Coordination Number Question

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Binyu You
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Joined: Wed Sep 30, 2020 9:37 pm

Coordination Number Question

Postby Binyu You » Sun Dec 06, 2020 2:18 am

I am still confused about how to determine the coordination number of molecules, for example, the example in Sapling [M(NH3)4Br2], what is the coordination number of this molecule and why?

Selena Quispe 2I
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Re: Coordination Number Question

Postby Selena Quispe 2I » Sun Dec 06, 2020 3:29 am

You can determine the coordination number by counting the number of bonds connected to the metal central atom (the ligands inside the brackets). In this case the coordination number of this molecule would be 6 because there are four ammine ligands and 2 Bromines in the brackets which means the ligands are in the coordination sphere so you would count them in your coordination number. If we were given [Cu(NH3)4] F2 then your coordination number would just be 4 as the fluorines are outside the coordination sphere. I hope this helps!!

Ashley Ko 3I
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Re: Coordination Number Question

Postby Ashley Ko 3I » Sun Dec 06, 2020 3:50 am

Hi! I agree with the above post. I also think it's important to keep in mind the denticity of the ligands in the coordination complex. For example, if one of the ligands is bidentate, then it could form 2 coordinate covalent bonds with the central atom (it would count as 2 instead of 1 towards the coordination number). Hope this helps!

Scot Widjaja Dis 1J
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Re: Coordination Number Question

Postby Scot Widjaja Dis 1J » Sun Dec 06, 2020 4:17 am

A simple way to think of the definition of Coordination Numbers is the number of bonds that are attached to the central transition metal cation. In your example, the coordination number is 6 because there are 6 covalent bonds with the central metal cation (4 from NH3 and 2 from Br). In this example, there are also 6 ligands but keep in mind that the coordination number does not always equal the number of ligates as some ligates are polydentate (form multiple bonds to central metal cation).

Leyla Anwar 3B
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Re: Coordination Number Question

Postby Leyla Anwar 3B » Sun Dec 06, 2020 11:42 am

Ashley Ko 2K wrote:Hi! I agree with the above post. I also think it's important to keep in mind the denticity of the ligands in the coordination complex. For example, if one of the ligands is bidentate, then it could form 2 coordinate covalent bonds with the central atom (it would count as 2 instead of 1 towards the coordination number). Hope this helps!

If there is a bidentate ligand does that mean the whole ligand is bidentate? Or can their be a bidentate bond on one side and a monodentate bond on the other? I'm not sure how naming would work if that was even the case though.

abby hyman
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Re: Coordination Number Question

Postby abby hyman » Sun Dec 06, 2020 11:50 am

Coordination number is the number of bonds but you must keep in mind that some ligands are bidentate/tridentate/tetradentate ect and would contribute 2 or more bonds. These additional bonds must be taken into account to find the correct coordination number.

Justin Lin 1B
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Re: Coordination Number Question

Postby Justin Lin 1B » Sun Dec 06, 2020 12:13 pm

The coordination number is the number of atoms/molecules bonded to a transitional metal. Anything inside of the bracket is part of the coordination sphere and connected to transition metal central atom. There are 4 NH3 molecules and 2 Br atoms attached to the transition metal, so the coordination number would equal 6 because there are 6 things bonded to the transition metal

Taha 2D
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Re: Coordination Number Question

Postby Taha 2D » Sun Dec 06, 2020 1:32 pm

just look at whats inside the square brackets. the numbers of atoms/molecules connected to the tm cation indicate coordination number.

Isabella Cortes 2H
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Re: Coordination Number Question

Postby Isabella Cortes 2H » Sun Dec 06, 2020 2:49 pm

you can determine the coordination compound by adding up all the bonds that the ligands can form with the TM. Usually, when I am finding the coordination compound, I will always identify how many bonding sites each ligand has and then note how many of each ligand there is. So in your example, I would note how NH3 is monodentate and there are 4 of those ligands, as well as two Br ligands which is monodentate. After adding everything up, you get a coordination number of 6.

Veeda Khan 2E
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Re: Coordination Number Question

Postby Veeda Khan 2E » Sun Dec 06, 2020 3:39 pm

A good starting point is to count the number of ligand molecules within the brackets (in this case 6). You can then figure out how they bond to the central atom.

Sedge Greenlee
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Re: Coordination Number Question

Postby Sedge Greenlee » Sun Dec 06, 2020 4:07 pm

In order to find the coordination number simply count the number bonds between the TM and ligands. OFten this will be one bond per one ligand as most coordination compounds we will see involve monodentate ligands. However, some ligands such as chelates can have multiple bonds per ligand, so make sure to always check how many bonds a ligand has rather than simply counting the number of ligands!

Chance Herbert 3A
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Re: Coordination Number Question

Postby Chance Herbert 3A » Sun Dec 06, 2020 4:19 pm

The coordination number is a value representing the number of atoms, molecules, or ions that are held by a central transition metal atom. It is important to note that denticity can vary and you count only the number of atoms inside brackets held by the transition metal!

Karina Grover 1A
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Re: Coordination Number Question

Postby Karina Grover 1A » Sun Dec 06, 2020 4:20 pm

Coordination number is the number of bonds that the transition metal forms with its ligands (within the coordination sphere). In the example you provided, the coordination number would be 6 because 4 NH3 and 2 Br are attached to a single metal.


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