Full text of DOI:10.1107/S0108270199014080

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
According to a search of the Cambridge Structural Database
(CSD release April 1999; Allen & Kennard, 1993), this is the
®rst reported crystal structure of a salt of diphenylacetic acid
with an alkali metal.
ISSN 0108-2701
Compound (I) crystallizes in the achiral, although non-
centrosymmetric, space group P421c (Jones, 1986) and both
enantiomers of the helical conformation of the diphenyl-
Sodium diphenylacetate, an infinite
columnar structure
J. A. PaixÄao,* F. V. Nascimento, A. Matos Beja and M.
Ramos Silva
Â
Ã
Departamento de Fõsica, Faculdade de Ciencias e Tecnologia, Universidade de
Coimbra, P-3000 Coimbra, Portugal
Correspondence e-mail: jap@pollux.fis.uc.pt
Received 1 September 1999
Accepted 1 November 1999
In the title compound, Na+ÁC14H11O2 , the diphenylacetate
ions have a conformation where the two phenyl rings and the
carboxylate group are oriented like the blades of a propeller,
each ion having a well de®ned helicity. The crystal structure of
the title compound is achiral, although non-centrosymmetric
(space group P421c); thus, ions with both (+) and ( ) helicities
are present in the crystal. Each Na+ ion is coordinated by four
carboxylate O atoms at distances in the range 2.207 (2)±
Ê
2.467 (3) A to form cubes of Na and O atoms which are linked
via the carboxylate C atoms into a columnar structure along
the rotoinversion axis.
Figure 1
ORTEPII (Johnson, 1976) plot of (I) viewed along the 4 axis (c axis).
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as spheres of arbitrary radii.
Comment
The molecule of diphenylacetic acid is achiral, but due to the
rotational mobility of the phenyl rings the molecule may
assume a helical chiral conformation where the two phenyl
rings and the carboxylate group are oriented like the blades of
a propeller. When forming molecular compounds with other
achiral molecules, such a conformation can induce a chiral
crystal structure. An interesting example of this situation
occurs in the 1:1 adduct of diphenylacetic acid and acridine,
which crystallizes from acetonitrile in a chiral crystal structure
(space group P212121) and spontaneously resolves the (+) and
( ) enantiomers (Koshima et al., 1996). This compound is
photoreactive and has been used in absolute asymmetric
synthesis by photodecarboxylating condensation performed in
the solid state. Our interest in this type of absolute asymmetric
synthesis led us to a systematic study of other compounds of
diphenylacetic acid, including the title compound, sodium di-
phenylacetate, (I), whose structure is reported here.
Figure 2
Stacking of the Na/O core along the c axis showing the columnar
structure. The phenyl groups have been omitted for clarity.
168 J. A. Paixao et al. Na+ÁC14H11O2
Acta Cryst. (2000). C56, 168±170
ꢀ
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metal-organic compounds
acetate ion are present in the unit cell. There is an ambiguity in
the absolute assignment of the x and y axes in such a high
symmetry non-centrosymmetric space group which can only
be resolved if a suf®ciently strong anomalous scatterer is
present. In fact, inverting the structure in P421c is equivalent
to the interchange of axes x ! y and y ! x. However, due to
the low value of the anomalous dispersion of all atoms,
including Na, at the Mo Kꢀ wavelength, it was not possible to
resolve in the present case the ambiguity in the absolute
assignment of the x and y axes.
The coordination of the diphenylacetate ions around the
metal ions is shown in Fig. 1 and Fig. 2. The carboxylate O1
atom and the Na+ ions alternate at the vertices of a distorted
cube centered at the origin of the 4 axis. Each Na+ ion is
coordinated by four O atoms (one O2 atom outside the cube
and three O1 atoms at adjacent vertices of the `cube') at
respectively; Koshima et al., 1996) and in the 1:1 adduct of
diphenylacetic acid and acridine (33.9, 50.3 and 13.0ꢁ,
respectively; Koshima et al., 1996). This shows that the phenyl
and carboxylate groups may rotate rather freely around the
single bonds joining them to the central C atom. Indeed, there
is evidence that these groups are suf®ciently mobile in solution
to allow inversion of helicity (Koshima et al., 1996).
There are no classical hydrogen bonds in this structure.
Cohesion is maintained mainly by electrostatic forces and
weaker van der Waals interactions. Interaction between ꢁ-
clouds and metal atoms does not appear to play a major role,
Ê
the shortest ring±metal distance being 3.812 (5) A. There is,
however, a relatively short distance between the H atom
Ê
attached to C10 and the C3±C8 phenyl ring [2.847 (5) A].
Experimental
Ê
distances in the range 2.207 (2)±2.467 (3) A. These distances
Compound (I) was prepared by neutralizing an ethanolic solution of
diphenylacetic acid (98%, Aldrich) with sodium hydroxide. Clear
transparent single crystals of prismatic form grew from the solution
by slow evaporation over a period of a few weeks, from which one
small crystal was selected and used for the X-ray analysis. Before data
collection, the quality of the crystal was checked by photographic
methods.
are close to the average Na+O2 distance [2.44 (16) A;
Ê
Bergerhoff & Brandenburg, 1995], except for the NaÐO2i
Ê
[symmetry code: (i) y, x, z] distance [2.207 (2) A], which is
somewhat shorter. The Na/O core forms a columnar structure
along the 4 axis, as seen in Fig. 2. The distorted cubes of Na
and O1 atoms alternate along the columns, with the
carboxylate groups, which act as bridges, joining adjacent
cubes. Interestingly, the carboxylate O2 atom is involved
solely in the bridging, while the O1 atom and its symmetry-
related counterparts make up the oxygen content of the cube
construction.
Crystal data
Na+ÁC14H11O2
Mo Kꢀ radiation
Cell parameters from 25
re¯ections
Mr = 234.22
Tetragonal, P421c
Ê
a = 18.944 (3) A
c = 6.3326 (11) A
Ê
V = 2272.6 (6) A
ꢂ = 9.99±13.94ꢁ
1
Ê
ꢃ = 0.123 mm
T = 293 (2) K
3
The carboxylate skeleton de®ned by atoms C1, C2, O1 and
Ê
O2 is planar to within 0.003 A. There is signi®cant asymmetry
Ê
between the bond distances C1ÐO1 [1.271 (3) A] and C1Ð
Z = 8
Dx = 1.369 Mg m
Prism, colourless
0.24 Â 0.24 Â 0.17 mm
3
Ê
O2 [1.226 (3) A], which deviate signi®cantly from the average
value of a typical delocalized double bond in carboxylate
Ê
anions [1.254 (10) A; Allen et al., 1987]. The asymmetry
between these two bonds is probably explained by the
different environments of the O1 and O2 atoms, O1 having
three Na+ ions as near neighbours, while O2 has just a single
alkaline ion in the ®rst coordination shell. This may also
induce the large asymmetry between the angles C2ÐC1ÐO1
[113.6 (2)ꢁ] and C2ÐC1ÐO2 [121.4 (3)ꢁ]. However, the angle
O1ÐC1ÐO2 [125.0 (3)ꢁ] is typical for a carboxylate group.
Data collection
Enraf±Nonius CAD-4 diffract-
ometer
Pro®le data from !±2ꢂ scans
Absorption correction: scan
(North et al., 1968)
Tmin = 0.923, Tmax = 0.982
2596 measured re¯ections
1598 independent re¯ections
1135 re¯ections with I > 2ꢄ(I)
Rint = 0.025
ꢂmax = 27.43ꢁ
h = 0 ! 18
k = 0 ! 24
l = 6 ! 8
3 standard re¯ections
frequency: 180 min
intensity decay: 2.0%
Re®nement
Re®nement on F2
R[F2 > 2ꢄ(F2)] = 0.038
wR(F2) = 0.106
S = 1.076
1598 re¯ections
154 parameters
H atoms riding
w = 1/[ꢄ2(Fo2) + (0.0518P)2
+ 0.4591P]
Ê
The shortest distance between two metal ions is 3.265 (2) A,
which greatly exceeds the sum of two ionic radii of Na+.
The dihedral angle between the least-squares planes of the
two phenyl rings is 89.35 (16)ꢁ. The dihedral angles between
each of the rings and the bridging plane de®ned by atoms C2,
C3 and C9 are 5.0 (3) (C3±C8) and 84.4 (3)ꢁ (C9±C14). The
carboxylate group makes an angle of 56.7 (3)ꢁ with the brid-
ging plane and angles of 54.61 (16) and 78.40 (17)ꢁ with rings
C3±C8 and C9±C14, respectively. The two phenyl rings and the
carboxylate plane have torsions around the single bonds to C2
in the same direction, like the blades of a propeller. This is
con®rmed by examining the torsion angles around C2 [H2Ð
C2ÐC1ÐO1 58.0, H2ÐC2ÐC3ÐC4 62.5 and H2ÐC2ÐC9Ð
C10 21.8ꢁ], which all have the same sign. These torsion angles
should be compared with the corresponding values in the
molecular crystal of diphenylacetic acid (48.2, 27.3 and 52.8ꢁ,
where P = (Fo2 + 2Fc2)/3
(Á/ꢄ)max < 0.001
3
Ê
Áꢅmax = 0.204 e A
3
Ê
0.169 e A
Áꢅmin
=
Table 1
Selected geometric parameters (A, ).
ꢁ
Ê
NaÐO2i
NaÐO1
NaÐO1ii
2.207 (2)
2.316 (2)
2.344 (2)
NaÐO1iii
NaÐNaiii
NaÐNaiv
2.467 (3)
3.265 (3)
3.476 (2)
O2iÐNaÐO1
O2iÐNaÐO1ii
O1ÐNaÐO1ii
119.12 (9)
149.79 (10)
87.14 (8)
O2iÐNaÐO1iii
O1ÐNaÐO1iii
O1iiÐNaÐO1iii
107.87 (9)
92.63 (9)
83.72 (8)
Symmetry codes: (i) y; x; 1 z; (ii) y; x; z; (iii) x; y; z; (iv) y; x; z.
J. A. Paixao et al. Na+ÁC14H11O2
169
ꢀ
Acta Cryst. (2000). C56, 168±170
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metal-organic compounds
Data collection: CAD-4 Software (Enraf±Nonius, 1989); cell
re®nement: CAD-4 Software; data reduction: HELENA (Spek, 1997);
program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a);
program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997b);
molecular graphics: ORTEPII (Johnson, 1976); software used to
prepare material for publication: SHELXL97.
References
Allen, F. H. & Kennard, O. (1993). Chem. Des. Autom. News, 8, 31±37.
Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor,
R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1Ð19.
Bergerhoff, G. & Brandenburg, K. (1995). International Tables for Crystal-
lography, Vol. C, pp. 683±684. Dordrecht: Kluwer Academic Publishers.
Enraf±Nonius (1989). CAD-4 Software. Version 5.0. Enraf±Nonius, Delft, The
Netherlands.
Johnson, C. K. (1976). ORTEPII. Report ORNL-5138. Oak Ridge National
Laboratory, Tennessee, USA.
Jones, P. (1986). Acta Cryst. A42, 57.
Koshima, H., Ding, K., Chisaka, Y. & Matsuura, T. (1996). J. Am. Chem. Soc.
118, 12059±12065.
The authors are indebted to Dr J. C. Prata Pina for his
invaluable assistance in the maintenance of the CAD-4
diffractometer. This work was supported by FundacËaÄo para a
Ã
Ciencia e para a Tecnologia (FCT).
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351±
359.
È
Sheldrick, G. M. (1997a). SHELXS97. University of Gottingen, Germany.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: LN1088). Services for accessing these data are
described at the back of the journal.
È
Sheldrick, G. M. (1997b). SHELXL97. University of Gottingen, Germany.
Spek, A. L. (1995). PLATON. University of Utrecht, The Netherlands.
Spek, A. L. (1997). HELENA. University of Utrecht, The Netherlands.
170 J. A. Paixao et al. Na+ÁC14H11O2
Acta Cryst. (2000). C56, 168±170
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Ä