Copper(II) complexes of pyrazol-3-yl amines. Synthesis, crystal and solution structure

The new ligand N,N'-bis(pyrazol-3-ylmethyl)-1,2-ethanediamine (L) was prepared. Reaction with copper(II) salts afforded the complexes [(L)Cu(NO3)]Cl (1) and {[(L)Cu(ClO4)](2)[(pzen-H)(2)Cu-2(ClO4)(2)]}(ClO4)(2) (3) which were characterized by X-ray crystallography. The latter complex was obtained in low yield from a crude sample of L which contained N-(pyrazol-3-ylmethyl)-1,2-ethanediamine (pzen) as an impurity. In the [(L)Cu(X)](+) cations square-pyramidal copper(II) is in-plane coordinated by tetradentate L, with the anion X in the apical position. The copper ions in dinuclear [(pzen-H)(2)Cu-2(ClO4)(2)] are bis(pyrazolate) bridged. In aqueous solution [(L)Cu](2+) is in pH-dependent equilibrium with a dimeric species. By precipitation with NaClO4 both monomeric [(L)Cu(ClO4)(2)] (2) and dimeric [(L-H)(2)Cu-2(ClO4)(2) (4) were isolable at pH 4.5 and pH 8.5, respectively. Based on spectroscopical and analytical data we suggest that 4 is a bis(pyrazolate) bridged complex in solution and in the solid state. (C) 1998 Elsevier Science S.A.