Question: Why does silver only can have a coordination number of 2?
Answer: At it this way; you have Ag(OH2)2 + 2NH3 –> Ag(NH3)2 + 2H2O
Now the Gibbs free energy will be favorable, which is what drives the reaction (thermodynamically driven).
Now delta G = delta H – T delta S
Now entropy isn’t driving the reaction so enthalpy will be. Now you can think about why enthalpy is driving the reaction and you have your answer.