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

Abstract

A 20-membered O4S2 macrocycle (L(2)) was synthesized as a ditopic ligating system toward hard and soft metal ions simultaneously. Five complexes (3-7) of L(2) 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 L(2) with Pb(ClO4)2·3H2O afforded a typical endocyclic mononuclear perchlorato complex [Pb(L(2))(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(L(2))2(NO3)2] (4) in which two exocyclic silver(I) ions are doubly linked by two nitrate ions. The treatment of L(2) with CuI gave a mixture of the exocyclic monomer complex [Cu(L(2))I] (5) and the exocyclic dimer complex [(Cu2I2)(L(2))2] (6), which were separated manually because of their brick and rhomboid shapes of the crystals, respectively. Furthermore, the reaction of L(2) with a mixture of CuI and NaI afforded a photoluminescent heteronuclear complex [Na2(Cu6I8)(L(2))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 L(2) with silver(I) nitrate in solution were monitored by the NMR titration. Photophysical and thermal properties for complex 7 were also investigated and discussed.