## Polydentate

Camila Bautista 3I
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Polydentate

By looking at the chemical formula of a molecule or compound, how can you tell what kind of "-dentate" it is?
There was a question in the homework that asked to state whether or not certain molecules were polydentate, and if not then to list the maximum number of places the ligand can bind simultaneously to a single metal center.
I couldn't quite answer that question for these molecules:
1. HN(CH2CH2NH2)2
2. CO3 with a 2- charge

What kind of dentate would those be and how can you tell?

VictoriaRoderick_3A
Posts: 42
Joined: Fri Sep 25, 2015 3:00 am

### Re: Polydentate

$HN(CH_{2}CH_{2}NH{2})_{2}$ would be polydentate, more specifically tridentate. Each of the three nitrogens has a lone pair, so those can be replaced by a bond.

$CO_{3}$ 2- can be either mono- or polydentate; however, it is more often monodentate. Remember that the molecular shape is trigonal planar. It can give one pair of electrons at one vertice, but it can also give two lone pairs on the other two vertices if the transition metal is small enough.

Ani Galfayan 1H
Posts: 27
Joined: Fri Sep 25, 2015 3:00 am

### Re: Polydentate

So to find out how many places a ligand can bond, would we have to draw the Lewis structure to determine how many lone pairs there are?

Riley Griesenbeck 3C
Posts: 15
Joined: Fri Sep 25, 2015 3:00 am

### Re: Polydentate

Drawing the Lewis structure would work, but for a compound like NH(CH2CH2NH2)2, the Lewis structure would be pretty big. Just by looking at the molecular formula you can see the each nitrogen will only form three bonds and, thus, will have a lone pair. Drawing the Lewis structure is effective but so is analyzing the formula.

Katherine Fitzgerald 1A
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

### Re: Polydentate

Have a further question on this 9C5(a). I tried drawing the lewis structure for HN(CH2CH2NH2)2 and don’t see how it generate three line pairs on the N molecules. Can someone draw and upload the proper structure and point out where the lone pairs are?

Chem_Mod
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### Re: Polydentate

Polydentate ligands range in the number of atoms used to bond to a central metal atom or ion. For example, EDTA is a hexadentate ligand (polydentate ligand) that has six donor atoms with electron pairs that can be used to bond to a central metal atom or ion. Bidentate ligands will have two donor atoms which allow them to bind a central metal atom or ion at two points (ex. ethylenediamine). HN(CH2CH2NH2)2 would be tridentate (polydentate) since it has three nitrogen atoms that have lone pairs to a bond to a metal center atom. CO3 with a 2- charge can either be monodentate or bidentate since it can bond with one or two oxygen atoms. It is typically monodentate.

205458163
Posts: 33
Joined: Wed Jun 26, 2019 12:15 am

### Re: Polydentate

Polydentate ligands range in the number of atoms used to bond to a central metal atom or ion. EDTA, a hexadentate ligand, is an example of a polydentate ligand that has six donor atoms with electron pairs that can be used to bond to a central metal atom or ion.

Zachary Menz 1D
Posts: 32
Joined: Wed Nov 07, 2018 12:17 am

### Re: Polydentate

To determine the kind of -dentate, figure out the number of lone pairs that can act as donors.

Bella Martin
Posts: 47
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Polydentate

Hello!
In reference to the 6th edition textbook question 33.b. about CO3 2-. I understand that the shape is trigonal planar but I am confused as to why it can only serve as a mono or bidentate ligand. Two of the oxygens have 3 lone pairs and the third oxygen has 2 lone pairs, so I don't understand why there cannot be more bindings to metal ions through all of these lone pairs. Thank you!