Strategies for the synthesis of porous metal phosphonate materials

Abstract

The use of bifunctional phosphonate anions and metal cations that can adopt different co-ordination environments is proposed as a strategy for synthesising porous metal phosphonates. The hydrothermal methods described use phosphonic acids and dialkylphosphonates, which are hydrolysed in situ by the acidic metal solutions, to derive the desired phosphonate anions. A series of isostructural hydroxymethylphosphonates, M(O₃PCH₂OH) [M = Zn, Co, Cu and Mn], which contain a hexagonal array of cylindrical channels (approximate diameter 5.7 Å), were prepared by reaction of the relevant metal acetate with diethyl hydroxymethylphosphonate. Zn(O₃PCH₂C(O)NH₂)·H₂O was prepared by reaction of zinc acetate and diethyl cyanomethylphosphonate. The structure was determined by single crystal X-ray diffraction and contains two orthogonal channel systems with water molecules situated at the intersections of the channels. Zn₃(O₃PCH₂CO₂)₂·nH₂O [n = 3, 4] was prepared by reaction of phosphonoacetic acid and zinc acetate. Single crystal analysis reveals the presence of channels in the [100] direction with a cross-section of 10.02 × 6.78 Å. All three of the Zn-based materials can be isomorphously doped with Co.