Hi Kiha,
The difference between ionic and coordinate covalent bonds is a little subtle, but this is definitely a coordinate covalent bond.
A coordinate covalent bond involves the sharing of electrons where both electrons in the bond come from one atom (as opposed to one electron from each bonding atom).
For example, the bond between H3N --> BF3 is a coordinate covalent bond.
An ionic bond involves the complete removal of electrons from one atom to another. Ionic compounds are pretty much always neutral overall, for example NaCl can be seperated into Na+ and Cl-.
In this case, you don't have this kind of charge separation, for example despite the fact that you have 4 NH3 molecules donating electrons to the copper centre, the entire molecule is still 2+ from the Cu2+ ion. That is, it is not conceivable that this complex was formed with the Cu taking electrons from NH3 in an ionic type relationship.
Something like CuCl2 however, would be ionic due to the fact that you have 2+ on the Cu, one for each electron donated to the chlorine.
To my knowledge, there is no such thing as a coordinate ionic bond.
Please let me know if any of this is unclear.