AMMRL: Determination of Equlibrium constant of coordinated water using

JOHNSON, Toni A (toni.johnson@uwimona.edu.jm)
Thu, 13 Dec 2007 10:44:35 -0500 (EST) 


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Hello Users,

Can anyone assist with the problem outlined in the e-mail below?

Toni Johnson
University of the West Indies
Kingston 7
Jamaica

LAWRENCE, Mark Alwin Washington wrote:


>Okay, the sample I 've given has 3 coordinated water molecules attached 
>to three different paramagnetic metal centres (2 Cr(III) and Fe(III)). 
>We expect the water coordinated to the Fe centre to dissociate first 
>similar to what is observed in the hexaaqua senario. 

What I am trying 
>to do with the sample I've given you is to determine the value for this 
>equilibrium constant based on the ratio of coordinated water to hydroxo 
>(H2O:OH) on the Fe centre. 

Why NMR? Well direct acid/base titration is 
>not showing much, not to mention these oxo-trinuclear complexes don't 
>behave themselves that well in solvents, so NMR or neutron diffraction 
>of the aqueous solution seems to be my best bet at this moment.
>
>
>Thanks a lot.
>
>Mark
>
>
>
>
>
>>

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 toni.johnson@uwimona.edu.jm; Tue, 30 Oct 2007 14:55:43 -0500 (EST)
Date: Tue, 30 Oct 2007 15:00:34 -0500 (EST)
From: "LAWRENCE, Mark Alwin Washington" 
Subject: Re: NMR
To: "JOHNSON, Toni A" 
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Okay, the sample I 've given has 3 coordinated water molecules attached 
to three different paramagnetic metal centres (2 Cr(III) and Fe(III)). 
We expect the water coordinated to the Fe centre to dissociate first 
similar to what is observed in the hexaaqua senario. What I am trying 
to do with the sample I've given you is to determine the value for this 
equilibrium constant based on the ratio of coordinated water to hydroxo 
(H2O:OH) on the Fe centre. Why NMR? Well direct acid/base titration is 
not showing much, not to mention these oxo-trinuclear complexes don't 
behave themselves that well in solvents, so NMR or neutron diffraction 
of the aqueous solution seems to be my best bet at this moment.

Patience is not an issue... and anything I get would be much 
appreciated. 

Thanks a lot.

Mark


JOHNSON, Toni A wrote:


>Mark,
>
>Could you write a brief description of what you want to achieve using 
>nmr and the type of compound. I would forward this info to Peter, 
>bruker applications specialist, and get further advice. I think this is 
>a little bigger than me. 
>
>For oxygen-17, the broadband probe would be ideal but is not calibrated 
>and I do not have the standards to do so. 
>
>If I use the inverse probe enrichment for O17 would be preferred.
>
>Send me the info and i will forward it. Based on the response we will 
>proceed. 
>
>Please be patient with me.
>
>Toni
>

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