D Block Chemistry & Coordination Complexes of Cobalt

In summary, coordination complexes of d block elements like cobalt can have up to 9 orbitals involved in their coordination schemes, allowing for coordination of 6 ligands even with 7 d electrons. The dative bonds formed between the ligands and the metal ion result in a sharing of electrons, rather than complete donation, and the ligands are responsible for owning 12 of the electrons in the complex.
  • #1
ampakine
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0
I'm a bit confused about how the d block elements form coordination complexes. Cobalt for example. It has 7 d electrons. In the +3 oxidation state it has 4 d electrons left (unless it loses its 4s electrons first) so I don't understand why it coordinates 6 ligands. The 6 ligands acting as Lewis bases donate 2 electrons each so wouldn't the cobalt atom end up with 16 electrons in its 3d orbital? I thought d orbitals can only hold 10 electrons.
 
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  • #2
ampakine said:
I'm a bit confused about how the d block elements form coordination complexes. Cobalt for example. It has 7 d electrons. In the +3 oxidation state it has 4 d electrons left (unless it loses its 4s electrons first) so I don't understand why it coordinates 6 ligands. The 6 ligands acting as Lewis bases donate 2 electrons each so wouldn't the cobalt atom end up with 16 electrons in its 3d orbital? I thought d orbitals can only hold 10 electrons.

Good question! However first a correction .. Co3+ actually has 6 d electrons not 4 (outer shell s-electrons are removed first when ionizing). So the complex has 18 electrons, not 16. Anyway, regarding your question, the point is that you need to consider all of the valence orbitals ... remember that you can have higher hybridizations (up to sp3d2)? So there are really 9 orbitals involved in the full coordination scheme .. e.g. for Co there are 5 3d-orbitals, 3 4p orbitals and 1 4s orbital. When Co3+ coordinates 6 ligands, it stores its own 6 d-electrons in the 3dxz, 3dyz and 3dxy orbitals. The 3dz2 and 3dx2-y2 are then hybridized with the 4p and 4s orbitals for form an octahedral arrangement of empty orbitals that accept the 6 donor pairs from the ligands.

Another relevant point is that the coordinating ligands don't really "donate" their electrons completely to the metal ion in the way that you implied in your post. They share them in a kind of weaker covalent interaction called a dative bond. So the Co ion doesn't really have "own" 18 electrons in its valence orbitals ... if it did it would have a charge of -9, right? A useful (but not strictly correct) way to think about it is that the ligands "own" 12 of the electrons, and only share them "a little bit" with the Co ion.
 
  • #3
Extremely concise and informative answer. Thanks! Don't even have any follow up questions. Yeah donate was the wrong word, I was wondering what the word for these kinda bonds is though, thanks.
 

1. What is the d block in chemistry?

The d block, also known as the transition metals, refers to the middle section of the periodic table where elements with partially filled d orbitals are located. These elements have unique properties such as multiple oxidation states, variable coordination numbers, and the ability to form colored compounds.

2. What is the role of cobalt in coordination complexes?

Cobalt is a transition metal that is commonly used in coordination complexes due to its ability to form stable bonds with other molecules. In these complexes, cobalt typically acts as a central atom surrounded by ligands, which are molecules or ions that donate electrons to the cobalt atom.

3. How are coordination complexes of cobalt used in industry?

Coordination complexes of cobalt have numerous industrial applications. They are used as catalysts in chemical reactions, as pigments in paints and dyes, and in the production of batteries and electronic devices. Cobalt complexes are also used in the production of pharmaceuticals and as additives in food and animal feed.

4. What is the structure of a coordination complex of cobalt?

The structure of a coordination complex of cobalt can vary depending on the type and number of ligands attached to the central cobalt atom. However, most coordination complexes have a central cobalt ion surrounded by ligands in a three-dimensional shape known as a coordination sphere. The coordination number, or the number of ligands attached to the cobalt ion, can range from 2 to 12.

5. How do coordination complexes of cobalt exhibit color?

Coordination complexes of cobalt are often colorful due to a phenomenon known as ligand field theory. When light is absorbed by a coordination complex, the energy is transferred to the electrons in the ligands, causing them to jump to a higher energy level. The color of the complex is determined by the amount of energy required for this jump, which is dependent on the type of ligands attached to the cobalt ion.

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