2D and 3D coordination polymers based on 2,2'-bipyrimidine and cyanide bridging ligands incorporating coordinated and guest ammonia molecules. Synthesis, crystal structures, magnetic properties and thermal analysis of {[Ni(CN)~4]~2[(Ni(NH~3)~2)~2(bpym)]·2H~2O}~n and {[Cu~2(CN)~2 (bpym)]·NH~3}~n