The titanium(I) salt of N,N-(diphosphonomethyl)glycine: synthesis, characterisation, porosity and proton conduction

Abstract

A new diphosphonic acid,N,N -(diphosphonomethyl)glycine, has been prepared. The titanium(iv) salt [Ti(dpmg)] of this acid has been characterised by X-ray powder diffraction, thermogravimetry, ³¹ P MAS NMR spectroscopy, isothermal N ₂ adsorption–desorption and ac conductivity measurements. Phosphorus is present in a mixture of bonded phosphonate and free phosphonic acid groups. The material is both amorphous and porous (BET specific surface area=119 m ² g ^-1 ), and its water content is relative humidity (RH)-dependent. Ti(dpmg) is a protonic conductor (at 90% RH and 90 °C, σ=3×10 ^-2 S cm ^-1 ), with conductivity exhibiting Arrhenius-type behaviour at constant RH. Conductivity and Arrhenius parameters are strongly dependent on the water content.