A Ditopic O4S2 Macrocycle and Its Hard, Soft, and Hard/Soft Metal Complexes Exhibiting Endo‑, Exo‑, or Endo/Exocyclic Coordination: Synthesis, Crystal Structures, NMR Titration, and Physical Properties

A 20-membered O4S2 macrocycle (L2) was synthesized as a ditopic ligating system toward hard and soft metal ions simultaneously. Five complexes (3–7) of L2 with different structures and coordination modes, including discrete to infinite forms, mono- to heteronuclear, and endo- to exo- and endo/exocoordination, were prepared and structurally characterized. First, the reaction of L2 with Pb­(ClO4)2·3H2O afforded a typical endocyclic mononuclear perchlorato complex [Pb­(L2)­(ClO4)2] (3) in which one lead­(II) is surrounded by the macrocycle adopting a “tight and bent” conformation. Meanwhile, the reaction with a softer metal salt AgNO3 resulted in the formation of the dinuclear bis­(macrocycle) complex [Ag2(L2)2(NO3)2] (4) in which two exocyclic silver­(I) ions are doubly linked by two nitrate ions. The treatment of L2 with CuI gave a mixture of the exocyclic monomer complex [Cu­(L2)­I] (5) and the exocyclic dimer complex [(Cu2I2)­(L2)2] (6), which were separated manually because of their brick and rhomboid shapes of the crystals, respectively. Furthermore, the reaction of L2 with a mixture of CuI and NaI afforded a photoluminescent heteronuclear complex [Na2(Cu6I8)­(L2)2­(CH3CN)4]n (7) in the endo/exocyclic coordination mode. In this case, the endocyclic sodium­(I) complex units are linked by the double-open cubanes-type cluster Cu6I8, yielding a two-dimensional network. The structural and binding properties of the complex of L2 with silver­(I) nitrate in solution were monitored by the NMR titration. Photophysical and thermal properties for complex 7 were also investigated and discussed.