What are the number of possible isomers of an octahedral complex: [Co(C2O4)2(NH3)2]– (including stereoisomers)?

The complex [Co(C2O4)2(NH3)2]– is an octahedral complex with two bidentate oxalate ions (C2O4)2- and two monodentate ammonia ligands (NH3).

1. Geometrical Isomers: In octahedral complexes, geometrical isomerism is possible when there are at least two different types of ligands. In this complex, there are two types of ligands, so geometrical isomerism is possible. However, because the oxalate ions are bidentate ligands, they must occupy adjacent positions on the octahedron. This means that there is only one possible arrangement of the ligands, so there is only one geometrical isomer.

2. Optical Isomers: Optical isomerism occurs when a molecule can form a non-superimposable mirror image. In this complex, the two ammonia ligands can either be adjacent to each other (cis) or opposite each other (trans). If they are adjacent, the complex is not optically active because it has a plane of symmetry. If they are opposite, the complex is optically active because it does not have a plane of symmetry. Therefore, there are two optical isomers: one optically active and one optically inactive.

So, the total number of possible isomers (including stereoisomers) for the complex [Co(C2O4)2(NH3)2]– is 3.