$[Cu(H_2O)_4]^{2+} + 4NH_3 \rightleftharpoons [Cu(NH_3)_4]^{2+} + 4H_2O$
$(i)$ $[Ni(CO)_4], \,sp^3$
$(ii)$ $[Ni(CN)_4]^{2-}, \,sp^3$
$(iii)$ $[CoF_6]^{3-}, \,d^2sp^3$
$(iv)$ $[Fe(CN)_6]^{3-}, \,sp^3d^2$