2D Corrugated Magnesium Carboxyphosphonate Materials: Topotactic Transformations and Interlayer “Decoration” with Ammonia

In this paper we report the synthesis and structural characterization of the 2D layered coordination polymer Mg­(BPMGLY)­(H₂O)₂ (BPMGLY = bis-phosphonomethylglycine, (HO₃PCH₂)₂N­(H)­COO^2–). The Mg ion is found in a slightly distorted octahedral environment formed by four phosphonate oxygens and two water molecules. The carboxylate group is deprotonated but noncoordinated. This compound is a useful starting material for a number of topotactic transformations. Upon heating at 140 °C one (of the two) Mg-coordinated water molecule is lost, with the archetype 2D structure maintaining itself. However, the octahedral Mg in Mg­(BPMGLY)­(H₂O)₂ is now converted to trigonal bipyramidal in Mg­(BPMGLY)­(H₂O). Upon exposure of the monohydrate Mg­(BPMGLY)­(H₂O) compound to ammonia, one molecule of ammonia is inserted into the interlayer space and stabilized by hydrogen bonding. The 2D layered structure of the product Mg­(BPMGLY)­(H₂O)­(NH₃) is still maintained, with Mg now acquiring a pseudo-octahedral environment. All of these topotactic transformations are also accompanied by changes in hydrogen bonding between the layers.