ULM-18, a Fluorinated Gallium Phosphate with Perforated Layers: XRD and NMR, Structure Determination, and HF Localization in a D4R

Ga 4 (PO 4 ) 5 HF−1.5 N 2 C 6 H 18 −H 2 O (or ULM-18) is an oxyfluorinated gallium phosphate obtained by hydrothermal synthesis using N, N, N ‘, N ‘-tetramethylethylenediamine as a template. The structure is described in the triclinic space group P -1 ( n °2) with a = 8.5264(7) Å, b = 9.2512(7) Å, c = 17.870(2) Å, α = 101.742(7)°, β = 99.137(7)°, γ = 87.020(6)°, V = 1362.3(2) Å 3, and Z = 2. The two-dimensional framework is built up from sheets containing double four-ring units (D4R) connected by PO 4 tetrahedra. Along [010] and [011], 8-ring channels makes the layers hollow. The D4R units consist of four PO 4 tetrahedra, three GaO 4 F trigonal bipyramids, and one GaO 5 trigonal bipyramid. The D4R structure contains a templating fluorine. 19 F MAS at high speed and 71 Ga DOR lead to elucidation of their environment. 31 P NMR MAS, RFDR, and double-quanta analyses are used to assign phosphorus. 31 P-{ 1 H} CPMAS shows that an hydrogen is inside the D4R unit. Those features together make this building unit a quite unusual D4R conformation. For sake of the rationalization of the framework construction, this D4R is compared to known MPO D4R (M = Al, Ga, Fe, V, Co), and the results of this comparison suggest a general scheme for proton insertion in the structure.