Hexaquacobalt(II) bis-(5-hydroxy-7-methoxy-4-oxo-2-phenyl-4H-chromene-6- sulfonate) tetrahydrate

Article abstract of DOI:10.1107/S0108270108006975

The title compound, [Co(H2O)6](C16H11O7S)2·4H2O, with cobalt(II) at the centre of symmetry, exhibits alternating hydro-philic and hydro-phobic regions. Hydro-philic regions are generated by O - H...O hydrogen bonds among sulfonate groups, involving solvent water mol-ecules and coordinated water mol-ecules; π-π stacking inter-actions assemble the flavone skeletons into columns which form the hydro-phobic regions. A three-dimensional network is built up from an extensive array of hydrogen bonds, π-π stacking inter-actions and electrostatic inter-actions between the cation and anion. As a salt of the sulfonated derivative of naturally occurring tectochrysin (5-hydr-oxy-7-methoxy-flavone), this compound offers enhanced solubility and potential biological activity over the natural product.

Full text of DOI:10.1107/S0108270108006975

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
the biological activity of tectochrysin, it is important to
prepare and study sulfonated derivatives that may offer
improved properties. In this paper, we report the crystal
structure of the cobalt(II) salt of 5-hydroxy-7-methoxy-
flavone-6-sulfonate, (I).
ISSN 0108-2701
Hexaquacobalt(II) bis(5-hydroxy-
7-methoxy-4-oxo-2-phenyl-4H-
chromene-6-sulfonate) tetrahydrate
Wu-Wu Lia,b and Zun-Ting Zhanga,b
*
As shown in Fig. 1, (I) consists of a [Co(H2O)6]2+ cation,
two 5-hydroxy-7-methoxyflavone-6-sulfonate anions and four
water molecules. The CoII ion, lying on an inversion centre,
has a nearly ideal octahedral environment consisting of six O
atoms from coordinated water molecules. The equatorial
plane of the octahedron is defined by atoms O1, O2, O1vi and
O2vi [symmetry code: (vi) ꢁx, ꢁy + 2, ꢁz + 2], with an average
aKey Laboratory of Medicinal Plant Resources and Natural Pharmaceutical Chemistry
(Shaanxi Normal University), Ministry of Education, Xi’an 710062, People’s Republic
of China, and bSchool of Chemistry and Materials Science, Shaanxi Normal
University, Xi’an 710062, People’s Republic of China
Correspondence e-mail: zhangzt@snnu.edu.cn
Received 28 January 2008
Accepted 12 March 2008
Online 20 March 2008
The title compound, [Co(H2O)6](C16H11O7S)2ꢀ4H2O, with
cobalt(II) at the centre of symmetry, exhibits alternating
hydrophilic and hydrophobic regions. Hydrophilic regions are
generated by O—Hꢀ ꢀ ꢀO hydrogen bonds among sulfonate
groups, involving solvent water molecules and coordinated
water molecules; ꢀ–ꢀ stacking interactions assemble the
flavone skeletons into columns which form the hydrophobic
regions. A three-dimensional network is built up from an
extensive array of hydrogen bonds, ꢀ–ꢀ stacking interactions
and electrostatic interactions between the cation and anion.
As a salt of the sulfonated derivative of naturally occurring
tectochrysin (5-hydroxy-7-methoxyflavone), this compound
offers enhanced solubility and potential biological activity
over the natural product.
Figure 1
The molecular structure of (I), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level.
Hydrogen bonds are shown as dashed lines.
Comment
Tectochrysin (5-hydroxy-7-methoxyflavone), a naturally
occurring flavonoid and one of the effective components of
propolis (Fujimoto et al., 2001), has many different biological
activities, including anticancer (Ahmed-Belkacem et al., 2005),
antioxidant (Lee et al., 2003) and trypanocidal activity
(Takeara et al., 2003). The aqueous solubility of flavonoids in
general is poor and their biological utilization rate is low. It is
therefore necessary to synthesize water-soluble flavonoid
derivatives in order to improve their possible biological
activities, and this may be achieved by the introduction of a
sulfonate group (Hiroyuki et al., 1996; Jiang et al., 2001). We
have synthesized some flavonoid sulfonates (Zhang & Wang,
2005; Wang & Zhang, 2005) and studied the biological activ-
ities of sodium 40,7-dihydroxyisoflavone-30-sulfonate (Liu et
al., 2003) and sodium 40-hydroxy-7-methoxyisoflavone-30-
sulfonate (Zhang et al., 2002). The results show that the
biological activities of flavonoid sulfonates are better in
comparison with the corresponding parent flavonoids. Given
Figure 2
Hydrogen-bond R22(8), R22(14) and S(6) motifs in (I). Displacement
ellipsoids are drawn at the 30% probability level and dashed lines
indicate hydrogen bonds. [Symmetry code: (v) ꢁx, ꢁy + 2, ꢁz + 1.]
m176 # 2008 International Union of Crystallography
doi:10.1107/S0108270108006975
Acta Cryst. (2008). C64, m176–m178

metal-organic compounds
˚
Co—O bond length 2.072 (2) A. The axes of the octahedron
(Hunter, 1994). The arrangement of the flavone skeletons of
(I) in an antiparallel fashion and stacked into columns along
the (101) direction is driven by these interactions. The
columns are linked by hydrogen-bond motifs R22(8) and
R22(14), forming the hydrophobic regions of (I) (Fig. 3). The
structure of (I) is quite different from the zinc complex of the
are defined by O3 and O3vi, with Co—O3/O3vi bond lengths of
2.1107 (19) A. The dihedral angle between rings A (C1–C6)
and C (C3–C4/O4/C8–C10) is 1.85 (11)ꢂ, and that between the
benzopyran system (A/C, atoms C1–C6/O4/C8–C10) and ring
B (C11–C16) is 1.95 (11)ꢂ. The flavone skeleton is essentially
planar, with the mean deviation from the least-squares plane
˚
related
5,7-dihydroxyflavone-6-sulfonate,
[Zn-
˚
being 0.0248 A; this is similar to what was found in tecto-
chrysin itself (Chantrapromma et al., 1989).
(5,7-dihydroxyflavone-6-sulfonate)(DMSO)]2ꢀH2O (DMSO =
dimethyl sulfoxide) (Zhang et al., 2006). The Zn compound is
a coordination polymer in which the cation and anion are
linked by Zn—O coordination bonds. By contrast, (I) is a
metal salt of 5-hydroxy-7-methoxyflavone-6-sulfonate in
which the cation and anion are linked together by hydrogen
bonds and electrostatic interactions.
Sulfonate groups, coordinated water molecules and solvent
water molecules in (I) are linked by numerous O—Hꢀ ꢀ ꢀO
hydrogen bonds (Fig. 1 and Table 1). For example, a hydrogen-
bond O1—H1Bꢀ ꢀ ꢀO12—H12Bꢀ ꢀ ꢀO9 chain exists between the
sulfonate group and a coordinated water molecule, bridged by
the solvent water molecule O12. Sulfonate atom O9 is
involved in a three-centred hydrogen bond, viz. O3—H3Bꢀ ꢀ ꢀ
O9 and O12—H12Bꢀ ꢀ ꢀO9. Additionally, cyclic hydrogen-
bond motifs R22(8) and R22(14) (Fig. 2) are formed by paired
‘soft’ hydrogen bonds C9—H9ꢀ ꢀ ꢀO5v and C12—H12ꢀ ꢀ ꢀO5v
[symmetry code: (v) ꢁx, ꢁy + 2, ꢁz + 1], respectively. An
independent hydrogen bond (O6—H6ꢀ ꢀ ꢀO5) forms an intra-
molecular S(6) motif (Fig. 2). The three sulfonate O atoms are
involved in seven O—Hꢀ ꢀ ꢀO hydrogen bonds. According to
Haynes et al. (2004), this indicates that the sulfonate group
behaves as a steric tightener, i.e. brings several hydrogen-bond
acceptors into close contact. The extensive array of hydrogen
bonds makes this region hydrophilic (Fig. 3).
Experimental
Tectochrysin (2.0 g) was added slowly to concentrated sulfuric acid
(10 ml) while stirring. The reaction was maintained at room
temperature for 15 h, then poured into a saturated aqueous NaCl
solution (50 ml) and a yellow precipitate appeared. After 5 h, the
precipitate was filtered and washed with saturated aqueous NaCl
solution until the pH value of the filtrate was 7. The precipitate was
recrystallized from an ethanol–water solution (1:1 v/v) to afford
sodium tectochrysin-6-sulfonate. The product was dried at 378 K for
10 h under vacuum (yield 75%). IR (cmꢁ1, KBr): ꢁ 3465, 1646, 1607,
1487, 1447, 1205, 1144, 1099, 1045, 899, 807, 771, 687. 1H NMR
(DMSO-d6, 300 MHz): ꢂ 13.15 (s, 1H, H–C5–OH), 7.58–7.88 (m, 5H,
H–C20, C30, C40, C50, C60), 6.77 (s, 1H, H–C8), 6.53 (s, 1H, H–C3), 3.88
(s, 3H, C7–OCH3). 13C NMR (DMSO-d6, 75 MHz): ꢂ 177.5 (C4),
162.1 (C7), 160.4 (C2), 158.8 (C8A), 156.2 (C5), 131.6 (C10), 130.5
(C40), 129.0 (C30, C50), 126.0 (C20, C60), 115.6 (C6), 107.6 (C4A), 106.6
(C3), 91.4 (C8), 56.4 (C7–OCH3). Analysis calculated for C16H11Na-
O7S (%): C 51.89, H 2.99; found C 51.15, H 3.21. An aqueous solution
of CoCl2ꢀ6H2O (10%, 5 ml) was mixed with a hot aqueous solution of
sodium tectochrysin-6-sulfonate (5%, 10 ml) and (I) was obtained
after 24 h. The compound was recrystallized from an ethanol–water
solution (3:1 v/v). Pink block-shaped crystals suitable for X-ray
analysis were obtained by slow evaporation of the solvent for about
5 d at room temperature (yield 81%). IR (cmꢁ1, KBr): ꢁ 3460, 1646,
1611, 1488, 1445, 1208, 1179, 1099, 1042, 887, 804, 769, 687.
Additionally, ꢀ–ꢀ stacking interactions between the flavone
skeletons are observed (Fig. 3). Ring B of the flavone skeleton
at (x, y, z) has stacking interactions with ring C of the flavone
at (ꢁx + 1, ꢁy + 2, ꢁz + 1), with a centroid–centroid [CgB–
CgC*; * indicates the symmetry operation (ꢁx, ꢁy + 2, ꢁz + 1)]
˚
distance of 3.5553 (16) A and a perpendicular distance (CgB
˚
on ring C*) of 3.429 (2) A. Ring B of the flavone at (x, y, z) has
stacking interactions with ring A of the flavone at (ꢁx + 1,
ꢁy + 1, ꢁz + 1), with a centroid–centroid [CgB–CgA#;
# indicates the symmetry operation (ꢁx + 1, ꢁy + 1, ꢁz + 1)]
˚
distance of 3.6396 (16) A and a perpendicular distance (CgB
˚
on ring A#) of 3.458 (2) A. These values are close to those
reported for typical aromatic ꢀ–ꢀ stacking interactions
Table 1
Hydrogen-bond geometry (A, ).
ꢂ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
O1—H1Bꢀ ꢀ ꢀO12
O1—H1Cꢀ ꢀ ꢀO8i
O2—H2Bꢀ ꢀ ꢀO12i
O2—H2Cꢀ ꢀ ꢀO10
O3—H3Bꢀ ꢀ ꢀO9
O3—H3Cꢀ ꢀ ꢀO11
O6—H6ꢀ ꢀ ꢀO5
0.82 (3)
0.81 (2)
0.81 (3)
0.82 (2)
0.83 (3)
0.82 (2)
0.82
0.82 (4)
0.83 (3)
0.82 (3)
0.82 (3)
0.96
1.97 (3)
2.00 (3)
1.94 (3)
2.10 (3)
1.98 (3)
1.93 (2)
1.80
2.19 (4)
2.10 (3)
2.02 (3)
2.02 (2)
2.52
2.765 (3)
2.801 (3)
2.751 (3)
2.894 (3)
2.793 (3)
2.744 (3)
2.549 (3)
2.976 (3)
2.912 (3)
2.837 (3)
2.789 (3)
3.430 (3)
3.340 (3)
3.429 (4)
164 (3)
172 (3)
173 (4)
164 (3)
165 (4)
168 (3)
151
160 (4)
166 (4)
169 (4)
158 (3)
159
O11—H11Bꢀ ꢀ ꢀO10ii
O11—H11Cꢀ ꢀ ꢀO8iii
O12—H12Bꢀ ꢀ ꢀO9
O12—H12Cꢀ ꢀ ꢀO10ii
C7—H7Cꢀ ꢀ ꢀO6iv
C9—H9ꢀ ꢀ ꢀO5v
Figure 3
A view of the packing of (I), illustrating the alternating hydrophilic and
hydrophobic regions and nonbonded contacts. CgA, CgB and CgC are the
centroids of rings A, B and C, respectively. Labels marked with a hash (#)
or an asterisk (*) are generated by the symmetry operations (ꢁx + 1,
ꢁy + 1, ꢁz + 1) and (ꢁx + 1, ꢁy + 2, ꢁz + 1), respectively.
0.93
0.93
2.48
2.54
154
159
C12—H12ꢀ ꢀ ꢀO5v
Symmetry codes: (i) ꢁx; ꢁy þ 1; ꢁz þ 2; (ii) x ꢁ 1; y; z; (iii) x ꢁ 1; y þ 1; z; (iv)
x þ 1; y; z; (v) ꢁx; ꢁy þ 2; ꢁz þ 1.
ꢃ
Acta Cryst. (2008). C64, m176–m178
Li and Zhang
[Co(H2O)6](C16H11O7S)2ꢀ4H2O m177

metal-organic compounds
Crystal data
SHELXTL (Sheldrick, 2008); software used to prepare material for
publication: SHELXTL.
[Co(H2O)6](C16H11O7S)2ꢀ4H2O
ꢅ = 83.597 (2)ꢂ
3
˚
Mr = 933.71
Triclinic, P1
V = 1000.7 (3) A
Z = 1
˚
a = 6.978 (2) A
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SQ3126). Services for accessing these data are
described at the back of the journal.
Mo Kꢃ radiation
ꢆ = 0.62 mmꢁ1
T = 296 (2) K
0.34 ꢄ 0.25 ꢄ 0.14 mm
˚
b = 7.2034 (2) A
˚
c = 20.145 (1) A
ꢃ = 83.970 (2)ꢂ
ꢄ = 89.286 (3)ꢂ
References
Data collection
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Bruker SMART CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Bruker, 1999)
Tmin = 0.814, Tmax = 0.915
5062 measured reflections
3500 independent reflections
2949 reflections with I > 2ꢇ(I)
Rint = 0.013
Refinement
R[F2 > 2ꢇ(F2)] = 0.037
wR(F2) = 0.131
S = 1.04
3500 reflections
311 parameters
10 restraints
H atoms treated by a mixture of
independent and constrained
refinement
ꢁ3
˚
Áꢈmax = 0.30 e A
ꢁ3
˚
Áꢈmin = ꢁ0.41 e A
H atoms bonded to C atoms were positioned geometrically
˚
(C—H = 0.93–0.96 A) and refined using a riding model, with Uiso(H) =
1.2Ueq(C). H atoms of the water molecules were found in difference
˚
maps and positionally refined with restraints of O—H = 0.82 (4) A
and Uiso(H) = 1.5Ueq(O). The phenol H atom was positioned
˚
geometrically, with O—H = 0.82 A, and included as a riding atom,
with Uiso(H) = 1.5Ueq(O).
Wang, X. B. & Zhang, Z. T. (2005). Z. Kristallogr. New Cryst. Struct. 220, 223–
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Data collection: SMART (Bruker, 1999); cell refinement: SMART;
data reduction: SAINT-Plus (Bruker, 1999); program(s) used to solve
structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine
structure: SHELXL97 (Sheldrick, 2008); molecular graphics:
ꢃ
m178 Li and Zhang [Co(H2O)6](C16H11O7S)2ꢀ4H2O
Acta Cryst. (2008). C64, m176–m178