Layered aluminophosphates II. Crystal structure and thermal behaviour of the layered aluminophosphate UiO-15 and its high temperature variants

Abstract

The synthesis and crystal structure of a novel layered aluminophosphate and its two high temperature variants are described. All three structures were solved from powder X-ray diffraction data. The as-synthesized material (UiO-15-as), with composition [NH 3 (CH 2 ) 2 NH 3 ] 2+ [Al 2 (OH) 2 (PO 4 ) 2 (H 2 O)] 2– ·H 2 O, crystallizes in the space group P1 with a=10.37490(13), b=6.60775(8), c=9.90937(11) A, α=90.762(1), β=115.265(1) and γ=90.162(1)°. In the aluminophosphate layers the five- and six-coordinated aluminium polyhedra form infinite chains along [010] that are crosslinked by phosphate groups. These layers are held together by a complex hydrogen bonding scheme involving the terminal oxygen atoms of the phosphate groups and the nitrogens of the ethylenediammonium ions. A high temperature variant exists around 125 °C (UiO-15-125). This compound, with composition [NH 3 (CH 2 ) 2 NH 3 ] 2+ [Al 2 (OH) 2 (PO 4 ) 2 ] 2– , crystallizes in the monoclinic space group P2 1 /c with a=10.28899(23), b=6.75080(13), c=9.62527(20) A and β=116.124(1)°. The transformation to UiO-15-125 involves removal of an interlamellar water molecule and another water molecule which is coordinated to aluminium. The infinite chains of aluminium polyhedra along [010] and the hydrogen bonding scheme of UiO-15-as is maintained in UiO-15-125. Another high temperature variant exists around 225 °C (UiO-15-225). This compound, with composition [NH 3 (CH 2 ) 2 NH 3 ] 2+ [Al 2 O(PO 4 ) 2 ] 2– , crystallizes in the monoclinic space group P2 1 /c with a=9.42781(37), b=6.91370(19), c=9.40823(27) A and β=113.002(1)°. The transformation to UiO-15-225 involves the release of a water molecule from UiO-15-125 and the formation of tetrahedral Al-O-Al bonding. UiO-15-225 is therefore the first compound among the aluminophosphates violating Loewensteins rule.