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 (L-9,10(D) and L-1,5(D)) and anthraquinone-based (L-1,5(A)) ditopic ligands containing two imidazole side arms as zinc coordination sites were designed. The L-9,10(D) and L-1,5(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 [(L-9,10(D))(L-1,5(A))(2)-(Zn2+)(2)]. However, once the charge-transfer interactions were perturbed by subtle modifications of the imidazole side arms (L-9,10(D)'((S)) and L-1,5(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 (L-9,10(D)'((S))) and acceptor (L-1,5(A)'((S))) ligands predominantly occurred to form homoassemblies [(L-9,10(D)'((S)))(4)-(Zn2+)(2) and (L-1,5(A)'((S)))(4)-(Zn2+)(2)]. As in the case of a homochiral pair (L-9,10(D)'((S)) and L-1,5(A)'((S))), self-complementary association (narcissistic self-sorting) occurred in the Zn2+ assembly with heterochiral combinations of the donor and acceptor ligands (L-9,10(D)'((S))/L-1,5(A)'((R)) and L-9,10(D)'((S))/L-1,5(A)'((R))/L-1,5(A)'((R))). Narcissistic self-sorting also took place between the positional isomer of the donor ligands (L-9,10(D) and L-1,5(D)) to form individual homoligand assemblies [((LD)-L-9,10)(4)-(Zn2+)(2) and ((LD)-L-1,5)(4)-(Zn2+)(2)]. Conversely, statistical association took place in the Zn2L4 assembly process of an isomorphous pair of the donor and acceptor ligands (L-1,5(D) and L-1,5(A)).