Theoretical Studies of Organometallic Compounds. 9. Structures and Bond Energies of the Methylcuprates CH3Cu, (CH3)2Cu-, (CH3)2CuLi, (CH3)2CuLi.cntdot.H2O, [(CH3)2CuLi]2, and [(CH3)2CuLi]2.cntdot.2H2O