Crystallographic studies on a series of salts of 2,3,7-trihydroxy-9-phenyl-fluorone

Article abstract of DOI:10.1016/j.molstruc.2008.12.020

2,3,7-Trihydroxy-9-phenyl-fluorone (hereafter H₃Z) has been synthesised in its H₄Z⁺, H₃Z, H₂Z^- and Z^3- protonation states. X-ray crystal structure determinations have been carried out for (H₄Z)(HSO₄), H₃Z, [EtⁱPr₂NH]H₂Z, solvated (PPh₄)H₂Z and solvated K₃Z. In each of these salts the 9-phenyl group adopts a different orientation so as to be involved in intermolecular aromatic interactions. The 3- and 6-phenolic carbon-oxygen bond lengths show that double bond character can be delocalised from the ketone to the deprotonated phenoxide across the conjugated π system of the fluorone.

Full text of DOI:10.1016/j.molstruc.2008.12.020

Journal of Molecular Structure 920 (2009) 466–471
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Crystallographic studies on a series of salts of 2,3,7-trihydroxy-9-phenyl-fluorone
*
*
Brendan F. Abrahams , Laura J. McCormick, Richard Robson
School of Chemistry, University of Melbourne, Vic. 3010, Australia
a r t i c l e i n f o
a b s t r a c t
2,3,7-Trihydroxy-9-phenyl-fluorone (hereafter H3Z) has been synthesised in its H4Z+, H3Z, H2Zꢀ and Z3ꢀ
protonation states. X-ray crystal structure determinations have been carried out for (H4Z)(HSO4), H3Z,
[EtiPr2NH]H2Z, solvated (PPh4)H2Z and solvated K3Z. In each of these salts the 9-phenyl group adopts a
different orientation so as to be involved in intermolecular aromatic interactions. The 3- and 6-phenolic
carbon–oxygen bond lengths show that double bond character can be delocalised from the ketone to the
Article history:
Received 23 October 2008
Accepted 3 December 2008
Available online 16 December 2008
Keywords:
X-ray crystallography
Fluorones
deprotonated phenoxide across the conjugated
p
system of the fluorone.
Ó 2009 Elsevier B.V. All rights reserved.
Amphoteric organic systems
1. Introduction
2. Experimental
2,3,7-Trihydroxy-fluorones, in particular the readily available 9-
phenyl derivative, I (hereafter H3Z), have been used extensively in
the spectrophotometric analysis of a wide range of metals [1]. H3Z
shows amphoteric character as a result of conjugative interactions
between the oxygen functions at positions 3- and 6-, as described
below. The hydroxy group at position 3- is distinctly more acidic
than the remaining two typically phenolic groups at positions 2-
and 7- as a result of the delocalisation of negative charge in H2Zꢀ
represented by II and III. Likewise the ‘‘quinone-like” C@O group
at position 6- is distinctly more basic than normal quinones (or
ketones) as a result of the delocalisation of the positive charge fol-
lowing protonation (to give H4Z+) as represented in IV and V.
We have found only two structural studies in the literature of com-
pounds related to or derived from H3Z. In 2003 Ward and co-work-
ers [2] reported the structure þof a binuclear ruthenium derivative
namely f½RuIIðPPh3Þ ðCOÞ ꢁ Zg PFꢀ in which the Z3ꢀ ion bridges a
NMR data were collected on a Varian Unity +400 Nuclear
Magnetic Resonance Spectrometers. Infrared spectra were
recorded using a BioRad 175 FTIR spectrometer. Elemental analy-
ses were performed by the Campbell Microanalytical Laboratory,
University of Otago, NZ.
2.1. Syntheses
2.1.1. 2,3,7-Trihydroxy-9-phenyl-fluorone (H3Z)
Benzaldehyde (96 lL, 0.942 mmol) was added to a suspension
of 1,2,4-triacetoxybenzene (500 mg, 1.98 mmol) in ethanol
(15 mL). Aqueous sulfuric acid (15 vol.%, 15 mL) was then added
to the mixture, which was held at 50 °C on a hotplate for four days.
H3Z formed as small orange rod-shaped crystals (104 mg,
0.325 mmol, 35% yield). Infrared, 1H NMR and 13C NMR spectra
presented below were carried out on synthesised (not commer-
cially available) fluorone. IR (KBr) 3461, 2451, 1641, 1619, 1532,
1475, 1442, 1416, 1394, 1347, 1297, 1276, 1233, 1205, 1158,
1131, 1030, 958, 865, 844, 828, 797, 772, 740, 707, 699, 656,
2
2
2
6
pair of RuII centres. In 2006, the structure of the sulfonated deriv-
ative seen in VI was reported [3]; interestingly the sulfonic acid
residue was present as the sulfonate anion and the fluorone
nucleus had been protonated.
627, 603, 599, 577, 449 cmꢀ1 1H NMR (400 MHz, d6-DMSO): d
.
Our main interest in these fluorones is in their metal derivatives,
but given the paucity of structural data available we considered
it worthwhile synthesising and carrying out X-ray structural deter-
6.79 (s, 2H), 7.28 (s, 2H), 7.51 (m, 2H), 7.72 (m, 3H) 13C NMR
(100.5 MHz, d6-DMSO): d 102.4, 107.6, 115.8, 128.1, 128.3, 128.9,
129.3, 129.6, 133.3, 147.7.
minations on crystalline solids containing H4Z+, H3Z, H2Zꢀ and Z3ꢀ
.
Reported below are the syntheses and X-ray crystal structures of
(H4Z)(HSO4), H3Z, [EtiPr2NH]H2Z, solvated (PPh4)H2Z and solvated
K3Z.
2.1.2. H4Z(HSO4)
2,3,7-Trihydroxy-9-phenyl-fluorone (75 mg, 0.234 mmol) was
suspended in a mixture of ethanol (2.5 mL) and aqueous sulfuric
acid (40 vol.%, 2.5 mL) and held at 50 °C in an oven. Large dark
orange hexagonal plate-shaped crystals (33 mg, 0.0789 mmol,
34% yield) formed after three days. IR (KBr): 3112, 1636, 1609,
1561, 1500, 1480, 1445, 1417, 1362, 1272, 1237, 1181, 1128,
* Corresponding authors. Tel.: +61 3 8344 0341/6469; fax: +61 3 9347 5180.
E-mail addresses: bfa@unimelb.edu.au (B.F. Abrahams), r.robson@unimelb.
edu.au (R. Robson).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.12.020

B.F. Abrahams et al. / Journal of Molecular Structure 920 (2009) 466–471
467
13C NMR (100.5 MHz, d6-DMSO): d 99.7, 102.4, 108.6, 117.3,
118.2, 128.5, 129.1, 130.5, 130.6, 134.6, 134.7, 135.5, 148.9,
154.3, 171.1 Anal. Calcd for (C19H11O5)(C24H20P)ꢂ(CH4O) C: 76.51
H: 5.11% Found C: 76.51 H: 5.33%.
2.1.5. K3Zꢂ2H2OꢂDMSO
A solution of potassium hydroxide (369 mg, 6.59 mmol) in
water was added to a suspension of H3Z (205 mg, 0.640 mmol) in
hot dimethylsulfoxide (5 mL). The red plate-shaped crystals
(154 mg, 0.281 mmol, 44% yield) that formed were filtered directly
from the hot purple solution and washed first with warm dimeth-
ylsulfoxide, then chloroform. IR (KBr) 3437, 2926, 2360, 2342,
1626, 1489, 1404, 1385, 1309, 1210, 1176, 1125, 1019, 1008,
832, 770, 703, 668, 658, 579, 451 cmꢀ1 1H NMR (400 MHz, D2O):
.
d 2.91 (s, 3H, DMSO), 6.07 (s, 2H), 6.44 (s, 2H), 7.18 (m, 3H), 7.40
(s, 2H) 13C NMR (100.5 MHz, d6-DMSO): d 103.25, 106.48, 114.57,
129.53, 129.68, 130.52, 136.28, 154.12, 174.48.
2.2. X-ray crystallography
In each of the structures outlined below, the crystal data are of
sufficient quality to enable the phenolic hydrogen atoms to be
clearly located. All hydrogen atoms were included at their geomet-
rically estimated positions. Structures 1–5 were solved using direct
methods and refined using SHELX-97 [4]. Analytical absorption
corrections were applied in the case of structures 1 and 2 using
Crysalis CCD software [5].
2.2.1. Crystal data for H3Z
Crystals of composition C19H12O5 were isolated as orange rods.
Crystal dimensions 0.20 ꢃ 0.016 ꢃ 0.015, Mr = 320.29 g molꢀ1
,
1044, 967, 881, 872, 856, 748, 707, 636, 603, 582, 522, 418 cmꢀ1
.
monoclinic, space group C2. Collection temperature 130 K,
a = 18.3932(6) b = 5.1209(2) c = 15.5362(5) Å, b = 100.376(3)°,
1H NMR (400 MHz, d6-DMSO): d 6.56 (s, 2H), 6.97 (s, 2H), 7.47
(m, 2H), 7.67 (m, 3H). 13C NMR (100.5 MHz, d6-DMSO): d 102.4,
108.7, 116.6, 129.0, 129.3, 130.2, 132.8, 147.9, 153.3, 155.5, 162.1
Anal. Calcd for (HSO4)(C19H13O5) C: 54.54 H: 3.37 S: 7.66% Found
C: 54.45 H: 3.53 S: 7.88%.
V = 1439.42(9) Å3, Z = 4, calc = 1.478 g cmꢀ3, k = 1.54184 Å 2hmax
q =
144.64°. All non-hydrogen atoms were refined anisotropically.
Final R1 = 0.0524 (I > 2 (I)) for 2046 unique reflections, 257
r
parameters, wR2 = 0.1360, GOF 0.914.
2.1.3. (EtiPr2NH)H2Z
2.2.2. Crystal data for (H4Z)(HSO4)
N-Ethyldiisopropylamine (Hünig’s base) (2 mL, 11.5 mmol) was
added to a solution of 2,3,7-trihydroxy-9-phenyl-fluorone (200 mg,
0.624 mmol) in boiling DMF (20 mL) and the solution allowed to
cool. Large red rod-shaped crystals (113 mg, 0.251 mmol, 40%
yield) were collected by vacuum filtration. IR (KBr) 3462, 3235,
2986, 2476, 1634, 1593, 1558, 1546, 1506, 1444, 1348, 1312,
1265, 1235, 1203, 1173, 1128, 1059, 1027, 959, 859, 828, 798,
C19H14O9S formed as large brown hexagonal crystals. Crystal
dimensions 0.21 ꢃ 0.20 ꢃ 0.10 mm. Mr = 418.36 g molꢀ1
, mono-
clinic, space group P21/n. Collection temperature 130 K,
a = 12.1173(1) b = 8.9613(10) c = 15.5100(1) Å, b = 94.728(1)°,
V = 1678.45(3) Å3, Z = 4, calc = 1.656 g cmꢀ3, k = 1.54184 Å, 2hmax
q =
146.92°. All non-hydrogen atoms were refined anisotropically. Final
R1 = 0.0352 (I > 2 (I)) for 3140 unique reflections, 270 parameters,
r
772, 745, 735, 701, 686, 657, 597, 578, 449, 408 cmꢀ1 1H NMR
.
wR2 = 0.1142, GOF 0.909.
(400 MHz, d6-DMSO): d 1.07 (m, 12H), 2.78 (m, 2H), 3.13 (m, 3H),
3.29 (m 2H), 6.21 (s, 2H), 6.47 (s, 2H), 7.36 (m, 2H), 7.62 (m, 3H).
13C NMR (100.5 MHz, d6-DMSO): d 14.6, 19.0, 48.60, 48.62, 50.7,
100.9, 104.5, 111.8, 128.6, 128.8, 129.1, 134.4, 146.5, 148.2,
153.1, 167.6. Anal. Calcd for (C8H20N)(C19H11O5)ꢂ0.1DMF C: 71.77,
H: 6.99, N: 3.37%. Found: C: 71.51, H: 6.99, N: 3.49%.
2.2.3. Crystal data for (EtiPr2NH)ZH2
Crystals of C27H31NO5 formed as red hexagonal plates. Crystal
dimensions 0.24 ꢃ 0.18 ꢃ 0.06 mm, Mr = 449.53 g molꢀ1
, mono-
clinic, space group P21/c. Collection temperature 130 K,
a = 7.7139(8) b = 23.491(3) c = 12.9472(14) Å, b = 93.617(2)°,
V = 2341.5(4) Å3, Z = 4,
q =
calc = 1.275 g cmꢀ3, k = 0.71073 Å 2hmax
2.1.4. (Ph4P)H2ZꢂMeOH
53.48°. All non-hydrogen atoms were refined anisotropically. Final
R1 = 0.0551 (I > 2 (I)) for 5297 unique reflections, 319 parameters,
2,3,7-Trihydroxy-9-phenyl-fluorone (100 mg, 0.312 mmol) and
tetraphenylphosphonium bromide (393 mg, 0.937 mmol) were
r
wR2 = 0.1287, GOF 0.959.
suspended in
0.937 mmol) in methanol (12 mL) and allowed to stand at room
temperature. After days, large red block-shaped crystals
a solution of N-ethyldiisopropylamine (160 lL,
7
2.2.4. Crystal data for (PPh4)(H2Z)ꢂMeOH
(100 mg, 0.145 mmol, 47% yield) formed on the wall of the reaction
container. IR (KBr) 3212, 3056, 1639, 1605, 1556, 1543, 1514, 1494,
1438, 1378, 1355, 1265, 1229, 1192, 1160, 1109, 1037, 996, 954,
922, 863, 836, 827, 799, 773, 753, 720, 704, 689, 658, 616, 591,
Crystals of (PC24H20)(C19H11O5)(CH4O) formed as red blocks.
Crystal dimensions 0.37 ꢃ 0.30 ꢃ 0.10 mm, Mr = 687.67 g molꢀ1
,
triclinic, space group P-1. Collection temperature 130 K,
a = 9.8493(9) b = 9.9679(9) c = 18.8715(18) Å,
b = 75.334(2)
= 86.848(2)°, V = 1730.3(3) Å3, Z = 2,
cmꢀ3 k = 0.71073 Å 2hmax = 54.74°. All non-hydrogen atoms were
a
= 74.888(2)
qcalc = 1.320 g
574, 534, 526, 452, 403 cmꢀ1
.
1H NMR (400 MHz, d6-DMSO): d
c
5.10 (s, 2H), 5.28 (s, 2H), 6.38 (s, 2H), 6.61 (s, 3H), 6.83 (m, 20H).

468
B.F. Abrahams et al. / Journal of Molecular Structure 920 (2009) 466–471
refined anisotropically. Final R1 = 0.0530 (I > 2r(I)) for 7570 unique
reflections, 463 parameters, wR2 = 0.1316, GOF 0.952.
2.2.5. Crystal data K3Zꢂ2H2OꢂDMSO
Crystals of K3C19H9O5ꢂ2H2OꢂC2H6SO formed as red plates. Crys-
tal dimensions 0.20 ꢃ 0.07 ꢃ 0.01 mm, Mr = 548.72 g molꢀ1, tri-
clinic, space group P-1. Collection temperature 130 K, a = 9.636(3)
Fig. 1. The H3Z asymmetric unit. Thermal ellipsoids are at the 50% probability level.
The phenyl ring is disordered over two orientations, each with 50% occupancy, only
one of which is shown here.
b = 10.002(3) c = 12.571(4) Å,
a
= 102.087(6) b = 90.381(7)
c = 98.
204(6)°, V = 1171.8(6) Å3, Z = 2
q
calc = 1.638 g cmꢀ3, k = 0.71073 Å
2hmax = 53.56°. All non-hydrogen atoms were refined anisotropi-
cally. The weakly diffracting nature of these very small crystals
resulted in elevated agreement values. Final R1 = 0.0951
(I > 2r(I)) for 4047 unique reflections, 298 parameters,
wR2 = 0.1992, GOF 0.931.
3. Results and discussion
3.1. H3Z
The neutral form of the fluorone, H3Z, was prepared by heating
a suspension of 1,2,4-triacetoxybenzene in a solution of benzalde-
hyde, ethanol and aqueous sulfuric acid. The fluorone unit itself is
very close to being planar, with the 9-phenyl ring disordered over
two orientations of equal occupancy. The two orientations are
inclined to the plane of the fluorone by 64.9(3) and 117.2(2)°.
The 3-phenolic carbon–oxygen bond (1.335(5) Å), although longer
than the carbonyl C@O double bond (1.281(5) Å), is shorter than
the other phenolic carbon–oxygen bonds (1.362(5) Å). This is
indicative of partial double bond character with some delocalisa-
tion from the 6-carbonyl group across the aromatic fluorone unit
and into the 3-carbon–oxygen bond, as described in the introduc-
tion. A list of phenyl group – fluorone angles and selected carbon–
oxygen bond lengths is presented in Table 1 (Fig. 1).
Hydrogen bonds between fluorone units result in the formation
of chains, shown in Fig. 2. The chains align themselves into layers
with all chains in a given layer running parallel to each other.
Layers stack in an ABAB fashion in the c-direction, with all chains
within a single layer running parallel to each other. The direction of
the chains in the ‘A’ layers differs by approximately 80° to the direc-
tion of the chains in the ‘B’ layers. The chains in one layer hydrogen
bond to the chains in one neighbouring layer to form a bilayer. Two
different views of the bilayers are presented in Fig. 3a and b. The 9-
phenyl groups extend above and below this bilayer. Fig. 3b shows
Fig. 2. One layer of H3Z hydrogen bonded chains, as viewed from above. The phenyl
ring on any given fluorone has the opposite orientation to those on the fluorone
units immediately beside it. Within a single chain the phenyl groups do not
necessarily have the same orientation.
a single bilayer represented by dark bonds. The phenyl groups
oriented up and down interdigitate with those of adjacent bilayers.
3.2. (H4Z)(HSO4)
(H4Z)(HSO4) was prepared by heating H3Z in an aqueous etha-
nol/sulfuric acid mixture. The protonation of the fluorone unit
leads to the lengthening of the carbon–oxygen bond in the 6-posi-
tion to 1.335(2) Å. The three phenolic carbon–oxygen bonds have
lengths of 1.367(2), 1.354(2) and 1.339(2) Å (Fig. 4).
The fluorone cation and bisulfate anions interact via hydrogen
bonds. Each ion is involved in five hydrogen bonds. The fluorone
cation acts as the hydrogen bond donor in four of these interac-
tions and as the acceptor in the remaining one. Conversely, the
bisulfate anion acts as the donor in only one of its hydrogen bonds
and the acceptor in the remaining four. This series of hydrogen
bonds results in the formation of a complex three-dimensional
hydrogen bonded network.
Table 1
Selected bond lengths and angles of the fluorone species.
C6–O6 (Å)
C3–O3 (Å)
C2–O2 (Å)
C7–O7 (Å)
Angle between phenyl ring and fluorone (°)
H3Z
1.281(5)
1.335(2)
1.265(2)
1.272(2)
1.28(1)
1.335(5)
1.339(2)
1.291(2)
1.288(2)
1.29(1)
1.362(5)
1.367(2)
1.359(2)
1.359(2)
1.33(1)
1.362(5)
1.354(2)
1.357(2)
1.359(2)
1.30(1)
117.2(2) and 64.9(3)
63.0(5)
73.9(6)
67.7(6)
72.4(3)
(H4Z)(HSO4)
(HNEtiPr2)(H2Z)
(PPh4)(H2Z)
K3Z

B.F. Abrahams et al. / Journal of Molecular Structure 920 (2009) 466–471
469
Fig. 4. A representation of the hydrogen bonds in (H4Z)(HSO4) surrounding (a) the
fluorone cation and (b) the bisulfate anion. Each fluorone cation forms hydrogen
bonds to five bisulfate anions and each bisulfate anion hydrogen bonds to five
fluorone cations. Thermal ellipsoids are at the 50% probability level. Hydrogen
atoms bound to carbon atoms have been removed from (b) for clarity.
Fig. 3. (a) The H3Z hydrogen bonded bilayer. Chains within a single layer are shown
in the same shade. Hydrogen bonds are represented by black and white striped
bonds. (b) The phenyl groups of two adjacent bilayers interdigitate. Both orienta-
tions of the phenyl rings are shown. Hydrogen bonds between fluorone units are
not shown.
crystals have edge lengths of several millimeters. The crystals have
a deep green, lustrous, highly reflective appearance when viewed
with reflected light however, the crystals appear red and transpar-
ent under transmitted light.
3.3. [EtiPr2NH]H2Z
(HNEtiPr2)H2Z, Fig. 5, was obtained by cooling a hot DMF solu-
tion of Hünig’s base and H3Z. As expected, the phenol group in the
3-position is deprotonated. The carbon–oxygen bonds in the 6- and
3-positions are 1.265(2) and 1.291(2) Å respectively, which is con-
sistent with significant double bond character in both bonds. The
2- and 7-phenolic carbon–oxygen single bonds have lengths of
1.359(2) and 1.357(2) Å. The terminal carbon on the ethyl group
on the trialkylammonium cation is disordered over several sites.
In the solid state, each H2Zꢀ unit forms hydrogen bonds to an
ethyldiisopropylammonium cation and to three other fluorones.
This results in a two-dimensional net of (6,3) topology, shown in
Fig. 6. The sheets are arranged such that the spaces in each sheet
are located directly above the spaces in the sheet below leading
to the formation of channels. The trialkylammonium cations are
located within these channels.
3.4. (PPh4)H2ZꢂMeOH
Fig. 5. The asymmetric unit of (HNEtiPr2)H2Z. Only one orientation of the
trialkylammonium cation is shown, and aliphatic hydrogen atoms have been
omitted for clarity. The thermal ellipsoids are at 50% probability level.
Crystals of (PPh4)H2ZꢂMeOH were obtained from a mixture of
H3Z, PPh4Br and Hünig’s base in methanol upon standing. These

470
B.F. Abrahams et al. / Journal of Molecular Structure 920 (2009) 466–471
Fig. 9. The three-dimensional network of K3ZꢂDMSOꢂ2H2O. The sheets depicted in
Fig 8 extend horizontally into the plane of the page and are bridged by solvent
water molecules. Solvent water molecules are shown as hatched circles and the
atoms of DMSO are shown as open circles.
Fig. 6. The (HNEtiPr2)H2Z hydrogen bonded sheets. The trialkylammonium cations
sit in the spaces within the sheets and are shown in black. Only one orientation of
the trialkylammonium cations is shown.
The carbon–oxygen bond involving the 3-phenoxy group in this
instance, as in the trialkylammonium salt, shows a very marked
shortening compared to that in the H3Z species, similar to that
found in the (EtiPr2NH)H2Z salt described above. In (PPh4)H2Z,
the 3- and 6-carbon–oxygen bonds have lengths of 1.288(2) and
1.272(2) Å, respectively. The carbon–oxygen framework of the flu-
orone monoanion is essentially identical to that observed in the tri-
alkylammonium salt discussed above. For corresponding bonds in
the PPh4 and HNiPr2Et salts, the largest variation in bond length
between these two structures is approximately 0.02 Å.
As in the H3Z structure, the fluorone units form hydrogen bonds
leading to the formation of chains (Fig. 7). These chains all run par-
allel, trapping the PPh4 cations in the spaces between them. The 9-
phenyl ring is inclined to the plane of the fluorone by a dihedral an-
gle of 67.7(6)°, which allows it to participate in edge-to-face aro-
matic interactions with one of the phenyl rings of a PPh4 cation.
Fig. 7. The cations in (PPh4)H2ZꢂMeOH surrounded by hydrogen bonded fluorone
chains. The phenyl ring on the H2Z anion is involved in an edge-to-face interaction
with one ring on the PPh4 cation. Methanol molecules are not shown.
3.5. K3Zꢂ2H2OꢂDMSO
The addition of aqueous KOH to a suspension of H3Z in hot
DMSO led to the formation of hygroscopic red crystals with green
iridescence. Each Z3ꢀ unit is associated with nine potassium cen-
tres. In addition to the expected short carbon–oxygen bonds at
positions 3- and 6- on the fluorone (1.29(1) and 1.28(1) Å, respec-
tively) the two remaining hydroxyl C–O distances are shorter than
those observed in the two H2Zꢀ salts: 1.33(1) and 1.30(1) Å in Z3ꢀ
,
1.354(2)–1.367(2) Å in the H2Zꢀ structures. There are three crystal-
lographically distinct K+ ions each of which links to three Z3ꢀ units.
Each Z3ꢀ unit in turn interacts with nine potassium ions with K–O
distances ranging from 2.63(1) to 3.03(1) Å.
As indicated in Fig. 8, a two-dimensional network is formed
through interaction of Z3ꢀ with K+ ions. The network is further sup-
ported by bridging oxygen atoms belonging to DMSO molecules.
The phenyl ring of the fluorone is inclined to the fluorone by
72.4(3)°. This phenyl ring participates in a pair of edge to face
interactions with a catechol-like group from the same sheet and
another catechol-like group belonging to an adjacent sheet. Water
molecules bridge potassium ions from adjacent sheets leading to
the generation of a three-dimensional network, Fig. 9.
4. Concluding remarks
Fig. 8. A 2D sheet resulting from potassium–fluorone interactions within
K3ZꢂDMSOꢂ2H2O. The potassium–oxygen interactions are shown as darker. Potas-
sium atoms are shown as large dark spheres and DMSO atoms are represented as
open circles.
The 9-phenyl-2,3,7-trihydroxyfluor-6-one has been synthesised
and structurally characterised in four different protonation states –

B.F. Abrahams et al. / Journal of Molecular Structure 920 (2009) 466–471
471
H4Z+, H3Z, H2Zꢀ and Z3ꢀ. The 3- and 6-phenolic carbon–oxygen
bond lengths indicate that double bond character is delocalised
across the conjugated system from the ketone to the deproto-
nated phenoxide. The orientation of the 9-phenyl ring with respect
to the fluorone unit varies from compound to compound in order
to participate in intermolecular aromatic interactions.
Acknowledgement
p
The authors gratefully acknowledge the Australian Research
Council for their financial support.
References
[1] Z. Li, Rev. Anal. Chem. 22 (2003) 257.
[2] A.P. Meacham, K.L. Druce, Z.R. Bell, M.D. Ward, J.B. Keister, A.B.P. Lever, Inorg.
Chem. 42 (2003) 7887.
5. Supporting Information
[3] S. Kamino, M. Doi, T. Yamaguchi, H. Tominaga, E. Amano, S. Umehara, M. Naito,
C. Yamazaki, Y. Fujita, X-ray Struct. Anal. Online 22 (2006) x35.
[4] G.M. Sheldrick, SHELX-97. Programs for Crystal Structure Analysis, University of
Göttingen, Germany, 1998.
[5] Oxford Diffraction 2006, Crysalis CCD and RED Version 1.171.29.2, Oxford
Diffraction Ltd., Wroclaw, Poland.
CCDC 705417–705421 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336 033).