We have synthesized a new type of acyclic bis(N2O2 chelate) ligand that affords a C-shaped O-6 site by the metalation of the N2O2 salamo sites. UV-vis titration clearly showed that complexation of H4L with M-II (Mn-II, Co-II, and Ni-II) affords the 1:3 complex [LM3](2+) in a cooperative fashion, whereas complexation with copper(II) gave two or more complexes in a stepwise fashion. The manganese(II) complex [LMn3(OAc)(2)(MeOH)(2)] crystallizes in the triclinic system, space group Pi, with unit cell parameters a = 9.584(6) angstrom, b = 13.666(9) angstrom, c = 15.566(10) angstrom, alpha = 108.702(8)degrees, beta = 95.255(4)degrees, gamma = 101.023(8)degrees, and Z = 2, and the cobalt(II) complex [LCo3(OAc)(2)(EtOH)(2)] center dot 2CHCl(3) crystallizes in the triclinic system, space group P (1) over bar, with unit cell parameters a = 13.291(6) angstrom, b = 13.913(7) angstrom, c = 14.599(8) angstrom, alpha = 88.27(2)degrees, beta = 67.391(15)degrees, gamma = 73.90(2)degrees, and Z = 2. In the crystal structures, three metal ions occupied both the N2O2 and O-6 sites of the ligand L4-. The resultant trinuclear complexes have a Cor S-shaped structure depending on the metal employed. The different nature of the N2O2 and O-6 sites of the ligand H4L leads to the site-selective introduction of two different d-block transition metals. An X-ray crystallographic analysis revealed the structures of the two heterotrinuclear complexes, [LZn2Mn(OAc)(2)(MeOH)(2)] and [LCu2Zn(OAc)2(H2O)].