STRUCTURES OF SOME ANTHRAQUINONE DYES. E.S.Alekseyeva, A.V.Yatsenko,V.A.Tafeenko and L.A.Aslanov,Chemistry Dept., Moscow State University, 119899 Moscow, Russia.

The impact of crystal packing and specific intermolecular interactions on molecular structure has been illustrated by the example of five anthraquinone derivatives. Compounds 1 and 2 show analogous behaviour in solutions: in non-polar solvents the form A is a predominant one, whereas polar solvents displace the equilibrium towards ketoenamine form B.

insert Fig. A B

1: R = H, R' = Ac, R" =p-tolyl; 2: R = mesityl, R' = Ph, R" = H

The crystal structure of 1 is built up from centrosymmetric dimers (interplanar distance 3.43 Å), where two molecules are H-bonded in addition. As a result only form B takes place in crystal. No signs of H-bonding or other specific interactions are observed in the crystal structure of 2, hence the crystal surrounding displaces here the equilibrium towards form A like low-polar solvent.

Visible spectra of anthraquinone dyes are also related to the motif of crystal packing. The crystal structures of 1,4-bis(mesitylamino)anthraquinone (3), 1,4-bis(phenylamino)anthraquinone (4) and 1-hydroxy-4-(p-tolylamino)anthraquinone (5) are built up from separated molecules, dimers and stacks with interplanar distance 3.35 and 3.50 Å respectively. As a result the maximum in reflection spectrum of 3 is blue shifted by 1000 cm^-1 relative to the absorption spectrum in solutions, whereas 4 shows red shift by 700 cm^-1 accompanied by the direct manifestation of vibrational structure.