Synthesis, structure, spectra and redox of Cu(ii) complexes of chelating bis(benzimidazole)—thioether ligands as models for electron transfer blue copper proteinsDedicated to Professor P. Natarajan on the occasion of his sixtieth anniversary. Electronic supplementary information (ESI) available: Fig. S1 showing the preliminary X-ray structure of the [Cu(L3)]+ cation, Figs. S2, S4 and S5 showing the cyclic and differential pulse voltammograms of complexes 1a, 3 and 4 respectively and Fig. S3 showing the cyclic voltammograms of complexes 2a and 2b. See http://www.rsc.org/suppdata/dt/b1/b103511h/