Factors determining the stability of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes with chosen aminoderivatives of pyrazole

The stability constants and structures of the complexes of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with 5-aminopyrazole, 3-amino-5-methylpyrazole an d 3-amino-5-hydroxypyrazole in aqueous solution have been determined by pot entiometric and spectrophotometric methods. The stability of the transition metal complexes of investigated pyrazoles depends on kind and position of the substitutent in the pyrazole ring. The contribution of pi(M-L) bonding to the coordination bonds and to the stability of complexes was also discus sed.