A novel phenanthlorine derivative, [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 1,1-dioxide (tdapO(2)), was prepared to act as a radical-anion building block for coordination polymers. The crystal structures and magnetic properties of the monovalent and mixed-valent radical-anion salts K center dot tdapO(2) and K center dot(tdapO(2))(2) were elucidated and confirm the possibility of tdapO(2) to act as a bridging ligand and its capability to exhibit magnetic ordering at 15 K.