## Chemistry: Molecular Approach (4th Edition)

\begin{align} & \begin{matrix} {} & Oxidation\,\,state & Coordination\,number \\ a. & +3 & 6 \\ b. & +2 & 6 \\ \end{matrix} \\ & \begin{matrix} c. & \,\,\,\,\,\,\,\,\,\,\,\,\,+2 & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,6 \\ d. & \,\,\,\,\,\,\,\,\,\,\,\,+2 & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,4 \\ {} & {} & {} \\ \end{matrix} \\ \end{align}
Coordination number: The number of molecules or ions directly bound to the metal atom in a complex is called coordination number. To determine the oxidation state of the central metal ion in the complex compound, the charges on the ligands bound to it should be known. a. ${{\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}Br \right]}^{2+}}$ The central metal atom in this complex is cobalt, Co. The central atom is bound to six ligands, five $N{{H}_{3}}$ and one $\text{B}{{\text{r}}^{-}}$group. Therefore, the coordination number of the central metal ion in this complex is 6. The ligands attached to the central metal atom are five NH groups and 1 $B{{r}^{^{-}}}$. Br is an anionic ligand, so it carries a negative charge. $N{{H}_{3}}$ is a neutral ligand. Therefore, it does not affect the oxidation state of the central metal ion. The total charge on the complex ion is $+\text{ }2.$ Consider the charge on the central metal ion be x. Then $x+0+\text{ }\left( -1 \right)=+2$ $x\text{ }=\text{ }+3$ The oxidation state of the central ion is $+3.$ b. ${{\left[ Fe{{\left( CN \right)}_{6}} \right]}^{4-}}$ The central atom in this complex is iron, Fe. The central metal atom is bound to six CN groups. Therefore, the coordination number of the central metal ion in this complex is 6. The ligands attached to the central metal atom are $6\text{ }C{{N}^{-}}$ groups. $C{{N}^{-}}$ is an anionic ligand. Thus, it has a negative charge. The total charge on the complex ion is $-\text{ }4.$ Let the charge on the central metal ion be ‘x.’ Then $x+\text{ }6\left( -1 \right)=-\text{ }4$ $x\text{ }=\text{ }+2$ The oxidation state of the central metal ion is $+2.$ c. ${{\left[ Co{{\left( ox \right)}_{3}} \right]}^{4-}}$ The central metal atom in this complex is cobalt, Co. The central metal atom is bound to three oxalates, $ox-2\text{ }\left( {{C}_{2}}{{O}_{4}}^{2-} \right)$ groups. Oxalate group is a bidentate ligand. It donates two pairs of electrons from the two oxygen atoms to the central metal atom. The three oxalate groups form six coordinate covalent bonds with the central metal atom. Therefore, the coordination number of the central metal ion in this complex is 6. The ligands attached to the central metal atom are three oxalates, $ox-2\text{ }\left( {{C}_{2}}{{O}_{4}}^{2-} \right)$ groups. This is an anionic bidentate ligand. The total charge on the complex ion is $-\text{ }4.$ Let charge on the central metal ion be ‘x.’ Then $x+\text{ }3\left( -2 \right)=\text{ }-\text{ }4$ $x\text{ }=+2$ The oxidation state of the central metal ion is $+2.$ d. ${{\left[ PdC{{l}_{4}} \right]}^{2-}}$ The central metal atom in this complex is palladium, Pd. The central metal atom is bound to $four\text{ }C{{l}^{-}}$ groups. Therefore, the coordination number of the central metal ion in this complex is 4. The ligands attached to the central metal atom are $four\text{ }C{{l}^{-}}$ groups. Cl is an anionic ligand. Thus, it carries a negative charge. The total charge on the complex ion is$-\text{ }2.$ Let the charge on the central metal ion be x. Then $x+\text{ }4\left( -\text{ }1 \right)=\text{ }-\text{ }2$ $x\text{ }=\text{ }+2$ The oxidation state of the central metal ion is $+2.$