Synthesis and structures of nitromethane complexes of furanotribenzo-21-crown-7 and dibenzo-21-crown-7

Single crystal X-ray diffraction analyses of two nitromethane complexes of furanotribenzo-21-crown-7 (1 and 2) and the nitromethane complex of dibenzo-21-crown-7 (3) are reported. The two nitromethane complexes 1 and 2 are polymorphic in that the macrocyclic ring adopts the 'dentist's chair' conformation in both structures, with a single nitromethane molecule coordinating to either the lower, concave (1) or upper, convex (2) face of the crown ether. Complex 3 adopts an entirely different conformation with a coplanar arrangement of the crown ether oxygen atoms binding a single nitromethane molecule.