What is trans effect in inorganic chemistry .plzz answer my question it's very urgent for me.tommorow is my exam plzz

The trans effect is the ability of a ligand to influence the substitution of another ligand which is positioned trans to it in any square planar complexed.

There are several theories proposed to explain the trans effect. Two of the theories are widely accepted. One is Electrostatic polarizability theory and Pi-binding theory.

(a) Electrostatic Polarizability theory: As per this theory, the ligand (L) attached to the central metal of a square planar complex would polarize the bond such that the bond between the metal and the ligand (X) trans to it would become weak. Thus, the ligand (X) it would be replaced/ substituted easily.

To exemplify, let us suppose a complex , in which all the ligands are X. As all the ligands are same, the primary positive metal ion Pt generates dipole which is canceled by the ligands. Hence, the net dipole remains zero, suggesting that none of the ligands would exhibit the trans effect.

However, in case of , one ligand is L and to its trans is X. The two X ligands trans to each other would cancel the dipole generated by the primary positive metal Pt. However, this is not the case with L ligand. As X ligand is trans to L, the dipole would not cancel each other as L is large than X and exhibit greater polarization.

The net result would be distortion or polarization of the Pt (II) and ligand L. This polarization takes place in such a way that the positive charge at the point of Pt (II) directly opposite to L is reduced. Thus, the attraction of X for Pt (II) is also reduced and the bond trans to L is weakened, resulting its replacement with the incoming nucleotide.

(B) π-bonding theory:

The above theory fails to explain the high trans effect in the π-bonding ligands such as  etc.

As per π-bonding theory, the π and π* orbitals of the π-bonding ligand accepts the pair of electrons from the filled d-orbitals of the metals, leading to π-backbonding.

In a square planar complex, , the dyz orbital having a pair of electrons, will overlap with the empty pz orbital of the ligand. This would lead to π-backbonding resulting in increased electron density towards the ligand and weaker towards the M-X bond which is trans to the M-L.

The incoming ligand Y would enter and its lone pair would be in the direction of diminished electron density i.e. M-X bond. It leads to the formation of intermediate complex  which would convert to  when the X is released.

The intermediate complex is distorted trigonal bipyramidal structure.