Gas-phase electron-diffraction investigations of, I. WF₆, ReF₆, OsF₆, IrF₆, PtF₆, O₂⁺PtF⁻₆, II. 3-aminoacrolein, III. 3-chloro-1-propanol, IV. 2,2',5,5'-tetramethyl-1,1'-distibacerrocene