Synthesis and precise characterization of large single crystals of as-synthesized CrAPO-5, H2.1[Cr0.08Al11.62P12O48]F1.2·1.6TEA

Abstract

Large single crystals of Cr-containing AlPO₄-5 aluminophosphate with various Cr contents up to 1100 um in length have been grown hydrothermally in a fluorine-containing medium with triethylamine (TEA) as a template. The large size and excellent quality of the crystals allowed a detailed definition of the template molecule including the hydrogen atom positions. Fluorine atoms were observed on the two-fold axis in four-rings of the framework. These F atoms completed the coordination environment of a part of the Al atoms to a distorted trigonal bipyramid with an Al–F distance of 2.126(6)Å. Based on chemical analyses and the diffraction evidence the chemical composition of the CrAPO-5 studied is CrAPO₅ H_2.1[cr_0.08Al_11.62P₁₂O₄₈]F_1.2· 1.6TEA. The space group of the as-synthesized AlPO₄-5 is confirmed to be P6cc.