Construction and Photoluminescent Properties of Schiff-Base Macrocyclic Mono-/Di-/Trinuclear Zn Complexes with the Common 2-Ethylthiophene Pendant Arm.

A new flexible 2-ethylthiophene pendant-armed dialdehyde (Htdd) was reacted with 1,3-propanediamine, [( S, S),( R, R),(±)]-1,2-diaminocyclohexane, and 1,2-bis(2-aminoethoxy)ethane, giving birth to 36-membered [2 + 2] Schiff-base macrocyclic trinuclear Zn complex 1, 18-membered [1 + 1] mononuclear Zn macrocycles 2-4, chiral/racemic 34-membered [2 + 2] dinuclear Zn complexes 5-9, and 46-membered [2 + 2] dinuclear Zn macrocycles 10-12 via Zn ion template-assisted Schiff-base condensation. It is worth mentioning that the secondary template effects for nitrate and halide counterions have been observed in the 1,3-propanediamine involved imine condensation. In all [2 + 2] Zn macrocycles, dinuclear complexes 5-9 display a full-folded molecular conformation, while trinuclear complex 1 and dinuclear complexes 10-12 exhibit distinct half-folded structures in the presence or absence of intramolecular π-π stacking interactions between two phenolic rings of the dialdehyde component. Interestingly, a solvent-induced single-crystal-to-single-crystal transformation was first achieved for two types of solvated mononuclear macrocycles 3a and 3b (HO vs CHCN) with folded and unfolded ligand conformations. In addition, the photoluminescent properties were studied for this family of Schiff-base macrocyclic Zn complexes as well as the dialdehyde precursor Htdd.