8.下列各錯合物(錯離子):① ZnCl2.2NH3;② ZnCl2.4NH3;③ PtCl2.2NH3;④ PtCl4.4NH3; ⑤ CrCl3.4NH3;⑥ Ni(CN)4 2-;⑦ Ni(CO)4;⑧ Cu(NH3)2(H2O)22+。哪些屬於平面四邊形結構? (寫代號即可)【 (10) 】(全對才給分)