New didentate bispyrazole ligands forming uncommon eight-ring chelates with divalent copper, zinc and cobalt

The novel ligands 1,3-bis(pyrazol-1′-yl)propane (bpp) and 1,3-bis(3′,5′-dimethylpyrazol-1′-yl)propane (bdpp) have been prepared by reacting 2 equiv. of the corresponding potassium pyrazolate with 1 equiv. of 1,3-dibromopropane. Compound 1,3-bis(5′-methylpyrazol-1′-yl)propane (bmpp) has been prepared from bpp by lithiation at the five position and the subsequent addition of iodomethane. These new ligands form M(II) coordination compounds with the general formula [M(ligand)X2] where X=Cl or NO3, and M=Cu, Zn, or Co. The single-crystal X-ray structures of [Cu(bmpp)(NO3)2], [Cu(bdpp)Cl2], [Zn(bdpp)Cl2], and [Zn(bpp)Cl2] show the ligands to act as didentate chelates forming an uncommon eight-atom chelate ring with the metal ion. In [Cu(bmpp)(NO3)2] each copper ion is distorted octahedrally surrounded, whereas the metal ions in the chloride complexes have distorted tetrahedral geometries. The spectral properties are in accord with the structural data.