What is the correct structure for transition metal complex ions?

[joeyjo100]

I'm getting myself muddled up, and don't know how to work out what the 3-d structure of transition metel complex ions.

For example, the compound [CoCl4] has a Cobalt +2 ion surrounded by four chloride ions. I've seen two different structures for it. One is tetrahedral, like methane, the other is sqaure planar.

Which structure is correct?

 

[SpectraCat]

Which one do you think is correct, based on your own analysis?

 

[joeyjo100]

well i would have guessed a tetrahedral shape for [CoCl4], just because there are 4 chloride ions, which would try and repel each other as much as possible.

The tetrahedral shape has a bond angle of 109 degrees compared to 90 degrees for a square planar shape, so this allows the greatest distance for the chloride ligands

 

[SpectraCat]

well i would have guessed a tetrahedral shape for [CoCl4], just because there are 4 chloride ions, which would try and repel each other as much as possible.

The tetrahedral shape has a bond angle of 109 degrees compared to 90 degrees for a square planar shape, so this allows the greatest distance for the chloride ligands

Ok .. that's a reasonable start. However you asked a similar question about square-planar vs tetrahedral geometries before, and I answered it. Why don't you go back to that response, and see if it gives you some additional insight.

 

[joeyjo100]

yeah. I forgot that I'd posted that, I've been in my own little revision world lately so things just keep coming and going.

And in fact I just looked back at the reply in my last post. I do admit that it's a bit over my head, but I guess that in itself is an answer. It means that I don't need to be worrying too much about it for the exam.

thanks for replying!

 

[SpectraCat]

yeah. I forgot that I'd posted that, I've been in my own little revision world lately so things just keep coming and going.

And in fact I just looked back at the reply in my last post. I do admit that it's a bit over my head, but I guess that in itself is an answer. It means that I don't need to be worrying too much about it for the exam.

thanks for replying!

No problem ... sorry if my reply was over your head. Please feel free to ask if you need or want clarification on any of the points. If you are in an introductory chemistry class, then it is likely that you only need to know the VSEPR arguments that you gave above in #3 to explain the structure. The difference between square-planar and tetrahedral geometries for coordination complexes is a more advanced topic that you will hit when you study inorganic chemistry at a higher level.