Molecular and crystal structure of pyrylium squarylium dyes

The crystal structures of new dyes: 4-[[3-[[2,6-bis-(tert-butyl)-4H-pyran-4 -ylidene]methyl]-2-oxido-4-oxo-2-cyclobuten-1-ylidene]methyl] 2,6-bis(tert- butyl)pyrylium (I) and its thio analog (II) were determined. Crystal data: space group P (1) over bar (I), P2(1)/n (II); a = 5.960(9) Angstrom (I), 10 .400(4) Angstrom (II); b = 9.366(3) Angstrom (I), 12.242(4) Angstrom (II); c = 13.948(3) Angstrom (I), 14.482(6) Angstrom (II); alpha = 70.43(2)degree s (I), 90.0 degrees (II); beta = 84.82(9)degrees (I), 94.65(3)degrees (II); gamma = 79.10(9)degrees (I), 90.0 degrees (II); V = 720.0 Angstrom (3) (I) , 1837.7 Angstrom (3) (II); Z = 1 (I), 2 (II); d(calc) = 1.131 g/cm(3) (I), 086 g/cm(3) (II); R1(F) 0.049 (I), 0.045 (II). The substituents are trans- oriented relative to the planar 4-membered ring. Bond length distribution p oints to a considerable electron density delocalization over the whole mole cule except the Bu-t groups. The pyrane rings are oriented differently rela tive to the central group; in II the rings lie in the same plane which is r otated through 7.7 degrees with respect to the central fragment, whereas in I they lie in parallel planes which are 1.38 Angstrom apart and deviate fr ont the central fragment to opposite sides, forming with it dihedral angles of 12.8 degrees. These conformational differences are possibly the result of the action of crystal field for ces. In molecules are arranged as overla pping stacks, whereas in II the pairwise parallel dye molecules are oriente d in such a way that their long molecular axes are perpendicular to rite lo ng axes of the neighboring pair, resulting in a herringbone packing.