A Schiff base lateral macrobicycle derived from 4,13‐diaza‐18‐crown‐6 in its protonated form

In the structure of the title compound, 28,31,36,39‐tetraoxa‐9,17,42‐triaza‐1,25‐diazoniapentacyclo23.8.5.1^11,15.0^3,8.0^18,23]nonatriaconta‐3,5,7,9,11,13,15,16,18,20,22‐undecene bis(perchlorate), C₃₃H₄₃N₅O₄²⁺·2ClO₄⁻ or (H₂L)(ClO₄)₂, the cation and one of the two independent anions lie on crystallographic twofold axes, while the second perchlorate anion is disordered about a centre of inversion. The conformation of the macrobicycle L is conditioned by two strong intramolecular hydrogen‐bonding interactions involving the pivot and imine N atoms, and is quite different from that observed when a metal ion is placed inside its cavity. The two imine groups are not coplanar with the pyridine moiety, and the deviation from planarity is considerably larger than that found in the corresponding Ba complex. Moreover, the fold of the macrobicycle in H₂L²⁺ causes a significant approach of the two pivot N atoms compared with their disposition in the Ba complex. This is the first X‐ray crystal structure analysis of an uncoordinated Schiff base lateral macrobicycle.