Reaction of [(n-C4H9)(4)N](4)[Sb8O12(OH)(20)] with (CH3)(2)-(t-C4H9)SiOH at 80 degreesC affords a new polyantimonate [(n-C4H9)(4)N](4)[Sb4O6(OH)(4){OSi(CH3)(2)(t-C4H9)}(6)]. Single crystal X-ray structural analysis of its CH2Cl2 solvate revealed that this polyantimonate is made from four octahedral SbO6 units that share edges with each other to form a planar Sb4O16 core. The silyl groups form a shallow pocket on each side of the anion, which contains a CH2Cl2 molecule. These pockets are not occupied with solvents in the CH3CN solvate.