Interactions of aromatic carboxylic acids with quinolin-8-ol (Oxine): Synthesis and the crystal structures of the proton-transfer compounds with the nitro-substituted benzoic acids

Article abstract of DOI:10.1071/CH01011

Proton-transfer compounds of quinolin-8-ol (oxine) with the nitro-substituted aromatic carboxylic acids 2-nitrobenzoic acid, [(C₉H₈NO⁺)(C₇H₄ NO₄^-)·H₂O] (1), 3-nitroben

Full text of DOI:10.1071/CH01011

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Aust. J. Chem. 2001, 54, 171–175
Interactions of Aromatic Carboxylic Acids with Quinolin-8-ol (Oxine):
Synthesis and the Crystal Structures of the Proton-Transfer Compounds
with the Nitro-Substituted Benzoic Acids
Graham Smith,A,B Urs D. WermuthA and Jonathan M. WhiteC
A Centre for Instrumental and Developmental Chemistry, School of Physical Sciences,
Queensland University of Technology, GPO Box 2434, Brisbane, Qld. 4001.
B Author to whom correspondence should be addressed(e-mail: g.smith@qut.edu.au).
C School of Chemistry, University of Melbourne, Parkville, Vic. 3052.
Proton-transfer compounds of quinolin-8-ol (oxine) with the nitro-substituted aromatic carboxylic
+
+
–
acids 2-nitrobenzoic acid, [(C9H8NO )(C7H4+NO4 )·H2O] (1), 3-nitrobenzoic acid, [(C9H8NO )(C7H4NO4)–]
–
(2),
4-nitrobenzoic
acid,
[(C9H8NO )(C7H4NO4 )(C7H5NO4)]
[(C9H8NO )2(C7H3N2O6 )2·3H2O] (4), 5-nitrosalicylic acid, [(C9H8NO ) (C7H4NO5 )] (5) and 3,5-dinitrosalicylic
(3),
3,5-dinitrobenzoic
acid,
+
+
–
–
+
–
acid, [(C9H8NO )(C7H3N2O7 )] (6) have been prepared and characterized by using both infrared spectroscopy and
single-crystal X-ray diffraction methods [(3), (4) and (6)]. In all compounds, protonation of the quinoline nitrogen
occurs together with primary hydrogen-bonding interactions involving this group and the carboxylate group of the
acid, while further peripheral associations, in the case of the trihydrate (4), also involving the water molecules, result
predominantly in simple chain polymeric structures.
Manuscript received: 5 February 2001.
Final version: 30 May 2001.
G
H
0
1
D
W
ermu, thJ. M. White
GI .nteS mraci tionhetsoalfC. arboxyli cAcidswithOixne
Introduction
adducts, the oxine forms cyclic R22(8) hydrogen-bonded
dimers via the hetero-nitrogen and the phenolic oxygen, with
peripheral secondary hydrogen bonds giving polymer
structures. This basic dimer is similar to what is found in the
crystal structure of the parent oxine.[11]
Quinolin-8-ol [8-hydroxyquinoline (oxine)] is well known as
a disinfectant and antiseptic agent as well as being a
particularly versatile molecule for use in metal complex
chemistry. The relative positions of the hetero-nitrogen (pKa
10.8) and 8-substituted phenol group, together with the
acidic nature of the latter (pKa 4.9), provide the textbook
example for selective interaction with metals, giving bis- and
tris-chelate complex systems which are often neutral. Under
basic conditions, essentially no selectivity is achieved but
with pH control, quantitative precipitation is possible, such
as with Mg2+ where the complex [Mg(oxine–)2] is a common
weighing form in gravimetric analysis.[1] While neutral
divalent metal complexes such as this and [Pd(oxine–)2][2] are
common, adducts involving metal complexes or metal salts
with free oxine are also known, e.g. {[Ni(oxine–)2]·oxine},[3]
[K+(oxine–)·oxine][4] and [K+(oxine–)·(oxine)2].[5] In
addition, metal complexes with both anionic and neutral
coordinated oxine species have been reported, e.g.
{[Ag(oxine–)(oxine)]·pyridine}[6] and the Ag complex unit
in {[Ag(oxine)2]+(p-toluenesulfonate–)}.[7]
Previous preliminary work by our group on cocrystals of
aromatic carboxylic acids with oxine gave some crystals
which proved unsuitable for structural analysis by single-
crystal X-ray methods[12] because of an apparent ten-
dency for twinning, while in its adduct with Kemp’s tri-
acid (cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic
+
[13]
–
acid), [(oxine )2(C12H17O6 )2·n(oxine)],
the partial
disordered oxine molecule in the lattice was progressively
lost during data collection without apparent destruction of
the crystallinity of the compound. This matter has been
further addressed in this study because of a similar
occurrence with one of the reported compounds. Reported
here is the preparation and characterization using
spectroscopic and single-crystal X-ray diffraction of a series
of six proton-transfer compounds of quinolin-8-ol (oxine)
with the nitro-substituted aromatic carboxylic acids 2-
nitrobenzoic acid (2-nba), [(oxine+)(2-nba–)·H2O] (1), 3-
nitrobenzoic acid (3-nba), [(oxine+)(3-nba–)] (2), 4-
nitrobenzoic acid (4-nba), [(oxine+)(4-nba–)(4-nba)] (3), 3,5-
dinitrobenzoic acid (dnba), [(oxine+)2(dnba–)2·3H2O] (4), 5-
nitrosalicylic acid (5-nsa), [(oxine+)(5-nsa–)] (5), and 3,5-
Neutral adducts with organic compounds are less
prevalent, but the structures of stable 1:1 adducts with
chloranil[8] and 1,3,5-trinitrobenzene[9] are known together
with the 2 : 1 proton-transfer adduct with 1,2,3-
trihydroxybenzene, [(oxine+)(thb–)·oxine].[10] In the neutral
© CSIRO 2001
10.1071/CH01011
0004-9425/01/030171

172
G. Smith et al.
dinitrosalicylic acid (dnsa), [(oxine+)(dnsa–)] (6). The crystal
structures of three of these [(3), (4) and (6)] have been
determined by single-crystal X-ray diffraction methods.
Results
Final atomic coordinates, bond distances and angles,
anisotropic thermal parameters and hydrogen atom
coordinates for adducts (3), (4) and (6) have been deposited
as an Accessory Publication.* Atom numbering schemes for
the associated molecule types and the hydrogen-bonding
schemes are shown in Figs 1–4.
Discussion
In all compounds reported here, as predicted on the basis of
pKa differences, proton transfer from the carboxylic acid
group to the hetero-nitrogen of the oxine molecule occurs,
together with primary O···N hydrogen-bond formation
between donor and acceptor atoms. However, in none of the
compounds do we find a primary cyclic hydrogen-bonded
R22(8) A–B heterodimer formed, involving the second
carboxylate oxygen and the 8-hydroxy substituent of oxine;
nor are there any A–A or B–B homodimers found (as with
the parent acids or with oxine itself [11]). Instead, this
molecule acts in a bridging mode to link the associated
molecular units into chain polymers through hydrogen
bonds. In addition, this adduct series with oxine shows a
greater tendency for formation of various stoichiometric
ratios than any of the previously studied Lewis base types.
Fig. 2. Extension of the trimer units in (3) through peripheral hydro-
gen bonds in the a cell direction.
[(oxine+)(4-nba–)(4-nba)] (3)
The structure of the 1 : 2 adduct of quinolin-8-ol with 4-
nitrobenzoic acid [(oxine+)(4-nba–)(4-nba)] (3) (Fig. 1)
Fig. 3. Atom numbering scheme and hydrogen bonding (shown as
broken lines) in the adduct hydrate (4).
comprises an A–A–B repeating unit in which the primary
interaction, after proton transfer from the first carboxylic
acid to the hetero-nitrogen of oxine, is formation of a single
hydrogen bond [N(1)–H(1)···O(7), 2.730(3) Å; N–H···O,
147(3)°]. The second carboxyl oxygen then forms a single
hydrogen bond with the carboxyl group of the second
(protonated) 4-nba molecule [O(6)···H(1)–O(2), 2.572(3) Å;
O···H–O, 170(3)°]. The polymer link is provided by the oxine
molecule through the 8-hydroxy group to a carboxylate
oxygen of the first 4-nba molecule [O(1)–H(24)···O(6)a,
2.730(3) Å; O–H···O, 147(3)° (a = 1+x, y, z)], giving a three-
centre interaction about O(6). The resulting chains form
along the a cell direction (Fig. 2). Neither the second
Fig. 1. Molecular configuration and atom numbering for the three
molecules in the hydrogen-bonded A–A–B trimer in adduct (3). Un-
less otherwise indicated, atoms are carbon.
*Copies are available, until 31 December 2006, from Australian Journal of Chemistry—an International Journal for Chemical Science, P.O. Box
1139, Collingwood, Vic. 3066.

Interactions of Carboxylic Acids with Oxine
173
carboxyl oxygen of molecule 2 nor the nitro groups of either
acid are involved in hydrogen bonding.
2.567(9) Å; O–H···O, 173(3)° (a = 1+x, y, z); O(1ЈЈ)–
H(1ЈЈ)···O(3)b, 2.562(9) Å; O–H···O, 171(3)° (b = –1+x, –
1+y, z); O(1:)–H(1:)···O(3Ј)c, 2.591(9) Å; O–H···O, 168(3)°
(c = –2+x, –1+y, z); O(1Ј)–H(1Ј)···O(3)d, 2.561(9) Å; O–
H···O, 165(3)° (d = x, y, z)]. The result is a hydrogen-bonded
chain polymer structure. Unlike a number of the compounds
involving the nitrosalicylic acids,[14,15] no interactions
involving the nitro oxygens are present. However, this
structure shows significant ␲–␲ association between the
dnsa and oxine molecules, a feature not common among
either the neutral or proton-transfer compounds or adducts of
the nitro-substituted aromatic carboxylic acids. Also as
expected, and similar to the parent acid and its compounds,
the intramolecular O(hydroxyl)···O(carboxyl) hydrogen
bond is present [O(2)···O(4), 2.462–2.472(8) Å].
[(oxine+)2(dnba–)2·3H2O] (4)
In the 2 : 2 adduct trihydrate of oxine with 3,5-dinitrobenzoic
acid, [(oxine+)2(dnba–)2·3H2O] (4), the primary A–B
interaction similar to that found in adduct (3) is present in both
independent molecule pairs in the asymmetric unit [N(1)–
H(11)···O(3), 2.829(3) Å;
N–H···O, 156(3)°; N(1Ј)–
H(11Ј)···O(2Ј), 2.701(3) Å; N–H···O, 152(3)°]. The A–B
pairs are joined into a ribbon polymer (Fig. 3) by peripheral
hydrogen bonds to the three water molecules [O(8), O(9),
O(10)] linking the carboxyl oxygens and the 8-hydroxy
substituent of the oxine molecules [O(2)···H(9A)–O(9),
2.686(3) Å; O···H–O, 169(3)°; O(9)···H(1Ј)–O(1Ј), 2.545(3)
Å; O···H–O, 165(3)°; O(9)–H(9B)···O(3Ј)a, 2.690(3) Å; O–
H···O, 175(3)° (a = 1 – x, ½+y, 1 – z); O(2Ј)···H(10B)–O(10),
2.754(3) Å; O–H···O, 169(3)°; O(8)···H(1)–O(1), 2.671(3) Å;
O···H–O, 167(3)°;O(8)–H(8B)···O(3)b, 2.707(3) Å; O–H···O,
171(3)° (b = –x, ½+y, 1 – z)]. The water molecules also
mutually interact [O(8)–H(8A)···O(10)a, 2.772(3) Å; O–
H···O, 175(3)°; O(10)–H(10A)···O(8)c, 2.958(3) Å; O–H···O,
158(3)° (c = 1+x, y, z)].
Some disorder and minor conformational variation in the
nitro groups of the dnsa molecules are present but are not
sufficient to contribute to the more serious structural
problem (described in Experimental), which manifests itself
as pseudo-symmetry (both translation and inversion) among
the four sets of molecular pairs in the crystallographic
asymmetric unit. By a legal shift of the origin in the space
group Pc in both the x direction (0.390) and the y direction
(0.063), a pseudo-translation (x, ½+y, z) is created, relating
the X, XЈЈ and X:, XЈ pairs. In addition, a pseudo-inversion
No nitro-group participation in hydrogen bonding is
found.
5
1
centre at (1/2, /8, /2) would create the P21/c cell (with the b
axis halved) from the previous unsuccessful structure
determination attempt.[12] Such pseudo-symmetry identifies
the possible presence of a stacking fault or inversion-related
twinning. The presence of the ‘ghost’ oxine may be an
artefact of such phenomena if ignored[16] but the
computational treatment necessary to handle the problem
will not be considered here. This argument, however, would
tend to obviate oxine as a contributing factor, having, as
previously mentioned, a tendency to act as a labile molecule
of crystallization despite its moderate melting temperature
(76°C). This was definitely the case with the cyclic 2 : 2
proton-transfer compound with Kemp’s triacid where a labile
disordered partial unassociated oxine molecule (occupancy
ca. 0.9) existed beside the stable dimeric acid–oxine cage
structure.[13] Oxine has been observed to undergo intrusive
solid-state reaction by diffusion into certain anhydrides,[17]
nitrophenols,[18] salicylic acid[19] and metal salts.[20] The
formation of the 2 : 1 proton-transfer adduct with 1,2,3-
trihydroxybenzene also proceeds in a similar manner by
intrusive solid-state reaction.[10] Of possible relevance to the
present examples, it was observed that with the
nitrophenols,[18] reaction proceeded more readily with
increased nitro-group substitution and with increased
molecular symmetry. It must be generally assumed that both
types of solid-state reaction involving oxine (either intrusive
or effusive, usually without crystal breakdown), occur by
similar mechanisms.
[(oxine+)(dnsa–)] (6)
The 1 : 1 proton-transfer compound of oxine with 3,5-
dinitrosalicylic acid, [(oxine+)(dnsa–)], is similar to the
previously discussed carboxylic acid–oxine cocrystals in
having the primary hydrogen-bonded dimeric repeat within
all four hetero-pairs in the crystallographic repeating unit
(Fig. 4). All interactions between the quinolinium proton and
the carboxylate oxygen are dimensionally and geometrically
similar [N(1)–H(1)···O(4), 2.730–2.790(9) Å; N–H···O, 149–
160(4)°]. Similar extensions to those found in (4) and (5) via
strong peripheral hydrogen bonds linking the protons of the
8-hydroxy substituent of oxine with one of the carboxyl
oxygens of dnsa are also found [O(1)–H(1)···O(3ЈЈ)a,
Experimental
Fig. 4. Atom numbering scheme and hydrogen bonding involving
the four independent A–B dimers in the crystallographic repeating unit
in the adduct (6).
All complexes were prepared from 1 : 1 molar amounts of quinolin-8-ol
(0.2 g, 1.4 mmol) and respectively, 2-nitrobenzoic acid (1), 3-
nitrobenzoic acid (2), 4-nitrobenzoic acid (3), 3,5-dinitrobenzoic acid

174
G. Smith et al.
(4), 5-nitrosalicylic acid (5) and 3,5-dinitrosalicylic acid (6).
Preparations involved heating under reflux for 10 min at ca. 90°C in 20
cm3 of 95% ethanol, the product being subsequently obtained by the
partial or total evaporation of the solvent at room temperature, yielding
for (1) large yellow prisms (m.p. 88–90°C); for (2), yellow
microcrystals (m.p. 130–131°C); for (3), yellow prisms (m.p. 195–
198°C); for (4), yellow prisms (m.p. 161–162.5°C); for (5) a yellow
powder (m.p. 180–182°C); for (6) orange needles (m.p. 244–250°C).
Elemental analyses indicated 1 : 1 stoichiometries for all adducts except
(3) (1 : 2), while (1) was a monohydrate. With (4), the presence of 1.5
waters was found from analysis, later confirmed in the crystal structure
determination as a 2 : 2 trihydrate. Found for (1): C, 58.2; H, 4.3; N, 8.5.
C16H14N2O6 requires C, 58.2; H, 4.2; N, 8.5%. Found for (2): C, 61.5;
H, 3.8; N, 8.8. C16H12N2O5 requires C, 61.5; H, 3.8; N, 9.0%. Found for
(3): C, 57.7; H, 3.6; N, 8.8. C23H17N3O9 requires C, 57.6; H, 3.6; N,
8.8%. Found for (4): C, 50.0; H, 3.5; N, 10.8. C32H28N6O17 requires C,
50.0; H, 3.7; N, 10.9%. Found for (5): C, 58.5; H, 3.6; N, 8.3.
C16H12N2O6 requires C, 58.5; H, 3.7; N, 8.5%. Found for (6): C, 51.8;
H, 2.9; N, 11.3. C16H11N3O8 requires C, 51.5; H, 3.0; N, 11.3%.
Attempts to prepare the adduct with 1,3,5-trinitrobenzoic acid using
either the general refluxing method in ethanol at elevated temperature
or the room-temperature variant (because of the ease of
decarboxylation of the acid even at moderate temperature) gave good
crystals of the previously described 1 : 1 oxine–1,3,5-trinitrobenzene
adduct.[9] Infrared spectra were recorded for all samples as pressed
disks in KBr on a Perkin–Elmer Spectrum 1000 Fourier-transform
infrared spectrometer.
by full-matrix least-squares (on F2) by using SHELXL-97[21] with
anisotropic thermal parameters for all non-hydrogen atoms. Hydrogen
atoms involved in the hydrogen-bonding interactions were located by
difference methods and both positional and thermal parameters were
refined while others were generally included at calculated positions in
the refinements as riding models. The values of A and B in the
weighting scheme w = [σ2(Fo)2+(AP)2+BP]–1 {where P = [max.
(Fo ,0)+2(Fc)2]/3} were 0.0783, 0.2461 (3), 0.0593, 0.1264 (4), and
2
0.1826, 0.7519 (6). With (3), the high thermal motion of the nitro-
oxygens of molecule 1 [O(4) and O(5)] resulted in these being modelled
over two independent sites with occupancies of 0.80 and 0.20
respectively. Compound (6), which we had previously investigated
unsuccessfully crystallographically,[12] when it was found to have what
appeared to be bad disorder in the space group P21/c with Z 4 in a unit
cell with half the present b axial parameter, was resolved in the lower-
symmetry space group Pc with Z 8. In this space group, pseudo-
symmetry is present with the molecules related by an approximate 21
screw operation and inversion symmetry. This is somewhat analagous
to, but not as severe as, the modulated structure described for the 1 : 1
proton-transfer adduct of 2,4,6-trinitrobenzoic acid with 2,6-
diaminopyridine.[22] In addition, the presence of a partial disordered
labile molecule of oxine contributes to the high refinement residual
which could be reduced from the table value (R 0.080) to ca. R 0.05 by
incorporating electron density equivalent to 90% of a ghost oxine
molecule having an occupancy of 0.08. This effect may also be due to
the presence of an overriding but inadequately modelled stacking fault
or an inversion twin. However, this structural problem could not be
further handled in this study and furthermore, the Pc model adequately
describes the basic hydrogen-bonded structural framework which is not
altered by the presence of the the unasssociated ‘ghost oxine’. A similar
phenomenon was observed for the structure of the 1 :1 proton-transfer
compound of Kemp’s triacid with oxine,[13] in which a partial
disordered oxine molecule of crystallization was lost progressively with
time during room-temperature data collection, without significant loss
in crystallinity.
Crystallography
Crystal Data
(3) [(C9H8NO+)(C7H4NO4–)(C7H5NO4)], CCDC 164598, mol. wt
–
479.4, triclinic, space group P1, a 7.052(2), b 7.497(2), c 21.121(6) Å,
α 97.94(2), β 97.35(3), γ 99.45(2)°, V 1077.9(5) Å3, F(000) 496, Z 2,
Dc 1.477 g cm–3, µ(Mo Kα) 1.16 cm–1, temperature 293(2) K. 4089
reflections measured [2θmax 51°: h, 0 to 8; k, –8 to 8; l, –25 to 24], 3756
unique (Rint 0.012). Final R1* 0.048 (F); wR2† 0.123 (F2) [2845
observed with I > 2.0␴(I)]; S 1.03. Crystal size 0.50 by 0.30 by
0.25 mm; max/min transmission factors, 0.82/0.70.
Conclusions
The series of quinolin-8-ol compounds with the nitro-
substituted benzoic acids studied here shows a greater
variability in composition and form than any of the other
Lewis-base compounds of the same acids previously studied.
The incorporation of water into the cocrystal make-up in two
of the examples [(1) and (4)] obviously influences the
stabilization of the crystal lattice, which in the case of the
trihydrate (4) links together rows of oxine and dnba
molecules to give an very stable and ordered structure. This
is in contrast to the 1 : 1 compound with dnsa (6), where a
probable stacking fault is present in the structure, and may be
similar to the badly twinned monohydrate (1) where no
structural analysis was possible, despite its macro-crystalline
morphology. Infrared spectroscopy has also proved useful, as
previously noted,[23] for the recognition of proton transfer in
compounds of the type found in this series, particularly with
those for which crystal structure determinations are not
possible e.g. (1), (2) and (5). As with the parallel study
involving the same series of acids with the analogous
nitrogen base 8-aminoquinoline,[24] disappearance of the
characteristic strong C=O stretching frequency at ca.1700
cm–1 is the most definitive sign in the composite spectrum of
proton transfer [except in the case of the 1 : 2 adduct (3)
where free acid is present]. The accompanying broad =N–H+
(4) [(C H NO+) (C H N O –) ·3H O], CCDC 164597, mol. wt
9
8
2
7
3
2
6
2
2
768.6, monoclinic, space group P21, a 14.9606(6), b 7.4287(5), c
15.633(1) Å, β 102.170(4)°, V 1698.4(2) Å3, F(000) 796, Z 2, Dc 1.503
g cm–3, µ(Cu Kα) 1.22 cm–1, temperature 293(2) K. 3851 reflections
measured [2θmax 150°: h, –18 to 0; k, 0 to 9; l, –19 to 19], 3705 unique
(Rint 0.022). Final R1 0.029 (F); wR2 0.084 (F2) [3564 observed with
I > 2.0σ(I)]; S 1.04; absolute structure parameter, 0.01(15). Crystal size
0.43 by 0.30 by 0.23 mm.
(6) [(C9H8NO+)(C7H3N2O7 )], CCDC 164599, mol. wt 373.3,
–
monoclinic, space group Pc, a 8.015(2), b 15.010(2), c 26.546(2) Å, β
95.52(2)°, V 3178.8(9) Å3, F(000) 1536, Z 8, Dc 1.560 g cm–3, µ(Cu
Kα) 1.11 cm–1, temperature 293(2) K. 7322 reflections measured
[2θmax 140°: h, –6 to 9; k, –12 to 18; l, –32 to 32], 7103 unique (Rint
0.013). Final R1 0.080 (F); wR2 0.210 (F2) [6101 observed with
I > 2.0σ(I)]; S 1.03; absolute structure parameter, 0.4(3). Crystal size
0.78 by 0.21 by 0.14 mm; max/min transmission factors, 0.87/0.64.
Data Collection, Structure Solution and Refinement
X-Ray diffraction data for all compounds were measured on Enraf–
Nonius CAD-4 diffractometers by using either crystal-
monochromatized Mo Kα X-radiation (λ 0.71073 Å) [compound (3)]
or Cu Kα X-radiation (λ 1.5418 Å) [compounds (4) and (6)]. Negligible
change in the intensities of three standards monitored throughout the
data collection periods for all adducts indicated no significant crystal
decomposition. Data were corrected for Lorentz and polarization
effects, extinction and for absorption [(3) and (6) only (analytical,
Gaussian)]. The structures were solved by direct methods and refined
*R1 = (⌺ | Fo | – |Fc|)/(⌺ |Fo|).
†wR2 = [⌺w(Fo – Fc )2/⌺w(Fo )2]½.
2
2
2

Interactions of Carboxylic Acids with Oxine
175
absorptions expected in the 2700–2250 cm–1 region of the
spectrum[25] are invariably unresolved within the broad and
extended hydrogen-bonded –OH absorptions centred
typically at ca. 3400 cm–1 [range: 3391 (2) to 3446 cm–1 (6)],
similar to those in the parent oxine (3405 cm–1).[26] However,
infrared spectroscopy remains a useful tool for the
identification of the nature of the interaction in such
compounds.
[11] W. W. Wendlandt, G. R. Horton, J. Inorg. Nucl. Chem. 1963, 25,
247; P. Roychowdhury, B. N. Das, B. S. Basak, Acta Crystallogr.,
Sect. B 1978, 34, 1047; S. H. Simonsen, D. W. Bechtel, Am.
Cryst. Assoc., Ser. 2 1980, 7, 23; T.Bannerjee, N. N. Saha, Acta
Crystallogr., Sect. C 1986, 42, 1408.
[12] G. Smith, D. E. Lynch, K. A. Byriel, C. H. L. Kennard, Aust. J.
Chem. 1995, 48, 133.
[13] G. Smith, U. D. Wermuth, J. M. White, Chem. Commun. 2000,
2349.
[14] Smith, D. E. Lynch, K. A. Byriel, C. H. L. Kennard, Aust. J.
Chem. 1995, 48, 1133.
[15] G. Smith, D. E. Lynch, K. A. Byriel, C. H. L. Kennard, Acta
Crystallogr., Sect. C 1996, 52, 231.
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Acknowledgments
The authors acknowledge financial support from the Centre
for Instrumental and Developmental Chemistry of the
Queensland University of Technology, The Australian
Research Council and the University of Melbourne. The
referee is thanked for the deconvolution of the pseudo-
symmetry problem with compound (6).
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