Ligand-directed Molecular Architectures: Self-assembly of Two-dimensional Rectangular Metallocycles and Three-dimensional Trigonal or Tetragonal Prisms

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Three angular ditopic ligands (1,3-bis(benzimidazol-1-ylmethyl)-4,6-dimethylbenzene L1, 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene L2, and 1,4-bis(benzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene L3) and one tripodal ligand 1,3,5-tris(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene L4 have been prepared. Reaction of these shape-specific designed ligands with different metal salts affords a series of discrete molecular architectures: [Ag2L12](BF4)2 1, [Ag2L22](CF3SO3)2 2, [CF3SO3- Ag2L32]CF3SO3 3, [CF3SO3- Ag2L33]CF3SO3 4, [ClO4- Cu2L24](ClO4)3 5, [4H2O Ni2L24Cl4]·6H2O 6, [BF4- Ag3L42](BF4)2 7, [ClO4- Ag3L42](ClO4)2 8, and [CuI32- Cu3L42]2[Cu2I4] 9. The compounds were characterized by elemental analysis, ESI-MS, IR, and NMR spectroscopy, and X-ray crystallography. 1 is a dinuclear metallacycle with 2-fold rotational symmetry in which two syn-conformational L1ligands are connected by two linearly coordinated Ag+ ions. 2 and 3 are structurally related, consisting of rectangular structures assembled from two linearly coordinated Ag+ ions and two L2 or L3ligands. The structure of 4 is a trigonal prismatic box consisting of two Ag+ ions in trigonal planar coordination linked by three L3 ligands, while the structures of 5 and 6 are tetragonal prismatic cages constructed by two square planar Cu2+ or Ni2+ ions linked by four L2 ligands. The topologies of 79 are similar to that of 4; however, these three structures are assembled from three linearly coordinated Ag+ or Cu+ ions and two tripodal ligands, representing an alternative strategy to assembling a trigonal prism. 1H NMR and ESI-MS were utilized to elucidate the solution structures of these macrocycles.