“…In all three phosphonate systems, the introduction of a small cation favors a tubular material over a layered material. The small cation could also be necessary for formation of the [SbO E] spiro-5 units: the unit is found in NaSb O (PO ) , while the few reported antimony(III) phosphates/phosphonates/phosphites synthesized hydrothermally in the absence of cations (6,41,42) contain only even-membered rings (Sb P , Sb P , Sb P , 2 ) or edge-sharing odd-membered rings. Certainly, more Sb P rings and [SbO E]-based spiro-5 motifs will be found, though it remains to be seen if the presence of these units will lead to nanoporous open antimony(III) phosphate/phosphonate frameworks.…”