organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
similar to that of S[CH CH C(O)OH] (Prout & Hernandez-
2
2
2
Cassou, 1982; Vasileva et al., 1992) and to the low-temperature
-form of 1,7-heptanedioic acid (pimelic acid; MacGillavry et
ꢀ
ISSN 0108-2701
al., 1948); cf. the structure of the ꢁ-form of the latter (Kay &
Katz, 1958; Housty & Hospital, 1966). All these structures are
composed of in®nite chains of molecules linked by hydrogen
bonds between the terminal carboxylic acid groups. Hence, the
structural difference observed for Se[CH C(O)OH] in rela-
0
3
,3 -Selenobis(propionic acid)
2
2
tion to its sulfur analogue S[CH C(O)OH] does not occur in
2
2
Khaled I. Doudin, Jon Songstad and Karl W. T oÈ rnroos*
the case of the Se[CH CH C(O)OH] molecule. In this
2
2
2
Department of Chemistry, University of Bergen, All e gaten 41, 5007 Bergen, Norway
compound, the two OÁ Á ÁO distances in a carboxylic acid dimer
Ê
are equal, 2.684 (2) A, and quite comparable to those
Ê
observed in S[CH CH C(O)OH] , 2.674 (3) A. The OÐ
2
2
2
Received 6 November 2000
Accepted 22 December 2000
ꢀ
HÁ Á ÁO bond angles deviate slightly from linearity, 175 (2) .
Ê
The shortest SeÁ Á ÁO distance, 3.5410 (11) A, is to a carbonyl
O atom and not to a hydroxyl O atom. Whereas the central
ꢀ
bond angle in S[CH CH C(O)OH] , 100.3 (2) (Prout &
2
In contrast to Se[CH C(O)OH] versus S[CH C(O)OH] , the
2
2
2
2
2
2
Hernandez-Cassou, 1982), is slightly larger than in Me S,
2
title compound, Se[CH CH C(O)OH] or C H O Se, is
10
2
2
2
6
4
ꢀ
9
8.8 (2) (Hayashi et al., 1989), the CÐSeÐC bond angle in
structurally quite similar to its sulfur analogue. The molecule
ꢀ
ꢀ
Se[CH CH C(O)OH] , 96.48 (8) , is quite comparable to that
2 2 2
has twofold symmetry. The CÐSeÐC bond angle is 96.48 (8)
ꢀ
Ê
and the SeÐC bond lengths are 1.9610 (14) A. The shortest
of Me Se, 96.3 (1) (Pandey & Dreisler, 1997). The CÐSe
2
Ê
bond lengths and all other bond lengths in Se[CH CH C-
2
SeÁ Á ÁO intermolecular distance is 3.5410 (11) A. The OÁ Á ÁO
2
Ê
distances in the carboxylic acid dimers are 2.684 (2) A. The
(O)OH] are as expected for this class of compounds. One
2
may also note that all torsion angles in the sulfur and selenium
compounds are quite similar; cf. entries in Tables 1 and 2.
temperature dependence of the IR spectrum suggests
tautomerism in the solid state.
Comment
0
The crystal structure of 2,2 -selenobis(acetic acid), Se[CH -
2
C(O)OH] , was reported recently (Doudin et al., 2000) and
2
shown to be very different from the structures of X[CH C-
2
(
O)OH] , with X = CH (Morrison & Robertson, 1949), X = O
2 2
(
Davey & Whitlow, 1973) and X = S (Paul, 1967). Whereas the
latter three compounds form in®nite chains through hydrogen
bonds between carboxylic groups, as is common for di-
carboxylic acids (Leiserowitz, 1976), Se[CH C(O)OH] attains
Figure 1
2
2
A view of the title compound with the atomic numbering of the
asymmetric unit. Displacement ellipsoids are drawn at the 50%
probability level.
a marked cis con®guration, forming dimers through four
almost parallel hydrogen bonds. The likely cause for this
dimerization is the presence of a rather strong SeÁ Á ÁO(OÐH)
Ê
contact, of only 3.081 (1) A, which forces one of the two acetic
Finally, some comments on the IR spectrum of
Se[CH CH C(O)OH] . It has long been known that this
acid moieties of the molecule into a rare antiperiplanar
conformation. In this work, we report on the structure of
Se[CH CH C(O)OH] , (I), investigating whether the
2
2
2
compound and several related ones, particularly compounds
with an odd number of atoms, display a doublet for the
carbonyl group (Agen aÈ s & Lindgren, 1968; Ramsis et al.,
1998). At room temperature, this doublet for Se[CH CH C-
2
2
2
apparent preference of a central Se atom to coordinate to a
hydroxyl O atom also in¯uences the structure of this
compound.
2
2
�
1
(O)OH] is observed at 1722 and 1685 cm in Nujol, at 1720
2
1
and 1697 cm in KBr and at 1712 and 1689 cm in KBr for
�
� 1
the dideuterated sample, Se[CH CH C(O)OD] . At ꢁ243 K
2
2
2
�
1
in KBr, however, the intensity of the peak at 1720 cm is
�
1
greatly reduced whereas the intensity of the peak at 1697 cm
is signi®cantly increased. This suggests that two con®gurations
for Se[CH CH C(O)OH] are present at room temperature,
2
2
2
The molecular structure of the title compound with the
atomic numbering scheme is shown in Fig. 1. Bond lengths,
angles and torsion angles are summarized in Table 1. It is
evident that the structure of the title compound is essentially
presumably due to tautomerism in the solid state (Sugawara &
Takasu, 1999), and that the structure of the title compound
represents the low-temperature ꢀ-form of Se[CH
(O)OH]
CH C-
2 2
.
2
ꢂ
Acta Cryst. (2001). C57, 439±440
# 2001 International Union of Crystallography
Printed in Great Britain ± all rights reserved 439