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 D 2 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) Å. 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.