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
why f elememnts kept sepertaly in periodic table

Radius of the first Bohr's orbit of hydrogen atom is: (1)1.06 Å                           (2) 0.222 Å (3) 0.28 Å                           (4)0.53A Ans: 0.53 Å

why does evaporation causes cooling

Q. Show the basic stucture of Esters? Ans. Esters have the general formula RCOOR'. Both R and R' are alkyl groups. Esters have the ester functional group: Anima

Chemical kinetics is study of the rates of chemical processes.                                                                         The detailed explanation at molecular leve

how to check the quality of sesame oil such as fat, nutrients, etc.,?

Baeyer's reagent - Tests of unsaturation It is 1% solution consisting of sodium carbonate. It is of pink in colour. An aqueous solution of the element, some drops of Baeyer's

Q. Determine the crude fibre content in the given of flour? To determine the crude fibre content in the given sample of flour. After undertaking this activity, you will be a

Ring-chain isomerism: This kind of isomerism is because of different modes of linking of carbon molecules, that is the isomers process either open chain or closed chain structu

Lassaigne method This is employed to detect halogen, nitrogen and sulphur. Organic compounds are fused along with dry sodium in a fusion-tube and fused mass after extraction wi