Determining Polydentate Structures Through Formula

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Lillian Xie 1K
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Joined: Fri Sep 25, 2015 3:00 am

Determining Polydentate Structures Through Formula

Postby Lillian Xie 1K » Wed Nov 11, 2015 4:15 pm

Textbook Question 17.33 asks (essentially), which of the following can be polydentate? Give the maximum number of places that the ligand can bind simultaneously to the metal center.
a) HN(CH2CH2NH2)2
b) (CO3)^2-
c) H2O
d) (C2O4)^2-


How do you determine whether a ligand is polydentate? I know that lone pairs contribute to whether or not ligand can be polydentate, but can you use this knowledge without envisioning the Lewis structure?

Thanks!

Orly Termeie 3I
Posts: 94
Joined: Fri Sep 25, 2015 3:00 am

Re: Determining Polydentate Structures Through Formula

Postby Orly Termeie 3I » Wed Nov 11, 2015 5:08 pm

When I went to the Undergraduate advisers and TA office hours, they told me the best way is to memorize the type of ligand (mono,bi,tri) for all the ligands in the course reader. Hope this helps!

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

Re: Determining Polydentate Structures Through Formula

Postby Ronald Yang 2F » Thu Nov 12, 2015 4:01 pm

I guess for HN(CH2CH2NH2)2 looking at the lone pairs could work, since only at the Nitrogens can it create coordinate covalent bonds with a transition metal. But, the thing is, a molecule may have an atom with lone pairs, but that atom may not form a coordinate covalent bond with a transition metal. For example, if we look at CO32-, it has one double bond with an oxygen and two single bonds with two oxygens. The double-bonded oxygen would not make a coordinate covalent bond because it's pretty stable as it is, even though it has a lone pair to donate(formal charge=0). However, the oxygens with formal charges of -1 can form coordinate covalent bonds with a transition metal, because donating an electron pair to make a coordinate covalent bond actually makes these oxygens more stable(formal charge would equal 0 and can be monodentate or bidentate ligand). This applies for molecules with multiple atoms that can "bite" a transition metal, so this applies to oxalate as well. If we were to look at something like water with one atom that can possibly form a coordinate covalent bond, you can just look at if an atom has lone pairs and deem it monodentate.


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