F-type or T-type aromatic-aromatic interaction in two isoflavone derivatives

Two isoflavone derivatives, 5,6,7,4'-tetramethoxyisoflavone (I) and 6,4'-dimethoxy- 7-ethoxy-5-hydroxylisoflavone (II), have been synthesized and their crystal structures were determined by H-1 NMR and single crystal X-ray diffraction studies. I is triclinic, space group P-1 with a = 7.828(1) angstrom, b = 10.285(2) angstrom, c = 11.608(2) angstrom, alpha = 104.90(2)degrees, beta = 110.546(9)degrees, gamma = 99.54(1)degrees and Z = 2. II is orthorhombic, space group Pna2(1) with a = 7.0244(6) angstrom, b = 15.0104(15) angstrom, c = 15.7538(15) angstrom, and Z = 4. Molecules of I are linked into two-dimensional structure by a combination of C-H center dot center dot center dot O hydrogen bond and F-type aromatic-aromatic interactions. II shows some discrepancies with I and the molecules are linked into columns by T-type aromatic-aromatic interaction.