PALLADIUM(II) AND PLATINUM(II) ETA-3-METHYLALLYL TRICHLOROTIN COMPLEXES .3. CRYSTAL-STRUCTURE ANALYSIS OF [PT(ETA-3-C4H7)(COD)]2[PT(ETA-3-C4H7)(SNCL3)3] (COD = CYCLO-OCTA-1,5-DIENE)