Naming a coordination compound I was asked to determine the coordination compound which has the name:

$$\text{triamminetrinitritocobalt(I)}$$

I thought it must be: $$\ce{[Co(NH3)3(ONO)3]^2-}$$

The $-2$ charge can be deduced by adding up the oxidation numbers. 

However, in this case, shouldn't the name be written as cobaltate instead of cobalt? Where is my mistake and what did I miss here?
Yes, you are correct: an -ate prefix is used when the complex has a net negative charge and the name should be triamminetrinitritocobaltate(I) ion

Reference:


  If the overall coordination complex is an anion, the ending "-ate" is attached to the metal center. Some metals also change to their Latin names in this situation. The rest of the metals simply have -ate added to the end (cobaltate, nickelate, zincate, osmate, cadmate, platinate, mercurate, etc. Note that the -ate tends to replace -um or -ium, if present).


Chemistry Libretexts - Nomenclature of Coordination compounds