Stereoselective oxidative addition reactions of dihalogens and copper(II) halides to square planar organoplatinum(II) complexes containing hard N and C donor atoms : Molecular structures of [bc,de bis-(8-dimethylamino-1-naphthyl)]-ef-diiodo- platinum(IV) and ab-dibromo[cf,de-bis(8-dimethylamino-1-naphtyl)]platinum(IV)