Crystal structure of hexaaquazinc(II) bis(monoethoxyformononetin- 3′-sulfonate) tetrahydrate, [Zn(H2O)6](C18H15O4SO3)2 · 4H2O

Abstract

C36H50O24S2Zn, triclinic, P1 (no. 2), a = 7.240(2) A, b = 8.593(2) A, c = 17.276(4) A, 0 = 80.788(4)°, = 82.971(3)°, , = 81.219(3)°, V = 1043.2 A, Z = 1, Rgt(F) = 0.068, wRref(F) = 0.248, T = 296 K. Source of material Formononetin (4 g) was dissolved into NaOH (50 ml, 5 %). Diethyl sulfate (6 ml) was added dropwise to the solution with vigorous stirring. Themixturewas stirred at room temperature for 3 h and some precipitation appeared. The precipitate was filtered and washed with water until the pH of the filtrate was 7 to obtain monoethoxyformononetin (4'-methoxy-7-ethoxylisoflavone, 3.5 g). Then,monoethoxyformononetin (2 g)was slowly added to the concentrated sulfuric acid (8ml), Themixturewas stirred at room temperature for 1 h and poured into a saturated NaCl solution (60 ml) and awhite precipitate formed. This precipitate was collected by filtration andwashedwith saturatedNaCl solution until the pH value of the filtrate was 7. Finally, the precipitate was recrystallized fromwater to afford sodiummonoethoxyformononetin-3'-sulfonate (yield, 80.40 %). Sodium monoethoxyformononetin-3'-sulfonate (1 g) was dissolved in water (10 ml), then mixed with saturated ZnSO4 · 7H2O solution (5 ml). The title compound were obtained from water after 24 h. It is a watersoluble derivative of formononetin, with potential medical applications. Crystals of the title compound suitable for single crystal X-ray analysis were recrystallized from water after two weeks at room temperature. Discussion Formononetin (4'-methoxy-7-hydroxyisoflavone), as an effective principals of isoflavone, display a wide range of biological activities, such as antioxidant [1], inhibiting cardiovascular disease [2,3] and balancing women’s hormone [4]. However, the biological utilization rate is low and the dose is high for its poor solubility, which limit its wide applications. Thus, it is necessary to synthesize a water soluble derivative of formononetin in order to study its possible biological effects. The crystal structure of the title compound is composed of a complex cation [Zn(H2O)6], two monoethoxyformononetin-3'sulfonate anion C18H15O4SO3$ and four lattice water molecules. Zn (II) lies on an inversion centre and is coordinated by six water molecules which forms a slightly distorted octahedral complex cation, in which the average bond length of Zn—O is 2.089 A. The dihedral angle between ring A (C10-C15) and ring C (C8C10/O9/C15-C16) is 4.1(2)°, and that of the benzopyrane moiety (C8-C16/O9) and ring B (C2-C7) is 9.6(2)°. The sulfo-group ($ SO3) of the isoflvone skeletons, the four lattice water molecules and the six coordinated water molecules are linked by eight kinds of hydrogen bonds among them. These hydrogen bonds not only link the isoflavone skeletons, coordinated water molecules and latticewatermolecules into together, but also play very important roles in the formation, stability and crystallization of the title compound. The isoflavone skeletons arrange in antiparallel fashion and the aromatic F-tape and T-tape $-$ stacking interactions exist together in harmony between them, consisting of a column along [010]. Fistly, two kinds of aromatic F-tape stacking interactions exist in the crystal structure of title compound. On one hand, the ringsC of two neighbour isoflavone skeletons stackwith each other with d(CgC-CgC) = 3.712(3)A, where Cg and Cg are the center of ring C of the neighboring isoflavone skeleton at (x,y,z) and (2$x,2$y,2$z), respectively. The interplanar spacing measures to 3.5497 A. On the other hand, the ring AC of isoflavone skeleton at (x,y,z) is nearly paralleled to the ringB at (2$x,1$y,2$ z), the dihedral angle between them being 9.6°. They stack with each other with d(CgAC-CgB) = 3.729(3) A and d(CgACCgB) = 3.729(3) A. In addition, anthoer T-tape stacking interaction between H17A and CgB [the centroid of ring B at (2$x,1$ y,2$z)] of 2.731(3)A is observed. The hydrogen bonds, aromatic F-tape and T-tape $-$ stacking interactions and the electrostatic interaction between the cation [Zn(H2O)6] and the anion sulfonate C18H15O4SO3$ lead to the moieties into supramolecule with a three-dimensional structure. Z. Kristallogr. NCS 224 (2009) 71-72 / DOI 10.1524/ncrs.2009.0029 71 © by Oldenbourg Wissenschaftsverlag, Munchen