Coordination Number

[Ruth Rosales 3D]

What would be the coordination number for:

[Co(SO4)(NH3)5]+

My initial thought would be 5. But it marks it as wrong.
I do struggle to find the coordination number, but sometimes I do it wrong, any tips on how to make the process easier?

Also: One of the times I counted I got six but I am not sure how. I tried it and marked it right.

I would still like to know how/why this is right. Thank you.

[Xinyu Li 1C]

You are really close. The coordination number for this compound is actually 6 because there are 6 coordinate covalent bond here, 1 from SO4 and 5 from (NH3)5. 1+5=6

Note: each NH3 contributes 1 coordinate covalent bond

[Connie Liang 3L]

The coordination number would be 6 because there's also an SO4 that needs to be accounted for. What helps me is counting up the number of molecules inside the coordination sphere (aka inside the brackets) other than the transition metal. That will be your number of ligands which is your coordination number.

[Natalie 3k]

To simplify it, I just think of the coordination number as how many atoms or other molecules are connected to the central atom. In this case the 5 NH3 molecules are connected and the 1 SO4 molecule is connected, so total there are 6, making the coordination number 6.

[Stuti Pradhan 2J]

The coordination number is the number of bonds formed to the transition metal, so in this case, there are 5 NH3 molecules and 1 SO4 molecule that are bonded to the cobalt, resulting in a coordination number of 6.

I recommend first counting how many ligands there are (so anything that is within the coordination sphere that is not the transition metal itself) and then figuring out is the ligand is monodentate, bidentate, tridentate, etc. Use that information to figure out how many bonds are formed and that should give you the coordination number.

Hope this helps!

[Aydin Karatas 1F]

To find the coordination number, you need to find out how many times each ligand can bind with the central metal. For example, the N on NH₃ has a lone pair that can be donated. Since it has one lone pair on one atom, it can only have one coordinate covalent bond with the central atom. Therefore, (NH₃)₅ would contribute 5 to the coordination number.

For SO₄, it could be monodentate or bidentate, so this is what I think: in this case, we're looking at an octahedral complex (6 ligands at corners of a central metal), so it would be most likely be monodentate because there are so many electron-dense species in the area that it wouldn't make too much sense for SO₄ to have 2 bonds.

Hope this helps.