Inter-ring and endo anomeric effects, and hydrogen-bonded supramolecular motifs in two 2,4,6,8-tetraazabicyclo[3.3.0]octane derivatives

In 2,4,6,8-tetrakis(4-chlorophenyl)-2,4,6,8-tetraazabicyclo-[3.3.0]octane, C28H22Cl4N4, the imidazolidine rings adopt envelope conformations, which are favoured by two equal endo anomeric effects. The molecule lies on a crystallographic twofold axis and molecules are linked into a three-dimensional framework via two C-H center dot center dot center dot Cl hydrogen bonds. In 2,4,6,8-tetrakis(4-methoxyphenyl)-2,4,6,8-tetraazabicyclo-[3.3.0]octane, C32H34N4O4, one of the methyl groups is disordered over two sets of sites and the same methyl group participates in an intermolecular C-H center dot center dot center dot O hydrogen bond, which in turn causes a considerable deviation from the preferred conformation. There are two unequal inter-ring anomeric effects in the N-C-N groups. Molecules are linked into corrugated sheets by one C-H center dot center dot center dot pi hydrogen bond and two independent C-H center dot center dot center dot O hydrogen bonds involving methoxy groups.