Novel Solid-State Molecular Self-Assemblies of Manganese (II) Constructed with Flexible Ligands:  Influences of π−π and C−H···π Interactions on Their Crystal Packing

Three supramolecular networks are synthesized by the combination of Mn(II) and flexible ligands [1,2-bis (4-pyridyl) ethane (bpe); 1,3-bis (4-pyridyl) propane (bpp); 4,4‘-bipyridyl disulfide (bpds)], characterized by single-crystal X-ray analysis. All three complexes have extended solid-state structure formed by π−π interactions, and there is an excellent opportunity to elucidate the difference in the formation of extended networks in these three complexes. Complex 1, which is reported in a paper earlier by our group, is an unprecedented three-dimensional (3D) “honeycomb”-like architecture constructed from a novel sinusoidal one-dimensional (1D) chain [Mn(bpe)(H2O)4]2+ through π−π interactions in which bpe is used as a bidentate bridging ligand. Complex [{Mn(bpp)3Cl2}(H2O)2] n 2 generates a “standing wave”-like architecture by π−π interactions from a neutral zigzag 1D chain of [Mn(bpp)3Cl2]. Complex [{Mn(bpds)2(dca)2(H2O)2}(H2O)4(bpds)] n 3 is a neutral monomer [Mn(bpds)2(dca)2(H2O)2], which is self-assembled to form a two-dimensional sheet by hydrogen bonding. These sheets interact to generate 3D supramolecular structure stabilized by an interesting “sandwiched” π-interaction involving both coordinated and solvated bpds. Solid-state fluorescence results of these flexible ligands and complexes are in agreement with their structures.