Chemistry > Coordination Compounds > 4.0 Werner's Co-ordination Theory
Coordination Compounds
1.0 Basics
2.0 Addition Salt
3.0 Nomenclature of Co-ordination Compounds
4.0 Werner's Co-ordination Theory
5.0 Valence bond theory
6.0 Crystal field splitting theory (CFST)
7.0 Effective atomic number
8.0 Magnetic Moment
9.0 Application of Crystal Field Splitting Theory (CFST)
10.0 Isomerism in Co-ordination compounds
11.0 Organo-metallic compounds
12.0 Stability of Co-ordination compounds
4.1 Bonding in Co-ordination number
Werner was the first to describe the bonding feature in coordination compounds, but theory could not answer basic questions like
- Why only certain atoms possess the remarkable property of formation of coordination compounds.
- Why the bonds in coordination compounds have directional properties.
- Why coordination compounds have characteristic magnetic (some are para magnetic while some are dia magnetic) and optical properties. Many approaches have been put fourth to explain the nature of bonding in coordination compounds viz .Valency bond theory (VBT), Crystal field theory (CFT), Ligand field theory (LFT), Molecular orbital theory (MOT). So, we shall focus on attention on elementary treatment of application of VBT and CFT to coordination compounds.
In order to going to the topic we should know the difference between strong and weak ligand:
- Strong ligand: These ligands cause forced pair-up of unpaired electrons, hence they form inner orbital complex.
- Weak ligand: These ligand does not disturb the electronic configuration of the metal. Hence they form outer orbital complex.
| S. No. | Weak ligand | Strong ligand | Border ligand |
| 1. | $C{l^ - }$ | $N{H_3}$ | ${C_2}O_4^{2 - }$ |
| 2. | $SCN{}^ - $ | $CO$ | $N{H_3}$ |
| 3. | ${F^ - }$ | $en$ | ${H_2}O$ |
| 4. | $O{H^ - }$ | $NO_2^ - $ | $EDTA$ |
| 5. | $B{r^ - }$ | $C{N^ - }$ |
