UNDERSET{Sodium\text{ }nitroprusside}{\mathop{N{{a}_{2}}S+N{{a}_{2}}[Fe{{(CN)}_{5}}NO]\xrightarrow{{}}}}\,\] \[\underset{Sodium\text{ }thionitroprusside}{\mathop{N{{a}_{4}}\left[ Fe{{\left( CN \right)}_{5}}NOS \right]}}\,\]