Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 3 / Section E / 45 / b

Each Pd(dppp) unit retains its chelating phosphine and offers two adjacent pyridyl binding sites at an approximately right angle. Three such units bridge pairs of metalloligands, giving $[{\mathrm{Fe}}_2{\mathrm{Pd}}_3{L}_2(\mathrm{dppp}{)}_3{]}^{10+}$, a trigonal bipyramid with two Fe vertices and three equatorial Pd vertices. All six outward pyridines are used: $2\times 3=3\times 2$. The Pd/Fe ratio is $3/2$, matching the reagent dose, and the cation charge is $2(2)+3(2)=10$ because the organic ligands are neutral.

The two donor sites left by dppp are cis, so each equatorial Pd joins one arm from each Fe cap. A mere mass-spectral maximum charge is not an independent structure determination, but its consistency with donor counting and binding geometry strongly selects this model.