Why do compounds having similar geometry have different magnetic moment?

Explanation

This is found to be the case with complex compounds even if the central metal atom is the same. The difference is due to the presence of weak and strong ligands. If ligand is weak (low CFSE), electrons will not pair up in the d - orbitals of metal ion and hence the complex will show high magnetic moment. If ligand is strong (high CFSE), electrons will pair up in d - orbitals of metal ion and will show a low value of zero magnetic moment. For example, both `[CoF_(6)]^(3-)` and `[Co(NH_(3))_(6)]^(3+)` have octahedral structure, but the former is paramagnetic while the latter is diamagnetic is nature.