Feb
17

Group 2-DMPS.pptxClick above links to download the power point slide. Thank you for downloading.
Feb
16

In
chemistry, a ligand is either an
atom,
ion, or
molecule that bonds to a central metal, generally involving formal donation of one or more of its
electrons. The metal-ligand bonding ranges from
covalent to more ionic. Furthermore, the metal-ligand bond order can range from one to three. Ligands are viewed as
Lewis bases, although rare cases are known involving
Lewis acidic.
Ligands are classified in many ways: their charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (
denticity or
hapticity). The size of a ligand is indicated by its
cone angle.
Type of Ligand
i)Monodentate ligand
- are ligands which coordinates through only one atom. Some examples are H2O, NH3, P(CH3)3, etc.
ii)Polydentate ligand
- are ligands which coordinate through two or more donor atoms.
- also referred to as chelating ligands when the donor atoms are bonded to the same metal centre.
- Polydentate ligand can be divided into 3 :
1. Bidentate ligand
- have two lone pairs, both can bond to the central metal ion.
- examples are 1,2-diaminoethane
2. Tetradentate ligand
- Has four lone pairs, all of which can bond to the central metal ion.
- Examples are vitamin B-12.
- Vitamin B-12 is required in the diet of all higher animals which is only synthesized by certain bacteria and molds.
3. Hexadentate ligand
- Has six lone pairs of electrons - all of which can form coordinate bonds with the same metal ion.
- The best example is EDTA.
Feb
16

1. In coordination compounds, central metal ions exhibit both primary and secondary valences
- the primary valency is ionizable
- the secondary valency is not ionizable
- the secondary valency corresponds to coordination number (the central metal ion and ligands are not ionizable)
2. Every metal atom has a fixed number of secondary valencies (coordination number(s))
3. The metal atom tends to satisfy both its primary valency as well as its secondary valency
- primary valency is satisfied by negative ions (metal ion has a positive charge)
- secondary valency (coordination number) is satisfied either by negative ions or by neutral molecules
- in certain cases, a negative ion may satisfy both types of valencies
4. The coordination number (secondary valencies) are always directed towards the fixed positions in space and this leads to definite geometry of the coordination compound
DMPS related to Werner’s Theory
- In this case, the primary valency is the central metal ions and the secondary valency is the DMPS
- For mercury, the primary valency (oxidation number) is +2 and the secondary valency corresponds to coordination number, which is 4.