Question

In the complex $[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_2{\left({\mathrm{NH}}_3\right)}_4{]}^{2+}$ the no. of unpaired electrons is

Answer 1

Cordinanation compounds:

• A coordination complex may be defined as a compound that results from the combination of two or more stable chemical species and retains its identity in the solid as well as the dissolved state.
• The cation to which one or more neutral molecules or ions are coordinated is called the central ion.
• The molecules or ions so attached are called ligands.
• The atom in the ligand which can donate the electron pair is called the donor atom.
• The total number of ligands attached to a central ion is called the coordination number of that ion.
• The central ion together with molecules or ions coordinated with it constitutes what is termed a coordination complex.

The number of unpaired electrons:

• In Tetraamminediaquanickel(II) ion $[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_2{\left({\mathrm{NH}}_3\right)}_4{]}^{2+}$ , $\mathrm{Ni}$ is in $+2$ oxidation state (since water and Ammonia ligands are neutral ligands)
• The electronic configuration of Nickel is $\left[\mathrm{Ar}\right]3{\mathrm{d}}^{8}4{\mathrm{s}}^2$

• There are 8 electrons in $3\mathrm{d}$ subshell and since the ${\mathrm{NH}}_3$ is a strong field ligand, the two unpaired electrons left get paired up.
• Hence the number of unpaired electrons becomes zero.

Therefore, in the complex $[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_2{\left({\mathrm{NH}}_3\right)}_4{]}^{2+}$ the no. of unpaired electrons is zero.