Molecular and crystal structure of pyrylium squarylium dyes

Abstract

The crystal structures of new dyes: 4-[[3-[[2,6-bis-(tert-butyl)-4H-pyran-4-ylidene]methyl]-2-oxido-4-oxo2-cyclobuten-]-ylidene]methyl]2,6-bis(tert-butyl)pyrylium (I) and its thio analog (II) were determined. Crystal data: space group P1 (I), P21/n (II); a = 5.960(9) A (I), 10.400(4) A (II); b = 9.366(3) A (I), 12.242(4) A (II); c = 13.948(3) A (I), 14.482(6) A (II); α = 70.43(2)° (I), 90.0° (II); s = 84.82(9)° (I), 94.65(3)° (II); γ = 79.10(9)° (I), 90.0° (II); V = 720.0 A3 (I), 1837.7 A3 (II); Z = I (I), 2 (II); dcalc = 1.131 g/cm3 (I), 086 g/cm3 (II); R1(F) 0.049 (I), 0.045 (II). The substituents are trans-oriented relative to the planar 4-membered ring. Bond length distribution points to a considerable electron density delocalization over the whole molecule except the But groups. The pyrane rings are oriented differently relative to the central group; in II the rings lie in the same plane which is rotated through 7.7° with respect to the central fragment, whereas in I they lie in parallel planes which are 1.38 A apart and deviate from the central fragment to opposite sides, forming with it dihedral angles of 12.8°. These conformational differences are possibly the result of the action of crystal field forces. In I molecules are arranged as overlapping stacks, whereas in II the pairwise parallel dye molecules are oriented in such a way that their long molecular axes are perpendicular to the long axes of the neighboring pair, resulting in a herringbone packing.