[Co(NH₃)₅(X)]Cl₂ (1) on reaction with aqueous NH₃ followed by the addition of NaNO₂/conc. HCI yields [Co(NH₃)₅(Y)]Cl₂ (2). Reaction of 1 with NaNO₂ results in [Co(NH₃)5(Z)]Cl₂ (3). Complex 2 shows two IR spectral bands at 1310 and 1430 cm^-1, whereas complex 3 shows the same at 1065 and 1470 cm^-1. X, Y and Z, respectively, are