Re2O7 + N2H4•H2O + 8KCN → 2K3[Re(CN)4O2] + N2 + 2KOH + 2H2O
Rhenium(VII) oxide react with hydrazine hydrate and potassium cyanide to produce potassium dioxotetracyanorhenate(V), nitrogen, potassium hydroxide and water. Potassium cyanide - concentrated solution.