Question

The oxidation state of a transition metal can be determined by looking at the ligands bonded to the metal. Every bond to a transition metal will increase the oxidation state of that metal by +1. For example in CoBr₂, there are two bromines bonded to the cobalt, and the cobalt will have a +2 oxidation state (Co²⁺). When neutral ligands (NH₃, PPh₃, etc.) are coordinated to the metal, they do not change the oxidation state of the metal. For example the palladium in Pd(PPh₃)₄ has an oxidation state of zero. Determine the oxidation state of the metal in each of the following. 

Answer 1

Oxidation state is the state of an element or an ion with respect to the number of electrons gained or lost from its neutral atom to form the compound or an ion.

If a ligand attached to metal has -1 charge, the change in O.S. of metal ion would be +1. If ligand has -2 charge, change O.S. of metal would be +2.

The neutral ligands do not change the oxidation state of the metal..

For polyatomic ion or complex, the sum of oxidation number of atoms of the ion must be equal to charge on the ion.

(a) Pd(OAc)₂ :

Let O.S. of Pd be x. The charge on OAc ligand is -1.

Since there are 2 OAc ligands, therefore -2 contribution to whole complex.

   x-2=charge on complex=0

therefore, x=2.

O.S/ of Pd is +2

(b) Pd (NR)₂(OAc)₂ :

NR is the nitrogen ligand, where R is the group attached to N.

Since NR is neutral ligand, therefore its contribution is 0. OAc has contribution of -1.

Let O.S. of Pd be x.

   x + 0 - 2 = 0

   therefore    x = +2

O.S/ of Pd is +2

(c) Pd (P(tBu)₃)₂ :

   P(tBu)₃ is a neutral ligand therefore it has 0 contribution to O.S. change.

hence O.S. of Pd is 0

(d) Pd(Ph)(RNH₂)(Br) :

RNH2 is neutral ligand therefore it has 0 contribution to O.S..

Br has -1 charge, Ph group has -1 charge

let O.S. of Pd be x

x+0-1-1=0

x= +2

therefore O.S. of Pd is +2