A series of open-framework tin(II) phosphates: A[Sn 4(PO 4) 3] (A=Na, K, NH 4)

Abstract

A new series of isostructural open-framework tin(II) phosphates with general formula A[Sn 4(PO 4) 3], where A=Na, K, NH 4, has been synthesized by hydrothermal methods. The crystal structures of NaSn 4(PO 4) 3 ( I) and KSn 4(PO 4) 3 ( II) have been solved by single crystal X-ray diffraction methods. Both phases crystallize in the trigonal space group R3 c (#161) with Z=6 and cell parameters a=9.5508(13) Å, c=24.083(3) Å for I, and a=9.7124(11) Å, c=24.363(3) Å for II. The structure consists of a negatively charged [Sn 4(PO 4) 3] − framework with channels running parallel to the a- and b-axes where the charge compensating A + cations are located. An interesting feature is that half of the channels are empty due to the specific geometry of the SnO 3 units—the lone electron pair of the tin atoms “protrudes” in these channels thus preventing the insertion of A +. The new phases have also been characterized by infrared and thermogravimetric analyses.