Coordination Compounds

Co-ordination compounds are compounds in which the central metal atom is linked to a number of ions or neutral molecules by co-ordinate bonds.

A hexadentate ligand has 6 lone pairs of electrons - all of which can form co-ordinate bonds with the same metal ion. The best example is EDTA.The EDTA ion entirely wraps up a metal ion using all 6 of the positions .

Co-ordination Number is the number of monodentate ligands attached to central atom/ion .

A complex ion contains a metal atom or ion known as the central metal atom or ion. It is sometimes also called a nuclear atom.

A complex ion is an ion that contains a metal cation binded to one or more small molecules or ions (such as NH₃, CN^- or OH^-). 

Chlorophyll, the pigment responsible for photosynthesis, is a coordinated compound of magnesium.

Important complex in which a metal is bound to only one kind of donor group are known as homoleptic complexe e.g., [CO (NH₃)₆)]³⁺ .In this componud the donor group is only NH_3.

The spatial arrangements of the important ligand atoms which are directly attached to the central atoms/ion definition terms a coordination polyhedron about the central atoms.

The Co-ordination sphere is written in square brackets.

Bidentate ligands are often referred to as chelating ligands because they can grab a metal atom in two places. A complex that contains a chelating ligand is called a chelate.

These  complexes  carry a negative charge. For example: [Ag (CN)2]^-

Two or more substances having the same molecular formula but different structural or spatial arrangement are called isomers.

When two identical groups (ligands) occupy adjacent positions, the isomer is called cis. It is not possible for co-ordination number of 2 and 3 and for tetrahedral complexes of co-ordination number 4. It is common in square planar and octahedral complexes. 

When polydentate ligands bind to the central metal ion, they form a ring called chelate and the ligand is referred as chelating ligand.

Alfred Werner suggested in 1893 that metal ions exhibit what he called primary and secondary valences. This first theory was called the Werner's theory of co-ordination compounds.

All the above mentioned three factors affect  the stability of the complex ion.

Bonding in a complex ion is due to electrostatic interactions between the positively charged nucleus of the central metal ion and electrons in the ligands i.e., attractive as well as repulsive interactions

These substances show permanent magnetism even when the magnetic field is removed. For example,  FeO and CrO2 Fe, Co, Ni show ferromagnetism even at room temperature.

Compounds, which give different ions in solution although they have same composition are called ionization isomers. There is an exchange in groups between the coordination sphere of the metal ion and ions outside the sphere.

This compound is blood red in colour. It is used to identify iron as Fe³⁺ ions.

Optical isomers rotate the plane of polarised light in opposite directions. They are called dextro and laevo (d and l) rotatory depending upon the direction in which plane polarised light is rotated .

This compound is Ilmenite. It is a antiferromagnetic substance.

This complex is square planar in shape with hybridisation,dsp² .It is diamagnetic because it has no unpaired electrons.

Anti-ferromagnetic substances are expected to possess paramagnetism or ferromagnetism on the basis of unpaired electrons present in them but actually they possess zero net magnetic moment. This is because of the alignment of dipoles is in a compensatory way so as to give a net zero dipole moment, then we get antiferromagnetic substances (MnO).