CH3 Al2(CH3)6 CH3 CH3 3c-2eCH桥 CH3 CH3 CH3 Al2(CH3)CL2 3c-4eC1桥 CH3 CH3 CH3 CH3 CH3 Al Al CH3 Al2 (CH3 )6 3c-2e CH3桥 Al2 (CH3 )4Cl2 3c-4e Cl桥