Synthesis and crystal structure of 2,4,6,8-tetrakis(3,5-di-tert-butylphenoxy)pyrimido[5,4-d]- pyrimidine: Expansion of the Piedfort concept

Abstract

The title host compound, C62H84N4O4, designed to self-assemble to form a new type of extended core Piedfort unit reminiscent of an eight-legged spider host, forms a number of crystalline inclusion compounds favouring oxygen-containing guest molecules. We have established the presence of this unit in the unsolvated molecular crystal at 100 K, which is monoclinic, space group P21/n, with Z = 8. The new Piedfort unit is chiral and its core structure closely approximates to D2 symmetry, with both enantiomers present in the crystal. Rather than being superposed with a staggered arrangement of nitrogen atoms, the rings are rotated by an angle of approximately 45 with respect to each other, and the shortest contact between them is 3.181 (2) A ° . The compound’s significant inclusion properties may be taken to suggest the participation of an extended Piedfort unit in the microcrystalline adducts formed. The presence of such a dimeric host unit in the clathrates has, however, not yet been established because of the current lack of suitable single crystals for X-ray analysis.