Editing Coordination complex (section)

=====Cis–trans isomerism and facial–meridional isomerism=====
[[Cis–trans isomerism]] occurs in octahedral and [[square planar]] complexes (but not tetrahedral). When two ligands are adjacent they are said to be '''cis''', when
opposite each other, '''trans'''. When three identical ligands occupy one face of an octahedron, the isomer is said to be facial, or '''fac'''. In a ''fac'' isomer, any two  identical ligands are adjacent or ''cis'' to each other. If these three ligands and the metal ion are in one plane, the isomer is said to be meridional, or '''mer'''. A ''mer'' isomer can be considered as a combination of a ''trans'' and a ''cis'', since it contains both trans and cis pairs of identical ligands.

<div align="center">
<gallery>
Image:Cis-dichlorotetraamminecobalt(III).png|{{chem2|''cis''\-[CoCl2(NH3)4]+}}
Image:Trans-dichlorotetraamminecobalt(III).png|{{chem2|''trans''\-[CoCl2(NH3)4]+}}
Image:Fac-trichlorotriamminecobalt(III).png|{{chem2|''fac''\-[CoCl3(NH3)3]}}
Image:Mer-trichlorotriamminecobalt(III).png|{{chem2|''mer''\-[CoCl3(NH3)3]}}
</gallery>
</div>