theoretical chemists.['' In
this context compounds with tin-element multiple bonds are
interesting; of these only the distannene 1[*]from Lappert et
al. and the stannaethene zt3]from Berndt et al. have been
characterized by X-ray structural analyses. A number of
groups have reported experimental evidence of stannaethenes
and ~tannanimines.[~'
Quantum chemical calculations of the
tin-carbon and tin-tin "double bond" have also been cond~cted.[~]
We report here the synthesis and molecular structure of
the adduct of diarylstannandiyl 316' and mesitylisocyanide 4,
Fig. 1. Structure of 5 in the crystal. Selected bond lengths [A] and angles ["I:
Snl-Cl 2.397(3), Snl-C11 2.306(2), Snl-C20 2.314(3), C1-N1 1.158(3), Nl-CZ
1.405(3), Snl-F2 2.72; C20-Snl-CIl 102.6(1), Cl-Snl-ClI 104.9(1), Cl-SnlC20 83.4(1), Snl-CI-NI 153.9(2), C1-Nl-C2 175.0(3). The stannaketenimine
frame without substituents is shown in the upper right.
R ' = (Me3Si)2CH
Dr. H. Grutzmacher
Anorganisch-chemisches Institut der Universitat
Irn Neuenheimer Feld 270 D-W-6900 Heidelberg
Dr. R. Herbst-Irmer, S. Freitag, Prof. Dr. G. M. Sheldrick
Anorganisch-chemisches Institut der Universitat
Tammannstrasse 4, D-W-3400 Gottingen (FRG)
This work was supported by the Dr.-Otto-Rohm-Gedachtnisstiftung,
Fonds der Chemischen industrie, and the Deutsche Forscbungsgemeinschaft (SFB 247).
Angew. Chem. Jnt. Ed. Engl. 31 (1992) No. 4
would lie in one plane. The comparison of the C11-Snl-C1
and C20-Snl-C1 bond angles (104.9(1) and 83.4(1)", respectively) points out the distortion of the pyramidal coordination geometry of the tin atom; this arises from the relatively
short Snl -F2 contact (2.72 .&).@I The Snl -C1 distance of
2.397(3) .& is significantly greater than the distances between
Snl and the @so carbon atoms C11 and C20 in the aryl rings,
0 VCH Verlagsgesellschafl mbH. W-6940 Weinheim. i992
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acid, structure, solis, molecular, associations, 130, state, carot
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