New nitronyl-nitroxide biradicals based on 2,2’-bipyridine, 1,10-phenanthroline, 1,8-naphtyridine and 3,6-di-(2-pyridyl)-pyridazine have been synthezised and characterized. Aldehyde + hydroxylamine condensation in the presence of a catalytic amount of SeO2 afforded, after oxidation a selective way to prepare the corresponding imino-nitroxide biradicals. Two bipyridine nitronyl-nitroxide biradicals (substituted in the 6,6’ and 5,5’ positions) have been characterized by a crystal structure determination. The 6,6’-substituted-2,2’-bipyridine and the 1,10-phenanthroline biradicals formed mononuclear Cu(II) and Ni(II) complexes which coordinate the two radicals to the central metal and display strong antiferromagnetic coupling at low temperature. The X-ray structures of the copper and nickel -2,2’-bipyridine-6,6’-biradical has also been determined.