Synthesis and Crystal Structure of Ulm-16, A New Open Framework Fluorinated Gallium Phosphate with 16-Ring Channels

Abstract

AbstractThe synthesis and characterization of ULM-16, a new fluorinated gallophosphate Ga4(PO4)F2• 1.5 NC6H14• 0.5 H2O • 0.5 H3O, is described. This material is hydrothermally prepared at 180°C using cyclohexylamine as the structuring agent. It cristallizes in the orthorhombic space group Pbcn (n° 60) with a = 27.329(4) Å, b = 17.377(2) Å, c = 10.2124(5) Å, V = 4849.6 (9) Å3and Z = 8. The structure is built up from vertex-linked GaO4and PO4tetrahedra, GaO4F trigonal bipyramids and GaO4F2octahedra forming hexameric units and infinite double crankshaft chains (calledccor UUDD). The hexameric unit is similar to that found in ULM-3, ULM-4, ULM-5 and ULM-8. The two types of building units are fully connected by vertex-sharing with respect to a strict Ga-P alternation. The 3-D framework consists of cylindrical tunnels delimited by sixteen and six polyhedra running along [001]. The cyclohexylamine molecules are trapped in the wider pores and interact with the bridging fluorine atoms and hydration water through hydrogen bonds. The ULM-16 topology is closely related to that of ULM-5 where, in ULM-16, the infinite crankshaft chains replace the isolated D4R cages of ULM-5. TGA curve (under argon) indicates that the ULM-16 structure is intact up to 800°C. Structural relationships will be stated explicitly for the different structures of the ULM-n series containing the hexameric units.