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
Q. Explain about Dihalide? Dihalides: Dichlorides and dibromides are formed by the lower members of the group, viz., Se, Te and Po. These are formed mainly by dissociation of t

determination of molecular masses using victor meyer method

Q. Define Elements and Compounds? Pure substances are categorized into two categories that are elements and compounds. An element is a substance that can't be separated into

The electronic configuration (outermost) of Mn +2   ion (atomic number of Mn= 25  ) in its ground state is: (1) 3d 5 , 4s o                          (2) 3d 4 , 4s 1   (3

Effect of Substituents on Acidity: The complete effect of a substituent on acidity of substituted benzoic acids is because of two factors. (i) Inductive effect: If the subs

The ionization energy of hydrogen atom is -13.6eV.  The energy required to excite the electron in a hydrogen atom from the ground state to the first excited state is (Avogadro's co

Iodometric Titrations and Iodimetric The reduction of free iodine to iodide ions and oxidation of iodide ions to free iodine takes place in these titrations. I 2 + 2e - →

Why p-nitro toluene is higher boiling point than o-nito toluene ?   Ans) The term hydrogen bonding is used to define dipole-dipole attractive forces of this type. The proton invol