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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: abcc on December 13, 2006, 12:54:20 AM

Title: iron 3 complex
Post by: abcc on December 13, 2006, 12:54:20 AM

It is known that the molecular formula of iron(III) thiocyanate complex is Fe[(SCN)6]3-. By using absorption spectroscopy, suggest an experimental method to confirm that the complex has six ligands coordinated to the iron centre.

How to answer this Question ???

Title: Re: iron 3 complex
Post by: Dan on December 13, 2006, 04:43:16 AM

You need to start by doing a full vibrational analysis, so you know what peaks to expect from the complex in the spectra. Then the spectra either confirm or refute the suggested structure.

If you're not familiar with this, get a book called "group theory for chemists" or something like that, there are loads of them.

I found this page too, I don't have time to look for a better one, read section 2.3 http://www.hull.ac.uk/php/chsajb/bonding/ho_2.html

Title: Re: iron 3 complex
Post by: abcc on December 13, 2006, 07:08:07 AM

Quote from: Dan on December 13, 2006, 04:43:16 AM

You need to start by doing a full vibrational analysis, so you know what peaks to expect from the complex in the spectra. Then the spectra either confirm or refute the suggested structure.

If you're not familiar with this, get a book called "group theory for chemists" or something like that, there are loads of them.

I found this page too, I don't have time to look for a better one, read section 2.3 http://www.hull.ac.uk/php/chsajb/bonding/ho_2.html

SO GREAT
THX A LOT ,CHEMIST ;D

Title: Re: iron 3 complex
Post by: miked17 on December 13, 2006, 09:14:38 AM

A pretty simple experiment also would be to just take a UV/vis spectrum of the sample. If the Iron only had 4 ligands it would be either square-planar or tetrahedral geometry, there would be relatively low splitting energy, and the complex would be high-spin. If it was high spin there would be 5 equally occupied d-orbitals and you wouldn't see any d-d transitions in the UV/vis spectrum, only charge-transfer bands.

Iron(III) coordinated to 6 SCN-, however, would be in octahedral geometry with a fairly strong ligand field and would be low spin, meaning you would likely see 4 clear d-d transitions and 2 charge transfer bands.

Title: Re: iron 3 complex
Post by: GCT on January 02, 2007, 08:42:35 PM

Also use the Tanabe Sugano Diagram to predict the UV-Vis spectral features for a six coordinate configuration(with SCN-, the complex would be low spin in nature), there's an online site that actually computes some of the important values for you with a few simple inputs, however I don't remember the exact address at the moment.