Zintl ions in molecular compounds are of fundamental interest for basic research and application. Two reactive antimony sources are presented that allow direct access to molecular polystibide compounds. These are Sb amalgam (Sb/Hg) and ultrasmall Sb0 nanoparticles (d=6.6±0.8nm), which were used independently as precursors for the synthesis of the largest f-element polystibide, [(Cp*2Sm)4Sb8]. Whereas the reaction of the nanoparticles with [Cp*2Sm] directly led to [(Cp*2Sm)4Sb8], Sm/Sb/Hg intermediates were isolated when using Sb/Hg as the precursor. These Sm/Sb/Hg intermediates [((Cp*2Sm)2Sb)2(μ-Hg)] and [((Cp*2Sm)3(μ4,η1:2:2:2-Sb4))2Hg] were synthetically trapped and structurally characterized, giving insight in the formation mechanism of polystibide compounds.