Abstract: | The structures of diaqua(1,7‐dioxa‐4‐thia‐10‐azacyclododecane)nickel dinitrate, [Ni(C8H17NO2S)(H2O)2](NO3)2, (I), bis(nitrato‐O,O′)(1,4,7‐trioxa‐10‐azacyclododecane)mercury, [Hg(NO3)2(C8H17NO3)], (II), and aqua(nitrato‐O)(1‐oxa‐4,7,10‐triazacyclododecane)copper nitrate, [Cu(NO3)(C8H19N3O)(H2O)]NO3, (III), reveal each macrocycle binding in a tetradentate manner. The conformations of the ligands in (I) and (III) are the same and distinct from that identified for (II). These differences are in agreement with molecular‐mechanics predictions of ligand conformation as a function of metal‐ion size. |