Which one of the following species responds to an external magnetic field?
\( [\mathrm{Co(CN)_6}]^{3-} \)
\( [\mathrm{Fe(H_2O)_6}]^{3+} \)
\([ \mathrm{Ni(CO)_4}] \)
\( [\mathrm{Ni(CN)_4}]^{2-} \)