Question

Determine the coordination number and oxidation number of the metal in each molecule: 1) [Co(en)2Cl2]SCN ; 2) Na2[PdBr6] ; 3) [Pt(en)2](ClO4)2 ; 4) [Co(NH3)4(OH2)2]Cl3.

Answer 1

The oxidation states of the groups are as follows :

Cl ---> -1 ----> monovalent ligand

en ----> 0 ------> bidendate ligand

SCN ----> -1     ----> monovalent ligand

Na ---> +1     ----> monovalent ligand

Br ---> -1     ----> monovalent ligand

ClO4 ----> -1     ----> monovalent ligand

NH3 ---> 0     ----> monovalent ligand

H2O ----> 0    ----> monovalent ligand

We know that the sum of the oxidation states of the elements in a given compound is equal to its charge.

Let a be the oxidation state of the central metal atom

1) [Co(en)2Cl2]SCN ---> coordination number 6

a+(2x0)+2(-1)+(-1) = 0

a = +3

2) Na2[PdBr6]   ---> coordination number 6

2(+1) + a + 6(-1) = 0

a = +4

3) [Pt(en)2](ClO4)2    ---> coordination number 4

a + 2(0) + 2(-1) = 0

a = +2

4) [Co(NH3)4(OH2)2]Cl3.   ---> coordination number 6

a + 4(0) + 2(0) + 3(-1) = 0

a = +3