The addition of PEtPh2 to NiBr2 at -78 degrees Celsius in CS2 gives a red complex with the formula (PEtPh2)2NiBr2 which is converted to a green complex of the same formula on standing at room temperature. The red complex is diamagnetic but the green complex has a magnetic moment of 3.2 B.M. a) Which of these is square planar and which is tetrahedral? State reasons for your choice. b) Rationalize the colors of these complexes in view of your choice.