Structure of 5,4'-dihydroxy-3,6,7,8-tetramethoxyflavone, calycopterin

C 19 H 18 O 8 , M r =374.3, monoclinic, P2 1 /c, a=17.156(6), b=6.781(5), c=15.541(4)A, β=105.46(2)°, V=1742(2)A 3 , Z=4, D m =1.40(2), D x =1.427(2)Mgm -3 , λ(MoKα)=0.71069A, μ(MoKα)=0.121mm -1 , F(000)=784, T=298K, R=0.066, for 1345 unique reflections. The γ-pyrone ring is planar and makes an angle of 3.1(5)° with the benzene ring. The phenyl ring is planar and makes an angle of 161.4(6)° with the pyrone ring. All the methoxy planes are nearly perpendicular to the plane of the γ-benzopyrone ring.