In the coordination compound [Co(NH3)2(H2O)2Cl2], what are the coordination number and oxidation number of cobalt?

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Multiple Choice

In the coordination compound [Co(NH3)2(H2O)2Cl2], what are the coordination number and oxidation number of cobalt?

Focus on two ideas: how many donor atoms are bound to the metal (coordination number) and what the metal’s oxidation state is based on ligand charges and the overall charge. In [Co(NH3)2(H2O)2Cl2], cobalt is bonded to six ligands: two neutral NH3, two neutral H2O, and two Cl–. Each donor atom counts as one toward the coordination number, so there are six donors total, giving a coordination number of 6. For the oxidation state, consider the charges of the ligands and the overall complex. NH3 and H2O are neutral, contributing 0. The two Cl– ligands contribute a total of −2. The whole complex is neutral, so the cobalt must supply +2 to balance the −2 from the chlorides. Therefore, the oxidation state of cobalt is +2. So the correct combination is six-coordinate with cobalt in the +2 oxidation state. (This aligns with the common octahedral geometry for six-coordinate metal centers.)

Focus on two ideas: how many donor atoms are bound to the metal (coordination number) and what the metal’s oxidation state is based on ligand charges and the overall charge.

In [Co(NH3)2(H2O)2Cl2], cobalt is bonded to six ligands: two neutral NH3, two neutral H2O, and two Cl–. Each donor atom counts as one toward the coordination number, so there are six donors total, giving a coordination number of 6.

For the oxidation state, consider the charges of the ligands and the overall complex. NH3 and H2O are neutral, contributing 0. The two Cl– ligands contribute a total of −2. The whole complex is neutral, so the cobalt must supply +2 to balance the −2 from the chlorides. Therefore, the oxidation state of cobalt is +2.

So the correct combination is six-coordinate with cobalt in the +2 oxidation state. (This aligns with the common octahedral geometry for six-coordinate metal centers.)

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