The influence of ms-substitution on the properties of 3,3′- bis(dipyrrolylmethenes) and their coordination compounds

We have compared the coordination properties of decamethyl-substituted 3,3′-bis-(dipyrrolylmethenes) (H2L) with different ms-spacers separating the dipyrrolylmethene domains: methylene -CH2-, methoxyphenylmethylene -CH(p-C6H4OMe)-, and trifluoromethylmethylene -CH(CF3)-. The stable binuclear homoligand complexes [M2L2] are formed in reactions of the ligands with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates. In the cases of all H2L ligands the thermodynamic constants of the complex formation reactions increase in the following series: Cu(II) < Cd(II) < Hg(II) < Ni(II) < Co(II) < Zn(II). The change in -CH2- ms-spacer to -CH(p-C6H4OMe)- or -CH(CF3)- results in a decrease in the constant of H2L complex formation by 1–4 orders of magnitude, the cation being the same. The influence of ms-substitution on the stability and luminescence properties of [M2L2] has been discussed.