Reaction of isophthaloyl dichloride (I) with 2-aminopyridine or 2-aminopyrimidine (O, 26O) provides a facile entry into a new class of imide-based ‘3+3’ macrocyclic trimer (IO)3, (26IO)3 (as trezimides), together with the known tetramer (IO)4, (26IO)4 (tennimide) scaffold.1-5 Trezimides can adopt two asymmetric conformations, isolated as (P) in (IO)3 and (R) in (26IO)3.2,4 The tennimide (26IO)4 structure exhibits three discrete conformations as cc/oc/oo, highlighting subtle geometric changes with the tennimide channel (pore) open (o) and/or closed (c). Macrocycle formation (competing with oligomer/polymer formation) relies on the ortho-pyr(im)idine N functionality and imide hinge ('COCO' twist) with the inherent flexibility of the isophthaloyl groups (Figures 1-5).