= Solution
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 \b[$[\mathrm{Fe}_2\mathrm{Pd}_3L_2(\mathrm{dppp})_3]^{10+}$], a \b[trigonal bipyramid] with two Fe vertices and three equatorial Pd vertices. All six outward pyridines are used: $2\times3=3\times2$. 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.
\Image[/past-exam-of-the-chemistry-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2022/paper-3-cages.png]
{title=Original connectivity models for the iron–palladium bipyramid and cube}
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