Binuclear Copper(II) Oxidation Products from Copper(I) Complexes with Tridentate Ligands. Magnetostructural Characterization

The bis-pyridine tridentate ligands (6-R-2-pyridylmethyl)−(2-pyridylmethyl) benzylamine (RDPMA, where R = CH3,
CF3), (6-R-2-pyridylmethyl)−(2-pyridylethyl) benzylamine (RPMPEA, where R = CH3, CF3), and the bidentate ligand
di-benzyl-(6-methyl-2-pyridylmethyl)amine (BiBzMePMA) have been synthesized and their copper(I) complexes
oxidized in a methanol solution to afford self-assembled bis-μ-methoxo-binuclear copper(II) complexes (1, 2, 4, 6)
or hydroxo- binuclear copper(II) complexes (3). Oxidation of the nonsubstituted DPMA (R = H) in dichloromethane
gives a chloride-bridged complex (5). The crystal structures for [Cu(MeDPMA)(MeO)]2(ClO4)2 (1), [Cu(RPMPEA)(MeO)]2(ClO4)2 (for 2, R= Me, and for 4, R = CF3), [Cu(BiBzMePMA)(MeO)]2(ClO4)2 (6), [Cu(FDPMA)(OH)]2(ClO4)2 (3), and [Cu(DPMA)(Cl)]2(ClO4)2 (5) have been determined, and their variable-temperature magnetic
susceptibility has been measured in the temperature range of 10−300 K. The copper coordination geometries are
best described as square pyramidal, except for 6, which is square planar, because of the lack of one pyridine ring
in the bidentate ligand. In 1−4 and 6, the basal plane is formed by two pyridine N atoms and two O atoms from
the bridging methoxo or hydroxo groups, whereas in 5, the bridging Cl atoms occupy axial−equatorial sites. Magnetic
susceptibility measurements show that the Cu atoms are strongly coupled antiferromagnetically in the bis-methoxo
complexes 1, 2, 4, and 6, with −2J > 600 cm-1, whereas for the hydroxo complex 3, −2J = 195 cm-1 and the
chloride-bridged complex 5 shows a weak ferromagnetic coupling, with 2J = 21 cm-1 (2J is an indicator of the
magnetic interaction between the Cu centers).