How to determine monodentate?

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How to determine monodentate?

Postby Chem_Mod » Thu Sep 22, 2011 5:31 pm

Question: How do you determine if a molecule is monodentate, bidentate, etc. for molecules CO3, H2O, oxalate, etc..? Also, how can you determine if something is chelating? And when writing down the formula of a coordination complex, what comes first: anion or neutral ions? (homework problem 16.29)

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Re: How to determine monodentate?

Postby Chem_Mod » Thu Sep 22, 2011 5:32 pm

Answer: A monodentate ligand has only one donor atom used to bond to the central metal atom or ion. Monodentate ligands are sometimes referred to as being "one toothed" because they bind to the central metal atom at one point. Some examples of monodentate ligands are chloride ions (referred to as chloro when it is a ligand), water (referred to as aqua when it is a ligand), hydroxide ions (referred to as hydroxo when it is a ligand), and ammonia (referred to as ammine when it is a ligand).

Bidentate ligands have two donor atoms which allow them to bond to a central metal atom or ion at two points. Common examples of bidentate ligands are ethylenediamine (en), and the oxalate ion (ox).

A polydentate ligand can be recognized by having more than 2 lewis base sites, such as multiple lone pair donating sites used to bond to a central atom or ion. EDTA, a hexadentate ligand, is an example of a polydentate ligand. EDTA has six donor atoms with electron pairs that can be used to bond to a central metal atom or ion.

A chelating ligand will have multiple lone pair sites, but they will have to be oriented in such a fashion that they will be able to interact with the metal's d-orbitals.

In a formula, the anionic ligands are listed before the neutral ones. The rules are less specific for compounds names than they are for formulas, see pg 624 in Atkins.


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