[en] Size-selected monoanionic tin clusters Sn_n⁻, n = 7 − 75, are stored simultaneously with electrons in a Penning trap to produce poly-anionic clusters by electron attachment. In addition to doubly and triply charged clusters with the size of the precursors, fragments such as Sn⁻_n−7, Sn⁻_n−10 or Sn_n−15 are observed in the lower size range (n ≲ 50). The latter come along with the clusters Sn⁻₁₀ and Sn⁻₁₅, probably due to fission of doubly charged clusters as in the case of the group-14 neighbor-element lead [König et al., Phys. Rev. Lett. 120, 163001 (2018)]. Furthermore, prominent doubly charged products Sn²⁻_n−15 seem to be produced by break-off of neutral decamers, a feature not yet observed for any other dianionic cluster. In addition, while almost no monomer evaporation is observed for singly charged clusters, this process does occur for doubly charged ones. Graphical abstract: .