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 (H 3 L) 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(H 2 L)](ClO 4 ) (1), cobalt(II) and manganese(II) ions yield mixed-valence Co I I I 2 Co I I (2a) and Mn I I 2 Mn I I I (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 CO 2 uptake from air in methanolic solutions containing a base in the case of complex 4.