Studies on nickel (II) complexes of some poly(1-pyrazolyl)alkane ligands

Summary The coordinating behaviour of tris(1-pyrazolyl)methane, HCpz₃ and 2,2-bis(1-pyrazolyl)propane, Me₂Cpz₂ ligands towards nickel(II) salts has been investigated. Tris(1-pyrazolyl)methane yields stable, solid complexes of the type Ni(HCpz₃)X.H₂O].nH₂O (X=Cl, n=2; AcO, N=1) and Ni(HCpz₃)₂]X₂ (X = Br, I, NO₃, or IO₄) whilst Me₂Cpz₂ ligand does not. However, Me₂Cpz₂ in the presence of poor coordinating polyanions such as BF ₄ ^– and PF ₆ ^– reacts readily to give stable complexes of the type Ni(Me₂Cpz₂)₂X]Y (X=Cl, NO₃, or AcO and Y=BF₄ or PF₆). The complexes have been characterised by elemental analysis, magnetic moments, electronic and infrared absorption spectra. An octahedral structure has been proposed for the complexes Ni(HCpz₃)X₂ · H₂O] · nH₂O with one water molecule occupying an axial position. An octahedral structure has also been proposed for the complex ions, Ni(HCpz₃)₂]²⁺ and Ni(Me₂Cpz₂)₂X]⁺(X = NO₃ or AcO) with the anion X acting as a bidentate ligand whilst Ni(Me₂Cpz₂)₂Cl]⁺ is considered to have a square pyramidal structure.