CH Al(CH3)6 CH3 CH 3c-2e ch 桥 3 CH3 CH3 CH3 Al(CH3)4Cl2 3c-4eCl桥CH3 CH3 CH3 CH3 CH3 Al Al CH3 Al2 (CH3 )6 3c-2e CH3桥 Al2 (CH3 )4Cl2 3c-4e Cl桥