Tunable Construction of Sandwich-Type Double-[1+1] and Half-Folded [2+2] Schiff-Base Complexes Controlled by the Combination of Primary and Secondary Template Effects

The first-row transition-metal ions Mn2+-Cu2+ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn2+-Cu2+ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co2+ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H-2 pdd precursor and the [1 + 1] Cu2+ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H-2 hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.

Automated summary

This study successfully synthesized three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes using transition-metal ions as effective templates, demonstrating precise control of the final products through the flexible nature of the macrocyclic ligands and subtle variations of the metal ions.