CoachIn an octahedral complex , the fac isomer has the three B ligands on one face of the octahedron, the mer isomer on a meridian (three positions in a plane through the metal). Linkage isomers differ by the atom through which an ambidentate ligand binds. Ionisation isomers exchange a ligand with a counter-ion, giving different ions in solution.
![Top: cis and trans isomers of MA_4B_2 (B ligands blue), fac and mer isomers of MA_3B_3 (B red). Bottom: the two enantiomers of a tris-chelate such as [Co(en)3]3+, viewed along the threefold axis, schematic: each chelate (blue arc) joins an upper and a lower position, and the three turn one way () or the other ().](/images/onecourse/chapters/chemistry-3/b2-coordination-complexes/fig-69690792f2c7.svg)
![Top: cis and trans isomers of MA_4B_2 (B ligands blue), fac and mer isomers of MA_3B_3 (B red). Bottom: the two enantiomers of a tris-chelate such as [Co(en)3]3+, viewed along the threefold axis, schematic: each chelate (blue arc) joins an upper and a lower position, and the three turn one way () or the other ().](/images/onecourse/chapters/chemistry-3/b2-coordination-complexes/fig-61bb91f0e162.svg)