[sdpd] I have a problem.

[Neeraj <neeraj...@jncasr.ac.in>]

Hello everybody,

I have a problem. I have an extended structure in which the framework
structure is negatively charged. I do have as guest species counter ions.
The total formula does not show the charge neutrality of the structure.
There is on Chloride anion which is unbalanced. We had put Potassium
chloride ions salt during th synthesis. Although K+ potassium ions are
present in the structure they are enough to neutralise the negative charge
of the framework but not that of the extra chloride ion. 

One of the suggestions which came up during discussion was that since K+
(potassium ion) and Cl- (chloride anion) are isoelectronic so their
scattering powers should be nearly equal. In that case could there be
anion-cation site disorder present in the structure ? If yes, then how is
that possible because it does not make any chemical sense as the structure
refines well even when I don't satisfy the charges. Neither the thermal
parameters of Cl- ion are high so that I can come to a conclusion that
there is a disorder at that site. Also the nearest neighbour connectivity
shows that the distance between the other metal(M) of the framework and
chloride (chlorine) corresponds to regular M-Cl distance, which should
be longer if there is a cation-anion disorder present at the same site. At
any given moment the ion is either chloride anion or potassium cation so
that the charge gets neutralised due to the disorder. 

Is the thinking correct? Whether such a thing that anion and cation
can be present at the same site due to disorder makes sense or not, if
they have the same scattering power. The ionic radii of the Cl- and K+
differ to a significant value.

If anybody has any suggestion to make I would be very glad.
Thanks
neeraj  


****************************************************************************

                               S. NEERAJ
                       INTEGRATED PhD. CHEMISTRY
                          CERAMICS LABORATORY 
                 CHEMISTRY AND PHYSICS OF MATERIALS UNIT
             JAWAHARLAL NEHRU CENTER FOR ADVANCED SCIENTIFIC
                                 RESEARCH
                         JAKKUR, BANGALORE 560064
               
		  phone : 0091-80-8462751 
		  fax   : 0091-80-8462766
	       
	               e-mail: neeraj...@jncasr.ac.in

****************************************************************************