Hi Ketan,

The coordination number is the number of ligands attached to the central ion . It is usually between two and nine. Though it may rise as much as sixteen. The term was originally defined in 1893 by Swiss chemist Alfred Werner.

To calculate the coordination number of a compound , we see the constituents in the coordination sphere or the square bracket and emitting the outer atom or atoms.

In the compound which you have mentioned the coordination number of Cu is four.

Hope you understand.