Synthesis and characterization of two aluminoarsenates with occluded ethylenediamine

Abstract

Two framework aluminoarsenates (designated AlAsO₄-5 and AlAsO₄-6 respectively) were synthesized hydrothermally in the presence of a template ethylenediamine by varying the composition of the reaction mixture. The compound AlAsO₄-5 is indexable on the basis of a monoclinic structure with a= 11.777, b= 18.960, c= 5.981 Å and β= 94.85°. The structure of AlAsO₄-6 is also monoclinic but a= 19.953, b= 6.636, c= 10.604 Å and β= 96.88°. Both compounds contain six-coordinated Al and the extra two ligands, that is those other than the four O atoms bridging between alternating Al and As, are believed to be hydroxyl groups. In contrast to most framework aluminophosphates, AlAsO₄-5 and AlAsO₄-6 have poor thermal stability. Calcination at elevated temperature results in not only the collapse of the framework structure but also the sublimation of As from the solid phases.