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)X-2] where X = Cl or NO3, and M = Cu, Zn, or Co. The single-crystal X-ray structures of [Cu(bmpp)(NO3)(2)], [Cu(bdpp)Cl-2], [Zn(bdpp)Cl-2], and [Zn(bpp)Cl-2] 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. (C) 2001 Elsevier Science B.V. All rights reserved.