Axial Shielding of 5d8 and 5d7 Metal Centers in Dimesitylplatinum Complexes with Unsaturated Chelate Ligands: Spectroscopic and Spectroelectrochemical Studies of Four Different Oxidation States. Organometallics, (14)3:1176--1186, 1995. [PUMA: diimine complex;bipyridine complex complex;dipyridophenazine dimesityl complex;shielding axial complex;tetraazaphenanthrene complex;bipyrimidine dimesitylplatinum complex;dimesitylplatinum bipyrazine complex;valence complex;platinum]