The segmental bidentate-tridentate ligand 5-{2’-[6"-(1"’-(3,5-dimethoxybenzyl)-1"’H-benzimidazol-2"’-yl)-pyridin-2"-yl]-1’-meyly-1’H-benzimidazol-5’ylmethyl}-1-methyl-2-(6""-methylpyridin-2"’-yl)-1H-benzimidazole (L(1)) reacts with Fe(II), Zn(II), and Co(II) in acetonitrile to give mononuclear head-to-head complexes [M(L(1))(2)](2+) where the two tridentate units of the ligands are pseudo-octahedrally coordinated to M(II). Detailed electrospray-mass spectrometeric (ES-MS), spectrophotometric, and H-1-NMR studies show that a second metal ion can react with [M(L(1))(2)](2+) to give homodinuclear C-2-symmetrical head-to-head double helical complexes [M(2)(L(1))(2)](4+) where the second cation is pseudotetrahedrally bound by the two remaining bidentate units of the ligands. When M = Fe(II), thermodynamic data show that the second metal ion is only weakly coordinated, while for M = Zn(II), Co(II), which display greater affinities for tetrahedral coordination, stable homodinuclear [M(2)(L(1))(2)](4+) are obtained in acetonitrile. Reaction of [Fe(L(1))(2)](2+) with Ag(I) produces the self-assembled C-2-symmetrical heterodinuclear double-helical complex [FeAg(L(1))(2)](3+) where Fe(II) occupies the pseudo-octahedral site defined by the two tridentate units of the ligands and Ag(I) lies in the remaining pseudotetrahedral site. Similarly, the trileptic ligand 1,1’-dimethyl-2,2’-bis[6-(methylpyridin-2-yl)-5,5’-{pyridine-2,6-diylbis[(1-methyl-1H-benzimidazole-2,5-diyl)methylene]}bis[1H-benzimidazole] (L(2)) reacts with Fe(II) and Ag(I) (stoichiometric ratio 1:2) to give the first self-assembled D-2-symmetrical heterotrinuclear complex [FeAg2(L(2))(2)](4+) where Fe(II) is located in the central pseudo-octahedral site (bistridentate) and Ag(I) occupy the two capping pseudotetrahedral sites. H-1-NMR measurements are compatible with a double-helical or a catenate structure for [FeAg2(L(2))(2)](4+). The selectivity of the self-assembly processes is discussed together with thermodynamic and structural factors required for the formation of helical heteropolynuclear complexes.