The IUPAC name of the complex [Co(NH₃)₅(ONO)]Cl₂ is:
Ligand binding atom matters!
Pentaamminenitrito-O-cobalt(III) chloride
Pentaamminenitrito-N-cobalt(III) chloride
Pentaamminenitro-cobalt(III) chloride
Pentaamminenitrito-cobalt(II) chloride
ONO ligand binds through oxygen, so the name is Pentaamminenitrito-O-cobalt(III) chloride.