The synthesis, spectroscopic and magnetic characterization of six new alkoxo-bridged dinuclear copper(II) complexes are described. All six compounds have the general formula [Cu2(L)4(O-R)2](A)2, in which R = CH3 or CH3CH2, L = 2-amino-3-bromo-5-methylpyridine ( abbreviated as L1), 2-amino-3-cyanopyridine (abbreviated as L2) and A = NO3¯ or ClO4¯ . The title compounds all consist of dinuclear units with bridging methoxo groups for [Cu2(L1)4(O-CH3)2](NO3)2 (C1), [Cu2(L1)4(O-CH3)2](ClO4)2 (C2), [Cu2(L2)4(OCH3) 2](NO3)2 (C3), [Cu2(L2)4(O-CH3)2](ClO4)2 (C4), and bridging ethoxo group for [Cu2(L1)4(O-C2H5)5](ClO4)2 (C5), [Cu2(L2)4(O-C2H5)2](ClO4)2 (C6), with two ligands linked to each copper via the pyridine N atom, providing a Cu2N2O2 unit. All complexes have been synthesized in one-step reaction and characterized by elemental analysis, FTIR and electronic spectra and by magnetic properties. The compounds exhibit antiferromagnetic interaction at room temperature. The UV-Vis spectra show three absorption bands attributed to d-d transition of copper(II) ion, ligand→ metal charge transfer and π→ π* or n→ π* transitions of the ligand. The FTIR spectra indicate Cu2N2O2 unit vibrations from 405 – 580 cm-1. All complexes show a room temperature magnetic moment between 1.37-1.52 B.M. per copper atom. The X-band electron spin resonance (ESR) studies indicate a weak half-field band, which is characteristic of the copper(II)-copper(II) dimer observed at about 1660 gauss. The observation of this band strongly suggests that the hyperfine structure arises from a triplet spin species. The spectra of samples in DMF or DMSO frozen at liquid nitrogen temperature show typical m = 1 transition.
