The first molecular antimony selenide anionic cluster, Sb12Se20(4-), is reported. The compound can be isolated as a PPh4+ salt from the reduction of Sb4Se4 with potassium in DMF. It contains two incomplete cubes connected to opposite sides of a corrugated Sb6Se6 ring by bridging selenides. The arachnid nature of the structure leads to formation of two large voids within the cluster. The cluster may be the largest molecular Zintl ion reported to date.