reading the new comments I think that the term stability needs some further comment.

This is a term that chemists uses in many different ways assuming that the meaning is always clear from the context. Indeed you can have thermodynmic or kinetc stabilty. I see that in the discussion this concept is related to different aspects of the complex. The following question posted by Aditya poses the question on the relationship between solubility and the stability of eeh complex.

I think that the best way to discuss the probelm of stability ( in this case the thermodynamic one) is to refer to free energy ( In this discussion I assume that we are working at constant pressure so this one is the DeltaF=DeltaH-TDeltaS) of the two thermodynamic states that are compared.

In the case of solubility what is comapred are the "pure" condensed state ( being it the solid or the liquid - not solvated - and the solution. Now the solubility depends on many factors. In order to analyse them it is useful to write down a Born Haber cycle comparing the starting and the final state following different termodynamic paths where you can single out the different contribution you are interested to compare. See the attached file

Yes, the stability of the metal complexes are also depending on counter ion

Yes, you have a nice example by copper(II) tetraachlocuprate whose geometry and structure depends on the counter ion. If I am not mistaken it is tetrahedral (Td point group) with potassium and D2d ( a squashed tetrahedron but not square planar) with ammonium. Of course this strongly depends on the sensitivity of the intramolecular energy on the enviroment interactions so it is not easily generalized but you should investigate each case carefully.

Of course it is tetrachlorocuprate !

Yes, It depends, See [M3Cr(Py)3(N3)3] M= Na; K or Cs); Spectrochimica Acta 1992!

Cetrainly, the stability of a metal complex depends on the counter ion.

Yes,

Certainly the stability of metal complexes are influenced by counter ions.

The ion which decrease the solubility , is it increases the stability or there is no direct correlations?

Yes, it does

I think there are examples of anticancer cationic ruthenium complexes with special counterions that lead to lower hygroscopy compared with simple halogenides and, thus, to easier storage of these drugs.

Bernhard Sir thank you very much for your valuable information , if you don't mind will you please give me the link of the journal .

Dear Aditya, here are two examples, one paper on cationic ruthenium complexes and one paper on ruthenate complexes, but with different interpretions of the hygroscopy:

http://pubs.acs.org/doi/abs/10.1021/jm060495o

http://www.sciencedirect.com/science/article/pii/S0020169396050165

reading the new comments I think that the term stability needs some further comment.

This is a term that chemists uses in many different ways assuming that the meaning is always clear from the context. Indeed you can have thermodynmic or kinetc stabilty. I see that in the discussion this concept is related to different aspects of the complex. The following question posted by Aditya poses the question on the relationship between solubility and the stability of eeh complex.

I think that the best way to discuss the probelm of stability ( in this case the thermodynamic one) is to refer to free energy ( In this discussion I assume that we are working at constant pressure so this one is the DeltaF=DeltaH-TDeltaS) of the two thermodynamic states that are compared.

In the case of solubility what is comapred are the "pure" condensed state ( being it the solid or the liquid - not solvated - and the solution. Now the solubility depends on many factors. In order to analyse them it is useful to write down a Born Haber cycle comparing the starting and the final state following different termodynamic paths where you can single out the different contribution you are interested to compare. See the attached file

Here is the file

Thank you Francesco sir and Bernhard sir for your very useful information.I am trying to prepare stable complexes having better aqueous solubility , I think your suggestions will help me a lot.

I think prof. Lelgi has suggested you the right things which will help you to prepare stable complexes

Koi baat nahi.

Because anticancer Pt and Ru complexes often react with water (ligand exchange) I think these papers are of significance for the design of stable drug candidates.

Yes, if complex falls apart by reacting with counterion. No, if intramolecular decomposition of complex occurs before reaction with counterion.

Reading the different interpretation of "stability", I would like to give an other aspect of the question.

Depending on the anion - the reaction of the anion and the complex-forming ligand (e.g. NH3) can affect on the "stability", both in solution and solid state.

For example, Ag or Cu-ammine complexes can be hydrolized with formation of ammonium salts, and Cu, Zn, Ni, Ag or Cd-ammine permanganates (perchlorates) can be exploded during heating due to the existence of the redox interaction of NH3 ligand and the anion. The perrhenates, however, because the perrhenates have no strong oxidizing power, do not explode during the same conditions. You can find a lot of papers in my RG page about these things, if you need some original paper, please do not hesitate to contact with me.

I have a small Q here, do you have any report on the effect of cationic surfactants on stability of metal complexes. It will be very interesting to study catalytic properties of such inter-ionic complexes. naturally this is also interesting as cellular structures as well as protein stabilities also depend on nature of cationic counterions.