What are the various factors which affect stability?, Chemistry

The stability of a complex relies on


1. Nature of central ion: the word nature means the charge density on the central ion i.e. greater is the charge density or larger the charge/radius ratio more is the stability of a complex. For example, out of complexes of Fe2+ and Fe3+, are more stable.

For example,
                                 
Fe3+ + 6CN-  1239_Central ion.png  [Fe(CN)6]3-; K = 1.2 × 1031
                                  
Fe2+ + 6CN- 
1239_Central ion.png  [Fe(CN)6]4- ; K = 1.8 × 106

For the ions which carry the same charge the one with a smaller size the more stable complexes. For example, among Cu2+, Ni2+, Co2+, Fe2+ complexes as the size of copper is the smallest therefore it gives the most stable complexes.

2. Nature of ligand

(a) Basic character of ligands: more basic is a ligand, greater is the ease with which it can donate its electrons and therefore more is the stability of the complex. For example, the complexes involving F- ions are more stable than those involving Cl- ions or Br- ions.

(b) Charge on ligands: for charged ligands, the higher the charge and the smaller their size, the more stable are the complexes.

(c) Chelate effect: also complexes containing chelate rings are usually more stable than similar complexes containing no rings. This is termed as chelate effect.

For example,
                       
Ni2+(aq) + 6NH3(aq) ? [Ni(NH3)6]2+(aq) log 935_Central ion1.png= 7.99
                       
Ni2+(aq) + 3 en(aq)
? [Ni(en)3]2+(aq) log 935_Central ion1.png= 18.1

3. Crystal field effects (Irving-William Order): the stability of high spin complexes of the ions between Mn2+ and Zn2+ with a given ligand frequently vary in the order:

Mn2+ < Fe+2 < Co+2 < Ni2+ < Cu+2 > Zn+2

This order is also called natural order and is consistent with charge to radius ratio concept. Radii of these ions are:

Mn+2 (0.91 Å); Fe+2 (0.83 Å); Co+2 (0.82 Å); Ni+2 (0.78 Å); Cu+2 (0.69 Å); Zn+2 (0.74 Å)

4. Class a and class b metals: chatt and Ahrland have classify the metals into three groups i.e. a, b and borderline on the basis of their electron acceptor properties.

(i) Class a metals: H, group 1 (alkali metals), group 2 (alkaline earths), the elements Sc to Cr; Al to Cl; Zn to Br, In, Sb, Sn, I. these metals form stable complexes with ligands containing N, O and F groups.

(ii) Class b metals: Rh, Pd, Ag, Ir, Pt, Au, Hg.

These elements have fully filled d-orbitals and therefore form more stable complexes with ligands whose donor atoms are heavier member of N, O and F groups.

(iii) Border line metals: elements from Mn to Cu, Tl to Po, Mo, Te, Ru, W, Re, Os, Cd. These do not follow a particular stability order.

The stability order of complexes of these elements with ligands follows the following order:

Class a elements:

F- > Cl- > Br- > I- > O > S > Se > Te > N >> P > As > Sb > Bi

Class b elements:    

F- < Cl- Br- < I- < O << S ≈ Se ≈ Te < N << P < As < Sb < Bi 

 

 

 

 

Posted Date: 6/25/2012 7:22:40 AM | Location : United States







Related Discussions:- What are the various factors which affect stability?, Assignment Help, Ask Question on What are the various factors which affect stability?, Get Answer, Expert's Help, What are the various factors which affect stability? Discussions

Write discussion on What are the various factors which affect stability?
Your posts are moderated
Related Questions
calculate the voltage of the cell mg/mg+//cd2+/cd at 250c.when[cd2+]=7*10-11 M,[mg2+]=1.0M and standerd electrode potential=1.97V.


name and chemical formula of blue vitriol


Method for Detection of Elements - Phosphorus Phosphorus is detected through fusing the organic compound along with sodium peroxide while phosphorus is converted into sodium ph


What are the various types of point defects? How are they caused?   (i) Vacancies: This refers to a missing atom or a vacant atomic site because of absence of a matri


Uses of Glucose (a) Glucose is used in the conservation of fruits and making of jams and jellies. (b) Glucose is used in the preparation of confectionary and as a sweetening

Dielectric loss: These losses occur because of electrons hopping from single lattice site to another in transition metal oxides.