Question

The compound ${\mathbf{WH}}_{\mathbf{2}}{\mathbf{\left(}{\mathbf{C}}_{\mathbf{5}}{\mathbf{H}}_{\mathbf{5}}\mathbf{\right)}}_{\mathbf{2}}$ acts as a base, but${\mathbf{TaH}}_{\mathbf{3}}{\mathbf{\left(}{\mathbf{C}}_{\mathbf{5}}{\mathbf{H}}_{\mathbf{5}}\mathbf{\right)}}_{\mathbf{2}}$ does not. Explain.

Short answer

The compound ${\mathrm{WH}}_2{\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}_2$acts as a base, but ${\mathrm{TaH}}_3{\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}_2$does not.

Step-by-step solution

Take the WH2(C5H5)2 compound

Let consider first,${\mathrm{WH}}_2{\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}_2$compound, the tungsten has donated two electrons to form a pair of ${\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}^{-}$ions; it becomes a role="math" localid="1663563584891" ${\mathrm{d}}^4$compound (ion). While in the case of ${\mathrm{TaH}}_3{\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}_2$tantalum becomes ${\mathrm{d}}^3$ compound (ion) when donating two electrons to form a pair of ${\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}^{-}$ ions.

Take the TaH3(C5H5)2 compound

Furthermore, when tungsten shares two electrons with bonded$\mathrm{H}$ atoms to form a single bonds, it has two electrons left to form a single bond with an approaching${\mathrm{H}}^{+}$ ion; it is thus a good base. By contrast, tantalum has already shared its three valence electrons with three$\mathrm{H}$ atoms and has little affinity for an additional${\mathrm{H}}^{+}$ ion.

Hence, the compound ${\mathrm{WH}}_2{\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}_2$acts as a base, but${\mathrm{TaH}}_3{\left({\mathrm{C}}_5{\mathrm{H}}_5\right)}_2$ does not.