Effects of terminal alkyl substituents on the low-dimensional arrangement of π-stacked molecules in the crystal structures of bisazomethine dyes

Abstract

Abstract Crystal structures of three bisazomethine dyes with dipropyl, dibutyl, and dihexyl substituents on their terminal amino groups are reported. To systematically interpret the effects of the terminal dialkyl substituents on the low-dimensional arrangements of the π–π stacked molecules, the structural features of the molecular geometries and the low-dimensional arrangements were compared with those in the reported crystal structure of two bisazomethine dyes, i.e. with terminal dimethylamino and diethylamino groups. Lattice energy calculations were also carried out to interpret the substitution effects from an energetic perspective. In the crystal structures of all five dyes, one-dimensional arrangements of the π–π stacked molecules were found. The slip angles between the π–π stacked molecules constituting the characteristic one-dimensional arrangements of the five bisazomethine dyes were distributed in the range of 24.66(4)–79.34(7)°. The lengths of the alkyl chains and projections of the terminal dialkyl substituents from the molecular planes in the five bisazomethine dyes were found to play significant roles in determining the slip angles between the π–π stacked molecules and the distances between the molecules aligned along the long molecular axes.