Endo- and Exocyclic Coordination of a 20-Membered N2O2S2-Macrocycle and Cascade Complexation of a 40-Membered N4O4S4-Macrocycle

A 20-membered N₂O₂S₂-macrocycle (L¹) and a 40-membered N₄O₄S₄-macrocycle (L²) were employed as a [1:1] and a [2:2] cyclization product, respectively, for the preparation of diverse types of supramolecular complexes including a cascade complex. Six complexes (1-6) of the smaller macrocycle L¹ including discrete to continuous forms, mono- to heteronuclear, and endo- to exo- and endo/exocoordination were prepared and their coordination modes were discussed systemically. First, the reaction of L¹ with CuI in the presence of trifluoroacetic acid afforded an exocyclic 1-D coordination polymer {[(μ₄-Cu₄I₄)(HL¹)₂](CF₃COO)₂} _n (1). Meanwhile, the reaction of L¹ with Cu(ClO₄)₂·6H₂O afforded a typical endocyclic mononuclear complex [Cu^II(L¹)](ClO₄)₂·H₂O (2). In the reactions of L¹ with CdX₂ (X = Br and I), isostructural sandwich-type complexes [Cd(L¹)₂Br₂] (3) and [Cd(L¹)₂I₂] (4) were isolated. The treatment of L¹ with Hg(ClO₄)₂ also afforded a sandwich-type complex [Hg(L¹)₂](ClO₄)₂ (5). One-pot reaction of L¹ with a mixture of HgI₂ and CdI₂ afforded a dumbbell-type heteronuclear complex {[Cd(L¹)]₂(μ-Hg₂I₆)}[Hg₂I₆] (6), in which the Cd(II) ion occupies the macrocyclic cavity. Further, such two endocyclic Cd(II) complex units are bridged by a square-type (μ-Hg₂I₆)^2- cluster remaining another same cluster separately. The comparative NMR data exhibited a higher affinity of Cd(II) over Hg(II) toward L¹, in the parallel to the situation occurred in the solid state. Meanwhile, complexations of the extra-large macrocycle L² is more challenging to afford some interesting dimercury(II) coordination products including a cascade complex. In solution, the dimercury(II) perchlorato complex of L² as a metalloligand shows a preferential binding of dabco (1,4-diazabicyclo[2,2,2]octane), but its dimercury(II) iodo complex has a much smaller affinity for dabco. In order to explain these results, the solid dimercury(II) complexes with different anions [Hg₂(L²)X₄] (7: X = I, 8: X = ClO₄) were prepared and characterized. Further, the dimercury(II) perchlorato complex 8 reacts with dabco to forms a cascade complex [Hg₂(L²)(μ-dabco)(ClO₄)₂](ClO₄)₂·2DMF·2ether (9), exhibiting its formation being metal-driven and coordinated anion-regulated. The observed cascade complexation both in solution and solid states is an example of the adaptive guest binding.