High-Throughput Synthesis of Pillared-Layered Magnesium Tetraphosphonate Coordination Polymers: Framework Interconversions and Proton Conductivity Studies

Novel pillared-layered framework materials were synthesized by high-throughput or microwave-assisted methodology that contain Mg2+ and the zwitterionic linker HDTMP (hexamethylenediamine-N,N,N0,N0-tetrakis(methylenephosphonic acid)). Three compounds were structurally characterized by X-ray powder diffraction. In the compound {Mg[(HO3PCH2)2N(CH2)6N (CH2PO3H2)2](H2O)}n(1), obtained at 140 ºC by hydrothermal or microwave-assisted reaction, the layers are built by isolated Mg2+ octahedra coordinated by oxygen atoms from six different zwitterionic HDTMP ligands. Each amino-bis(methylenephosphonate) moiety links three Mg2+ ions, bridging two of them through one phosphonate group and connecting the third polyhedron in a monodentate fashion. In Compound 2, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n, hydrothermally synthesized at 180 C, the layers are composed of bidentate amino-bis(methylenephosphonate) moieties connected to three Mg2+ ions, with one of the phosphonate groups acting as a bridging ligand. Various subtle structural changes are noted for the other two compounds. Thermodiffraction of 1 reveals that a crystalline-to-crystalline phase transformation occurs concomitantly with its dehydration, leading to a new anhydrous phase, namely, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n(1deh). This process is fully reversible upon equilibrating the solid at room temperature. The reported compounds can adsorb ammonia and CO2. Compound 1 exhibits a moderate proton conductivity, ~1.5 x 10-5 S·cm-1 at 80 ºC and 95% RH, that increases a half order of magnitude after experiencing a complete dehydration/rehydration process

Barium Sulfate Crystallization in the Presence of variable Chain Length Aminomethylenetetraphosphonates and cations (Na+ or Zn2+)

Barium sulfate is a common scale in oil production installations that is treated and controlled with phosphonate inhibitors. A fundamental understanding of how these inhibitors operate, however, is only slowly emerging. In this paper, we investigate the effect on barium sulfate crystallization of two very similar phosphonate molecules that only differ in their backbone spacing, ethylenediamine-N,N,N',N'-tetra(methylenephosphonic acid) (EDTMP) and hexamethylenediamine-N,N,N',N'-tetr(methylenephosphonic acid) (HDTMP). It was found that the inhibitory efficacy of the organic molecules depends on their structural differences but also on the presence of other cations such as Zn2+. It appears that both stereochemical considerations and complexation strength differences between the two phosphonate additives result in different inhibitory powers. In the presence of zinc cations and EDTMP, it is found that inhibition is related to the concentration of uncomplexed ("free") organic