配合物同分异构体中“经式”和“面式”是什么意思?

6 coordinated complex MA3B3 (M=central metal ion; A and B = two different ligands) generally is in octahedral type of structure.
When 3 A (or 3 B) ligands occupy two axial positions and an equatorial position,you have a mer-isomer (“经式”同分异构体).
When 3 A (or 3 B) ligands occupy one axial position and two equatorial positions (three corners of a triangle face),you have a fac-isomer (“面式”同分异构体).

对于配位数为6的MA3B3八面体配合物，如M(NH3)3Cl3，它存在两种几何异构体，有三个NH3 或者三个Cl 相邻的称为面式，三个NH3可组成一个不穿过中心金属M的平面，具有C3v对称性；有两个NH3或者两个Cl相对的称为经式，其三个NH3组成的平面穿过中心金属M，具有C2v对称性。