Model Energy (eV/atom) Unit cell volume /Å Zn for In substitutions is largely utilized to enhance the TE performance of promising Zintl phase with Ca5Ga2As6-type like Ca5ZnxIn2-xSb6 and Eu5ZnxIn2-xSb6. However, significant discrepancies between experimental results and theoretical predictions are quite often observed like the unexpected metallic transport (electron and hole) in the p-doped Eu5In1.5Zn0.5Sb6. As discussed above, predicting the phase width of the solid solution in alio-valent substitution is challenging and, additional phases usually form including phase segregation. For the reported work on Ca5ZnxIn2-xSb6, Snyder and co-workers mainly focuses on the experimental determination of the transport properties, but they acknowledged the existence of a secondary Zn-rich phase in the system which was not structurally characterized, and a very modest than expected improvement of the TE performance upon doping. It is therefore of prime importance to carefully analyze the subtle structural impacts of such alio-valent substitution on the system, particularly in connection with the coordination site preference between In and Zn. Our findings suggest that Zn for In substitution in Ca5ZnxIn2-xSb6 system may have generate a phase segregation with the formation of a secondary Zn-richer phase, since that systems are structurally related to the title compound, by featuring also the 'double pentagonal tube' polyanion.