Chlorine dioxide is quite possible. Ox with -2 Cl with +3 == unstable CL-O2 ion with neg1 charge. Ions are common. a -1 ion would be soluable in water without a supporting +1 ion to make the salt since water is ionic all by itself. Check with your Chem prof and perhaps a more advanced book.

BTW this is inorganic chem not bio or organic. No carbon here.