Targeted Synthesis of an Highly Stable Aluminium Phosphonate Metal-Organic Framework Showing Reversible HCl Adsorption

A concept for obtaining isoreticular compounds with tri-instead of tetravalent metal cations using highly acidic reaction conditions was developed and successfully applied in a high throughput study using N,N'-piperazinebis(methylenephosphonic acid) (H4PMP), that resulted in the discovery of a new porous aluminium phosphonate denoted CAU-60 center dot 6HCl. The high-throughput study was subsequently extended to other trivalent metal ions. Al-CAU-60 center dot 6HCl demonstrates reversible desorption of HCl (18.3 wt% loading) with three distinct compositions observed with zero, four or six HCl molecules per formula unit. Structural changes were followed in detail by powder X-ray diffraction, EDX analysis as well as IR spectroscopy. Rapid desorption of HCl in water within minutes and subsequent adsorption from the gas phase and from aqueous solution are shown. Furthermore, it is possible to adsorb HBr into the guest free Al-CAU-60 framework, demonstrating the high stability of this compound.

Automated summary

A concept for obtaining isoreticular compounds with tri-instead of tetravalent metal cations using highly acidic reaction conditions was developed and successfully applied in a high throughput study. This study led to the discovery of a new porous aluminium phosphonate denoted CAU-60·6HCl. The compound demonstrated reversible desorption of HCl, with varying compositions observed and high stability when adsorbing HBr.