Crystal structure of usnic acid sodium salt 2 1/2 hydrate

Usnic acid, 1,3(2H,9bH)-dibenzofurandione-2,6-diacetyl-7,9-dihydroxy-8,9b-dimethyl, (1) was isolated from the lichenUsnea barbata by supercritical CO2 extraction. The corresponding sodium salt 2 1/2 hydrate was obtained by reacting the acid with sodium carbonate. (C18H15O7Na·2.5 H2O) × 2,M r =822.68, triclinic,P1,a=14.179(8),b=7.369(4),c=9.109(6)A,α=88.47(2),β=105.35(2),γ=92.27(2)°,V=917(2)A3,Z=1,D x =1.490 g cm−3, λ(MoKα)=0.71073 A,μ=1.32 cm−1,F(000)=430,T=293(2)K. The structure was solved by direct methods and refined toR=0.038 for 3229 observed reflections. Both Na ions are pentacoordinated. Their coordination polyhedra are distorted square pyramids bound together by a common water molecule (OW1). The molecules are also joined together by a common water oxygen (OW2) in an infinite chain which lies parallel to theb-axis. The chains are held together by hydrogen bonds. The conformation of usnic acid in the complex differs from that found previously by a rotation of the acetyl group bound to the cyclohexadienone ring.