Explain the following observations. Use diagrams where possible and/or necessary, to aid your explanations:
a. Carbon monoxide is a very poor Lewis base in the presence of, and toward, H+, but it is an excellent Lewis base toward Ni.
b. Many complexes exhibiting charge transfer bands in the visible region of the EMR spectrum are unstable in sunlight.
c. The NCS- ion is a good colorimetric agent for Fe(III)
d. A given Cu2+ complex, [CuX6]2+ is green, while another, [CuY6]2+ is blue
e. A d8 metal, coupled with a strong ligand field, favours the formation of square planar complexes.