Zinc-Ion-Stabilized Charge-Transfer Interactions Drive Self-Complementary or Complementary Molecular Recognition

Here, we show that charge-transfer interactions determine whether donor and acceptor ditopic ligands will associate in a complementary or self-complementary fashion upon metal-ion clipping. Anthracene-based ( 9,10 L D and 1,5 L D ) and anthraquinone-based ( 1,5 L A ) ditopic ligands containing two imidazole side arms as zinc coordination sites were designed. The 9,10 L D and 1,5 L A systems associated in a complementary fashion (L A /L D /L A ) upon clipping by two zinc ions (Zn2 +) to form an alternating donor–acceptor assembly [( 9,10 L D )­( 1,5 L A )2–(Zn2 +)2]. However, once the charge-transfer interactions were perturbed by subtle modifications of the imidazole side arms ( 9,10 L D ′ ( S ) and 1,5 L A ′ ( S ) ), self-complementary association (L D ′/L D ′/L D ′/L D ′ and L A ′/L A ′/L A ′/L A ′) between the donor ( 9,10 L D ′ ( S ) ) and acceptor ( 1,5 L A ′ ( S ) ) ligands predominantly occurred to form homoassemblies [( 9,10 L D ′ ( S ) )4–(Zn2 +)2 and ( 1,5 L A ′ ( S ) )4–(Zn2 +)2]. As in the case of a homochiral pair ( 9,10 L D ′ ( S ) and 1,5 L A ′ ( S ) ), self-complementary association (narcissistic self-sorting) occurred in the Zn2 + assembly with heterochiral combinations of the donor and acceptor ligands ( 9,10 L D ′ ( S ) / 1,5 L A ′ ( R ) and 9,10 L D ′ ( S ) / 1,5 L A ′ ( R ) / 1,5 L A ′ ( R ) ). Narcissistic self-sorting also took place between the positional isomer of the donor ligands ( 9,10 L D and 1,5 L D ) to form individual homoligand assemblies [( 9,10 L D )4–(Zn2 +)2 and ( 1,5 L D )4–(Zn2 +)2]. Conversely, statistical association took place in the Zn2L4 assembly process of an isomorphous pair of the donor and acceptor ligands ( 1,5 L D and 1,5 L A ).