An Unsymmetrical Tripodal Ligand with NOS₂-Donor Set:  Coordination Chemistry with Nickel(II) and Zinc(II)^†

The synthesis of the novel tripodal ligand [N(CH₂CH₂CH₂OH)(CH₂CH₂SH)₂] H₃-4 is reported. The aliphatic tetradentate ligand is equipped with an unsymmetrical NOS₂ donor set. It reacts with Ni(OAc)₂·4H₂O or Zn(BF₄)₂·xH₂O to give the complexes [Ni(H-4)]₂ 5 and [Zn(H-4)]₄ 6, respectively. The molecular structures of 5 and 6 have been determined by X-ray diffraction. In both cases multinuclear, μ-thiolato-bridged complexes, wherein the ligand coordinates with only three (NS₂) of the four donor groups, had formed. The dinuclear complex 5 adopts a butterfly geometry and contains nickel(II) ions in a square-planar NS₃ coordination environment. Cyclic voltammetry experiments indicate that the nickel centers in 5 are electron-rich but not overly sensitive toward oxidation. Complex 6 is tetranuclear and the four thiolato-bridged metal centers form a ring. It shows a distorted tetrahedral coordination geometry for the zinc(II) ions in an NS₃ coordination sphere. In both complexes the hydroxyl functionalized ligand arm of the tripodal ligand remains uncoordinated.