One‐Step Versus Multistep Equilibrium of Carbazole‐Bridged Dinuclear Zinc(II) Complex Formation: Metal‐Assisted π‐Association and ‐Dissociation Processes

This work demonstrates a selection criteria that determines whether molecular assembly occurs through a one‐step or stepwise manner in ligand‐bridged dinuclear zinc(II) (Zn 2+ ) complex formation, which is associated with the π stacking of building blocks. The building blocks of carbazole ligands ( L 1 and L 4 ) that contain two imidazole moieties at the 3,6‐positions form 4:2 complexes (i.e., [ L ] 4 (Zn 2+ ) 2 ) at a molar ratio of 0.50 ([Zn 2+ ]/[ L ] 0 =0.50), thereby providing π stacking between the carbazole ligands. At the molar ratio of 0.67 ([Zn 2+ ]/[ L ] 0 =0.67), the 4:2 complexes change to 3:2 complexes (i.e., [ L ] 3 (Zn 2+ ) 2 ) with no π‐stacked carbazole unit. In contrast, when the imidazole groups in L 1 are replaced with benzoimidazole groups ( L 3 ), L 3 also yields the 4:2 complex [( L 3 ) 4 (Zn 2+ ) 2 ] at a molar ratio of 0.50. However, there is no structural transition from ( L 3 ) 4 (Zn 2+ ) 2 to other complex species above a molar ratio of 0.50. Similarly, when two imidazole groups are introduced into the carbazole ring at 2,7‐positions ( L 5 ), L 5 also gives the 4:2 complex [( L 5 ) 4 (Zn 2+ ) 2 ] that shows no structural transition to other complex species at a higher molar ratio.