Among V(CO)6, Cr(CO)5, Mn(CO)5, Fe(CO)5, [Co(CO)3] 3 , [Cr(CO)4] 4 and Ir(CO)3, the total number of species isoelectronic with Ni(CO)4 is _______________. [Given, atomic number: V = 23, Cr = 24, Mn = 25, Fe = 26, Co = 27, Ni = 28, Cu = 29, Ir = 77] ( IIT Ad 2024 Paper-1)