Polynuclear Complexes of the Pendent-Arm Ligand 1,4,7-Tris(acetophenoneoxime)-1,4,7-triazacyclononane

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)](ClO4) (1), cobalt(II) and manganese(II) ions yield mixed-valence CoIII2CoII (2a)
and MnII2MnIII (4) complexes, whereas nickel(II) produces a tetranuclear [Ni4(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 St = 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 St = 7.0 for 4. The large ground-state spin value of St = 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.