A Design Strategy for Single-Stranded Helicates using Pyridine-Hydrazone Ligands and PbII.

The reactions of py-hz ligands (L1-L5) with Pb(CF3 SO3 )2 ⋅H2 O resulted in some rare examples of discrete single-stranded helical PbII complexes. L1 and L2 formed non-helical mononuclear complexes [PbL1(CF3 SO3 )2 ]⋅CHCl3 and PbL2(CF3 SO3 )2 ][PbL2CF3 SO3 ]CF3 SO3 ⋅CH3 CN, which reflected the high coordination number and effective saturation of PbII by the ligands. The reaction of L3 with PbII resulted in a dinuclear meso-helicate [Pb2 L3(CF3 SO3 )2 Br]CF3 SO3 ⋅CH3 CN with a stereochemically-active lone pair on PbII . L4 directed single-stranded helicates with PbII , including [Pb2 L4(CF3 SO3 )3 ]CF3 SO3 ⋅CH3 CN and [Pb2 L4CF3 SO3 (CH3 OH)2 ](CF3 SO3 )3 ⋅2 CH3 OH⋅2 H2 O. The acryloyl-modified py-hz ligand L5 formed helical and non-helical complexes with PbII , including a trinuclear PbII complex [Pb3 L5(CF3 SO3 )5 ]CF3 SO3 ⋅3CH3 CN⋅Et2 O. The high denticity of the long-stranded py-hz ligands L4 and L5 was essential to the formation of single-stranded helicates with PbII .