The ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane (H3L) has been synthesized and its coordination properties toward Cu(II), Ni(II), Co(II), and Mn(II) in the presence of air have been investigated. Copper(II) yields a mononuclear complex, [Cu(H2L)](CIO4) (1), Cobalt(II) and manganese(II) ions yield mixed-valence (Co2CoII)-Co-III (2a) and (Mn2MnIII)-Mn-II (4) complexes, whereas nickel(II) produces a tetranuclear [Ni-4(HL)(3)](2+) (3) complex. The complexes have been structurally, magnetochemically, and spectroscopically characterized. Complex 3, a planar trigonal-shaped tetranuclear Ni(II) species, exhibits irregular spin-ladder. Variable-temperature (2-290 K) magnetic susceptibility analysis of 3 demonstrates antiferromagnetic exchange interactions (J = -13.4 cm(-1)) between the neighboring Ni(II) ions, which lead to the ground-state S-t = 2.0 owing to the topology of the spin-carriers in 3. A bulk ferromaganetic interaction (J = +2 cm(-1)) is prevailing between the neighboring high-spin Mn(II) and high-spin Mn(III) ions leading to a ground state of S-t = 7.0 for 4. The large ground-state spin value of S-t = 7.0 has been confirmed by magnetization measurements at applied magnetic fields of 1, 4 and 7 T. A bridging monomethyl carbonato ligand formation occurs through an efficient CO2 uptake from air in methanolic solutions containing a base in the case of complex 4.