What is the meaning of 'anion water' in coordination chemistry?
I’m pretty sure that ‘anion water’ is a term they use to describe water which coordinates the anions by hydrogen bonding rather than having anything to do with the cations. This is again to be separated from interstitial water, whose job it is to stabilise either of the other water types by hydrogen bonding without interacting with cations or anions at all. (Or maybe, whose job it is to fill voids in the crystal structure).

Ammonia in coordination compounds typically does what water does if it is not interstitial or hydrogen-bonding to anions, thus the distinction and the mention.