= Solution
Without a blocking diphosphine, square-planar Pd(II) can bind four terminal pyridines. If there are $N$ Fe units and $M$ Pd centres, saturation requires $3N=4M$. The given ratio $M/N=0.75$ and charge $2(N+M)=28$ yield \b[$N=8$, $M=6$]. Thus \b[$[\mathrm{Fe}_8\mathrm{Pd}_6L_8]^{28+}$] has Fe at the eight cube corners and Pd at the six face centres. Each corner Fe connects through its three arms to the three neighbouring face-centre Pd atoms; each Pd accepts four pyridines around its square face.
There are 24 Fe-unit-to-Pd connections, checked independently as $8\times3=6\times4$. It is useful to distinguish the cube of eight Fe nodes from its dual octahedron of six Pd nodes: both describe the same assembly, with different node sets.
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