The crystal structures of a ketone and related acetal macrocycle containing 2,6-pyridino and polyether subunits

1,3,5-Tri[2,6]pyridina-6,9,12-trioxacyclododecaphane-2,4-dione, C21H17N3O7, crystallizes in space group A2/a with a= 20.124(6), b= 12.194(3), c= 15.385(2)A, β= 92.13(2)°, and Z= 8. Refinement using 1 882 diffractometer-measured data yields R 0.038. The corresponding 2,4-bis(ethylenedioxy)-1,3,5-tri[2,6]pyridina-6,9,12-trioxacyclododecaphane, C25H25N3O7, crystallizes in space group P21/c with a= 10.454(4), b= 27.144(7), c= 9.168(3)A, β= 115.09(2)°, and Z= 4. Refinement based upon 2 173 diffractometer-measured data yields R 0.054. The conformation of the diacetal macrocycle is globular; the main backbone of the molecule wraps around a central cavity in a shape somewhat like the seam of a tennis ball. The diketone molecule exhibits a much more open conformation. In both molecules, the linkage of the polyether chain to the pyridine ring is essentially cis to the nitrogen atom. A partial localization of double bonds of the asymmetrically substituted pyridine rings of both structures is noted.